Redox and adsorption processes of hydrolyzed uranyl species on a mercury electrode from sodium chloride solutios

Reduction and adsorption processes of hydrolyzed uranyl species on the mercury drop electrode, from 0.55 mol L −1 NaCl, were studied by electrochemical cathodic stripping techniques: cyclic voltammetry, alternating current voltammetry, chronoamperometry and double potential step chronocoulometry. The only uranyl species adsorbed on the Hg electrode (between pH 5 and 7) was found to be uncharged uranyl dihydroxide, as well as its reduction product. At bulk concentrations between 3 and 5 μmol L −1 that reactant forms an adsorbed compact film as a result of surface polymerization, nucleation or other condensation processes. The adsorption isotherm at pH 6.2 and −0.2 V was measured. It was fitted with a Frumkin type isotherm. At the plateau. a reduction current corresponding to 6.7 × 10 −9 mol cm −2 of uranyl ions was measured. This represents on the average 7 adsorbed layers of UO 2 (OH)   2 0 , presuming an orthorhombic crystal cell structure. Multilayer adsorption is certain even if a polymeric form of uranyl dihydroxide was considered.