Effects of Coexisting Anions on Arsenite Adsorption of Newly Developed Iron Hydroxide

Abstract

The effects of various anions on the removal of arsenite by a newly developed iron hydroxide synthesized from ferrous sulfate, sodium hypochlorite, and sodium hydroxide were examined. The adsorption isotherm of arsenite was of the Freundlich type, that of phosphorus was of the Langmuir type, and that of fluoride was of the Henry type. The maximum amounts of anion adsorbed after 24 hours of contact were 0.50 mmol As•g^-1 for arsenite, 0.45 mmol PO₄-P•g^-1 for phosphorus, and 0.85 mmol F•g^-1 for fluoride. Judging from the distribution coefficient of coexisting individual anions and various coexisting anions, arsenite adsorption was inhibited by PO₄^3-; however, only a slight inhibition was observed in the presence of HCO₃^- and F^-. No inhibition was observed in the presence of NO₃^-, NO₂^-, Cl^-, or SO₄^2-. The amount of arsenite adsorbed by the newly developed iron hydroxide in the column filtration experiments was reduced to 66% in the presence of PO₄^3-. Only small reductions was observed in the presence of F^-.