Improving the efficiency of the carbothermal reduction of red mud by microwave treatment

Abstract

In this work, we studied the effect of microwave treatment of red mud briquettes containting more than 48% of Fe on the process of iron reduction under various conditions of heat treatment. Research samples were collected from red mud formed during the production of alumina from bauxite at the Ural Aluminum Smelter. The chemical composition of mud samples was examined by X-ray fluorescence analysis. The composition of initial mud and that of agglomerates obtained after treatment in microwave and muffle furnaces was studied using the X-ray diffraction method. Phase transitions and structural changes occurring under the effect of heating were studied by scanning electron microscopy. The experimental briquettes comprising red mud and charcoal were treated at 850°C and 1000°C in a microwave furnace (under the frequency of 2.45 GHz and the power of 900 W). For reference, briquettes of analogous composition were heat-treated in a muffle furnace under the same conditions. It was found that, under the conditions of microwave heating to 1000°C for 10 min, hematite is completely reduced to metallic iron after the addition of wustite. An analysis of the m i-crostructure of the samples after microwave treatment showed that the particles of metallic iron in the as-obtained pellet-agglomerates have a larger size than in those after conventional thermal heating in a muffle furnace. The metallized phases of reduced iron at the end of heat treatment in a microwave furnace create a stable durable body of agglomerates. The evidence-based parameters of the process can become a basis for designing a technology for recycling such an industrial material as red mud. The obtained high-strength pellets from red mud with a high content of reduced iron (up to 85%) may be used as an alternative charge material for ferrous metallurgy. The proposed technology for recycling red mud into pellet-agglomerates can be applied in various industries to reduce environmental impact on the production areas of alumina plants.