5-year leaching experiments to evaluate a modified bauxite residue: remediation of sulfidic mine tailings

The ALTEO company produces approximately 300,000 tons per year of bauxite residue after alumina extraction, which is washed and dried in a press filter to produce Bauxaline®. In this study, different ways for recovering and reusing this residue were explored, namely transformation into a vegetated soil, use in acid mine drainage depollution, and application in sulfide-mine tailings remediation. The Bauxaline® was therefore transformed into modified bauxite residue (MBR), resulting in reduced alkalinity, salinity, and sodicity. To counterbalance the net acid generation potential of two sulfidic mine tailings with 1 mol H⁺ kg^-1 (1.5% sulfide) and 3.3 mol H⁺ kg^-1 (5.3% sulfide), respectively, various treatments were applied. These treatments included the addition of 10% MBR or 10% MBR plus limestone, or by limestone only, within 40-l lysimeters. Six lysimeters were monitored over a 5-year period to assess the long-term emissions from treated materials. Vegetation was tested under various conditions, and its impact on emission was evaluated. The emissions of mine tailings treated with MBR and limestone were very low. The mine tailings with limestone showed intermittent peaks of emission, probably due to the coating of calcite grain by ferric oxide, hindering contact with percolating water. Vegetation successfully grew in the treated tailings. This study demonstrated that the alkalinity of limestone can temporarily immobilize elements in sulfidic mine tailings, with a reduction factor of emissions of 300 and 40 for the two mine tailings, respectively. For long-term immobilization, the alkalinity provided by both limestone and MBR and the Al and Fe oxides of MBR are more effective and necessary for long-term immobilization, with a reduction factor of 300 and 900, respectively.