Thermal and kinetic study of manganese dithionate from absorbing or leaching solution via TG/XRD/IC analysis

ABSTRACT

Mangano-manganic oxide can be prepared through thermal decomposition of manganese sulfate from the absorption or leaching solution, so desulfurization by pyrolusite or leaching pyrolusite with sulfur dioxide should be fully exploited for the recovery of manganese salt. However, upon preparing MnSO₄ using above techniques, manganese dithionate is an inevitable by-product, which lowers the purity of the industrial raw material MnSO₄ and exerts negative influences on pyrolysis technology. Information regarding thermal decomposition of solid-state manganese dithionate is scarce. To recycle manganese dithionate efficiently, pyrolysis mechanism and kinetics were systematically investigated by thermal decomposition method. The characteristics of thermal decomposition products were determined by thermogravimetric analysis techniques (TG), X-ray diffraction (XRD), and Ion chromatography (IC). The experimental results revealed that both desulfurization and following dehydration of MnS₂O₆·H₂O were a one-step process, and the desulfurization occurred at about 150°C lower than the dehydration at 230°C. As increasing pyrolysis temperature to 900°C, the manganese sulfate was firstly formed, and to 1100°C, Mangano-manganic oxide was obtained by losing sulfur oxides. Consequently, the kinetic parameters for each decomposition steps of manganese dithionate were determined by the Coasts and Redfern (CR) integral method. The as-obtained experimental and kinetic results may provide theoretical guides for recycling manganese dithionate.