Synergistic extraction and separation of lanthanum (III) and cerium (III) using a mixture of 2-ethylhexylphosphonic mono-2-ethylhexyl ester and di-2-ethylhexyl phosphoric acid in the presence of two complexing agents containing lactic acid and citric acid

Lanthanum and cerium were synergistically extracted and separated in chloride medium using a mixture of 2-ethylhexylphosphonic mono-2-ethylhexyl ester (HEHEHP) and di-2-ethylhexyl phosphoric acid (D2EHPA) with lactic acid (LA) and citric acid (H3cit) as the complexing agents. Synergistic effects were observed for the extraction of La and Ce with the mixed extractant; and the maximum synergistic coefficients were obtained at XHEHEHP = 0.8. A maximum βCe/La of 8.88 and the maximum extraction capacity of 53.48 g/L were obtained in the presence of two complexing agent. Organo–Ce complexes in organic phases were examined based on FT-IR, 1H, and 31P NMR spectra. The cation-exchange mechanism and coordination effect between Ce and P = O ligands were verified. Results showed that the mixture system in the presence of complexing agents exhibited a higher extraction efficiency and selectivity during the extraction and separation of adjacent rare earths.