Green Process for the Preparation of MnCO3 and Recovery of By-Product Mg-Containing (NH4)2SO4 Solution

The conventional manganese carbonate preparation process faces challenges such as low resource utilization efficiency and difficulties in treating by-product Mg-containing ammonium sulfate solution. In this study, a two-stage leaching process was developed to efficiently extract Mn and Mg from the ore. NH4HCO3 was used as a precipitant to convert Mn2+ in the leachate to MnCO3, achieving a Mn precipitation efficiency of 99.89%, and the resulting product contained 44.45% Mn, meeting the first-class product indicators of HG/T 4203-2011 (Chinese standard on manganese carbonate for industrial use). To further enhance resource utilization, a combined stripping–adsorption process was designed to treat the Mg-containing ammonium sulfate solution generated during the carbonization process. Subsequently, the economically valuable gypsum and magnesium oxide products were prepared. Additionally, 88.20% of the NH3 in the solution was stripped and recycled to prepare NH4HCO3 and then used during carbonization. Finally, a purified solution free of ammonia nitrogen was obtained using 001×7 resin to dynamically adsorb the filtrates obtained during the stripping process, and the maximum adsorption capacity of resin for ammonia nitrogen was 51.14 mg/g. This process provides a novel approach to achieving clean production in the manganese carbonate production industry.