Magnesium vapor condensation in thermal-reduction magnesium production: Mechanisms, control strategies, and prospects

Magnesium vapor condensation is a key step in thermal-reduction magnesium production because it connects MgO reduction, vapor transport, crude-magnesium formation, and subsequent purification. Condensate morphology, powder formation, impurity loading, and direct metal recovery jointly determine the downstream refining burden and the stability of product quality. According to the atmosphere in the condensation zone, available studies on magnesium vapor condensation are classified in this review into three systems: single-vapor systems, inert-gas systems, and reactive-gas systems. The controlling mechanisms are discussed in terms of phase equilibrium, supersaturation-driven nucleation, gas-phase mass transfer, and reaction coupling. As the condensation atmosphere becomes more complex, the dominant control shifts from phase transformation governed mainly by Mg partial pressure, temperature gradient, and heterogeneous nucleation to a coupled process involving noncondensable-gas dilution, interfacial diffusion resistance, and flow-field organization. In Mg–CO reactive-gas systems, condensation is further affected by the reverse, or reversion, reaction, oxidation, and MgO/C by-product formation, which makes condensate morphology and stable metallic-Mg recovery more difficult to control. Progress has been made in gradient condensation, carrier-gas regulation, rapid quenching, moving-bed condensation, liquid/solid capture, and reaction-pathway regulation. However, a unified understanding across different atmospheres, key mass-transfer and reaction parameters, long-term operating data, and industrial design criteria for coupled heat and mass transfer remain insufficient. This review therefore establishes an analytical framework centered on atmosphere composition, phase transformation, mass-transfer resistance, and reaction coupling. The framework is expected to support the identification of condensation bottlenecks in thermal-reduction magnesium production and the optimization of subsequent condenser design.