Trivalent uranium water

Uranium exists in the +3, +4, +5, and +6 oxidation states. The +5 state dispropor-tionates to the +4 and +6 states and is of little importance. Trivalent uranium reduces water and therefore there is no stable aqueous chemistry of U3+ although compounds do exist. 

Trivalent uranium ion reduces water to hydrogen. Hence, stable aqueous solutions of trivalent uranium compounds cannot be prepared. Compounds of tetravalent uranium are generally similar to those of zirconium or thorium, except that some uranium compounds can be oxidized to the hexavalent form. Compounds of pentavalent uranium are of little importance because they disproportionate readily into tetravalent and hexavalent forms. The properties of hexavalent uranium are generally similar to those of hexavalent molybdenum or tungsten. In aqueous solution hexavalent uranium forms the uranyl ion UO2 ... 

UO3SO4-H3SO4 solution is placed in a cooled glass cylinder which houses the cathode space. A clay cell contains the anode. The best results are obtained with an Hg cathode and a carbon rod anode. The Hg layer is placed on the bottom of the cathode vessel the electrical connection is made with a copper wire sealed into a glass tube. The reaction proceeds quite rapidly at 3-5 amp. Any material which separates during the electrolysis is redissolved by addition of some water. At the end the cathode liquid becomes dark green with a steel-blue to black-violet fluorescence. If the electrolysis continues beyond the tetravalent state, the reddish brown color (in transmitted light) of trivalent uranium becomes apparent however, this compoimd is very unstable and is quickly reoxidized in air to tetravalent uranium. 

While actinide metals are easily soluble in some mineral acids such as HCl an.d HCIO4, they are typically found in solution in valences IV to VI. However, Baluka and co-workers first reported in 1981 that dissolution of U and Np metals in superacids produces initially trivalent actinides (Baluka et al. 1981). The UV-visible spectra of the U and Np solutions, shown in fig. 2, are characteristic of the trivalent actinides found in aqueous acidic or basic systems. Avens and colleagues (1988) have dissolved both Pu and Am metal and observed trivalent species by UV-visible spectroscopy. The stability of oxidation state (111) for U, Np and Pu is all the more striking especially in light of the lower stability of the series U (lll)-Pu (111) relative to higher oxidation states e.g., trivalent uranium (111) is able to reduce water under normal conditions. In addition to the unusually low oxidation state obtained, another feature of actinide dissolution in... 

The Table shows a great spread in Kd-values even at the same location. This is due to the fact that the environmental conditions influence the partition of plutonium species between different valency states and complexes. For the different actinides, it is found that the Kd-values under otherwise identical conditions (e.g. for the uptake of plutonium on geologic materials or in organisms) decrease in the order Pu>Am>U>Np (15). Because neptunium is usually pentavalent, uranium hexavalent and americium trivalent, while plutonium in natural systems is mainly tetravalent, it is clear from the actinide homologue properties that the oxidation state of plutonium will affect the observed Kd-value. The oxidation state of plutonium depends on the redox potential (Eh-value) of the ground water and its content of oxidants or reductants. It is also found that natural ligands like C032- and fulvic acids, which complex plutonium (see next section), also influence the Kd-value. 

In natural oxic waters, americium is present in the trivalent and thorium in the tetravalent state while uranium is hexavalent, U02. The total concentrations of uranium and thorium in surface sea water are 1.1-1.5X10 and 2.5 X10 M, respectively in both the Atlantic... 

Plutonium in irradiated fuel elements may be chemically separated from uranium. On treatment of a mixture of hexavalent uranium and tetravalent plutonium with divalent iron, plutonium is reduced to the trivalent stage. The stable uranyl nitrate is unaffected. In liquid-liquid extraction with tri-n-butyl phosphate (TBP) and kerosene, uranium goes into the organic phase, while plutonium stays in the water phase. 

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