Sustainable recovery of metallic Fe and oxides from bauxite residue via H2 reduction: Enhancing purity and recovery rates

Abstract

Bauxite Residue (BR), an alkaline waste from the Bayers process, holds significant metal oxides. This study explored a method to recover metals from BR simultaneously, involving H₂ reduction with NaOH, followed by combined water leaching and a two-stage wet magnetic separation process. The investigation delved into the effects of factors (temperature, H₂ quantity, time, and NaOH addition) on phase transformations, the recovery of Al and Na in the sodium aluminate as well as metallic Fe, and the separation of non-magnetic fractions (containing CaO, SiO₂, TiO₂). At 900 °C, complete conversion of iron oxides to metallic Fe was achieved. Sodium aluminate formation from aluminum oxyhydroxides increased with higher temperatures, time, and NaOH addition. Through the response surface methodology (RSM) approach, the study identified optimal H₂ reduction conditions for concurrent metal recovery: 900 °C for 120 min with 20 wt% NaOH where Fe, Fe grade, Al, and Na recovery was 88.1 %, 69.1 %, 93.8 %, and 92.6 % respectively. This closed-loop process facilitates efficient and sustainable recovery of metallic Fe, Al, and Na (in sodium aluminate solution), and non-magnetic fractions abundant in Ca, Si, Ti, and REEs, thereby supporting the principles of a zero-waste economy.