5 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 vast quantities of bauxite residue generated globally necessitate environmentally responsible disposal strategies. This study investigated the long-term (5-year) behavior of modified bauxite residue (MBR) with an initial pH of 8.5, using lysimeters to test various configurations: raw MBR, sand/soil capping, revegetation, and used MBR (UMBR) previously applied for acid mine drainage remediation. Throughout the 5-year 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 material clogging risk and suitability for salt-tolerant plant growth. Emission of potentially toxic elements (except V) decreased rapidly after the first year to low levels. Leachate concentrations consistently remained below LD50 for Hyelella Azteca, at least an order of magnitude lower by the experiment's end (except for first-year Cr). Sand capping performed poorly, while revegetation and soil capping slightly increased emissions, though these were negligible given the low final emission 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.