Synthesis of a New Chelating Iminophosphorane Derivative (Phosphazene) for U(VI) Recovery

Abstract

A new synthetic chelating N–hydroxy–N–trioctyl iminophosphorane (HTIP) was prepared through the reaction of trioctylphosphine oxide (TOPO) with N–hydroxylamine hydrochloride in the presence of a Lewis acid (AlCl3). Specifications for the HTIP chelating ligand were successfully determined using many analytical techniques, 13C–NMR, 1H–NMR, FTIR, EDX, and GC–MS analyses, which assured a reasonable synthesis of the HTIP ligand. The ability of HTIP to retain U(VI) ions was investigated. The optimum experimental factors, pH value, experimental time, initial U(VI) ion concentration, HTIP dosage, ambient temperature, and eluents, were attained with solvent extraction techniques. The utmost retention capacity of HTIP/CHCl3 was 247.5 mg/g; it was achieved at pH = 3.0, 25 °C, with 30 min of shaking and 0.99 × 10−3 mol/L. From the stoichiometric calculations, approximately 1.5 hydrogen atoms are released during the extraction at pH 3.0, and 4.0 moles of HTIP ligand were responsible for chelation of one mole of uranyl ions. According to kinetic studies, the pseudo–first order model accurately predicted the kinetics of U(VI) extraction by HTIP ligand with a retention power of 245.47 mg/g. The thermodynamic parameters ΔS°, ΔH°, and ΔG° were also calculated; the extraction process was predicted as an exothermic, spontaneous, and advantageous extraction at low temperatures. As the temperature increased, the value of ∆G° increased. The elution of uranium ions from the loaded HTIP/CHCl3 was achieved using 2.0 mol of H2SO4 with a 99.0% efficiency rate. Finally, the extended variables were used to obtain a uranium concentrate (Na2U2O7, Y.C) with a uranium grade of 69.93% and purity of 93.24%.