Kinetics of isothermal reduction of carbon-containing silicomanganese dust

Silicomanganese dust contains large amounts of valuables, such as Si and Mn, which can be used as raw materials for smelting silicomanganese. However, adding the dust directly to the submerged arc furnace can affect the permeability of burden due to the fine particle size of the dust, resulting in incomplete reduction reactions during the smelting process. In this paper, the silicomanganese dust with graphite powder and other additives were pressed to form the carbon-containing dust briquettes, and the self-reduction process of the dust briquette was investigated by isothermal thermo-gravimetric method with different C/O ratios, contents of fluxing agents and reduction temperatures. Various reduction kinetic models for the dust briquettes at different temperatures were established. The result shows that the reaction fraction of the dust briquette is more than 90% at C/O ratio of 1.2 with optimal reduction efficiency. The addition of CaF2 contributes to decrease the melting point and viscosity of the dust briquettes, thus increasing the reduction rate. As the reduction temperature increases, the reduction rate of the dust briquette increases. The reduction reaction rate of the dust briquette is controlled by gas-phase diffusion. Meanwhile, the reduction process of the dust briquette is analyzed kinetically with the reaction time of 5 min as dividing line. The apparent activation energies for the two diffusion stages are 56.10 kJ/mol and 100.52 kJ/mol, respectively. The kinetic equations are expressed as [1-(1-ƒ)1/3]2 = 0.69⋅e-56100/RTt and [1-(1-ƒ)1/3]2 = 2.06⋅e-100520/RTt.