Separation of rare-earth ions from ethylene glycol (+LiCl) solutions by non-aqueous solvent extraction with Cyanex 923

Abstract

The separation of a mixture of rare earths by non-aqueous solvent extraction with two immiscible organic phases has been studied. The more polar organic phase was ethylene glycol with dissolved lithium chloride and the less polar organic phase was the extractant diluted in n-dodecane. Cyanex 923 was found to be the most performant extractant amongst the investigated acidic, basic and solvating extractants: Cyanex 272, Cyphos IL 101, Aliquat 336, bis(2-ethylhexyl)amine, trioctylphosphine oxide (TOPO) and Cyanex 923. The replacement of the aqueous chloride feed solutions by non-aqueous ethylene glycol feed solutions had a profound effect on the distribution ratios and separation factors. The separation factors for extraction of pairs of rare earths from aqueous chloride solutions by Cyanex 923 are too low to be of practical use. On the contrary, a mixture of rare earths can be separated conveniently in four different groups by extraction with Cyanex 923 from ethylene glycol (+LiCl) solutions. The influence of several parameters such as the chloride concentration, the type of chloride salt, the addition of other polar solvents to the ethylene glycol phase, the addition of second extractant to the less polar organic phase, and the addition of complexing agents to the ethylene glycol phase has been studied. The extraction mechanism for extraction of ytterbium(III) was studied by slope analysis experiments. The ytterbium(III) species in the ethylene glycol phase and the extracted species in the n-dodecane phase were determined by EXAFS. Furthermore, a conceptual flow sheet for the fractionation of rare earths from an ethylene glycol (+LiCl) feed solution into different groups by extraction with Cyanex 923 has been proposed. The new extraction system is useful for extraction of scandium and for separation of scandium from the other REEs.