Five Years of Leaching Experiments to Evaluate Land Spreading of a Modified Bauxite Residue Before and After Treatment of Acid Mine Drainage: Sand or Soil Capping and Revegetation

The global generation of bauxite residue necessitates environmentally responsible disposal strategies. This study investigated the long-term (5-year) behavior of bauxite residue whose pH was lowered to 8.5, called modified bauxite residue (MBR), using lysimeters to test various configurations: raw MBR or used MBR (UMBR) previously applied for acid mine drainage remediation, sand or soil capping, and revegetation. Throughout the experiment and across all configurations, the pH of the leachates stabilized between 7 and 8 and their salinity decreased. Their low sodium absorption ratio (SAR) indicated minimal risk of material clogging and suitability for salt-tolerant plant growth. Leaching of potentially toxic elements, except vanadium, decreased rapidly after the first year to low levels. Leachate concentrations consistently remained below LD50 for Hyalella azteca and were at least an order of magnitude lower by the experiment’s end, except for first-year chromium. Sand capping performed poorly, while revegetation and soil capping slightly increased leaching, though these were negligible given the low final leaching levels. Revegetated MBR shows promise as a suitable and sustainable solution for managing bauxite residues, provided the pH is maintained above 6.5. This study highlights the importance of long-term assessments and appropriate management strategies for bauxite residue disposal.