Reduction of U(VI) in laser liquids POCl₃-SnCl₄-²³⁵UO ²⁺₂ -Nd³⁺

Abstract

U(IV) is irreversibly accumulated during synthesis of laser liquids POCl₃-SnCl₄-²³⁵UO ²⁺₂ -Nd³⁺ prepared from various initial Nd(III) and U(VI) compounds, irrespective of the way of their introduction. The rate of U(IV) accumulation in POCl₃-SnCl₄-²³⁵UO ²⁺₂ -Nd³⁺ solutions increases with increasing UO ²⁺₂ and Nd³⁺ concentrations; for laser liquids with the Nd³⁺ luminescence lifetime τ > 150 μs the observed rate constant of U(IV) accumulation by the second-order reaction k ₂[U⁴⁺] is equal to (3 ± 1) × 10⁻⁵ 1 mol⁻¹ s⁻¹ at T = 380 K. U(IV) is accumulated during storage of POCl₃-SnCl₄-²³⁵UO ²⁺₂ -Nd³⁺ solutions in hermetically sealed glass cells at room temperature and upon irradiation of solutions by xenon lamp light in the spectral region of UO ²⁺₂ absorption. The U(VI) reduction proceeds by chemical and photochemical activation of uranyl with formation of stable U⁴⁺ complexes with dichlorophosphate ions and also with Nd³⁺. Deactivation of the uranyl ion excitation with proton-and chlorine-containing impurities prevents U(VI) reduction.