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 SO4), nitrate (as NO3-N), phosphate (as PO4-P) ions and silicate (as SiO2) 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-1As(V) both at pH 3 and pH 7.