Authors:S. Lehmann, G. Geipel, G. Grambole, and G. Bernhard
Heavy metals like the actinides possess a high risk potential to the environment not only because of their radiotoxicity but
also due to their chemical toxicology. Uranium as one of the major actinide elements has to be considered in particular. Under
reducing conditions, tetravalent uranium occurs primarily in the environment. To date, a lack of appropriate analytical techniques
that featured sufficient sensitivity made it difficult to study the aqueous phosphate chemistry of uranium(IV) as such complexes
show only low solubility. A novel time-resolved laser fluorescence spectroscopy system was set up recently and optimized to
do research on uranium(IV). By application of this laser system we could successfully study uranium(IV) phosphate in concentration
ranges where no precipitation or formation of colloids occurred. At pH = 1.0, U4+ and one uranium(IV) phosphate complex existed in parallel in aqueous solution. The complex could be identified as [U(H2PO4)]3+. Determination of its corresponding complex formation constant via two different evaluation methods resulted in the finding
. Both values prove that [U(H2PO4)]3+ is a very stable complex in solution under experimental conditions. As they are in very good agreement with each other, the
total complex formation constant was determined by means of the weighted average out of (1) and (2). It was calculated to
Liquid-liquid extraction is used for one-atom-at-a-time separations of transactinide elements from heavy-ion reaction product mixtures. It is suitable for this purpose because it is fast, provided that a chemical system with negligible kinetics is used, and it can be used for continuous separations. It is, however, not quite easy to determine the uncertainties of the measured distribution coefficients or complex formation constants. In this paper methods for such estimates will be discussed.
Authors:Robin Steudtner, Thuro Arnold, Gerhard Geipel, and Gert Bernhard
Cryogenic techniques are currently used in scanning tunnelling microscopy (STM) and single molecule spectroscopy. Recently
such cryogenic devices have also been adapted to time resolved laser-induced fluorescence spectroscopy (TRLFS) systems applied
to uranium(VI). In our study, we interpret TRLFS results obtained for the uranyl(VI) glucose system at room temperature (RT)
and under cryogenic conditions of 153 K (cryo-TRLFS). A uranyl(VI) glucose complex was only identified by cryo-TRLFS measurements
at pH 5 and not by RT measurements. The uranyl(VI) glucose complex was characterized by five emission bands at 499.0, 512.1,
525.2, 541.7, and 559.3 nm and a fluorescence lifetime of 20.9 ± 2.9 μs. The uranyl(VI) glucose complex formation constant
was calculated for the first time to be logßI=0.1 M = 15.25 ± 0.96. Cryo-TRLFS investigation opens up new possibilities for the determination of complex formation constants
since interfering quenching effects often encounter at RT are suppressed by measurements at cryogenic conditions.
Authors:V. Tsoupko-Sitnikov, Yu. Norseev, and V. Khalkin
Dependence upon pH of Ac and Th distribution coefficients between the cation exchange resin and buffer citrate solutions had been investigated; the optimal conditions are suggested for effective separation of the elements in this system. These results are in successful accordance with such conditions calculated on the basement of Ac and Th citrate complex formation constants.The generator method for225Ac periodical separation from229Th samples is developed.229Th storage in solution between separations excludes the contamination of actinium final solution with radiolysis products and provides 100-% yield of this isotope and its high radiochemical purity. The parent nuclide loss after continuous use of the generator does not take place.
Authors:S. Van Hövell Tot Westerflier, J. Binsma, H. Stein, and C. Vandecasteele
Cadmium sulfide particles were prepared by precipitation from acid solution. A radiotracer technique with109Cd was applied to measure the solubility of cadmium sulfide at various pH's. Filtration, centrifugation, ultracentrifugation, and dialysis were used to separate the particles from the solution. Only the last two techniques proved to be successful. The solubility of cadmium sulfide in water (pH=7) is found to be: 7.9·10–5 mol·l–1 in contrast with the literature value of 9.0·10–6 mol·l–1. At low pH (1–4), the solubility agrees fairly well with the solubility calculated on the basis of generally accepted values for the solubility product and for the various complex formation constants, while at high pH (4–14) the solubility is higher than expected.
Ion association has been studied by positron lifetime spectroscopy in aqueous solutions containing the Ni2+ and SO
ions at 294 K with the double aim of assessing the reliability of the method for quantitative determination of complex formation constants and of probing the validity of various expressions to calculate single-ion activity coefficients at high ionic strength. The existence of two complexes, identified as NiSO4 and Ni2SO
, is shown by the data analysis. Considering the formation constant of the former, KI=(196±10)M–1, determined in previous works leads to discarding several of the expressions commonly used for activity corrections. Two possible values are retained for KI, (193±20)M–1 and (179±20)M–1, while KII related to Ni2SO
is better defined, as (2.57±0.14)M–1.
Authors:Meng Wei, Qian’ge He, Xiaogui Feng, and Jing Chen
The crystal structure, melting range, decomposition temperature, solubilities in aqueous and organic phase, and distribution
ratio in biphase system of N,N,N′,N′-tetramethyl diglycolamide (TMDGA) have been studied in the present work. Water-soluble TMDGA with very low solubility in
kerosene or 30 % trialkyl phosphine (TRPO)/kerosene meets the primary requirement to act as the stripping agent in TRPO process
which has been developed for actinides partitioning from high level waste. Slope analysis, electrospray ionization mass spectrometry
(ESI–MS) and spectrophotometric titration indicate that in weak and moderate acidic aqueous solution, up to three TMDGA molecules
form complexes with Zr4+, trivalent lanthanides (Ln3+), trivalent actinides (An3+) or tetravalent actinides (An4+). Their complex formation constants determined by liquid–liquid extraction method follow the order predicted by the electrostatic
model of 4f and 5f elements and the covalent model of 4d transition elements: Ln3+ ~ An3+ < An4+ ≪ Zr4+. Hydrolysis of actinide cations, especially An4+, in the media of low acidity, reduces the complexation stability. In addition, the effect of aqueous acidity and temperature
has been investigated. No obvious influence of temperature on Np4+ complexes has been found. However, the influence on Am3+ and Pu4+, especially on their 1:1 or 1:2 complex species with TMDGA, is relatively considerable. Strong affinity of TMDGA to An3+ and An4+ implies that TMDGA has potential to strip An3+ and An4+ from TRPO.