Solar Carbothermic Reduction of Dolime as a Promising Option to Produce Magnesium and Calcium

The use of solar energy to produce metals from their oxides via the carbothermic reduction process is a cleaner alternative to traditional combustion-based processes with an added value of a significantly reduced CO₂ emission footprint. In this study, the potential contribution of solar energy to the pyrometallurgical production of magnesium was analyzed and compared to the common industrial process. The most energy-consuming step is the carbothermic reduction of the oxide. The reduction was thermodynamically examined and experimentally investigated. While previous studies in the field were based mostly on using MgO, this work focused on dolomite (CaCO₃·MgCO₃) as the feedstock for the carbothermic reduction process. A thermogravimeter (TGA) was used to investigate the kinetics of the reaction under different conditions. The thermogravimetric results show that a full reduction of MgO in dolime (calcined dolomite, MgO·CaO) is achievable around 1600 °C under atmospheric pressure. According to the results, at the same temperature and in the presence of a sufficient amount of carbon, CaO in dolime is reduced to elemental calcium only after the reduction of MgO has ended. Therefore, stepwise coproduction of magnesium and calcium in a single reaction chamber could be possible via carbothermic reduction of dolime. It is also shown that the amounts of magnesium and calcium produced can be controlled by regulating the temperature and dolime-to-carbon ratio. A comparison of carbothermic reduction experiments on different feedstocks indicates that dolime is reduced faster than MgO. These findings indicate the potential of carbothermic reduction of dolime as a promising option to produce magnesium and calcium from dolomite.