A critical review on separation and extraction of scandium from industrial wastes: Methods, difficulties, and mechanism

Scandium (Sc) is a typical dispersed rare earth element. The sources of Sc mainly include primary sources(natural ores) and secondary sources(some industrial by-products or industrial waste), mainly distributed in Russia, China and Australia. The demand of scandium for aerospace, metallurgy and laser industry is increasing year by year, which results in the shortage of Sc sources. Natural Sc sources are rare because Sc rarely accumulates into independent ores and deposits in geological processes Fortunately, it has been found that large amounts of Sc are also found in industrial wastes, which should be turned into another huge stock of Sc if it can be effectively separated and extracted from these wastes. However, to separate and extract scandium effectively is still a challenging problem due to low scandium content, complex production process and low productivity. Many efforts had been done by researchers in the past 30 years. In this review, we summarizes the typical methods of extracting scandium including solvent extraction, ion exchange, solid phase adsorption, etc. and discussed the difficulties in practical applications and separation mechanisms. This review demonstrates many outstanding research achievements have been reported in recent years that solvent extraction technology occupies a dominant position in the separation of scandium, and ion exchange and solid phase adsorption also gradually show their respective advantages. As one of the latest research advances in solid phase adsorption, surface ion imprinting materials can combine the advantages of carrier and scandium in solvent extraction technology for the surface modification of adsorption materials. This method can solve the difficulties of selective adsorption, which is worth continuous attention in future studies.