An environmentally friendly approach for the extraction and recovery of Mn from pyrolusite by ammonium sulfate roasting-water leaching and ammonium carbonate precipitation

With the growth of the new energy industry, the requirements for manganese have increased significantly. In this paper, the method of manganese extraction from pyrolusite using ammonium sulfate roasting and water leaching was presented. At the optimal process parameters: mass ratio of (NH₄)₂SO₄ to pyrolusite of 2:1, the roasting temperature of 420°,C and duration of 120 min, the leaching efficiency of Mn and Fe was 94.55% and 54.38%, respectively. The mechanism analysis shows that MnO₂ and Fe₂O₃ in pyrolusite were converted to (NH₄)₂Mn₂(SO₄)₃, (NH₄)₃Fe(SO₄)₃, and NH₄Fe(SO₄)₂ by roasting with ammonium sulfate. Iron was removed from the leaching solution with the addition of ammonia. Afterward, manganese carbonate products were prepared from iron-free manganese sulfate solution by adding ammonium carbonate at a stirring duration of 60 min, a reaction temperature of 40°C, a pH of 7, and a molar ratio of ammonium carbonate to the manganese of 1.1:1, the precipitation efficiency of manganese could reach 99.8%, and the obtained manganese carbonate products were compliant with the industry standards. The ammonia released during the roasting process could be absorbed to regenerate (NH₄)₂SO₄ and the final filtrate after evaporation and crystallization could be used to recycle (NH₄)₂SO₄, both of which were used again into roasting process to reduce the consumption of raw material. In this process, the roasting temperature was only 420°C, which was significantly lower than the pyrometallurgical process suggested in earlier studies.