Regulating CaSi2 in High-Calcium Metallurgical-Grade Silicon via Aluminum Incorporation

The production of organic silicon (Si) monomer from metallurgical-grade silicon (MG–Si) is hindered by CaSi₂, leading to a decreased yield of (CH₃)₂SiCl₂. Therefore, strict control of CaSi₂ content is essential. However, the existing MG–Si oxidation refining process fails to prevent the precipitation of FeSi₂ and the reduction of Si₈Al₆Fe₄Ca content, while simultaneously decreasing CaSi₂ content. To address this issue, a novel method of adjusting aluminum (Al) content in MG–Si to reduce CaSi₂ content and increase Si₂Al₂Ca or Si₈Al₆Fe₄Ca content was proposed. The results indicated that the impurity ratio in MG–Si directly influenced the type of precipitating intermetallics. Specifically, when m(Al/Ca) < 1.35, CaSi₂, FeSi₂, and Si₂Al₂Ca were present. When 1.35 < m(Al/Ca) < 1.35 + 0.48 m(Fe/Ca), FeSi₂, Si₂Al₂Ca, and Si₈Al₆Fe₄Ca were encountered. Additionally, when the Al content m(Al/Ca) > 1.35 + 0.48 m(Fe/Ca), only Si₂Al₂Ca and Si₈Al₆Fe₄Ca were observed. Upon adjusting the Al content in high-Ca MG–Si to m(Al/Ca) > 1.35, CaSi₂ was effectively eliminated. Furthermore, within the experimental range, the average content of Si₈Al₆Fe₄Ca precipitates increased from 12.84 to 37.94 wt pct after adjusting the Al content in the melt, representing a maximum increase of ~ 2.95 times. This study successfully elucidated the regulation of calcium (Ca)-containing intermetallics in high-Ca MG–Si, paving the way for the production of high-quality MG–Si raw materials for silicone monomer synthesis.