Development of a solvometallurgical process for the separation of yttrium and europium by Cyanex 923 from ethylene glycol solutions

Abstract

Recycling of critical raw materials such as rare-earth elements (REEs) is increasingly crucial in the development of a sustainable economy. Separation of individual REEs (mainly yttrium and europium) from lamp phosphor waste has become essential due to the substantial stockpiling of end-of-life fluorescent lamps. The mutual separation of Y(III) and Eu(III) from aqueous chloride solutions with solvating extractants by conventional extraction methods is highly inefficient. Hence, separation of Y(III) and Eu(III) was investigated using a novel technique called “non-aqueous solvent extraction”. Unlike conventional solvent extraction, the new approach uses two immiscible organic phases (more polar (MP) and less polar (LP)) instead of an aqueous and an organic phase. The present work describes a new solvometallurgical process for the separation of Y(III) and Eu(III) from ethylene glycol solutions using the solvating extractant Cyanex 923 in an aliphatic diluent. This extraction system exhibits improved separation compared to extraction from aqueous solutions. Following predictions based on a McCabe-Thiele diagram, a three-stage counter-current extraction simulation was carried out to extract Y(III) quantitatively, with 7% co-extraction of Eu(III) at a volume phase ratio of MP:LP of 1.5:1. The co-extracted Eu(III) was selectively scrubbed in two stages using an Y(III) scrub solution. Y(III) was recovered from the loaded less polar organic phase by precipitation stripping with an aqueous oxalic acid solution and a subsequent calcination step. Y2O3 with a purity of more than 99.9% was obtained. A complete process flow sheet, comprising extraction, scrubbing and stripping steps for the separation of Y(III) and Eu(III) is reported. The feasibility of the developed process was successfully demonstrated in continuous mode using a battery of mixer-settlers.