Diphosphonium salts as effective extractants for the separation of uranium(vi) from nitric acid media

Abstract

We report a new class of diphosphonium salts as highly efficient extractants for uranium(VI) from nitric acid solutions. By varying the anion (bromide or nitrate) and the linker length in the cation, their properties can be tuned, with doubly charged ligands providing markedly higher extraction efficiency than traditional monocationic phosphonium salts. The extraction process is strongly influenced by the linker length and shows high selectivity in the presence of lanthanides. Using Raman spectroscopy, XANES, and single-crystal X-ray diffraction, we establish that uranium(VI) is extracted by all ligands as anionic nitrate complexes UO₂(NO₃)₃⁻ and UO₂(NO₃)₄²⁻, while under nitric acid deficiency uranyl forms rare mixed bromide–nitrate species.