Purification of metallurgical-grade silicon by Sn–Si refining system with calcium addition

Abstract

Purification of metallurgical-grade silicon (MG–Si) by a combination of solvent refining and super gravity separation and acid leaching has been studied. MG–Si was alloyed with tin, and based on this system, the removal of main impurities in MG–Si by solvent refining was investigated. Furthermore, phosphorus removal by calcium addition in molten Si and Sn–Si melt was also studied. Inductively Coupled Plasma (ICP) chemical analysis revealed main impurities including B and P could be efficiently removed by the Sn–Si process and acid leaching. The content of P further reduced when Ca was added to the Sn–Si refining system. Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM–EDS) analysis showed that the formation of compounds between P and several elements in the grain boundaries during the solvent refining process was an important routine of P removal. The maximum weight percent of P in P-containing impurity phases reached to 17.8% in the refined Si after the Sn–Si refining process with Ca addition.