Precipitation of Free O2− in Molten CaCl2 Using MgCl2

Molten CaCl 2 is increasingly recognized for its potential in developing innovative mineral and material processing technologies as an effective solvent and electrolyte. However, controlling the accumulation of free O 2− remains a major challenge. This work explores the feasibility of eliminating free O 2− in molten CaCl 2 by adding MgCl 2 . Thermodynamic analysis suggests that the introduction of Mg 2+ favors the precipitation of O 2− as insoluble MgO (Mg 2+ + O 2− → MgO↓). Experimental results confirm a rapid and vigorous reaction producing sub-micron MgO particles, which initially suspend, then coalesce, and eventually settle at the bottom. The process’s efficiency depends on the dosage of MgCl 2 added. A sub-stoichiometric dosage inadequately removes O 2− , while a hyper-stoichiometric dosage disrupts the melt stability due to the widespread dispersion of soluble Mg(II) and MgO particles. A near-stoichiometric dosage, on the other hand, leads to optimal performance by facilitating the formation of Mg 2 O 2+ , enabling localized MgO precipitation and thus preventing contamination of the bulk melt. These findings provide a foundation for designing more efficient and environmentally friendly molten CaCl 2 -based processes for industrial applications.