Purification of Metallurgical-Grade Silicon by Acid Leaching

Purification of metallurgical-grade silicon (MG-Si), used in many applications such as the medical industry, polymer industry and the solar cells manufacturing. Removal of impurities from MG-Si is critical in these applications. The MG-Si studied in the present research contained various iron, calcium, and aluminum impurities. The hydrometallurgical purification method with different types of acids as solvents was chosen to refine MG-Si. Effects of hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid in combination with each other as a solvent for purification of MG-Si were investigated. Additionally, the effects of temperature and particle size of MG-Si were evaluated. In this study, in comparison with previous studies, samples with a larger particle size (in the range of 53 to 300 microns), less refining time (1 to 6 h) and relatively higher temperatures (30 to 70 C-circle) were studied. The results indicated that the highest purity of MG-Si was achieved by HCl (25%) + HF (5%) and followed by HCl (25%) + H2SO4 (30%), HNO3 (25%) + HCl (25%), HNO3 (5%) and H2SO4 (25%), respectively. It was also found that with particle size 53 mu m, applying a temperature of 50 C-circle for 6 h resulted in high efficiency and purity (99.96%) of MG-Si.