Iron arsenic adsorption

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... 

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... 

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. 

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. 

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. 

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. 

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. 

Goldberg S. (1986) Chemical modeling of arsenate adsorption on aluminum and iron oxide minerals. Soil Sci. Soc. Am. J. 50, 1154-1157. 

FeClj was then added to the slurries to evaluate the effect of HFO precipitation on As(V) adsorption. Additional synthetic ground water was added to each slurry to make the final volume 500 mL. In one experiment, 10 mg/L Fe(III) was added. The slurries were then equilibrated for 3 days to allow complete precipitation of HFO. NaOH was then added to slowly increase pH. Slurries were equilibrated for 1 day following each addition of 0.1 N NaOH, followed by 0.4 itm filtering of 20 mL aliquots for As(V) and P(V) analysis. Additional FeCl3 was then added to increase the Fe(III) concentration to 100 mg/L and the experiment was repeated as above. Arsenate adsorption for the 100 mg/L Fe(III) concentration was measured for initial As(V) concentrations of 145 and 1000 lig/L. The iron additions of 10 and 100 mg/L are equivalent to 0.1 and 1.0 mg/g of basalt. 

VIBRATIONAL SPECTROSCOPY Infrared and Raman spectroscopies have proven to be useful techniques for studying the interactions of ions with surfaces. Direct evidence for inner-sphere surface complex formation of metal and metalloid anions has come from vibrational spectroscopic characterization. Both Raman and Fourier transform infrared (FTIR) spectroscopies are capable of examining ion adsorption in wet systems. Chromate (Hsia et al., 1993) and arsenate (Hsia et al., 1994) were found to adsorb specifically on hydrous iron oxide using FTIR spectroscopy. Raman and FTIR spectroscopic studies of arsenic adsorption indicated inner-sphere surface complexes for arsenate and arsenite on amorphous iron oxide, inner-sphere and outer-sphere surface complexes for arsenite on amorphous iron oxide, and outer-sphere surface complexes for arsenite on amorphous aluminum oxide (Goldberg and Johnston, 2001). These surface configurations were used to constrain the surface complexes in application of the constant capacitance and triple layer models (Goldberg and Johnston, 2001). 

Apted MJ, Waychunas GA, Brown GE Jr (1985) Structure and speciation of iron complexes in aqueous solutions determined by X-ray absorption spectroscopy. Geochim Cosmochim Acta 492081-2089 Arai Y, Elzinga EJ, Sparks DL (2001) X-ray absorption spectroscopic investigation of arsenite and arsenate adsorption at the aluminum oxide-water interface. J Colloid Interface Sci 235 80-88. 

Unlike authigenic mineral precipitation, sorption is clearly an important mechanism controlling dissolved As(V) concentrations. Arsenic adsorption onto oxide minerals (specifically iron oxides and hydroxides) has been invoked in interpreting the occurrence and mobility of arsenic in lake sediments (68,69,73,74,89,90),... 

The chemical part AG° corresponds in most cases to specific adsorption on reactive surface hydroxyl groups, whereas the electrical part AG is due to the cou-lombic interaction. In the first part, it arises quite naturally the concept of binding site as the place on the surface where the adsorbate binds these sites can be associated with individual hydroxyl groups, but not necessarily, because when bidentate adsorption takes place, as in the case of phosphate or arsenate adsorption onto iron oxides, two hydroxyls may be considered as forming a single site. 

In addition to effects on the concentration of anions, the redox potential can affect the oxidation state and solubility of the metal ion directly. The most important examples of this are the dissolution of iron and manganese under reducing conditions. The oxidized forms of these elements (Fe(III) and Mn(IV)) form very insoluble oxides and hydroxides, while the reduced forms (Fe(II) and Mn(II)) are orders of magnitude more soluble (in the absence of S( — II)). The oxidation or reduction of the metals, which can occur fairly rapidly at oxic-anoxic interfaces, has an important "domino" effect on the distribution of many other metals in the system due to the importance of iron and manganese oxides in adsorption reactions. In an interesting example of this, it has been suggested that arsenate accumulates in the upper, oxidized layers of some sediments by diffusion of As(III), Fe(II), and Mn(II) from the deeper, reduced zones. In the aerobic zone, the cations are oxidized by oxygen, and precipitate. The solids can then oxidize, as As(III) to As(V), which is subsequently immobilized by sorption onto other Fe or Mn oxyhydroxide particles (Takamatsu et al, 1985). 

Liu F, De Cristofaro A, Violante A (2001) Effect of pH phosphate and oxalate on the adsorption/desorption of arsenate on/from goethite. Soil Sci 166 197-208 Livesey NT, Huang PM (1981) Adsorption of arsenate by soils and its relation to selected properties and anions. Soil Sci 131 88-94 Manceau A (1995) The mechanism of anion adsorption on iron oxides Evidence for the bonding of arsenate tetrahedra on free Fe(0, OH)6 edges. Geochim Cosmochim Acta 59 3647-3653. 

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