Abstract:

The direct acid leaching process of low-grade rhodochrosite has problems such as long and complex process flow and large discharge of waste water and residue.In this paper，the low-grade rhodochrosite from Guizhou was used as raw material，and the effects of leaching conditions on the leaching of manganese and the main impurities of calcium，magnesium and iron were investigated by additive-assisted leaching.The phase，morphology and leaching kinetics of manganese before and after leaching were also analyzed.The results were compared with those of the direct acid leaching process.The results revealed that the leaching rate of manganese was 94.36% and the selective leaching rate was 61.57% under the conventional leaching conditions of sulfuric acid concentration of 0.5 mol/L，leaching temperature of 55 ℃，solid-liquid ratio of 0.08 g/mL and reaction time of 120 min.For additive-assisted leaching（solid-liquid vatio of 0.04 g/mL），the leaching rate of manganese was 93.65%，the selective leaching rate was 89.67%.Under such circumstances，gypsum phases were more likely to form in the leaching residue，and calcium was more likely to remain in the residue phase rather than in the solution phase，which was conducive to improving the selective leaching rate of Mn²⁺.The leaching kinetics analysis showed that the leaching of manganese belonged to the diffusion control of the solid product layer，and the activation energy of the conventional leaching reaction was 4.85 kJ/mol，and the activation energy of the additive-assisted leaching reaction was 1.20 kJ/mol.The impurity components could be effectively inhibited at the source the leaching process by additive-assisted leaching，which provided a research basis for the subsequent impurity removal process and the preparation of high-purity manganese products.

Key words: low-grade rhodochrosite, additive-assisted leaching, metal impurities, leaching kinetic