Feasibility of Bauxite Residue in Pollution Mitigation and Resource Recovery

Bauxite residue is an industrial waste generated from the alumina refining industry, raising great concerns about environmental pollution. The primary problem for bauxite residue is its high alkalinity and salinity. This beneficial reuse of bauxite residue is desirable for the sustainable management of this waste stream. Bauxite residues can be used as an option of flue gas desulfurization to reduce the toxicity associated with high alkalinity. In this dissertation, it was first identified the linkage between the characteristics of the bauxite residues and their acid neutralization capacity (ANC). Further options of beneficial use were investigated according to the characteristics of bauxite residues. With the iron oxide-rich mineralogy, bauxite residue exhibited excellent capabilities to remove aqueous phosphate at environmentally relevant concentrations. Given that phosphate is an important nutrient, the removal and concentration of phosphorus with bauxite residue could be a strategy for the recovery of phosphorus as a resource. With its cation exchange capacity, bauxite residues were also found to be able to remove ciprofloxacin as an extensively used antibiotic and potential water pollutant. These findings show that bauxite residues could be used as feasible sorbents for pollution mitigation as well as resource recovery. The beneficial use was further demonstrated in the utilization of bauxite residues as an additive in anaerobic digestion, which is frequently implemented for the stabilization of organic waste and the production of biogas as a renewable energy source. My work shows that bauxite residues could be readily neutralized by the buffering capacity of the digestate in the anaerobic digestion without negatively impacting process performance. More importantly, the addition of bauxite residue could enhance the availability of phosphorus in the digestate which is desirable for the land application of anaerobic digestate as a soil supplement. In summary, this work has developed multiple pathways for the sustainable management of bauxite residue as a hazardous material with integrated applications in pollution mitigation and resource recovery.