New Insights into Silicon Purification by Alloying–Leaching Refining: A Comparative Study of Mg–Si, Ca–Si, and Ca–Mg–Si Systems

In the present work, a comparative study of the silicon alloyingleaching purification process was carried out on the recently developed MgSi system, the CaSi system, and the novel ternary CaMgSi system. Insights were provided into the integrated process from aspects of thermodynamic assessment, microstructural analysis, experimental observation, computational simulation, and analytical modeling. The main silicide precipitates of the three MgSi, CaSi, and CaMgSi alloys studied were determined as Mg2Si, CaSi2, and ternary Ca7Mg7.5 +/- dSi(14), respectively. Other metallic impurities were found to form complex silicides embedded inside the main precipitate, where P also segregated and precipitated according to the interaction with the alloying elements. All of the impurities were further carried away with the removal of the main precipitates through the subsequent leaching process. It was found that the ternary CaMgSi alloy exhibits a cleaner leaching process due to the unique crystal structure of Ca7Mg7.5 +/- dSi(14). A novel crackingshrinking principle-based kinetics model was developed to further describe the impurity removal process. The segregation behavior of P was also modeled through a thermodynamic approach and Ca was found to have stronger P affinity compared to Mg. It was finally concluded that the novel CaMgSi ternary alloy system exhibited better performance overall as compared to the other two binary alloys.