Amid the continuing rise in global demand for magnesium metal, the considerable reserves of magnesium within magnesium slag remain insufficiently recovered, resulting in notable resource wastage and increased vulnerability to supply chain instability. Current mainstream approaches for the comprehensive utilization of magnesium slag have yet to demonstrate feasibility for large-scale industrial deployment. In this work, a novel synergistic activation approach—vacuum carbothermal reduction coupled with CaF₂ catalysis—is proposed. This method enables precise regulation of key parameters within the reduction system to harness the full potential of the intrinsic Ca₂SiO₄ phase in magnesium slag. Under high-temperature conditions, Ca₂SiO₄ interacts in situ with added CaF₂ flux to generate a low-melting-point eutectic system, substantially reducing the reaction’s activation energy and accelerating mass transfer. These combined effects promote the efficient reduction of MgO and the highly selective liberation of Mg(g). Experiments show that this technology achieves a MgO reduction rate ≥90 % in magnesium slag, with a direct collection efficiency rate ≥85.14 %, and the purity of regenerated crystallized magnesium stabilizes at ≥88.18 %. Extending the holding time has been proven to have a dual optimization effect: first, by enhancing the catalytic efficiency of CaF₂, the MgO reduction efficiency is improved by 5.51 % (when the holding time is extended by 1 h); second, it promotes uniform nucleation and equiaxed crystal growth of Mg(g) at only further increasing the purity of crystallized magnesium by +5.24 %, but it also significantly enhances its grain integrity and microstructural uniformity. This regenerated magnesium crystal, characterized by high purity and low defect density, provides an excellent microstructural foundation for subsequent plastic forming or service applications.

Low reduction efficiency is a critical issue that limits the advancement of the magnesium vacuum carbothermal reduction smelting process. This investigation introduces a novel magnesium smelting process that substitutes magnesium fluoride (MgF₂) for calcium fluoride (CaF₂) as a catalyst in the vacuum carbothermal reduction of magnesium. The viability and optimal operating conditions of the new method were assessed through thermodynamic calculations of Gibbs free energy in the MgOC–MgF₂ system. Additionally, the catalytic effects of MgF₂ on the reduction of MgO were examined under different holding times in vacuum conditions. Analytical results indicated a significant improvement in the reduction efficiency of MgO upon the incorporation of MgF₂. MgF₂ serves a catalytic function in the reduction process. When F⁻ acts, it elevates the relative concentration of Mg in the reduction system and promotes the reduction reaction. Improvements in reduction efficiency are observed as the holding period duration increases and with higher concentrations of MgF₂. However, the improvement in reduction efficiency tends to plateau when the concentration exceeds 7 %. The resulting magnesium condensate exhibits a robust crystalline structure, with a purity of 79.39 %. The crystallization outcomes are influenced by the degree of reverse reactions. Compared to CaF₂, MgF₂ offers significant economic, environmental, and catalytic advantages. This process supports the goals of sustainable, green development and aligns with clean production standards in the magnesium metallurgy sector.

Magnesium (Mg), as one of the most abundant elements in earth’s crust, is the lightest structural metal with extensive applications across various industries. However, the performance of Mg-based products is highly dependent on their impurity levels, and the lack of high-purity Mg, along with efficient purification method, has posed significant challenge to its widespread industrial adoption. This study investigates the impurity behavior in Mg ingots during the vacuum gasification purification process. Through the analysis of binary phase diagrams, iron (Fe)-based foam material was selected for the filtration and purification of Mg vapor in a vacuum tube furnace. A novel approach combining vacuum gasification, vapor purification, and directional condensation is proposed. The effect of filter pore sizes and filtration temperatures on the efficacy of impurity removal was evaluated. Experimental results demonstrate that Fe-based foam with a pore size of 60 ppi, at a filtration temperature of 773 K, effectively removes impurities such as calcium (Ca), potassium (K), sodium (Na), manganese (Mn), silicon (Si), aluminum (Al), and various oxides, sulfides, and chlorides from the vapor phase. Consequently, high-purity Mg with a purity level exceeding 5N3 was obtained in the condensation zone.

Magnesium (Mg) alloy is widely used in aerospace and automotive industries as an excellent lightweight metal material to reduce carbon emissions. The expansion of Mg alloy applications and the increasing demands for these materials have significantly facilitated the generation of Mg alloy scrap. The recycling of Mg resources is crucial for promoting both environmental sustainability and economic viability. However, current recycling effect is unsatisfactory. Therefore, this paper provides a comprehensive review of the entire recycling process, including scrap classification, separation and sorting, pre-treatment, and recycling. This paper explores the generation of Mg alloy scrap and its reincorporation into industrial products. This review outlines various Mg scrap recycling technologies based on different phase states. These include liquid-state recycling (such as flux refining, impurity removal additives, fluxless refining, compound treatment, and direct remelting), solid-state recycling (involving hot extrusion, equal-channel angular pressing (ECAP), friction stir extrusion (FSE), and spark plasma sintering (SPS)), vapor-state recycling (comprising vacuum distillation and sublimation), electrochemical recycling (solid oxide membrane (SOM) electrolysis, RE-12™ electrorefining, and non-aqueous solution electrorefining), and Mg secondary alloy development. The advantages and existing challenges associated with each method are compared and discussed, and the current obstacles to the future recycling of complex scrap are examined.

The increasing demand for magnesium as a next-generation structural material highlights the significance of incorporating CaF₂ as a catalyst to enhance the efficiency of vacuum carbothermal reduction of magnesium (VCTRM). This study investigates the thermodynamic theory and catalytic mechanism of CaF₂ in the VCTRM process. Catalytic reduction experiments and molecular dynamics simulations were conducted to gain a comprehensive understanding of the process. Thermodynamic calculations indicate that in vacuum carbothermal reduction, the primary reaction occurs between MgO and C. Analysis shows that CaF₂'s catalytic action primarily involves F^-, Ca²⁺ and melt eutectic. Our experiments demonstrate that the addition of CaF₂ significantly increases the reduction rate. Furthermore, the mass loss rate increases with both the quantity of CaF₂ added and the holding time, stabilizing at additions over 5%. Experiments conducted at temperatures above the melting point of CaF₂ exhibited a pronounced catalytic effect. The resultant magnesium showed optimal structure and crystallization, with a purity of 87.84%. Notably, while CaF₂ remained in the residue, it was not detected in the condensate, confirming its catalytic role. Molecular dynamics simulations revealed that molten CaF₂ sabotages the structure of magnesium oxide, with F^- dispersing onto the surface of MgO, thus enhancing the reaction between MgO and C to form CO. However, no chemical reaction was observed between C, MgO, and CaF₂. The occurrence of the carbothermal reduction reaction at high temperatures depends on the concentration of the reducing agent C, with CaF₂ influencing the reaction rate. This research elucidates the theoretical and mechanistic foundations of CaF₂-catalyzed VCTRM, aligning with the green energy-saving concept and significantly advancing the green and efficient VCTRM process.

Magnesium (Mg) alloys are widely used lightweight structural materials for automobiles and help reduce carbon emissions. However, their use increases the production of Mg alloy scrap, which is recycled at a much lower rate than aluminum, and its greater complexity poses challenges to existing recycling processes. Although vacuum distillation can be used to recycle Mg alloy scrap, this requires optimizing and maximizing metal recirculation, but there has been no thermodynamic analysis of this process. In this study, the feasibility and controllability of separating inclusions and 23 metal impurities were evaluated, and their distribution and removal limits were quantified. Thermodynamic analyses and experimental results showed that inclusions and impurity metals of separation coefficient lgβ_i ≤ -5, including Cu, Fe, Co, and Ni below 0.001 ppm, could be removed from the matrix. All Zn entered the recycled Mg, while impurities with -1 < lgβ_i < -5 such as Li, Ca, and Mn severely affected the purity of the recycled Mg during the later stage of distillation. Therefore, an optimization strategy for vacuum distillation recycling: lower temperatures and higher system pressures for Zn separation in the early stage, and the early termination of the recovery process in the later stage or a continuous supply of raw melt can also prevent contamination during recycling. The alloying elements Al and Zn in Mg alloy scrap can be further recovered and purified by vacuum distillation when economically feasible, to maximize the recycling of metal resources.

We hereby report a green and simple volatilization-condensation process to prepare high-purity magnesium in different crystal forms under vacuum condition. This method can be also used for the analysis of other metals, which can be separated by the same concept. In addition, Mg condensation is a very fast process, and the corresponding easy growth of the Mg crystals is promoted when the concentration of magnesium vapor is raised. From the view of crystallization, ultrafast crystal growth of high-purity magnesium is a barrier-free and orderly process. Interestingly, different condensed forms of Mg obtained via this ultrafast volatilization-condensation process are showing different purities. The distinct morphological formation of Mg in different condensed form is probably attributed to the differences of surface energy change of Mg during the condensation process.