Hydrometallurgical refining of metallurgical silicon

The paper presents the results of refining silicon of metallurgical grades based on leaching of impurities with inorganic acids. Silicon samples were studied by metallographic and X-ray fluorescent methods of analysis, as well as X-ray spectral microanalysis. To improve the quality of this alloying element, we carried out experimental work on its hydrometallurgical purification with solutions of various acids (10 % H2SO4 , HCl, HNO3 , 4 % HF) and their mixtures. Values of changes in the Gibbs energy were calculated for reactions of interaction with reagents of the main impurity inclusions recorded in the studied silicon samples (FeSi2 , Fe2Si, FeSi, AlFeSi, AlFeSi2 , Al3FeSi2 , FeSi2Ti, FeAlTiSi, TiSi2 , Ca2Si). The experiments were carried out on silicon samples with a particle size of –200 μm with constant stirring by a magnetic stirrer at a temperature of 60 °С, duration 1 h and L:S = 5:1. Determination of concentration of the impurity elements in the solution after leaching was made by the atomic emission method of analysis. When hydrofluoric acid is used as a solvent, the best results are obtained for purification of iron, aluminum, and titanium (concentration in solution, mg/dm3, respectively: 2380, 831, 145). The maximum concentration of calcium in the solution (147 mg/dm3 ) was achieved by hydrochloric acid treatment of fine silicon. The most effective for transferring impurities into solution is a mixture of sulfuric and hydrofluoric acids at a ratio of 1:1. Using a mixture of H2SO4 and HCl as a solvent (at a ratio of 1:3) made it possible to achieve sufficiently high mass concentrations of impurity elements in the leaching solution. The degree of silicon purification from iron was 33.32 %, aluminum – 54.64 %, calcium – 65.77 %, titanium – 15.64 %.