Synergistic leaching mechanism of chloride ions for extracting manganese completely from manganese carbonate ores

In this study, manganese is extracted completely from manganese carbonate ores by means of leaching with sulfuric acid under the synergistic effect of chloride ions. It is demonstrated that the introducing of chloride ions shows a positive effect on manganese leaching and the leaching efficiency of manganese could reach 99.5% under the optimal leaching conditions. Kinetic studies show that the leaching process of manganese has its own characteristics that is controlled by mixing before 10 min, and then controlled by diffusion after 10 min, with an apparent activation energy of 20.0 and 7.4 kJ mol-1, respectively. Furthermore, the synergistic leaching mechanism of chloride ions is proposed based on phase, morphology and pore structure characterization of the reaction products, which indicates that manganese compounds are hard to react with sulfuric acid in the absence of chloride ions due to the CaSO4 layer wrap on their surface which hinder the diffusion of manganese. The introducing of chlorine ions can not only reduce the thickness of CaSO4 layer but also increase the specific surface area and pore volume of the leaching residue owing to the ion effect that facilitating ion diffusion and eventually promoting the manganese leaching.