Bauxite Residue Neutralization Potential Using Biogenic Sulfuric and Citric Acids

Remediation of bauxite residue (BR) represents an important requirement in some applications aiming to the residue of large-scale utilization such as agronomic applications. The high operational cost of chemical neutralization is one of the main impediments for using this technology in ameliorating BR's traits such as high alkalinity and sodicity. This study applied a biotechnological approach to neutralize the BR using biogenic sulfuric and citric acids, produced by the bacterium Acidithiobacillus thiooxidans and by the fungi Aspergillus niger, respectively, in comparison to their ACS reagent grade equivalents. Batch tests containing BR (20% w/v) mixed with acidic solutions had solid (XRD, XRF, and SEM) and liquid (pH, EC, and ICP-OES) phases evaluated separately. Results showed that the biogenic H2SO4 was more effective in partial BR neutralization (final pH similar to 8) and sodium content decreasing (similar to 35%), indicating the potential of this biotechnological route in the BR remediation prior utilization.