Behavior of Yttrium and Other Impurities in the Production of Scandium Oxide from Bauxite Residue

BauxitesBauxite in the North of EuropeanEuropean Russia are characterized by a high scandiumScandium content (up to 350 ppm calculated as Sc2O3). Most of scandiumScandium is embedded into the structure of aluminumAluminum-containing minerals, as well as into zircon ZrSiO4 and apatite. These minerals break down during the pressure digestion of the bauxitesBauxite, so scandiumScandium is re-precipitated and sorbed on the surfaceSurface of bauxite residueBauxite residue particles. UC RUSAL has developed and pilot tested the extraction of scandium oxideScandium oxide from bauxite residueBauxite residue using a sodium bicarbonate solution that enables to dissolve up to 50% of scandiumScandium into the solution followed by precipitation of the concentrate and purificationPurification to obtain 99.0% Sc2O3. The extraction uses actual liquors from aluminaAlumina production and flue gases. BauxitesBauxite contain a number of REMREM elements (e.g. zircon, titaniumTitanium, hafnium, copperCopper, yttriumYttrium, thoriumThorium, etc.). Chemical behaviour of said REMsREM during the sodium bicarbonate digestion is similar to the behaviour of scandiumScandium. To obtain pure scandium oxideScandium oxide (2N) (Sc2O3 ≥ 99.0 wt.%) without radioactive impurities, effective purificationPurification technology was developed. Moreover, resulting mutual neutralisationNeutralisation of some streams allows obtaining a high-grade REMREM concentrate. The additional advantage of this process lies in reducing the carbon footprintCarbon footprint of aluminaAlumina production due to the use of flue gases containing up to 8 vol.% CO2, as well as alkali neutralisationNeutralisation in the bauxite residueBauxite residue.