Alternative and sustainable sources of rare earth elements (REE) are critical to sustain a green energy future. Approximately 300 million tonnes of bauxite are processed annually primarily to extract alumina, but can contain moderate concentrations of REE, offering a potential alternative resource. The REE in bauxites are associated with a range of mineral phases, including iron oxy-hydroxides, fluorocarbonates (bastnaesite) and phosphates (xenotime). These minerals have been bioleaching targets in other deposits, through microbially-mediated organic acid production or redox reactions. Sequential extractions of Turkish bauxites show that between 4 and 17% total REE are acid soluble (acetic acid) and a further 17 to 42% are reducible (hydroxylammonium chloride) and 2 to 24% are oxidisable (hydrogen peroxide). To target the acid soluble fraction, we used Aspergillus sp. to produce organic acids. To target the reducible and oxidisable fractions we used Acidithiobacillus ferrooxidans grown on either sulphur or ferrous iron.
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