Mathieu Chassé

Abstract: Scandium (Sc) has unique properties, highly valued for many applications. Future supply is expected to rely on unusually high-grade (up to 1000 ppm) lateritic Sc ores discovered in Eastern Australia. To understand the origin of such exceptional concentrations, we investigated Sc speciation in one of these deposits. The major factors are unusually high concentrations in the parent rock together with lateritic weathering over long time scales in a stable tectonic context. At microscopic and atomic scales, by combining X-ray absorption near edge structure spectroscopy, X-ray diffraction and microscopic and chemical analyses, we show that Sc-rich volumes are associated with iron oxides. In particular, Sc adsorbed on goethite accounts for ca 80 % of the Sc budget in our samples. The remaining is incorporated in the crystal structure of hematite, substituting for Fe3+. Scandium grades reflect the high capacity of goethite to adsorb this element. In contrast, the influence of hematite is limited by the low levels of Sc that its structure can incorporate. These crystal-chemical controls play a major role in lateritic Sc deposits developed over ultramafic–mafic rocks.

TL;DR: In this article, the evolution of scandium speciation during chemical weathering is unknown, limiting the understanding of the processes controlling its dynamics in the critical zone, and the authors use a multiscale mineralogical and spectroscopic approach involving electron microprobe, laser-ablation-inductively coupled plasma mass spectrometry, selective leaching and X-ray absorption nearedge structure spectroscopy, complemented by mass transfer calculations.

TL;DR: In this article, a meta-analysis of about 13,000 analyses of scandium content in garnet grains showed that, below the spinel-garnet transition, this phase carries about three-quarters of the Sc budget of the mantle.

TL;DR: In this paper, the pigments composed of chromium were characterized by X-ray diffraction (XRD), UV-visible spectroscopy and Xray absorption near edge structure spectroscope (XANES).

TL;DR: A detailed comparative study of Sc K-edge X-ray absorption near-edge structure spectroscopy (XANES) reference spectra of three Sc-bearing compounds is presented, revealing the specificities of the Sc pre-edge, indicating that core-hole screening is weaker than for Ti4+- bearing compounds.