Purification of MnSO4 solution obtained from manganese sludge 2026 Minerals

Manganese-rich anode sludge is a common by-product of the zinc roasting-leaching-electrowinning (RLE) process. It primarily consists of oxidized manganese, along with smaller amounts of lead, zinc, calcium, and other minor metals. The presence of these impurities necessitates the development of new recycling strategies to enable efficient utilization of the sludge. This study presents a novel purification method for MnSO4 solution aimed at producing battery-grade MnSO4·H2O (Mn > 32 wt-%, transition metal < 10 mg/kg each). The process involves sulfide precipitation followed by selective crystallization, facilitated by the addition of H2SO4. Sulfide precipitation was studied in two stages as commercial iron-containing MnS was ineffective for iron removal. Both commercial and self-synthesized MnS were efficient in removing over 99% of zinc with a single addition. However, particle passivation occurred during the process, requiring multiple additions of MnS to initiate partial iron removal. Ultimately, the iron content of the pregnant leaching solution (PLS) was minimized by adjusting the pH to almost 4 prior to filtration. Additionally, Mn separation from Ca, K, and Mg was examined through sulfuric acid-assisted reactive crystallization at varying sulfuric acid concentrations and temperatures. The method achieved good separation from Ca and K, whereas Mg was incorporated into MnSO4·H2O crystals via lattice substitution.