Abstract
Using dropping mercury electrode, the electrochemical behaviours of uranyl ion dissolved in fused potassium thiocyanate at 185°C were investigated through ordinary polarography and chronopotentiometry. Reproducible polarogram and chronopotentiogram, both consisted of two reduction waves for uranyl ion were obtained. Limitting current for the first step of the polarogram was proportional to the uranyl ion concentration and the square root of the mercury height at constant depolarizes concentration, but not for the second. No linear relationship was obtained in the log [il(id - i)] vs. E plots for both the first and second waves. The i0τ11/2-values for the first step of chronopotentiogram at constant uranyl ion concentration were independent of the current density at the polarized electrode and proportional to the bulk concentration. A plot of log {(τ11/2 - t1/2)/t1/2} vs. E yields a straight line for the first step and the average reciprocal slope (0.0993) is in good agreement with the theoretical value (0.091) in the case of n = 1 at 185°C. The ratio of τ2/τ1 was calculated for two successive reduction steps to be about 3. According to these observations it is clearly concluded that electroreduction procces of uranyl ion is diffusion-controlled and proceeds to two steps as follows ;UO22+ + e = UO2+ (1)UO2++ e = UO2 (2) The diffusion constant of uranyl ion in this melt at 185°C was calculated from Sand's equation to be 6.56 × 10-7 cm2/sec, which is about one-third compared with that for lead ion in the same melt at the same temperature.
