Synergistic, extractive, and selective separation of light, medium, and heavy rare earth elements using Cyanex 572 and Alamine 336 from a chloride medium

In this study, the solvent extraction of rare earth elements (REEs) of different groups of light (LREE), medium (MREE), and heavy (HREE) from a chloride medium using the mixture of Cyanex 572 (cationic extractant, organophosphorus-based) and Alamine 336 (anionic extractant, amine-based) was studied. The results showed higher extraction efficiency for HREEs when sole Cyanex 572 was used. However, the addition of Alamine 336 to Cyanex 572 increased the extraction efficiency of LREEs and MREEs. The optimal volumetric ratio of Alamine 336 to Cyanex 572 for maximum extraction efficiency, under the studied conditions, was concluded to be 1:1 at a total extractant concentration of 30 % v/v. The synergistic enhancement factor when using this system for the extraction of LREEs and MREEs varied from 2 to 76 at different pH values and Alamine 336 ratios. To analyze the synergistic effect of the addition of Alamine 336 to Cyanex 572 on REE extraction, slope analysis and Fourier transform infrared spectroscopy measurement were performed. It was concluded that the role of Alamine 336 could be that of a proton ion extractor (released from the Cyanex 572 structure during REEs extraction) for REECl2+ complexes and that of a phase modifier for Cyanex 572 for REECl2+ complexes.