Oxidation behavior and kinetics of sulfide by synthesized manganese oxide minerals

Purpose Sulfur is distributed widely in soils and sediments. Sulfide oxidation causes acid mine wastewater, toxicity, and corrosion. Manganese oxide minerals usually affect the migration, transformation, and fate of sulfur. To understand the oxidation behaviors of S2- and influence factors, reaction process and kinetics were investigated by using different manganese oxides. Materials and methods Three types of manganese oxide minerals (birnessite I, birnessite II, and cryptomelane) were synthesized and participated in the oxidation of S2- (200 mg L-1). Oxidation products were characterized by spectrophotography, ion chromatography, X-ray diffraction, and scanning electron microscopy. The influences of pH, the amount of manganese oxides, temperature, and mineral structure on the initial oxidation rate of S2- were investigated. Reduction products of manganese oxides and the further transformation process in air were studied. Results and discussion The total conversion of S2- to SO (3) (2-) , S2O (3) (2-) , and SO (4) (2-) was no more than 15%, and S was likely to be the main oxidation product when oxidized by birnessite I (AOS 3.83). The initial oxidation rate followed a pseudo-first-order kinetic law, and the apparent rate constants (k (obs)) of S2- oxidation increased with elevating temperature, decreasing pH, and increasing the quantity and Mn(III) content of manganese oxides. Manganese oxides were deoxidized to Mn(OH)(2) and then oxidized to Mn3O4 in air, which was further transformed into beta-MnOOH. Conclusions S was the main oxidation product. The initial oxidation rate of S2- followed a pseudo-first-order kinetic law, was affected by temperature, pH, and the amount of manganese oxide, and significantly depended on the content of active Mn(III) available in manganese oxides. Oxidation ability was found to follow: birnessite II > cryptomelane > birnessite I with similar manganese AOS. Mn(OH)(2) powder can be slowly oxidized to MnOOH by O-2 in air.