Separation of magnesium vapor and carbon monoxide during the vacuum carbothermal reduction of MgO by employing the polycrystalline silicon cutting waste as the separation agent

With the rapid development of magnesium-based materials, the worldwide demand for magnesium has increased dramatically. Vacuum carbothermal reduction (VCR) method is a potential technology to replace the highly energy-intensive Pidgeon process for magnesium production. However, this process is limited by the bottleneck problem, e.g., the separation of magnesium vapor and carbon monoxide during the carbothermal reduction. In this paper, a new strategy for separating magnesium vapor and carbon monoxide during the VCR by employing polycrystalline silicon cutting waste (PSCW) as the separation agent is proposed. The separation mechanism of magnesium vapor and carbon monoxide by PSCW was investigated thoroughly. It is proved that the magnesium vapor can react with silica in PSCW to produce magnesium oxide, while carbon monoxide cannot react with the PSCW under the same conditions, by which the magnesium vapor and carbon monoxide was separated efficiently. The magnesium oxide was then dissolved by using hydrochloric acid to recycle Si from the reduced PSCW. The results show that a high-purity Si was obtained and its recovery rate attained 86.9%. Additionally, the magnesium used in the experiment could be recycled from the leaching solution in the form of MgCl2 & sdot;6H2O and its purity attained 99.94%. Based on these, it is thus suggested that a novel process for separating magnesium vapor and carbon monoxide was achieved, which is not only beneficial for the cost reduction, but also for the environmental protection.