We recently discovered a neutral dicalcium uranyl tricarbonate complex, Ca 2 UO 2 (CO 3 ) 3 (aq.), in uranium mining related waters [1]. We are now reporting a further validation of the stoichiometry and the formation constant of this complex using two analytical approaches with time-resolved laser-induced fluorescence spectroscopy (TRLFS) species detection: i) titration of a non-fluorescent uranyl tricarbonate complex solution with calcium ions, and quantitative determination of the produced fluorescent calcium complex via TRLFS; and ii) variation of the calcium concentration in the complex by competitive calcium complexation with EDTA 4− .Slope analysis of the log (fluorescence intensity) versus log [Ca 2+ ] with both methods have shown that two calcium ions are bound to form the complex Ca 2 UO 2 (CO 3 ) 3 (aq.). The formation constants determined from the two independent methods are: i) log β • 213 = 30.45 ± 0.35 and ii) log β • 213 = 30.77 ± 0.25. A bathochrome shift of 0.35 nm between the UO 2 (CO 3 ) 3 4− complex and the Ca 2 UO 2 (CO 3 ) 3 (aq.) complex is observed in the laser-induced photoacoustic spectrum (LIPAS), giving additional evidence for the formation of the calcium uranyl carbonate complex.EXAFS spectra at the L II and L III -edges of uranium in uranyl carbonate solutions with and without calcium do not differ significantly. A somewhat better fit to the EXAFS of the Ca 2 UO 2 (CO 3 ) 3 (aq.) complex is obtained by including the U-Ca shell. From the similarities between the EXAFS of the Ca 2 UO 2 (CO 3 ) 3 (aq.) species in solution and the natural mineral liebigite, we conclude that the calcium atoms are likely to be in the same positions both in the solution complex and in the solid.This complex influences considerably the speciation of uranium in the pH region from 6 to 10 in calcium-rich uranium-mining-related waters.

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Chemical speciation of U(VI) in natural seepage water and corresponding model solutions was investigated by time-resolved laser-induced fluorescence spectroscopy. Calculations of uranium speciation in this medium show that U0 2 (C0 3 )3~ and U0 2 (C0 3 )|" should be the major individual components. Due to the very low fluorescence intensity, the pure uranyl carbonato complexes could not be measured directly by TRLFS. However, a uranium fluorescence spectrum was recorded from seepage water samples. The TRLFS investigations show that the main component of uranium in this seepage water is a calcium uranium carbonato complex. The main fluorescence wavelengths of this complex are at 463.9, 483.6, 502.8, 524.3 and 555.4 nm. The fluorescence lifetime of the species is 64±17 ns. This study shows that the calcium content of the water has a great influence on the uranium speciation. For the first time, the existence of a calcium uranium carbonato complex -(Ca 2 [U0 2 (C0 3 ) 3 ] |

The periodic table provides a classification of the chemical properties of the elements. But for the heaviest elements, the transactinides, this role of the periodic table reaches its limits because increasingly strong relativistic effects on the valence electron shells can induce deviations from known trends in chemical properties. In the case of the first two transactinides, elements 104 and 105, relativistic effects do indeed influence their chemical properties, whereas elements 106 and 107 both behave as expected from their position within the periodic table. Here we report the chemical separation and characterization of only seven detected atoms of element 108 (hassium, Hs), which were generated as isotopes (269)Hs (refs 8, 9) and (270)Hs (ref. 10) in the fusion reaction between (26)Mg and (248)Cm. The hassium atoms are immediately oxidized to a highly volatile oxide, presumably HsO(4), for which we determine an enthalpy of adsorption on our detector surface that is comparable to the adsorption enthalpy determined under identical conditions for the osmium oxide OsO(4). These results provide evidence that the chemical properties of hassium and its lighter homologue osmium are similar, thus confirming that hassium exhibits properties as expected from its position in group 8 of the periodic table.