Abstract

      This study investigated the effect of pH and coexisting ions on As(III) adsorption using batch experiment and discovered that pH strongly influenced As(III) adsorption. However, differences in background ionic strengths of 0.001 N NaNO₃ and 0.1 N NaNO₃ had no effect on the sorption trend. The isotherms followed Freundlich model with K_f  of 27.91, 35.67, and 43.76 (mg/g)(L/mg)ⁿ at pH 6, 7, and 9 respectively. The kinetic studies showed  D_app values of (6.52 ± 0.024) × 10^-7 cm²/s and (6.22 ± 0.043) × 10^-7 cm²/s for the 38 µm and 500 to 600 µm particle sizes. The biot numbers of the sorption derived were 1.84 × 10^-2 and 5.89 × 10^-1 respectively. The presence of CO₃^2- had more impact than SO₄^2- ion but the presence of 300 mg/L NH₄⁺ - N had no significant impact on  As(III) adsorption between pH 4 and 8 and so was the presence of 0.1 mg/L Ca²⁺ ion between pH 4 and 6.5. However, about 10% loss of the sorption capacity of Kemiron occurred between pH 6.5 and 9 in the presence of Ca²⁺ ion. The presence of 5 mg/L Ni(II) and Se(IV) also showed that Se(IV) was a stronger inhibitor of As(III) sorption than Ni(II).

Key words:  Arsenite, ground water, Freundlich, diffusion coefficient, Ghana