Electrothermal processing of chrysotile-asbestos wastes with production of ferroalloy and extraction of magnesium into the gas phase

The article presents the results of an experimental study on the processing of wastes from chrysotile-asbestos production at Kostanay Minerals JSC. An electrothermal technology for the extraction of magnesium and siliceous ferroalloy from the chrysotile-asbestos wastes is proposed. The influence of the amount of coke and steel shavings on the technological parameters of the obtained alloys is determined. The results of derivatographic and SEM analyses of the chrysotile-asbestos waste samples are presented. The studies included planning experiments using the second-order rotatable designs (Box-Hunter plans), graphical optimization of technological parameters, and electric melting of a charge in a graphite crucible using a single-electrode arc furnace. Adequate regression equations were obtained explaining the effect of the amount of coke and steel shavings added to the chrysotile-asbestos waste on the extraction degree of silicon into the alloy and the silicon concentration in the alloy. By the electric melting of the charge, high-quality FS25 grade ferrosilicon with a silicon content of 24.4-29.2% and FS45 grade ferrosilicon with a silicon content of 41.6-45% were obtained. It was established that FS45 grade ferrosilicon with the extraction degree of silicon into the alloy from 75 to 85.4% is formed in the presence of 33.6-38% of coke and 16-20.8% of steel shavings. FS25 grade ferrosilicon is formed in the presence of 30-38% of coke and 29.4-40% of steel shavings; the extraction degree of silicon is 68.6-73.8%.