Abstract

As one of the strongest inorganic oxidizers in natural environments, manganese oxides participate in the oxidation processes of dissolved sulfides, affecting their migration, transformation, and toxicity. The amount of and sites for Mn(III) influence significantly the oxidation activity of Mn(IV) oxides. As an easily formed Mn oxide in supergene environments, manganite consists of Mn(III)O6 octahedra; further study is needed of the interaction processes of manganite and dissolved sulfide. In the present study, the interaction mechanisms of dissolved sulfide and manganite were studied systematically.The influences of pH, temperature, and oxygen atmosphere were also investigated in detail. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the crystal structures, compositions, and micromorphologies of manganite and the intermediate products. The sulfide species were identified by visible spectroscopy, high-performance liquid chromatography, UV-visible (UV-Vis) spectroscopy, and ion chromatography during the reaction process. The results indicated that in a nitrogen atmosphere, elemental sulfur was formed as the main oxidation product of dissolved sulfide by manganite at the initial stage, and polysulfide ions were observed as the intermediates. Elemental sulfur was further oxidized slowly to S2O32-. The initial oxidation rate of dissolved sulfide by manganite increased with temperature from 20 to 40°C. The reaction rate increased at first and then decreased as the pH changed from 4.0 to 12.0, and the greatest oxidation rate was achieved at pH 8.0. In the presence of oxygen, S2O32- was the main product. The oxidation rate of dissolved sulfide decreased, and manganite exhibited significant catalytic activity and stability with respect to the oxidation of dissolved sulfide in the oxygenated aqueous systems. These findings are of fundamental significance in understanding the interaction and transformation of dissolved sulfide and manganese oxides in nature.

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