The story of Sc in bauxite residues and its journey from ore to waste to value

Bauxite residue (BR) is a massive waste stream generated worldwide from Alumina production that is intensely studied for its potential reuse and as a secondary resource for various metals. More recently the recovery of the technology metal Scandium (Sc), which can be enriched in BRs, has attracted the interest of research and industry. Sc enrichment in BR was discovered more than 25 years ago, however there is a lack of comprehensive knowledge about its association and distribution. Geochemical and mineralogical insights that provide a connection between the Sc occurrence in the primary bauxite ore and the BR are scarce.

In this study, we present the results of detailed mineralogical investigations on BRs of different geological backgrounds and on the Sc behavior during the recovery process by leaching. The results were determined by combining wet chemical, microtextural and structural analyses with statistical design of experiments. They provide an understanding of how the Sc association changes from ore to waste depending on the primary bauxite and the chosen leaching conditions. The primary bauxite and the atmospheric conditions during bauxitization determine how Sc is distributed in the BR. BRs derived from karstic bauxites formed under partly reducing conditions are hence more prone to contain higher mass fractions of easily leachable Sc than BRs derived from lateritic bauxites. The recovery achieved by leaching therefore depends on the Sc distribution and will furthermore determine the viability of Sc recovery from BR. The research was funded by the EU's H2020 SCALE program under GA No. 730105.