Preparation of Battery-Grade Manganese Sulfate by Directional Purification of Fluoride Precipitation: Process Optimization and Mechanism Analysis

Manganese is an important strategic resource for the new energy industry, and the preparation of high-purity manganese sulfate is crucial for lithium battery positive electrode materials. This study aims to thoroughly remove Ca 2+ and Mg 2+ impurities in rhodochrosite acid leaching solution, and proposes a directional purification method based on MnF 2 precipitant. Through single factor experiments and response surface optimization, the effects of MnF 2 addition, temperature, pH, and reaction time on impurity removal have been systematically studied. Under the optimized conditions (MnF 2 addition 2.35 times the theoretical value, temperature 86.94 °C, pH 4.0, reaction time 45.92 min), the removal rates of Ca 2+ and Mg 2+ reached 99.93% and 98.98%, respectively. Combining thermodynamic analysis with an E-pH diagram to explore the precipitation mechanism of impurities, the results show that the preferential precipitation of CaF 2 and MgF 2 originates from the strong coordination ability of Ca 2+ /Mg 2+ with F - (hard and soft acids and bases, HSAB, theory) and the ionic radius matching effect (r + /r −  = 0.75). In addition, MnF 2 was efficiently recovered by water-washing precipitation–evaporation crystallization method, and battery-grade manganese sulfate was successfully prepared. This study provides theoretical support and technical reference for the efficient purification of rhodochrosite leaching solution and the green preparation of battery-grade manganese sulfate.