EFFECT OF SOLUTION CHEMISTRY ON ARSENIC SORPTION BY Fe- AND

Drinking-water treatment residuals (WTR) have been proposed as a low-cost alternative sorbent for arsenic (As)–contaminated aquatic and soil systems. However, limited information exists regarding the effect of solution chemistry on As sorption by WTR. A batch incubation study was carried out to investigate the effect of solution pH (3-9) on As(V) sorption by Al- and Fe- based WTR as a function of solid: solution ratio (SSRs) and initial As concentration. The effect of competing ligands (phosphate-P(V) and sulfate), and complexing metal (calcium) on As(V) sorption envelopes at the optimum SSR (200 g L-1) was also evaluated. At 200 g L-1 SSR, maximum As(V) sorption ( ~ 100%) exhibited by the Fe-WTR was limited at the pH range of 3-7, whereas, the Al-WTR demonstrated ~100 % As(V) sorption in the entire pH range. The negative pH effect on As(V) sorption became more pronounced with increasing initial As concentrations and decreasing SSR. Sorption of As(V) by surfaces of both WTR decreased in the presence of P(V), exhibiting strong pH dependence. Only for the Fe-WTR, increased dissolved iron concentrations at pH> 7 supported a Fe-hydroxide reductive dissolution mechanism to account for the enhanced As sorption at alkaline pH. Addition of sulfate did not influence As(V