Synergistic extraction of rare earth elements from HNO3 solutions with a mixture of CCD and HDBP in a polar diluent

The extraction of Ln(III) (except Pm), La(III), and Y(III) from HNO3 solutions with dibutyl hydrogen phosphate (HDBP), chlorinated cobalt dicarbollide (CCD), and their mixture in a polar diluent, mixture of o-chloronitrobenzene (OCNB) and CCl₄ (1: 1), was studied. A synergistic effect is observed for all the examined elements. For the series La-Dy, it reaches a maximum at the HDBP to CCD molar ratio of 3: 1, and for the series Tb-Lu, at the HDBP to CCD molar ratio of 9: 1. The synergistic effect is observed at the HDBP to CCD molar ratios of up to 700: 1 and 1500: 1 for heavy and light lanthanides, respectively. At higher ratios, the magnitude of the synergistic effect does not exceed the uncertainty of its determination. This fact indicates that one CCD molecule can activate several hundreds of HDBP molecules, enhancing their extraction ability. The degrees of separation of neighboring lanthanides do not noticeably change on introducing CCD into the extraction system. The key component of the hypercomplex is the CCD anion, with the role of the CCD proton being insignificant. A complex of variable composition, containing lanthanide, CCD, and HDBP, is formed in the organic phase.