Effect of pH on Adsorption of Arsenic and Selenium from Landfill Leachate by Clay Minerals

Abstract

Adsorption of As(V), As(III), and Se(IV) anions from municipal landfill leachate solutions by the clay minerals kaolinite and montmorillonite is strongly dependent upon solution pH.The H₂AsO₄^‐ and HSeO^‐₃ ions are the apparent primary As(V) and Se(IV) species being adsorbed by the clay minerals. Activation of the anion adsorption sites on the clay minerals by H⁺ ions is important in determining the amount of HSeO₃^‐ ions adsorbed by the clay minerals, but it is apparently not important in determining the amount of H₂AsO₄^‐ ions adsorbed.Montmorillonite adsorbed more As(V), As(III), and Se(IV) anions than kaolinite. Although no definite proof is given, the higher adsorption by montmorillonite is attributed to a higher edge surface area.The results of the study suggest that disposal of As and Se wastes in municipal landfills, especially under alkaline conditions, could produce ground water contamination by As and Se.