Dry disposal of bauxite residues in abandoned mine open pits

摘要

Bauxite residues exit the process stream as a highly alkaline slurry with low solids content rendering their land disposal a difficult issue. The objective of this study was to develop a methodology for environmentally safe dry disposal of bauxite residues in abandoned mine open pits. The methodology includes dewatering and controlled disposal of bauxite residues, capping with waste rock or treated bauxite residues and, finally, development of a vegetation cover. This methodology is mainly based on bauxite residue properties, which possess low hydraulic conductivity if compacted at optimum moisture content. Several parts of this scheme were investigated at laboratory and pilot field scale. Simulation of an abandoned mine that was planned to be rehabilitated was also performed. Based on the results obtained, the main risk due to bauxite residues disposal is associated with the alkalinity of the material and initially high Na and Al concentrations in the leachate that progressively decrease due to the depletion of these elements. Both the field tests and simulation indicate that the amount of drainage water will be minimal, i.e. approximately 3% of the annual precipitation.