Improvement of utilization efficiency of magnesite by (NH4)2SO4 roasting–water leaching process

(NH4)2SO4 roasting–water leaching process was studied as a method for improving the utilization efficiency of magnesite. Transformation of the mineral phases during roasting was evaluated by X-ray diffraction (XRD) analysis, combined with thermogravimetry−differential thermal analysis (TG−DTA). The data were compared with the phase transformation of MgO during roasting using (NH4)2SO4. The experimental results demonstrated that at a (NH4)2SO4/ magnesite (MgO in ore) molar ratio of 1.6:1, roasting temperature of 475 °C, and roasting time of 2 h using a particle size of ~74 μm, the magnesium extraction rate reached a maximum of 98.7%. The phase transformation during roasting could be summarized as follows: MgCO3 was transformed into (NH4)2Mg2(SO4)3, and then decomposed into MgSO4. The reaction followed the mixed control mechanism involving chemical reaction control and diffusion control, with an apparent activation energy of 33.02 kJ/mol.