Study of the Possibility of Obtaining Non-Decomposing Slag During Low-Carbon Ferrochrome Production

Methods are analyzed for stabilizing self-disintegrating slags in melting low-carbon ferrochrome, and the main reasons for breakdown are considered. Four methods are shown for stabilizing oxide melts of which a promising method for preventing breakdown under contemporary production conditions for chromium ferroalloys by mixing melts is a reduction in the content of dicalcium silicate with a reduction in the CaO/SiO₂ ratio in oxide melt to a value of less than 1.4. However a reduction in CaO/SiO₂ slag basicity to < 1.7 leads to a reduction in the degree of chromium reduction. With a the aim of maintaining a high degree of chromium extraction into molten metal it is proposed to conduct melting with excess siliceous reducing agent, which undoubtedly leads to an increase in silicon in the ferrochrome obtained. A study of the molten slag characteristics showed that with an increase in silicon content in metal up to 5% there is a reduction in the residua content of Cr₂O₃ in slag to 6%. The fundamental possibility of obtaining on an industrial scale non-disintegrating slag with a residual content up to 6.0% Cr₂O₃ with basicity > 1.33 is demonstrated by experiment (during melting low-carbon ferrochrome containing not less than 5% Si). However, according to the specifications of GOST 4757–91 and the international standard ISO 5448-81 the silicon content in low-carbon ferrochrome should not exceed 1.5%, in view of which the silicothermal process for process for preparing ferrochrome by a mixing method should be separated into two stages. The first stage is preparation of siliceous semiproduct (low-carbon ferrochrome containing Si ≈ 5%) and non-disintegrating slag with reduced basicity (CaO/SiO₂ = 1.3–1.4). The second stage is refining the semiproduct with respect to silicon with preparation of highly basic slag (CaO/SiO₂ = 1.8–1.9) and ferrochrome with the required silicon content (less than 1.5%). The possibility of obtaining a non-disintegrating slag during melting low-carbon ferrochrome with subsequent processing into building rubble will make it possible to improve the ecological situation in the vicinity of ferroalloy enterprises, to reduce slag dump and adjacent territory contamination and dust content, and also to reduce the amount of slag, loss of chromium, and to increase productivity of the process with a reduction in specific consumption of lime and electrical energy.