Hydrogen Reduction of Hazardous Bauxite Residue for Green Steel and Sustainable Alumina Production.

This study introduces a novel approach in sustainable metallurgy for the efficient utilization and valorization of bauxite residue, aimed at producing sustainable alumina and green steel. The integrated process combines hydrogen reduction, alkaline leaching, and smelting of the leaching residue. Initially, the bauxite residue was pelletized with calcite and quicklime to create self-hardened pellets, leveraging the cementing effect of quicklime with water. These pellets underwent hydrogen reduction, achieving over 95% reduction, resulting in the formation of metallic iron and a leachable calcium aluminate phase for alumina recovery. The reduced pellets were then subjected to alkaline leaching, extracting 62% alumina. Subsequently, smelting at 1550 °C facilitated the near-complete separation of iron and calcium-rich slag. The process was analyzed using various analytical techniques, including X-ray diffraction, electron probe microanalysis, and inductively coupled plasma mass spectroscopy, complemented by thermodynamic calculations using FactSage 8.1 software. Iron oxide reduction to metallic iron was achieved at 1000 °C for 120 min, while sodium carbonate leaching effectively extracted alumina from the calcium aluminate slag. However, residual alumina was attributed to the formation of indissoluble gehlenite and a dense calcium carbonate layer that impeded leaching kinetics. Successful iron separation during smelting required temperatures above 1500 °C, though this process was challenged by the high viscosity of the oxide matrix and the purity of the iron.

Graphical abstract: