Sorption of aqueous Pb2+ ion on synthetic manganese oxides-intercalated with exchangeable cations

This paper describes the preparation, characterization, and application of three different synthetic manganese oxides (K–MO, H–MO, and Mg–MO). K–MO was synthesized by the reduction of potassium permanganate in an aqueous acidic medium. H–MO was prepared by an ion exchange reaction of K–MO with H+, while Mg–MO was prepared by reaction of H–MO and an aqueous Mg2+ salt solution under reflux. The subsequent solid products were characterized by a chemical composition analysis, XRD, XPS, FT-IR, SEM, and BET measurements. XPS spectra revealed that only tetravalent manganese ions coordinated octahedrally with oxygens. XRD patterns showed that K–MO turned into a layer-structured material while Mg2+ ions were incorporated into the gallery space of the tunnel-structured Mg–MO. Each type of manganese oxide was used in a sorption study of aqueous Pb2+ at 25 °C. The sorption of Pb2+ ions by manganese oxide resulted in increases of the concentrations of pre-intercalated ions (potassium ions, protons, or magnesium ions) and Mn2+ ions. In spite of the smaller surface area and pore volume, K–MO showed greater sorption capacity for Pb2+ ions than that of Mg–MO under the present experimental conditions, thus suggesting that ion exchange is the main mechanism for the sorption of Pb2+ ions on manganese oxides. The results are anticipated to be applicable to the removal of heavy metal ions from wastewater and the prevention of migration of ions in landfill leachates.