Electrothermal re-processing of dust produced during ferromanganese production

This study investigates the feasibility of recovering ferroalloy from dust produced during the smelting of ferrosilicon manganese at the Taraz Metallurgical Plant LLP. Typically, the dust comprises (%wt.): MnO - 53.3; SiO₂ - 24.0; MgO - 5.4; CaO - 9.6; Al₂O₃ - 3.8; Fe₂O₃ - 1.5; ZnO - 1.8; PbO - 0.6. To determine the optimal process parameters, thermodynamic modelling was deployed using the HSC-5.1 software package to analyse results from a second-order rotatable experimental design (a Box-Hunter design). Dust was pelletised in a bowl granulator followed by electric smelting in combination with coke and steel chips in a single-electrode arc furnace with a power of up to 15 kV×A; the steel chips were added as a source of iron. The study shows that at equilibrium in the presence of iron, components of the dust reacted with carbon forming manganese silicides and FeSi at temperatures above 1300^ºC and 1400^ºC, respectively. By increasing the amount of carbon in the charge from 14 to 30% by weight of dust, the extraction of silicon and manganese into the alloy is increased to 44.7 and 92%, respectively, at a temperature of 1800^ºC. The MnC22 and MnC25 grades of ferrosilicon manganese are obtained when the amount of carbon is equal to 20-30% by weight of dust, allowing 56.4-79.3% of Si and 67.7-84.3% of Mn to be extracted into the alloy over the temperature range of 1600-1800ºC. The time taken for electric smelting of the dust is reduced by 16-18% by increasing the amount of both carbon from 18 to 36% and steel chips from 2 to 6% which resulted in a corresponding increase in the extraction of Si and Mn into the alloy from 20.9 to 60% and 68.3-82.1%, respectively. Thermodynamic modelling of the system at equilibrium was deployed to determine the temperature effect on the distribution of silicon, manganese, zinc and lead in the "dust components - carbon - iron" system, the extraction efficiency of silicon, manganese and iron into ferroalloy, and the content of these metals in the alloy. The electric smelting produces grade MnC22 of ferrosilicon manganese from a combination of granular dust, 30% coke and 6% steel chips resulting in an alloy containing silicon and manganese at 20.5 and 65.8%, respectively.

ferroalloys, dust, electric smelting, thermodynamic modelling, rotatable design, ferrosilicon manganese