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Adsorption studies for arsenic removal using modified chabazite

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Adsorption studies for arsenic removal using modified chabazite
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Vakharkar, Ashutosh S
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Arsenite
Arsenate
Zeolite
Freundlich
Langmuir
Dissertations, Academic -- Environmental Engineering -- Masters -- USF   ( lcsh )
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government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
theses   ( marcgt )
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ABSTRACT: Arsenic contamination in drinking water has been a cause of serious concerns across the United States as well as throughout the world. Over 70 million people in Eastern India, Bangladesh, Vietnam, Taiwan, and Northern China have been victims of arsenic poisoning. The USEPA has classified arsenic as a Class A carcinogen and recently reduced the Maximum Contaminant Level (MCL) in drinking water from 50ppb to 10ppb. The deadline for all the water utilities to meet this level is 23rd January 2006. To meet those drinking water standards, small water utilities need low cost and effective arsenic removal techniques. Natural zeolites such as Chabazite are excellent sorbents for several metallic and radioactive cations. Modifying the zeolite structure can effectively enhance the adsorption capacities of these zeolites for removal of heavy metals. The present work investigates the adsorption capacities of Cuprous and Ferrous treated Chabazite for removal of arsenic.This investigation is a part of a broader project directed at developing an effective pretreatment process that uses modified Chabazite in conjugation with Microfiltration (MF) or Ultrafiltration (UF) for removal of organic and inorganic contaminants. The goal of this research is to determine how well Cuprous and Ferrous treated Chabazite sorbs arsenic in its trivalent and pentavalent state. The other objectives of this research are to examine which modification of the chabazite has the higher removal efficiency of arsenic. This study will also compare arsenic adsorption on the modified zeolites in response to competitive adsorption of various anions present in natural source waters such as sulfates, hydroxides, and chlorides. The potential benefit of this study is to find the most effective treatment of for removal of arsenic species from aqueous solutions.This investigation may provide small water utilities, with a cost effective way for removal of arsenic and thus meet the recommended new regulatory maximum contaminant level (MCL).
Thesis:
Thesis (M.S.E.V.)--University of South Florida, 2005.
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Includes bibliographical references.
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by Ashutosh S. Vakharkar.
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Title from PDF of title page.
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Document formatted into pages; contains 86 pages.

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Adsorption Studies For Arsenic Re moval Using Modified Chabazite by Ashutosh S.Vakharkar A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Environmental Engineering Department of Civil and Environmental Engineering College of Engineering University of South Florida Major Professor: Robert P. Carnahan, Ph.D., P.E., D.E.E. Marilyn Barger, Ph.D., P.E. Scott Campbell, Ph.D. Date of Approval: November 15, 2005 Keywords: arsenite, arsenate zeolite, Freundlich, Langmuir Copyright 2005, Ashutosh S.Vakharkar

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Dedication I would like to dedicate this thesis to my family. To my fath er, Satish Vakharkar, my mother, Gayatri Vakharkar and my brothe r, Abhijit (my lucky charm). It was my fathers dream to see his eldest son as a su ccessful engineer, which I hope I will realize soon. For all his support, financially and emoti onally I will remain ever indebted to him. Without the support, encouragement, and unders tanding of my family, I would not have been able to complete this thesis.

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Acknowledgements I would like to start by thanking my major professor, Dr. Robert P. Carnahan, for all his guidance and support during the past two years. His interest in studies related to purification of drinking wate r and other environmental issues and his dedication to research is highly inspiring. His continuous support, both emotionally and financially ensured that graduate studies were completed without any obstacles. I would like to take the time to thank Dr. Marilyn Barger who was instrumental in providing valuable suggestions and inputs during the entire duration of the project. Without her guidance it would have had been diff icult to present the thesis in its current form. I would also like to take this opportunity to thank Dr Scott Campbell for his valuable time and suggestions. I am very grateful to work with Miles B eamguard on this project. I did learn a lot from his practical approach to various situa tions and altogether it was a very enjoyable and rich experience to share the lab space with him. A special mention goes to Catherine High who has been ever willing to provide supp ort with issuing the purchase orders and appointments throughout the length of graduate studies. Thanks to Dr. Maya Trotz for help with arsenic analysis on the Graphite AA. Appreciation goes to people in the Geology Department, Ol esya, and Roy who conducted initial arsenic analysis. I w ould also like to thank my friends and my roommates who have been a constant source of support and encouragement. I would like to recognize the Order of Naval Research (ONR), for funding the main project, Zeolite Pretreatment for Microfiltration and Ultrafiltration Systems used in Desalination Treatment of Contaminated Water, of which my research was a small part.

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i Table of Contents List of Tables................................................................................................................. ....iv List of Figures......................................................................................................................v Abstract....................................................................................................................... ......vii Introduction................................................................................................................... .......1 Research and Objectives......................................................................................................3 Literature Review.................................................................................................................4 Occurrence..............................................................................................................4 Arsenic Chemistry..................................................................................................5 Exposure.................................................................................................................7 Health Hazards........................................................................................................7 Review of Arsenic Removal Methods.................................................................................8 Methods..............................................................................................................................10 Coagulation/Precipitation.....................................................................................10 Ion Exchange........................................................................................................12 Activated Alumina................................................................................................13 Reverse Osmosis...................................................................................................15 Adsorption Processes............................................................................................16 Adsorbent Materials..............................................................................................17 Granular Ferric Hydroxide........................................................................17 Iron Oxide Coated Sand............................................................................17 Manganese Green Sand Filters.................................................................18 Pyrite Fines...............................................................................................19 Activated Carbon......................................................................................19 Zero-Valent Iron.......................................................................................19 Zeolites......................................................................................................20 Need For Finding Cost Effective Methods of Arsenic Removal.......................................21 Background on Zeolites.....................................................................................................23 Chabazite...............................................................................................................24

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ii Background on Adsorption Isotherms...............................................................................25 Freundlich Isotherms............................................................................................25 Langmuir Isotherms..............................................................................................27 Materials and Experimental Methods................................................................................29 Materials...............................................................................................................29 Experimental Procedures......................................................................................30 Phase I: Pretreatment of Chabazite.......................................................................31 Phase II: Batch Studies.........................................................................................33 Kinetic Studies..........................................................................................33 Equilibrium Studies..................................................................................34 Results and Discussion......................................................................................................36 Kinetic and Equilibrium Studies in De-ionized Water.........................................37 Kinetic Studies..........................................................................................37 Equilibrium Studies..................................................................................40 Kinetic Studies for Determination of Effect of Stoichiometric Ratio...................42 Kinetic Studies Using Chabazite Mo dified with Same Anion and Different Cations.......................................................................................42 Kinetic Studies Using Chabazite Modified with Same Cation and Different Anions.......................................................................................45 Results from Long Term Equilibrium Studies Using Diffe rent Modified Chabazite in Dechlorinated Tap Water.................................................................47 Results from Kinetic Studies for Arsenic Adsorption in Various Source Waters49 Relationship between Mass of Zeolite and Arsenic Removal..............................52 Uptake/Leaching Studies......................................................................................53 Conclusions........................................................................................................................55 Engineering Significance and Recommendations.............................................................56 Modification of Zeolite.........................................................................................56 Modification of Zeolite Using Various Metal Salts..................................56 Modification of Zeolite Using Various Concentrations............................57 Effect of Particle Size on Arsenic Adsorption..........................................57 Bench Scale Tests Using Actual Source Waters...................................................58 Column Studies.....................................................................................................59 References..........................................................................................................................60 Appendices.........................................................................................................................63

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iii Appendix A: Chabazite Physical Pr operties and Arsenic Analysis..................................64 Preparation of Arsenic Trioxide solution For Batch Studies................................65 Arsenic Analysis...................................................................................................66 Appendix B: Determination of Order of Reaction............................................................68 Integral Method of Analysis.................................................................................68

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iv List of Tables Table 1 Summary of Studies Done on Arsenic Removal by Coagulation (Forlini, 1998)......................................................................................................11 Table 2 Mean Annual Costs per Household for Each System/ Utility Size.....................21 Table 3 Results from Kinetic Studies Us ing Different Modified Chabazite in De-Ionized Water.................................................................................................38 Table 4 Order of Reaction and Reaction Rate Constant for Modified Zeolites in De-ionized Water.................................................................................................3 9 Table 5 Langmuir and Freundlich Isotherm Coefficients in De-ionized Water...............41 Table 6 Results from Kinetic Studies Using Chabazite Modified with Same Anion and Different Cations................................................................................44 Table 7 Expected Arsenate Compounds and Metal/ Arsenic Molar Ratio.......................44 Table 8 Order of Reaction and Reaction Rate Constant for Chabazite Modified With Same Anion and Different Cations.............................................................44 Table 9 Results from Kinetic Studies Using Chabazite Modified with Same Cation and Different Anions......................................................................46 Table 10 Langmuir and Fre undlich Isotherm Coefficients for Ferrous Sulfate Modified Chabazite in Dechlorinated Tap Water..............................................49 Table 11 Results from Kinetic Studies Using Different Source Waters...........................51 Table 12 Order of Reaction and Reaction Rate Constants for Kinetic Studies With Ferrous Sulfate Modifi ed Chabazite in Various Source Waters...............51 Table 13 Uptake Data for Metals Used in Modification of Chabazite.............................54 Table 14 Matrix of Bench Scale Tests and Water Quality Parameters for Development of a Full Scale Pr ocess Using Modified Chabazite as Adsorbent.....................58 Table A1 Chabazite Physical Properties...........................................................................64

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v List of Figures Figure 1 Occurrence of Arsenic in Groundwat er in the United States (Figure adopted from USGS National Water Quality Assessment -2001)....4 Figure 2 Arsenic Trioxide Speciation at Different pH Ranges....................................5 Figure 3 Arsenic Pentoxide Specia tion at Different pH Ranges..................................6 Figure 4 Number of Drinking Water Utilities Exceeding the New Maximum Contaminant Level.........................................................................................8 Figure 5 Effect of pH on Activated Alumina Performance (USEPA, 2000).............14 Figure 6 Mean Annual Costs per Household vs. Utility Size....................................22 Figure 7 Cage Like Structure of Chabazite................................................................24 Figure 8 Freundlich Isotherm for Ad sorption of Arsenic on Portland Cement (Figure adopted from Kundu, Pal et al., 2004)............................................26 Figure 9 Langmuir Isotherm for Adsorption of Arseni c on Portland Cement (Figure adopted from Kundu, Pal et al., 2004)............................................28 Figure 10 Mettler AE 260 Delta Range Analytical Balance........................................30 Figure 11 Blue M Stabil Therm Gravity Oven.............................................................30 Figure 12 Batch Reactors for Pretreatment of Chabazite.............................................31 Figure 13 Chabazite Before and Afte r Copper (I) Chloride Treatment.......................32 Figure 14 Chabazite Before and Af ter Iron (II) Chloride Treatment...........................32 Figure 15 Chabazite Before and Af ter Iron (II) Sulfate Treatment..............................33 Figure 16 Kinetic Studies for Adsorption of Arsenic with Cu and Fe Species............33 Figure 17 Kinetic Runs for Arsenic Removal Using Modified Chabazite In De-ionized Water.........................................................................................37 Figure 18 Langmuir Adsorption Isotherm for Modified Ch abazite in De-ionized Water............................................................................................................40 Figure 19 Freundlich Adsorption Isotherm for M odified Chabazite in De-ionized Water.........................................................................................41 Figure 20 Kinetic Studies for Arseni c Adsorption Using Same Anion and Different Cations in Dechlorinated Tap Water............................................43

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vi Figure 21 Kinetic Studies for Arse nic Adsorption Using Same Cation and Different Anions in Dechlorinated Tap Water......................................45 Figure 22 Langmuir Isotherm for Equilibrium Studies Using Ferrous Sulfate Modified Chabazite in Dechlorinated Tap Water............................47 Figure 23 Freundlich Isotherm for L ong Term Equilibrium Studies Using Ferrous Sulfate Modified Chabazite in Dechlorinated Tap Water..............48 Figure 24 Results from Kinetic Studies for Arsenic Adsorption Using Ferrous Sulfate Mo dified Chabazite in Different Source Waters.............................50 Figure 25 Relationship Between Arsenic Removal and Mass of Zeolite.....................53 Figure A1 Varian AA Spectra Zeeman Graphite Furnace............................................67 Figure B1 First Order Kinetic Rate for Copper Modified Chabazite In De-ionized Water............................................................................................................69 Figure B2 Second Order Kinetic Rate for Copper Modified Chabazite In De-Ionized Water.........................................................................................69 Figure B3 First Order Kinetic Rate for Fe rrous Chloride Modified Chabazite In De-ionized Water.........................................................................................70 Figure B4 Second Order Kinetic Rate for Fe rrous Chloride Modified Chabazite In De-ionized Water.........................................................................................70 Figure B5 First Order Kinetic Rate for Fe rrous Sulfate Modified Chabazite in Deionized Water...............................................................................................71 Figure B6 Second Order Kinetic Rate for Fe rrous Sulfate Modified Chabazite in De-ionized Water.........................................................................................71 Figure B7 First Order Kinetic Rate fo r Copper Modified Chabazite With Same Anion..................................................................................................72 Figure B8 Second Order Kinetic Rate fo r Copper Modified Chabazite With Same Anion..................................................................................................72 Figure B9 First Order Kinetic Rate fo r Ferrous Modified Chabazite With Same Anion..................................................................................................73 Figure B10 Second Order Kinetic Rate fo r Ferrous Modified Chabazite With Same Anion..................................................................................................73 Figure B11 Second Order Kinetic Rate for Modified Chabazite With Different Anion (Chloride)......................................................................... 74 Figure B12 Second Order Kinetic Rate for Modified Chabazite With Different Anion (Sulfate) ............................................................................74 Figure B13 Kinetic Rate Determination for Ferrous Sulfate Modified Chabazite in Different Source Waters..............................................................................75

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vii Adsorption Studies For Arsenic Removal Using Modified Chabazite Ashutosh S.Vakharkar ABSTRACT Arsenic contamination in drinking wate r has been a cause of serious concerns across the United States as well as throughout the world. Over 70 million people in Eastern India, Bangladesh, Vietnam, Taiwan, and Northern China have been victims of arsenic poisoning. The USEPA has classified arsenic as a Class A carcinogen and recently reduced the Maximum Contaminant Level (MCL) in drinking water from 50ppb to 10ppb. The deadline for all the water ut ilities to meet this level is 23 rd January 2006. To meet those drinking water standards, sma ll water utilities need low cost and effective arsenic removal techniques. Natural zeolites such as Chabazite are excellent sorben ts for several metallic and radioactive cations. Modifyi ng the zeolite structure can effectively enhance the adsorption capacities of these zeolites for re moval of heavy metals. The present work investigates the adsorption capacities of Cuprous and Ferrous treated Chabazite for removal of arsenic. This invest igation is a part of a broader project directed at developing an effective pretreatment process that us es modified Chabazite in conjugation with Microfiltration (MF) or Ultrafiltration (U F) for removal of organic and inorganic contaminants. The goal of this research is to determine how well Cuprous and Ferrous treated Chabazite sorbs arsenic in its trivalent and pe ntavalent state. The other objectives of this research are to examine which modificati on of the chabazite has the higher removal efficiency of arsenic. This study will also compare arsenic adsorption on the modified

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viii zeolites in response to competitive adsorption of various anions present in natural source waters such as sulfates, hydroxides, and chlorides. The potential benefit of this study is to find the most effective treatment of for removal of arsenic species from aqueous solu tions. This investigation may provide small water utilities, with a cost effective way for removal of arsenic and thus meet the recommended new regulatory maximum contaminant level (MCL).

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1 Introduction Arsenic is the 20 th most abundant element found in the earths crust. It occupies nearly 0.00005% of the entire earths surf ace (Gulledge, 1973). Arsenic that occurs in most natural waters is in inorganic form, namely As (III) and As (V). These two ions namely, arsenic trioxide a nd arsenic pentoxide are eith er naturally occurring or byproducts of industrial waste. The pr edominant species for As (III) are H 3 AsO 3 and for As (V) are H 2 AsO 4 and HAsO 4 2. Ingestion of inorganic arse nic results in both cancer and non-cancer related health effects (NRC, 199 9). The USEPA has classified arsenic as a Class A carcinogen. Chronic exposure to low arsenic levels (less than 50 ppb) has been linked to health complications, including cancer of the skin, kidney, lung, and bladder, as well as other diseases of the skin, and th e neurological and car diovascular systems (USEPA, 2000). The USEPA has recently reduced the maximum contaminant level (MCL) of arsenic in drinking water from 50 ppb to 10 p pb. All the water utili ties must meet this standard by 23 rd January 2006. Since nearly 97% of the water systems affected by the new regulatory standard are small systems, it is vital that cost effective and affordable treatment technologies are developed. The majo r concern that faces any small community is whether the treatment of arsenic is going to require the construc tion of a centralized treatment facility or whether treatment is to be accomplished at the po int-of-use. In either case, there are major decisions that must be ma de that require a sign ificant investment on the part of the community. Several technologies are effective in lowe ring total arsenic in aqueous solutions namely, coagulation/precipitation, ion exch ange, adsorption proc esses, and reverse osmosis. Materials that have shown capacit ies for arsenic sorpti on include activated alumina; iron media (granular ferric hydroxide, iron oxide coated sand, iron pyrites), synthetic ion exchange resins, fly ash. Arsenic has also shown high affinity for sorption

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2 on natural zeolitic materials such as Chabazite. Natural zeolites such as Chabazite have crystalline structure characteri zed by large pore sizes and large surface areas. This makes them excellent sorbents for several metallic and radioactive cations. Modifying the zeolite structure by treatment w ith metals such as copper or iron effectively enhances the sorption capacity for arsenic. Arsenic cont aminant levels of 50 ppb can be easily achieved through conventional methods such as coagulation, ion exchange, activated alumina, and reverse osmosis; however to achie ve levels less than 10 ppb requires use of more expensive technologies.

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3 Research and Objectives This research consists of comparative equilibrium and kinetic studies of arsenic sorption using copper and ferrous modified ch abazite. Modifying the zeolite structure can effectively enhance the adsorption capacity of the natural zeolite for removal of heavy metals. This investigation is a part of a broader project aimed at developing an effective pretreatment process used in conjugation with microfiltration (MF) or ultrafiltration (UF) for removal of organic and inorganic contaminants. The goal of this research is to determine the capacity of Copper (I) and Iron (Fe II) treated chabazite to adsorb arsenic in its trival ent and pentavalent state. The objectives are: to conduct equilibrium and kinetic studies using modified zeolites in de-ionized water, dechlorinated tap water and gr ound water which assesses the competitive adsorption capacity for arsenic in the presence of other species to compare selectivity of cuprous and ferrous modified chabazite to conduct equilibrium and kinetic studies for arsenic adsorption using modified zeolites in presence of other competi ng ions like chlorides, hydroxides and sulfates. These studies would be conducted using a matrix of low and high concentrations of competing species. All these studies should help establish th e operating parameters, needed to design a cost effective treatment system for small utilities.

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Literature Review Occurrence Arsenic (As) is a naturally occurring el ement present in food, water, and air. Known for centuries to be an effective poison; however, some animal studies suggest that arsenic may be an essential nutrient at low concentrations (National Research Council, 1999). It is ubiquitous in the environment and occupies approximately 0.00005% of the earths crust and its presence has been reporte d in several parts of the world, like USA, China, Chile, Bangladesh, Taiwan, Mexico, Argentina, Poland, Canada, Hungary, Japan, and India (Robertson, et al., 1986) Arsenic is a common minera l found in many western st ates of the U.S., it is present in many groundwater supplies serv ing small communities. Figure 1 shows the occurrence of and concentrations of arse nic in groundwater supplies for the various 4 states. Figure 1 Occurrence of Arsenic in Groundwat er in the United States (Figure adopted from USGS Nationa l Water Quality Assessment -2001)

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Arsenic occurs in two primary forms; organic and inorganic. Organic species of arsenic are predominantly found in foodstuffs, such as shellfish, as monomethyl arsenic acid (MMAA), dimethyl arsenic acid (DM AA), and arseno-sugars Inorganic arsenic occurs in two oxidation states namely arsenite (As III) and arsenate (As V). As (III) consist primarily of arsenious acid (H 3 AsO 3 ) in natural waters, while As (V) consist primarily of anionic species (H 2 AsO 4 and HAsO 4 2) in natural waters (Clifford and Lin, 1995). Most natural waters contain the more t oxic inorganic forms of arsenic rather than organic species. Ground waters contain predominantly As ( III) since reduci ng conditions prevail, while natural surf ace waters contain As (V) as the dominant species. The aqueous chemistry of arsenic is important, since the chemistry of speciation of arsenic controls the selection of treatment processes. Arsenic Chemistry Arsenite As (III) is slightly soluble in water forms arsenious acid (HAsO 2 ). The dissolution reaction for arsenic tr ioxide is as shown below: Log Concentration vs pH for As(III) log[H+] log[OH-] H3AsO3 H2AsO3HAsO32AsO33-14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 01234567891011121314 pHLog C Figure 2 Arsenic Trioxide Speci ation at Different pH Ranges 5

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As 2 O 3 + H 2 O 2HAsO 2 (Pontius, 1994) Arsenic pentoxide, the oxidi zed form of arsenic trioxide forms arsenic acid (H 3 AsO 4 ) in water, As 2 O 5 + 3H 2 O 2H 3 AsO 4 (Pontius, 1994) Log Concentration vs pH for As(V) log[H+] log[OH-] H3AsO4 H2AsO4HAsO42AsO43-14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 01234567891011121314 pHLog C Figure 3 Arsenic Pentoxide Speciation at Different pH Ranges The rate of oxidation of arsenic (III) to arsenic (V) at neutral pH is very slow, but proceeds rapidly in presence of strong alkaline or acidic solutions (Sorg, 1978). Furthermore, the arsenic cycle in water is not signi ficantly affected by mi crobial action. Certain microorganisms are able to methylate arseni c to form organic as well as inorganic compounds. However, the methylation reaction is not thermodynamically favored in aqueous solutions and hence it does not alter th e existence of arsenic in solution to a great extent (Pierce, 1980). 6

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7 Exposure Significant exposure to arse nic occurs through both anthropogenic and natural sources. Arsenic in the earths surface is re-r eleased into the air by volcanoes and is a natural contaminant of some deep-water wells The primary route of exposure to arsenic for humans is ingestion; however exposure via inhalation while considered minimal, occurs periodically in some regions (Hering and Chiu, 1998) Occupational exposure to arsenic is common in the smelting industry a nd is increasing in th e microelectronics industry. The general population is exposed to low levels of arsenic through the commercial use of inorganic arsenic com pounds in common products such as wood preservatives, pesticides, herbicides, fungici des, and paints; and also through the burning of fossil fuels in which arsenic is a contaminant. Health Hazards People exposed to water contaminated with arsenic generally show arsenical skin lesions, which are a late manifestation of ar senic toxicity. Long-term exposure to arsenic contaminated water may lead to various dis eases such as conjunctivitis, hyperkeratosis, hyper pigmentation, cardiovascular diseases, disturbance in the peripheral vascular and nervous systems, skin cancer, (Kiping, 1977; WHO (World Health Organisation), 1981; Pershagen, 1983). Arsenic contamination in ground water of Taiwan is well known (Lu, 1990a, b) and has resulted in arsenism and black-foot disease. The effects on the lungs, uterus, genito-urinary tract, and other parts of the body have been detected in the advance stages of arsenic toxicity. A dditionally, high concentrations of arsenic in drinking water also result in an increase in stillbirths and spontaneous abortions (Csanady and Straub, 1995). The USEPA through the use of epidemio logical data tried to establish the maximum contaminant level (MCL), which minimizes the adverse effects of arsenic toxicity. Smith et al. (1992) reported that th e population cancer risks due to arsenic in US water supplies are comparable to those from environmental tobacco smoke and radon in homes. This has forced the EPA to consider lowering the current arsenic MCL in drinking water to as low as 10ppb.

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Review of Arsenic Removal Methods Since nearly 97% of the water systems af fected by the new regulatory standard in the United S tates are small systems, it is vital that cost effective and affordable treatment technologies are developed. Currently, unde r the 50 ppb standard only 0.51% of all Community Water Systems (CWS) have reported arsenic levels over the MCL. If the new MCL were effective today, 6.18% of all CWS would be over the 10 ppb MCL. This 6.18% or 3034 CWS must implement additiona l treatment or find alternative water sources before the 2006 deadline (USEPA, 2000). 0 100 200 300 400 500 600 700 800 900 1000UTILITIES EXCEEDING 10 pp < 1 0 0 1 0 1 5 0 0 5 0 1 1 0 0 0 1 0 0 1 3 3 0 0 3 3 0 1 1 0 0 0 0 1 0 0 0 0 5 0 0 0 0 5 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0UTILITY SIZE OR NO OF CONNECTIONS GROUNDWATER SURFACE WATER Figure 4 Number of Drinking Water Utilitie s Exceeding the New Maximum Contaminant Level 8

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9 Several technologies are effective in lowering arsenic concentrations in aqueous solutions namely, coagulati on/precipitation, ion exchange, adsorption processes, and reverse osmosis. However, for small communities adsorption appears to be the most practical because of operational considerations Materials available for sorption of arsenic include activated alumina; iron media, synt hetic ion exchange resins, and fly ash. In absence of alternative wate r supply, the major concern of any small community is whether the treatment of arsenic is going to require the construc tion of a centralized treatment facility or whether treatment is to be accomplished at the po int-of-use. In either case, there are major decisions that must be made that will require a significant investment on the part of the community. Several design criteria and assumptions need to be established before selecting a treatment process. These include maximum flow rate, average flow rate, finished water quality, method of waste discharge, Technically Based Local Lim its (TBLLs) for arsenic and Total Dissolved Solids (TDS), availability of land, labor commitment, acceptable percent water loss, and State or Primary Agen cy requirements are more issues that must be determined (USEPA 2000). The form of arsenic determines criteria used in choosing the method for treatment. Negatively charged arsenic ions facilitate removal by adsorption, anion exchange, and co-precipitative processes. Sinc e the net molecular charge of arsenite is neutral at natural pH levels (6-9), this form is not easily removed. However, the net molecular charge of arsenate is negative (-1 or -2) at natural pH leve ls, enabling it to be removed by these technologies. Conversion of ar senite to arsenate is critical to these arsenic treatment processes. Hence pre-oxidation is key for optimal performance of any treatment technology.

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10 Methods Coagulation/Precipitation Coagulation/Precipitation with metal salts is the most common treatment process used for arsenic removal in the United States (Buswell, 1943). During coagulation and filtration, metals are removed through three main mechanisms (Edwards, 1994): Precipitation: the formation of the insoluble compounds Al (AsO 4 ) or Fe (AsO 4 ) Co-precipitation: the incorporation of sol uble arsenic species into a growing metal hydroxide phase Adsorption: the electrostatic binding of soluble arsenic to the external surfaces of the insoluble metal hydroxide. All three of these mechanisms can i ndependently contribute towards metal removal. In the case of arsenic removal, dir ect precipitation has not been shown to play an important role. However, co-precipitati on and adsorption are both active arsenic removal mechanisms. Numerous studies have shown that filtration is an important step to ensure efficient arsenic removal. After coagul ation and simple sedimentation, Hydrous Aluminum Oxide (HAO) and Hydrous Ferrous Oxide (HFO) along with the sorbed arsenic can remain suspended in colloidal form. Coagulation and sedimentation without filtration achieved ar senate removal efficiencies of 30%; after filtration through a 1.0micron filter, efficiency was improved to over 96%. In field applications, some plants improve arsenic removal with two-stag e filtration (Hering, Sancha, 1999b). Coagulation/Filtration (C/F) is unlikely to be used solely for arsenic removal, as it is highly uneconomical [Johnston 2001]. The mo st important design criterion affecting the capital cost in very small and small wate r systems is the filtration rate, which affects the size of filter structure and the volume of filter media. Operation and maintenance

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11 costs are primarily affected by costs of chemicals (coagulants and polymer dosages) [USEPA 2002). Table 1 Summary of Studies Done on Arse nic Removal by Coagulation (Forlini, 1998) Coagulant Dosage Influent Arsenic Concentration (mg/L) pH Form of Arsenic Lowest Achievable Arsenic Concentration Reference Hydrated Lime Ca (OH) 2 N/A 0.075 11.1 As (V) 0.004 mg/L McNeil, 1994 Ferric Sulfate Fe 2 (SO 4 ) 3 10-50 mg/L 0.020 5-8 As (V) 0.001 mg/L Gulledge, 1973 Alum Al (OH) 3 10-50 mg/L 1.6 5-8 As (V) 0.013 mg/L Gulledge, 1973 Ferric Chloride FeCl 3 3-10 mg/L 1.6 7.18-7.8 As (V) 0.074 mg/L Scott, 1995 Hydrated Lime Ca (OH) 2 1250 mg/L 0.59-0.60 11.8 As (III) 0.060 mg/L Dutta, 1991 Arsenic removal by coagulation method is a function of the following: coagulant type (Alum or ferric coagulation) pH of source waters coagulant dosage initial concentration of As (III) and As (V) co-occurring inorganic solutes (i.e. SO 4 2, PO 4 3, Cl -1 ) chemical form of As (i.e. As (III) or As (V)) pore size of filter media

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12 Ion Exchange Ion exchange is a physical/chemical proce ss in which ions are exchanged between a solution phase and a solid resin phase. Th e resin is typically an elastic threedimensional hydrocarbon network containing a large number of ionizable groups electro statically bound to the resin. Ar senic removal (only arsenate in this case) is accomplished by continuously passing water under pressure through one or more columns packed with strong base anion exchange resin (SBR) in either chloride or hydroxide form. These resins are insensitive to pH in the range of 6.5 to 9.0. (USEPA, 2000; reference to Clifford et al., 1998). The exchange affinity of various ions is a function of the net surface charge. Therefore, the efficiency of the ion exchange process for arsenate removal depends strongly on the solution pH and the concentration of other competing anions, notably sulfates, and nitrates, and infl uent arsenic concentration. The selectivity for competing ions is a function of type of resin and the specific anion concentration. Exhaustion occurs when all sites on the resi n beads have been filled by contaminant ions. USEPA expects ion exchange treatment to become a common technology for arsenic removal in central facilities. Ion exchange is generally recommended for use in systems having low sulfates (<120 mg/l) and low TDS [NWRA 2001]. Competing ions such as sulfates, nitrates selenium, and fluorides in water greatly affect the regeneration frequency, which aff ects the operation and ma intenance costs of a facility. One of the primary concerns related to ion exchange (IX) treatment is the phenomenon known as chromatographic peaki ng, which can cause arsenic and nitrate levels in the treatment effluent to exceed thos e in the influent stream. This can occur if sulfates or ions with greater selectivity for the resins are present in the raw water or the bed is operated past exhaustion. Because sulf ate is preferentially exchanged, incoming sulfate anions may displace previously adsorb ed arsenic and nitrate ions. In most ground waters, sulfates are present in concentrations that are orders of magnitude greater than arsenic and are preferentially removed by the resin. SO 4 2> HAsO 4 2> NO 3 -1 CO 3 2> NO 2 -1 > Cl

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13 Disposal of ion exchange resins and regenerant, which produces arsenic-rich brine, is a major problem associated w ith ion exchange. Thus, the USEPA does not consider ion exchange for Point of Use/Po int of Entry (POU/POE) compliance to the MCL [USEPA 2000 reference to Kempic J.B. et.al, 2000]. However, there are a few emerging technologies that may significantly imp rove ion exchange treatment for arsenic removal. Most of the new emerging tec hnologies still under investigation are: Advanced ion exchange operation with indefinite brine recycle Arsenate, As (V), selective resins Continuous counter current ion exchange [Samuel Perry 2002] Activated Alumina Activated alumina (AA) is a porous, granular material with ion exchange properties. The media, alum inum trioxide, is prepared through the dehydration of aluminum hydroxide at high temperatures. Activated alumina (AA) is currently considered the best adsorbent for arseni c removal. The removal of arsenic by AA adsorption can be accomplished by continuously using a packed bed column and controlling the pH at 5.5 to 6.0. Hence, AA should be put into use in a centralized facility where pH adjustments can be made and pH is better controlled. The level of competing ions, also affects the performance of AA for arsenic removal, although not in the same manner nor to the same extent as ion exchange. The following selectivity sequence has been established for AA adsorption: OH -1 > H 2 AsO4 -1 > Si (OH) 3 O -1 > F -1 > HSeO 3 -1 > TOC > SO 4 2> H 3 AsO 3 The selectivity of AA for arsenite remova l is poor, owing to the overall neutral molecular charge at pH levels below 9.2. Theref ore, pre-oxidation of arsenite to arsenate is again essential for effective treatment.

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Effect of pH on Activated Alumina 0 4000 8000 12000 16000 20000 012345678910 Water pHBed Volumes To Exhaustion Figure 5 Effect of pH on Activated Alumina Performance (USEPA, 2000) Activated alumina column runs operat ed under acidic conditions (pH 5.5 -6.0) have 5 to 20 times longer run times than wh en operated under natu ral pH [USEPA 2000]. The technologies and market for alumina-base d adsorptive media continue to expand. There are several emerging proprietary medi a, commonly referred to as modified AA, which contain alumina in a mixture with othe r substances such as iron and sulfur. In some instances, these media have greater overall adsorptive capacities, enhanced selectivity, and/or greater ove rall operational flexibility than conventional AA, thus making them more cost-effective. Efficiency of the media is excellent (typically > 95%). Activated Alumina adsorption is considered less expensive than the membrane separation, and is more versatile than the ion exchange process [Chen 1999]. The kinetics of arsenic removal with activ ated alumina is slower than with ion exchange resins; and therefore some arseni c leakage is often observed in activated alumina systems [Johnston 2001]. Activated Alumina also requires the storage of dangerous chemicals, such as sulfuric aci d and sodium hydroxide for regeneration and 14

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15 pH adjustment. This leads to added costs and for advanced training of operators. AA media can either be regenerated on-site or disposed of in appropriate site. On-site regeneration typically produces 15-25 bed volumes of caustic waste. Therefore, the waste solution typically contains high levels of TD S, aluminum, and soluble arsenic. In most cases, this arsenic level will exceed 5.0 mg/L Toxic Concentration (TC), and the waste stream will be classified as a hazardous liquid. For these reasons AA is considered infeasible option for arsenic removal for most small systems. Reverse Osmosis Membrane technologies offer a versatile approach for meeting multiple water quality objectives [Hering, 1996]. Membrane t echnologies are attractiv e arsenic treatment processes for small water systems. They can address number of water quality problems while being relatively easy to operate. The molecular weight cut-off of microfiltration (MF) and ultrafiltration (UF) processes necessitates the use of a coagulation to generate arsenic-laden floc. Membrane filtration also has advantage of removing many contaminants like bacteria, sa lts, and various heavy metals. In recent years, a new generation of Reverse Osmosis (RO) and Nanofiltration (NF) membranes have been developed that are less expensive and operate at lower pressures, yet allow improved flux and are capab le of efficient rejection of both arsenate and arsenite. Some of the new membranes, operated at pressures ranging from 40-400 psi, were able to reject from 96-99% of arsena te in spiked natural waters (Waypa et.al,). The authors attribute this rejection to the re latively large molecular weight of arsenate and arsenite, rather than charge repulsion. Ar senic removal is independent of pH and the presence of competitive solutes, but somewhat dependent upon temperature. Removal efficiency in membranes are independent of the total dissolved solids concentration and are typically in range of 75% for As (III) and 95% for As (V) (Kang, Kawasaki, et.al, 2000). For drinking water treatment, typical operating pressures with membrane processes are between 100 and 350 psi. For exam ple, ultrafiltration (UF) membranes are able to remove over 99.9% of bacteria, Giardia, and viruses. In addition, the membrane does not adsorb arsenic, so di sposal of used membranes woul d be simple. For a Point-of-

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16 use system, operation and maintenance requirem ents are minimal, no chemicals need be added, and maintenance would consist of ensu ring a reasonably constant pressure, and periodically wiping the membrane clean. Membrane operations as a part of a cen tralized treatment facility for small systems are uneconomical. Some of the factor s that discourage the use of membrane applications in small systems are listed below: High capital and operational costs, Low water recovery rates (Problem posed by many small water utilities located in regions with limited water supplies), Requirement of high quality infl uent water to the RO train, High operating pressures, Risks associated with membrane fouling Adsorption Processes Adsorption is defined as the accumulation of materials at an interface, the liquid/solid boundary layer. It is a mass transf er process where a substance is transferred from the liquid phase to the surface of a solid and becomes bound by chemical or physical forces. Adsorption can ta ke place on suspende d particles, as pa rt of the process of coagulation/co-precipita tion, or on fixed media. Since adsorption is a surface phenomenon, the greater the surface area of the medium, the greater its capacity to accumulate material. Each adsorbent medium has different associated properties, performances, and costs. The factors involved with se lection of adsorbent for ar senic removal in drinking water are surface area of adsorbent, adsorpti on kinetics, pH of the water, competing species (adsorption), pressure drop and occluding species, adsorption bed design, and regeneration/backwashing requirements.

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17 Adsorbent Materials Several proprietary iron-based adsorption materials have been developed recently. These materials generally have high removal efficiency and capacity. Some of these materials are listed below in detail. Granular Ferric Hydroxide Granular Ferric Hydroxide (GFH) pro cess was recently developed at the Technical University of Berlin, Departme nt of Water Control that combines the advantages of the coagulation-filtration pro cess with fixed bed adso rption. A field study reported by Simms et al. (2000) confirms the efficacy of GFH for arsenic removal. Over the course of this study, a 5.3 MGD GFH plant located in the Un ited Kingdom was found to reliably and consistently reduce average in fluent arsenic concentr ations of 20 g/L to less than 10 g/L for 200,000 Bed Volumes (BV) (over a year of operation) at an empty bed contact time (EBCT) of 3 minutes. The most significant weakness of this tec hnology appears to be its cost. Currently, GFH media costs approximately $4,000 per ton. However, if a GFH bed can be used several times longer than an alumina bed, for example, it may prove to be the more cost effective technology. The field study presented above tested Activated Alumina (AA) as well as GFH and found that GFH was more e fficient and used small adsorption vessels and less media to achieve the same level of arsenic removal. In a ddition, unlike AA, GFH does not require pre-oxidation to arsenate for removal. GFH is a technology that combines long run length with no need for pH adjustment. Due to lack of published data, it has not been listed as a Best Availa ble Technology (BAT) for small systems. Iron Oxide Coated Sand Iron oxide coated sand (IOCS) is a rare process, which has shown some tendency for arsenic removal. IOCS consists of sand grains coated with ferric hydroxide, which are used, in fixed bed reac tors to remove various dissolved metal species. The metal ions are exchanged with the surface hydroxides on the IOCS. Several studies have shown that IOCS is effective for arsenic removal. F actors such as pH, arsenic oxidation state,

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18 competing ions, empty bed contact time (EBCT), and regeneration have significant effects on the removals achieved with IOCS Joshi and Chaudhuri showed that iron oxide coated sand (IOCS) is able to remove both ar senite and arsenate. A simple fixed bed unit was able to treat a bout 160-190 bed volumes of water containing 1000 g/L arsenite and 150-165 bed volumes of water containing 1000 g/L arsenate. Flushing with 0.2 N sodium hydroxide regenerates the media. The oxi dation state of arsenic plays a role in its removal, As (V) appears to be more easily removed than As (III). Benjamin et al. (1998) showed that As (V) sorption onto IOCS wa s much more rapid than As (III) sorption during the first few hours of expos ure and slower thereafter. pH appears to have an effect on arsenic adsorption by IOCS. Results indica ted that increasing th e pH from 5.5 to 8.5 decreased the sorption of As (V) by approximately 30 percen t. Sand can be similarly coated with manganese dioxide, which, also happens to be a good oxidant, and can be used for removal of arsenite as well as arsenate. Manganese Green Sand Filters Greensand is a granular material composed of the mineral glauconite, which has been coated with manganese oxide. It is a natural zeolite that will remove iron, manganese, arsenic, sulfide, and many othe r anions. Greensand, which is similar to manganese dioxide coated sand, is strongly oxid izing, and is able to remove both arsenite and arsenate. The media is typically re charged by applicat ion of potassium permanganate, which reestablishes the oxidizi ng environment, and deposits a fresh layer of manganese oxide on grain surfaces (F icek, 1996). Viraraghavan and others (1999) showed that greensand could reduce arsenite levels from 200 g/L by about 40% in the absence of iron. When ferrous iron was also present, arsenite rem oval improved to above 80% (Subramanian et al., 1997; Viraraghavan et al., 1999). Little information is available about the capacity of greensand for arsenic re moval, or the effects of pH or competing anions on arsenic removal.

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19 Pyrite Fines Pyrite (FeS 2 ) has a high surface area and is suitable for adsorption of arsenic species in solution. It was found that pyrite at a concentration of 10g/L removed 95% of arsenic (III) from solutions with pHs ranging from 7-9. Pyrite also removed 98% of As(V) from solutions having pHs ranging from 4 to 7. The contact times required to achieve equilibrium concentration were very short in the optimal pH range for both As (V) and As (III) (Zoboulis, 1993). Activated Carbon The adsorption of specific substances from solutions with activated carbon is a widely used process. Various authors have examined the use of activated carbon in removal of arsenic from aqueous soluti ons. Eguez and Cho (1995) measured the adsorption capacity of activated carbon for As (III) and As (V) at various pH values. Diamadopoulos et al. (1993) found that carbon with higher ash content was more effective in removing As (V) while; Rajakovic (1992) found that carbon pretreated with Ag +1 or Cu +2 ions improved As (III) adsorption but reduced As (V) adsorption. Lorenzen (1995) concluded from his study that arsenic is most eff ectively removed from aqueous solutions at a pH of 6.0 using an activated carbon pre-treated with Cu (II) solution. Zero-Valent Iron Most of the adsorption processes above rely on arsenate adsorption on to surface of metal oxides. However, arsenic also has a strong affinity for reduced metal surfaces such as sulfides. A system using zero-valent iron filings can be used either ex-situ or insitu to reduce arsenate and to produce ferrous iron. The ferrous ions precipitate out with sulfide, which is also added to the system. Arsenite is removed either through coprecipitation or through adsorption onto pyrite. This system is promising for use in rural areas, because of the low cost of materials, and the simp le operation. However, treated water is very high in ferrous iron, and must undergo treatment for removal of iron before distribution or consumption (Lackovic et al., 2000). A similar system using zero-valent iron to treat water stored in individual hom es was tested in Bangladesh and West Bengal

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20 (the so-called: three kolshi filter). This ma terial removed approximately 95% of arsenic from waters containing 2000 g/L arsenic and in the presence of sulfate at pH 7. (Ramaswami et al., 2000). Zeolites Over the last 40 years or so, zeolites have been used as ion exchange media and for their catalytic properties. Zeolites have be en widely used in the wastewater industry for removal of malodorous gases such as carbon dioxide, ammonia, hydrogen sulfide, hydrogen disulfide etc. Zeolites have also b een used to remove heavy metal ions and radioactive isotopes (such as cesium and str ontium) from industria l wastes. Apart from high sorption capacities natural zeolites present a additional benefit due to their low costs. Zeolites can be tailo red to selectively ad sorb certain ionic and non-ionic compounds by chemical pre-treatment. While cation exchange has been described as the mechanism for metal removal, in case of arsenic where arse nious and arsenic acid remains undissociated, a molecular complex sorption mechanism is involved (Gonzalez, J. Mattusch, 2001). Zeolites have been found to naturally contain iron in th eir crystalline lattice and show that a capacity to retain and adsorb iron ions. Arsenic has shown high affinity for sorption towards natural zeolitic materials such as chabazite. Modifying the zeolite structure by treatment with metals such as Copper and Iron effectively enhances this adsorption capacity. Literature review s uggests only one report concerning arsenic removal using the natural zeolites cl inoptilolite and chabazite (Bonnin, 1997). The following process may be presumed to be involved in ar senic adsorption at the basic and acid Br nsted sites (Elizalde-Gonzalez, 2000): 1. Z-O +(ads) H-OAs (OH) 2 for As (III) at pH 4 and 7 2. Z-O H + + (ads) O-As (OH) 2 for As (III) at pH 11 3. Z-O H + + (ads) O-AsO (OH) 2 for As (V) at pH 4 The adsorption studies conducted for arse nic removal using zeolites is mainly focused on clinoptilolite. However, the saturation capacity of the zeolite tuffs is inversely related to silicon dioxide c ontent and directly to iron content present in the zeolite structure (Elizalde-Gonzalez, 2001).

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21 Need For Finding Cost Effective Methods of Arsenic Removal In recent years, a tremendous amount of research has been conducted to identify novel technologies for arsenic removal, partic ularly low-cost, low-t ech systems that can be applied in rural areas. Most of thes e technologies rely on oxidation of arsenite, followed by filtration through some porous mate rial, where arsenic removal is effected through adsorption and co-precipitation. Adsorp tive technologies are likely to be the treatment of choice for many small systems. Adsorptive technologies are likely to: Achieve high arsenic removal over a wide pH range; Avoid competition from commonly occurr ing co-contaminants (sulfate, nitrate, etc; Be used in relatively simple treatment trains; and, Not be hazardous waste when used on a throwaway basis. Table 2 shows the mean annual costs for t hose households serv ed by systems that might need further treatment under the new MCL. Table 2 Mean Annual Costs per Household for Each System/ Utility Size System Size Mean Annual Cost Per House hold <100 326.82 $ 101-500 162.5$ 501-1000 70.72$ 1001-3300 58.24$ 3300-10000 37.71$

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The average household trying to meet the new arsenic standard of 10ppb will face approximately $31.85 increase in cost of their water bills. Ho wever, there is an economy of scale, for e.g. cost is expected to be $326.82 per household for systems serving <100 people, and $162.50 per househol d for systems serving 101 500 people. Figure 6 shows the relation between mean annual cost pe r household vs. utility size or number of connections. 326.82 162.5 70.72 58.24 37.71 050100150200250300350 <100 101-500 501-1000 1001-3300 3300-10000Utility Size (# of Connections)Mean Annual Costs ($/yr) Figure 6 Mean Annual Costs per Household vs. Utility Size Groundwater systems should ascertain if pre-oxidation is necessary by determining if the arsenic is present as ar senic (III) or arsenic (V). Ground water systems with predominantly As (V) will probably not need pre-oxidation to meet the MCL. Arsenic removal efficiency will vary ac cording to many site-specific chemical, geographic, environmental and economic c onditions. Hence, any technology should be tested under field conditions before implemen tation. With array of options available for source substitution and arsenic removal tech nologies, it is not always clear which alternate water source is best for a given set ting. In all cases, technologies should meet several basic technical criteria. The key to selecting an appropr iate technology (or technologies) is to involve community memb ers in all stages of the process, from technology selection to oper ation and maintenance. 22

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23 Background on Zeolites Zeolites are hydrated aluminosilicates of the alkaline and alkaline earth metals. About 40 natural zeolites have been identi fied during the past 200 years; the most common are analcime, chabazite, clinoptilolite, erionite, ferrierite, heulandite, laumontite, mordenite, and phillipsite. More than 150 zeo lites have been s ynthesized; the most common are zeolites A, X, Y, and ZMS-5. Na tural and synthetic zeolites are used commercially because of their unique adsorp tion, ion exchange, molecular sieve, and catalytic properties (Robert Virt a, US Geological Survey 2001). Zeolites are micro porous crystalline solids with well-defined structures. Generally, they contain silicon, aluminum, and oxygen in their framework and cations, water and/or other molecules within their pores. A defining feature of ze olites is that their frameworks are made up of 4-connected netw orks of atoms. The framework structure may contain linked cages, cavities, or channe ls, which are of the proper size to allow small molecules to enter. Their crystalline framework is arranged in an interconnecting lattice structure. The arrangement of these el ements in a zeolite crystal creates a porous silicate structure with interconnecting channels that range in size from 2.5 to 4.3 angstroms, depending on the zeolite mineral. Th is structure allows zeolites to perform the following functions i.e. adsorption, ion exchange etc, consistently within a broad range of chemical and physical environments. Zeolites have often been studied for their properties of adsorption and ion exchange. Each zeolite mineral has a distinct ion exchange selectivity and capacity. This ion exchange capacity is primarily due to replacement of Si +4 by Al +3 in the crystalline structure. The ion exchange and adsorption processes occurs when water molecules can pass through the channels and pores allowing cations present in the solution to be exchanged for cations previously adsorbed in the structure. Factors affecting the process

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include ionic strength of th e solutions, pH, temperature, and the presence of other competing cations in the solution. These f actors can affect both the ion exchange selectivity and capacity of th e specific zeolite mineral. Chabazite and clinoptilolite are the two natural zeol ites that have commercial applications. Because of their high silica to alumina ratios, (2:1 for chabazite, and 5:1 for clinoptilolite), these minerals are stable and are less likely than the synthetic zeolites to dealuminate in acidic solutions. Chabazite Chabazite's structure has a typical zeolite openness that allows large ions and molecules to reside within the overall framew ork. The size of these channels controls the size of the molecules or ions that can be sorbed in the structure. The channels thus act as chemical sieve allowing some ions to pass th rough while blocking others ions. Chabazite has a cage like structure as shown in Figure 7. Figure 7 Cage Like Structure of Chabazite It has chemical formula of Ca 2 [(Al 2 O 4 ). (SiO 2 ) 8 ]. 6H 2 O which results in Si /Al ratio of 4.1 and ion excha nge capacity of 3.70 meq/gm. The physical properties of the chabaz ite used in this study are as follows: Effective Pore Diameter: 4.3A 0 Density: 1.73gm/cm 3 Surface Area: 520.95m 2 /gm. 24

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25 Background on Adsorption Isotherms The most important physiochemical aspect s in evaluating the adsorption process are the kinetics and equilibrium of adsorption. Kinetic Studies describe how fast the reaction proceeds towards equilibrium and define the reaction constant or adsorption coefficient. Equilibrium studies give the capac ity of the adsorbent (Ho, 1995) for specific contaminants. Isotherms are graphical representations of the mass of contaminant adsorbed per unit dry mass of adsorbent. In order to use isotherms to estimate the mass adsorbed, an instantaneous equilibrium must be reached between the adsorbent and the adsorbate, and the isotherm mu st be considered reversible. There are many different types of isotherms used for determining capacity of adsorbents. However, Langmuir adsorption isotherms and Freundlich adsorption isotherms (Muhammad, Parr et al., 1998) are the most widely used in water treatment. Freundlich Isotherms Herbert Max Finley Freundlich, a Germ an physical chemist, presented an empirical adsorption isotherm for non-ideal systems in 1906. The Freundlich isotherm is the earliest known rela tionship describing the adsorption equation and is often expressed as: Q e = K f C e 1/n (Casey, 1997) where: Q e is the adsorption density (mg of adsorbate per g of adsorbent). C e is the concentration of adsorbate in solution (mg/l). K f and n are the empirical constants depe ndent on several environmental factors and n is greater than one.

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The equation in the linear form by taki ng the logarithmic of both sides is as follows: Log Q e = Log K f + 1/n Log C e Figure 8 Freundlich Isotherm for Ad sorption of Arsenic on Portland Cement (Figure adopted from Kundu, Pal et al., 2004) Figure 8 depicts Freundlich adsorption isotherm for arsenic adsorption using Portland cement. If a plot of Log C e vs. Log Q e yields a straight line it confirms that the adsorption process complies with Freundlich Equation. The equilibrium constants for the above equation are determined from the slope and the intercept. The two model parameters, K f and n represent the sorption capacity and sorption intensity, respectively (Weber et al., 1991). A large value of n signifies that any large change in concentration at equilibrium would not affect the adsorption on the media. When n is equal to 1, the partitioning between the solid and liquid phase is linear and Freundlich coefficient (K f ) becomes same as distribution coefficient K d The Freundlich model does not account for finite adsorption capacity at high concentratio ns of solute, but wh en considering trace constituent adsorption, ignoring such physical constraints is us ually not critical. 26

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27 Langmuir Isotherms Irving Langmuir, an American chemist developed a relationship between amount of gas adsorbed on the surface and the pressu re of that gas. Such equations are now referred to as Langmuir adsorption isotherm s. The Langmuir isotherm is based on the following three assumptions: Adsorption cannot proceed beyond a monolayer coverage All surface sites are equivalent (adsorption energy for all sites is same) and can accommodate, at most, one adsorbed atom The ability of a molecule to adsorb at a given site is independent of the occupation of neighboring sites. The Langmuir Isotherm is represented as given below: C e /Q e = 1/ (Q max K L ) + C e /Q max where: Q e is the adsorption density at the equilibrium solute concentration C e ( mg of adsorbate per g of adsorbent) C e is the concentration of adsorbate in solution (mg/l) Q max is the maximum adsorption capacity corresponding to complete monolayer coverage (mg of solute adso rbed per g of adsorbent) K L is the Langmuir constant related to adsorption /desorption energy (l of adsorbent per mg of adsorbate)

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Figure 9 Langmuir Isotherm for Adsorption of Arsenic on Portland Cement (Figure adopted from Kundu, Pal et al., 2004) The linear form is obtained by plotting C e /Q e against C e The Langmuir constants Q max and K L can be evaluated from the slope and intercept of linear equation. The adsorption energy K L is obtained from the slope of the best-fit line and the maximum adsorption capacity of the adsorbent is determined from the intercept. Figure 9 depicts Langmuir adsorption isotherm developed for arsenic adsorption using Portland cement. 28

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29 Materials and Experimental Methods Materials The materials used in the series of ba tch equilibrium experiments included the zeolite, chabazite, and reagents for pretreat ment of chabazite. The materials used are listed below: Chabazite Chabazite obtained for this investigation was procured from GSA Resources, Tucson, Arizona. The chabazite was obtained in 20 lbs canister. The material safety data sheet (MSDS) for the chabazi te is listed in Appendix C Arsenic Arsenic used as a adsorbate in the experiments was from Fisher Chemicals Co, in form of arsenic trioxide (As 2 O 3 ) (99.9%). It was used in th e experiments at 100 parts per billion (ppb). Copper Chloride Copper Chloride used for pretreatment of chabazite in this experiment was obtained from Acros Organics. Co, in form of Copper (I) Chloride (95%) It was used in pretreatment at a concentration of 0.01M. Ferrous Chloride Ferrous Chloride used for pretreatment of chabazite in this experiment was obtained from Fisher Chemi cals Co in form of Iron (II) Chloride, Tetrahydrate (FeCl 2 .4H 2 O). It was used in pretreatment at a concentration of 0.1M. Ferrous Sulfate Ferrous Sulfate used for pretreatment of chabazite in this experiment was obtained from Acros Organics. Co in form of Iron (II) Sulfate Heptahydrate reagent ACS (FeSO 4 .7H 2 O). It was used in the pretreat ment at a concentration of 0.1M.

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Experimental Procedures The experimental work for this project is broken down into number of sub tasks. These include modification of zeolites us ing cuprous and ferrous salts, conducting equilibrium and kinetic studies for arsenic (II I) adsorption using th e modified zeolites, plotting graphs for adsorption isotherms using Langmuir or Freundlich Isotherms. Figure 10 Mettler AE 260 Delta Range Analytical Balance Figure 11 Blue M Stabil Therm Gravity Oven 30

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Phase I: Pretreatment of Chabazite High purity sodium chabazite, an aluminum-silicate that was dried, reactivated, and allowed to equilibrate with air was proc ured in 20 lbs drum from GSA Resources. Zeolite modification is performed by adding 5 grams of 400 mesh zeolite /liter of DI water (sieve size 38 m). Figure 12 Batch Reactors for Pretreatment of Chabazite 1. Copper Chloride treated chabazite 20 grams of Chabazite (-40 mesh) was treated with 0.01M Copper (I) Chlori de solution in a 4L multipurpose polycarbonate reactor. The mixing was carri ed out at 300 rpm in a batch reactor for a period of 24 hrs at room temperat ure. The copper treated zeolite was then rinsed with DI water, sieved through a 400-mesh screen and dried for in a Blue M Stabil-Therm Gravity Oven at a temperature of 103o C for a period of 2 hours. The dried material is then weighed, labele d, and stored in desiccators for future use. Figure 12 depicts chabazite befo re and after copper pretreatment. 2. Ferrous Chloride treated chabazite 20 grams of Chabazite (-40 mesh) was treated with 0.1M Ferrous Chloride so lution in a 4L multipurpose polycarbonate reactor. The mixing was carried out at 300 rpm in a batch reactor for a period of 24 hrs at room temperature. The iron (II) treated zeolite was then rinsed with DI water, sieved through a 400-mesh screen and dried for in a Blue M Stabil-Therm 31

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Gravity Oven at a temperature of 103o C for a period of 2 hours. The dried material is then weighed, labeled, and stor ed in desiccators for future use. Figure 14 depicts chabazite before and after iron (II) chloride, tetrahydrate pretreatment. 3. Ferrous Sulf ate treated chabazite: 20 grams of Chabazite (-40 mesh) was treated with 0.1M Ferrous sulfate solution in a 4L multipurpose polycarbonate reactor. The mixing was carried out at 300 rpm in a batch reactor for a period of 24 hrs at room temperature. The iron (II) treated zeo lite was then rinsed with DI water, sieved through a 400-mesh screen and dried for in a Bl ue M Stabil-Therm Gravity Oven at a temperature of 103o C for a period of 2 hours. Th e dried material is then weighed, labeled, and stored in desiccat ors for future use. Figure 15 depicts chabazite before and af ter iron (II) sulfate hept ahydrate pretreatment. Figure 13 Chabazite Before and Afte r Copper (I) Chloride Treatm ent Figure 14 Chabazite Before and Af ter Iron (II) Chloride Treatment 32

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Figure 15 Chabazite Before and Af ter Iron (II) Sulfate Treatment Phase II: Batch Studies Kinetic Studies Figure 16 Kinetic Studies for Adsorption of Arsenic with Cu and Fe Species The kinetic studies were carried out in ja r testing machines or ECE Compact Laboratory Mixers. For equilibrium tests, aliquots 100 l of standard arsenic trioxide solution was added to 3 jars filled with lit er of de-ionized/dechlo rinated tap water/prechlorinated groundwater. 0.5grams of the treated chabazite (adsorbent ) was measured and added for the kinetic runs in each of three 1 L jars, (A, B, and C) of the laboratory mixer. 33

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34 The kinetic tests were conducted for a pe riod of 6 hours at speed of 180 rpm. During this 6-hour test run, 20 ml sample was pulled from jar A for arsenic analysis. At the same time, 20 ml was taken from Jar B and injected into jar A to maintain the same solid /solution ratio. Similarly, 20 ml will be transferred from jar C to jar B for the same reason. Sampling frequency for the kinetic runs was as follows: 1) 5 minutes interval for the first 30 minutes. 2) 10 minutes interval from 30 to 60 minutes. 3) 15 minutes interval from 60 to 120 minutes. 4) 1 hr interval from 120 to 360 minutes. The samples (20 ml) were then filtered using a 0.45 m Fisher brand Nylon filter into a Nalgene passport IP2 Narrow mouth HDPE bottles. The bottles were acidified with 200 l of concentrated HCl acid to obtain a pH of 2.5-3 and then stored at 4 o C until arsenic analysis could be performed. The in itial and final pH wa s measured each time. These samples were then analyzed for arsenic species using Atomic Absorption Spectroscopy. Equilibrium Studies 1. Short Term Equilibrium Studies The batch equilibrium studies involved using identical volumes and concentration of arsenic exposed to different quantities of adsorbent. For equilibrium tests, aliquots 100 l of standard arsenic trioxide solution was added to 6 jars filled with liter of deionized water/dechlorinated tap water/pre-ch lorinated ground water. Different amounts of copper or iron treated chabazi te (0.25, 0.5, 0.75, 1.0, and 2.0 g/L) were measured using a Mettler AE 260 Delta Range analytical balance and added to the jars. One jar served as a control in order to detect any adsorption of arsenic on to the jars. Simultaneous runs for Cu treated and Fe treated zeolites will be conducted. The short-term equilibrium tests were performed for 6 hrs period with samples taken at time 0 minutes (before the zeolite is added) and time 360 minutes (after the equi librium run is complete). The samples (20 ml) were then filtered using a 0.45 m Fisher brand Nylon filter into a Nalgene passport

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35 IP2 Narrow mouth HDPE bottles. These samples were then analyzed for arsenic species using Atomic Absorption Spectroscopy. 2. Long Term Equilibrium Studies Long-term equilibrium studies for adsorp tion were performed for a period of 90 days. For long term equilibrium studies 100 l of arsenic trioxide solution was added to 6 dark colored glass bottles containing 1 liter dechlorinated tap water. Different amounts of copper or iron treated chabazite (0.25, 0.5, 0.75, 1.0, and 2.0 g/L) were measured and added to the dark colored bottles. One bottle se rved as a control in order to detect any adsorption of arsenic on to the glass bottle. These sample bottles were stored in a refrigerator at a temperature of 4 O C and were shaken every 10 days. The initial and final pH was measured. 20 ml samples were then pulled out from these glass bottles and filtered using a m Fisher brand Nylon filter into Nalgene passport IP2 Narrow mouth HDPE bottles. These samples were then analyzed for arsenic species using Atomic Absorption Spectroscopy. Arsenic Analysis was conducted using Varian AA Zeeman Graphite Furnace. The graphite furnace method is described in detail in Appendix A.

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36 Results and Discussion The results of adsorption studies conducted for removal of arsenic using different forms of modified chabazite will be presented in the following order: Results from kinetic and equilibrium studi es for arsenic adsorption in de-ionized water using three modified zeolites (Coppe r chloride modified chabazite, ferrous chloride modified chabazite and ferr ous sulfate modified chabazite). Results from kinetic studies in tap water to determine the effect of stoichiometric ratio on arsenic adsorption using thre e different modified zeolites (Copper chloride modified chabazite, ferrous ch loride modified chabazite and ferrous sulfate modified chabazite). Results from equilibrium studies in dechlorinated tap water using all the modified zeolites. Results from kinetic studi es in different source wa ters (de-ionized water, dechlorinated tap water, pre-chlorinated tap water and groundw ater) using ferrous sulfate modified chabazite. The kinetic data was analyzed using the integral method for determining the order of reaction. This method is especially useful in describing reaction rates for elementary reactions such as A Products or A+B Products

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Integral method was used to analyze the ki netic data in order to estimate the rate of reactions and order of reactions, and a desc ription of this method and analysis of the data may be found in Appendix B. The equilib rium data was analyzed using Langmuir and Freundlich isotherm equations. These equati ons are most widely used for analysis of equilibrium data. Kinetic and Equilibrium Studies in De-ionized Water Kinetic Studies De-ionized water was used to study arse nic adsorption rate on three different modified zeolites in the absence of any co mpeting ions. The relative rates of arsenic adsorption by these different zeolites in de-ionized water are presented in Figure 17. 0 10 20 30 40 50 60 70 80 90 100 050100150200250300350400 Time (minutes)Arsenic Concentration in ug/ L CuCl2 Modified Chabazite FeCl2 Modified Chabazite FeSO4 Modified Chabazite Figure 17 Kinetic Runs for As Removal Usi ng Modified Chabazite In De-ionized Water 37

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38 Two set points were used to compare the results of kinetic data, 30 minutes and 360 minutes. Kinetic studies revealed that the rate of arsenic adso rption is the highest within the first 30 minutes and hence 30 minut es was selected as the first set point. Pseudo equilibrium was reached after 360 minutes for all the kinetic studies. 360 minutes was therefore chosen as the second set point for analysis of kinetic data. Table 3 Results from Kinetic Studies Using Different Modified Chabazite in De-Ionized Water Removal at 30 minutes Removal at 360 minutes Type of Chabazite Initial Conc.* of Arsenic ( g/L) Conc. ( g/L) % Removal Conc. ( g/L) % Removal Cuprous Chloride Modified Chabazite 100 58 42 % 38 62 % Ferrous Chloride Modified Chabazite 100 91 9 % 78 22 % Ferrous Sulfate Modified Chabazite 100 76 24 % 59 41 % Conc: Concentration Table 3 shows that cuprous chloride modi fied chabazite had the highest rate for arsenic adsorption for both set points, and re sulted in 20 % more arsenic removal after 360 minutes than the other two metal salts. The data for the kinetic studies showed that the adsorption on zeolite could be approximate d by a second order reaction given below. dC A /dt = kC A 2 (See Appendix B)

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39 where: dC A /dt = rate of reaction k = reaction rate constant and C A = concentration of arsenic in solution Table 4 Order of Reaction and Reaction Rate Constant for Modified Zeolites in Deionized Water Type of Chabazite Rate Equation Reaction Rate Constant (k) (liter/mol.min) Order of Reaction Cuprous Chloride Modified Chabazite r A = 3e-05C A 2 3e-05 2 Ferrous Chloride Modified Chabazite r A = 7e-06C A 2 7e-06 2 Ferrous Sulfate Modified Chabazite r A = 1e-05C A 2 1e-05 2 The reaction rate constants and order of reactions for all three modified zeolites are summarized in Table 4. The rate of adsorption for cuprous chloride modified chabazite proceeds four and a half times faster than ferrous chloride modified chabazite, and three times faster than ferrous sulfate m odified chabazite. It can be concluded that cuprous modification of chabazite has the hi ghest rate for arsenic adsorption in the absence of competing ions.

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Equilibrium Studies The results of the equilibrium studies using cuprous modified chabazite and ferrous modified chabazite are shown in Figures 18 and 19. Both the Langmuir and Freundlich isotherm equations were tested to see if they fit the equilibrium data. The equilibrium data was linearized and plo tted to obtain the Langmuir and Freundlich coefficients. For the Langmuir equation the inverse of adsorption capacity (1/Q e ) was plotted against the inverse of equilibrium concentration (1/C e ). For the Freundlich equation the adsorption capacity Q e and the equilibrium concentration C e were plotted on logarithmic scale. Langmuir equation coefficients, the maximum adsorption capacity (Q max ) and the adsorption/deso rption energy constant (K L ) are represented by the slope and intercept of the linear equation respectively. Equilibrium data fitted to Freundlich equation gives the adsorption affinity (n) and Freundlic h coefficient (K F ) for a given adsorbent. y = 0.3105x + 0.0002 R2 = 0.7585 y = 0.0584x + 0.0021 R2 = 0.6983 0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.0000.0500.1000.1500.2000.2500.3001/Ce (L/ug)1/Qe (gm/ug ) Equilibrium runs for Fe treated Chabazite Equilibrium runs for Cu treated Chabazite Figure 18 Langmuir Adsorption Isotherm for Modified Chabazite in De-ionized Water 40

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y = 0.5645x + 1.4958 R2 = 0.7929y = 0.774x + 0.8124 R2 = 0.785 0.000 0.500 1.000 1.500 2.000 2.500 3.000 0.000 0.500 1.000 1.500 2.000 Log CeLog Qe Equilibrium runs for Fe treated Chabazite Equilibrium Runs for Cu treated Chabazite Figure 19 Freundlich Adsorption Isotherm for Modified Chabazite in De-ionized Water Table 5 Langmuir and Freundlich Isotherm Coefficients in De-ionized Water Langmuir Coefficients Freundlich Coefficients Type of Modified Chabazite Q max ( g/gm) K L ( g/L) R 2 K F n R 2 Cuprous Modified Chabazite 477 0.035 0.70 31.31 1.77 0.80 Ferrous Modified Chabazite 5000 6.4e-04 0.76 6.49 1.29 0.79 Table 5 summarizes the adsorption coe fficients obtained for Langmuir and Freundlich equations obtained from Figur es 18 and 19. The maximum adsorption capacity for ferrous treated zeolite (Q max ) using the equilibrium data was approximately ten times the maximum adsorption capacity obtained by copper modified zeolite. Cuprous chloride used in modification of chabazite = 0.01N Ferrous sulfate and Ferrous chloride used in modification of chabazite = 0.1N. 41

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42 The equilibrium data shows that concentra tion of metal ions used in modification process directly affects the adsorption capa city of zeolite. Table 5 shows that the coefficients K L and K F are higher for cuprous modified chabazite than ferrous modified chabazite, which means that more arsenic adsorption, could be expected on cuprous modified chabazite. Freundlichs equation states that highe r the value of n the stronger the bond between the adsorbate and the adsorbent. Higher n value for cuprous modified chabazite along with higher adsorption coefficients ob tained from Langmuir and Freundlich equations suggests st rongly that cuprous chloride modification of chabazite has a better affinity for arsenic adsorption in de-ionized water. Kinetic Studies for Determination of Effect of Stoichiometric Ratio Results of the effect of stoichiometric ratio on arsenic adsorp tion are presented in two parts: (a) kinetic studies using chabazite modified with solutions containing same anion and different cations and (b) kinetic studi es using chabazite modified with solutions having same cation and different anions. Kinetic Studies Using Chabazite Modified with Same Anion and Different Cations These studies were conducted using cupr ous chloride and ferrous chloride modification of chabazite. Figure 20 presents the results of these in dechlorinated tap water.

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0 10 20 30 40 50 60 70 80 90 100 050100150200250300350400Time (mins)Arsenic Concentration in ug/L Cu Modified Chabazite Fe Modified Chabazite Figure 20 Kinetic Studies for Arsenic Adso rption Using Same Anion and Different Cations in Dechlorinated Tap Water Results of arsenic removal using chabazite modified with same anion (Cl -1 ) but different cations (i.e. Cu +1 and Fe +2 ) after 30 minutes and 360 minutes are shown in Table 6. When the modified chabazite is contacte d with arsenic soluti on it forms insoluble metal arsenate compounds with the adsorbed metal ions, thus re moving arsenic from solution (L. Lorenzen et.al., 1995). Table 7 shows the expected metal arsenate compound and the metal/arsenic molar ratio. Higher metal/arsenic ratio signifies greater arsenic removal from the solution. Table 6 shows that arsenic removal from dechlorinated tap water is slightly higher for cuprous chloride modified chabazite than ferrous chloride modified chabazite. This may be attributed to a slightly higher metal /arsenic molar ratio in case of cuprous chloride modified chabazite as is seen from Table 7. 43

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44 Table 6 Results from Kinetic Studies Using Chabazite Modified with Same Anion and Different Cations Removal at 30 minutes Removal at 360 minutes Type of Chabazite Initial Concentration of Arsenic ( g/L) Concentration ( g/L) % Removal Concentration ( g/L) % Removal Cuprous Chloride Modified Chabazite 100 70 30 % 46 54 % Ferrous Chloride Modified Chabazite 100 76 24 % 48 52 % Table 7 Expected Arsenate Compou nds and Metal/ Arsenic Molar Ratio Metal/Cation Expected Compound Metal/Arsenic Molar Ratio Cu (I) Cu 2 AsO 4 OH 2 Fe (II) Fe 3 (AsO 4 ) 2 1.33 Table 8 Order of Reaction and Reaction Rate Constant for Chabazite Modified with Same Anion and Different Cations Type of Chabazite Rate Equation Reaction Rate Constant (k) (liter/mol.min) Order of Reaction Cuprous Chloride Modified Chabazite r A = 4e-05C A 2 4e-05 2 Ferrous Chloride Modified Chabazite r A = 2e-05C A 2 2e-05 2

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The data for kinetic studies showed that adsorption could be approximated to a second order reaction. Data in Table 8 shows that the ad sorption rate for cuprous modified chabazite is twice the rate of adso rption for ferrous modified chabazite. Thus Tables 6, 7 and 8 suggest that selection of cations used in modification of zeolites is important in determining the zeolites capacity for arsenic adsorption and its removal from the solution. Kinetic Studies Using Chabazite Modified with Same Cation and Different Anions Figure 21 shows the results of kinetic studies for arsenic removal using ferrous sulfate and ferrous chloride in dechlorinated tap water. The rates for arsenic adsorption are similar in the first 30 minutes of kinetic studies; however, the data indicates ferrous chloride modified chabazite reached equi librium after 50 minutes. Arsenic adsorption using ferrous sulfate modified chabazite proc eeds at the same rate and achieved an arsenic removal (~95%). The results from ki netic runs using chabazite modified with same cations and different anions in dechlorinated tap water are summarized in table 9. 0 10 20 30 40 50 60 70 80 90 100 050100150200250300350400Time (mins)Arsenic Concentration in ug / FeSO4 Modified Chabazite FeCl2 Modified Chabazite 45 Figure 21 Kinetic Studies for Arsenic Adso rption Using Same Cation and Different Anions in Dechlorinated Tap Water

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46 Table 9 Results from Kinetic Studies Using Chabazite Modified with Same Cation and Different Anions Removal at 30 mins Removal at 360 mins Type of Chabazite Initial Concentration of Arsenic ( g/L) Concentration ( g/L) % Removal Concentration ( g/L) % Removal Ferrous Chloride Modified Chabazite 100 63 37 % 57 43 % Ferrous Sulfate Modified Chabazite 100 65 35 % 5 95 % In case of ferrous sulfate m odified zeolite, data (~85%) showed that the rate of adsorption could be approximated by a second order reaction (See Appendix B). However, for ferrous chloride modified chabazite the data did not fit either the first order or second order which suggested that fractional order might better explain the rate of adsorption (See Appendix B). Following the assumption that arsenic is ad sorbed by formation of metal arsenate compound formation, same amount of arsenic should be adsorbed by ferrous chloride modified chabazite and ferrous sulfate modifi ed chabazite. However, the results obtained from kinetic studies suggests otherwise wh ich leads to the conclusion that arsenic adsorption on chabazite is not a function of metal arsenate compound formation alone, and that the anions used in modification pr ocess plays an equall y important role in arsenic removal from the solution.

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Results from Long Term Equilibrium St udies Using Different Modified Chabazite in Dechlorinated Tap Water Long-term equilibrium studies (90 days) were conducted using cuprous chloride modified chabazite, ferrous chloride modifi ed chabazite, and ferrous sulfate modified chabazite. Langmuir and Freundlich equations were tested to see if they fit the equilibrium data. It was observed that both the above equations provided a very poor fit to the equilibrium data in case of cuprous chloride modified chabazite and ferrous chloride modified chabazite. Non linear isothe rms, not considered a part of this study might better explain the relationship between sorption capacity and equilibrium concentration for equilibrium data obtaine d using these zeolit es. Figures 22 and 23 illustrate the Langmuir and Freundlich equation fitted to equilibrium data for studies in dechlorinated tap water using ferro us sulfate modified chabazite. y = 0.0069x + 0.0009 R2 = 0.9674 0.000 0.001 0.002 0.003 0.004 0.0000.0500.1000.1500.2000.2500.3000.3500.400 1/Ce (L/ug) 1/Qe (gms/ug ) Equilibrium runs using FeSO4 chabazite Figure 22 Langmuir Isotherm for Equilibrium Studies Using Ferrous Sulfate Modified Chabazite in Dechlorinated Tap Water 47

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Comparing the linear form of Langmuir equation C e /Q e = (1/Q max .K L )+C e /Q max to linear equation obtained from Fi gure 22 we obtain the following: Maximum adsorption capacity Q max = 1111 g/gm and Langmuir Constant K L = 0.131 L/ g. The Langmuir equation for arsenic ad sorption on ferrous sulfate modified chabazite can be represented as 1111 130.01 130.0 )/( Ce Ce gmgQe y = 0.3527x + 2.356 R2 = 0.9706 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 0.000.501.001.502.002.50 Log Ce Log Qe Equilibrium Studies for FeSO4 modified chabazite Figure 23 Freundlich Isotherm for Long Term Equilibrium Studies Using Ferrous Sulfate Modified Chabazite in Dechlorinated Tap Water Comparing the linear form of Freundlich equation log Q e = log K F +1/n log C e with the linear equation in Figure 23 we obtain the Freundlich Coefficient K F = 226.98 and Adsorption intensity n = 2.83 48

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The Freundlich equation for arsenic adso rption using ferrous modified chabazite can be represented as: 352298.226 C Qe Table 10 Langmuir and Freundlic h Isotherm Coefficients for Ferrous Sulfate Modified Chabazite in Dechlorinated Tap Water Langmuir Coefficients Freundlich Coefficients Type of Modified Chabazite Qmax ( g/gm) KL (liter/ g) KFn Ferrous Sulfate modified chabazite 1111 0.131 226.98 2.83 Since high arsenic adsorption was obser ved using ferrous sulfate m odified chabazite (See Table 10) and both the isothe rm equations provided a good fit with the equilibrium data, further kine tic studies were conducted using ferrous sulfate modified chabazite. Results from Kinetic Studies for Arsenic Adsorption in Various Source Waters Figure 24 shows results from kinetic studi es for arsenic (III) adsorption using different source waters, namely deionized water, dechlorinated tap water, typical groundwater (irrigation/reclaimed water used for University of S outh Florida) and prechlorinated tap water (obtained from water treatment plant in University of South Florida). Ferrous sulfate modified chabazite was used to study arsenic removal from these different source waters. 49

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0 10 20 30 40 50 60 70 80 90 100 0306090120150180210240270300330360 TimeArsenic (III) Concentration, ug/L Deionized Water Ground Water Prechlorinated Water Dechlorinated Tap Water Figure 24 Results from Kinetic Studies for Arsenic Adsorption Using Ferrous Sulfate Modified Chabazite in Different Source Waters Table 11 summarizes the results of thes e kinetic studies from various source waters using ferrous sulfate modified chab azite. Table 11 shows that arsenic adsorption was similar from dechlorinated tap water and pre-chlorinated tap water. Arsenic adsorption on ferrous sulfate modified chab azite from ground water and de-ionized water progressed at a very slow rate. 50

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51 Table 11 Results from Kinetic Studies Using Different Source Waters Removal at 30 mins Removal at 360 mins Type of Source Waters Initial Concentratio n of Arsenic ( g/L) Concentration ( g/L) % Removal Concentration ( g/L) % Removal Dechlorinated Tap 100 63 37 % 5 95 % Prechlorinated Tap 100 52 48 % 9 91 % Ground 100 68 32 % 23 77 % De-Ionized 100 76 24 % 59 41 % Table 12 shows the order of reaction and th e reaction rate constant obtained from kinetic studies for these source waters The da ta shows that arsenic adsorption on ferrous sulfate modified chabazite essentially follows a second order reaction for all source waters. Table 12 Order of Reaction and Reaction Rate Constants for Kinetic Studies with Ferrous Sulfate Modified Chabazite in Various Source Waters Type of Source Water Rate Equation Rate Constants (liter/mol.min) Order of Reaction Dechlorinated Tap r A = 7e-04C A 2 7e-04 2 Prechlorinated Tap r A = 2e-04C A 2 2e-04 2 Ground r A = 1e-04C A 2 1e-04 2 De-Ionized r A = 1e-05C A 2 1e-05 2

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52 Table 12 shows that the rate of adsorption in dechlorinated tap water is essentially 70 times larger than de-ionized tap water. Similar observations can be made from Table 12 for arsenic adsorption in pre-chlorinated tap water and de-ioni zed water (20 times), and ground water and de-ionized water (10 times). The presen ce of total dissolved solids does affect the rate of arsenic adsorption on ferrous sulfate modified chabazite. A possible explanation for this phenomenon is that the ionic mobility of arsenic in deionized water is less than that of arsenic sp ecies in the source waters. This might affect the driving force and the adsorption equilibriu m within the system. In other source waters e.g. groundwater, other ions may be present which may contribute to driving the arsenic ions towards the chabazite su rface thus ensuring higher ad sorption on the surface and consequently higher removal from the solution. Relationship between Mass of Zeolite and Arsenic Removal The equilibrium studies give the relationship between the mass of the zeolite and the amount of contaminant removed. It also provides information regarding the optimum dose to be used in coagulation/batch e xperiments to maximize removal of given contaminant. Figure 25 depicts the relationship between mass of zeolite and removal efficiency using cuprous chloride modified chabazite, ferrous chloride modified chabazite and ferrous sulfate modified chabazite. Figure 25, shows that for the same amount of zeolite, ferrous sulfate modified chabazite adsorbs more arsenic from the dechlorinated tap water. When ferrous sulfate modified chabazite is applied at a dose of 1gram per liter of a solution of 100 g/L of arsenic, approximately 95% of arsenic is removed from the solution. Further addition of th e ferrous sulfate modified chab azite does not result in any significant adsorption. In case of ferrous chlo ride chabazite, using the same dosage of 1 gram per liter, approximately 60% of arseni c is removed from the solution, while using copper chloride chabazite around 50% arsenic removal is achieved. This infers that for the same amount of chabazite used, using fe rrous sulfate for modification of chabazite would be more economical than any ot her metal salts used in this study.

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0 10 20 30 40 50 60 70 80 90 100 0.250.50.751 2 Mass of modified chabazite in gms Arsenic Removal (% ) CuCl 0.01N FeCl2 0.1N FeSO4 0.1N Figure 25 Relationship Between Arsenic Removal and Mass of Zeolite Uptake/Leaching Studies Previous studies (Carnahan et.al, 1998) ha ve shown that the arsenic present on the zeolite surface do not leach from the spent media and does pass the TCLP (Toxicity Characteristic Leaching Procedure) test and can be disposed off in a landfill. The major concern with using zeolite coated with metal salts was leaching of metal ions into the solution. To verify this leaching study wa s conducted. Water quality analyses were performed for the presence of calcium, ma gnesium, copper and iron. Samples were analyzed before and after in troduction of modified chabazite in water (no arsenic was present in water). The results of leaching studies are displayed in Table 13 below. 53

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54 Table 13 Uptake Data for Metals Used in Modification of Chabazite Metals Analyzed Ca Cu Fe Mg Tap Water (mg/L) 77.16 0.78 0.14 3.74 Cu treated chabazite (mg/L) 73.17 0.46 0.06 3.97 Uptake / Leaching 3.99 0.31 0.08 0.24 % Uptake /Leaching 5.17 40.34 57.66 6.34 Tap Water (mg/L) 77.16 0.78 0.14 3.74 Fe treated chabazite (mg/L) 70.93 0.31 0.07 3.71 Uptake / Leaching 6.23 0.47 0.07 0.03 % Uptake/Leaching 8.07 60.70 50.36 0.80 Table 13 shows that none of the metals us ed in modification of chabazite leached into the solution. Chabazite modified with metal salts adsorbed some the metal ions in addition to arsenic from the aqueous solution. Cuprous modified chabazite adsorbed 40% of copper ions and 58% of ferrous ions from the aqueous solution in addition to a small percentage of calcium ions (5%). Ferrous modified chabazite adsorbed 60% of copper ions, 50 % of ferrous ions 8% calcium and 1% magnesium from the aqueous solution. Hence it can be inferred that metal ions used for modification form a strong bond with chabazite and do not leach off the surface in aqueous phase.

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55 Conclusions The objectives for this st udy were to compare the adsorption capacities of copper and ferrous modified chabazite for removal of arsenic in differe nt source waters and examine which method for coating/modification of the zeolite (i.e. chab azite in this case) results in greater removal efficiency for ar senic removal. The conclusions derived from this study were: Arsenic adsorption on modified chabazite could be approximated to follow a second order reaction for all th e three different salts used in modification process. Cuprous chloride modification of chabazi te had the highest rate for arsenic adsorption in absence of competing i ons. Langmuir and Fr eundlich equations concluded that cuprous ch loride modification had better affinity for arsenic adsorption in de-ionized water. Selection of various cations and anions used for modification of chabazite and concentration of these salts do affect ar senic adsorption rates thus affecting its removal from the solution. Presence of total dissolved so lids affect the rate of arse nic adsorption on chabazite Modification of chabazite by ferrous sulfate presents the most economical option for arsenic removal in dechlorinated ta p water (Approximately 95% removal from solution containing 100 g/L of arsenic). Metal ions used in modification of zeoli te do not leach in the solution and hence process can be safely used for arsenic removal.

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56 Engineering Significance and Recommendations The purpose of this research was to find a low cost alternative adsorption material that removed arsenic from drinking water. Th e specific focus of this study was to develop a treatment method for using modified zeolite (i.e. chabazite in this case) that removed arsenic from source waters. The experiment s conducted in this study are preliminary development of a low cost adsorbent. These studies established the relationship between various treatment methods used for modificatio n of chabazite and removal efficiency for arsenic. Ferrous sulfate modi fied chabazite exhibited the highest adsorption capacity for arsenic among the different metal salts used for modification. Hence, more arsenic adsorption is obtained using le ss amount of ferrous sulfat e modified chabazite. Thus ferrous sulfate modified chabazite could be put to use for commercial application for arsenic removal using short bed columns. To test the feasibility of using ferrous sulfate modified chabazite in short bed columns some recommendations are made based on the studies conducted. Modification of Zeolite Modification of Zeolite Using Various Metal Salts Chabazite modification in this study was carried out us ing metal salts of copper and iron. Manganese can also be used for m odification of chabazite. Manganese has been used worldwide for coating of various adso rbents. Manganese occupies a higher position in the periodic table than Iron (Atomic Numb er of manganese is 25.Atomic Number of iron is 26) because of which manganese has a higher oxidation state (Mn 6+ ) than iron (Fe 2+ or Fe 3+ ). Thus manganese would function as oxidant and would oxidize arsenic (III) to arsenic (V) and further improve removal efficiency. Studies should be conducted using

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57 salts with presence of metal ions in varyin g stoichiometric ratios. For e.g. while using ferrous ion for modification, treatment of chabazite should be carried out using the following: FeSO 4 (Fe: SO 4 : 1:1), FeCl 2 (Fe: Cl: 1:2) and Fe 3 (PO 4 ) 2 (Fe: PO 4 : 1.5:1) Similarly, while using copper for modifi cation of chabazite, various copper salts listed below can be used to determine the effect of stoichiometric ratio. CuCl (Cu: Cl: 1:1), Cu 3 (PO 4 ) 2 (Cu: PO 4 : 1.5:1), Cu 2 SO 4 (Cu: SO 4 : 2:1). The results obtained suggest that stoichiometr ic ratio of different metal salts do affect arsenic adsorption on chabazite and hence bench scale tests ma y help evaluate the impact of stoichiometry of metal salts in treatment process used for modification of zeolite. Modification of Zeolite Using Various Concentrations A correlation was observed between the concen trations of metal salts used in the treatment of zeolite (loading rate) and arseni c adsorption on zeolite surface. However, the observations were inconclusive and bench scale studies should be performed where chabazite is treated with meta l salts of varying concentratio ns ranging from 0.01M to 1.0 M (depending on solubility of metal salt in de-ionized water). These studies would be a good indicator of the cation exchange capacity of the chabazite, the lo ading rate of metal ions on the zeolite surface and ar senic adsorption on the zeolite. Effect of Particle Size on Arsenic Adsorption Particle size of media used in adsorpti on affects the adsorption process. It has been demonstrated that adsorption on the medi a increases with decrease in particle size. Small particles have increased surface area and therefore greater adsorption capacity because more adsorption sites are available. Hence more arsenic adsorption would take place on powdered chabazite than its granular counterpart. Chabazite used in this study had an average effective pore diameter of 4.3 A O Arsenic adsorption studies should be conducted using the zeolite chabazite in different particle size rang ing from (80 mesh to

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58 400 mesh). These studies will help elucidate effect of particle size on arsenic adsorption on the zeolite. Bench Scale Tests Using Actual Source Waters In this study arsenic contamination was simulated in th e laboratory using deionized, dechlorinated tap water spiked with arsenic at 100ppb. Arsenic adsorption studies should be conducted using source waters where arse nic contamination is natural (i.e. run off from tailings and mining deposits etc). Source waters obtained from states such as Arizona, California, Florida, Idaho, Nevada, and Wisconsin are representative of arsenic contaminated waters in the United States. Bench scale studies performed using various source waters would also address the issue of competition fr om other interfering ions for adsorption sites on chabazite surface. The matrix of bench scale tests that s hould be performed and parameters that should be monitored is summarized below Table 14 Matrix of Bench Scale Tests and Water Quality Parameters for Development of a Full Scale Process Using Modi fied Chabazite as Adsorbent Bench Scale Tests based on process variables Water Quality Parameters to be Monitored Effect of Particle Size Distribution Arsenic (III), TDS Effect of pH (4-10) pH, Arsenic (III) Effect of Total Dissolved Solids (500ppm-1500ppm) pH, Arsenic (III), Total Dissolved Solids, conductivity Effect of Competing Ions like SO 4 2, PO 4 3, SiO 4 4, Cl -1 HCO 3 1Ca 2+ Mg 2+ Fe 2+ Fe 3+ Cu + arsenic (III), SO 4 2, PO 4 3, SiO 4 4, Cl -1 Effect of Initial Arsenic Concentration Arsenic (III) Effect of Zeolite Dosage Arsenic (III) Effect of Contact Time pH, Arsenic (III)

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59 Column Studies Column studies are a good i ndicator of the no of bed vol umes that can be run to exhaustion with any adsorbent. Short column using zeolite, chabazite, would give an indepth analysis about arseni c adsorption process. Rapid Small Scale Column Test (RSSCT) is a new method for design of fullscale fixed bed adsorbers from small-scale column studies. RSSCTs provide the benefit of capturing the changes in water quality (pH, effect of interferences) and gives insight into operations regimes such as empty bed contact time and surface loading rates. Th e experiments in RSSCTs are conducted for shorter time durations than full-scale column s and the results from RSSCT can be easily extrapolated to a full-scale operation. Batc h equilibrium studies help in predicting the capacity of adsorbent for different source waters. They also provide valuable insight into the effect of interferences and selectivity of the adsorbent. However, column studies are required to establish process ki netics and surface loading of the adsorbent material. These tests would be useful where pilot and full-scale studies are not possible. All the above-mentioned steps should help in development of a robust treatment process for modification of chabazite and in turn help in providing a new low cost adsorbent material for re moval of arsenic (III).

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60 References Borgono, J.M., Greiber, R. 1972. Epidemiologi cal study of arsenism in the city of Antofagasta. In: Trace Substances in Environmental Health, vol. 5. D.C. Hemphill, ed. University of Missouri, Columbia, MS. pp. 13-24. Buswell, A.M. 1943 War problems in analys is and treatment. Jour AWWA, 35(10), 1303. Clifford, D. and C.C. Lin (1995). Ion Exch ange, Activated Alumina, and Membrane Processes for Arsenic Removal from Ground water, Proceedings of the 45th Annual Environmental Engineering Conference, University of Kansas, February 1995. Clifford, Dennis, G. Ghurye, and A. Tripp. 1998. Arsenic Ion Exchange Process with Reuse of Spent Brine. In Proceedings. of 1998 Annual AWWA Conference. Denver, Colorado. Diamadopoulos E, Ioannidis S & Sakellaro poulos GP (1993), As (V) removal from aqueous solutions by fly ash. Water Research, 27(12) 1773. Driehaus, W., Jekel, M. R. and Hilderbrandt, U. 1998 Granular ferric hydroxide a new adsorbent for the removal of arsenic from natural water. J Water Supply Research and Technology-AQUA. 47 (1), 30-35. Dutta, A., Chaudhuri, M.1991. Removal of Arsenic from groundwater by lime softening with powdered coal additive .J Water SRT v40 n1.pp25-29. Ferguson, J. F. and Gavis, J. 1972 A review of arsenic cycle in natural waters. J. Water Research. 6,1259-1274. Ficek, Kenneth J. Potassium Permanganate and Manganese Greensand for Removal of Metals, Water Quality Associ ation Convention, March 1994. Gulledge, J. H. and OConner, J. T. (1973) Removal of Arsenic (V) from Water by Adsorption on Aluminum and Ferric H ydroxides. Jour. AWWA 65(8), 548-552.

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61 Hering, J.G., and V.Q. Chiu (1998). The Chemistry of Arsenic: Treatment and Implications of Arsenic Speciation and O ccurrence, AWWA Inorganic Contaminants Workshop, San Antonio, TX, February 23-24, 1998. Huang, C.P. and P.L. Fu. 1984. Treatment of Arsenic (V)-containing Water by the Activated Carbon Process. J. Water Pollution. Control Fed. 56: 233. Joshi, A. and Chaudhuri, M. 1996 Removal of arsenic from ground water by iron oxidecoated sand. Journal of Environm ental Engineering, 122(8), 769772. Joshida, I., Kobayshi, H. & Veno, K. 1976 Se lective adsorption of arsenic ions on silica gel impregnated with ferric hydroxid e. Analytical Letters 9, 1125. Kipling MD (1977) Arsenic. In: Lenihan J, Fl etcher WW eds. The chemical environment. Glasgow, Blackie, pp 93. L.V. Rajakovic, Sorption of Arsenic onto Ac tivated Carbon Impregnated with Metallic Silver and Copper, Separation Scien ce Technology, 27, (11), (1992), 1423-33. Lackovic, J.A., Nikolaidis, N.P. and Dobbs, G. 2000 Inorganic arsenic removal by zerovalent iron. Environmental Engi neering Science, 17(1), 29-39. Lorenzen, L., Vandeventer, J. and Landi, W. 1995 Factors Affecting the Mechanism of the Adsorption of Arsenic Species on Activat ed Carbon. Minerals Engineering, 8(4-5), 557-569. Lu FJ. 1990. Blackfoot disease: arseni c or humic acid? Lancet 336(8707): 115-116. McNeill, L., Edwards, M. Arsenic Removal vi a softening Critical Issues in Water and Wastewater treatment: Nati onal Conference on Environmental Engineering 1994.pp 640645.ASCE .New York.1994. Mihaly Csanady & Ilona Straub, Health da mage due to water pollution in Hungary. NAS (1977) Medical and biol ogic effects of environm ental pollutant: Arsenic, Washington, DC, National Academy of Sciences. National Research Council (NRC) (1999), Arse nic in drinking Wate r. National Academy Press, Washington, D.C. Penrose, W.R. (1974). CRC Crit. Re v. Environ. Control 4:465. Pontius, Frederick W., Kenneth G. Brown and Chien-Jen Chen. Health Implications of Arsenic in Drinking Water. Jour AWWA 86 (9) (1994): 52-63.

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62 Sancha, A.M. 1999b Removal of arsenic from drinking water supplies. Proceedings, IWSA XXII World Congress and Exhibition, Buenos Aires, Argentina. Simms, J. and F. Azizian (1997). Pilot Plan t Trials on the Removal of Arsenic from Potable Water Using Activated Alumina, Proceedings AWWA Water Quality Technology Conference, November 9-12, 1997. Smith, A.H., C. Hopenhayn-Rich, M.N. Bates, H.M. Goeden, I. Hertz-Picciotto, H.M. Duggan, R. Wood, M.J. Kosnett and M.T. Smith. 1992. Cancer risks from arsenic in drinking water. Env. Health Perspective. 97:259-267. Sorg, T. J. and Logsdon, G. S. (1978). Treatment Technology to Meet the Interim Primary Drinking Water Regulations for Inor ganics: Part 2. Jour. AWWA 70 (7), 379393. Subramanian, K.S., Viraraghavan, T ., Phommavong, T. and Tanjore, S. 1997 Manganese greensand for removal of ar senic in drinking water. Water Quality Research Journal of Canada, 32(3), 551-561. USEPA (2000). Technologies and Costs for Removal of Arsenic from Drinking Water, EPA 815-R-00-028, Prepared by Malcolm Pirnie Inc. under contract 68-C6-0039 for EPA ORD, December 2000. Vagliasindi, F.G.A., Benjamin, M., Arsenic Removal and its Speciation in Adsorption Reactors. American Water Works Associ ation Annual Conference and Exposition, Dallas, Texas, June 1998. Vahter, M., E. Marafante. In vivo methylation and detoxifica tion of arsenic. Royal Soc. Chem. 66: 105-119, 1988. Weber, W.J., P.M. McGinley, and L.E. Katz, Sorption phenomena in subsurface systems: Concepts, models, and effects on contaminant fate and transport. Water Research, 499-528, 1991. Welch, A.H., West John, D.B., Helsel, D.R., and Wanty, R.B., 2000, Arsenic in ground water of the United States-occurrence and geochemistry: Ground Water v.38 no.4, p.589-604.

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63 Appendices

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64 Appendix A: Chabazite Physical Properties and Arsenic Analysis Table A1 Chabazite Physical Properties Form Powder or Granules Color Light Brown (Dry Brightness 43) Ring Members 8 Crystal Size Chabazite Less than 1 micron Crystallinity + 90% Density 1.73 g/cm 3 Pore Size 4.1 by 3.7 Angstroms Effective Pore Diameter 4.3 Angstroms Cavity Size 11.0 by 6.6 Angstroms Total Pore Volume .468 cm 3 /g Surface Area 520.95 m 2 /g Crystal Void Volume .47 cm 3 /cm 3 Packing Density Approx. 577kg/m 3 (36 lbs./ft 3 ) SiO 2 /Al 2 O 3 Ratio Approx. 4:1 Moisture as packaged Less than 10% by weight Ion Exchange Capacity 2.60 meq/g

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65 Appendix A (Continued) Preparation of Arsenic Trioxide solution For Batch Studies Arsenic trioxide solution required for kinetic and equilibrium studies was prepared using instruction given in the Standard Methods for Water and Wastewater, 19 th Edition, 1995 . Stock Arsenic (III) Solution: Dissolv ed 1.320gms of arsenic trioxide As 2 O 3 in water containing 4gms of NaOH. It was then diluted to 1L to get 1g/L of As (III) solution. Intermediate Arsenic (III) Solution: Diluted 10 ml of stock As solution to 1000ml with water containing 5ml of concentrated HCl to get 1mg/L of As (III) solution. Standard Arsenic (III) Solution: Dilute 10 ml of intermediate As (III) solution to 1000ml of water containing the same concentr ation of acid used for sample preservation to get 100 g/L of As (III) solution.

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66 Appendix A (Continued) Arsenic Analysis Arsenic analysis was conducted using graphite furnace atomic absorption spectrometry method. The method used was ASTM 2972-93C. A detailed description of the method used is provided below: Graphite Furnace Atomic Absorption Spectrometry (GFAA) (EPA 200.9, SM 3113 B, ASTM 2972-93 C, SW-846 7060A) In the graphite furnace atomic absorption spectrometry technique, a small volume of sample (typically 5 to 50 L) is injected into a graphite tube positioned in the optical path of an atomic absorption spectrophotometer An electrical furnace is used to heat the tube sequentially through dryi ng, charring, and finally, an atomization step. A light beam from a hollow cathode lamp or electrode le ss discharge lamp (EDL) containing the element of interest is directed through the t ube, into a monochromator, and into a detector that measures the amount of light absorbed by the free ground state atoms. The amount of light absorbed by the free ground state atoms is directly proportional to the concentration of the analyte in solution within the linear calibration range of the instrument. Because the greater percentage of analyte atoms are vaporized and dissociated within the light beam passing through the graphite tube, great er analytical sensit ivity is obtained and lower detection limits are possible as compar ed with flame atomic absorption. The limit of detection can be extended by increasing the injection volume or by using a multiinjection technique. These techniques effec tively increase the total amount of analyte placed in the tube resulting in greater ab sorbance. ASTM 2972-93 C utilizes standard graphite tubes and off-the-wall-atomization. The major highlights of this method are described below: Method Used: ASTM 2972-93 C Lamp Used: UltrAA high intensity cathode lamp Matrix Modifier: 150 mg/L as NiNO3 Wavelength: 193.7nm Standards: 10, 20 and 50 ppb Measurement mode: Peak Height

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Appendix A (Continued) Figure A1 Varian SpectrAA Zeeman Graphite Furnace 67

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68 Appendix B: Determination of Order of Reaction Integral Method of Analysis Procedure: The integral method of analysis always puts a partic ular rate equation to the test by integrating and comparing th e predicted concentration versus time curve with the experimental concentration versus time data. The integral method is especially useful for fitting simple reaction types corresponding to elementary reactions. To find a rate equation using the integral method lets consider the following example Reactant A decomposes in a batch reactor A Products The composition of A in the reactor is measured at various times. To find a rate equation that fits the data star t by guessing the simplest rate form, or first order kinetics. This means a plot of ln (Cao/Ca) versus time should give a straight line through the origin. If this plot fails to give us a strai ght line, it means that first order kinetics cannot reasonably represent the data and another rate form must be guessed. Proceed to guess the rate equation to be second order. This suggests that a plot of 1/Ca versus time should give a straight line. If this plot gives a st raight line then the equation is of the second order with the intercept representing the init ial concentration and sl ope representing the rate constant, k. If this plot fails to give a straight line th en the second order kinetic form is rejected as well and fractional method should be used as calculations with higher order such as third order rate form are tedious and not recommended.

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Appendix B (Continued) Rate Determination for Modified Chabazite with Different Salts In De-ionized Water CuCl 1st Order DI y = 0.0006x + 0.1875 R2 = 0.72660.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 050100150200250300350400TimeLn (CuCl-0/CuCl) Figure B1 First Order Kinetic Rate for Coppe r Modified Chabazite in De-Ionized Water CuCl 2nd Order DI y = 3E-05x + 0.0159 R2 = 0.75320.0000 0.0050 0.0100 0.0150 0.0200 0.0250 0.0300 050100150200250300350400Time1/CCu Figure B2 Second Order Kinetic Rate for Copper Modified Chabazite in De-Ionized Water 69

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Appendix B (Continued) FeCl2 1st Order y = 0.0006x + 0.0522 R2 = 0.83050.00 0.05 0.10 0.15 0.20 0.25 0.30 0 100 200 300 400TimeLn (FeCl2-0/FeCl 2 Figure B3 First Order Kinetic Rate for Ferr ous Chloride Modified Chabazite in DeIonized Water FeCl2 2nd Order y = 7E-06x + 0.0106 R2 = 0.85560.0000 0.0020 0.0040 0.0060 0.0080 0.0100 0.0120 0.0140 050100150200250300350400Time1/C FeCl 2 70 Figure B4 Second Order Kinetic Rate for Ferro us Chloride Modified Chabazite in DeIonized Water

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Appendix B (Continued) FeSO4 1st Order y = 0.0009x + 0.2299 R2 = 0.6993 0.000 0.100 0.200 0.300 0.400 0.500 0.600 0100200300400 TimeLn (FeSO4-0/FeSO4) Figure B5 First Order Kinetic Rate for Ferrous Sulfate Modified Chabazite in De-Ionized Water FeSO4 2nd Order y = 1E-05x + 0.0123 R2 = 0.7747 0.0000 0.0020 0.0040 0.0060 0.0080 0.0100 0.0120 0.0140 0.0160 0.0180 0100200300400 Time1/CFeSO4 Figure B6 Second Order Kinetic Rate for Fe rrous Sulfate Modified Chabazite in DeIonized Water 71

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Appendix B (Continued) Rate Determination with Same Anion and Di fferent Cations In Dechlorinated Tap Water CuCl 1st Order y = -0.0013x + 1.9225 R2 = 0.7166 1.70 1.75 1.80 1.85 1.90 1.95 2.00 020406080100120140 TimeLog Cu C Figure B7 First Order Kinetic Rate for C opper Modified Chabazite with Same Anion CuCl 2nd Order y = 4E-05x + 0.0119 R2 = 0.7416 0.0000 0.0050 0.0100 0.0150 0.0200 020406080100120140 Time1/CuC l Figure B8 Second Order Kinetic Rate for C opper Modified Chabazite with Same Anion 72

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Appendix B (Continued) FeCl2 1st Order y = -0.0006x + 1.9229 R2 = 0.8532 1.650 1.700 1.750 1.800 1.850 1.900 1.950 2.000 2.050 0 100 200300400 TimeLog FeCl 2 Figure B9 First Order Kinetic Rate for Ferr ous Modified Chabazite with Same Anion FeCl2 2nd Order y = 2E-05x + 0.0118 R2 = 0.8844 0.0000 0.0050 0.0100 0.0150 0.0200 0.0250 050100150200250300350400 Time1/FeCl2 Tap wat e Figure B10 Second Order Kinetic Rate for Ferr ous Modified Chabazite with Same Anion 73

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Appendix B (Continued) Rate Determination with Same Cation and Di fferent Anions in Dechlorinated Tap Water FeCl2 2nd Order y = 0.0001x + 0.0126 R2 = 0.5851 0.0000 0.0020 0.0040 0.0060 0.0080 0.0100 0.0120 0.0140 0.0160 0.0180 05101520253035 Time1/FeCl2 Figure B11 Second Order Kinetic Rate for M odified Chabazite with Different Anion (Chloride) FeSO4 2nd Ordery = 0.0002x + 0.0114 R2 = 0.8356 0.0000 0.0020 0.0040 0.0060 0.0080 0.0100 0.0120 0.0140 0.0160 0.0180 05101520253035 Time1/FeSO4 Figure B12 Second Order Kinetic Rate for M odified Chabazite with Different Anion (Sulfate) 74

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Appendix B (Continued) 75 Rate Determination for Ferrous Modified Chabazite in Different Source Waters Figu y = 1E-05x + 0.0126 R2 = 0.9152 Deionized y = 0.0001x + 0.0113 R2 = 0.9569 Ground y = 0.0002x + 0.012 R2 = 0.9872 Prechlorinated Tap y = 0.0007x 0.0021 R2 = 0.9747 Dechlorinated Tap -0.0500 0.0000 0.0500 0.1000 0.1500 0.2000 0.2500 050100150200250300350400 Time (Mins)1/As Concentration Deionized Water Groundwater Prechlorinated Tap Water Dechlorinated Tap Water re B13 Kinetic Rate Determination for Ferrous Sulfate Modified Chabazite in Different Source Waters


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Adsorption studies for arsenic removal using modified chabazite
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ABSTRACT: Arsenic contamination in drinking water has been a cause of serious concerns across the United States as well as throughout the world. Over 70 million people in Eastern India, Bangladesh, Vietnam, Taiwan, and Northern China have been victims of arsenic poisoning. The USEPA has classified arsenic as a Class A carcinogen and recently reduced the Maximum Contaminant Level (MCL) in drinking water from 50ppb to 10ppb. The deadline for all the water utilities to meet this level is 23rd January 2006. To meet those drinking water standards, small water utilities need low cost and effective arsenic removal techniques. Natural zeolites such as Chabazite are excellent sorbents for several metallic and radioactive cations. Modifying the zeolite structure can effectively enhance the adsorption capacities of these zeolites for removal of heavy metals. The present work investigates the adsorption capacities of Cuprous and Ferrous treated Chabazite for removal of arsenic.This investigation is a part of a broader project directed at developing an effective pretreatment process that uses modified Chabazite in conjugation with Microfiltration (MF) or Ultrafiltration (UF) for removal of organic and inorganic contaminants. The goal of this research is to determine how well Cuprous and Ferrous treated Chabazite sorbs arsenic in its trivalent and pentavalent state. The other objectives of this research are to examine which modification of the chabazite has the higher removal efficiency of arsenic. This study will also compare arsenic adsorption on the modified zeolites in response to competitive adsorption of various anions present in natural source waters such as sulfates, hydroxides, and chlorides. The potential benefit of this study is to find the most effective treatment of for removal of arsenic species from aqueous solutions.This investigation may provide small water utilities, with a cost effective way for removal of arsenic and thus meet the recommended new regulatory maximum contaminant level (MCL).
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