Extraction of Less Common Metals (REEs and Sc) from Greek Bauxite Residue

Less common metals including rare earth elements (REEs), as well as Scandium (Sc), play a central role in the development of twenty-first-century economies. Common REE applications are in electronics, renewable energy, the automotive industry, defense and aerospace, medical and health care, glass and ceramics, catalysts, magnets, and metallurgy. Scandium’s main applications are in aluminum alloys, solid oxide fuel cells, and in laser technology. REEs and Sc are relatively scarce in nature, and there are a lot of efforts to extract and refine them from several primary and secondary resources such as bauxite residue (BR). This paper describes the mineralogy of REEs and Sc in Greek BR. Then, it summarizes the efforts done by NTUA to extract and refine REEs and Sc either by direct leaching through H₂SO₄ and ion exchange or by direct leaching with task-specific ionic liquids such as the betainium bistriflimide (HbetTf₂N) and subsequent stripping with acidic HCl solutions.