Advances in scandium recovery beyond state of the art

Scandium (Sc) has attracted a lot of attention in the last decades because of the unique technological applications of this element. It is a key component in solid oxide fuel cells and aluminium alloys, which are especially produced for the aerospace industry. Unfortunately, there exist very few scandium deposits. Thus, scandium is generally recovered from secondary raw materials or by-products from the production of uranium, nickel laterites or titanium dioxide pigment processing. Recovery of scandium from the leachates has mainly been performed by solvent extraction, ion exchange or a combination of these two techniques. The co-extraction of iron, aluminium and titanium during these hydrometallurgical operations creates problems and extensive purification is required to produce a high-quality product. Therefore, selective and advanced ways to isolate scandium from iron, were developed on a laboratory scale. In highly acidic solutions, scandium can be selectively retained by inorganic metal(IV) phosphate materials via a cation exchange reaction. Amorphous and crystalline layered titanium(IV) and zirconium(IV) phosphates have demonstrated excellent potential for the separation of scandium from bauxite residue leachate. It was found that the selectivity of the inorganic metal phosphates originates from size selection and phosphate coordination. In addition, it was also found that a supported ionic liquid phase (SILP) betainium sulfonyl (trifluoromethanesulfonylimide) poly(styrene-co-divinylbenzene), prepared by covalent linking of the ionic liquid to the resin, shows an excellent uptake rate of rare-earth elements (REE) from acidic media, in particular of Sc, Y, Nd, Dy. Furthermore, a scandium concentrate can be obtained via successive selective precipitations. The addition of ammonia solution for the removal of iron from the leachate is followed by scandium phosphate precipitation via dibasic phosphates. The purity of the resulting concentrate, containing 20-70% scandium phosphate, depends on the impurity level of the initial solution. The concentrate can be further purified with less effort than by direct processing of the scandium containing solutions. With the emphasis on scandium recovery in several Horizon2020 EU-funded research projects, i.e. REDMUD, SCALE and REMOVAL, more alternative processes for scandium recovery will become available in the near future.

Jaar van publicatie:2018

Toegankelijkheid:Open