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Mobilization of Arsenite by Competitive Interaction with Silicic Acid

^a Dep. of Crop and Soil Environmental Sci., Virginia Tech, Blacksburg, VA 24061
^b Dep. of Geoscience, Virginia Tech, Blacksburg, VA

View larger version (22K): [in a new window]   Fig. 1. Oxyanion adsorption on goethite as a function of pH. (A) Arsenite adsorption for two initial solution concentrations (0.05 and 0.10 mM). (B) Silicic acid adsorption as a function of pH for three initial solution concentrations (0.10, 0.50, and 1.00 mM). Symbols represent experimental data, lines represent predicted Si and As(III) adsorption for the optimized Charge Distribution Multisite Surface Complexation (CD MUSIC) model fit to experimental data (Log K values listed in Table 1). Suspension density 1 g L–1, background electrolyte 0.01 M NaNO3.

View larger version (31K): [in a new window]   Fig. 2. Zeta potential at the plane of shear, based on electrophoretic mobility measurements, as a function of pH (A) zeta potential for As(III) adsorption at two initial solution concentrations (0.05 and 0.10 mM). (B) zeta potential for Si adsorption at three initial solution concentrations (0.10, 0.20, 0.50, and 1.00 mM). Symbols represent experimental data, lines represent the Charge Distribution Multisite Surface Complexation (CD MUSIC) model predicted zeta potentials for Si and As(III) adsorption, assuming the plane of shear is located 2.6 nm from the head of the 2-plane. Suspension density 1 g L–1, background electrolyte 0.01 M NaNO3.

View larger version (26K): [in a new window]   Fig. 3. Arsenite adsorption in the presence of silicic acid as a function of As and Si concentration and addition order. Suspension density 1 g L–1, background electrolyte 0.01 M NaNO3.

View larger version (27K): [in a new window]   Fig. 4. Silicic acid adsorption in the presence of As(III) as a function of Si and As concentration and addition order. Suspension density 1 g L–1, background electrolyte 0.01 M NaNO3.

View larger version (38K): [in a new window]   Fig. 5. Schematic representation of depicting polymerized silica on the goethite surface being displaced by As(III), but not released into the bulk solution.

View larger version (22K): [in a new window]   Fig. 6. (A) Charge Distribution Multisite Surface Complexation (CD MUSIC) model predictions for oxyanion adsorption for the competitive adsorption of Si and As(III) on goethite. (B) CD MUSIC model predictions for zeta potential for the competitive adsorption of Si and As(III) on goethite. Model predictions are based on the equilibrium constants calculated from single ion adsorption of As(III) and Si. Symbols represent experimental data, lines represent CD-MUSIC model predictions. Suspension density = 1 g L–1, background electrolyte 0.01 M NaNO3.

View larger version (21K): [in a new window]   Fig. 7. (a) Charge Distribution Multisite Surface Complexation (CD MUSIC) model predictions for oxyanion adsorption for the competitive adsorption of Si and As(III) on goethite. (b) CD MUSIC model predictions for zeta potential for the competitive adsorption of Si and As(III) on goethite. Model predictions are based on the equilibrium constants calculated from single ion adsorption of As(III) and Si. Symbols represent experimental data, lines represent CD-MUSIC model predictions. Suspension density = 1 g L–1, background electrolyte 0.01 M NaNO3.

View larger version (27K): [in a new window]   Fig. 8. Arsenite equilibrium solution concentration in the presence and absence of silicic acid. (a) As(III)T = 0.05 mM (b) As(III)T = 0.10 mM.