Adsorption of dimethylarsinate (DMA) monomethylarsonate (MMA), and arsenate on goethite (alpha FeOOH

ADSORPTION OF DIMETHYLARSINATE (DMA), MONOMETHYLARSONATE (MMA), AND ARSENATE ON GOETHITE (α-FeOOH) ZHANG JUNSHE ( M.Eng., Tianjin University ) A THESIS SUBMITED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMICAL & BIOMOLECULAR ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2005 DEDICATION To my mother and father ACKNOWLEDGEMENTS First, I am particular grateful to my supervisors, A/P Robert Stanforth and A/P Simo Olavi Pehkonen, for their continual encouragement, support and inspiration throughout the entire investigation. Their kind understandings and characters make the study pleasing. I would also like to thank my colleagues, Mr. Jiao Lei, Mr. Zhong Bin, Mr. Tian Kun, Ms. Thet Su Hliang, Dr. Xu Ran, Mr. Xu Tongjiang and all other friends who shared with me their knowledge and experience as well as their support. Special thanks go to Ms. Li Fengmei, Ms. Chia Yuit Ching, Mr. Chia Phai Ann and Ms. Li Xiang for their instructions with the equipment. I wish to thank my parents, my wife Li Meiling, and two younger sisters for their support and understanding. Finally, I would like to express my sincere gratitude to the National University of Singapore for providing a research scholarship to make this research project possible. i TABLE OF CONTENTS ACKNOWLEDGEMENTS i TABLE OF CONTENTS . ii SUMMARY . v LIST OF FIGURES vii LIST OF TABLES xii LIST OF SYMBOLS . xiv NOMENCLATURE . xvii Chapter Introduction . 1.1 Arsenic in natural systems .1 1.2 Arsenic adsorption on goethite 1.3 Objectives and scope .4 Chapter Literature Review 2.1 Aqueous speciation of arsenic .7 2.2 The physical properties of goethite 2.3 Surface complexation models (SCMs) .10 2.4 Charge development on the goethite surface .12 2.5 Interaction between arsenic and the goethite surface .16 2.5.1 Surface species of adsorbed arsenic 17 2.5.2 Proton-anion adsorption ratios 19 2.5.3 Adsorption kinetics .20 2.5.4 Competitive adsorption between arsenic and phosphate .23 Chapter Materials and Methods . 25 3.1 Synthesis and characterization .25 ii 3.2 Adsorption isotherms .25 3.3 Adsorption edges .26 3.4 Methods to determine surface coverages .26 3.5 CO2-free system .27 3.6 Acid-base titration .28 3.7 Arsenic and phosphate analysis and error analysis 28 3.8 Zeta potential .29 3.9 Effective particle sizes .29 3.10 Adsorption and desorption kinetics 30 3.11 Back titration to determine proton-anion adsorption ratios 30 3.12 Competitive adsorption between arsenic and phosphate 31 Chapter Results and Discussion 32 4.1 Characterization of goethite .32 4.1.1 Specific surface area and porosity of goethite .32 4.1.2 Morphology of goethite 34 4.1.3 Acid-base titration .37 4.1.4 Estimation of the density of reactive sites .39 4.2 Solubility of goethite and ferric arsenate .41 4.3 Adsorption edges .43 4.3.1 Error analysis 44 4.3.2 Effect of pH and background electrolyte on the uptake of DMA 44 4.3.3 Effect of pH and background electrolyte on the uptake of MMA .47 4.3.4 Effect of pH and background electrolyte on the uptake of arsenate 49 4.3.5 Adsorption edges of three arsenic species .51 4.4 Adsorption isotherms .53 4.4.1. Methods to determine surface coverages and error analysis .53 4.4.2 Adsorption isotherms at pH 4.00 and 7.20 56 4.4.3 Effect of the solids concentration 60 4.5 Adsorption and desorption kinetics 64 4.5.1 Error analysis 64 4.5.2 Zeta potential and effective particle size .65 iii 4.5.3 Effect of background electrolyte concentrations on adsorption kinetics 72 4.5.4 Effect of pH on absorption kinetics .77 4.5.5 Rate-determining step during adsorption 79 4.6 Proton-anion adsorption ratios .86 4.6.1 Charge development on the goethite surface .87 4.6.2 Method to calculate proton-anion adsorption ratios 96 4.6.3 Error analysis .97 4.6.3 Proton-anion adsorption ratios 98 4.7 Competitive adsorption between arsenic and phosphate 111 4.7.1 Error analysis 112 4.7.2 Effect of the order of addition .112 4.7.3 Replacing the adsorbed anion with another anion .120 4.8 Acid-base properties of surface groups and adsorption mechanism .131 4.9 Environmental implications and industrial applications .133 Chapter Conclusions and Recommendations . 136 5.1 Summary .136 5.2 Recommendation future research .141 References 144 Appendices . 160 A Desorbility of arsenate at pH 4.00 using 0.1 M NaNO3 solution 160 B Fraction of various charged hydroxyls on the goethite surface 162 C Publications .164 iv SUMMARY Arsenic (As) is highly toxic to humans and is widespread in aquatic environments, soils, and sediments due to natural and anthropogenic sources. The bioavailability of arsenic in oxidized systems is mainly influenced by its interactions with the mineral surface. Adsorption is one of these important interactions. Adsorption of inorganic arsenic on goethite (α-FeOOH) has been studied for many years; however, the adsorption mechanism of arsenic is still in debate and the reactivity of the goethite surface is not well understood. The purpose of this study was to investigate the adsorption mechanism of three arsenic species – arsenate, monomethylarsonate (MMA), and dimethylarsinate (DMA)-on goethite and chemical properties of the goethite surface by comparing the individual adsorption edges, isotherms, and effect on zeta potential of the three arsenic species, and the competitive adsorption behaviors between the three arsenic species and phosphate. Adsorption kinetics and proton-anion adsorption ratios provide very useful insight into the chemical properties of the goethite surface. DMA, MMA, and arsenate form inner-sphere complexes by ligand exchange on the goethite surface. At low surface coverages, MMA and arsenate predominately adsorb as bidentate complexes; however the contribution of monodentate complexes is important at high surface coverages. As pH decreases and the surface coverage increases, some adsorbed arsenate is protonated. The low affinity of DMA for goethite compared with MMA or arsenate and the influence of electrolyte anion and carbonate on the adsorption of DMA suggests that DMA only forms monodentate complexes. Adsorbed DMA can be completely v displaced by phosphate, but only a portion of adsorbed MMA or arsenate can be displaced by phosphate, indicating that adsorption of MMA or arsenate is not totally reversible with respect to phosphate. The non-exchangeable part of MMA or arsenate is attributed to bidentate complexes, although some bidentate complexes are also exchangeable. DMA only exchanges with phosphate adsorbed as monodentate complexes. There are two types of reactive sites on the goethite surface for MMA or arsenate based on the affinity: high-affinity sites and low-affinity sites. On the high affinity sites MMA or arsenate adsorbs as bidentate complexes, and a part of the adsorbed MMA or arsenate on these sites cannot be displaced by phosphate. Monodentate complex formation is the dominant mechanism on the low affinity sites, and adsorption isotherms of MMA or arsenate on these sites follow Freundlichian behavior. It seems that only one type of reactive sites exists for DMA, since logarithmic plots of all adsorption data of DMA fall on one straight line. The heterogeneity also gives rise the Elovichian kinetics of the three arsenic species adsorption. Neither a 2-pK model, nor a two-site 1-pK or two-site 2-pK model can interpret both the proton-arsenic adsorption ratio and the effect of adsorption of the three arsenic species on the zeta potential. Singly coordinated hydroxyls are the reactive sites on the goethite surface, but the contribution of other hydroxyls to the total surface charge and particle charge is significant at certain pH values. Thus a 1-pK MUSIC (Multisite Complexation) model should be used in describing the adsorption of anions on the goethite surface. vi LIST OF FIGURES Figure 2.1 Crystal morphology of large goethite twin (a) and the goethite particle (b) reported by Cornell and Schwertmann (2003) 10 Figure 2.2 Schematic representation of the surface structure of the (101) face 16 Figure 2.3 Proposed AsO4 surface complexes on the goethite surface. .18 Figure 4.1 N2-adsorption and desorption isotherms on goethite at 77.4K 33 Figure 4.2 Pores sizes distribution of goethite based on BJH method .34 Figure 4.3 TEM image of goethite crystals .35 Figure 4.4 FESEM image of goethite crystals .35 Figure 4.5 AFM image of goethite crystals. .36 Figure 4.6 Optical microscopy of goethite aggregates in suspension .37 Figure 4.7 A schematic presentation of goethite crystals .37 Figure 4.8 Acid-base titration curves of goethite at three NaNO3 concentrations. Goethite concentration is 10 g L-1. 39 Figure 4.9 Activity of single ion species and total FeIII ion concentrations in equilibrium with goethite as a function of pH 42 Figure 4.10 Total As concentrations without scorodite precipitation in equilibrium with goethite as a function of pH 43 Figure 4.11 The uptake of DMA as a function of pH and concentrations of NaNO3. Goethite concentration is 1.98 g L-1, and the initial DMA concentration is 68 µM. 45 Figure 4.12 The uptake of DMA as a function of pH in 1.0 M NaCl, NaNO3 and NaClO3. Goethite concentration is 1.98 g L-1, and the initial DMA concentration is 60 µM. 46 Figure 4.13 The uptake of DMA as a function of pH in an open and a close system in 0.01 M NaNO3. Goethite concentration is 1.2 g L-1, and the initial DMA concentration is 59 µM. 48 Figure 4.14 The uptake of MMA as a function of pH and concentrations of NaNO3. Goethite concentration is 1.98 g L-1, and initial the MMA concentration is 213 µM 48 vii Figure 4.15 The uptake of MMA as a function of pH in an open and a close system in 0.01 M NaNO3. Goethite concentration is 1.2 g L-1, and the initial MMA concentration is 93 µM. 49 Figure 4.16 The uptake of arsenate as a function of pH and NaNO3 concentrations. Goethite concentration is 1.98 g L-1, and the initial arsenate concentration is 180 µM 50 Figure 4.17 The uptake of arsenate as a function of pH in an open and a close system in 0.01 M NaNO3. Goethite concentration is 1.2 g L-1, and the initial arsenate concentration is 72 µM. 51 Figure 4.18 The uptake of the three arsenic species on goethite as function of pH in 0.01 M NaNO3. Goethite concentration is 1.2 g L-1 and the initial arsenic concentration is 70 µM. 52 Figure 4.19 Adsorption isotherms of the three arsenic species on goethite at pH 4.00 in 0.01 M NaNO3. Goethite concentration is 1.2 g L-1 57 Figure 4.20 Adsorption isotherms of the three arsenic species on goethite at pH 7.20 in 0.01 M NaNO3. Goethite concentration is 1.2 g L-1 57 Figure 4.21 Logarithmic plots of adsorption of MMA and arsenate at two pH values in 0.01 M NaNO3. Filled symbols for adsorption at pH 4.00 and open symbols for adsorption at pH 7.20. Goethite concentration is 1.2 g L-1. .60 Figure 4.22 Adsorption isotherms of DMA at pH 4.00 in 0.1 M NaNO3 with four solids concentrations .61 Figure 4.23 Adsorption isotherms of MMA at pH 4.00 in 0.1 M NaNO3 with four solids concentrations .62 Figure 4.24 Adsorption isotherms of arsenate at pH 4.00 in 0.1 M NaNO3 with four solids concentrations .63 Figure 4.25 Surface coverages (a) and zeta potential (b) of DMA adsorbed on goethite as a function of pH in 0.001 M NaNO3 with three initial DMA concentrations. Goethite concentration is 0.25 g L-1 67 Figure 4.26 Surface coverages (a) and zeta potential (b) of MMA adsorbed on goethite as a function of pH in 0.001 M NaNO3 with three initial MMA concentrations. Goethite concentration is 0.25 g L-1 68 Figure 4.27 Surface coverages (a) and zeta potential (b) of arsenate adsorbed on goethite as a function of pH in 0.001 M NaNO3 with three initial arsenate concentrations. Goethite concentration is 0.25 g L-1 69 Figure 4.28 The effective particle sizes of goethite at different initial DMA concentrations in 0.001 M NaNO3. Goethite concentration is 0.25 g L-1. .70 viii References and Surface Complexation Modeling, J. Colloid Interface Sci., 234, pp.204-216. 2001. Grafe, M., M. J. Eick and P. R. Grossl. Adsorption of Arsenate (V) and Arsenite (III) on Goethite in the Presence and Absence of Dissolved Organic Carbon, Soil Sci. Soc. Am. J., 65, pp.1680-1687. 2001. Grossl, P. R., M. Eick, D. L. Sparks, S. Goldberg and C. C. Ainsworth. Arsenate and Chromate Retention Mechanisms on Goethite. 2. Kinetic Evaluation Using a Pressure-Jump Relaxation Technique, Environ. Sci. Technol., 31, pp.321-326. 1997. Gunnarsson, M. Z. Abbas, E. Ahlberg, S. Gobom and S. Nordholm. Corrected DebyeHuckel Analysis of Surface Complexation: II. A Theory of Surface Charging, J. Colloid Interface Sci., 249, pp.52-61. 2002. Gupta, S. and K. Y. Chen. Arsenic Removal by Adsorption, J. Water Pollut. Control Fed., 50, pp.493-506. 1978. Hiemstra, T., J. C. M. Dewit and W. H. van Riemsdijk. Multisite Proton Adsorption Modeling at the Solid-Solution Interface of (hydr)Oxides - A New Approach .2. Application to Various Important (hydr)Oxides, J. Colloid Interface Sci., 133, pp.105-117. 1989a. Hiemstra, T. and W. H. van Riemsdijk. A Surface Structura Approach to Ion Adsorption: The Charge Distribution (CD) Model, J. Colloid Interface Sci., 179, pp.488-508. 1996. Hiemstra, T. and W. H. van Riemsdijk. Surface Structural Ion Adsorption Modeling of Competitive Binding of Oxyanions by Metal (hydr)Oxides, J. Colloid Interface Sci., 210, pp.182-193. 1999. 149 References Hiemstra, T., W. H. van Riemsdijk and G. H. Bolt. Multisite Pproton Adsorption Modeling at the Solid-Solution Interface of (hydr)Oxides - A New Approach. 1. Model Description and Evaluation of Intrinsic Reaction Constants, J. Colloid Interface Sci., 133, pp.91-104. 1989b. Hiemstra, T., P. Venema and W. H. van Riemsdijk. Intrinsic Proton Affinity of Reactive Surface Groups of Metal (hydr)oxides: The Bond Valence Principle, J. Colloid Interface Sci., 184, pp.680-692. 1996. Hindmarsh, J. T., C. O. Abernathy, G. R. Peters and R. F. Mchurdy. Environmental Aspects of Arsenic Toxicity. In Heavy Metals in the Environment, ed by B. Sakar, pp. 217-231. New York: Marcel Dekker. 2002. Hingston, F. J. A Review of Anion Adsorption. In Adsorption of Inorganics at the SolidLiquid Interfaces, ed by M. A. Anderson and A. J. Rubin, pp.51-90. Ann Arbor: Ann Arbor Science. 1981. Hingston, F. J., A. M. Posner and J. P. D. F. S. Quirk. Competitive Adsorption of Negatively Charged Ligands on Oxides Surfaces, Discuss. Faraday Soc., 52, pp.334-342. 1971. Jackson, B. P. and W. P. Miller. Effectiveness of Phosphate and Hydroxide for Desorption of Arsenic and Selenium Species from Iron Oxides. Soil Sci.Soc.Am.J., 64, pp.616-1622. 2000. Jain, A., K. P. Raven and R. H. Loeppert. Arsenite and Arsenate Adsorption on Ferrihydrite: Surface Charge Reduction and Net OH- Release Stoichiometry, Environ. Sci. Technol., 33, pp.1179-1184. 1999. 150 References Janusz, W.L. Electrical Double Layer at the Metal Oxide-electrolyte Interface. In Interfacial Forces and Fields: Theory and Applications, ed by J.P.Hsu, pp.135-207. New York: Marcel Dekker. 1998. Karim, M. Arsenic in Groundwater and Health Problems in Bangladesh, Water Res., 34, pp.304-310. 2000. Kenyon, E. M. and M. F. Hughes. A Concise Review of the Toxicity and Carcinogenicity of Dimethylarsenic Acid (DMA), Toxicology, 160, pp. 227-236. 2001. Kosmulski, M., S. Durand-Vidal, E. Maczka and J. B. Rosenholm. Morphology of Synthetic Goethite Particles, J. Colloid Interface Sci., 271, pp.261-269. 2004. Kovaceive, D., Cop, A., Bradetic, A., Kallay, N., Pohlmeier, A., Narres, H.-D. and H. Lewandowski. Interfacial Equilibrium at a Goethite Aqueous Interface in Presence of Amino Acids, Progr.Colloid Polym Sci., 117, pp.32-36, 2001 Kreller, D. I., G. Gibson, G.W. vanLoon and J. H. Horton. Chemical Force Microscopy Investigation of Phosphate Adsorption on the Surface of Iron (III) Oxyhdroxide Particles, J. Colloid Interface Sci., 254, pp.205-213. 2002. Ladeira, A. C. Q., V. S. T. Ciminelli, H. A. Duarte, M. C. M. Alves and A. Y. Ramos. Mechanism of Anion Retention from EXAFS and Density Functional Calculations: Arsenic (V) Adsorbed on Gibbsite, Geochim. Cosmochim. Acta, 65, pp.1211-1217. 2001. Ler, A. Metal Ions Adsorption on Phosphated and Unphosphated Goethite. M.Eng.Thesis, National University of Singapore. 2001. Li, L. Phosphate Adsorption on Goethite (alpha-FeOOH). M.Eng.Thesis, National University of Singapore. 1998. 151 References Li, L. and R. Stanforth. Distinguishing Adsorption and Surface Precipitation of Phosphate on Goethite (alpha-FeOOH), J. Colloid Interface Sci., 230, pp.12-21. 2000. Liu, F., A. D. Cristofaro and A. Violante. Effect of pH, Phosphate and Oxalate on the Adsorption/Desorption of Arsenate on/from Goethite, Soil Sci., 166, pp.197-208. 2001. Lumsdon, D. G., A. R. Fraser, J. D. Russell and N. T. Livesey. New Infrared Band Assignments for the Arsenate Ion Adsorbed on Synthetic Goethite (alpha-FeOOH). J. Soil Sci., 35, pp.381-386. 1984. Lumsdon, D. G. and L. J. Evans. Surface Complexation Model Parameters for Goethite (alpha-FeOOH), J. Colloid Interface Sci., 164, pp.119-125. 1994. Lutzenkirchen, J. Comparison of 1-pK and 2-pK Versions of Surface Complexation Theory by the Goodness of Fit in Describing Surface Charge Data of (hydr)Oxides, Environ. Sci. Technol., 32, pp.3149-3154. 1998. Lutzenkirchen, J. Surface Complexation Models of Adsorption: A Critical Survey in the Context of Experimental Data. In Adsorption: Theory, Modeling, and Analysis, ed by J. Toth, pp.631-710. New York: Marcel Dekker. 2002. Lutzenkirchen, J., J.-F. Boily, L. Lovgren and S. Sjoberg. Limitations of the Potentiometric Titration Technique in Determining the Proton Active Site Density of Goethite Surfaces, Geochim. Cosmochim. Acta., 66, pp.3389-3396. 2002. Madrid, L. and P. Dearambarri. Adsorption of Phosphate by two Iron Oxides in Relation to Their Porosity, J. Soil Sci., 36, pp.523-530. 1985. Malotky, D. T. and M. A. Anderson. The Adsorption of the Potential Determining Arsenate Anion on Oxide Surfaces. Colloid and Interface Science: Proceedings of the International Conference on Colloids and Surfaces, 50th Colloid and Surface 152 References Science Symplosium, Vol.4, ed by M. Kerker, pp.281-295. New York: Academic Press. 1976. Manceau, A. The Mechanism of Anion Adsorption on Iron-Oxides - Evidence for the Bonding of Arsenate Tetrahedra on Free Fe(O,Oh)(6) Edges, Geochim. Cosmochim. Acta, 59, pp.3647-3653. 1995. Mandal, B. K. and K. T. Suzuki. Arsenic around the World: A Review, Talanta, 58, pp. 201-235. 2002. Manning, B. A. and S. Goldberg. Modeling Competitive Adsorption of Arsenate with Phosphate and Molybdate on Oxide Minerals, Soil Sci. Soc. Am. J., 60, pp.121131. 1996. Matis, K. A., A. I. Zouboulis, D. Zamboulis and A. V. Valtadorou. Sorption of As(V) by Goethite Particles and Study of Their Flocculation, Water, Air, Soil Pollut. A, 111, pp.297-316. 1999. Naono, H. and R. Fujiwara. Micropore Formation due to Thermal Decomposition of Acicular Microcrystals of alpha-FeOOH, J. Colloid Interface Sci., 73, pp.406-415. 1980. Naono, H., K. Nakai, T. Sueyoshi and H. Yagi. Porous Texture in Hematite Derived from Goethite: Mechanism of Thermal Decomposition of Goethite, J. Colloid Interface Sci., 120, pp.439-450. 1987. Neoh, L. S. Desorption of Phosphate from Goethite. Ph.D Thesis, University of Western Australia. 1975. O'Reilly, S. E., D. G. Strawn and D. L. Sparks. Residence Time Effects on Arsenate Adsorption/Desorption Mechanisms on Goethite, Soil Sci. Soc. Am. J., 65, pp.6777. 2001. 153 References Parravano, G., and M. Boudart. Chemisorption and Catalysis on Oxide Semiconductor. In Advances in Catalysis Vol.7, ed by W. G. Frankenburg, V. I. Komarewsky, and E. K. Rideal, pp.47-74. New York: Academic Press. 1955. Pavlatou, A. and N. A. Polyzopoulos. The Role of Diffusion in the Kinetics of Phosphate Desorption-the Relevance of the Elovich Equation, J. Soil Sci., 39, pp.425-436. 1988. Petrick, J. S., B. Jagadish, E. A. Mash and H. V. Aposhian. Monomethylarsonous Acid (MMA) and Arsenite: LD50 in Hamsters and in Vitro Inhibition of Pyruvate Dehydrogenase, Chem. Res. Toxicol, 14, pp.651-656. 2001. Powder Diffraction File. pp.155-160. Newtown Square: International Centre for Diffraction Data.1998. Prelot, B., F. Villieras, M. Pelletier, G. Gerard, F. Gaboriaud, J. J. Ehrhardt, J. Perrone, M. Fedoroff, J. Jeanjean, G. Lefevre, L. Mazerolles, J. L. Pastol, J. C. Rouchaud and C. Lindecker. Morphology and Surface Heterogeneities in Synthetic Goethites, J. Colloid Interface Sci., 261, pp.244-254. 2003. Raven, K. P., A. Jain and R. H. Loeppert. Arsenate Adsorption on Ferrihydrite: Kinetics, Equilibrium, and Adsorption Envelopes, Environ. Sci. Technol., 32, pp.344-349. 1998. Rietra, R., T. Hiemstra and W. H. van Riemsdijk. The Relationship between Molecular Structure and Ion Adsorption on Variable Charge Minerals, Geochim. Cosmochim. Acta, 63, pp.3009-3015. 1999. Rietra, R., T. Hiemstra and W. H. van Riemsdijk. Electrolyte Anion Affinity and Its Effect on Oxyanion Adsorption on Goethite, J. Colloid Interface Sci., 229, pp.199-206. 2000. 154 References Rietra, R., T. Hiemstra and W. H. Van Riemsdijk. Interaction between Calcium and Phosphate Adsorption on Goethite, Environ. Sci. Technol., 35, pp.3369-3374. 2001. Rouquerol, F., J. Rouquerol and K. S. W. Sing. Adsorption by Powders and Porous Solids : Principles, Methodology and Applications. pp.1-27. San Diego: Academic Press. 1999. Rudzihksi, W. and P. Panczyk. Surface Heterogeneity Effect on Adsorption Equilibria and Kinetics: Rationalization of the Elovich Equation. In Surfaces of Nanoparticles and Porous Materials, ed by J. A. Schwarz and C. I. Contescu, pp.355-391. New York: Marcel Dekker. 1998. Ryden, J. C., J. R. Mclaughlin and J. K. Syers. Mechanisms of Phosphate Sorption by Soils and Hydrous Ferric Oxide Gel, J.Soil Sci., 28, pp.72-92. 1977. Saito, T., L. K. Koopal, W. H. van Riemsdijk, S. Nagasaki and S. Tanaka. Adsorption of Humic Acid on Goethite: Isotherms, Charge Adjustments, and Potential Profiles, Langmuir, 20, pp.689-700. 2004. Saurez, D. L., S. Goldberg and C. Su. Evaluation of Oxyanion Adsorption Mechanisms on Oxides Using FTIR Spectroscopy and Electrophoretic Mobility. In Mineral-Water Interfacial Reaction: Kinetics and Mechanism, ed by D. L. Sparks and T. J. Grundl, pp.136-178. Washingtown,DC: Amercian Chemical Society. 1999. Schindler, P. W. and H. R. Kamber. Die Aciditat von Silanolgruppen, Helv. Chim. Acta, 51, pp.1781-1786. 1968. Shayan, A. and B. G. Davey. A Universal Dimensionless Phosphate Sdsorption Isotherm for Soil, Soil Sci. Soc. Am. J., 42, pp.878-884. 1978. 155 References Smith, R.W. and E. A. Jenne. Recalculation, Evaluation, and Prediction of Surface Complexation Constants for Metal Adsorption on Iron and Manganese Oxides, Environ. Sci. Technol., 25, pp.525-531.1991. Sparks, D. L. Environmental Soil Chemistry. pp.133-244. San Diego: Academic Press. 2003. Stanforth, R. Adsorption Kinetics and Isotopic Exchange of Phosphate on Goethite. Ph.D Thesis, University of Wisconsin-Madison. 1981. Strauss, R., G. W. Brummer and N. J. Barrow. Effects of Crystallinity of Goethite. 2. Rates of Sorption and Desorption of Phosphate, Eur. J. Soil Sci., 48, pp.101-114. 1997. Stumm, W. Chemistry of the Solid-Water Interface. pp.43-157. New York: John Wiley & Sons. 1992. Stumm, W., C. P. Huang and S. R. Jenkins. Specific Chemical Interactions Affecting the Stability of Dispersed System, Croatica Chem. Acta, 42, pp.223-245. 1970. Sun, X. H. and H. E. Doner. An Investigation of Arsenate and Arsenite Bonding Structures on Goethite by FTIR, Soil Sci., 161, pp.865-872. 1996. Tejedor-Tejedor, M. I. and M. A. Anderson. Protonation of Phosphate on the Surface of Goethite as Studied by CIR-FTIR and Electrophoretic Mobility, Langmuir, 6, pp. 602-611.1990. Trivedi, P., L. Axe and J. Dyer. Adsorption of Metal Ions onto Goethite, Single-adsorbate and Competitive Systems, Colloid Surf. A-Physicochem. Eng. Asp. 191, pp.107121. 2001. 156 References Van Riemsdijk, W. H., G. H. Bolt, L. K. Koopal and J. Blaakmeer. Electrolyte Adsorption on Heterogeneous Surfaces, Adsorption Models, J.Colloid Interface Sci., 109, pp. 219-228. 1986. Van Riemsdijk, W. H. and T. Hiemstra (1993). Adsorption to Heterogeneous Surfaces. In Metals in Groundwater, ed by H.E.Allen, E.E. Perdue and D.S.Brown, pp.1-31 Boca Raton: Lewis Publishers. 1993. Vanaderdeelen, J. and L. Baert. Adsorption and Exchangeability of Phosphate on Gibbsite, Pedologie, XXI, pp.360-366. 1971. Vangeen, A., A. P. Robertson and J. O. Leckie. Complexation of Carbonate Species at the Goethite Surface-Implications for Adsorption of Metal-Ions in Natural-Waters, Geochim. Cosmochim. Acta, 58, pp.2073-2086. 1994. Venema, P., T. Hiemstra, P. G. Weidler and W. H. van Riemsdijk. Intrinsic Proton Affinity of Reactive Surface Groups of Metal (Hydr) Oxides: Application to Iron (hydr) Oxides, J. Colloid Interface Sci., 198, pp.282-295. 1998. Villalobos, M. and J. O. Leckie. Carbonate Adsorption on Goethite under Closed and Open CO2 Conditions, Geochim. Cosmochim. Acta, 64, pp.3787-3802. 2000. Villalobos, M. and J. O. Leckie. Surface Complexation Modeling and FTIR Study of Carbonate Adsorption to Goethite, J. Colloid Interface Sci., 235, pp.15-32. 2001. Villalobos, M., M. A. Trotz and J. O. Leckie. Variability in Goethite Surface Site Density: Evidence from Proton and Carbonate Sorption, J. Colloid Interface Sci., 268, pp. 273-287. 2003. Violante, A. and M. Pigna. Competitive Sorption of Arsenate and Phosphate on Different Clay Minerals and Soils, Soil Sci. Soc. Am. J., 66, pp.1788-1796. 2002. 157 References Waltham, C. A. and M. J. Eick. Kinetics of Arsenic Adsorption on Goethite in the Presence of Sorbed Silicic Acid, Soil Sci. Soc. Am. J., 66, pp.818-825. 2002. Watanabe, C., A. Kawata, N. Sudo, M. Sekiyama, T. Inaoka, M. Bae and R. Ohtsuka. Water Intake in an Asian Population Living in Arsenic-Contaminated Area, Toxicol. Appl. Pharmacol., 198, pp.272-282. 2004. Waychunas, G. A., B. A. Rea, C. C. Fuller and J. A. Davis. Surface-chemistry of Ferrihydrite .1. EEAFS Studies of the Geometry of Coprecipitated and Adsorbed Arsenate, Geochim. Cosmochim. Acta, 57, pp.2251-2269.1993. Weidler, P. G., G. Degovics and P. Laggner. Surface Roughness Created by Acidic Dissolution of Synthetic Goethite Monitored with SAXS and N2-adsorption Isotherms, J. Colloid Interface Sci., 197, pp.1-8. 1998. Westall, J. and H. Hohl. A Comparison of Electrostatic Models for the Oxide/Solution Interface, Adv.Colloid Interface Sci., 12, pp.265-294. 1980. Willett, I. R., C. J. Chartres and T. T. Nguyen. Migration of Phosphate into Aggregated Particles of Ferrihydrite, J.Soil Sci., 39, pp.275-282. 1988. Xu, H, Allard, B. and A. Grimvall. Effects of Acidification and Natural Organic Materials on the Mobility of Arsenic in the Environment, Water Air Soil Pollut, 57-58, pp.269-286. 1991. Zeltner, W. A. and M. A. Anderson. Surface-charge Development at the Goethite Aqueous-Solution Interface -Effects of CO2 Adsorption, Langmuir, 4, pp.469-474. 1988. Zhao, H. S. The Competitive Adsorption of Phosphate and Arsenate on Goethite. M.Eng. Thesis, National University of Singapore. 2000. 158 References Zhao, H. S. and R. Stanforth. Competitive Adsorption of Phosphate and Arsenate on Goethite, Environ. Sci. Technol., 35, pp.4753-4757. 2001. Zhong, B. Proton Interaction during Phosphate Adsorption on Goethite. M.Eng. Thesis, National University of Singapore. 2004. 159 Appendices Appendices A Desorbility of arsenate at pH 4.00 using 0.1 M NaNO3 solution 3.0 Langmuir fitting 2.5 -2 Γ (µmol m ) 2.0 1.5 1.0 0.5 0.0 100 200 300 400 500 600 Ce(µM) Figure A.1 Adsorption isotherm of arsenate at pH 4.00 in 0.1 M NaNO3. Goethite concentration is 1.2 g L-1. The adsorption isotherm of arsenate at pH 4.00 is well described by the following equation: Γ = 2.92 × 0.12Ce + 0.12Ce (A.1) The surface coverage of arsenate equilibrium with 40 µM arsenate is 2.41 µmol m-2 based on equation A.1. After replacing arsenate solution with 0.1 M NaNO3 at pH the surface coverage of arsenate can be calculated if the adsorption of arsenate is assumed to be reversible. Let the equilibrium concentration of arsenate to be C, and the surface coverage 160 Appendices of arsenate Γ after desorption reaches equilibrium, then Γ and C can be calculated from following two equations: Γ = 2.92 × 0.12C + 0.12C 1.2 × 27 × Γ + C = 27 × 1.2 × 2.41 Γ is 1.92 µmol m-2, corresponding to a desorbility of 20%. 161 (A.2) (A.3) Appendices B Fraction of various charged hydroxyls on the goethite surface We consider the adsorption of ions on the goethite surface a result of the following surface reactions: int K1 FeOH + H + ←⎯⎯ → FeOH 2+ int K2 FeO − + H + ←⎯⎯ → FeOH int KA FeOH 2+ + NO3− ←⎯⎯ → FeOH 2+ − NO3− int KC FeO − + Na + ←⎯⎯ → FeO − − Na + (B.1) (B.2) (B.3) (B.4) The mass equations for the surface sites (reaction B.1 and B.2), and the formation of ion pairs (reaction B.3 and B.4) are: K1int = [ FeOH 2+ ] exp( Fψ / RT ) [ FeOH ]{H + } (B.5) K 2int = [ FeOH ] exp( Fψ / RT ) [ FeO − ]{H + } (B.6) K Aint = [ FeOH 2+ − NO3− ] exp(− Fψ β / RT ) [ FeOH 2+ ]{NO3− } (B.8) K Cint = [ FeO − − Na + ] exp( Fψ β / RT ) [ FeO − ]{Na + } (B.9) N s = [ FeOH ] + [ FeOH 2+ ] + [ FeO − ] + [ FeOH 2+ − NO3− ] + [ FeO − − Na + ] (B.10) Introducing the notation: [ FeOH ] = Ns + K + f + + K − f − + K A f A + KC fC (B.11) [ FeOH 2+ ] K+ f+ θ+ = = Ns + K + f + + K − f − + K A f A + KC fC (B.12) θ0 = 162 Appendices θ− = [ FeO − ] K− f− = Ns + K + f + + K − f − + K A f A + KC fC (B.13) θA = [ FeOH 2+ − NO3− ] KA fA = Ns + K + f + + K − f − + K A f A + KC fC (B.14) θC = KC fC [ FeO − − Na + ] = + K + f + + K − f − + K A f A + KC fC Ns (B.15) f + = exp(− f − = exp( Fψ − 2.3 pH ) RT Fψ + 2.3 pH ) RT f A = {NO3− }exp[ f C = {Na + }exp[ K+ = K int (B.16) (B.17) F (ψ β −ψ ) RT F (ψ −ψ β ) K − = int K2 RT − 2.3 pH ] (B.18) + 2.3 pH ] (B.19) KA = K K int [ FeOH 2+ ] − [ FeO − ] = (θ + − θ − ) N s = ( int A K Cint K C = int K2 (B.20) K+ f+ − K− f− ) N s (B.21) + K + f + + K − f − + K A f A + KC fC If Ki and fi (i=+,-,A,C) are constant before and after anions adsorption, then the value of right hand of equation B.21 will reduce after adsorption because the Ns decreases. 163 Appendices C Publications 1. Zhang J.S., Stanforth R., Arsenate, monomethylarsonate, and dimethylarsinate adsorption on goethite (α -FeOOH), 77th ACS Colloid and Surface Science Symposium, Atlanta, Georgia, June 2003. 2. Zhang J.S., Stanforth R., The slow adsorption reaction between arsenics species and goethite (α-FeOOH): diffusion or heterogeneous surface reaction control, Langmuir 2005, 21: 2895-2901. 3. Zhang J. S., Stanforth, R., Pehkenon, S.O., Effect of replacing hydroxyls with methyl groups on arsenic (V) species adsorption on goethite (α-FeOOH) (Submitted to Journal of Colloid and Interface Science). 4. Zhang J.S., Stanforth R., Pehkenon, S.O.,Competitive Adsorption between Arsenic Species and Phosphate on Goethite (α-FeOOH). (In preparation) 5. Zhang J.S., Stanforth R., Pehkenon, S.O., Investigate Chemical Properties of Surface Hydroxyls on the Goethite (α-FeOOH) Surface. (In preparation) 164 [...]... Volume of goethite suspension (L) V1 Volume of acid used in back titration (L) V2 Volume of arsenic stock solution added to goethite suspension (L) z Charge of ions α Parameter of Elovich equation or the protonation degree of arsenic β Parameter of Elovich equation or the protonation degree of arsenic γ Protonation degree of singly coordinated groups in 2-pK model δ Protonation degree of adsorbed arsenate. .. plot of Γ vs ln t Goethite concentration is 1.98 g L-1, and the initial arsenate concentration is 130 µM .79 Figure 4.40 Effect of mixing methods (ultrasonication vs magnetic stirring) on the adsorption kinetics of arsenate at pH 4.20 in 0.001 M NaNO3 Goethite concentration is 1.98 g L-1 and the initial arsenate concentration is 120 µM .82 ix Figure 4.41 Adsorption (at pH 4.00) and desorption... xiii LIST OF SYMBOLS C Concentration of acid or base used in acid-base titration (µM) or constant capacity in equation 4.45 (F m-2) CA,s Concentration of stock arsenic solution (µM) CA,e Equilibrium concentration of arsenic (µM) C0 Initial concentration (µM) Cd Concentration of arsenic in desorption solution (µM) Ce Equilibrium concentration (µM) CH Concentration of acid used in back titration (µM) Cs... initial arsenate concentration is 120 µM 74 Figure 4.34 Adsorption of DMA on goethite at pH 4.00 at three NaNO3 concentrations as described by a plot of Γ vs ln t Goethite concentration is 1.98 g L-1, and the initial DMA concentration is 130 µM .75 Figure 4.35 Adsorption of MMA on goethite at pH 4.00 at three NaNO3 concentrations as described by a plot of Γ vs ln t Goethite concentration... Chapter 1 introduction on the adsorption of DMA and MMA on goethite (16 Bowell, 1994; Xu et al., 1991; Lafferty and Loppert, 2005) Iron oxides and oxyhydroxides such as hematite and goethite show a strong affinity for arsenic and numerous studies have quantified and modeled arsenic adsorption on goethite (Cornell and Schwertmann, 2003) 1.2 Arsenic adsorption on goethite Adsorption data is frequently... described by a plot of Γ vs ln t Goethite concentration is 1.98 g L-1, and the initial arsenate concentration is 130 µM .78 Figure 4.38 Adsorption of MMA on goethite at three pH values in 0.1 M NaNO3 as described by a plot of Γ vs ln t Goethite concentration is 1.98 g L-1, and the initial arsenate concentration is 217 µM .78 Figure 4.39 Adsorption of arsenate on goethite at three pH values... concentration is 1.98 g L-1, and the initial MMA concentration is 217 µM 76 Figure 4.36 Adsorption of arsenate on goethite at pH 4.00 at three NaNO3 concentrations as described by a plot of Γ vs ln t Goethite concentration is 1.98 g L-1, and the initial arsenate concentration is 120 µM .76 Figure 4.37 Adsorption of DMA on goethite at two pH values in 0.1 M NaNO3 as described by a plot of Γ... Relationship between the proton-MMA adsorption ratio and the surface coverage of MMA at two pH values Goethite concentration is 2.0 g L-1 and NaNO3 concentration is 0.001M .104 Figure 4.50 Zeta potential as a function of MMA surface coverages at pH 4.00 and 6.77 Goethite concentration is 0.25 g L-1 and NaNO3 concentration is 0.001M 105 Figure 4.51 Relationship between proton -arsenate adsorption. .. pH 10.0 and 12.0) kinetics of DMA in 0.1 M NaNO3 Goethite concentration is 1.98 g L-1, and the initial DMA concentration is 130 µM 84 Figure 4.42 Adsorption (at pH 4.00) and desorption (at pH12.0) kinetics of MMA and arsenate in 0.1 M NaNO3 .Goethite concentrations is 1.98 g L-1 The initial concentration of MMA is 217 µM and arsenate is 120 µM .85 Figure 4.43 Two proton affinity constants... properties of surface groups on the goethite surface and the adsorption mechanism of two methylated arsenicals on goethite by comparing the adsorption equilibrium and kinetics of arsenate, MMA, and DMA on goethite at the same experimental conditions The objectives of this study are given below: 1 Effect of methyl groups in arsenic compounds on its affinity for goethite DMA (pK=6.27) (CRC Handbook of Chemistry . purpose of this study was to investigate the adsorption mechanism of three arsenic species – arsenate, monomethylarsonate (MMA), and dimethylarsinate (DMA)- on goethite and chemical properties of. concentrations. Goethite concentration is 1.98 g L -1 , and the initial arsenate concentration is 120 µM 74 Figure 4.34 Adsorption of DMA on goethite at pH 4.00 at three NaNO3 concentrations. deviation of the replicates and standard deviation of proton-anion adsorption ratios. 97 Table 4.15 Proton-DMA adsorption data at pH 4.25 a 98 xiii Table 4.16 Proton-DMA adsorption data