The effect of competition by chloride and sulfate anions on the adsorption of arsenate ion onto activated alumina

Abstract

Interactions of arsenate ions with sulfate and chloride anions in aqueous solutions containing various amounts of activated alumina were studied in the laboratory on a batch mode basis with the goal of understanding the competition of the anions for adsorption sites on the activated alumina. The results of this study showed that the presence of 15 meq/L chloride anion depresses the ability of the arsenate to be adsorbed by F-1 activated alumina initial liquid phase arsenate ion concentration of 5 mg/L at pH 6. Alternatively, 30 meq/L sulfate anion caused an increase in the arsenate ion adsorption. Additionally, the arsenate ion loading capacity of the activated alumina was lower with the presence of 15 meq/L chloride anion than with the presence of 30 meq/L sulfate anion. In tests with no added anions, arsenate ion loading capacity was only slightly lower than tests with 30 meq/L sulfate anion. It is also clearly shown that the ability of activated alumina to adsorb arsenate ion is affected by the presence of chloride and sulfate anions, but the effects are not noticeable when the initial arsenate concentration to activated alumina ratio is less than 25 mg arsenate anion to 1 g activated alumina. The overall results of this study appear applicable to improving our understanding of the performance behavior of pilot scale or commercial sized packed bed activated alumina reactors.