Clean and efficient co-recovery of magnesium and calcium from dolomite via hydrochloric acid leaching and selective Ca(OH) 2 precipitation

Dolomite is an abundant carbonate mineral and an important source of magnesium and calcium. Hydrochloric acid leaching provides a practical route for recovering magnesium and calcium from dolomite, with a comparatively simple flowsheet and relatively low energy demand. However, conventional ammonia-based selective precipitation introduces NH4+ and generates large volumes of NH4Cl-containing effluent, increasing the burden of downstream treatment. To address this issue, we replaced aqueous ammonia with a Ca(OH)2 suspension as the precipitant, enabling Mg/Ca recovery while avoiding the generation of ammonium-containing waste. Under optimised leaching conditions, Mg and Ca leaching efficiencies reached 98.1% and 99.0%, respectively. Precipitation experiments further examined the effects of Ca(OH)2 suspension dosage, reaction time, and temperature. After selective precipitation, the Mg(OH)2 product reached a purity of 93.33%. The post-precipitation filtrate was mainly CaCl2 solution, which can be further processed to produce anhydrous CaCl2. The Mg(OH)2 was calcined at 500°C for 3 h to yield MgO with a purity of 91.17%. Overall, this work provides a cleaner route for the efficient utilisation of magnesium and calcium from dolomite.