Adsorption of Cs onto Biogenic Birnessite: Effects of Layer Structure, Ionic Strength, and Competition Cations

Abstract

Although the adsorption of cesium (Cs) onto phyllosilicate minerals has been widely studied, the effect of Cs on redox-sensitive biogenic Mn oxide is not well understood. In this study, the structural transformation of biogenic birnessite stimulated by commonly occurring natural heavy metals, and the influence of those metals on the adsorption behavior of Cs over a wide range of concentrations (1 × 10–10 to 0.1 mol/L) was carefully examined via solution chemistry and X-ray absorption fine structure techniques. The Cs was reversibly adsorbed onto the mineral surface to form an outer-sphere coordination for all biogenic birnessite samples. The presence of heavy metals (e.g., Zn and Ni) during bio-oxidation of Mn(II), followed by acid treatment, increased the number of available layer vacancies, which consequently increased the adsorption capacity of Cs in the final product. The analysis of the dependence of sorption values on the ionic strength showed distinct results on biogenic birnessite and chemically s...