Relative vacuum reduction innovative processes applied in primary magnesium production—Comprehensive analysis of thermodynamics, resource, energy flow, and carbon emission

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.