Arsenate adsorption

For a reconstmcted surface, the effect of an adsorbate can be to provide a more bulk-like enviromnent for the outemiost layer of substrate atoms, thereby lifting the reconstmction. An example of this is As adsorbed onto Si(l 11)-(7 X 7) [37]. Arsenic atoms have one less valence electron than Si. Thus, if an As atom were to replace each outemiost Si atom in the bulk-temiinated stmcture, a smooth surface with no impaired electrons would be produced, with a second layer consisting of Si atoms in their bulk positions. Arsenic adsorption has, in fact, been found to remove the reconstmction and fomi a Si(l 11)-(1 x l)-As stmcture. This surface has a particularly high stability due to the absence of dangling bonds. 

Arsenate is readily adsorbed to Fe, Mn and Al hydrous oxides similarly to phosphorus. Arsenate adsorption is primarily chemisorption onto positively charged oxides. Sorption decreases with increasing pH. Phosphate competes with arsenate sorption, while Cl, N03 and S04 do not significantly suppress arsenate sorption. Hydroxide is the most effective extractant for desorption of As species (arsenate) from oxide (goethite and amorphous Fe oxide) surfaces, while 0.5 M P04 is an extractant for arsenite desorption at low pH (Jackson and Miller, 2000). 

Arai Y, Elzinga EJ, Sparks DL (2001) X-ray absorption spettroscopy investigation of arsenite and arsenate adsorption on the aluminium oxide-water interface J Colloid Interf Sci 235 80-88... 

Hongshao Z, Stanforth R (2001) Competitive adsorption of phosphate and arsenate ongoethite. Environ Sci Technol 35 4753—4757 Hsia TH, Lo SL, Lin CF, Lee DY (1994) Characterization of arsenate adsorption on hydrous iron oxide using chemical and physical methods. Colloid Surface A 85 1-7... 

Kampf N, Scheinost AC, Schultze DG (2000) Oxides minerals. In Sumner ME (ed) Handbook of soil science, CRC Press, Boca Raton (FL), F125-F168 Jain A, Loeppert RH (2000) Effect of competing anions on the adsorption of arsenate and arsenite by ferrihydrite. J Environ Qual 29 1422-1430 Jain A, Raven KP, Loeppert RH (1999) Arsenite and arsenate adsorption on ferrihydrite surface charge reduction and net OH release stoichiometry. Environ Sci Technol 33 1179-1184... 

Lafferty BJ, Loeppert RH (2005) Methyl arsenic adsorption and desorption be-hatior on iron oxides. Environ Sci Technol 39 2120—2127 Le XC (2002) Arsenic speciation in the environment and humans. In Frankenberger WT Jr (ed) Environmental chemistry of arsenic. Marcel Dekker, Inc. New York, pp 95-116... 

Pigna M, Colombo C, Violante A (2003) Competitive sorption of arsenate and phosphate on synthetic hematites (in Italian). Proceedings XXI Congress of Societa Italiana Chimica Agraria SICA (Ancona), pp 70-76 Quirk JP (1955) Significance of surface area calculated from water vapour sorption isotherms by use of the B. E. T. equation. Soil Sci 80 423-430 Rancourt DG, Fortin D, Pichler T, Lamarche G (2001) Mineralogical characterization of a natural As-rich hydrous ferric oxide coprecipitate formed by mining hydrothermal fluids and seawater. Am Mineral 86 834-851 Raven K, Jain A, Loeppert, RH (1998) Arsenite and arsenate adsorption on ferrihydrite kinetics, equilibrium, and adsorption envelopes. Environ Sci Technol 32 344-349... 

Violante A, Krishnamurti GSR, Pigna M (2008) Mobility of trace elements in soil environments. In Violante A, Huang PM and Gadd G (eds) Wiley-JUPAC series on biophysico-chemical processes of metals and metalloids in soil environments. John Wiley Sons, Hoboken, USA Waltham AC, Eick MJ (2002) Kinetic of arsenic adsorption on goethite in the presence of sorbed silicic acid. Soil Sci Soc Am J 66 818-825 Waychunas GA, Fuller CC, Rea BA, Davis J (1996) Wide angle X-ray scattering (WAXS) study of two-line ferrihydrite structure Effect of arsenate sorption and counterion variation and comparison with EXAFS results. Geochim Cos-mochim Acta 60 1765-1781... 

Goldberg, S. Johnston, C.T (2001) Mechanisms of arsenic adsorption on amorphous oxi-... 

Izumi, F. (1993) Rietveld analysis program RIE-TAN and PREMOS and special applications. In Young, R.A. (ed.) The Rietveld Method, Oxford, Oxford University Press, 236-253 Jackson, B.P. Miller, W.P. (2000) Effectiveness of phosphate and hydroxide for desorption of arsenic and selenium species from iron oxides. Soil Sci. Soc. Am. J. 64 1616-1622 Jain, A. Raven, K.P. Loeppert, R.EI. (1999) Ar-senite and arsenate adsorption on ferrihy-drite Surface charge reductions and net OEI-release stoichiometry. Environ. Sci. Techn. 

Munch, J.C. Ottow, J.C.G. (1982) Einflufi von Zellkontakt und Eisen(III)-Oxidform auf die bakterielle Eisenreduktion. Z. Pflanzener-nahr. Bodenk. 145 66-77 Munoz, J.A., Gonzalo, A. Valiente, M. (2002) Arsenic adsorption by Fe(III)-loaded open-celled sponge. Thermodynamic and selectivity aspects. Envir. Sci. Techn. 36 3405-3411. Murad, E. Bishop, J.L. (2000) The infrared spectrum of synthetic akaganeite, P-EeOOH. Am. Min. 85 716-721... 

Rau, M. Rieck, D. Evans, J.W. (1987) Investigation of iron oxide reduction by TEM. Metallurgical Transactions 188 257-278 Raven, K.P. Jain, A. Loeppert, R.H. (1998) Ar-senite and arsenate adsorption on ferrihy-drite Kinetics, equilibrium, and adsorption envelopes. Environ. Sci. Techn. 32 344-349 Rea, B.A. Davis, J.A. Waychunas, G.A. (1994) Studies of the reactivity of the ferrihydrite surface by iron isotopic exchange and Moss-bauer spectroscopy. Clays Clay Min. 42 23-34... 

Figure 2.7 Stern (inner sphere and outer sphere) and Gouy arsenic adsorption complexes associated with the surfaces of iron oxide minerals.

Interferences with arsenic adsorption and ion exchange Dissolved organics and anions may interfere with arsenic adsorption and ion exchange in both natural environments and water treatment systems. In some cases, chemical species directly compete with arsenic for adsorption sites. They may also desorb and replace arsenic. Vanadium is one element that could interfere with the adsorption of arsenic onto mineral surfaces. In most cases, vanadium is not abundant in water. However, alkaline (pH 7.0-8.8) groundwaters in the loess aquifers of La Pampa, Argentina contain up to 12mgL 1 of vanadium (Smedley et al., 2005). The vanadium readily hinders the sorption of As(V) onto iron (III) (oxy)(hydr)oxides (Chapter 3). 

Besides phosphate, silica is known to commonly compete with As(V) for sorption/ion exchange sites on a wide variety of iron(III) and aluminum compounds (Clifford and Ghurye, 2002), 227 (Su and Puls, 2003), 2582 (Holm, 2002 Smith and Edwards, 2005 Zhang et al., 2004 McNeill, Chen and Edwards, 2002), 146. Silica may directly compete with arsenic for sites or polymerize on adsorbent surfaces and eliminate surface charges that are favorable for arsenic adsorption (Stollenwerk, 2003), 89. 

Goldberg, S. and Johnston, C.T. (2001) Mechanisms of arsenic adsorption on amorphous oxides evaluated using macroscopic measurements, vibrational spectroscopy, and surface complexation modeling. Journal of Colloid and Interface Science, 234(1), 204-16. 

Jain, A., Raven, K.P. and Foeppert, R.H. (1999) Arsenite and arsenate adsorption on ferrihydrite surface charge reduction and net OH - release stoichiometry. Environmental Science and Technology, 33(8), 1179-84. 

Lafferty, B.J. and Loeppert, R.H. (2005) Methyl arsenic adsorption and desorption behavior on iron oxides. Environmental Science and Technology, 39(7), 2120-27. 

Anderson, M.A., Ferguson, J.F. and Gavis, J. (1976) Arsenate adsorption on amorphous aluminum hydroxide. Journal of Colloid and Interface Science, 54, 391-99. 

Chen, T. (1994) Arsenate adsorption in soil and its mechanism. China Environmental Science, 5, 85-91. 

Dupont, L., Jolly, G. and Aplincourt, M. (2007) Arsenic adsorption on lignocellulosic substrate loaded with ferric ion. Environmental Chemistry Letters, 5(3), 125-29. 

Gu, Z., Deng, B. and Yang, J. (2007) Synthesis and evaluation of iron-containing ordered mesoporous carbon (FeOMC) for arsenic adsorption. Microporous and Mesoporous Materials, 102(1-3), 265-73. 

Jang, M., Shin, E.W., Park, J.K. and Choi, S.I. (2003) Mechanisms of arsenate adsorption by highly-ordered nano-structured silicate media impregnated with metal oxides. Environmental Science and Technology, 37(21), 5062-70. 

Lenoble, V., Bouras, O., Deluchat, V. et al. (2002) Arsenic adsorption onto pillared clays and iron oxides. Journal of Colloid and Interface Science, 255(1), 52-58. 

Maity, S Chakravarty, S., Bhattacharjee, S. and Roy, B.C. (2005) A study on arsenic adsorption on polymetallic sea nodule in aqueous medium. Water Research, 39, 2579-90. 

Munoz, J.A., Gonzalo, A. and Valiente, M. (2002) Arsenic adsorption by Fe(III)-loaded open-celled cellulose sponge. Thermodynamic and selectivity aspects. Environmental Science and Technology, 36(15), 3405-11. 

Zhang, Y., Yang, M., Dou, X.-M. et al. (2005) Arsenate adsorption on an Fe-Ce bimetal oxide adsorbent role of surface properties. Environmental Science and Technology, 39(18), 7246-53. 

Commonly, arsenite exhibits low adsorption potential for oxides or clay edges because the former exhibits high pKas (9.22 and 13.52). Recall that maximum adsorption of an oxyanion by an oxide takes place at pH closest to its pKa. Arsenate adsorption is nearly at maximum in the pH range of 3 to 11 because it encompasses the range of its three pKa values, 2.22, 6.98, and 11.52 (see Chapter 4). 

Fuller, C. C., J. A. Davis, and G. A. Waychunas. 1993. Surface chemistry of ferrihydrite Part 2. Kinetics of arsenate adsorption and coprecipitation. Geochim. Cosmochim. Acta 57 2271-2282. 

Goldberg, S., S. M. Lesch, D. L. Suarez, and N. T. Basta. 2005. Predicting arsenate adsorption by soils using soil chemical parameters in the constant capacitance model. Soil Sci. Soc. Am. J. 69 1389-1398. 

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