High-efficiency and environment-friendly separation and recovery of manganese from braunite via the ammonium sulfate roasting-water leaching process: Behavior and mechanism

Manganese ore is a key raw resource for the development of new energy, new materials, and other emerging industries, as well as a basic raw material for the steel industry. As resources of the main high-grade pyrolusite are depleting, it is of strategic importance to develop and utilize other manganese oxide ores. This paper proposed the two-stage ammonium sulfate roasting-water leaching process for high-efficiency and environment-friendly separation and recovery of manganese from braunite ((Mn2O3)3MnSiO3). The first-stage was sulfation roasting, which could convert Mn and Fe in braunite into (NH4)2Mn2(SO4)3, (NH4)3Fe(SO4)3, NH4Fe(SO4)2 and Fe2(SO4)3; the second-stage was selective roasting, that could decompose (NH4)2Mn2(SO4)3 into MnSO4, and decompose (NH4)3Fe(SO4)3, NH4Fe(SO4)2 and Fe2(SO4)3 into Fe2O3. Under the optimum leaching conditions, the leaching efficiency of Mn reached 97.79%, while the leaching efficiency of Fe was only 1.52%, and a solution with a concentration of 93.36 g/L for Mn was obtained. The NH3 volatilized during roasting was absorbed by the water solution to get an ammonia solution which was used to precipitate Mn from the leaching solution. The precipitation efficiency of Mn was 99.48% under optimal conditions. Manganese oxide products such as Mn3O4 or Mn2O3 could be obtained by drying and calcining Mn-rich precipitates. The final filtrate was neutralized with H2SO4 and then evaporated and crystallized to give an (NH4)2SO4 product, enabling the recycling of ammonia. The process proposed in this paper is not limited to the treatment of braunite, but can also be applied to the processing of other manganese oxide ores and has a wide application potential. Compared to the traditional reduction roasting-acid leaching process, this process is more efficient and environmentally friendly.