Neutralization of Bayer bauxite residue (red mud) by various brines: A review of chemistry and engineering processes

Bauxite residues from the alumina industry are highly alkaline and should be neutralized before using them for industrial or agricultural purposes. This review evaluates the effectiveness of seawater and other brines as neutralizing agents, which have advantages over alternatives such as mineral acids. Brines not only lower pH but also prevent reversion by immobilizing alkalinity in the form of Ca and Mg minerals such as hydrotalcite, which can also bind to potential contaminants. The analysis of solid residues, leachates, and supernatant liquors from brine neutralization demonstrated that Ca- and Mg-rich brines (natural and synthetic) can outperform seawater by lowering the pH and total alkalinity of the bauxite residue. The use of industrial waste brines to lower the alkalinity of bauxite residue can be a cost-effective and environmentally friendly “waste management by waste” technique. • Bauxite residue neutralization by various brines was reviewed. • Reduction of residue pH and alkalinity using brines was well demonstrated. • Ca- and Mg- rich brines enhance the long-term stabilization of product residue. • Large-scale use of industrial brines for residue neutralization appears promising.