High Temperature Reduction of Bauxite Residue

Abstract

The present study focused on investigating the high-temperature reduction of bauxite residue, also known as red mud. A series of reduction experiments on red mud was performed to investigate the influences of temperature (1400, 1450, and 1500 ◦C), reaction time (15, 30, and 60 min) and reductant addition (7 and 14% carbon). A reduction experiment using a combination of carbon and plastic in the form of linear low-density polyethylene (7% carbon and 5% LLDPE) was also tested. The experiments were carried out in a vertical tube furnace using a graphite crucible under an argon atmosphere. Phases formed after the reduction process was analyzed using a scanning electron microscope equipped with an energy dispersive spectroscopy detector. At 7% carbon addition for all reduction temperatures and times, the reduction process of red mud produced metal and slag. The metal mainly consisted of iron with main trace elements of Si, Ti, P, S, and V. The slag mainly consisted of Na2O, Al2O3, SiO2, CaO, and TiO2 components with residual iron oxide of less than 3.5 wt.%. Increasing the carbon addition to 14% at 1450 ◦C significantly increased the Si content in metal up to 19.1 wt.% and significantly decreased Na2O in slag to less than 0.1 wt.%. The experiment with 7% carbon + 5% LLDPE addition gave a similar reduction extent to the experiment with only 7% carbon addition. The combustion of the LLDPE occurred before the reduction took place, and hence the LLDPE did not significantly contribute to the reduction process.