A Pyridine Amine Extractant for Separation of La³⁺ and Ce³⁺ in HNO₃ Solution

The separation of lanthanum and cerium is of great significance for improving the material properties and promoting scientific and technological progress. In this paper, a pyridine amine extractant, (1<i>R</i>,2<i>S</i>)-<i>N</i>1,<i>N</i>2-bis((5-methylpyridin-2-yl)methyl)cyclohexane-1,2-biamine (cis-BMPyMChBA), was designed for the separation of lanthanum and cerium. The aim is to use this extractant to catalyze the oxidation of tri- to tetravalent cerium and to increase the separation efficiency between lanthanum and cerium. The effects of the temperature, diluent, extractant concentration, and pH were evaluated to the extraction and separation performance of lanthanum and cerium. The experimental results demonstrate that cis-BMPyMChBA exhibits high selectivity for cerium, with a separation factor for lanthanum and cerium reaching 122.9. The coordination mechanism between cis-BMPyMChBA and cerium ion was clarified through the combined use of extraction isotherm, Job's curve, spectroscopic methods, and density functional theory (DFT) calculation. It involved the interaction between the secondary amine N atom and the pyridine N atom and the metal ion in which the cerium ion underwent a valence change from trivalent to tetravalent before extraction. This was found to be more conducive to the separation of lanthanum and cerium.