Goethite, a tailor-made host for the critical metal scandium: The FexSc(1-x)OOH solid solution

Scandium is the subject of increasing interest and is even becoming critical for a number of institutions in Europe and the U.S.A. among others because of its economic value and supply risk. Despite this growing awareness, little is known about its geochemical behaviour. Recent studies have shown that Sc can be strongly associated with iron oxides including goethite but the mode of interaction is not yet fully understood. We investigated the incorporation of Sc in goethite structure in controlled batch systems. For the first time, we show the formation of a solid FeOOH-ScOOH solution consistent with an ideal solution despite significant differences in atomic radii between Sc 3+ and Fe 3+ . We believe that beyond this fundamental knowledge concerning the affinity of Sc for goethite, these results provide important insights into Sc speciation in primary or secondary sources, including Sc-rich lateritic deposits and bauxite residues after alumina extraction, for the future design of extraction processes with a low environmental footprint, as an alternative to current energy-intensive technologies.