5 years of leaching experiments to evaluate a modified bauxite residue. Part 1: transformation into a soil and storage of immobilized heavy metals from acid mine drainage

Abstract

Abstract ALTEO company produces approximately 300,000 tons per year of bauxite residue washed and dried in a press filter, so-called Bauxaline®, after extraction of the alumina. The study explored different ways of recovery and re-use for this residue, namely transformation into a vegetated soil, acid mine drainage depollution, and sulfide-mine tailings remediation. The soluble alkalinity of the material was transformed into solid phase alkalinity by reaction with atmospheric CO2 and precipitation of carbonates in limestone following the addition of gypsum (calcium sulfate dihydrate), and the resulting sodium sulfate was leached. The Bauxaline® was so transformed into modified bauxite residue (MBR), with reduced alkalinity, salinity and sodicity. A total of sixteen lysimeters of 40 liters volume each and one lysimeter of 700 liters were set up and allowed 5-years monitoring, to assess long-term emissions from MBR and MBR having reacted with acid mine drainage. Vegetation was tested on various conditions and its impact on emission was evaluated. The emissions are compliant with EU inert waste or non-hazardous waste storage requirements. The material can be easily vegetated. This study demonstrates that red mud can be transformed into an soil, that acid mine drainage can be depolluted at pilot scale site by MBR, and that the metal-laden MBR can be stored on-site and revegetated by natural topsoil or better by MBR.