Efficient leaching of manganese from electrolytic manganese residue and recovery of the leaching solution: Reuse and purification

Electrolytic manganese residue (EMR) is a hazardous solid waste, while it also contains resources of Mn over 7 %. In this study, sulfuric acid with high concentration was used to leach Mn from EMR, and the leaching solution was reused and purified to produce battery-grade manganese sulfate. The optimal leaching conditions for EMR were determined through single-factor experiments and response surface methodology. Under the conditions of H2SO4 concentration at 5.4 mol/L, liquid-solid ratio at 4.8 mL/g, and temperature at 80 degrees C, the highest Mn leaching efficiency of 99.12 % was achieved. The kinetics of leaching Mn from EMR follows the Avrami model. The leaching characteristics were described according to the basic hypothesis made by the Avrami equation and the fitted Avrami index. The kinetic process is macroscopically regarded as the inverse process of nonequilibrium crystallization. According to the Arrhenius equation, the leaching of Mn is controlled by the mixture of diffusion and reaction with an apparent activation energy of 19.8 kJ/mol. The EMR leaching solution was then reused for the leaching step of rhodochrosite ore to simulate actual production. The secondary leaching solution was purified using neutralization, sulfide precipitation, and fluoride precipitation, and manganese sulfate with high purity was produced from it by evaporative crystallization. This study provides a low-cost and high-efficiency process for leaching and recovering Mn from EMR, which can also reduce the environmental risk.