Magnesium plays an important role in biomedicine, new energy vehicles, aerospace and other fields because of its excellent physical and chemical properties. China is a major source of magnesium worldwide, with the output of primary magnesium accounting for >80% of the world’s total annual output. The smelting process represented by the Pidgeon process plays the leading role in China because of its simple process flow and equipment and the flexibility of the production scale. However, the Pidgeon process always has the problems of low utilization of reduction heat, a short lifetime of the reduction tank, a high cost of the reduction furnace, and a discontinuous production process. Therefore, how to produce magnesium in a clean, efficient and continuous manner has been the focus of industry development research. In this work, from the perspective of the preparation of magnesium by thermal reduction, the production of high-purity magnesium, and the recycling of waste magnesium alloys, the research status of magnesium preparation by direct vacuum and relative vacuum processes was reviewed, including the reduction mechanism, migration and condensation patterns and production efficiency of magnesium. The effects of the reducing agent, reduction temperature, holding time and other factors on the preparation of magnesium were emphasized. Finally, by comparing the production processes of magnesium by direct vacuum and relative vacuum methods, the advantages and disadvantages of the two methods for the preparation of magnesium were mainly discussed, and the future development of magnesium was proposed.

Magnesium and magnesium alloys, serving as crucial lightweight structural materials and hydrogen storage elements, find extensive applications in space technology, aviation, automotive, and magnesium-based hydrogen industries. The global production of primary magnesium has reached approximately 1.2 million tons per year, with anticipated diversification in future applications and significant market demand. Nevertheless, approximately 80% of the world's primary magnesium is still manufactured through the Pidgeon process, grappling with formidable issues including high energy consumption, massive carbon emission, significant resource depletion, and environmental pollution. The implementation of the relative vacuum method shows potential in breaking through technological challenges in the Pidgeon process, facilitating clean, low-carbon continuous magnesium smelting. This paper begins by introducing the principles of the relative vacuum method. Subsequently, it elucidates various innovative process routes, including relative vacuum ferrosilicon reduction, aluminum thermal reduction co-production of spinel, and aluminum thermal reduction co-production of calcium aluminate. Finally, and thermodynamic foundations of the relative vacuum, a quantitative analysis of the material, energy flows, carbon emission, and production cost for several new processes is conducted, comparing and analyzing them against the Pidgeon process. The study findings reveal that, with identical raw materials, the relative vacuum silicon thermal reduction process significantly decreases raw material consumption, energy consumption, and carbon dioxide emissions by 15.86%, 30.89%, and 26.27%, respectively, compared to the Pidgeon process. The relative vacuum process, using magnesite as the raw material and aluminum as the reducing agent, has the lowest magnesium-to-feed ratio, at only 3.385. Additionally, its energy consumption and carbon dioxide emissions are the lowest, at 1.817 tce/t Mg and 7.782 t CO₂/t Mg, respectively. The energy consumption and carbon emissions of the relative vacuum magnesium smelting process co-producing calcium aluminate (12CaO·7Al₂O₃, 3CaO·Al₂O₃, and CaO·Al₂O₃) are highly correlated with the consumption of dolomite in the raw materials. When the reduction temperature is around 1473.15 K, the critical volume fraction of magnesium vapor for different processes varies within the range of 5%–40%. Production cost analysis shows that the relative vacuum primary magnesium smelting process has significant economic benefits. This paper offers essential data support and theoretical guidance for achieving energy efficiency, carbon reduction in magnesium smelting, and the industrial adoption of innovative processes.

Compared with vacuum continuous magnesium smelting process, it has important advantages of significantly lower energy consumption and carbon emissions, which makes it possible to realize green magnesium smelting. In the process of industrialization, the reduction efficiency of prefabricated pellets affects both the yield of metallic magnesium and the utilization efficiency of reducing slag. In this paper, the pore-forming agent was added to the prefabricated pellets, and the mechanism of different pore-forming stages was analyzed by micro-nano simulation. The results show that the dehydration pore-forming stage has the greatest influence on the reduction rate of pellets. A theoretical model of the relationship between porosity and reduction efficiency of prefabricated pellets in a relatively vacuum atmosphere was established, which was well verified by dehydration pore-forming stage, calcination pore-forming stage and reduction pore-forming stage. It is verified by experiments that the reduction efficiency of prefabricated pellets can be increased from 91.42% to 99.93% after adding pore-forming agent.