Study of boron distribution between silicon and slags of CaO-SiO₂, MgO-SiO₂, CaO-MgO-SiO₂, and CaO-Al₂O₃-SiO₂ systems under reducing conditions

Abstract

We study the distribution of boron between silicon and slag of the CaO-SiO2, MgO-SiO2, CaO-MgO-SiO2, and CaO-Al2O3-SiO2 systems under reducing conditions with the purpose of determining the feasibility of using boroncontaining materials to eliminate slagging in the melting zone during industrial silicon smelting in ore smelting furnaces. To that end, we used model slags obtained by melting chemically pure oxides, as well as silicon-based alloys with an admixture of boron. High-purity 5N silicon produced by Kazakhstan Solar Silicon LLP was used. Boron alloys were manufactured independently by melting silicon with boron. The experiments included holding liquid slag and alloys in graphite crucibles at a temperature of 1600°C under poorly reducing conditions. The boron content in slag and silicon samples was analyzed by inductively coupled plasma mass spectrometry. The boron distribution coefficient in the above systems was established to range from 2 to 2.5 for the entire melt area of these systems at 1600°C. The boron distribution coefficient was demonstrated to decrease under an increase in the content of Al2O3 in the CaO-Al2O3-SiO2 triplet system, which agrees with the data obtained by other authors. The use of graphite crucibles in experiments creates reducing conditions, similar to those in the hearth of an ore smelting furnace. Therefore, this approach provides more adequate data in predicting the equilibrium boron content in silicon in comparison with the experiments conducted using alumina crucibles by other authors. It was also found that the boron distribution coefficient does not depend on the magnesium oxide content in double (MgO-SiO2) and triplet (CaO-MgO-SiO2) systems. In conclusion, our results lift restrictions on the content of boron in boron-containing fluxes during industrial silicon smelting.