Extractive Separation of Scandium from Rare Earth Elements

Abstract

The extractive separation of scandium and rare earth metals (REM) was studied. The extractants used are trialkylbenzylammonium di-2-ethylhexylphosphate (TABAC-D2EHPA, binary extractant) and trioctylphosphine oxide (TOPO). The effect of concentration and nature of mineral acids on the scandium recovery was studied. Changing the HNO3 concentration in the range of 0.01 – 2.0 mol/L does not affect the extraction of metals by binary extractant, extraction corresponds to the following row: La, Eu, Gd < Tb <Y < Er < Yb < Sc, Th, that allows to separate scandium from rare earth metals by single extraction. Extraction of scandium by trioctylphosphineoxide from HCl solution proceeds quantitatively in the range of 0.5 – 7.0 mol/L, an increased HNO3 concentration leads to the decrease in scandium extraction. The conditions for the extractive separation of scandium and REM using TOPO solution were determined: scandium can be isolated selectively at the HNO3 concentration of 0.5 mol/L REM are transferred into the organic phase at the HNO3 concentration of 5.0 mol/L. It was determined that the organic phase extracts the compounds of the following composition: (ScA3 + R3R′NCl) (HA - D2EHPA, R3R'NCl - TABAC) and [Sc(NO3)3·3TOPO].