Development and investigation of the technological process of plasma carbothermal reduction of slag from secondary metallurgy of aluminum

Abstract

Based on a critical analysis of the current state and prospects of development of the problem of pyrometallurgical recovery/extraction of aluminum from aluminum-bearing industrial waste, the need to replace traditional, electrocarbonothermic processes and melting process units with innovative, plasma carbothermal processes and furnace-reactors, with the possibility of reverse feeding and recovery of gasified during melting metal and metal oxide components is substantiated. On the basis of this analysis a new technological scheme of smelting with a new design of plasma-arc furnace-reactor, which provides a solution to the problem using a special hollow double-shell graphite cathode connected to the system of circulating supply of gases separated from the reaction zone, was developed and presented. The proposed technological scheme also differs in the use of such highly active liquid and gaseous reagents as carbon-containing reducing agents as calcium carbide (CaC₂) and methane (CH₄). The main features of chemism of reducing processes are described. It is shown that by replacing traditional coke with anodized calcium carbide and natural gas (methane) the recovery rate of aluminum oxide (Al 29-34%) and silica (SiO₂) and hematite (Fe₂O₃) present with it increases to 80-99%. Specific power consumption is reduced by 35-40%, the 90-95% reduction in the loss of target elements, the 80% reduction in the emission of greenhouse carbon dioxide, which is replaced by a very valuable recyclable synthesis gas - CO-H₂. By additionally feeding separate portions of quartzite and steel-rolling scale in the furnace-reactor, a complex alloy-ligature of Fe-Si-Al-Ca system is melted, with the ratio of components: 1:[1.3-2]:[1.3-1.2]:[0.9-1.25]. With the introduction into industrial practice of the plasma carbothermal process of aluminum reduction from secondary aluminum dumping slags accumulated in the world (4 million tons/year), it will be possible to return up to 1-1.5 million tons/year of aluminum to the production processing cycle.