Effect of solution chemistry on aqueous As(III) removal by titanium salts coagulation.

Abstract

Solution chemistry is of great importance to the removal of arsenic by coagulation through influencing the speciation of arsenic, the in situ precipitation of metal salts coupled with the adsorption and coprecipitation behavior of arsenic during coagulation. While the researches on the influence of solution chemistry in As(III) removal by titanium salts, a promising candidate for drinking water treatment was still deficient. Batch tests were performed to evaluate the removal of As(III) by titanium salts coagulation under solution chemistry influences. The results indicated that As(III) removal by Ti(SO4)2 and TiCl4 increased first and then decreased with the rising of solution pH from 4 to 10. TiCl4 preformed better in As(III) removal than Ti(SO4)2 at pH4-8, but the opposite trends were observed at pH9-10. XPS analysis indicated that the involvement of surface hydroxyl groups was primarily responsible for As(III) adsorption on Ti(IV) precipitates. As(III) removal was inhibited in the presence of SO42- mainly by competitive adsorption, especially at elevated SO42- concentration under acidic and alkaline conditions. F- exerted a greater suppressive effect than SO42- via indirectly hindering Ti(IV) precipitate formation, and through direct competitive adsorption with H3AsO3, the inhibitive effect increased as F- concentration increased and depended highly on solution pH. As(III) removal was promoted by co-existing Fe(II) primarily through the facilitation of Ti(IV) precipitation, especially under neutral and alkaline conditions, while it was inhibited to a different extent by the presence of high-concentration Mn(II) possibly via competitive adsorption. The presence of Ca2+ and Mg2+ enhanced the removal of As(III), but the positive effect did not increase as ionic concentration elevated.