Preparation of High Purity Manganese Sulphate from Low-Grade Rhodochrosite

"In our work, the preparation technique of high pure manganese sulfate directly from low-grade rhodochrosite ore (MnCO3) was studied and improved intensively, including the effective leaching process and the short purifying process. Based on the same ion effect, the repeated leaching of rhodochrosite with sulfuric acid is proposed to improve the solubility of Mn2+ and inhibit the dissolution of the impurities Ca2+ and Mg2+. Moreover, the repeated leaching process could make full use of rhodochrosite and lower the dosage of sulfuric acidas raw material. With the aid of theoretical calculation, Ba(OH)2 was chose to adjust the pH value of manganese sulfate solution, and BaF2 to remove Ca2+ and Mg2+completely in the process of purifying. The results demonstrate that the extraction ratio and the recovery ratio of manganese reached 94.3% and 92.7%, respectively, which shows the prospect of industrial application. In manganese sulfate production, the heavy metal impurities have been decreased to less than 1ppm. Moreover, the content of calcium, magnesium and sodium has been decreased to less than 20ppm, which meets the standards of high pure reagent for energy and electronic materials. Our study enlightens an approach to the sustainable application of low-grade rhodochrosite.Introduction Low-grade manganese carbonate ores (=14%) becomes gradually the main resources for exploitation and applications in China according to national mineral resources survey (Tan et al 2004 and Singh et al 2017). Therefore, the electrolytic deposition technique of rhodochrosite faces great challenges including low electrolysis efficiency, high-resource input and high-pollution discharge (Fu et al 2010, Michelis et al 2009, Zhang et al 2013). Recently, more and more amount of manganese series with high or super high purity such as MnSO4, MnO2, Mn3O4 and MnO is demanded with the development of energy and electronic materials. Due to low-grade ores containing multiple elements such as iron, silicon, calcium and magnesium, conventional preparation of manganese sulphate with high purity from electrolytic product is characterized by long production-cycle and high-energy consumption (Subrat et al 2011, Mpho et al 2013). By contrast, hydrometallurgical method combined with thermal decomposition, hydrothermal synthesis and sol-gel processes has been widely studied because of its high efficiency, low consumption and low cost (Chen et al 2008). But the key problem in direct preparation of manganese series form low-grade rhodochrosite is to remove completely the multiple impurities such as iron, silicon, calcium and magnesium (Liu et al 2014). So it is urgent to develop a sustainable alternative approach with character of short process, high efficiency and environmental friendly."