Hydroxamate complex hydrolysis Andrieux et al THE HYDROLYSIS OF HYDROXAMIC ACID COMPLEXANTS IN THE PRESENCE OF NON-OXIDISING METAL IONS 2: NEPTUNIUM (IV) IONS

Hydroxamic acids are salt free, organic compounds with affinities for cations such as Fe, Np and Pu and have been identified as suitable reagents for the control of Pu and Np in advanced nuclear fuel reprocessing. The results of a UV-visible-near IR spectrophotometric study of the 1:1 and 2:1 complexes formed between formoand acetohydroxamic acids (FHA, AHA) and Np(IV) ions are interpreted using speciation diagrams for the identification of the species present at diferent pH and ligand to metal ratios. A kinetic model that describes the instability of the complex due to the hydrolysis of the hydroxamate moeity, previously developed for the Fe(III)-AHA complexes [1], is tested here against experimental Np(IV)-FHA data. Consequently, the complexation constant for formation of the 1:1 Np(IV)-FHA complex in nitric acid is estimated at K1 = 2715, and indications are that complexation protects the ligand against hydrolysis at 0.1 > pH > -0.1.