Design aspects of a selective leaching process for scandium recovery from bauxite residue

The exploitation of Bauxite Residue (BR) of Aluminium industry as a resource for production of Rare Earth Elements (REEs), with main focus on Scandium (Sc), seems to emerge as a well promising perspective for a new symbiotic era in the metallurgical processes. Within the European Union (EU) context, this concept is fully aligned with the EU’s target for sustainable access to critical raw materials as being of high importance for economy, competitiveness and the environmental protection. BR, either as alkaline wet red mud, or as dried ferroalumina, has to be treated with a leaching process of enhanced selectivity for REEs and of the lower possible yield for the main elements. The liquid leachate product of this process is led to other advanced extraction methods that could enhance their concentration from ppm level to higher percentages. This work presents the investigation of design aspects for an acidic selective leaching process, which is based on sulphuric acid as leaching agent and it is focused on Sc, because it is the far most valuable trace element of BR and the maximization of its specific recovery (mg Sc/ L of used acid) has been proven to be critical for the process [1]. Simultaneously, the experimental investigation aimed at the lower possible iron (Fe) leaching yields, as long as it is the most abundant cationic element in most of BRs, and especially in examined Greek BR (Aluminium of Greece S.A.), in such an extent that imposes complications to the following enrichment stages. Furthermore, this process preserves the bulk quantity of BR metallic content in precipitated solids and therefore it allows its further metallurgical exploitation