USF Libraries
USF Digital Collections

Hydraulic performance of polymer modified bentonite

MISSING IMAGE

Material Information

Title:
Hydraulic performance of polymer modified bentonite
Physical Description:
Book
Language:
English
Creator:
Schenning, Jessica A
Publisher:
University of South Florida
Place of Publication:
Tampa, Fla.
Publication Date:

Subjects

Subjects / Keywords:
barriers
liners
swell index
engineered clay
permeability
Dissertations, Academic -- Civil Engineering -- Masters -- USF   ( lcsh )
Genre:
government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

Summary:
ABSTRACT: Bentonite clay is widely used in barrier systems due to its low hydraulic conductivity and it high swell capacity. Exposure to inorganic solutions can cause significant increases in hydraulic conductivity, due to changes in the surface chemistry and fabric. This phenomenon can be attributed to a reduction in the thickness of the double layer, due to the cation exchange capacity of the clay. The clay can be modified with polymers to render it less susceptible to chemical attack. The treatment process allows the clay to be engineered to enhance specific properties, such as permeability and sorption. In the present study, engineered soils are prepared by sorbing organic polymers to the surface of Na-bentonite. Three classes, cationic, anionic and nonionic polymers are investigated. The sorbents are water-soluble compounds based on the polymerization of acrylamides (PAM). Mixing and sample preparation techniques are developed and discussed. The interaction of the polymeric compounds and the clay mineral surface are evaluated by testing the liquid limit, swell index and specific gravity of the soils. Permeability tests are performed to determine if the polymer treatment enhances the hydraulic performance of the clay when permeated with highly concentrated salt solutions. The effect of permeant, void ratio, initial wetting condition and preparation techniques are found to have a significant affect on the hydraulic conductivity.
Thesis:
Thesis (M.S.C.E.)--University of South Florida, 2004.
Bibliography:
Includes bibliographical references.
System Details:
System requirements: World Wide Web browser and PDF reader.
System Details:
Mode of access: World Wide Web.
Statement of Responsibility:
by Jessica A. Schenning.
General Note:
Title from PDF of title page.
General Note:
Document formatted into pages; contains 144 pages.

Record Information

Source Institution:
University of South Florida Library
Holding Location:
University of South Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 001478761
oclc - 56389868
notis - AJS2451
usfldc doi - E14-SFE0000403
usfldc handle - e14.403
System ID:
SFS0025095:00001


This item is only available as the following downloads:


Full Text

PAGE 1

Hydraulic Performance of Polymer Modified Bentonite by Jessica A. Schenning A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Civil Engineering Department of Civil and Environmental Engineering College of Engineering University of South Florida Major Professor: Alaa Ashmawy, Ph.D. Manjriker Gunaratne, Ph.D. Rajan Sen, Ph.D. Date of Approval: July 6, 2004 Keywords: Engineered Clay, Permeability, Swell Index, Liners, Barriers Copyright 2004, Jessica A. Schenning

PAGE 2

DEDICATION I would like to dedicate this thesis to my husband, without whose support I would not have been able to continue my education to this degree. I would also like to express thanks to my family for their encouragement throughout my education.

PAGE 3

ACKNOWLEDGMENTS I would like to express my sincere appreciation to my major professor, Dr. Alaa Ashmawy, for his inspiration, guidance and support throughout this study. I also would like to thank Dr. Manjriker Gunaratne and Dr. Rajan Sen for their service as committee members. For their assistance in the lab, I wish to extend a special thanks to Jeremy Runkle and Whitney Allen. This research was supported by the National Science Foundation and the Department of Civil and Environmental Engineering at the University of South Florida. I would also like to recognize Jane Davis of Emerging Technologies for her advice and the donation of materials.

PAGE 4

TABLE OF CONTENTS LIST OF TABLES iv LIST OF FIGURES v ABSTRACT xi CHAPTER 1 INTRODUCTION 1 1.1 Background 1 1.2 Research Scope and Objective 2 1.3 Organization of Thesis 3 CHAPTER 2 MATERIALS 4 2.1 Bentonite 4 2.1.1 Clay Mineralogy 5 2.1.1.1 Swelling and Adsorption 7 2.1.1.2 Cation Exchange Capacity 9 2.1.1.3 Diffuse Double Layer 13 2.1.2 Experimental Materials 19 2.2 Polymers 21 2.2.1 Chemical Composition 21 2.2.2 Clay-Polymer Interaction 23 2.2.2.1 Cationic Interaction 24 2.2.2.2 Anionic Interaction 25 2.2.2.3 Nonionic Interaction 26 2.2.3 Experimental Materials 27 2.2.3.1 Polymer Titration 30 2.2.3.2 Theoretical Charge Density 32 CHAPTER 3 EXPERIMENTAL BACKGROUND AND LITERATURE REVIEW 34 3.1 Clay Fabric 34 3.2 Permeability Theory 35 3.3 Geosynthetic Clay Liners 37 3.3.1 Valence 38 3.3.2 Concentration 40 3.3.3 Pre-Hydration 40 3.3.4 Void Ratio 41 i

PAGE 5

3.3.5 Testing Procedures 42 3.4 Modified Clays 42 3.4.1 Organobentonites 43 3.4.2 Polymer Treatment 44 CHAPTER 4 EQUIPMENT AND EXPERIMENTAL METHODS 46 4.1 Testing Program 46 4.2 Sample Preparation 47 4.2.1 Mixing Procedure 47 4.2.2 Grinding Technique 48 4.3 Equipment 50 4.4 Permeability Measurement 52 4.4.1 Sample Preparation 52 4.4.2 Consolidation Technique 52 CHAPTER 5 TESTS AND RESULTS 56 5.1 Swell Index 56 5.2 Liquid Limit 61 5.3 Specific Gravity 63 5.4 Permeability Tests 65 5.4.1 Permeant Solutions 65 5.4.2 Test Measurements 66 5.4.3 Permeant 67 5.4.4 First Wetting Solution 71 5.4.5 Void Ratio 73 5.4.6 Polymer Charge 75 5.4.7 Gradient 77 5.4.8 Electrical Conductivity and pH 79 CHAPTER 6 DISCUSSION AND ANALYSIS 81 6.1 Mixing Ratio 81 6.2 Effect of Sample Preparation 82 6.3 Swell Index 83 6.4 Effect of Permeant 83 6.5 Effect of Pre-hydration 84 6.6 Effect of Void Ratio 85 6.7 Effect of the Mechanism of Interaction 85 6.7.1 Effect of Cationic Interactions 86 6.7.2 Effect of Nonionic Interactions 88 6.7.3 Effect of Anionic Interactions 89 CHAPTER 7 CONCLUSIONS AND RECOMMENDATIONS 91 7.1 Summary 91 7.2 Conclusions 91 ii

PAGE 6

7.3 Recommendations for Future Work 92 REFERENCES 94 APPENDICES 97 Appendix A: Permeability Test Results 98 Appendix B: Swell Index Test Results 123 Appendix C: Liquid Limit Test Results 126 iii

PAGE 7

LIST OF TABLES Table 2.1 Hydrated Radii of Cations 18 Table 2.2 Polymer Material Data 28 Table 2.3 EC and pH of Experimental Polymers 29 Table 2.4 Standard Titration Solutions 30 Table 2.5 Experimental Charge Densities of Polymers 32 Table 5.1 Experimental Values of Liquid Limits 62 Table 5.2 Measured Specific Gravity 64 Table 5.3 Pre-hydrated vs. Non-Pre-hydrated 72 Table 5.4 Effect of Void Ratio With Deionized Water Permeant 74 Table 5.5 Effect of Polymer and Permeant on Hydraulic Conductivity 77 Table 5.6 Electrical Conductivity and pH of Permeants 79 Table 6.1 Polymer Mix at %CEC of Clay 81 Table A.1 Laboratory Permeability Tests 98 iv

PAGE 8

LIST OF FIGURES Figure 2.1 Mineral Layers (a) Silicon Tetrahedral (b) Octahedral 5 Figure 2.2 Montmorillonite (a) Layered Structure (b) Mineral Stacking 6 Figure 2.3 Clay-Water Interactions (a) Hydrogen Bonding (b) Ion Hydration (c) Dipole Attraction 8 Figure 2.4 Cation Association 9 Figure 2.5 Methylene Blue (a) Molecule (b) Clay Surface Adsorption 10 Figure 2.6 Experimental Values of CEC of Na-Bentonite 12 Figure 2.7 Ion Distribution in Diffuse Double Layer 14 Figure 2.8 Ion Distribution in Interacting Double Layers 16 Figure 2.9 Electric Potential Distributions 17 Figure 2.10 Stern Layer and the Potential Distribution 19 Figure 2.11 Experimental Liquid Limit of Na-Bentonite 20 Figure 2.12 Experimental Swell Index of Na-Bentonite 20 Figure 2.13 Polyacrylate 21 Figure 2.14 Polyacrylamide 22 Figure 2.15 Poly(acrylic acid) 22 Figure 2.16 Adsorption of Uncharged Polymer on Clay 24 Figure 2.17 Clay Interaction 24 Figure 2.18 Interaction Between Anionic Polymers and Clays 26 v

PAGE 9

Figure 2.19 Polymer Granules 27 Figure 2.20 EC and pH Measurement Devices 29 Figure 2.21 Titration Setup (a) Cationic (b) Anionic 31 Figure 3.1 Clay Fabric (a) Dispersed (b) Collapsed (c) Aggregated 35 Figure 3.2 Mechanism of Flow (a) Hydraulic (b) Chemical 36 Figure 3.3 Effect of Valence 39 Figure 3.4 Effect of Void Ratio 41 Figure 4.1 Clay Polymer Interaction (a) Not Heated (b) Heated 48 Figure 4.2 Clay Sample After Drying 49 Figure 4.3 Mechanical Crushing (a) Ball Mill (b) Grinder 49 Figure 4.4 Modified Clay in Powder Form 50 Figure 4.5 Permeability Cell 51 Figure 4.6 Consolidation of Sample in Permeameter 53 Figure 4.5 Laboratory Pressure Panel Setup 54 Figure 5.1 Hydrated Swell Volume 57 Figure 5.2 Swell Index in Deionized Water 58 Figure 5.3 Effect of Charge Density on Swell Index 59 Figure 5.4 Effect of Polymer on Swell Volume 60 Figure 5.5 Experimental Values of Liquid Limits 62 Figure 5.6 Heated vs. Non-Heated Clays 63 Figure 5.7 Permeability Measurement Values 66 Figure 5.8 Effect of Valence on High Cationic Modified Clay 68 vi

PAGE 10

Figure 5.9 Effect of Valence on Low Cationic Modified Clay 68 Figure 5.10 Effect of Valence on Nonionic Modified Clay 69 Figure 5.11 Effect of Valence on Low Anionic Modified Clay 70 Figure 5.12 Effect of Valence on Medium Anionic Modified Clay 70 Figure 5.13 Effect of Pre-hydration Condition 71 Figure 5.14 Pre-hydrated vs. Non-Pre-hydrated 72 Figure 5.15 Effect of Void Ratio on Modified Clay Permeated with DI Water 73 Figure 5.16 Effect of Void Ratio on High Cationic Clay Permeated with CaCl 2 74 Figure 5.17 Effect of Void Ratio on Nonionic Clay Permeated with CaCl 2 75 Figure 5.18 Effect of Polymer Clay Permeated with H 2 O 76 Figure 5.19 Effect of Polymer When Permeated With CaCl 2 76 Figure 5.20 Effect of Polymer 77 Figure 5.21 Effect of Gradient 78 Figure 5.22 EC and pH of Effluent of Nonionic Clay Permeated with CaCl 2 80 Figure 5.23 EC and pH of High Cationic Permeated With MgCl 2 80 Figure 6.1 Effect of Valence on Modified Clay 84 Figure 6.2 Effect of Void Ratio 85 Figure 6.3 Cationic Polymer Interaction 86 Figure 6.4 Nonionic Polymer Interaction 88 Figure 6.5 Anionic Polymer Interaction 89 Figure A.1 Coefficient of Permeability vs. Duration 1-Ch 99 Figure A.2 Coefficient of Permeability vs. Pore Volume 1-Ch 99 Figure A.3 Coefficient of Permeability vs. Duration 2-Ch 100 vii

PAGE 11

Figure A.4 Coefficient of Permeability vs. Pore Volume 2-Ch 100 Figure A.5 Coefficient of Permeability vs. Duration 3-Ch 101 Figure A.6 Coefficient of Permeability vs. Pore Volume 3-Ch 101 Figure A.7 Coefficient of Permeability vs. Duration 4-Ch 102 Figure A.8 Coefficient of Permeability vs. Pore Volume 4-Ch 102 Figure A.9 Coefficient of Permeability vs. Duration 5-Ch 103 Figure A.10 Coefficient of Permeability vs. Pore Volume 5-Ch 103 Figure A.11 Coefficient of Permeability vs. Duration 6-Ch 104 Figure A.12 Coefficient of Permeability vs. Pore Volume 6-Ch 104 Figure A.13 Coefficient of Permeability vs. Duration 1-Cl 105 Figure A.14 Coefficient of Permeability vs. Pore Volume 1-Cl 105 Figure A.15 Coefficient of Permeability vs. Duration 2-Cl 106 Figure A.16 Coefficient of Permeability vs. Pore Volume 2-Cl 106 Figure A.17 Coefficient of Permeability vs. Duration 3-Cl 107 Figure A.18 Coefficient of Permeability vs. Pore Volume 3-Cl 107 Figure A.19 Coefficient of Permeability vs. Duration 1-N 108 Figure A.20 Coefficient of Permeability vs. Pore Volume 1-N 108 Figure A.21 Coefficient of Permeability vs. Duration 2-N 109 Figure A.22 Coefficient of Permeability vs. Pore Volume 2-N 109 Figure A.23 Coefficient of Permeability vs. Duration 3-N 110 Figure A.24 Coefficient of Permeability vs. Pore Volume 3-N 110 Figure A.25 Coefficient of Permeability vs. Duration 4-N 111 viii

PAGE 12

Figure A.26 Coefficient of Permeability vs. Pore Volume 4-N 111 Figure A.27 Coefficient of Permeability vs. Duration 1-Al 112 Figure A.28 Coefficient of Permeability vs. Pore Volume 1-Al 112 Figure A.29 Coefficient of Permeability vs. Duration 2-Al 113 Figure A.30 Coefficient of Permeability vs. Pore Volume 2-Al 113 Figure A.31 Coefficient of Permeability vs. Duration 3-Al 114 Figure A.32 Coefficient of Permeability vs. Pore Volume 3-Al 114 Figure A.33 Coefficient of Permeability vs. Duration 1-Am 115 Figure A.34 Coefficient of Permeability vs. Pore Volume 1-Am 115 Figure A.35 Coefficient of Permeability vs. Duration 2-Am 116 Figure A.36 Coefficient of Permeability vs. Pore Volume 2-Am 116 Figure A.37 Coefficient of Permeability vs. Duration 3-Am 117 Figure A.38 Coefficient of Permeability vs. Pore Volume 3-Am 117 Figure A.39 Coefficient of Permeability vs. Duration 4-Am 118 Figure A.40 Coefficient of Permeability vs. Pore Volume 4-Am 118 Figure A.41 Coefficient of Permeability vs. Duration 5-Am 119 Figure A.42 Coefficient of Permeability vs. Pore Volume 5-Am 119 Figure A.43 Coefficient of Permeability vs. Duration 1-B 120 Figure A.44 Coefficient of Permeability vs. Pore Volume 1-B 120 Figure A.45 Coefficient of Permeability vs. Duration 2-B 121 Figure A.46 Coefficient of Permeability vs. Pore Volume 2-B 121 Figure A.47 Coefficient of Permeability vs. Duration 3-B 122 Figure A.48 Coefficient of Permeability vs. Pore Volume 3-B 122 ix

PAGE 13

Figure B.1 Swell Index of High Cationic Modified Clay 123 Figure B.2 Swell Index of Low Cationic Modified Clay 123 Figure B.3 Swell Index of Nonionic Modified Clay 124 Figure B.4 Swell Index of Low Anionic Modified Clay 124 Figure B.5 Swell Index of Medium Anionic Modified Clay 125 Figure B.6 Swell Index of Unmodified Bentonite Clay 125 Figure C.1 Liquid Limit Not Heated High Cationic 126 Figure C.2 Liquid Limit Not Heated Low Cationic 126 Figure C.3 Liquid Limit Not Heated Nonionic 126 Figure C.4 Liquid Limit Not Heated Low Anionic 127 Figure C.5 Liquid Limit Not Heated Medium Anionic 127 Figure C.6 Liquid Limit Heated High Cationic 127 Figure C.7 Liquid Limit Heated Low Cationic 128 Figure C.8 Liquid Limit Heated Nonionic 128 Figure C.9 Liquid Limit Heated Low Anionic 128 Figure C.10 Liquid Limit Heated Medium Anionic 129 Figure C.11 Liquid Limit Heated and Not Heated Bentonite 129 x

PAGE 14

HYDRAULIC PERFORMANCE OF POLYMER MODIFIED BENTONITE Jessica A. Schenning ABSTRACT Bentonite clay is widely used in barrier systems due to its low hydraulic conductivity and it high swell capacity. Exposure to inorganic solutions can cause significant increases in hydraulic conductivity, due to changes in the surface chemistry and fabric. This phenomenon can be attributed to a reduction in the thickness of the double layer, due to the cation exchange capacity of the clay. The clay can be modified with polymers to render it less susceptible to chemical attack. The treatment process allows the clay to be engineered to enhance specific properties, such as permeability and sorption. In the present study, engineered soils are prepared by sorbing organic polymers to the surface of Na-bentonite. Three classes, cationic, anionic and nonionic polymers are investigated. The sorbents are water-soluble compounds based on the polymerization of acrylamides (PAM). Mixing and sample preparation techniques are developed and discussed. The interaction of the polymeric compounds and the clay mineral surface are evaluated by testing the liquid limit, swell index and specific gravity of the soils. Permeability tests are performed to determine if the polymer treatment enhances the hydraulic performance of the clay when permeated with highly concentrated salt solutions. The effect of xi

PAGE 15

permeant, void ratio, initial wetting condition and preparation techniques are found to have a significant affect on the hydraulic conductivity. xii

PAGE 16

CHAPTER 1 INTRODUCTION 1.1 Background Disposal of solid wastes in landfill facilities has, in some cases lead to contamination of the groundwater, by failing to retain leachates. Environmental and health awareness has lead to rigorous regulation of the municipal solid waste landfills, and therefore a focus to design more secure landfills by improving the lining and covering systems. Currently, the most effective hydraulic barriers are composite systems, which include combination geomembrane/clay lining systems and geosynthetic clay liner. Bentonite clay is widely used in these composites for waste containment due to its low hydraulic conductivity, high swelling potential and high cation exchange capacity. When exposed to high concentrations of inorganic pollutants, degradation of the bentonite clay can occur and a subsequent increase in the hydraulic conductivity. This phenomenon is attributed to the changes that occur in the diffuse double layer of the bentonite, due to its cation exchange capacity. Particularly, when the replacement of sodium ions is with higher valence ions, such as calcium occurs. The development of alternative methods for better containment is centered on engineered clays with improved hydraulic and sorptive characteristics. Organic compounds and polymers can be used to modify bentonite clay for this purpose. Researchers have indicated the suitability of organically modified clays for landfill lining (Lo et al., 1997). Various 1

PAGE 17

manufacturers have proposed polymer treatment of the clay as a means of resisting contamination, but the performance of such materials in the long term and in aggressive environments has not been fully evaluated (Ashmawy et al., 2002). 1.2 Research Scope and Objective This study aims to evaluate polymer modified bentonite clay for use as alternative liners. The research project addresses technical issues related to the hydraulic, mechanical, and chemical compatibility of polymer-modified clays in landfill lining applications. The main objectives of this study are: 1. 2. 3. To establish preparation techniques for the polymer modified clays. To evaluate the mechanical and hydraulic properties with respect to their chemical stability. To relate the effect of the polymer to the clay mineralogy and evaluate their chemical interaction. This research evaluates the hydraulic performance of clays modified with anionic, nonionic and cationic polymers under prolonged exposure to inorganic leachates. Laboratory permeability tests were performed on the each of the modified clays under various conditions to assess hydraulic conductivity. The permeants used in this study were NaCl, CaCl 2 and MgCl 2 The affect of the ionic charge and charge density of the polymer, void ratio, permeant solution and wetting conditions on the permeability are examined. Additional laboratory tests were conducted to better characterize the other engineering properties of the modified clay. 2

PAGE 18

1.3 Organization of Thesis Chapter 2 discusses the materials used for this study. Bentonite clay mineralogy, information concerning the diffuse double layer and its interactions, adsorption and cation exchange mechanisms are discussed. Experimental characterization of the bentonite used in this investigation includes specific gravity, liquid limit, swell index and cation exchange capacity. Background material related to polymers, such as chemical compositions and effect of charge with respect to clay interactions are presented. Chapter 3 reviews past literature and introduces topics related to this thesis, such as the factors affecting hydraulic performance of pure bentonite and sorption and hydraulic characteristics of modified clays. The previous findings have been used as guidelines for the experimental methods carried out in this research. The equipment and experimental methods are outlined in Chapter 4. The procedures developed for sample preparation and test set-up are described in detail. Chapter 5 presents the experimental data. This includes specific gravity, liquid limit, swell index, and permeability measurements for the modified clays. Chapter 6 includes analysis of the experimental data. Discussion of the effect of clay-polymer interactions on the mechanical properties of the soil, as well as the rationalization of experimental variables is presented. Chapter 7 summarizes experimental findings and concludes with suggestions for future work. 3

PAGE 19

CHAPTER 2 MATERIALS 2.1 Bentonite Montmorillonite is a clay mineral within the smectite group. It forms by weathering or hydrothermal alteration of other aluminum-rich minerals and is particularly common in altered volcanic ashes called bentonite. Bentonite clay occurs at several stratigraphic horizons within the Ordovician Platteville and Decorah Formations, which are widely exposed in Wyoming, Wisconsin, North Dakota, South Dakota and Utah. This bentonite was formed mostly in the Cretaceous to Miocene age, but are known to be as old as Jurassic and as recent as Pleistocene. To be economically mineable, bentonite deposits must be close to the surface. The material overlying the bentonite must first be removed using a bulldozer or excavator. The surface of the bentonite bed must be carefully scraped to remove impurities. Depending on the thickness and grade variation, the bentonite may be scraped off one layer at a time or excavated with bucket loaders. The bentonite is processed by drying, grinding and bagging. Bentonite, termed the clay of a 1000 uses is used commercially in everything from cosmetics and pharmaceuticals, to hazardous waste treatment. In construction, bentonite plays a large role in drilling operations and many environmental retention applications. The unique engineering properties of bentonite are directly related to the clay mineralogical structure. 4

PAGE 20

2.1.1 Clay Mineralogy Clay minerals are a part of the phyllosilicate mineral family, but due to differences in layering, crystal formation and substitutions, they can range widely in properties. Bentonite is a naturally occurring hydrated aluminum silicate. Although sodium bentonite has its name because the majority of the exchangeable cations adsorbed are sodium, it is important to note that other cations such as calcium and magnesium are present in lesser quantities. The basic building blocks of the clay mineral are tetrahedral and octahedral structures. The silicon tetrahedron, (Si 4 O 10 ) 4are organized such that the base oxygens are shared to form a sheet structure, shown in Figure 2.1. The thickness of the silicon sheet in a clay mineral structure is 4.63 (b) (a) Aluminums Ma g nesiums etc. H y drox y ls Silicones Ox yg ens Figure 2.1 Mineral Layers (a) Silicon Tetrahedron (b) Octahedron ( After Mitchell 1993 ) The octahedral sheet is made up of aluminum or magnesium coordinated with oxygens or hydroxyls. Depending on the valence of the cations present in sheets, different minerals are formed. Dioctahedral structures are formed when the coordinated cation is 5

PAGE 21

trivalent, such as aluminum. Gibbsite has the composition of Al 2 (OH) 6 and is found in bentonite Similarly, trioctahedral structures are formed when divalent cations are present. Brucite, Mg 3 (OH) 6 has magnesium as the coordinated cation. The thickness of the octahedral sheet in a clay mineral structure is 5.05 Smectite has a 2:1 basic mineral structure, meaning that there are two tetrahedral silica sheets layered with one octahedral aluminum sheet. The total basal spacing of the layered structure is 9.6 to 21 Montmorillonite is dioctahedral, with a composition of (OH) 4 Si 8 Al 4 O 20 H 2 O, prior to any substitutions being made, shown in Figure 2.2. However, approximately every sixth aluminum ion is replaced with a magnesium cation through isomorphous substitution. Since Al 3+ is replaced by Mg 2+ the result is a net negative charge in the mineral structure. 9.6 to H2O + Cations in interlayer spacing ( a ) ( b ) Figure 2.2 Montmorillonite (a) Layered Structure (b) Mineral Stacking (After Mitchell, 1993) Surrounding these structures are loosely held hydrated cations, which are attracted by the net negative charge of the particle. The negative charge comes from isomorphous substitution of Al 3+ for Si 4+ in the silica sheet or a divalent ion for the Al 3+ in the tetrahedral sheet. However, broken bonds near the particle edge can also account for some of the negative charge. 6

PAGE 22

A particle of bentonite has a plate-like shape with a very high aspect ratio, about 1:100. One particle is approximately 100 nm in width and 4 to 5 nm in height. The large length of the particle is typically no more than 1 to 2 m. This high aspect ratio yields a very large specific surface, 800 m 2 /gram, including the interlayers. The specific surface in combination with the net charge and weak bonds gives bentonite its high potential to swell and readily exchange cations. There are five possible types of interlayer bonding possible in layer silicates (Marshall, 1964, Mitchell, 1993). Parallel layers that are neutral are bound by weak van der Waals forces. When there are opposing layers oxygens and hydroxyls, or hydroxyls and hydroxyls, such as in gibbsite, hydrogen bonding can occur and remain stable in the presence of water. Neutral silicate layers are held by hydrogen bonds that are weakened and separated in the presence of water molecules. The cations that are present to balance negative charge help to bond the layers together. These bonds are weak and easily separated when water and other polar fluids are adsorbed on the surface. 2.1.1.1 Swelling and Adsorption Water is adsorbed on or associated with the particle surface through hydrogen bonds, ion hydration, attraction by osmosis and dipole attraction, as shown in Figure 2.3. Water penetrates the intercrystalline structure causing the silicate layers to separate; this phenomenon is called interlayer swelling. Several layers of water dipoles can form into stacked, tetrahedral structures, causing the separation. Water is adsorbed on to the particle surface by hydrogen bonds. Interlayer cations become hydrated with large energy of hydration; enough to overcome the weak van der Waals attraction between layers (van Olphen, 1977). Clays also swell due to forces of repulsion between adjacent particles. This repulsive energy is the difference in osmotic pressure between the midpoint of two plates and the solution. Electrolyte concentration, cation valance, dielectric constant and pH of a solution affect the repulsive forces. During this expansion 7

PAGE 23

the basal spacing increases from approximately 9.6 when dried at 100C to 12.5 to 21 when wet due to the presence of water in the interlayer. Water dipoles have a charge distribution that allows ion hydration. Cations attract the negative side of the water molecule, while anions attract the positive side. If the energy of hydration is less than that of normal water, the water molecule becomes a hydration shell for the ion. Even when not hydrated, ions cause the water molecules to have a certain arrangement and orientation. Due to the high concentration of ions, the water dipole is strongly attracted to the mineral surface, through diffusion by osmosis. This can cause an arrangement of the dipoles, which leads to a disorientation at the midplane region when two particles are close. To balance these charges cations are present midway between the particles. ( a ) ( b ) ( c ) Figure 2.3 Clay-Water Interactions (a) Hydrogen Bonding (b) Ion Hydration (c) Dipole Attraction (After Mitchell, 1993) There are three mechanisms of association for ions (van Olphen, 1977). Inner sphere cations are not hydrated and are held tightly through ion fixation involving ionic or covalent bonding. Outer sphere cations are hydrated ions that are adsorbed on the particle surface. In the diffuse ion swarm, hydrated ions associate through electrostatic attraction with particle, but do not bind to the surface. The ions located in the outer sphere complex and the diffuse ion swarm are relatively loosely held by the particle and 8

PAGE 24

can be easily leached, and therefore are considered to be readily exchangeable. These mechanisms of association are shown in Figure 2.4. Figure 2.4 Cation Association (After van Olphen, 1977) 2.1.1.2 Cation Exchange Capacity In solution, the cations adsorbed on the surface can be replaced by other cations. The cations that are associated with the clay surface through electrostatic attraction, which are the outer sphere complexes and the diffuse ions are considered readily exchangeable (Sposito, 1989). The replacing power is the ability of a cation to replace another and is primarily a function of the valence and ion size. Typically, the higher valence replaces lower valence cations and ions with smaller ionic radii are less replaceable than larger ions. The trend of replaceability is as follows: Na + < K + < Mg 2+ < Ca 2+ However, in highly concentrated solutions of a cation with low replacing power, it is possible for the lower to replace a higher-powered cation through mass action. The cation exchange capacity of clay is caused by the unbalanced negative charge resulting from isomorphous substitution, broken bonds along the particle edges and replacement. Since most of the negative charge is caused by the isomorphous 9

PAGE 25

substitution of a lesser valance cation, the exchange capacity is a measurement of the degree of this substitution. The cation exchange capacity is the quantity of positively charged ions that a clay mineral can accommodate on its negative charged surface. The cation exchange capacity, CEC is typically expressed as milliequivalents per 100 grams (mEq/100 g) and can be determined experimentally using the methylene blue test. The constant surface charge density is used to characterize clay particles and can be found by dividing the CEC by the specific surface. The methylene blue test yields a methylene blue capacity, which gives an estimate of the total cation exchange capacity, as well as approximation of the specific surface of a clay sample. The test works by replacing the natural exchangeable cations of the clay with methylene blue compounds. Taylor (1985) presented the following reaction for the irreversible process: Na Bentonite + Methylene Blue Hydrochloride MB Clay + Na Chloride Methylene blue is an organic base in combination with an acid and has a chemical composition C 16 H 18 N 3 SCl. The particle, shown in Figure 2.5 has dimensions of approximately 17 x 7.6 x 3.25. After the exchange, the methylene blue particles are adsorbed to the entire external surface of the clay particle, which allows for an approximation of the specific surface. After all the natural ions of the clay are replaced, saturation is achieved. This is the end point and noted by the formation of a blue "halo" around a drop of solids placed on filter paper. (a) (b) Figure 2.5 Methylene Blue (a) Molecule (b) Clay Surface Adsorption (After Taylor, 1985 and Santamarina et al.,2002) 10

PAGE 26

The maximum adsorption of the methylene blue corresponds to the cation exchange capacity of the clay and the specific surface of the clay particles. Many researchers have reported values of cation exchange capacity determined from methylene blue testing in the range of 70 to 130 mEq/100g (Taylor, 1985; Higgs, 1988; Santamarina et al., 2002). The cation exchange capacity and the surface charge density of the bentonite used in this study were determined experimentally. The procedure used was the European Standard spot test as outlined by Santamarina et al. (2002). The procedure is as follows: 1. The bentonite was dried for 24 to 48 hours at 100C prior to testing. 2. 1.0 gram of dry Fisher Brand, methylene blue hydrochloride powder was weighed and added to 200 mL of deionized water. The solution was magnetically stirred for 10 minutes. 3. 0.5 to 2.0 grams of the dried bentonite was measured and placed in a small beaker. 20 to 50 mL deionized water was added and stirred to make a loose, homogeneous soil suspension. The mass of soil and volume of water were recorded. 4. The methylene blue solution was added in 0.5 mL increments as soil suspension was stirred magnetically for at least 5 minutes. 5. After each addition, a glass rod was used to remove a small drop of the suspension and place it on Fisher Brand P4 filter paper. 6. This process was repeated until a permanent blue halo was formed around the drop and the final volume of methylene blue added is recorded To ensure experimental quality, this test was repeated several times using different amounts bentonite. It should also be noted that longer mixing times were permitted than required by the standard to give adequate time for the exchange to occur and ensure repeatablilty. The following equation was used to determine the cation exchange capacity of the bentonite, expressed as milliequivalents per 100 grams: 11

PAGE 27

g) (mEq/100 (g)wt dry(cc) solutionMBof( g )wt dryMB x (cc) addedClayg100x.Vol1000x87.319MB.C.E.C Figure 2.6 shows the range of experimentally determined values for the cation exchange capacity. The average value for the cation exchange capacity of the bentonite used in this study was determined to be 85.54 mEq/100g, but all values fell in the range of 80 to 90 mEq/100g. 75808590CEC (mE/100g) 0.5 g 1.0 g 1.5 g 2.0 g Figure 2 .6 Experim e ntal Values of CEC o f N a Bent onite The experimental specific surface of the clay was also calculated using the following equation: )g(wtdryClay1AAN5.0(mL)solution MB of .Vol(g)dry wt MB87.3191SMBvs where N is the number of 0.5 mL increments added, A v is Avagadros number (6.02 x 10 23 /mole) and A MB is the area covered by one molecule of methylene blue (assumed to be 130 2 .) The average specific surface of this bentonite was found to be 677.62 m 2 /gram. This value is with in the expected range for montmorillonite, which is 400 to 800 m 2 /gram (Mitchell, 1993). Santamarina et al. (2002) reported 700 m 2 /gram for Na-montmorillonite with methylene blue determination. 12

PAGE 28

The charge density of the clay can be determined knowing the cation exchange and the specific surface. The charge density is given by the following expression: 2mCF where F is a Faraday, or 96,500 Coulombs and is given by the following expression: 2mmeqSSCEC Using the experimental values determined for the cation exchange capacity and the specific surface the charge density of the bentonite is determined to be approximately 0.1218 C/m 2 The values of the cation exchange, specific surface and charge density are important to the clays interaction with polymers. 2.1.1.3 Diffuse Double Layer Cations neutralize the negative charge of the clay surface. Additional salt precipitates are associated with the surface of the clay. When the clay is wet, the salt precipitates go into solution. There is a high salt content at the mineral surface due to adsorbed cations. The escaping tendency due to diffusion and the opposing electrostatic attraction leads to ion distributions adjacent to a clay particle in suspension as shown in the Figure 2.7 (Mitchell, 1993). 13

PAGE 29

Figure 2 .7 Ion D istribution i n D iffuse Double L ayer (After Mitchell, 1993) This area adjacent to the particle surface is called the diffuse double layer or adsorbed layer. The Gouy-Chapman Theory describes the behavior of this region. The assumptions made by the theory are, first that there is no interaction between the ions, which are considered to be point charges. Next, the charge on the particle surface is considered to have a uniform distribution. Finally, the permittivty of the molecules does not depend on their location. This theory is for the one-dimensional conditions only and the particle surface must be large with respect to the thickness of the diffuse layer. The ion distribution in the charged surface region is determined by the temperature and the energy required to bring the ion from an infinite distance away to the point where the electrostatic potential is to be considered. This distribution is given by a Boltzmann equation: kTEEexpnni0i0ii n i is the number of ions of type i per unit volume of bulk solution, E is the potential energy, T is the temperature in Kelvin and k is the Boltzmann constant. This relationship is combined with the Poison equation, which relates potential, charge and distance, gives 14

PAGE 30

one expression for potential and ion concentration, as a function of distance from the surface in the diffuse layer. The Poison-Boltzmann equation is relevant for the case of a single cation and single anion with equal valence and represented by the following expression: kTevsinhven2dxdi022 The distribution of ions in the double diffuse layer is influenced by the surface potential and the properties of the pore fluid. The slope of the potential function of the clay surface is given by: 2zsinh)kTn8(210 where n 0 is the concentration of ions at the surface, is the static permittivty, k is the Boltzmann constant, T is the temperature in degrees Kelvin, and z is equal to the potential at the surface. The potential function decreases exponentially at increasing distances from the surface. This model is for a single diffuse layer that has no interaction with the diffuse layers of other particles. The double layers of clay particles overlap causing interaction between the two diffuse regions. Figure 2.8 models two parallel clay plates and the charge distribution in the interacting area. The distribution of the potential has a similar shape in this region. The distance between the two particles is 2d. Due to this region of overlap there is the development of a midplane potential. 15

PAGE 31

Figure 2.8 Ion Distribution in Interacting Double Layers (After Mitchell, 1993) The distance from the surface to center of gravity of the diffuse layer is defined as the thickness of the double layer and is expressed by 212200ven2DkTK1 The double layer is affected by changes in surface potential, electrolyte concentration, cation valence, and dielectric constant of the electrolyte, as well as pH and ion size. Since the low hydraulic conductivity of bentonite is primarily due to the adsorbed molecules, restricting the pore space active in flow, bentonite is sensitive to changes in composition of the pore fluid that influence the thickness of the adsorbed layer (Shackelford et al., 2000). The properties of bentonite are greatly influenced by the thickness of the double layer. The thicker the layer, the less the likely the clay particles are to flocculate in suspension. This is because the extent overlap of double layers indicates the amount of interparticle of repulsion. If the layers are collapsed due to high electrolyte concentration or higher valence ion, the clay will not swell to the same extent because swelling pressures are associated with greater interactions (Mitchell, 1993). 16

PAGE 32

As the concentration of ions of the increases, the double layer thickness is suppressed, due to the inverse relationship in the expression 1/K. Increases in electrolyte concentration reduce the surface potential, but also greatly increase the decay of potential with distance (Mitchell, 1993). This is demonstrated in Figure 2.9. The potential approaches the clay surface as the concentration increases. This distribution affects the midplane potential and reduces interparticle interactions. Electric Potential Distance from Colloidal Particle Figure 2.9 Electric Potential Distributions The contraction of high swelling clays in ionic solution is due to a compression of the clay double layer (van Olphen, 1977). This is due to diminished particle interactions. Cation valence has an inverse relationship to the thickness of the double layer. Due to preferential adsorption, polyvalent cations collapse the double layer by replacing more than one monovalent cation. Commonly divalent, Ca 2+ replaces naturally occurring Na + in bentonite suppressing the diffuse double layer. Cations that are present in the diffuse double layer are hydrated, meaning that they have a shell of water molecules surrounding them. Table 2.1 gives values for the radius of the hydrated ions of interest. 17

PAGE 33

Table 2 .1 Hydrated Radii of Cations Ion Hydrated Radius () K + 3.8 5.3 Na + 5.6 7.9 Ca 2+ 9.6 Mg 2+ 10.8 The Gouy-Chapman Theory was improved to better define the layer immediately next to the particle. Stern-Gouy model does not make the assumption that the adsorbed cations are point charges, rather assumes the size of the hydrated ion. The Stern layer is a thin film of hydrated cations and oriented water dipoles that are immobilized by strong interaction with the clay surface. This layer falls in between the surface and the diffuse layer. The concentration of the hydrated cations near the surface is a function of the electric potential of the negative charge of the clay. Similar to the Gouy-Chapman theory, this concentration decreases at increasing distances from the particle surface. The Debye length, is the distance to the center of the diffuse layer and is given by: 220Fv2RT where is the static permittivty, T is the temperature in degrees Kelvin, F is Faradays constant. The effect of the Stern layer on cation concentrations can be seen in Figure 2.10. It extends out further from the surface than predicted by the Gouy-Chapman theory because the ion takes up space. The larger the hydrated ion, the greater the thickness of the Stern layer. 18

PAGE 34

Figure 2.10 Stern Layer and the Potential Distribution (After Mitchell, 1993) 2.1.2 Experimental Materials The clay used in this study is Extra High Yield Bentonite, which is a sodium bentonite from Wyoming. It is premium grade bentonite powder, processed and manufactured by Wyo-Ben, Inc. This material is designed for use as an efficient lubricant for drilling applications. The clay is packaged in 50-lb bags and was stored in bins at room moisture and temperature. A series of laboratory tests have been conducted to classify the geotechnical soil properties of the bentonite used in this study. These values will be used to evaluate the effect of the various polymers on the bentonite and the extent of interaction. The experimental values for soil properties of the polymer-modified clays are presented in Chapter 5. Bentonite has a very high liquid limit due to its ability to adsorb water on the very large specific surface of the particle and to allow water into the interlayer. The liquid limit of the sodium bentonite has been widely published to be in the range of 330% to 600% (Bardet, 1997; Mitchell, 1993). The liquid limit of the bentonite used was experimentally determined to be approximately 550% as shown in Figure 2.11. 19

PAGE 35

y = 19.422x + 161.95w = 550.39%200300400500600700800101520253035Displacement (mm)Moisture Content (%) Figure 2.11 Experimental Liquid Limit of Na-Bentonite Sodium Bentonite clay is widely known for its high swelling characteristics. Sodium bentonite clay has the ability to absorb four to five times its own weight in water and can swell five to fifteen times its dry volume at full-unconfined saturation. Researchers have reported the swell index of sodium bentonite to range between 25 to 65 mL/2g (Mitchell, 1993; Bardet, 1997). This is attributed to the amount of cation exchange capacity and the hydration of the adsorbed cations. The swell index for the experimental sodium bentonite was found to be 60 mL/2g. The effect of ion type and concentration was also evaluated. This causes suppression of the swelling characteristics of the clay, as shown in Figure 2.12 and is directly related to the thickness of the double layer. 010203040506070NaClKClMgCl2CaCl2Liquid solutionSwelling Index mL/ 2 1 M 0.1 M 0.01 M Figure 2.12 Experimental Swell Index of Na-Bentonite 20

PAGE 36

2.2 Polymers 2.2.1 Chemical Composition Polymers are formed by chemical reactions in which a large number of repeating molecules called monomers are joined sequentially to form a chain. The physical and chemical properties of a polymeric chain are completely different then the properties of the monomers that make it up. Both naturally occurring and synthetic polymers exist. While synthetic polymers are commercially available in a wide of range molecular weights, typically polymers are naturally high molecular weight compounds. Polyelectrolytes are water-soluble polymers that are comprised of many repeating units that are polymerized to have a net ionic charge. Depending on the monomer used, they can have a positive charge (cationic), negative charge (anionic) or have electrical neutrality (nonionic.) Naturally, these polymers tend to exist in coils, curled around one another, however, when they are put into solution the polymer chains uncurl and lengthen due to the repulsive forces between the ionized groups. Although, there are many different types of polymers commercially available, this discussion will focus on derivatives of the polymerization of acrylamide, as this is the material used in the study. Acrylamide is a derivative of the acrylate family of polymers, which have the chemical structure shown in Figure 2.13. Figure 2.13 Polyacrylate 21

PAGE 37

Polyacrylamide or PAM is a polymer known for its great affinity for water and is commonly used in products such as in diapers and potting soil. Polyacrylamide is an acrylate polymer formed from acrylamide subunits. The chain of polyacrylamide has hydrogen on every other carbon replace by an amide group, and is given by the structure in Figure 2.14. Figure 2.14 Polyacrylamide The amide functional group is -CONH and it allows for linking between polymer strands. One molecule can react with the same group of another molecule, forming a link between them with the structure CONHCO. The unlinked amide groups can form hydrogen bonds with water because they contain NH 2 groups. This allows polyacrylamide to absorb many times its mass in water. In the presence of ionic substances, the polyacrylamide will release the absorbed water due to interference with the hydrogen bond. These polymers can be easily cross-linked, meaning that parallel chains can be covalently bonded together. The polyacrylamide structure can be cross-linked or non-cross-linked, but since the cross-linked bond is more rigid the cross-linked polymers are not water-soluble. All the polymers used in this study have polyacrylamide backbones but the net ionic charge is obtained by further polymerization. The anionic and nonionic are formed using poly(acrylic acid) which has the structure shown in Figure 2.15. Figure 2.15 Poly(acrylic acid) 22

PAGE 38

The cationic derivatives are much more complex, typically involving co-polymerization with quaternary ammonium ion (NH 4 + ). There are many possible structures for any of these polymers, but they are classified according to net charge and density of the charge along the polymer chain. 2.2.2 Clay Polymer Interaction Three classes of polymers, cationic, anionic and nonionic are used to modify the clay in this study. The clay-polymer interaction varies according to the molecular weight, surface charge and charge density of the polymer. The nature of these interactions is of interest because it affects the engineering properties of the soil. A polymer chain is long and flexible which allows the polymer to adopt various shapes and to be attached by numerous segment-surface bonds. A typical interfacial conformation consists of tails, loops and trains. Trains have intimate contact with the clay surface, while the tails and loops are not adsorbed. Polymer adsorption is pictured in Figure 2.13. Generally, the adsorption of a polymer increases with the length of the chain, up to a limiting molecular weight. However, all polymers may not be able to enter the interlayers of the clay structure, due to their molecule or coil size. X-ray diffraction analysis has indicated that some polyacrylamide polymers have successfully entered the interlayer spacing (Gungor and Ece, 1999). Polymers compete with water molecules for adsorption of the surface. 23

PAGE 39

Hydrated cations Polymer chain Clay p article Water molecules Figure 2.16 Adsorption of Uncharged Polymer on Clay (After Theng, 1979) Adsorption of polymers will cause changes in the double layer of the clay. The changes in the Gouy layer are attributed to the loops and tails, while changes in the Stern layer are attributed to the trains, shown in Figure 2.14. Because these regions are altered, so is the net interaction energy of the region. In some cases, the polymer will form a bridge between two adjacent plates, thus reducing the forces of tension between the two. Stern Layer Gouy Layer Adsorbed Cations Hydrated Cations Anion Adsorbed Polymer Chain Figure 2.17 Clay Interaction (after Theng, 1979) 2.2.2.1 Cationic Interaction Cationic polyacrylamide is a non-crosslinked long-chain polymer made of the monomer acrylamide. The presence of the co-polymer, quaternary ammonium group 24

PAGE 40

within the backbone of this molecule ensures that it maintains its very strong cationic charge. The co-polymer is a cationic derivative of acrylic acid. Polycations are absorbed via the cation exchange capacity of the clay. The bentonite has monovalent sodium as its exchangeable cation, which can be easily replaced by one of the many charges along the chain. Higher charge density polymers have a higher adsorption capacity. When polymers of low cationicity are absorbed, a significant proportion of the polymer extends away from the surface in loops and tails (Breen and Watson, 1998). This has been shown to lead to interparticle bridging and/or wrapping of the clay particle. However, at values greater than 15% active polymer, the polymer is found to collapse onto the surface, with few loops or trains. This process is not likely to be reversed because it would require instantaneous desorption of all trains of the polycation and diffusion away from the surface (Breen, 1999). 2.2.2.2 Anionic Interaction Anionic polyacrylate is a polymer of acrylamide. The structure is (CH2=CHCOO H) and it is synthesized from the linear polymerization of acrylic acid. Since the basic polymer unit is acrylic acid the polymer has the potential to carry a high charge along its chain. The surface of the clay particle is negative, so it would be expected that an anionic polymer would be repelled. However, early work by Ruehrwein and Ward (1952) and Parfitt and Greenland (1970) has shown that anionic adsorption is possible. The bonding mechanisms of polyanions are electrostatic attraction, hydrogen bonding and van der Waals forces. Due to repulsive forces anionic polymers can remain suspended winding through the diffuse layer. At lower pH levels, electrostatic repulsion is weakened and there is increased chain coiling, which allows for some anion adsorption (Theng, 1979). As the charge density increases, the chain becomes longer and less flexible, which promotes bridging. In the presence of salts, the negative charges are shielded from one another allowing the polyanion to coil and collapse on the clay surface 25

PAGE 41

(Breen, 1999). This essentially coats the polymer and adsorbed cation, potentially forming a protective layer. It has also been suggested that another mechanism of anionic interaction is through complexation, ionic bonding or coordination to the cations naturally present at the clay surface shown in Figure 2.15. Anionic polymers Clay p article Figure 2.18 Interaction Between Anionic Polymers And Clays (After Theng, 1979) The positive crystal edges of the octahedral sheet offer a site for anion exchange. Complexation of polyacrylic acid with Al 3+ ions can account for some uptake. This allows for the formations of a soil fabric, through interparticle bridging. In relation to nonionic and polycationic polymers, the polyanionic demonstrates less adsorption and while there is complexation and interaction with the surface and ions in the diffuse layer, there is minimal intercalation. 2.2.2.3 Nonionic Polymers Unlike the charged polymers, the nonionic tends to remain in a random coil conformation in solution. When the polymer comes in contact with a sorbing substrate, such as the particle surface, there is a tendency for the polymer molecule to collapse and spread out (Theng, 1979). The driving force for this adsorption is the entropy gain that is associated with the desorption of numerous molecules. 26

PAGE 42

Polyacrylamide can be strongly adsorbed to and/or associated with the particle surface. Depending on the size, or molecular weight, some polyacrylamide chains can be accessible to all surfaces of the sodium bentonite, due to the separation of the silicate layer caused by swelling. Coordination complexes can be formed between the exchangeable cations and the amide groups of the polymer, which explains the strong binding of the polymers, particularly in divalent systems (Tanihara and Nakagawa, 1975). When the nonionic polymer is added to the clay without the presence of electrolytes, a network of polymer-clay links is formed. If electrolytes are then introduced, the polymer chain is likely to spread out over the surface and interparticle bridging is maintained. 2.2.3 Experimental Materials The polymers used for this study were supplied by Emerging Technologies, Inc. All polymers are synthetic, organic water-soluble polymers based on the polymerization of polyacrylamide. The polymers were white, granular solids and were stored in air-tight containers at room temperature prior to use, shown in Figure 2.16. Figure 2.19 Polymer Granules The exact chemical composition of the polymers was considered to be proprietary information and, therefore, not supplied by the company. The technical data supplied by Emerging Technologies are listed in Table 2.2. It also should be noted that the melting 27

PAGE 43

point for all the polymers is > 200C. The anionic polymers used are comprised of units of acrylic acid, which provide the negative electrical charge. The cationic polymers however, rely on three functional groups to impart the active charge and the specific chemical make up was not supplied. Table 2.2 Polymer Material Data Product Charge Bulk Density (lbs/ft 3 ) Molecular Weight (Daltons x 10 6 ) Weight Percent Ionic Solution Viscosity 0.5% in Dist Water (CP) Effective pH Range 10G-80A Medium Anionic 44 3 4 40 > 4500 6 13 10G-70A Low Anionic 42 3 4 15 > 2000 5 12 10G-20 Nonionic 41 4 6 N/A > 200 0 13 10G 90C Low Cationic 36 3 4 12 15 > 1000 1 13 10G-100C High Cationic 38 10 55 > 5000 1 13 The electrical conductivity and pH was measured for all the polymers. 0.25 grams of each of the polymers was slowly and carefully added to a beaker with 400 mL of deionized water and magnetically stirred for 1.5 to 2 hours until all of the polymer was dissolved. The electrical conductivity of the solutions was measured using the Accumet AB30, 4-cell conductivity meter and the pH using the Accumet AP63 pH meter shown in Figure 2.17. Both instruments were calibrated with the standardizing solutions prior to measurement. The results of these measurements are shown in Table 2.3 28

PAGE 44

Figure 2.20 EC and pH Measurement Devices Table 2.3 EC and pH of Experimental Polymers Polymer Dry wt. (g) DI (mL) EC (mS/cm) pH 10G 100C 0.25 400 171.2 3.92 10G 90C 0.25 400 47.71 4.71 10G 20 0.25 400 21.66 7.12 10G 70A 0.25 400 68.95 6.91 10G 80A 0.25 400 155.1 7.96 The charge of a polymer is the amount of the net electrical potential along its chain. If the length of the chain is unknown, the amount of charge in a given amount of material must be determined. The charge density titration can be performed on a polymer to evaluate the amount of material absorbed on to its surface. The amount of material absorbed is proportional to surface charge of the polymer. 29

PAGE 45

2.2.3.1 Polymer Titration The colloid titration method is one way to estimate the net charge density. What is actually measured is the capacity of the mixture to adsorb a polyelectrolyte of opposite net charge. A small amount of indicator dye is added to a known volume of cationic solution. The cationic polymer solution is titrated with a negatively charged solution with known properties. Complexation between the dye and the negatively charged polymer causes the color-change at the endpoint. This process is slightly modified for the anionic polymers, where a back titration must be performed. A small amount of the anionic is first treated with the cationic standard and then titrated with the negative solution. At the endpoint the amount adsorbed can be calculated and related to the surface charge density of the polymer. To better characterize the polymers to be used for clay modification, polymer titrations were performed. This procedure enables the electrostatic charge of an unknown polyelectrolyte to be determined. Table 2.4 shows the solutions that were to be prepared for the titration. Table 2.4 Standard Titration Solutions Chemical Formula Purpose Strength Toluidine Blue O, TBO C 15 H 6 ClN 3 S Indicator Solution 1g/L Dimethyl-1,5-diazaundecamethylene polymethobromide, DDPM C 13 H 30 Br 2 N 2 Cationic Standard 0.0381633g/L (0.0002 N) Poly(vinyl sulfate) Potassium Salt, PVSK C 2 H 3 O 4 SK Anionic Standard 0.5g/L 30

PAGE 46

The experimental procedure, Charge Density Determination for Organic Polyelectrolytes was followed. First, all solutions were prepared to the concentrations given above. The PVSK must be standardized with the DDPM to obtain the normality of the PVSK. The PVSK was placed in a burette on a ring stand centered over a magnetic stirring plate with a solution of 10 mL of the DDPM containing 2 drops of the TBO. The PVSK was added to this solution until streaks of purple appeared in the solution. The solution was then added dropwise until a light purple color was achieved. The total amount of PVSK added was recorded and used to calculate its normality. The titrations were performed on 0.0125% polymer solutions. The experimental setup is shown in Figure 2.17. The cationic were titrated to a purple endpoint, directly, similar to the process of the standardization. The anionic polymeric solutions were treated with the cationic standard prior to the back titration. 1 mL of polymer was mixed with 10 mL of DDPM and 2 drops of TBO. This solution was then titrated to a purple endpoint. To minimize experimental error, all tests were repeated several times for each of the polymeric solutions. PVSK PVSK Anionic Polymer + DDPM + TB O Cationic Polymer + TBO (a) (b) Figure 2.21 Titration Setup (a) Cationic (b) Anionic Table 2.5 gives the results of the polymer titration. The values were calculated with assumption that the polymers had a purity of 95%. The pH of the solution can 31

PAGE 47

greatly affect the outcome of the titration for cationic polymers. Since the cationic polymers used are assumed to be quaternary, whose charge remains constant at wide ranges of pH, no pH adjustment or monitoring was performed. Table 2.5 Experimental Charge Densities of Polymers Polymer Charge Density (mEq/100g) 10G 100C 294.7 10G 90C 95.5 10G 20 NA 10G 70A 186.2 10G 80A 423.9 2.2.3.2 Theoretical Charge Density A theoretical method of determining the charge density was also evaluated. For the anionic polymers, the only unit imparting charge on the polymer chain is acrylic acid. Knowing the formula weight of acrylic acid, as well as the number of equivalents per unit and the mole percent active, allows the calculation of the charge density of the anionic polymers to be determined. The manufacturer, for the purpose of carrying out this calculation, supplied the number of equivalents and the mole % active. gram100mEq100000active%molesequivalentof#WeightFormula1 This theoretical calculation gives the high anionic polymer (10G-80A) a charge density of 444.44 mEq/100 grams and the medium anionic polymer (10G-70A) a charge density of 166.66 mEq/100 grams. The value obtained experimentally for the low anionic was higher than the theoretical value calculated. The medium anionic was higher theoretically than experimentally. This could be due to a number of factors. 32

PAGE 48

Assumptions were made for the purity of the polymers, and the mole % active was supplied in a range. Experimental error with titrations could lead to inaccurate results, particularly with the preparation of the standard and polymer solutions, which requires the measurement of very small masses and mixing of very dilute solutions. 33

PAGE 49

CHAPTER 3 EXPERIMENTAL BACKGROUND & LITERATURE REVIEW 3.1 Clay Fabric Na-bentonites have a small crystal size and high water binding capacity, which allow the clay to exist in a dispersed arrangement. The hydrated sodium ions surround the clay particles and contribute to the thickness of the diffuse double layer. The electrostatically bound hydrated shells hinder pore waster flow through this region, which gives the bentonite its low permeability characteristics. When cation exchange occurs in the bentonite, in particular the replacement of monovalent cations with polyvalent cations, there is an alteration in the clay fabric. The dispersed clay tends to aggregate or become more coarsely dispersed caused by changes in the diffuse layer and reduction of interparticle forces. Egloffstein (2001) reported that exchanging calcium for bentonite for the natural bentonite resulted in a loss of water of 6% to 12%. Figure 3.1 shows three different clay fabrics. The first fabric, Figure 3.1(a) shows a dispersed particle arrangement. This is the natural structure when Na-bentonite is hydrated, allowing water molecules enter the interlayer spacing and causing the clay to swell. After hydration, if the clay is exposed to a divalent solution, gradual cation exchange occurs, collapsing the diffuse layer resulting in the fabric shown in Figure 3.1(b). The third fabric, Figure 3.1(c) has an aggregated particle association. This structure is the consequence of exposure to a polyvalent solution without prior hydration. This abrupt transformation limits water mitigation into the interlayer space because the 34

PAGE 50

electrostatic forces between the cation and the clay particle surface are larger than the hydration forces of the divalent cation (Ashmawy et al., 2002). Figure 3.1 Clay Fabric (a) Dispersed (b) Collapsed (c) Aggregated (After Ashmawy et al.,2002; Egloffstein, 2001) Several investigators have reported that the order that permeant liquids are introduced to bentonitic barrier materials can have a significant effect on the final hydraulic conductivity (Shakelford et al., 2000; Ashmawy et al., Daniel et al., 1993). The permeability is influenced by these changes because the flow path is affected. The dispersed fabric results in the lowest permeability because the homogeneous arrangement has the least amount of flow-efficient pore space. On the other hand, the aggregated fabric allows the greatest amount of flow because of the formation of open pore space. Mitchell (1993) describes the soil fabric consisting of three parts, the microfabric, minifabric and macrofabric, which can all affect the flow of fluid. The microfabric consists of the natural particle aggregates, which in the presence of water are well dispersed and allow little flow through the soil. The minifabric is described as an inter-assemblage of pore and aggregates, which can carry greater volumes of flow. Cracks and fissures in the soil fabric are considered to be part of the macrofabric. 3.2 Permeability Theory Soils can conduct the flow of fluid, electricity, chemicals and heat. For relevance to the current study fluid and chemical flow will be discussed. Hydraulic flow through a 35

PAGE 51

soil mass is demonstrated in Figure 3.2 (a). According to Darcys law, there is a proportional relationship between the flow rate and the hydraulic gradient for porous media, which is represented by the following expression: q h = k h i h A where q h is the hydraulic flow, i h is the hydraulic gradient, A is the cross sectional area of flow and k h is the coefficient of permeability of the soil or porous media. In a given soil the value of k h may vary a few orders of magnitude, as a result of changes in fabric, void ratio and water content (Mitchell, 1993). For this reason, the coefficient of permeability is a parameter that is thoroughly investigated, particularly when the performance of a hydraulic barrier is vital. Laboratory tests can be conducted to determine the coefficient of permeability of soil. The two main types of tests are constant head and falling head permeability tests, each have many variations with numerous experimental setups. H C1 C2 (a) (b) Figure 3.2 Mechanism of Flow (a) Hydraulic (b) Chemical Chemical flow, or diffusion, is driven by a chemical potential and concentration gradient, shown in Figure 3.2 (b) and is defined by Ficks law. Diffusion is the movement of chemical molecules from a region of higher concentration to one of lower concentration. Ficks first law is applicable only to steady state diffusion, and is given by the following expression: ADiJcD 36

PAGE 52

where D is the diffusion coefficient, i c is the chemical gradient, and A is the cross sectional area of the flow. However, Ficks second law for transient diffusion is used for analysis of diffusive flow in soils because it considers the time rate of change of concentration with distance. Coupled flow is a flow of one type, driven by a different type of potential gradient. The transport of pore water containing chemicals under a hydraulic gradient is called advection. The advective transport is related to the velocity of the fluid, while the non-advective transport is called the diffusive flux. In laboratory permeability tests where the soil is permeated with chemical solutions the primary mechanism of chemical transport is advection. Bentonite can display a membrane-like property that affect the chemical transport by causing the restriction or retardation of certain ions due to electrostatic forces in the diffuse double layer. Sorption, or the binding of chemicals on solids, is significant because it retards the rate of chemical transfer. Chemicals in soils tend to establish a balance between the amount on the solid surfaces and the amount in solution. Some chemicals exist primarily in the liquid phase, while others are strongly adsorbed and exist primarily on the solid surfaces due to the cation exchange of the mineral surface. Ion exchange processes are equilibrium processes, which means that the exchange occurs until an adsorption balance between the clay surface and the solution is achieved. Malusis and Shackelford (2004) evaluated the hydraulically driven and diffusive chemical transport in GCL to evaluate the coupled solute transport theory. Solute transport analyses for natural and engineered barriers consisting of low permeability clays are performed using models based on advective-dispersive transport theory. 3.3 Geosynthetic Clay Liners Geosynthetic clay liners (GCLs) are composite materials that consist of a very thin layer of bentonite sandwiched between two layers of geotextile or bonded to a geomembrane. They are increasingly used as hydraulic barriers in lining systems. GCLs 37

PAGE 53

are effective barriers because of the unique properties of bentonite. In the presence of water, the bentonite swells to seal holes and create a very low permeability lining. However, when this liner is permeated with liquids other than water, such as in the case of a landfill, increases in hydraulic conductivity have been reported in many cases. Several companies have marketed chemical resistant bentonites that have been treated to maintain hydraulic performance in the presence of chemicals. The soil additives and methods of treatment are typically proprietary information. Many laboratory studies have been conducted on the bentonite from various geosynthetic clay liners, treated and non-treated to evaluate the performance of the commercial products (Ruhl and Daniel, 1997; Shan and Lai, 2002; Ashmawy et al., 2002; Shackelford, at al., 2000). Although no long-term testing has been fully carried out, research results appear promising in many cases. In reviewing the literature on hydraulic testing of bentonite and GCLs, it can be seen that there are factors that affect the hydraulic performance which are thoroughly investigated. All the factors relate directly to the properties of the clays micro and macro structure and include valence and concentration of the electrolyte, void ratio, first wetting condition, and gradient. Correlations between index properties and hydraulic conductivity have been made, as well. These findings will be discussed in the following section in detail. 3.3.1 Valence The influence of valence has been shown to be evident in free swell tests conducted on GCL bentonite by Shackelford, et al. (2000). The test was performed according to ASTM D 5890, The Standard Test for Swell Index of Clay Mineral Components of Geosynthetic Clay Liners. The bentonite was hydrated with deionized water and three different 0.025 M chloride solutions. The results, shown in Figure 3.1, show the change in swell according to the valence of the cation. 38

PAGE 54

The highest valence cation, Al 3+ has the largest affect on the swelling capacity of the clay, which is consistent with the Gouy-Chapman and Stern-Gouy theories. The swell in deionized water is only slightly larger that in the LiCl, due to the monovalency of the cation. The Li + may replace the Na + but the little change in swell because the minimal change in double layer thickness due to the 1:1 exchange. Permeability tests were also conducted on the GCL bentonite permeated with the same concentration solutions as above. The findings were consistent with changes in the thickness of the diffuse layer. The hydraulic conductivity reported for the monovalent permeant was 3 orders of magnitude lower than that of the divalent. Figure 3.3 Effect of Valence (After Shackelford et al., 2000) Jo et al. (2001) investigated the influence of single-species salt solutions of various concentration, cation valence and pH on the swelling and hydraulic conductivity of nonprehydrated GCLs. It was found that monovalent cations reduce the swelling to different degrees depending on the hydrated radius of the cation. Divalent cations suppressed the swell more notably than the monovalent, however the species was found to be less influential on the degree of swell. Valence, concentration and pH were found to have analogous effects on swelling and hydraulic conductivity. Ruhl and Daniel (1997) described the response of geosynthetic clay liners to permeation with various chemical solutions and leachates. Ca 2+ solutions were found to be far more aggressive to the GCLs than real leachates due to the lower concentration of 39

PAGE 55

cations. Contaminant resistant bentonites produced variable results, as some are more resistant to specific chemicals. Experimental results have shown that Ca 2+ from dilute solutions can gradually exchange the naturally occurring Na + on the exchange complex, resulting in gradual compression of the adsorbed layer and consequent gradual increase in hydraulic conductivity (Shakelford et al., 2002). This is shown to occur at very large pore volumes of flow, which indicates that the cation exchange can occur over a long period of time. 3.3.2 Concentration The concentration of a permeant influences the hydraulic and swell properties of GCL bentonite. Concentrations were varied from 0.01 to 0.1 M. It is shown that as the electrolyte concentration increases, the swell volume decreases and the hydraulic conductivity increases, which indicate a reduction in the thickness of the double layer. This is consistent with the equations for the thickness of the double layer. At 1M the interlayer spacing is nearly as small as possible, consisting of about four monolayers of water regardless of cation spacing (Zhang et al., 1995). Shackelford et al. (2000) discussed the factors affecting the hydraulic conductivity of GCLs permeated with high concentrations of monovalent and any concentration of divalent solutions. The importance of allowing the test to run for sufficient period of times was highlighted. 3.3.3 Pre-Hydration Pre-hydration has been highlighted in the literature as an important consideration in the performance of bentonite and CGLs. Ashmawy et al. (2002) demonstrated the effect of pre-hydration on untreated and polymer treated bentonite. The significant increases in hydraulic conductivity were attributed to the changes that occur in the fabric. 40

PAGE 56

It was found that the polymer treated clays only demonstrated limited improvement over the unmodified bentonite. Shan et al. (2002) evaluated the effect of hydrating liquid on the hydraulic properties of GCLs and similar conclusions are made of the importance of pre-hydration. Jo et al. (2001) found that at concentrations of 1M and above the effect of valence was not observed for nonprehydrated samples. Chemical resistant GCLs were tested in nonprehydrated conditions and found to have very high hydraulic conductivities, which indicates the sensitivity of even treated clays to the first wetting fluid. Ruhl and Daniel (1997) warn that laboratory tests where samples are fully prehydrated may not simulate actual field conditions and predict values for the permeability that are far lower than when implemented in the field. 3.3.4 Void Ratio Void ratios are found to have a considerable impact on the permeability of bentonite and GCLs. The thickness of the diffuse layer determines what portion of the voids is available for flow. At lower void ratios there thickness of the double layer is reduced, which means that there is a higher midplane potential and a more crowded diffuse ion swarm. This greatly restricts flow, whereas if particle are further apart there is less interaction between the diffuse layers allowing higher hydraulic conductivity. Figure 3.4 Effect of Void Ratio ( after Shackelford et al., 2000) 41

PAGE 57

The effect of varying the voids can be seen in Figure 3.2 where e bf is the final bulk void ratio. It can be seen that the trend is the greater the void ratio, the higher the permeability. The effect of varying the void ratio appears to be independent of the effect of change in the thickness of the adsorbed layer. The trends of change are fairly uniform despite the changes in cation concentration. The effect of the void ratio is found to be more prominent in soils that have not been prehydrated. 3.3.5 Testing Procedures Hydraulic conductivity alone does not give a clear indication as to when a test should be terminated. Shakelford et al. (1998) suggest using the electrical conductivity and pH as an indicator of the chemical composition of the effluent to determine chemical equilibrium. If chemical equilibrium is not achieved, there is still a long-term potential for an increase in hydraulic conductivity. Hydraulic gradient can have an affect on the hydraulic conductivity due to the high seepage flows. The ASTM standard recommends a maximum of 30 for the hydraulic gradient; however, Rad et al. (1994) have shown that the hydraulic conductivity of a GCL is unaffected at gradients as much as 2800. 3.4 Modified Clays Sensitivity to pore fluid conditions can be reduced by modifying the clay. The engineered modifications use the cation exchange capacity of the clay to sorb organic compounds to the surface. The hydraulic and sorptive properties can be enhanced depending on the compound used to treat the clay. Chemically resistant bentonites have been developed for applications where chemical interactions are likely to affect the adsorbed layer and consequently, the hydraulic conductivity (Shackelford et al., 2000). 42

PAGE 58

3.4.1 Organobentonites Modified clays have shown great potential as adsorbents for organic pollutants. Organobentonites are clays that have been organically modified to increase pollutant retention and resist pollutant transport. Extensive research has been conducted on the sorptive properties of these materials (e.g. Bartelt-Hunt et al., 2003; Lo et al., 1997). Organic compounds interact with play particles by adsorption, ion exchange and intercalation. The properties of the organoclays are a function of the base clay and organic compound. When an organic molecule enters the interlayer or penetrates between the silicate layers, the molecule is said to have intercalated. Size is a limiting factor for these interactions. Some organic compounds are larger than the exchange sites of the surface of the clay, which hampers ion exchange. Similarly if a compound is too large it is prevented from entering the interlayer. Organic compounds have been shown to force the spacing of the interlayers apart (Li et al., 1996). Organophillic clays are commonly manufactured to enhance the sorptive properties to target organic compounds. Organobentonites are the most common of this type. They are made by exchanging the naturally occurring Na 2+ Ca 2+ and Mg 2+ with an organic compound, typically quaternary ammonium cations. The sorption of nonpolar organic pollutants has been found to be several magnitudes greater on organobentonites than unmodified clays. This process changes the clay from a hydrophilic, or water loving to a hydrophobic, or water hating clay. Organobentonites can retain low permeability in the presence of nonpolar liquids and are stronger and less compressible than unmodified clay (Bartelt-Hunt et al., 2003). In research by Bartelt-Hunt et al. (2003) and Redding and Burns (2002), the clays were prepared in quaternary ammonium cations solutions at percentages of the cation exchange capacity of the clay, ranging from 20% to 125% to assess the organic uptake. The quantity of the organic cation was determined by 43

PAGE 59

ZGMWMCECMfcationclaycation where f is the fraction of CEC satisfied by the organic cation, M cation is the mass or organic cation required to achieve the desired fraction of CEC, CEC is the cation exchange capacity of the base clay, M clay is the mass of the base clay, GMW cation is the gram molecular weight of the organic cation and Z is the moles of charges per equivalent. Using this equation to determine the quantity, organic solutions were added to the Na-bentonite. This allowed the effect on the surface chemistry be related to the actual organic uptake to be quantified. The presence of large particle forces opening the interlayer was verified by the result of lower specific gravity of the soil due to a less dense configuration. A trend of increasing organic content with decreasing density was observed. The free swell of the organobentonite in organic phase liquids was 2 to 4 times the volume of the unmodified bentonite. The hydraulic conductivity of organobentonites has been found to be unacceptably high. Techniques such as mixing the modified clay with unmodified clay to improve hydraulic response are currently being investigated at the University of Virginia. 3.4.2 Polymer Treatment Polymer modification of the bentonite has been introduced commercially in GCLs and drilling muds, however data concerning the treatment process is limited. One study conducted by Liao (1989) investigated polymer/bentonite/soil admixtures as hydraulic barriers. A blend of water soluble, high molecular weight linear and cross-linked acrylamide based polymers were used as admixtures at 1 wt%. The permeants used were brine and gasoline. Some of the polymers, which were all proprietary, were found to improve the hydraulic performance, while others had little impact. It was concluded that polymer modification can be effective for creating low permeability seals. A great deal of research has been conducted on clay polymer interactions for water treatment and 44

PAGE 60

industrial process applications. Although many of these studies are for different engineering applications, the findings can be applied for modification of clay for containment purposes. Gungor and Ece (2002) examined the adsorption of nonionic polymers on Na-Bentonite and found that the extent of interaction was determined by a number of parameters including polymer concentration, molecular weight, functional groups of the polymer, clay/water ratio, surface charge of the clay particles, pH and temperature. Adsorption occurs when the polymer has preferential affinity to the surface over water molecules. Their studies revealed that the polymer interaction occurred only at the particle surface not the interlayer. Polymers were shown to bridge particles, which resulted in larger aggregated particles. For this bridging to occur the polymer loops must be able to span the distance between particles caused by electrostatic repulsion, or the thickness of the double layer. Breen and Watson (1998) investigated polycation exchanged clays. The polycations were adsorbed. The conclusion was that polycation-exchanged clays offer the promise to be tailored as adsorbents for organic pollutants. The study did not examine the hydraulic properties of the soils, but focused on the polymer uptake and pollutant sorption capacity. Churchman (2001) examined the formation of complexes between bentonite and various cationic polyelectrolytes, one of which was polyacrylamide. Clay polymer reactions were found to be complete at low polymer/clay ratios. The focus of this research was to remove nonionic and anionic pollutants. It was found that lower polymer loadings resulted in the largest amount of nonionic uptake, while higher loadings were more likely to adsorb anionic pollutants. 45

PAGE 61

CHAPTER 4 EQUIPMENT AND EXPERIMENTAL METHODS 4.1 Testing Program A laboratory-testing program was carried out to determine the effect of polymer modification on the mechanical, hydraulic, and chemical properties of bentonite clay. After reviewing the current literature, it was concluded that a water-soluble polymer would be desirable for this experimental study. Polyacrylamides are abundant polyelectrolytes, commercially available in a wide variety of forms and charge densities. Since ions play such a vital role in the performance of bentonite clay, polymers with different charge and charge densities were evaluated. A total of five different polymers were used to treat bentonite clay. Liquid limit, swell index, specific gravity and hydraulic conductivity tests were performed. The modified clays were evaluated for their performance in the presence of aggressive inorganic solutions. Experimental variables include, charge and charge density, polymer to bentonite ratio, chemical solution and concentration and void ratio. Due to the number of experimental variables, a test matrix was established to reduce the number of tests and ensure that adequate comparisons and conclusions could be drawn from the data. The tests performed can be found in Appendix A. 46

PAGE 62

4.2 Sample Preparation Since the commercial methods used to treat bentonite are unknown, a technique to achieve soil polymer interactions was developed for the soil samples. The extent of the interaction was only evaluated by comparing the performance of the modified clay. The process of sample preparation was the most rigorous portion of the laboratory experimentation. The following describes the mixing techniques used for the treatment and modification of the soils. 4.2.1 Mixing Procedure Two weight percent ratios of polymer to bentonite mixes were examined in this study, 0.5 wt% and 1.0 wt%. All polymers were dissolved in deionized water using a magnetic stirrer prior to mixing with the bentonite. Approximately 0.025% solutions were prepared by very slowly adding the granular polymer to the deionized water. It was necessary to add the polymer very slowly to avoid flocculation of the polymer granules. The stirrer was set on medium mixing speed and stirring times ranged from 45 minutes to 3 hours for the polymers to be completely dissolved. The bentonite was dried at 50C, measured and placed in a large metal bowl. The polymer solution was then added directly to the dry clay and mixed with an electric hand mixer. The beaker was flushed several times with deionized water, which was added to the mix to ensure that all the polymer solution was added. Additional deionized water was added slowly to bring the mixture to a thick slurry. In order to enhance polymer dispersion and to ensure that the mixture was homogeneous, the soil was mixed for 45 minutes with the electric hand stirrer. The slurry was then covered and permitted to hydrate for 24 hours. After the 24-hour period, a small amount of water was added and the slurry was mixed for another 10 minutes. The presence of adsorbed water on the interaction of the clay and polymers was evaluated by testing two drying conditions. Two sets of soils were prepared one that was 47

PAGE 63

heated to 100C, dried and processed, the other simply mixed to an appropriate water content and tested directly. The soils were dried to remove the water adsorbed to the surface, reducing the distance between the polymer chain and the surface, promoting interaction and adsorption, as shown in Figure 4.1 After the mixing process, the soils were placed in the oven and dried at 100C for 48 hours. When removed from the oven the modified clays were stored in airtight containers, until ready to be further processed. (a) (b) Wate r Molecules Polyme r Chai n Clay Plate Adsorbed Polymer Figure 4.1 Clay Polymer Interaction (a) Not Heated (b) Heated 4.2.2 Grinding Technique After the soils were dried in the oven at 100C, processing was required to obtain a powder form. This process was key to the properties exhibited by the clay. If the clay particles were left too large, the water would only interact with the exterior surface, greatly reducing the swelling characteristics and hence the performance of the clay. When removed from the oven, the clay was in large, very hard clumps. Pounding on the sample between two sheets of metal, as well as forcing it through a metal mesh with a heavy hammer was the technique used to crush it into small pieces. The clay at the beginning and the end of this process can be seen in Figure 4.2. 48

PAGE 64

Figure 4.2 Clay Sample After Drying The next phase of the grinding process involved one of the two mechanical processes, which were a ball mill and a grinder. The ball mill contained 100 stainless steel balls, which crushed the sample. The clay samples were placed in the ball mill and permitted to crush for 24 hours. The powder was separated with a sieve and the remaining large particles were placed back in the ball mill to crush for another 24-hour period. This process was repeated until the entire sample was crushed. (a) (b) Figure 4.3 Mechanical Crushing: (a) Ball Mill (b) Grinder A grinder was also used to crush samples and was found to be a highly efficient because it was designed to reduce material to small particles. This method was very fast and resulted in far less loss of material than the ball mill method for preparing the modified clay sample. 49

PAGE 65

Both the procedures for the grinder and the ball mill can be standardized to obtain uniform sample production. The grinder has settings for coarseness, speed and the number of passes through the machine that can be controlled. The ball mill does not offer variable speeds, however the number of steel balls, as well as the tumbling time can be modified. The clay was finally pulverized by hand with a mortar and pestle, to ensure a fine powder and visually inspected to be homogeneous throughout. The grain size distribution of the modified soils was not evaluated but the product was a very fine powder, similar in texture to the original pure bentonite, see Figure 4.4. The powders were stored in airtight containers prior to testing. Figure 4.4 Modified Clay in Powder Form 4.3 Equipment All the permeability tests were run in rigid wall permeameter cells. The basic apparatus, ordered from CETEC was manufactured for the constant head permeability test. The cell had to be modified to suite this experimental application. 3-inch inner diameter, inch thick clear acrylic pipe was cut into 6-inch sections to serve as the rigid wall of the permeameter. These sections were then marked with the height in millimeters from the base of the cell to allow for of the change in head of the influent. The outflow standpipes were made out of clear acrylic burettes with graduation marks to the 0.2 mL. The burettes had an inner diameter of inch and could hold up to 33 mL of effluent. The burettes were permanently fixed to the cells and sealed using silicone sealant. The 50

PAGE 66

top plate of the manufactured permeameter had an inlet value. A Swageloc fitting was added to make the cell compatible with the pressure tubes. Porous plates were used as a filter medium to maintain the consistency of the sample during preparation and testing. The porous plates had to be modified to prevent any channeling along the side of the rigid-wall and to avoid any material escaping during the consolidation phase. The porous plates are 3-inches in diameter and -inch thick, before modification. A small groove was scored in the edge of each of the porous plates using a handsaw. The purpose of cutting this groove was to seat an o-ring 2.5-in in diameter. Silicone sealant was used create a good seal between the porous plate, o-ring and cell wall. Two-inch diameter clear acrylic pipes were cut to use as an internal piston for consolidation and template to ensure that when the cell was setup the maximum sample thickness was constant at 7-mm for all tests. Figure 4.5 shows a diagram of the permeameter after the modifications. Clay Sample Influent Internal Piston/Template Rigid Wall Knobs Pressure Inlet Effluent Outflow Pipe Porous Plates Figure 4.5 Permeability Cell 51

PAGE 67

4.4 Permeability Measurement 4.4.1 Sample Preparation The following procedure for the preparation of a sample was developed and all samples were tested in this manner. The powdered modified clay was dried at 100C for 24 hours prior to weight measurement. Depending upon the test, 15 to 25 grams of dried sample was weighed and 150 to 200 mL of deionized water was added. The sample was prepared over its liquid limit to the consistency of thick slurry. Although the volume swells greater than the final desired volume, it was required to ensure that sample is entirely hydrated. The sample was mixed for approximately 40 minutes until homogeneous, and covered for 24 hours to allow full hydration. This method was adopted to allow for full saturation of the sample, which is outlined in the ASTM standard. The permeameter was then assembled placing one porous plate at the bottom of the cell with a piece of P4 filter paper cut to size on top of it. To ensure that the exact desired amount of material was placed in the cell, the difference of mass was taken. Since both the original mass of soil and volume of water added were known, assuming the mixture is homogenous, the exact amount of material added to the cylinder was calculated through mass reduction. Depending upon the void ratio desired for the test, either 10 or 20 grams (dry weight) was added to the cell. The sample was then placed into the cell and another filter paper was wetted onto the top porous plate, which was fitted into the top of the cell. 4.4.2 Consolidation Technique The consolidation portion of the sample preparation was started by pushing the porous plate to the surface of the slurry using the piston. The sample thickness, prior to consolidation varied according to the amount and type of polymer used in the clay, as the 52

PAGE 68

liquid limits varied and some were more prone to swell than others. A few inches of water were added to both the influent and effluent sides of the sample to monitor the pore fluid that was draining from the top and bottom of the sample during the consolidation phase. The porous plate was placed at a 90 angle with the wall of the cell, which ensured a good seal. The internal piston is centered on top of the porous plate and the top portion of the cell was assembled. The effluent valve was ensured to be in the open position. The screws were tightened very slowly to allow for pore water pressure inside the sample to dissipate. The knobs were turned approximately 1/32 of a turn every 15 to 20 minutes or whenever the pressure had dissipated. The purpose of consolidating the sample in this manner is to create an even distribution of the void ratio within the fully saturated sample. The process of consolidation can be seen in Figure 4.6. Figure 4.6 Consolidation of Sample in Permeameter Once the permeameter was closed tightly with the piston inside, the sample thickness was 7 mm. The top was removed, once all the pore water pressure had dissipated and the water was removed from the cell. Any soil that was present above the top porous plate was collected, dried and weighed. The weight was then subtracted from the total mass of the sample for accurate determination of the void ratio. This minimal loss occurred primarily at the beginning of the consolidation phase and was due to the porous plate not having good contact with the cell initially. 53

PAGE 69

The permeants used in this study were deionized water and three 1 molar synthetic inorganic salt solutions (NaCl, CaCl 2 and MgCl 2 .) The 1 M solutions were prepared by using the formula weight to determine the appropriate amount of dry chemical. Fisher Brand chemicals, in granular and crystalline form, were then dissolved in deionized water at room temperature. The electrical conductivity and pH of the permeant was measured and recorded, and then it was poured on top of the porous plate. The piston was placed back in the cell to restrict the sample from swelling and the top of the permeameter was secured tightly. Two mL of deionized water was then added to the effluent side of the cell so that an initial reading could be recorded and the burette was covered to prevent evaporation of the effluent. The permeability tests were conducted according to ASTM D 5856 Measurement of Hydraulic Conductivity of Porous Material Using a Rigid-Wall, Compaction Mold Permeameter, Test Method D. This test is a falling head test in which the headwater drops and the tailwater rises. The pressure required for this test was supplied by a laboratory pressure panel setup. Each station has a knob that applies the pressure, which can be monitored by a digital readout. The pressure tubes from the pressure panel were connected to the inflow side of the permeability cell, initial readings for the inflow and outflow were recorded and the desired pressure was applied using the pressure panels shown in Figure 4.6. Figure 4.7 Laboratory Pressure Panel Setup 54

PAGE 70

Readings of the inflow, outflow and pressure were recorded periodically. When the volume of the outflow was sufficient, the leached sample was removed completely from the burette using a small pipette and the electrical conductivity and pH were measured using the Accumet AB30, 4-cell conductivity meter and the Accumet AP63 pH meter. Deionized water was added to bring the level to 2 mL, just as in the beginning of the test. Each of the effluent samples was diluted with 2-mL of deionized water due the initial condition required. The necessary calculations to consider this dilution were taken in to account. To examine the effect of the gradient the pressure was varied over the course of the tests. After the permeability stabilized, the pressure was increased to increase the gradient across the sample. According to the ASTM, the test was halted when there were less than a 25% change in four or more consecutive values of hydraulic conductivity. Also, 2-pore water flows were considered the minimum flow quantity prior to the termination of any test. 55

PAGE 71

CHAPTER 5 TESTS AND RESULTS 5.1 Swell Index The swelling of a clay is caused by the type of cation adsorbed on the surface and the interaction between the cations, clay surface and water molecules. The effect of the polymer to the swell property must be evaluated to ensure that the ability to form a seal is not too greatly diminished. The test method used for quantifying the swelling property for use in geosynthetics clay liners is ASTM D 5890 Standard Test Method for Swell Index of Clay Mineral Component of Geosynthetic Clay Liners. This index tests is useful for establishing the relative quality of the swell properties of the modified clay mineral, as well as assessing its compatibility with a permeant liquid. The test was performed on each of the modified clay powders prepared at 1 wt% and heated to 100C. Deionized water was used as the control and tests were run in solutions of NaCl, KCl, CaCl 2, and MgCl 2 to assess the effect on the swelling properties due to the collapse of the diffuse double layer. The concentration of these solutions was varied to demonstrate the effect of molarity on the size of the diffuse double layer. Prior to the test all samples were oven dried for 24 hours at 100C to ensure that most of the water was removed from the sample. Solutions were prepared at 0.01 M, 0.1 M and 1M and 90 mL of each was placed in a 100 mL graduated cylinder. As specified in ASTM D 5890, 2 grams of the soil was weighed out for each cylinder. Every ten minutes, 0.1 gram of the soil was sprinkled slowly over the surface of the solution until all of the 2 grams had been added. Then additional solution was added to raise the 56

PAGE 72

volume to 100 mL. The temperature was then recorded and the cylinder covered to sit undisturbed for an additional 20 hours and hydrate, shown in Figure 5.1. After this period, the temperature was taken and the free swell volume of the hydrated clay mineral was then recorded in units of mL/2g. Figure 5.1 Hydrated Swell Volume Figure 5.2 shows the affect of the polymer treatment on the swell index of the clay in deionized water. There is little differentiation between the affects of different types of polymer treatment, but overall the presence of polymer reduces the free swell capacity of the clay sample. The heated bentonite was mixed in a slurry, heated and processed exactly as the modified soils, only without the addition of any polymers. This shows that the preparation of the clay samples accounts for a significant portion of this reduced swelling behavior. 57

PAGE 73

010203040506070BentoniteHeated BentoniteHigh CationicLow Cationic NonionicLow AnionicHigh AnionicSwell Index (mL/2g) DI Wate r Figure 5.2 Swell Index in Deionized Water The swell index test results, in Figure 5.3 demonstrates the effect of the concentration and valence and compare the influence of the polymer present on the swelling capacity of the clay. There is a clear trend in all the tests that the higher the concentration, the lower swell indexes. In dilute solutions (0.01 M), the behavior is closest to tests run in deionized water, while higher concentrations result in much lower values for the swell index. The valence also affects the amount of swell. Monovalent solutions, particularly NaCl exhibit the highest swell because the sodium ion has a large hydration radius and if it becomes associated with the mineral surface there is minimal reduction of the diffuse layer. For the case of divalent solutions, which have higher replaceability power and can replace two monovalent cations, the diffuse layer collapses, resulting in much less swell potential. The NaCl solutions permit greater volumes of swell than the soils in KCl solutions, due to the nature of the bond they form with the mineral surface. Even though both solutions are monovalent, the KCl forms a slightly stronger bond than the NaCl, which reduces the diffuse double layer and in turn reduces the swell volume. 58

PAGE 74

010203040506070NaClKClMgCl2CaCl2Swell Index (mL/2 g Bentonite High Cationic Low Cationic Nonionic Low Anionic Medium Anionic1 M Solutions 010203040506070NaClKClMgCl2CaCl2Swell Index (mL/2 g Bentonite High Cationic Low Cationic Nonionic Low Anionic Medium Anionic0.1 M Solutions 010203040506070NaClKClMgCl2CaCl2Swell Index (mL/2 g Bentonite High Cationic Low Cationic Nonionic Low Anionic Medium Anionic0.01 M Solutions Figure 5.3 Effect of Charge Density on Swell Index 59

PAGE 75

The influence of polymer charge is also demonstrated in Figure 5.4. This particular data set is for high cationic and medium anionic polymer treated clays tested in the three concentrations and the swell volumes are plotted as a function of the type of solution. It can be seen that the slope, which has a downward trend, decreases as the molarity increases. It can be seen that the 1M KCl has a larger impact on the swell than the divalent solutions for both the cationic and the anionic solutions. This trend is not observed in bentonite, so it may be attributed to the presence of the polymer. The cationic polymer clay consistently shows superior swelling potential. This indicates that the anionic polymer contributes to the reduction of the diffuse layer more than the cationic polymer. This could also be a sign that the cationic polymer has a greater affinity for water. Figure Effect of Polymer Charge on Swell Index L 0510152025303540 0 1 2 3 4 5iquid solutioni 0.01 M Anionic 0.01 M Cationic 0.1 M Anionic 0.1 M Cationic 1 M -Anionic 1 M Cationic N aCl KCl MgCl2 CaCl2 Swellng Index mL/ 2 Swell I ndex ( mL/2g) Figure 5.4 Effect of Polymer on Swell Volume There are several possible sources of inconsistency for the swell index test such as failing to spread the clay evenly over the surface, friction between the graduated cylinder and the soil and possibly not waiting adequate time for hydration. Bentonite clay can exhibit swelling up to 400 hours (Lin, 1998), but ASTM suggests only a 16-hour period for hydration. Additional swell index experimental data can be found in Appendix C. 60

PAGE 76

5.2 Liquid Limit The liquid limit test was performed on all the modified clays. The ASTM Standard, which outlines the Casagrande method, cannot be performed effectively on bentonite, so the British standard of the Cone Penetration Test was followed. The cone penetration apparatus has a dial gage that measures the displacement of a free-falling cone into a soil sample. The weight of the cone is calibrated such that when the displacement is equal to 20 mm, the soil has reached the liquid limit. The procedure was repeated at increasing water contents, with at least two displacements below and two displacements above 20 mm. The series of data was plotted to obtain the liquid limit. Clays were prepared with 0.5 wt% and 1.0 wt% polymer for testing. Two sets of samples were tested (1) immediately after being mixed and hydrated and (2) after being oven dried at 100C for at least 24 hours and prepared as described in Chapter 4. Figure 5.5 groups the polymer by charge and charge density and shows the effect of weight % polymer and heat. Additional test results can be found in Appendix C. An increase in weight percent of these polymers lead to an increase in the liquid limit in all cases for anionic and nonionic clays. This trend was maintained even after heating, the samples containing 1.0 wt% had a higher liquid limit than samples of 0.5 wt%. This similarity in behavior may be related to the types of polymer. The nonionic and anionic polymers have a very similar poly(acrylic acid) structural backbone, but difference in charge. The results show that the difference charge density between medium and low anionics had a minimal impact. When compared to the liquid limit of pure bentonite for the non-heated case, the addition of anionic polymers increased the liquid limit. This was not true, however when the heated samples were compared with the heated pure bentonite, as decrease in liquid limit was measured. The nonionic polymer in the unheated case had the most notable influence on the liquid limit, but when heated the behavior was similar to that of the anionic modified clays. The behavior of the cationic modified clay was different than the others and no notable trend could be observed. The amount of polymer did not consistently change the liquid limit, nor did the charge density of the polymer. The high cationic reduced the 61

PAGE 77

liquid limit below that of pure bentonite, while the values increased for the low cationic. Even the amount of polymer added did not display results consistent with the trend for anionic clay. The liquid limit increased with increasing polymer content for the low cationic, but decreased with increasing polymer content for the high cationic. Although, both are cationic the polymers they have different structures, which could be responsible for the inconclusive trends. Another probable reason for this data is the polymers affinity for water, which may be different for these polymers. Unlike the others, the high cationic did not display a large reduction in liquid limit from non-heated to heated, which may indicate that polymer exchange for the hydrated ions took place in the non-heated case. 020040060080010001200MediumAnionicLow AnionicNonionicLow CationicHigh CationicLL (%) 0.5 wt% Polymer 1.0 wt% Polymer 0.5 wt% Polymer Heated 1.0 wt% Pol y mer Heated Figure 5.5 Experimental Values of Liquid Limits Table 5.1 Experimental Values of Liquid Limits Weight % High Anionic Low Anionic Nonionic Low Cationic High Cationic 0.5 Not Heated 626.37 635.12 908.03 626.7 533.5 1.0 Not Heated 651.57 671.63 1004.27 691.94 498.04 0.5 Heated 421.37 402.95 382.02 411.02 382.02 1.0 Heated 460.41 525.79 457.6 291.44 419.26 62

PAGE 78

200400600800100012000.752.25Liquid Limi t 0.5% High Anionic 1.0% High Anionic 0.5% Low Anionic 1.0% Low Anionic 0.5% Nonionic 1.0% Nonionic 0.5% Low Cationic 1.0% Low Cationic 0.5% High Cationic 1.0% High Cationic Bentonite 11.251.51.752 Not Heated Heated Figure 5.6 Heated vs. Non-Heated Clays In all cases, heating the sample decreased the liquid limit, as can be seen in Figure 5.6. The effect of the polymer followed the same trend for both anionics and the nonionic. The pure bentonite was processed and the liquid limit was tested to evaluate the effect of the heat. The bentonite before heating had a liquid limit of 550% and after the oven drying and grinding process unmodified bentonite had a liquid limit of 445%. This indicates that the reduction in liquid limit was not solely due to better interaction between the clay surface and the polymer, but also the sample preparation process accounts for some of the reduction. 5.3 Specific Gravity The specific gravity is a measurement of the ratio between the unit masses of soil particles and water. The specific gravity was determined according to ASTM D 854, Standard Test Method for Specific Gravity of Soils. The materials tested were the 1wt% polymer modified clays that were heated to 100C, as well as the pure bentonite. The ASTM standard calls for a minimum dry mass of 20 grams, however due to the swelling 63

PAGE 79

properties of the clay only 10 grams of dry material was used for this series of tests. The specimen was dried in the oven at 100C for 24 hours prior to testing. A 500 mL pycnometer was calibrated and water was deaired prior to measurement. The dry sample of known mass, approximately 10 grams, was added to an empty pycnometer and deionized water was added to cover the sample. Although the standard does not specify, the sample was agitated at this time to ensure that the entire sample was wetted. The soil was permitted to soak for a 24-hour period. The pycnometer was then filled to just beneath the calibration mark and the sample was deaired using a vacuum pump for a minimum of 10 minutes or when no air bubbles could be seen rising to the top of the pycnometer. The weight and the temperature of the soil were recorded and the specific gravity was calculated using the following equation: )]([baoosMMMMG Where M o is the mass of sample of oven dried soil in grams, M a is the mass of pycnometer filled with water and soil in grams and M b is the mass of pycnometer filled with water in grams. As specified by the ASTM standard the value was corrected for temperature. A minimum of three tests was run for each soil type and the average was taken to be the value of the specific gravity of each soil. The presence of the polymer, in some cases appears to reduce the specific gravity of the clay, as can be seen in Table 5.2. Table 5.2 Measured Specific Gravity Soil Specific Gravity Pure Bentonite 2.54 High Cationic 2.29 Low Cationic 2.50 Nonionic 2.53 Low Anionic 2.54 Medium Anionic 2.56 64

PAGE 80

The values of the specific gravity less than that value determined for bentonite indicate a less dense configuration. This is similar the behavior observed in organobentonites, which has been attributed to the intercalation of the large organic molecules (Redding and Burns, 2000). The anionic and nonionic modified clays showed little change from the measured value of pure bentonite. The medium anionic polymer slightly increased the specific gravity. The cationic polymers reduced the specific gravity, with the high charge density polymer reducing it significantly. It is possible that the high cationic separated the crystal structure upon entering the interlayer creating a less dense crystalline arrangement and thus a lower specific gravity. 5.4 Permeability Tests The test setup and methods were conducted as described in Chapter 4 for all the permeability tests. The following section describes the test measurements and presents the data collected. 5.4.1 Permeant Solutions The base line permeant was deionized water and the other permeants were all 1 M synthetic inorganic solutions, which were selected to simulate the aggressive chemical environment of a landfill. The effect of cation valence and size on the hydraulic performance of the modified bentonite is evaluated. The NaCl is monovalent with a large hydrated ion radius, while CaCl 2 and MgCl 2 are divalent, with different hydrated ion sizes. Only permeation with a single salt species at a constant concentration of 1 M was evaluated in this study. 65

PAGE 81

5.4.2 Test Measurements The tests were performed on all samples to evaluate the effect of polymer treatment. The procedure outlined in Chapter 4 was followed to run all tests. The measurements of inflow height, outflow volume and time were used to calculate the permeability using the following equation as outlined by the ASTM Standard for this experimental setup: 21outinoutinhhlnaaAtLaak where h 1 = (h 1 -h 2 ) initial + [(P 1 -P 2 )/ w ] initial and the h 2 = (h 1 -h 2 ) final + [(P 1 -P 2 )/ w ] final. Since the outflow of the permeameter is graduated to record the volume, an extra conversion had to change this measurement into a head. Figure 5.7 shows how these measurements were made from this test set up. The value of P out is equal to zero and the cross sectional area of the inflow, a in is equal to the cross sectional area of the sample, A. P2 aout ain h1 A L P1 h2 Figure 5.7 Permeability Measurement Values 66

PAGE 82

The factors varied during the permeability tests included permeant liquid, void ratio, first wetting solution and gradient. Since the aim of this investigation is to asses the polymers influence on the hydraulic performance when permeated with inorganic solutions, deionized water was used as the base line permeant for all the tests. All permeability test results are presented in Appendix A. The permeability data is reported as a function of the pore volumes of flow and duration of the test. Some of the plots contain points that are inconsistent with the general trends of the graph. These points can be attributed to pressure fluctuations caused by the pressure panel. Particular scatter is observed in the initial data points, which coincide with lower gradients. Generally, the data is more stable at gradients of 500 and above. There were several tests performed. To organize the data and obtain a clear picture of the effectiveness of the polymer treatment, the results are grouped according to the experimental variables, which are permeant, first wetting solution, void ratio, and polymer. 5.4.3 Permeant Figure 5.8 shows the results of the high cationic clay at a void ratio of 7.14, permeated with each of the permeant solutions. The test with CaCl 2 was carried out to 12 pore volumes of flow to obtain the termination criterion. This demonstrates the effect of the valence and hydrated ion size of the permeant on the coefficient of permeability. Deionized water had the lowest permeability of 3.43x10 -9 cm/s, followed by NaCl, MgCl 2 and CaCl 2 which were 1.45x10 -8 cm/s, 1.09x10 -7 cm/s and 3.93x10 -8 cm/s, respectively. This follows the same trend as the replaceability power. The divalent cations replace the natural sodium and collapse the double layer. The behavior of the high cationic modified soil with respect to the valence of the permeant is similar to the behavior reported for GCL bentonite. Aside from pressure fluctuations, stable values of permeability were observed after 2 pore volumes of flow. 67

PAGE 83

1.0E-101.0E-091.0E-081.0E-071.0E-061.0E-050.02.04.06.08.010.0Pore volumeCoefficient of permeability, k (cm/s) DI Water NaCl MgCl2 CaCl2 High Cationice = 7.14 Continued to 12 pore volumes Figure 5.8 Effect of Valence on High Cationic Modified Clay It can be seen from Figure 5.9 that the low cationic clay at a lower void ratio of 3.07 had a slightly different trend. The MgCl 2 permeant results in the highest permeability value of 2.78x10 -9 cm/s. The CaCl 2 has a lower permeability of 7.05x10 -10 cm/s followed by the deionized water with a permeability of 2.35x10 -10 cm/s. The data was fairly unstable until about 1 pore volume of flow, when the gradient for the MgCl 2 and CaCl 2 was increased. The MgCl 2 test was carried out to 12.5 pore volumes of flow. 1.0E-111.0E-101.0E-091.0E-081.0E-070.01.02.03.04.05.06.0Pore volumeCoefficient of permeability, k (cm/s) DI Water MgCl2 CaCl2 Low Cationice = 3.07 Continued to 12.5 pore volumes Figure 5.9 Effect of Valence on Low Cationic Modified Clay 68

PAGE 84

The nonionic clay was tested with deionized water and CaCl 2 at void ratios of 3.07 and 3.14, as shown in Figure 5.10. There was a slight difference in the void ratio due to a small amount of material loss during the consolidation phase of the sample preparation. The increase in the coefficient of permeability when exposed to divalent CaCl 2 is from 1.61x10 -10 to 3.49x10 -10 cm/s. The effect of the polymer interaction may be responsible for the minimal increase in hydraulic conductivity when exposed to divalent solution. 1.0E-111.0E-101.0E-091.0E-081.0E-070.01.02.03.04.0Pore volumeCoefficient of permeability, k (cm/s) DI Water, e=3.07 CaCl2, e=3.14 N onionic Figure 5.10 Effect of Valence on Nonionic Modified Clay At a void ratio of 3.07, the low anionic clay was permeated with deionized water, NaCl and CaCl 2 and the results are shown in Figure 5.11. The hydraulic performance when permeated with NaCl and CaCl 2 is essentially the same, having coefficient of permeability values of 2.8x10 -9 cm/s and 2.95x10 -9 cm/s. The deionized water permeant resulted in a lower value 1.28x10 -9 cm/s. The scatter in the initial portion of the deionized water data was due to pressure panel fluctuations at the low pressure, which stabilized at higher gradients. 69

PAGE 85

1.0E-101.0E-091.0E-081.0E-070.01.02.03.04.05.06.07.0Pore volumeCoefficient of permeability, k NaCl CaCl2 DI Water Low Anionice = 3.07 Figure 5.11 Effect of Valence on Low Anionic Modified Clay Figure 5.12 shows the test results for medium anionic modified clay permeated with deionized water, NaCl and CaCl 2 at a void ratio of 3.07 The test with NaCl solution results in the lowest permeability of 8.11x10 -11 cm/s. The deionized water gives 1.85x10 -10 cm/s and CaCl 2 3.58x10 -10 cm/s. The medium anionic maintained a low hydraulic conductivity and the variation when permeated with different solutions was within one order of magnitude. It is interesting to note that the NaCl permeant resulted in significantly lower hydraulic conductivities for the medium anionic. Although the variation is small, it is different than what is typically observed in pure bentonite samples. This is possibly due to the negative polymers association with the hydrated NaCl cation. 1.0E-111.0E-101.0E-091.0E-080.00.51.01.52.02.5Pore volumeCoefficient of permeability, k DI Water NaCl CaCl2 Medium Anionice = 3.07 Figure 5.12 Effect of Valence on Medium Anionic Modified Clay 70

PAGE 86

5.4.4 First Wetting Solution Figure 5.13 demonstrates the effect of first wetting solution and pre-hydration. The modified clays were mixed directly with a 1M solution of CaCl 2 and permeated with the same chemical. The sample preparation followed the same procedure; however instead of adding deionized water to create a slurry, 1M CaCl 2 was used. The samples were consolidated in the same manner and the fluid dissipated from the pores was discarded and replaced with fresh 1M CaCl 2 1.0E-091.0E-081.0E-071.0E-061.0E-051.0E-040.05.010.015.020.0Pore volumeCoefficient of permeability, k (cm/s) High Cationic, e=3.07 Nonionic, e=3.07 Medium Anionic, e=3.07 Bentonite, e = 3.07 Permeant: CaCl2 Figure 5.13 Effect of Pre-hydration Condition A significant increase in the hydraulic conductivity was observed and the polymer was not found to enhance the performance of the clay. When compared to the pre-hydrated condition increase ranged from one up to four orders of magnitude as shown in Table 5.3 and Figure 5.14. This comparison demonstrates changes in clay fabric formation, when exposed directly to divalent cations. Overall, it is clear that the hydration is key to the formation of the dispersed particle arrangement required to maintain low values of permeability. The cationic had similar measurements of permeability to pure bentonite, while all the treatment with the other polymers tested 71

PAGE 87

demonstrated an increase between one and two orders of magnitude. This may be attributed to the cationic adsorption on the surface of the clay. Exposure to divalent solutions may not have caused further reduction in the thickness of the diffuse double layer, due to interaction with the cationic polymer. The other polymers have different associations with the clay than the cation exchange mechanism, which could allow a more prominent alteration of the clay fabric resulting in higher hydraulic conductivities. Table 5.3 Pre-hydrated vs. Non-Pre-hydrated Clay Type Pre-hydrated H 2 O Permeability (cm/s) Hydrated Directly CaCl 2 Permeability (cm/s) High Cationic 1.60 x 10 -8 3.87 x 10 -7 Nonionic 3.49 x 10 -10 6.73 x 10 -6 Medium Anionic 3.58 x 10 -10 6.15 x 10 -6 Pure Bentonite 2.98 x 10 -10 4.44 x 10 -7 High Cationi c NonionicMedium Anioni c Bentonite H2OCaCl2 1.0E-111.0E-101.0E-091.0E-081.0E-071.0E-061.0E-05 H2O CaCl2Coefficient of Permeability, k (cm/s) Figure 5.14 Pre-hydrated vs. Non-Pre-hydrated 72

PAGE 88

5.4.5 Void Ratio The void ratio effect on the hydraulic conductivity of the modified clays was evaluated by examining two conditions. The void ratios were determine by calculating the oven-dried weight of the sample, specific gravity and the volume the soil occupied, which was constant due to the permeability cell setup. The oven-dried weights chosen for this study were 10 grams and 20 grams, which gave void ratios of 7.14 and 3.07, respectively. In every test run, regardless of the polymer treatment the void ratio of the soil greatly influence the measurement of permeability. This is consistent with results of previous research conducted at the University of South Florida on pure bentonite samples. This effect is likely to be more prominent in the treated clays, because of their diminished swell capacity. Bentonite samples were not tested for their change in hydraulic conductivity due to void ratio changes. Figure 5.15 compares the effects of void ratio for the high cationic, nonionic and medium anionic when permeated with deionized water. The effect of void ratio demonstrates a clear trend; the higher the void ratio, the higher the hydraulic conductivity. The values of permeability for all the modified clays at a lower void ratio are all very similar, given in Table 5.4; however at higher void ratios some variability can be observed. The change in void ratio had the most effect on the nonionic clay, followed by the high cationic and the medium anionic clays. 1.0E-111.0E-101.0E-091.0E-081.0E-070.00.51.01.52.02.53.03.5Pore volume High Cationic, e = 3.07 High Cationic, e = 7.14 Nonionic, e = 3.07 Nonionic, e = 7.14 Medium Anionic, e = 3.07 Medium Anionic, e = 7.14 Permeant: DI H2O Coefficient of permeability, k Coefficient of Permeabilit y k ( cm/s ) Figure 5.15 Effect of Void Ratio on Modified Clay Permeated with DI Water 73

PAGE 89

Table 5.4 Effect of Void Ratio With Deionized Water Permeant Modified Clay e = 3.07 e = 7.14 High Cationic 1.66x10 -10 3.43x10 -9 Nonionic 1.61x10 -10 5.20x10 -9 Medium Anionic 1.56x10 -10 1.51x10 -9 When permeated with a divalent solution (CaCl 2 ) the same trend occurs, however the extent of influence was less than with water, shown in Figure 5.16. It would be expected that the effect of void ratio would be less prominent in deionized water than in ionic solutions due to changes in the clay fabric, but this was not observed. The permeability was fairly high when compared to the other modified clays. Although the performance was not enhanced, this demonstrates that polymer-clay interaction took place. The cationic polymer adsorbed on the surface may create a fabric that is less sensitive to the change in void ratio. It is that the polymer clay system may cause a different redistribution of voids upon exposure to the divalent solution, compared to unmodified bentonite. 74 1.0E-101.0E-091.0E-080.05.010.015.0Pore volume e = 3.17 e = 7.14 1.0E-071.0E-061.0E-05 High CationicPermeant: CaCl2 Coefficient of permeability, k Coefficient of Permeabilit y, k ( cm/s ) Figure 5.16 Effect of Void Ratio on High Cationic Clay Permeated with CaCl 2

PAGE 90

The nonionic clay was permeated with CaCl 2 at the two void ratios and the results are shown in Figure 5.17. As with all the other tests, the trend of increasing permeability with increasing void ratio is observed. Similar to the test permeated with DI water, the variation between the hydraulic conductivity for the two void ratios is most prominent with nonionic clay than the high cationic clay. The nonionic clays permeability changed from 2.45x10 -9 at a void ratio of 7.14 to 3.49x10 -10 at a void ratio of 3.07. 1.0E-101.0E-091.0E-081.0E-070.01.02.03.04.05.06.0Pore volume e = 3.17 e = 7.14 N onionicPermeant: CaCl2 Coefficient of permeability, k Coefficient of Permeabilit y, k ( cm/s ) Figure 5.17 Effect of Void Ratio on Nonionic Clay Permeated with CaCl 2 5.4.6 Polymer Charge All the modified soils and bentonite at a void ratio of 3.07 were permeated with deionized water. With the exception of the low anionic clay, which had a higher coefficient of permeability, all the clays performed relatively the same. The high cationic, medium anionic and nonionic actually performed slightly better than the unmodified bentonite. A trend can be observed in the permeability measurements of initially higher values until the values stabilize. This is likely due to a redistribution of the voids. 75

PAGE 91

1.0E-101.0E-091.0E-080.00.51.01.52.02.53.03.5Pore volumeCoefficient of permeability, k Low Cationic High Cationic Low Anionic Medium Anionic Bentonite Nonionic Permeant: H2Oe = 3.07 Figure 5.18 Effect of Polymer Clay Permeated with H 2 O In the presence of 1M CaCl 2 and increase in the coefficient of permeability was noted for all the modified soils, as well as the bentonite. This was expected due to the valence and hydrated ion size of the CaCl 2 The medium anionic and nonionic modified clays maintained reasonably low hydraulic conductivity despite the exposure to a divalent solution. The low anionic clay did not perform well in comparison to the unmodified bentonite. The hydraulic conductivity of the high cationic soil, which is not shown in the Figure 5.18, increased two orders of magnitude, indicating a diminished double layer. Figure 5.19 Effect of Polymer When Permeated With CaCl 2 1.0E-101.0E-091.0E-080.00.51.01.52.02.53.03.54.04.55.0Pore volumeCoefficient of permeability, k Low Cationic Medium Anionic Bentonite Nonionic Low Anionic Permeant: CaCl2e = 3.07 Continued to 9 pore volumes 76

PAGE 92

Figure 5.19 compares the performance according to the variation in charge of the polymer used to treat the bentonite. It can be seem that the high cationic and the low anionic clays do not improve the performance of unmodified bentonite. Both soils have significant increases in permeability when exposed to CaCl 2 All the treated soils maintained similar hydraulic conductivity when permeated with deionized water, with the exception of the low anionic polymer, which increased the hydraulic conductivity. 1.0E-111.0E-101.0E-091.0E-081.0E-07High CationicLow CationicNonionicLow AnionicMedium AnionicBentoniteCoefficient of Permeability, k (cm/s) CaCl2 H2O e = 3.07 Figure 5.20 Effect of Polymer Table 5.5 Effect of Polymer and Permeant on Hydraulic Conductivity Permeant High Cationic Low Cationic Nonionic Low Anionic Medium Anionic Bentonite H 2 O 1.66E-10 2.34E-10 1.61E-10 1.28E-09 1.85E-10 2.98E-10 CaCl 2 1.60E-08 7.05E-10 3.49E-10 2.95E-09 3.58E-10 7.33E-10 5.4.7 Gradient Laboratory hydraulic gradients should duplicate field conditions; however testing would take an unacceptable amount of time, so gradients are increased. The increase can cause uneven consolidation resulting in inaccurate values of permeability resulting in erroneously low values for the permeability. To evaluate the influence of the gradient on 77

PAGE 93

the coefficient of permeability, the gradient was increased over the course of the test. Previous tests conducted at the University of South Florida have revealed little or no affect in this particular rigid wall setup. This may be in part due to the placement of the internal piston to hold the volume constant. Since there was little influence in previous testing, high gradients were adopted for these experiments. The gradients for all tests typically started in the range of 100 to 500 and were increased up to 3000 in some cases. Figure 5.20 is an example of the variation of gradient throughout the test. This test is the low cationic permeated with CaCl 2. It can be seen that for the full range of gradients, little change in the hydraulic performance was observed. Low pressures presented a stability problem for the laboratory pressure panel, which accounts for the initial fluctuations. Pressures resulting in a gradient of 500 typically had less fluctuation. For cases of known fluctuation the change in pore volumes of flow was accounted for, but the measurement of the coefficient of permeability was discarded. This allows for accurate comparisons of the data. 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-071.0E-060.00.51.01.52.02.53.03.5Pore volumeCoefficient of permeability, k (cm/s) 10G-90CPermeant: CaCl2e = 3.07 i = 2000i = 2500i = 1000i = 500 Figure 5.21 Effect of Gradient 78

PAGE 94

5.4.8 Electrical Conductivity and pH Table 5.6 shows the measured values for chemical permeants. These measurements were taken prior to the start of the test and were not monitored during the test. The measurements were made with the Accumet AB30, 4-cell conductivity meter and the pH using the Accumet AP63 pH meter, which were calibrated prior to measurement. Table 5.6 Electrical Conductivity and pH of Permeants Chemical Electrical Conductivity (mS/cm) pH Deionized Water 0.0034 6.98 NaCl (Sodium Chloride) 92.9 6.2 MgCl 2 (Magnesium Chloride) 119.2 6.19 CaCl 2 (Calcium Chloride) 150.1 10.27 The electrical conductivity and pH of the effluent was measured to determine when and if the samples had reached stability. The measured values for electrical conductivity were adjusted to account for the 2-mL dilution in addition to any required dilution to prepare enough fluid for measurement. The values measured of the effluent could be compared to the initial values of the influent. Chemical stability was not used as a termination criterion and therefore not all tests were permitted to run until chemical equilibrium was achieved. There is the possibility that polymer leaching had an impact on the measurement of the electrical conductivity and the pH of the effluent. Figure 5.21 shows the electrical conductivity profile of the effluent for a test on nonionic modified clay permeated with CaCl 2 The electrical conductivity appears to reach equilibrium in the range of 130.5 mS/cm and the pH was in the range of 6.8 to 7. The electrical conductivity and the pH of the influent were measured to be 150.1 mS/cm and 10.27. Chemical stability was achieved at approximately twelve days, which corresponds to about four pore volumes of flow. 79

PAGE 95

1.0E+001.0E+011.0E+021.0E+034.06.08.010.012.014.016.018.0Duration (days)Electrical conductivity (mS/cm) 55.566.577.588.59pH EC pH 10G-20Permeant: CaCl2e = 7.14 Figure 5.22 EC and pH of Effluent of Nonionic Clay Permeated with CaCl 2 Figure 5.22 shows the high cationic clay permeated with MgCl 2, which appears to reach chemical equilibrium with respect to the electrical conductivity in the range of 100 mS/cm and pH in the range 6.8 to 7.0. The influent had a measured electrical conductivity and pH of 119.2 mS/cm 6.19, respectively. Chemical stability seems to have been achieved at approximately five days, which corresponds to four pore volumes of flow. Since the equilibrium electrical conductivity values are slightly lower than the measured inflow values, it is possible that some chemical retention is occurring. 1.0E-011.0E+001.0E+011.0E+021.0E+030.02.04.06.08.010.012.0Duration (days)Electrical conductivity (mS/cm) 55.566.577.588.599.510pH EC pH 10G-100CPermeant: MgCl2e = 7.30 Figure 5.23 EC and pH of High Cationic Permeated With MgCl 2 80

PAGE 96

CHAPTER 6 DISCUSSION AND ANALYSIS 6.1 Mixing Ratio The polymer to clay ratio was mixed according to the dry weight percent. However, organically modified clays are prepared by mixing organic cationic solutions at percentages of the total cation exchange of the bentonite. This ratio for the polymer treatment of clays can be examined for the charged polymers with the information obtained from the polymer titration, methylene blue test and the limited information supplied from the manufacturer of the polymers. For the samples prepared at 1.0 wt%, for example there was 1 gram of polymer for every 100 grams of bentonite. The experimentally determined value for the cation exchange capacity of the bentonite was 83 mEq/100g. The polymer titrations gave charge densities for each of the polymers that were converted in to compatible units of mEq/100g. With all this information, the ratio of polymer added to the total cation exchange capacity of the clay can be approximated. The results for a 1.0 wt% mixture are presented in Table 6.1. Table 6.1 Polymer Mix at %CEC of Clay Polymer % CEC of Bentonite High Cationic 3.47 Low Cationic 1.12 Nonionic Not Evaluated Low Anionic 2.19 Medium Anionic 4.99 81

PAGE 97

The ratios are quite low in comparison to percentages reported for ororganobentonites, where solutions containing as much as 125% of the cation exchange of the bentonites were used to treat the clay. The polymer modified clays demonstrated markedly different properties with a small amount of polymer addition, which lead to the decision to test polymer treatment at 1.0 wt%. This drastic change in property could possibly be attributed to the inert portion of the polymers. 6.2 Effect of Sample Preparation The sample preparation technique was developed through literature review of organobentonites. Redding and Burns (2000) treated clays with organic solutions and used similar techniques to process the samples. The processing of the polymer modified clays, which involved the sample being oven-dried at 100C and pulverized to a powder, had an influence on the properties of the modified soils. The swell index and liquid limit tests were performed on both heated and unheated samples of bentonite to better assess the clays response to the preparation process. The swelling was reduced from 60 mL/2grams to 41 mL/2 grams for the sample that was processed. The liquid limit of the bentonite was reduced from 550% to 445%. These are substantial changes in the properties. Although, the effects the processing had on the hydraulic properties were not evaluated in this study, it is likely that the performance would be impacted. Many researchers have linked properties such as swell index and liquid limit to the hydraulic conductivity (Shackelford et al., 2000; Jo et al., 1997)). The effect of this processing technique may inhibit this relationship. Researchers at the University of South Florida have investigated the effect of heat on the mineral structure using X-ray diffraction (XRD). It has been found that the changes were insignificant in sample heated to 50C due to the unaffected presence of interlayer water. However, when heated to 100C the XRD test results revealed changes in the microstructure due to the removal of the tightly bound water molecules from the interlayer. 82

PAGE 98

The reduction of the sample into a fine powder also may have affected the properties of the clay. The grinding process imparts a great deal of heat in the microstructure due to breaking of bonds, potentially having a similar effect as oven drying. The particle size distribution is another variable. Although, samples were processed in the same manner, because the particles were so fine, only visual inspection was used to ensure uniformity. This process in addition to the presence of polymers could lead to a variation in particle sizes which could affect the properties. 6.3 Swell Index The swell index was more affected by the sample preparation process than the polymer interactions. The results for the swell behavior of the polymer treated clays in solutions of different valences are consistent with the findings of for bentonite (Shackelford et al., 2000). The trend of replaceability could be observed in the swell volumes, indicating that the cations had an impact on the diffuse double layer of the modified clays. Highly concentrated (1M) solutions suppressed the swell volume the most, while dilute solutions (0.001M) exhibited volumes similar to deionized water. Generally, the greater the concentration, the less impact the valence had on the swell volume. The variation between the swell in MgCl 2 and CaCl 2 was far less notable than the variation between NaCl and KCl. Jo et al. (2001) found similar finding and attributed the difference in sensitivity between monovalent and polyvalent to osmotic swelling, which is generally only associated with monovalent cations. 6.4 Effect of Permeant The type, valence and concentration have been well documented as influential factors affecting the hydraulic conductivity of bentonite and GCLs (Ruhl and Daniel, 1997; Jo et al., 2001). The valence of the cation present in the permeant influenced the 83

PAGE 99

permeability of the modified clays. Figure 6.1 shows various tests all at a void ratio of 3.07 in monovalent and divalent solutions. It can be seen that the trend is the greater the valence, the higher the hydraulic conductivity. This agrees with the Gouy-Chapman theory and was expected from the work of previous researchers. 1.0E-111.0E-101.0E-091.0E-081.0E-070123Cation ValenceHydraulic Conductivi t High Cationic Low Cationic Nonionic Low Anionic Medium Anionic Bentonite Coefficient of Permeability, k (cm/s) e = 3.07 Figure 6.1 Effect of Valence on Modified Clay 6.5 Effect of Pre-hydration When the soils are exposed to chemical solutions, changes occur in the soil fabric, which cause a redistribution of the voids. This effect is considerably more pronounced when the soil is not prehydrated. Results from tests were consistent with findings reported by Rulh and Daniel (1997) and Ashmawy et al. (2002) who reported that the highest hydraulic conductivity of GCL bentonite occurred when the clay is not hydrated prior to permeation with chemicals. The nonionic and anionic polymers, which have lower hydraulic conductivities than bentonite when pre-hydrated, had much higher values when not pre-hydrated. 84

PAGE 100

6.6 Effect of Void Ratio The experimental data shows that the void ratio has an effect of the hydraulic conductivity. As expected from the literature, the greater the void ratio, the greater the value of permeability. Figure 6.2 shows the coefficients of permeability for the clays at the two void ratios. This is because with the increase in void ratio, there is a greater flow path for the permeant to travel. When the permeant is divalent, the path is even more flow efficient due to changes in the clay fabric. 1.0E-101.0E-091.0E-081.0E-071.0E-061.53.55.57.5Void RatioCoefficient of Permeability High Cationic, H2O High Cationic, CaCl2 Nonionic, H2O Nonionic, CaCl2 Medium Anionic, H2O Bentonite, CaCl2 Bentonite, H2O Figure 6.2 Effect of Void Ratio 6.7 Effect of the Mechanism of Interaction The hydraulic performance and index properties of the clay were affected by the treatment of polymer and the technique used to produce the modified clays. This discussion will analyze the response to treatment by charge of polymer and mechanism of clay polymer interaction. It was originally thought that it would be reasonable to compare the effect of charge and charge density. However, it is important to note that direct comparisons cannot be drawn between the behaviors of the three classes of polymer modified clays because the each of the polymers has a very different in chemical 85

PAGE 101

make-up, which alters the clay polymer interaction. Comparisons can be made about the effect of the polymers on the clay and inferences made about the interactions. 6.7.1 Effect of Cationic Interactions After reviewing the literature, it was initially hypothesized that the cationic polymers would have the strongest interaction with the bentonite, due the cation exchange capacity of the clay. Assuming that this interaction takes place, the expectation is that the cationic clays would exhibit the best performance and produce the most chemical resistant barrier of the modified soils. However, the results indicate a much different trend with respect to the hydraulic conductivity. The high cationic modified clay demonstrated no improvement over unmodified bentonite, while the low cationic did show minimal improvement. The primary reason for this variation in performance is thought to be the type of polymer chosen for the treatment. The high cationic polymer may not have the same affinity for water molecules as the natural sodium. The high cationic polymers may have exchanged for the naturally occurring sodium adsorbed to the clay surface, shrinking the double layer. This would cause the high cationic polymer to have a similar affect as a polyvalent cation, such as Ca 2+ or Mg 2+ Rather than help reduce the permeability in the presence of highly concentrated solutions, the collapsed configuration allows the permeants to pass at high rates. The low cationic clay has less charge and a lower molecular weight, which would have to a different and more ideal interaction with the mineral surface. + + + + + + + Figure 6.3 Cationic Polymer Interaction 86

PAGE 102

This thought contradicts the behavior exhibited in the swell index test. If the above were true, the swelling would be expected to be the lowest in unmodified bentonite. The high cationic clays, which exhibited the highest swell capacities, also displayed the highest hydraulic conductivity when the sample was pre-hydrated. This differs from the trend observed in bentonite, where higher swell volumes are associated with lower hydraulic conductivities (Jo et al., 2001). Organically modified bentonites have demonstrated behavior contrary to that of unmodified bentonite with respect to this relationship, as well. The difference in swelling response may be due to changes in the surface chemistry of the clay. The low anionic displayed moderate swell and had a very slight improvement over bentonite. Previous research performed at the University of South Florida has found that the swell test is not a good indicator of the hydraulic performance of polymer-modified clays. Rather, it was determined that the liquid limit of polymer treated clay, has a more defined relationship to the hydraulic conductivity. It has been found that the higher the liquid limit, the lower the hydraulic conductivity. The high cationic polymer has a lower liquid limit in both the heated and the non-heated samples than the unmodified bentonite, which may explain the higher permeability. The low cationic had the lowest liquid limit of all the polymers tested, which contradicts relationship between the liquid limit and the permeability. The lack of an identifiable trend limits this analysis. The cationic clay performed better than the other modified clays and similar to the bentonite when permeated directly with CaCl 2 without pre-hydration. The effect of prehydration on permeability has been investigated for bentonite and contaminant resistant bentonite (Ruhl and Daniel, 1997). The results varied over two orders of magnitude for the contaminant resistant bentonite, which indicates that the variation in treatment has a large impact on the performance, particularly when not pre-hydrated. The permeability of pure bentonite increases due to cation exchange and collapse of the diffuse layer, but pre-hydration greatly reduces the effect. The pre-hydration has less of an effect on the cationic clay because the cation exchange has likely already occurred during the formation of the polymer clay fabric. 87

PAGE 103

Another possible source of this behavior of the cationic modification is the size of the polymer. Molecular weight can play an important role in surface interactions and the high cationic polymer has a molecular weight 10 x 10 6 Daltons, which indicates a very large molecule in comparison to the size of the clay particle. This polymer may not have the opportunity to intercalate due to its size, hence minimizing interactions. The results showed that the low cationic modified soil had lower permeability than the high cationic. The low cationic have a smaller molecular weight of 3 to 4 x 10 6 Daltons, therefore the size of lower charge density polymer may account for its performance. 6.7.2 Effect of Nonionic Interactions The nonionic polymer interacts with the clay by the formation of coordination complexes with the exchangeable cations. The polymers tend to spread out over the surface of the clay. This association is very different from that of the cationic polymer because the replacement of the natural cations does not take place, which is key to explaining the differences in the hydraulic response. When spread out, the polymer coats the clay, which may protect also the adsorbed cations rendering the clay more resistant to chemical attack. + + + + + + Figure 6.4 Nonionic Polymer Interaction High liquid limits have been correlated to increased hydraulic performance in bentonite, which agrees with the performance of the nonionic clay. The nonionic polymer demonstrated the highest liquid limit as well as low permeability, which is in line with the correlation between hydraulic conductivity and liquid limit. Low permeability was maintained when exposed to monovalent and divalent solutions. Although improvement 88

PAGE 104

over the unmodified bentonite was slight, long-term exposure was not evaluated. The stability of the pre-hydrated nonionic clay may be promising at greater pore volumes of flow. When the nonionic clay was exposed directly to salt it performed worse than the unmodified clay, which points out that prehydration is essential to maintain low permeability. Without knowing more about the exact nature of the clay polymer interaction and its effect on the clay fabric no definitive conclusion can be drawn from this behavior. The presence of the polymer may have caused the thickness of diffuse double layer to be suppressed or more sensitive to direct exposure to the divalent solution. It is also possible that interparticle bridging occurred, causing an aggregated fabric even prior to exposure to the divalent solution. The swell behavior followed the same trend as the other soils when tested for swell index and aside from the overall effect of the polymer treatment process on the swell, no correlation can be made to the hydraulic performance. 6.7.3 Effect of Anionic Interactions The mechanism of interaction of the anionic polymer is similar to the nonionic; complexation with the adsorbed cations. The negative charge of the polymer spreads out due to electrostatic repulsion of the mineral surface, which could promote interparticle bridging between the cations. Although there may be a reduction in the size of the double diffuse layer. The performance of the medium anionic clay can be attributed the formation of a fabric that is more protected from chemical attack. + + + + + + Figure 6.5 Anionic Polymer Interaction 89

PAGE 105

It is possible that this system is more sensitive to the pre-hydration condition because the protective polymer layer may become easily dissociated from the surface in the presence of divalent cations. Since the diffuse layer thickness is already reduced from the interaction with the polymer, subsequent collapse is rapid. However, when the clay is pre-hydrated it is probable that there is the formation of a hydration shell around the whole bentonite-polymer complex. Similar to unmodified bentonite, the presence of water greatly reduced the hydraulic conductivity. The added protection of the polymer enhanced the hydraulic performance for the medium anionic, when permeated with divalent solution slightly over that of bentonite. The low anionic did not have the same hydraulic response as the medium anionic. This behavior can not be explained without having more information about the specific polymers; however it is likely due to the lesser charge and the chemical structure of the clay. The property tests did not demonstrate clear trends, which limits the extent of analysis that can be carried out. The trend of the swell volume for the anionic clays in the various solutions at different concentration was generally the same all the other soils tested. However, the swell volume was generally the least, when compared to cationic and nonionic clays. For the medium anionic, this is inconsistent with test results from bentonite, where swell volume is closely related to hydraulic conductivity. 90

PAGE 106

CHAPTER 7 CONCLUSIONS AND RECOMMENDATIONS 7.1 Summary Changes in the clay fabric cause significant increases in the hydraulic conductivity of clay when permeated with high concentrations of inorganic solutions. The aim of this study was to examine the characteristics of polymer amended clays for the potential use in barrier systems. Sodium bentonite was modified by sorbing cationic, nonionic, and anionic, water-soluble, polymers on to the mineral surface of the clay. The index properties and the hydraulic conductivity were determined for comparison with unmodified bentonite to evaluate the modified clays resistance to chemical attack. 7.2 Conclusions It can be concluded that interaction occurred between the polymers and the clay mineral surface due to changes in the hydraulic and index properties of the amended clay. Due to the different charges and molecular structure of the polymeric compounds, each polymer associated with the clay in a different manner. Comparisons can be made as to the effect of a polymer; however the lack of identifiable trend in the results greatly limits the analysis of the materials. The most significant result from this study is that presence of the high cationic polymer did not necessarily enhance the hydraulic performance of the bentonite. This indicates that utilizing the cation exchange capacity of the clay for polymer sorption may not be effective in reducing the permeability of the clay. The low 91

PAGE 107

anionic clay, also did not demonstrate positive effect on the hydraulic performance of the bentonite. However, the results could not be related to the index properties and therefore are inconclusive. The hydraulic conductivity of the clay modified with nonionic and medium anionic, and low cationic polymers demonstrated slight improved performance over unmodified bentonite when the samples were prehydrated. The polymers may have chemical resistant potential, but no definitive conclusion can be made without further investigation of the hydraulic performance. It can be concluded, however that nonprehydrated samples treated with nonionic and anionic polymers do not perform well. As previously demonstrated in pure bentonite, prehydration, void ratio and permeant solution had a considerable affect on the performance of all the treated clays. 7.3 Recommendations for Future Work During the course of this study, several other points of interest were identified that could potentially be beneficial to a complete investigation. These topics were not included in this study, but are recommendations for future work. A full characterization of the polymer, including the chemical make-up and charge density would allow for a better assessment of the polymer bentonite relations. The preparation technique was not concluded to be beneficial, and therefore it is not recommended that same mixing procedure be used in the future for polymer modification of bentonite. A possible solution is to adopt a dry mixing procedure and to eliminate the heating and grinding process, which were influential on the properties of the clay. However, if a similar preparation technique were used, it would be valuable to have a better illustration of the interaction and surface chemistry, which could be obtained by analyzing the modified clays with the scanning electron microscope. The polymer could be added as a percentage of the cation exchange capacity of the clay, rather than a weight percent. The addition of much larger amounts of polymer could also be investigated for 92

PAGE 108

the hydraulic response. Another, potential method for improving the mixture of the soil would be to prepare the soil as outlined in this thesis and mix the treated bentonite with unmodified bentonite creating a non-homogeneous mixture. Experimentally, a few topics worthy of further investigation were encountered. First, long term analysis of the effluent to determine full chemical equilibrium would be desirable. In this study, only advective flow was analyzed, however the scope could be expanded to include diffusive flow along with the development of the retention and sorptive characteristics of the treated clay. While information pertaining to the clay-polymer relationship and its influence of the hydraulic properties of bentonite has been investigated, the test results are inconclusive as to whether or not polymer-modification can enhance hydraulic performance. Although this study was not conclusive concerning the specific polymer interactions and the effect on hydraulic conductivity, additional research may be promising. Polymers have the potential to improve the properties and performance of bentonite, as has been demonstrated in commercially sold contaminant resistant bentonites. 93

PAGE 109

REFERENCES Ashmawy, A.K., El-Hajji, D., Sotelo, N., and Muhammad, N. (2002), Hydraulic Performance of Untreated and Polymer-Treated Bentonite in Inorganic Landfill Leachates, Clay and Clay Minerals, Vol. 50, No. 5, pp. 546-552. Breen, C., (1999) The Characterization and use of Polycation-exchanged Bentonite, Applied Clay Science, Vol. 15, pp. 187-219. Breen, C., and Watson, R. (1998), Polycation-Exchanged Clays as Sorbants for Organic Pollutants: Influence of Layer Charge on Pollutant Sorption Capacity, Journal of Colloid anf Interface Science, Vol. 208, pp. 422-429. Bartelt-Hunt, S.L., Burns, S.E., and Smith, J.A. (2003), Nonionic organic solute sorption onto two organobentonites as a function of organic-carbon content, Journal of Colloid and Interface Science, Vol. 266, pp. 251-258. Churchman, G.J. (2002), Formation of Complexes Between Bentonite and Different Cationic Polyelectrolytes and Their Use as Sorbents for Non-ionic and Anionic Pollutants, Applied Clay Science, Vol. 21, pp. 177-189. Egloffstein, T.A. (2001), Natural Bentonites-influence of the ion exchange and partial desiccation on permeability and self-healing capacity of bentonites used in GCLs, Technical Note, Geotextiles and Geomembranes, Vol. 19, pp. 427-444. Gungor, N., and Ece, O.I. (1999), Effect of the Adsorption of Non-ionic Polymer Poly(vinyl)pyrolidone on the Rheological Properties of Na-Activated Bentonite, Materials Letters, Vol. 39, pp. 1-5. Higgs, N.B. (1988) Methylene Blue Adsorption as a Rapid and Economical Method of Detecting Smectite, Geotechnical Testing Journal, Vol. 11, No. 1, pp. 68-71. Jo, H.Y., Katsumi, T., Benson, C.H., and Edil, T.B. (2001), Hydraulic Conductivity and Swelling of Nonprehydrated GCLs Permeated with Single-Species Salt Solutions, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 127, No. 7, pp. 557-567. 94

PAGE 110

Li, J. Smith, J.A., and Winquist, A.S. (1996), Permeability of Earthen Liners Containing Organobentonite to Water and Two Organic Liquids, Environmental Science and Technology, Vol.320, No. 10, pp. 3089-3093. Liao, W.A. (1989), Polymer/Bentonite/Soil Admixtures as Hydraulic Barriers,SPE Drilling Engineering, June, pp.153-161. Lo, I.M., Mak, R.K., and Lee, S.C.H. (1997), Modified Clays for Waste Containment and Pollutant Attenuation, Journal of Environmental Engineering, Vol.123 No. 1, pp. 25-32. Malusis, M.A., and Shackelford, C.D. (2004), Predicting Solute Flux through a Clay Membrane Barrier, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 130, No. 5, pp. 477-487. Malusis, M.A., Shackelford, C.D., and Olsen, H.W. (2003), Flow and Transport Through Clay Membrane Barriers, Engineering Geology, Vol. 70, pp. 235-248. Mitchell, J.K,. Fundamentals of Soil Behavior, Second Edition, John Wiley and Son, Inc., New York, New York, 1993. Petrov, R.J., Rowe, K., and Quigley, R.M. (1997), Comparison of Laboratory-Measured GCL Hydraulic Conductivity Based in Three Permeameter Types, Geotechnical Testing Journal, Vol. 20, No. 1, pp. 49-62. Redding, Andria And Burns, Susan, (2000), Compressibility And Index Properties Of Organic Exchanged Bentonite, Geotechnical Special Publication, ASCE, No. 105, P. 142-150. Ruhl, Janice L. and Daniel, David E. (1997), Geosynthetic Clay Liners Permeated with Chemical Solutions And Leachates, Journal Of Geotechnical And Geoenvironmental Engineering, Vol. 123, No. 4, Apr, pp.369-381. Santamarina, J.C., Klein, K.A., Wang, Y.H., and Prencke, E. (2002), Specific Surface: Determination and Relevance, Canadian Geotechnical Journal, Vol. 39, pp. 233-241. Shackelford, Charles D., Benson, Craig H., Katsumi, Takeshi., Edil, Tuncer B., and Lin, L. (2000), Evaluating The Hydraulic Conductivity Of GCLs Permeated With Non-Standard Liquids, Journal of Geotextiles and Geomembranes, Vol. 18, Pp. 133-161. Shan H.-Y., Lai Y.J., (2002), Effect Of Hydrating Liquid On The Hydraulic Properties Of Geosynthetic Clay Liners, Geotextiles And Geomembranes v 20, n 1, February, pp. 19-38. 95

PAGE 111

Sposito, G., The Chemistry of Soils, Oxford University Press, Inc, New York, New York, 1989. Taylor, R.K. (1985), Cation Exchange in Clays and Mudrocks by Methylene Blue, Journal of Chem.Tech Biotechnol., Vol. 35A, pp. 195-207. Tanihara, K. and Nakagawa, M. (1975), Flocculation Treatment of Waste Water Container Montmorillonite. IV. Interlamellar Complex Formation Between Various Ion Forms of Montmorillonite and Poly(ethylene oxide) or Polyacrylamide, Nippon Kagaku Kaidhi, No. 5: 782-789. Theng, B.K.G., Formation and Properties of Clay-Polymer Complexes, Elsevier Scientific Publishing Company, New York, New York, 1979. van Olphen, H,, An Introductions to Clay Colloid Chemistry, Second Edition, John Wiley and Sons, Inc., New York, New York, 1977. 96

PAGE 112

APPENDICES 97

PAGE 113

Appendix A Permeability Test Results Table A.1 Laboratory Permeability Tests Test Polymer Permeant Void Ratio Pre-Hydrated 1st Wetting Liquid 1-Ch High Cationic H 2 O 7.14 Yes H 2 O 2-Ch High Cationic H 2 O 3.07 Yes H 2 O 3-Ch High Cationic NaCl 7.14 Yes H 2 O 4-Ch High Cationic CaCl 2 7.14 Yes H 2 O 5-Ch High Cationic CaCl 2 7.14 Yes H 2 O 6-Ch High Cationic MgCl 2 7.14 Yes H 2 O 7-Ch High Cationic CaCl 2 3.07 No CaCl 2 8-Ch High Cationic CaCl 2 7.14 No CaCl 2 1-Cl Low Cationic H 2 O 3.07 Yes H 2 O 2-Cl Low Cationic CaCl 2 3.07 Yes H 2 O 3-Cl Low Cationic MgCl 2 3.07 Yes H 2 O 1-N Nonionic H 2 O 7.14 Yes H 2 O 2-N Nonionic H 2 O 3.07 Yes H 2 O 3-N Nonionic CaCl 2 7.14 Yes H 2 O 4-N Nonionic CaCl 2 3.07 Yes H 2 O 5-N Nonionic CaCl 2 3.07 No CaCl 2 1-Al Low Anionic H 2 O 3.07 Yes H 2 O 2-Al Low Anionic NaCl 3.07 Yes H 2 O 3-Al Low Anionic CaCl 2 3.07 Yes H 2 O 1-Am Medium Anionic H 2 O 7.14 Yes H 2 O 2-Am Medium Anionic H 2 O 3.07 Yes H 2 O 3-Am Medium Anionic NaCl 3.07 Yes H 2 O 4-Am Medium Anionic CaCl 2 3.07 Yes H 2 O 5-Am Medium Anionic MgCl 2 3.07 Yes H 2 O 6-Am Medium Anionic CaCl 2 3.07 No CaCl 2 1-B Bentonite H 2 O 3.07 Yes H 2 O 2-B CaCl 2 3.07 Yes H 2 O 3-B Bentonite MgCl 2 3.07 Yes H 2 O 4-B Bentonite CaCl 2 3.07 No CaCl 2 Bentonite 98

PAGE 114

Appendix A (continued) 1.0E-101.0E-091.0E-081.0E-071.0E-06051015Duration (days)Coefficient of permeability, k (cm/s) 10G-100CPermeant: DI Watere = 7.14 Figure A.1 Coefficient of Permeability vs. Duration 1-Ch 1.0E-101.0E-091.0E-081.0E-070.01.02.03.04.05.06.07.0Pore volumeCoefficient of permeability, k (cm/s) 10G-100CPermeant: DI Watere = 7.14 Figure A.2 Coefficient of Permeability vs. Pore Volume 1-Ch 99

PAGE 115

APPENDIX A (continued) 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-0701020304050607Duration (days)Coefficient of permeability, k (cm/s) 10G-100CPermeant: DI Watere =3.07 0 Figure A.3 Coefficient of Permeability vs. Duration 2-Ch 1.00E-111.00E-101.00E-091.00E-081.00E-070.00.51.01.52.02.53.03.54.0Pore volumeCoefficient of permeability, k (cm/s) 10G-100CPermeant: DI Watere =3.07 Figure A.4 Coefficient of Permeability vs. Pore Volume 2-Ch 100

PAGE 116

Appendix A (continued) 1.0E-111.0E-101.0E-091.0E-081.0E-071.0E-061.0E-051.0E-0405101520253035Duration (days)Coefficient of permeability, k (cm/s) 10G-100CPermeant: NaCle = 7.14 Figure A.5 Coefficient of Permeability vs. Duration 3-Ch 1.0E-101.0E-091.0E-081.0E-071.0E-061.0E-050.01.02.03.04.05.06.07.0Pore volumeCoefficient of permeability, k (cm/s) 10G-100CPermeant: NaCle = 7.14 Figure A.6 Coefficient of Permeability vs. Pore Volume 3-Ch 101

PAGE 117

Appendix A (continued) 1.0E-091.0E-081.0E-071.0E-061.0E-050246810Duration (days)Coefficient of permeability, k (cm/s) 10G-100CPermeant: CaCl2e = 7.14 12 Figure A.7 Coefficient of Permeability vs. Duration 4-Ch 1.0E-081.0E-071.0E-061.0E-050.02.04.06.08.010.012.014.016.0Pore volumeCoefficient of permeability, k (cm/s) 10G-100CPermeant: CaCl2e = 7.14 Figure A.8 Coefficient of Permeability vs. Pore Volume 4-Ch 102

PAGE 118

Appendix A (continued) 1.0E-101.0E-091.0E-081.0E-071.0E-0605101520Duration (days)Coefficient of permeability, k (cm/s) 10G-100CPermeant: CaCl2e = 3.07 Figure A.9 Coefficient of Permeability vs. Duration 5-Ch Po 1.0E-101.0E-091.0E-081.0E-071.0E-061.0E-050.02.04.06.08.010.012.014.0re volumeCoefficient of permeability, k (cm/s) 10G-100CPermeant: CaCl2e = 3.07 Figure A.10 Coefficient of Permeability vs. Pore Volume 5-Ch 103

PAGE 119

Appendix A (continued) 1.0E-091.0E-081.0E-071.0E-061.0E-050123456Duration (days)Coefficient of permeability, k (cm/s) 10G-100CPermeant: MgCl2e = 7.30 7 Figure A.11 Coefficient of Permeability vs. Duration 6-Ch 1.0E-091.0E-081.0E-071.0E-060.01.02.03.04.05.06.07.08.0Pore volumeCoefficient of permeability, k (cm/s) 10G-100CPermeant: MgCl2e = 7.30 Figure A.12 Coefficient of Permeability vs. Pore Volume 6-Ch 104

PAGE 120

Appendix A (continued) 1.0E-111.0E-101.0E-091.0E-081.0E-07051015Duration (days)Coefficient of permeability, k (cm/s) 10G-90CPermeant: DI H2Oe = 3.32 Figure A.13 Coefficient of Permeability vs. Duration 1-Cl Po 1.0E-111.0E-101.0E-091.0E-080.00.51.01.52.02.53.03.54.0re volumeCoefficient of permeability, k (cm/s) 10G-90CPermeant: DI H2Oe = 3.32 Figure A.14 Coefficient of Permeability vs. Pore Volume 1-Cl 105

PAGE 121

Appendix A (continued) 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-071.0E-06051015Duration (days)Coefficient of permeability, k (cm/s) 10G-90CPermeant: CaCl2e = 3.07 Figure A.15 Coefficient of Permeability vs. Duration 2-Cl A.1 Coefficient of Permeability vs. Duration 1-Ch 1 Po 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-071.0E-060.00.51.0.52.02.53.03.5re volumeCoefficient of permeability, k (cm/s) 10G-90CPermeant: CaCl2e = 3.07 Figure A.16 Coefficient of Permeability vs Pore Volume 2-Cl 106

PAGE 122

Appendix A (continued) 1.0eabili 1.0E-111.0E-101.0E-09E-081.0E-071.0E-06051015Duration (days)Coefficient of permty, k (cm/s) 10G-90CPermeant: MgCl2e = 3.07 Figure A.17 Coefficient of Permeability vs. Duration 3-Cl 1.0E-111.0E-101.0E-091.0E-081.0E-071.0E-060.02.04.06.08.010.012.014.016.0Pore volumeCoefficient of permeability, k (cm/s) 10G-90CPermeant: MgCl2e = 3.07 Figure A.18 Coefficient of Permeability vs. Pore Volume 3-Cl 107

PAGE 123

Appendix A (continued) 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-071.0E-0602468Duration (days)Coefficient of permeability, k (cm/s) 10G-20Permeant: H2Oe = 7.14 10 Figure A.19 Coefficient of Permeability vs. Duration 1-N Po 1.0E-111.0E-101.0E-091.0E-081.0E-071.0E-060.02.04.06.08.010.012.0re volumeCoefficient of permeability, k (cm/s) 10G-20Permeant: H2Oe = 7.14 Figure A.20 Coefficient of Permeability vs. Pore Volume 1-N 108

PAGE 124

Appendix A (continued) 1.00E-111.00E-101.00E-091.00E-081.00E-070510152025Duration (days)Coefficient of permeability, k (cm/s) 10G-20Permeant: H2Oe = 3.07 Figure A.21 Coefficient of Permeability vs. Duration 2-N 1.00E-111.00E-101.00E-091.00E-080.00.51.01.52.0Pore volumeCoefficient of permeability, k (cm/s) 10G-20Permeant: H2Oe = 3.07 Figure A.22 Coefficient of Permeability vs. Pore Volume I-N 109

PAGE 125

Appendix A (continued) 1.0E-111.0E-101.0E-091.0E-081.0E-071.0E-061.0E-05051015Duration (days)Coefficient of permeability, k (cm/s) 10G-20Permeant: CaCl2e = 7.14 Figure A.23 Coefficient of Permeability vs. Duration 3-N Po 1.0E-101.0E-091.0E-081.0E-070.01.02.03.04.05.06re volumeCoefficient of permeability, k (cm/s) 10G-20Permeant: CaCl2e = 7.14 .0 Figure A.24 Coefficient of Permeability vs. Pore Volume 3-N 110

PAGE 126

Appendix A (continued) 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-071.0E-060.00.51.01.52.02.53.03.54.0Pore volumeCoefficient of permeability, k (cm/s) 10G-20Permeant: CaCl2e = 3.14 Figure A.25 Coefficient of Permeability vs. Duration 4-N 10 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-071.0E-0605152025Duration (days)Coefficient of permeability, k (cm/s) 10G-20Permeant: CaCl2e = 3.14 Figure A.26 Coefficient of Permeability vs. Pore Volume 4-N 111

PAGE 127

Appendix A (continued) 1.0E-111.0E-101.0E-091.0E-081.0E-071.0E-0605101520Duration (days)Coefficient of permeability, k (cm/s) 10G-70APermeant: H2Oe = 3.25 Figure A.27 Coefficient of Permeability vs. Duration 1-Al 1.0E-111.0E-101.0E-091.0E-081.0E-071.0E-060.00.51.01.52.02.53.03.5Pore volumeCoefficient of permeability, k (cm/s) 10G-70APermeant: H2Oe = 3.25 Figure A.28 Coefficient of Permeability vs. Pore Volume 1-Al 112

PAGE 128

Appendix A (continued) 1.0E-111.0E-101.0E-091.0E-081.0E-071.0E-060246810Duration (days)Coefficient of permeability, k (cm/s) 10G-70APermeant: NaCle = 3.07 12 Figure A.29 Coefficient of Permeability vs. Duration 2-Al 1.0E-111.0E-101.0E-091.0E-081.0E-071.0E-060.01.02.03.04.05.0Pore volumeCoefficient of permeability, k (cm/s) 10G-70APermeant: NaCle = 3.07 Figure A.30 Coefficient of Permeability vs. Pore Volume 2-Al 113

PAGE 129

Appendix A (continued) 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-071.0E-060510Duration (days)Coefficient of permeability, k (cm/s) 10G-70APermeant: CaCl2e = 3.07 15 Figure A.31 Coefficient of Permeability vs. Duration 3-Al 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-071.0E-060.02.04.06.08.010.0Pore volumeCoefficient of permeability, k (cm/s) 10G-70APermeant: CaCl2e = 3.07 Figure A.32 Coefficient of Permeability vs. Pore Volume 3-Al 114

PAGE 130

Appendix A (continued) 1.0E-111.0E-101.0E-091.0E-081.0E-070246810Duration (days)Coefficient of permeability, k (cm/s) 10G-80APermeant: H2Oe = 7.14 12 Figure A.33 Coefficient of Permeability vs. Duration 1-Am Po 1.0E-111.0E-101.0E-091.0E-081.0E-070.01.02.03.04.0re volumeCoefficient of permeability, k (cm/s) 10G-80APermeant: H2Oe = 7.14 Figure A.34 Coefficient of Permeability vs. Pore Volume 1-Am 115

PAGE 131

Appendix A (continued) 1.0E-131.0E-121.0E-111.0E-101.0E-091.0E-081.0E-0705101520Duration (days)Coefficient of permeability, k (cm/s) 10G-80APermeant: H2Oe = 3.07 Figure A.35 Coefficient of Permeability vs. Duration 2-Am 1.0E-131.0E-121.0E-111.0E-101.0E-091.0E-081.0E-070.00.51.01.52.02.5Pore volumeCoefficient of permeability, k (cm/s) 10G-80APermeant: H2Oe = 3.07 Figure A.36 Coefficient of Permeability vs. Pore Volume 2-Am 116

PAGE 132

Appendix A (continued) 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-07051015202530Duration (days)Coefficient of permeability, k (cm/s) 10G-80APermeant: NaCle = 3.10 Figure A.37 Coefficient of Permeability vs. Duration 3-Am 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-070.00.51.01.52.02Pore volumeCoefficient of permeability, k (cm/s) 10G-80APermeant: NaCle = 3.10 .5 Figure A.38 Coefficient of Permeability vs. Pore Volume 3-Am 117

PAGE 133

Appendix A (continued) 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-07051015Duration (days)Coefficient of permeability, k (cm/s) 10G-80APermeant: CaCl2e = 3.07 Figure A.39 Coefficient of Permeability vs. Duration 4-Am 1.0E-111.0E-101.0E-091.0E-081.0E-070.00.51.01.52.02.53Pore volumeCoefficient of permeability, k (cm/s) 10G-80APermeant: CaCl2e = 3.07 .0 Figure A.40 Coefficient of Permeability vs. Pore Volume 4-Am 118

PAGE 134

Appendix A (continued) 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-07024681012Duration (days)Coefficient of permeability, k (cm/s) 10G-80APermeant: MgCl2e = 7.21 14 Figure A.41 Coefficient of Permeability vs. Duration 5-Am 1.0E-111.0E-101.0E-091.0E-081.0E-070.00.51.01.52.02.53.03.5Pore volumeCoefficient of permeability, k (cm/s) 10G-80APermeant: MgCl2e = 7.21 Figure A.42 Coefficient of Permeability vs. Pore Volume 5-Am 119

PAGE 135

Appendix A (continued) 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-070510152025Duration (days)Coefficient of permeability, k (cm/s) BentonitePermeant: H2Oe = 3.07 Figure A.43 Coefficient of Permeability vs. Duration 1-B 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-070.00.51.01.52.02.5Pore volumeCoefficient of permeability, k (cm/s) BentonitePermeant: H2Oe = 3.07 Figure A.44 Coefficient of Permeability vs. Pore Volume 1-B 120

PAGE 136

Appendix A (continued) 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-071.0E-06051015Duration (days)Coefficient of permeability, k (cm/s) BentonitePermeant: CaCl2e = 3.07 Figure A.45 Coefficient of Permeability vs. Duration 2-B 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-071.0E-060.01.02.03.04.05.0Pore volumeCoefficient of permeability, k (cm/s) BentonitePermeant: CaCl2e = 3.07 Figure A.46 Coefficient of Permeability vs. Pore Volume 2-B 121

PAGE 137

Appendix A (continued) 1.0E-121.0E-111.0E-101.0E-091.0E-081.0E-070246810Duration (days)Coefficient of permeability, k (cm/s) BentonitePermeant: MgCl2e = 3.07 12 Figure A.47 Coefficient of Permeability vs. Duration 3-B 1.0E-111.0E-101.0E-091.0E-081.0E-070.01.02.03.04.0Pore volumeCoefficient of permeability, k (cm/s) BentonitePermeant: MgCl2e = 3.07 Figure A.48 Coefficient of Permeability vs. Pore Volume 3-B 122

PAGE 138

Appendix B: Swell Index Test Results 051015202530354000.20.40.60.811.2Liquid Solution Concentration (M) Swell Index mL/2g NaCl KCl MgCl2 CaCl2 High Cationic Figure B.1 Swell Index of High Cationic Modified Clay 0510152025303500.20.40.60.811.2Liquid Solution Concentration (M) Swell Index mL/2g NaCl KCl MgCl2 CaCl2 Low Cationic Figure B.2 Swell Index of Low Cationic Modified Clay 123

PAGE 139

Appendix B (Continued) 051015202530354000.20.40.60.811.2Liquid Solution Concentration (M) Swell Index mL/2g NaCl KCl MgCl2 CaCl2 N onionic Figure B.3 Swell Index of Nonionic Modified Clay 0510152025303500.20.40.60.811.2Liquid Solution Concentration (M) Swell Index mL/2g NaCl KCl MgCl2 CaCl2 Low Anionic Figure B.4 Swell Index of Low Anionic Modified Clay 124

PAGE 140

Appendix B (Continued) 0510152025303500.20.40.60.811.2Liquid Solution Concentration (M) Swell Index mL/2g NaCl KCl MgCl2 CaCl2 Medium Anionic Figure B.5 Swell Index of Medium Anionic Modified Clay 0102030405060708000.20.40.60.811.2Liquid Solution Concentration (M) Swell Index mL/2g NaCl KCl MgCl2 CaCl2 Bentonite Figure B.6 Swell Index of Unmodified Bentonite Clay 125

PAGE 141

Appendix C: Liquid Limit Test Results 200250300350400450500550600650051015202530Displacement (mm)Moisture Content (% ) 1.0 wt% High Cationic 0.5 wt% High Cationic Figure C.1 Liquid Limit Not Heated High Cationic 20030040050060070080090051015202530Displacement (mm)Moisture Content (% ) 1.0 wt% Low Cationic 0.5 wt% Low Cationic Figure C.2 Liquid Limit Not Heated Low Cationic 2004006008001000120014001015202530Displacement (mm)Moisture Content (% ) 1.0 wt% Nonionic 0.5 wt% Nonionic Figure C.3 Liquid Limit Not Heated Nonionic 126

PAGE 142

Appendix C (Continued) 2003004005006007008001015202530Displacement (mm)Moisture Content (% ) 1.0 wt% Low Anionic 0.5 wt% Low Anionic Figure C.4 Liquid Limit Not Heated Low Anionic 20030040050060070080081318232Displacement (mm)Moisture Content (% ) 1.0 wt% Medium Anionic 0.5 wt% Medium Anionic 8 Figure C.5 Liquid Limit Not Heated Medium Anionic 1001502002503003504004505005505101520253Displacement (mm)Moisture Content (% ) 1.0 wt% High Cationic 0.5 wt% High Cationic 0 Figure C.6 Liquid Limit Heated High Cationic 127

PAGE 143

Appendix C (Continued) 01002003004005006007005101520253035Displacement (mm)Moisture Content (% ) 1.0 wt% Low Cationic 0.5 wt% Low Cationic Figure C.7 Liquid Limit Heated Low Cationic 010020030040050060051015202530Displacement (mm)Moisture Content (% ) 1.0 wt% Nonionic 0.5 wt% Nonionic Figure C.8 Liquid Limit Heated Nonionic 70 01002003004005006000510152025303Displacement (mm)Moisture Content (% ) 1.0 wt% Low Anionic 0.5 wt% Low Anionic 5 Figure C.9 Liquid Limit Heated Low Anionic 128

PAGE 144

Appendix C (Continued) 01002003004005006008131823Displacement (mm)Moisture Content (% ) 1.0 wt% Medium Anionic 0.5 wt% Medium Anionic 28 Figure C.10 Liquid Limit Heated Medium Anionic 020040060080001020304Displacement (mm)Moisture Content (%) Heated Bentonite Not Heated Bentonite 0 Figure C.11 Liquid Limit Heated and Not Heated Bentonite 129


xml version 1.0 encoding UTF-8 standalone no
record xmlns http:www.loc.govMARC21slim xmlns:xsi http:www.w3.org2001XMLSchema-instance xsi:schemaLocation http:www.loc.govstandardsmarcxmlschemaMARC21slim.xsd
leader nam Ka
controlfield tag 001 001478761
003 fts
006 m||||e|||d||||||||
007 cr mnu|||uuuuu
008 040811s2004 flua sbm s000|0 eng d
datafield ind1 8 ind2 024
subfield code a E14-SFE0000403
035
(OCoLC)56389868
9
AJS2451
b SE
SFE0000403
040
FHM
c FHM
090
TA145 (ONLINE)
1 100
Schenning, Jessica A.
0 245
Hydraulic performance of polymer modified bentonite
h [electronic resource] /
by Jessica A. Schenning.
260
[Tampa, Fla.] :
University of South Florida,
2004.
502
Thesis (M.S.C.E.)--University of South Florida, 2004.
504
Includes bibliographical references.
516
Text (Electronic thesis) in PDF format.
538
System requirements: World Wide Web browser and PDF reader.
Mode of access: World Wide Web.
500
Title from PDF of title page.
Document formatted into pages; contains 144 pages.
520
ABSTRACT: Bentonite clay is widely used in barrier systems due to its low hydraulic conductivity and it high swell capacity. Exposure to inorganic solutions can cause significant increases in hydraulic conductivity, due to changes in the surface chemistry and fabric. This phenomenon can be attributed to a reduction in the thickness of the double layer, due to the cation exchange capacity of the clay. The clay can be modified with polymers to render it less susceptible to chemical attack. The treatment process allows the clay to be engineered to enhance specific properties, such as permeability and sorption. In the present study, engineered soils are prepared by sorbing organic polymers to the surface of Na-bentonite. Three classes, cationic, anionic and nonionic polymers are investigated. The sorbents are water-soluble compounds based on the polymerization of acrylamides (PAM). Mixing and sample preparation techniques are developed and discussed. The interaction of the polymeric compounds and the clay mineral surface are evaluated by testing the liquid limit, swell index and specific gravity of the soils. Permeability tests are performed to determine if the polymer treatment enhances the hydraulic performance of the clay when permeated with highly concentrated salt solutions. The effect of permeant, void ratio, initial wetting condition and preparation techniques are found to have a significant affect on the hydraulic conductivity.
590
Adviser: Ashmawy, Alaa
653
barriers.
liners.
swell index.
engineered clay.
permeability.
690
Dissertations, Academic
z USF
x Civil Engineering
Masters.
773
t USF Electronic Theses and Dissertations.
4 856
u http://digital.lib.usf.edu/?e14.403