Effect of gas composition and temperature on reduction characteristic in red mud-coal composite pellets

The disposal of red mud, which is the by-product obtained from alumina production, has brought about environmental pollution because of its caustic nature as well its metal and alkaline contents. Red mud-coal composite pellets were directly reduced to deal with red mud. The influences of reduction temperature and gas composition on the reaction were studied. Experiment results indicated that the optimum reaction parameters were a temperature of 1100 °C and an H2 atmosphere. Reduction degrees in H2 and CO atmospheres were significantly higher than those in N2 atmosphere. Reduction did not strictly follow the Fe2O3 → Fe3O4 → FeO → Fe sequence in N2 atmosphere, and this phenomenondid not occur in H2 atmosphere. This gas–solid combination reduction process is appropriate for recovering Fe from Bayer red mud. Meanwhile, the microstructure and phase transformation of the reduction process were investigated via scanning electron microscopy and X-ray diffraction.