A novel process to recycle coal gasification fine slag by preparing Si-Fe-Al-Ca alloy

Maximizing the use of valuable components in coal gasification slag is of great significance for resource recovery and the environment due to the huge annual emission of coal gasification slag. This study successfully produced Si-Fe-Al-Ca alloy with a composition of 63.83 wt% Si, 19.73 wt% Fe, 7.09 wt% Al, 6.32 wt% Ca, 1.70 wt% Ti, 0.03 wt% P, 0.66 wt% Mn, 0.05 wt% Cr, 0.53 wt% C, and 0.06 wt% others through electric arc furnace smelting from mixed coal gasification fine slag. The alloy composition is close to the standard 65% ferrosilicon, which can be used in the deoxidation of the molten steel industry. Moreover, the alloy yield was increased from 20.53% to 67.78% by using the residual carbon of the coal gasification slag as the reductant directly instead of adding petroleum coke. The transformation of coal gasification fine slag during the smelting process and the formation mechanism of the alloy were studied and the carbothermal reduction mechanism of Al₂O₃ and CaO can be explained by the reduction and decomposition theory of carbides. The complex liquid phase of the reactant system and product system in the smelting process made the carbothermal reaction of Al₂O₃ and CaO easier to occur, but it also brought the problem that the reactions were not fully completed.