The measurement of the diffusion coefficient of U(VI) in aqueous uranyl sulfate solutions
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I.
THE batch type electrolytic reduction of U(VI),
which is currently being performed at the Ningyo-toge works of PNC, Japan, is an excellent technique to reduce U(VI) to U(IV). 1'2 This process has been used under the limiting current condition of the reduction of U(VI) to U(IV) on the titanium cathode. Therefore, it is extremely important to know the diffusion coefficient of U(VI) for accurately evaluating the maximum rate of U(VI) reduction. The porous-diaphragm cell technique 3 and optical method4 have been widely employed for determining the diffusion coefficient of various electrolytes in aqueous solutions, but these methods are inconvenient and also require chemical analysis of diffusing species. One of the other methods is a rotating-disc electrode method. 5 However, this method needs an expensive apparatus to satisfy the conditions for the relationship derived by Levich. 6a Furthermore, a simultaneous determination of kinematic viscosity of the solution is also required. We determined the diffusion coefficients of U(VI) in uranyl sulfate solutions conveniently under various conditions by comparing the limiting current densities for the reduction of U(VI) to those for the electrodeposition of copper under the same hydrodynamic condition of forced convection. The diffusion coefficients of CuSO4-H2SO4 solutions have been reported as a function of CuSO4 and H 2 S O 4 concentrations over the temperature range of 298 to 313 K. 4 Also, limiting current can be clearly detected in the copper electrodeposition in these solution systems before hydrogen gas evolution is initiated. 7 The method employed and the results obtained are reported here. II.
Function
INTRODUCTION
EXPERIMENTAL PROCEDURES
ReXco~der1
[
gene;mor
@ A: Anodic compartment B: Agar salt bridge C: Cathodic compartment D: Cathode
F: Cation selective membrane
P: Anode
R: Reference electrode M: Magnetic stirrer W: Water bath
Figure 1 shows the experimental apparatus used in this study. A rectangular vessel made of vinyl chloride resin was
Fig. 1--Experimental apparatus used for copper electrodeposition and electrolytic reduction of U(VI).
YASUHIRO AWAKURA, Lecturer, and HIROSHI MAJIMA, Professor, are with the Department of Metallurgy, Kyoto University, Kyoto, Japan 606. KOJI SATO, formerly Graduate Student, Department of Metallurgy, Kyoto University, Kyoto, Japan, is with Hitachi Metals, Ltd., Japan. SHUICHIRO HIRONO is Manager, Mining and Ore Processing Division, Ningyo-toge Works, Power Reactor and Nuclear Fuel Development Corporation, 1550 Kamisaibara, Tomata-gun, Okayama Prefecture, Japan 708 -06. Manuscript submitted January 29, 1986.
vertically divided into two compartments by a cationic exchange membrane fixed at the center of the vessel, and used as an electrolytic cell. The cathode compartment was filled with 0.2 dm 3 of uranyl sulfate solution or cupric sulfate solution, while the anode compartment was filled with 0.2 dm 3 of 1 mol dm -3 H2504 solution. A 1.5 cm •
METALLURGICALTRANSACTIONSB
VOLUME I8B, MARCH 1987-- 19
1.5 cm t
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