In situ remediation of bauxite residue by sulfuric acid leaching and bipolar-membrane electrodialysis

Abstract

In situ remediation of a bauxite residue by integrating a storage area with CSIRO's soda recovery process was evaluated. The process consisted of the following steps: bauxite residue is neutralized with sulfuric acid; the slurry is separated into a neutralized residue and a leachate. The residue is sent to a storage area and washed with rainfall. The leachate and drainage/runoff from the storage area are collected and purified; sodium sulfate in the solution is then split into sodium hydroxide and sulfuric acid using bipolar-membrane electrodialysis. Finally, the sodium hydroxide is used in a Bayer refinery and the sulfuric acid is used for neutralization of bauxite residue. This study investigated the optimum conditions and remediation of the bauxite residue. pH rebounding was observed after sulfuric acid neutralization of bauxite residue. Considering this rebound, the most suitable pH was set at 4.5. Washing remediated the residue to accomplish the goals for bauxite residue rehabilitation. Furthermore, sodium hydroxide and sulfuric acid were recovered by bipolar-membrane electrodialysis. Cost-benefit analysis for an assumed one million tons refinery showed 10% return on investment. Evaluation of the advantages of neutralized residue and technical improvements are expected to make this process feasible for remediation of bauxite residue.