Environmental Impacts of Novel Routes for Sc Production from Bauxite Residues and Tio2 Production Wastes

Authors
Hengevoss, Dirk; Lenz, Markus; Misev, Victor; Feigl, Vitoria

Abstract
Scandium (Sc) is high-valued element and a key component in producing high strength aluminum alloys but Sc supply is limited. Sc-producing countries are China (66%), Russia (26%) and Ukraine (7%). The use of Sc containing waste streams such as bauxite residue (BR) from alumina production and acid waste (AW) from TiO2 production with new processing technologies promises to be more sustainable compared with traditional Sc production. A first processing chain from AW considered novel selective extraction by ion-exchange, purification with solvent extraction, fractional crystallization, and calcination. The global warming potential (GWP) of Sc2O3 produced in such way summed up to more than the double of the GWP published for a conventional AW route. Differences between the GWP of the novel and conventional AW routes will be discussed at the conference. In a second processing chain, acid resistant nanofiltration was performed as an alternative to ion-exchange to extract Sc from AW. The higher GWP of Sc2O3 production compared to the published value is mainly due to scaling effects of nanofiltration. A third processing chain considered BR and included mineral acid leaching, selective extraction by ion-exchange and further steps mentioned above. The GWP was similar like our estimated value of Sc2O3 production from REO concentrate in China. However, the BR route had the highest GWP of the three novel process chains. One should note that – in contrast to traditional Sc production – only Sc and no other REE will be won. All emissions are allocated to Sc. The use of the filter cake as raw material for cement production would be in favour for the third processing chain and would also reduce other environmental impact categories than the GWP. This project has received funding from EU Horizon 2020 under grant agreement No 730105 (www.scale-project.eu/) and was supported by the Swiss State Secretariat for Education, Research and Innovation under contract number 16.0155.