Spectroscopic study of Np(V) oxidation to Np(VI) in 3mol/dm~3 nitric acid at elevated temperatures

摘要

Optical absorption spectra of Np in 3mol/dm~3 nitric acid at elevated temperatures were measured using an optical glass cell with a water jacket having a light path of 1 cm. Molar extinction coefficients of Np(VI), ε_T M~(?1) cm~(?1), were obtained at various temperatures (297, 313, 334, 352, and 372 K). The values of T were found to decrease with increasing temperature and could be described by the equation ε_T = ?0.14T + 85.5, where T is the temperature. Oxidation of Np(V) to Np(VI) in 3M nitric acid at elevated temperatures (336, 342, 354, and 362 K) was observed using the optical glass cell. Oxidation of Np(V) was promoted by increasing the temperature and proceeded as a pseudo-first order reaction with respect to Np(V) concentration. The rate equation in the temperature range of 336–362 Kwas obtainedas follows: ?d[Np(V)]_t/dt = 2.2×10~7 exp[?65×10~3/(RT)][Np(V)]_t, where R, T, and [Np(V)]_t indicate the gas constant, temperature, and Np(V) concentration at time t, respectively.