Studies on selection of solvent extractant system for the separation of trivalent Sm, Gd, Dy and Y from chloride solutions

In this paper, solvent extraction of mixture of rare-earths (Sm(III), Gd(III), Dy(III) and Y(III)) from chloride solutions using acidic, neutral and basic type extractants and their mixtures has been investigated. The main objective of the work was to select a suitable solvent extractant system for the separation of mixture of rare-earths using organophosphoric acid (TOPS 99), phosphonic acid (PC 88A), phosphinic acid (CYANEX® 272), monothiophosphinic acid (CYANEX® 302), phosphine oxide (CYANEX® 923, CYANEX® 921) and amine based (ALAMINE® 336, ALIQUAT™ 336) extractants. The composition of the synthetic mixture of rare-earths was Sm — 1.835 g/L, Gd — 0.862 g/L, Dy — 0.303 g/L, Y — 0.589 g/L which was prepared according to the leach liquor of the Korean domestic ore. From the effect of aqueous phase acidity and extractant concentration on the extraction efficiency of rare-earths, PC 88A (0.1 mol/L) considered as better extractant with high separation factor for Dy–Y pair with Sm–Gd pair. Mixture of extractants has shown no significant effect on the separation factors of rare-earths than individual extractants.

► Solvent extraction of rare-earths using individual and mixture of regents were reported.
► 100% extraction of rare-earths was found with 1 mol/L TOPS 99.
► Zero percent extraction was observed with 1 mol/L ALAMINE® 336 and ALIQUAT™ 336.
► A separation factor (β = DDy+Y/DSm+Gd) of 173.4 was obtained using 0.1 mol/L PC 88A.
► Mixture of extractants has shown no significant effect on the separation factors.