Authors: Éva Ujaczki, Lisa O’Donoghue, Patricia Cusack, Mark Healy, Teresa Curtin and Ronan Courtney
Summary: The scope of the Al Source project is to determine the optimisation of state-of-the-art technologies that could offer potential in the reuse of bauxite residue to recover valuable elements.
Bauxite residue is an inevitable secondary product that is generated in the extraction of alumina (aluminium oxide) from bauxite by the Bayer process. The global inventory of bauxite residue has exceeded 4.6 billion tonnes and grows by approximately 120 million tonnes per annum. The large volumes of stockpiled residue represent an opportunity to investigate the recovery of rare earths and also the use of the residue as a filter for phosphorus in waste water. In addition, residue landfills receive negative press regarding the potential environmental damage if the residue is not managed correctly. Innovative projects such as the Al Source project provide an opportunity to promote more positive aspects, including technology development, waste as a resource and potential economic benefits.
Rare earth materials have been classified as critical raw materials at the European Union level. The recovery of rare earths from residues helps to secure the supply of essential resources (rare earths are used extensively in modern day electronic products) while also developing a circular economy for such materials. The Al Source project was directly aligned with A Resource Opportunity – Waste Management Policy in Ireland, in which maximum value is sought from wastes by researching their reuse potential as a source of rare earth materials or as a filter medium for removing phosphorus from wastewater.
Two utilisation techniques were evaluated for bauxite residue to highlight its reuse value. Rare earth content was determined and a baseline characterisation and composition aspect was created. Extraction techniques were optimised and evaluated for the recovery of gallium (Ga) from bauxite residue, achieving 86 mg of Ga from 1 kg of bauxite residue, corresponding to 71% of the total. Second, a process for recovering phosphorus (P) from agricultural wastewater using bauxite residue was developed. Modified residue can be used to absorb P from wastewaters at up to 2.7 mg P/g bauxite residue. Reuse as a source of rare earth elements or in wastewater treatment facilities may be an appropriate option for bauxite residue.
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