Influence mechanism of B2O3 additive on the vacuum silicothermic reduction process for magnesium production from calcined magnesite

Abstract

This work investigated how B₂O₃ as an additive affects the processing characteristics of silicothermic reduction of calcined magnesite for magnesium production. It aimed at preventing the pulverization of slag and mitigating the related environmental pollutions, while enabling the utilization of sensible heat carried with the slag by-products. Special emphasis was laid on understanding the structure variation of slag by-products and its implicated mechanism. Thermodynamic calculations were performed to determine the phase diagrams and equilibrium phases formed during the reduction as a function of temperature and B₂O₃ additive. The results revealed a reduction in slag melting temperature by approximately 20 °C with 2 % B₂O₃ addition. Furthermore, the phases, morphologies, and existence form of related elements contained in the slag by-products were characterized. The mechanism of vacuum silicothermic reduction with B₂O₃ addition was discussed. The results suggested that B₂O₃ increased the bridging oxygen content in the silicate structure within the slag by-products, strengthening the network connections of silicate structure and enhancing the degree of polymerization. This consequently prevented the slag from pulverization and maintained the chemical pathway of reduction. Being in the pellet state, the spent slag can be easier treated with greatly suppressed dust pollution. On this B₂O₃-modified silicothermic reduction, sustainable strategies can then be developed to save energy and reduce environmental risk in the process of magnesium production.