Efficient and sustainable separation of yttrium from heavy rare earth using functionalized ionic liquid [N1888][NDA]

The separation of adjacent rare earth (RE) is one of the most difficult separation tasks, especially the separation and purification of yttrium (Y) from heavy rare earth (HREE). In the traditional Y separation process, the organic phase composed of acidic extractants such as naphthenic acid (HA) and neodecanoic acid (NDA) need to be saponified with sodium hydroxide or ammonia in each cycle. The resulting alkali consumption and saponification wastewater have negative impacts on the environment. In this article, a bifunctional ionic liquid [methyltrioctyl ammonium][neodecanoate] ([N-1888][NDA]) was synthesized. The extraction capacity, stripping property and recycling stability of [N-1888][NDA] were systematically studied. On this basis, the separation process of Y was developed. The separation factors (beta) of Ho/Y and Er/Y were 2.64 and 4.32, especially the Lu/Y reached 16.27. A higher separation factor is of significance for the separation of Y from HREEs. The extraction sequence of rare earth elements (REEs) with [N-1888][NDA] follows the positive sequence extraction, which is the same as that in neodecanoic acid system. In addition, the separation process of industrial HREE feed liquid containing 0.20 mol L-1 REEs (Y, 88.87 mol.%) was studied. By adjusting the extraction conditions, salting-out reagent such as NaCl did not need to be used in the aqueous phase, which helps to avoid high salt components in RE products. Through the fractional extraction experiment of 11-stage extraction and 4-stage scrubbing, the Y product with a purity of 99.03 mol.% was obtained. The organic phase composed of [N-1888][NDA] was stable after being regenerated with NaOH for recycling extraction.

Automated summary

This article introduces the application of a new ionic liquid [N-1888][NDA] in the separation of rare earth elements. By studying its extraction capacity, stripping property, and recycling stability, an efficient separation process for yttrium was developed. The experimental results showed that this process has a high separation factor and can produce high-purity yttrium without the use of salting-out reagents.