Effect of competing anions on arsenate adsorption onto maghemite nanoparticles

This paper reports the effect of several competing anions on arsenate adsorption with maghemite nanoparticles. Sulphate (as SO ₄), nitrate (as NO ₃-N), phosphate (as PO ₄-P) ions and silicate (as SiO ₂) were studied in dual solution with arsenate. Moreover, the combined effect of ions and other water characteristics were examined with a natural groundwater sample which was spiked with a certain amount of arsenate. Arsenate batch adsorption experiments were carried out with two different kinds of maghemite-a commercially available one and a homemade one using the sol-gel process. Sulphate (≤250 mg·L ^-1) and nitrate (≤12 mg·L ^-1) had a negligible effect on the arsenate (0.5 mg·L ^-1) adsorption at pH 3. However, both phosphate (≤2.9 mg·L ^-1) and silicate (≤50 mg·L ^-1) had an adverse impact on arsenate (≤3 mg·L ^-1) adsorption at pH 7. Phosphate (≤1.5 mg·L ^-1) showed minimal competition with arsenate (0.5 mg·L ^-1), while silicate (≤10 mg·L ^-1) inhibition was insignificant for all studied As(V) concentrations at pH 3. The removal of arsenate from the groundwater sample was as efficient as from laboratory water for 0.5 mg·L ^-1 As(V) both at pH 3 and pH 7.