Surface complexation modeling of the removal of arsenic from ion-exchange waste brines with ferric chloride

Abstract

Brine disposal is a serious challenge of arsenic (V) removal from drinking water using ion-exchange (IX). Although arsenic removal with ferric chloride (FeCl 3) from drinking waters is well documented, the application of FeCl 3 to remove arsenic (V) from brines has not been thoroughly investigated. In contrast to drinking water, IX brines contain high ionic strength, high alkalinity, and high arsenic concentrations; these factors are known to influence arsenic removal by FeCl 3. Surface complexation modeling and experimental coagulation tests were performed to investigate the influence of ionic strength, pH, Fe/As molar ratios, and alkalinity on the removal of arsenic from IX brines. The model prediction was in good agreement with the experimental data. Optimum pH range was found to be between 4.5 and 6.5. The arsenic removal efficiency slightly improved with higher ionic strength. The Fe/As ratios needed to treat brines were significantly lower than those used to treat drinking waters. For arsenic (V) concentrations typical in IX brines, Fe/As molar ratios varying from 1.3 to 1.7 were needed. Sludge solid concentrations varying from 2 to 18 mg L −1 were found. The results of this research have direct application to the treatment of residual wastes brines containing arsenic.