Investigation of Sc recovery from bauxite residues
Source: BAM, FB 4.4, Marie Gentzmann
The technology metal scandium (Sc) is considered a critical raw material in the European Union since 2017 and is currently one of the most expensive elements on the market. It is of great importance for the energy transition since it is an enabler for future technologies such as solid oxide fuel cells and lightweight materials. However, like many other critical raw materials, Sc is currently only produced outside Europe. To establish a Sc value chain in Europe that uses secondary raw materials for sustainable raw material extraction, bauxite residue (also called red mud) is one of the most intensively studied materials. This residue accumulating during alumina production can be enriched in Sc and therefore represents a potential source. In the Horizon2020 project SCALE (GA° 730105) BAM investigated the occurrence of Sc in various bauxite residues. The aim was to gain a better understanding of the mineralogy, geochemistry and distribution of the element in order to increase the fundamental knowledge needed to develop recovery processes. The publication compares three different bauxite residues that originate from bauxites (the main aluminum ore) of different geological background.
The behavior of the bauxite residue during Sc recovery is investigated by a set of experiments, which is planned and evaluated by statistical methods. The recovery is generally achieved by acid leaching e.g., using sulfuric acid. Different leaching conditions are compared to understand how to enable a high Sc recovery. Therefore, parameters such as temperature or acid concentration are varied and their influence on the recovery process is investigated. Subsequently, the mineralogy of the leaching residues is studied, to gain insights in potentially Sc-bearing mineral phases. The investigations show that bauxite residues of different geological background exhibit fundamental differences in leaching behavior. In particular, the fraction of Sc that is recovered under mild leaching conditions varies strongly. In the Bayer process, a certain fraction of the Sc is dissolved from the bauxite ore and redistributed to the bauxite residue. It can adsorb to particle surfaces in the bauxite residue or incorporate into new, readily soluble phases. This fraction is mainly influenced by the environmental conditions during bauxite formation. In conclusion, an estimate of the recovery potential of Sc and favorable leaching conditions can be derived from the knowledge of the geology and geochemistry of the source materials.
Understanding scandium leaching from bauxite residues of different geological backgrounds using statistical design of experiments
Marie C. Gentzmann, Andrea Paul, Juan Serrano, Christian Adam
published in Journal of Geochemical Exploration, Volume 240, Article number 107041, 2022
BAM division Analytical Chemistry; Reference Materials
BAM department Process Analytical Technology
BAM division Materials and the Environment
BAM department Thermochemical Residues Treatment and Resource Recovery