An efficient and clean method for the selective extraction and recovery of manganese from pyrolusite using ammonium sulfate roasting-water leaching and carbonate precipitation

Manganese is a fundamental metal raw material that plays a crucial role in sustainable economic and social development. With the battery industry undergoing rapid advancements in the recent years, there has been a consistent rise in the demand for manganese. This study proposes a new scheme for selectively extracting manganese from pyrolusite by the sulfation roasting-water leaching process, while the iron is enriched in the leaching residues in the form of Fe2O3. With a 1.5:1 mass ratio of ammonium sulfate to pyrolusite, a roasting temperature of 650 °C, and a duration of 120 min, the extraction efficiency of manganese was observed to be 96.15%, while iron extraction was only 1.45%. And the leaching residues containing mainly 54.62% SiO2 and 36.10% Fe2O3 were obtained, which could be enriched with iron by flotation. Subsequently, the purified leaching solution was subjected to manganese precipitation using ammonium bicarbonate. Under optimal conditions, the precipitation efficiency of manganese was 99.63%, and the manganese carbonate products were obtained with a particle size of approximately 1–1.5 μm spherical structure, which met the requirements of the industrial manganese carbonate quality standard (HG/T4203-2011). The mechanism studies have proven that MnO2 in pyrolusite was first converted to (NH4)2Mn2(SO4)3 and then to MnSO4, while Fe2O3 was converted to (NH4)3Fe(SO4)3, NH4Fe(SO4)2, Fe2(SO4)3 in turn and finally decomposed to Fe2O3. The ammonia produced during the roasting process can be absorbed to regenerate ammonium sulfate products, and the filtrate from the manganese precipitation can also be crystallized by evaporation to obtain ammonium sulfate products, both of which can be used in the roasting process to reduce production costs. The process of this study proposed is simple and does not require any strong acid or alkali reagents. It offers high efficiency, is environmentally friendly, and is easy to operate, thus providing a new idea and scheme for the multi-component resource utilization of manganese oxide ore.