Abstract
Summary A study of the U(VI)/U(V) couple in lithium hydroxide solutions has been carried out by polarography, at concentrations of uranium(VI) and lithium hydroxide at which the former is soluble and stable. Electrochemical reduction of uranium(VI) was found to be pH independent and the limiting current diffusion controlled; uranium(V), identified as the product, precipitates, but does not undergo disproportionation. The electrode process is reversible at LiOH≥1 M , while at LiOH≤0.2 M it is totally irreversible. The standard potential of the U(VI)/U(V) couple has been evaluated from the reversible behaviour. The charge of the electroactive species ( z =−1), the transfer coefficient (α=0.49) and the standard formal rate constant ( k 0 =3.5×10 −2 s −1 ) were evaluated from the irreversible waves applying the Frumkin correction for the double layer. The nature of the hydrolysed species of uranium(VI) and uranium(V) in highly alkaline solutions is discussed and a kinetic scheme is proposed for the electrode process.
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