Arsenite adsorption

All procedures for removal of the arsenate were conducted by the method (ii). Feeding solutions used in the adsorption operation for arsenate were prepared by dissolving Na2HAs047H20 into water, and those used in the arsenite adsorption were prepared by dissolving NaAs02 into water. The pH of these solutions was adjusted with HNO3. 

Ona-Nguema, G., Morin, G., Juillot, F. et al. (2005) Jr. EXAFS analysis of arsenite adsorption onto two-line ferrihy-drite, hematite, goethite, and lepidocrocite. Environmental Science and Technology, 39(23), 9147-55. 

Masue, Y., Loeppert, R.H. and Kramer, T.A. (2007) Arsenate and arsenite adsorption and desorption behavior on coprecipitated aluminum iron hydroxides. Environmental Science and Technology, 41(3), 837-42. 

For the pH values of leachate in these experiments (6.5 to 7.5), the As(V) species in reactions 6 and 7 predominate. Arsenate concentrations were below detection limits throughout the experiments however, after reactive organic carbon concentrations in the core decreased to the level where reduction of O2 was incomplete, geochemical modeling predicted oxidation of As(lll) to As(V). Because As(V) was not detected in core effluent, it was not possible to derive equilibrium constants for these adsorption reactions on this core material, and the equilibrium constants listed in Dzombak and Morel (1990) were used in the model. For reaction 6, the Log Kas(v)i was 23.51 and for reaction 7, the Log Kas(v)2 was 10.58. Arsenite adsorption was modeled by ... 

Figure 8.1. Magnitude and pH dependency of As(V) (arsenate) and As(ni) (arsenite) adsorption on hydrous ferric oxide reaction conditions were 50 /xM arsenic reacted with 0.03 g hydrous ferric oxide. (Data from Dixit and Hering, 2003.)...

Use of surface speciation models for prediction of adsorption and transport requires specification of the mode of bonding and speciation of oxyanions on oxide surfaces. FTIR spectroscopy (especially ATR and DRIFT) offers the potential to establish symmetry of surface species, protonation, and determination of monodentate or bidentate bonding. Determination of surface speciation is greatly enhanced when the spectroscopic information is combined with measurements of electrophoretic mobility (EM), calculation of point of zero charge and proton balance measurements before and after adsorption. We review adsorption of phosphate, carbonate, boron, selenate and selenite on Fe and A1 oxides. New preliminary spectra and EM and proton balance information for arsenate and arsenite adsorption on amorphous Fe and A1 oxide suggest that HASO4 and H2ASO3 are the dominant surface species. 

Kinetics of Arsenic Adsorption. Arsenite adsorption on hematite is rapid, attaining equilibrium within 50 minutes and follows a first-order adsorption rate expression (42). The removal of arsenite is partially diffusion controlled and... 

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