Reduction of Uranyl VI species by individual metals

Although there are quite extensive studies concerning the effect of certain fission products on UO2 deposition in fused chlorides [25, 26], the influence of foreign elements contacting an uranyl-containing melt on the speciation of uranium has been but little studied. For example, some interaction of uranyl(VI) ions with metalhc platinum in a NaCl-KCl melt was noted by Smirnov and Skiba [27] but not by Stromatt [19]. The reaction between U02 and metallic molybdenum in this melt was also observed [26] but the mechanism of the process was not investigated. 

An extensive study concerning the interaction of uranyl-containing melts with a range of chemical elements was conducted previously [21-23] and in the present work and the main results are discussed below. The elements studied varied in their electrochemical properties and included zirconium, niobium, molybdenum, silver, palladium and tellurium. 

Zirconium and niobium, as the most electronegative metals used, reduce uranyl ions to a number of species. Following the reaction by in situ electronic absorption spectroscopy measurements allowed determination of the soluble species formed. Examples of the spectra recorded upon reaction of uranyl-containing melts with zirconium and niobium are shown in Figmes 6.13.4 and 6.13.5. The reaction normally resulted in the initial 

In principle metallic zirconium and niobium should reduce U(IV) to U(III), for example  

Molybdenum and silver have similar electrochemical properties and are more electropositive than zirconium and niobium. The reaction of molybdenum with uranyl(VI)-containing melts was studied between 550 and 750 °C in NaC-2CsCl-based melts and also at 750 C in melts based on LiCl, 3LiCl-2KCl and NaCl-KCl. After introducing molybdenum into the melt the absorbance in the visible region of the spectra 

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