Study on separation of heavy rare earth elements by solvent extraction with organophosphorus acids and amine reagents

• The paper compares the separation of heavy REEs with organophosphorus and amine extractants.
• The steps of extraction, scrubbing and stripping were rigorously investigated.
• The best separation factors for the adjacent elements were obtained with DEHPA and IONQUEST®801.
• The McCabe–Thiele diagram was drawn to estimate the number of extraction and stripping stages.
• From the extractants investigated, IONQUEST®801 showed better performance.

The present work describes a study of the separation of rare earth elements (REE) from heavy REE concentrate through solvent extraction. Seven extractants were investigated: three organophosphorus acids (DEHPA, IONQUEST®801 and CYANEX®272), a mixture of DEHPA/TOPO (neutral ester) and three amines (ALAMINE®336, ALIQUAT®336 and PRIMENE®JM-T). The organophosphorus extractants were investigated in hydrochloric and sulphuric media whereas the amines performance was assessed in a sulphuric medium. The variables investigated were: concentration of the extractant agent, aqueous phase acidity, aqueous/organic volumetric ratio, contact time, stripping agent concentration (hydrochloric acid solution) and the selective stripping step. In the extraction step, the best separation factors for the adjacent elements were obtained with DEHPA and IONQUEST 801. For 1.0 mol L−1 DEHPA in an initial acidity of 0.3 mol L−1 H+, the separation factor was 2.5 Tb/Dy, 2.1 Dy/Ho, 1.9 Ho/Er, 2.0 Ho/Y and 1.1 Y/Er; for 1 mol L−1 IONQUEST 801 in 0.3 mol L−1 of H+ it was 2.7 Tb/Dy, 2.4 Dy/Ho, 2.1 Ho/Er, 2.1 Ho/Y e 1.5 Y/Er. The study concluded that for the extractants investigated, IONQUEST 801 is the most indicated for the separation of heavy REE because it has lower affinity with the REE compared to the affinity of DEPHA/REE, which makes the strip of the REE from Ionquest 801 easier than from DEHPA. Moreover, the number of stages necessary for the stripping of the REE from IONQUEST 801 is much lower than that observed when DEPHA is employed.