The extraction of scandium with tetraoctyldiglycolamide from solutions of mineral acids is studied, and the effect of the diluent on the distribution coefficients of scandium and a number of elements is determined. It is shown that the scandium extraction is most efficient from nitric-acid media. The optimal conditions are found for nitric-acid leaching of red mud for further concentration of scandium by extraction with tetraoctyldiglycolamide as an extractant.

The extraction behavior of Na and K during lithium isotope separation using benzo-15-crown-5 (B15C5) in chloroform as the extractant was investigated. It was found that potassium was extracted better than sodium and lithium, the metal: B15C5 ratio in the extracted compound was 1: 1 for all metals. It was shown that in the extraction systems with a LiCl concentration higher than 5 mol L-1, B15C5 was noticeably transferred into aqueous solutions, while concentrated LiCl solutions had a salting-out effect with respect to Na and K.

To study the complexing processes occurring in the extraction systems, the extraction of acetic, propionic (methylacetic), monochloroacetic, dichloroacetic and trichloroacetic acids using benzo-15- crown-5 as an extractant is considered. The extraction isotherms of acids with the pure solvent and 1 M benzo-15-crown-5 in chloroform are determined. The dependences of the distribution ratios of the considered acids on the extractant concentration in the organic phase are presented. Based on the experimental data and the “blank” extraction isotherm equations, the acid: benzo-15-crown-5 ratio in the complexes formed in the extract have been calculated (minus the contribution of extraction with the pure solvent). No complexation of methylacetic acid with benzo-15-crown-5 occurs, and the stability of the complexes of chloro-substituted acetic acids rises in the order acetic acid < monochloroacetic acid < dichloroacetic acid < trichloroacetic acid.

A systematic study for scandium extraction with benzo-15-crown-5 in chloroform from trichloroacetate solutions has been performed. The presence of free trichloroacetic acid in extraction system has been found to prevent scandium transfer into organic phase. Scandium is extracted from neutral trichloroacetate solutions as partially hydrolyzed trichloroacetate complexes, the extracted compound includes two crown ether molecules. The presence of nitrate anions has no effect on scandium distribution ratios and nitrate anion is not involved in extracted compound composition. Optimal process conditions for selective scandium recovery from concentrated solutions of rare-earth nitrates in the presence of lithium trichloroacetate with high separation factors (> 100) on the use of B15C5 as extractant have been determined.