Separation of Thorium from Light Rare Earth Elements from Monazite Chloride Leach Liquor

Monazite is one of the main light rare earth element (REE) minerals and is associated with the presence of Th. This poses challenges in processing due to the strong radiation present in this mineral. However, the use of Th as a nuclear fuel, after the transformation of ²³²Th into ²³³U, has been considered a better option than the currently more widespread use of ²³⁵U. Therefore, the separation of Th from the REE after leaching is an essential step that requires optimization.

In this study, the treatment of a leach solution in a hydrochloric medium from dephosphorized monazite is addressed. The separation of Th from light REEs was performed by solvent extraction with Cyanex 572 or 272. The tests considered included (1) the ratio of the monazite leaching liquor and organic solution, (2) the initial pH values, and (3) the concentration of the extractants. The aqueous-phase samples were analyzed by Inductively Coupled Plasma Optical Emission spectroscopy (ICP-OES). It was observed that at low pH, 60% of the Th was extracted by Cyanex 272 and 90% by Cyanex 572 in one single step. Acidity had little effect on Th extraction. The extractions of light REEs by Cyanex 272 and 572 were negligible in most cases, but for pH values greater than 2, Cyanex 272 extracted a considerable fraction of these elements, which did not occur with Cyanex 572. The results show that Th can be easily separated from light REEs in an acidic and hydrochloric medium by both Cyanex 272 and Cyanex 572.