Uranium uranyl compounds

The general electrochemical behavior of uranium in aqueous solutions is dominated by the reduction of the hexava-lent uranyl moiety, 1102. As shown in Table 1, the potential for the UO2 /UO2 couple is 0.089 0.002 V versus SHE, as determined from formal potential data in C104 solutions (0.5-3.0 M) [49, 50aj. The electrochemical reduction of uranyl compounds has been a thoroughly studied... 

Uranium Compounds with Lower Oxidation States. Pour 5 ml of a uranyl nitrate solution into a test tube, add 1 ml of a 10% hydrochloric acid solution, and drop one or two small pieces of zinc into the tube. How can the change in the solution s colour be explained Pour the solution into three test tubes. Pour a potassium permanganate solution dropwise into one tube. What happens What properties do uranium(lV) compounds have ... 

Among the elements known before transuranium elements started to be synthesized in 1940, uranium has a unique characteristic, the extreme stability of the triatomic uranyl ion OUO+z. Not only are the numbers of uranium(VI) compounds larger than of U(IV), and far larger than of the two other oxidation states U(V) and U(III) known from non-metallic compounds, but until the preparation of UOFj discussed below, the only two U(VI) compounds known to contain less than two oxygen atoms per uranium atom were the octahedral molecules UFe and UQ6. 

The closed-shell system thorium(IV) shows no electron transfer satellites (15). Protactinium is too rare and too radioactive to be measured by us, but certain uranyl compounds such as RbUC>2(02N0)3 show satellites about 3.5 eV above /(IJ4/5/2) and 7(U4/7/2) probably due to electron transfer to the empty 5/ shell. The somewhat peculiar photo-electron spectra of uranium compounds are further discussed Chapter IIF. 

Uranium(vi) compounds are expected to be diamagnetic, with their Sq (f°) ground state. However, compounds like UFe and uranyl complexes in fact exhibit temperature-independent paramagnetism, explained by a coupling of paramagnetic excited states with the ground state. 

The uranous compounds correspond to the basic oxide, UOj, and are usually green or blue in colour. They may be prepared by reduction of uranyl salts in solution under the influence of light (see below), but they are the more unstable and the solutions are readily oxidised back by air to uranyl compounds, especially in the presence of platinum black or of salts of iron or copper. In the uranous compounds uranium shows considerable chemical similarity to thorium, the terminal member of Group IV (see p. 4). 

Table 12.4 lists the signatures for processes using UF gas. In the conversion step, one could look for uranyl fluoride, but the isotopic ratio would not change from uranium ore (i.e., no fractionation). However, an analytical method that yielded oxidation states of atomic uranium and fluoride, such as ESCA (electron spectrometry for chemical analysis), could be used to identify the uranyl compound. 

Why do stoichiometrically identical complexes [U02Si04] (XXI) and [U02P04] (XXII) have different structures Indeed, in the structure of XXI, there are uranophane-type sheets with CNu = 7 and Si04" 7/T (Fig. 13a), whereas the structures of uranium micas contain sheets of the XXII type that have CNu = 6 and P04 7/K (Fig. 13b). Taking into account, that, in uranyl compounds the coordination mode of phosphate ions is either or this question can be re-formulated as Why is only the phosphate coordination mode realized in the [U02P04] complexes ... 

Gentry et al. (1976) have recently shown, on the basis of isotopic analyses, that uranium introduction may have occurred far more recently than was previously supposed. However, they find also that, in some instances, the uranium was introduced before coalification was complete since the haloes have been compressed with the coal as it increased in rank. These results are consistent with laboratory and field work by Szalay (1964) who showed that the insoluble humic acids in peat are capable of concentrating uranium from very dilute solutions in natural waters. Sorption occurs as uranyl humate , the process following the normal kinetics of the Langmuir adsorption equation. (Where uraninite occurs in association with peat or other carbonaceous matter, the uranium may thus have been initially sorbed as a uranyl compound which was later reduced to uraninite.)... 

So far as is known, there is no biological component in the processes which lead to the formation of deposits such as Yeelirrie in ceilcrete (Dall Ag-lio et al., 1974). In such deposits the uranium is present in uranyl compounds, the precipitation of which appears to depend on the solubility relationships of uranyl and other ions, including complexes containing vanadium, in waters of varying composition carbonate concentration appears to have been especially important. 

The solution photochemistry of the actinides begins with uranium none has been reported for actinium, thorium, and protactinium. Spectra have been obtained for most of the actinide ions through curium in solution (5). Most studies in actinide photochemistry have been done on uranyl compounds, largely to elucidate the nature of the excited electronic states of the uranyl ion and the details of the mechanisms of its photochemical reactions (5a). Some studies have also been done on the photochemistry of neptunium (6) and plutonium (7). Although not all of these studies are directed specifically toward separations, the chemistry they describe may be applicable. 

Emanations from radioactive substances affect photographic plates just as ordinary visible light does. Becquerel s discovery of radioactivity resulted from the unexpected exposure of such a plate, wrapped in black paper, by a nearby enclosed sample of a uranium-containing compound, potassium uranyl sulfate. After a photographic plate has been developed and fixed, the intensity of the exposed spot is related to the amount of radiation that struck the plate. Quantitative detection of radiation by this method is difficult and tedious. 

Figure 8. XPS spectra of three uranyl compounds taken within 40 eV of EF. The uranium 6p3/ splitting varies with U — Or separation 8.

Solutions of tetravalent uranium salts are usually prepared by reduction of the corresponding uranyl compounds. Reduction may be effected by metallic zinc or at the cathode of an electrolytic cell ... 

Polymers can complex the uranyl ion, the most common naturally occurring, water-soluble form of uranium, for both environmental and industrial purposes. Select salts of diacids, dioximes, etc., salts of polyacrylic acids, polyacrylic acid itself and a wide variety of carboxylic acid-, sulfonate- and sulfate-containing resins are capable of removing the uranyl ion to 10" to 10 mol These complexed uranyl compounds have... 

Acute Effects on Animals and Humans Eor humans and animals, uranium and its salts are highly chemotoxic. Dermatitis, renal damage and acute arterial lesions may occur. Uranyl compounds readily com-... 

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