Effect of pH on adsorption of chromium from landfill‐leachate by clay minerals

Abstract

Abstract Adsorption of Cr(VI) and Cr(III) species by kaolinite and montmorillonite clay minerals was found to be highly dependent upon the pH of the clay suspensions and the physical‐chemical properties of the clay minerals. Adsorption of Cr(VI) decreased as pH increased and the HCrO4 ‐ ion was the Cr(VI) species predominantly adsorbed. More Cr(VI) was adsorbed from leachate solutions than from pure K2CrO4 solutions. The adsorption of Cr(III) increased as the pH of the suspensions increased. About 30 to 300 times more Cr(III) than Cr(VI) was adsorbed by both clays and the amounts of Cr(III) adsorbed corresponded to cation exchange‐adsorption of hydrolyzed Cr(III) species. The adsorption of Cr(III) is 3% to 14% lower in leachate than in pure Cr(NO3)3 solutions. The results of the study suggest that landfill disposal of Cr(VI) wastes represents a potential pollution hazard due to its high mobility in earth materials and that safe disposal may require conversion of Cr(VI) in the wastes to Cr(III).