Hydrogen reduction of bauxite residue and selective metal recovery

Abstract

Bauxite residue (BR) is an industrial by-product generated during the production of alumina from bauxite ores in the Bayer process. BR is environmentally hostile due to it is high alkalinity and fine particle size distribution. In this work, BR is blended with NaOH and subsequently reduced with hydrogen, in order to develop an intermediate material rich in magnetite and sodium aluminate, and by doing so, enable the recovery of iron, aluminium as well as sodium. Several process parameters, such as sodium dosage, reduction temperature and soaking time, on the qualities of the final material, were assessed. The highest conversion degree from hematite to magnetite was 96 % and it occurred for 20 wt% NaOH addition to BR, and reduction with 5 vol% H2, for 120 min at 500 °C. The aluminum oxides were transformed into water-soluble sodium aluminate phases, with a range of other interesting metals enriched in the resulting residue. The work herein demonstrates the potential of the suggested process as a near zero-waste process for BR.