Recovery of scandium from various sources: a critical review of the state of the art and future prospects

Scandium is one of the most valuable rare-earth elements, and its extraction is centralized in China. For this reason, the search for new scandium sources is required to supply the demand. Bauxite residue is considered a secondary scandium resource. It has estimated around 4 billion tons of bauxite residue worldwide with 20–200 mg/kg of scandium. The hydrometallurgical route is considered advantageous due to its low content. However, the acid leaching generates silica gel reducing the extraction rate and making the solid/liquid separation difficult. H2O2 can be used to avoid its synthesis, and the parameters during the leaching must be explored. Despite the studies in the literature about scandium extraction from bauxite residue, there is a lack of investigation about suppressing the synthesis of silica gel in the acid reaction. The present study aimed at the scandium extraction from bauxite residue by H2SO4 and H3PO4 leaching. The use of H2O2 was evaluated to avoid silica gel formation. The effect of time, temperature, and acid concentration was evaluated. Results showed that scandium extraction is directly related to iron extraction. The H2O2 contributed to silicon oxide formation during the acid reaction but declined scandium extraction by half. The leaching rate increased from 25 to 90 °C achieving 99% for iron and aluminum and 91% for scandium. The increase of H2SO4 concentration increased the titanium leaching. The leaching of metals using H3PO4 was similar to H2SO4 leaching. Moreover, the extractive process focused on near-zero-waste generation is essential to avoid waste stored in dams.

Extraction of Scandium from Critical Elements-Bearing Mining Waste: Silica Gel Avoiding in Leaching Reaction of Bauxite Residue

Contrasted microbial community colonization of a bauxite residue deposit marked by a complex geochemical context

Contrasted microbial community colonization of a bauxite residue deposit marked by a complex geochemical context.

Comparative atmospheric leaching characteristics of scandium in two different types of laterite nickel ore from Indonesia

Investigation of scandium in bauxite residues of different origin

Understanding scandium leaching from bauxite residues of different geological backgrounds using statistical design of experiments

Microscopic knowledge of the structural, energetic, and electronic properties of scandium fluoride is still incomplete despite the relevance of this material as an intermediate for the manufacturing of Al–Sc alloys. In a work based on first-principles calculations and X-ray spectroscopy, we assess the stability and electronic structure of six computationally predicted ScF3 polymorphs, two of which correspond to experimentally resolved single-crystal phases. In the theoretical analysis based on density functional theory (DFT), we identify similarities among the polymorphs based on their formation energies, charge-density distribution, and electronic properties (band gaps and density of states). We find striking analogies between the results obtained for the low- and high-temperature phases of the material, indirectly confirming that the transition occurring between them mainly consists of a rigid rotation of the lattice. With this knowledge, we examine the X-ray absorption spectra from the Sc and F K-edge contrasting first-principles results obtained from the solution of the Bethe–Salpeter equation on top of all-electron DFT with high-energy-resolution fluorescence detection measurements. Analysis of the computational results sheds light on the electronic origin of the absorption maxima and provides information on the prominent excitonic effects that characterize all spectra. A comparison with measurements confirms that the sample is mainly composed of the high- and low-temperature polymorphs of ScF3. However, some fine details in the experimental results suggest that the probed powder sample may contain defects and/or residual traces of metastable polymorphs.

https://doi.org/10.1021/acs.inorgchem.2c04357

Marie C. Gentzmann

Papers

Investigation of scandium in bauxite residues of different origin

Understanding scandium leaching from bauxite residues of different geological backgrounds using statistical design of experiments

Electronic Structure and Core Spectroscopy of Scandium Fluoride Polymorphs