Kinetics and mechanism of manganese reductive leaching from electrolytic manganese anode slag with elemental sulfur in sulfuric acid solution

Recycling EMAS in an eco-friendly manner is crucial to alleviate the demand for manganese resource and reduce environmental pollution. Hydrometallurgical reductive leaching of EMAS with elemental sulfur is proposed, but sulfur is chemically inert. To improve the rate and degree of reductive dissolution of EMAS using elemental sulfur. Reductive leaching kinetics of EMAS by elemental sulfur with the aid of H2SO4 at atmospheric pressure have been conducted. A shrinking core model was used to explain the leaching data obtained, and the apparent activation energy was determined to be 63.8 kJ mol-1, indicating the leaching was controlled by chemical reation. The reaction order with respect to sulfuric acid concentration and mass ratio of sulfur to EMAS were 2.6 and 0.9, respectively. The leaching rate equation was established based on the shrinking core model, and good agreement between experimental data and predicted rate curves was obtained. Mechanism of reductive leaching was reasonably speculated with the assistance of X-ray diffraction and scanning electron microscope, revealing that the manganese reduction and sulfur oxidation progressed step by step, following the order Mn4+-> Mn3+-> Mn2+ and S0 -> S1+-> S2+-> S4+-> S6+. The ring opening reaction of [S8]center dot+ was identified as the rate -determining step. The results of this research provide a theoretical guidance for improving the speed and degree of manganese reduction leaching.