Radionuclide speciation techniques

For experimental studies, a chemical thermodynamic modelling approach could theoretically reduce unnecessary experimental effort and hence the overall cost of a research project. Once experiments are underway, the computer simulation should also offer valuable assistance in the interpretation of results. Modelling techniques with particular reference to radionuclide speciation have been discussed by Cross and Day (1986) who pointed out that models are only as good as the thermodynamic data upon which they are based. For example, formation constants (a prerequisite for chemical modelling) are invariably generated in idealised laboratory conditions and their use seldom reflects the natural environment... 

Salbu B, Lind OC, Barretzen P, and Oughton DH (2001) Advanced speciation techniques for radionuclides associated with colloids and particles. In Brechignac F and Howard B (eds.) Radioactive Pollutants - Impact on the Environment, pp. 243-260. Les Ulis Cedex A EDP Sciences. 

Pollard, P.M. (1985) A survey of the current potential analytical techniques for the speciation of radionuclides in nuclear waste repository groundwaters and simulation leachates. AERE R.11496. UKAEA Harwell, Oxon, UK, 41 pp. 

Gel electrophoresis (GE) is a common separation technique in protein analysis and it has also been used for the speciation of metals bound to proteins [86]. In most applications, metals have been detected by autoradiography, limiting the studies to those elements for which a relatively stable radionuclide exists [87]. As an example, 75Se radiotracer allowed Se to be detected after two-dimensional GE (2-DE) separation [88]. Owing to the high sensitivity and isotopic capability of ICP-MS, this technique has been proposed as the detection tool of choice for elements in gel. The efbcient transport of the sample from the protein spot on gel to plasma has been achieved by laser ablation (LA) [89, 90] and electrothermal (ET) atomization [62, 91] techniques. The... 

Good summaries of accepted experimental techniques can be found in the references that are cited for individual radionuclides in the sections below. Nitsche (1991) provides a useful general summary of the principles and techniques of solubility studies. A large number of techniques have been used to characterize the aqueous speciation of radionuclides. These include poten-tiometric, optical absorbance, and vibrational spectroscopy. Silva and Nitsche (1995) summarize the use of conventional optical absorption and laser-based photothermal spectroscopy for detection and characterization of solution species and provide an extensive citation list. A recent review of the uses of Raman and infrared spectroscopy to distinguish various uranyl hydroxy complexes is given by Runde et al. (2002b). 

A variety of methods have been used to characterize the solubility-limiting radionuclide solids and the nature of sorbed species at the solid/water interface in experimental studies. Electron microscopy and standard X-ray diffraction techniques can be used to identify some of the solids from precipitation experiments. X-ray absorption spectroscopy (XAS) can be used to obtain structural information on solids and is particularly useful for investigating noncrystalline and polymeric actinide compounds that cannot be characterized by X-ray diffraction analysis (Silva and Nitsche, 1995). X-ray absorption near edge spectroscopy (XANES) can provide information about the oxidation state and local structure of actinides in solution, solids, or at the solution/ solid interface. For example, Bertsch et al. (1994) used this technique to investigate uranium speciation in soils and sediments at uranium processing facilities. Many of the surface spectroscopic techniques have been reviewed recently by Bertsch and Hunter (2001) and Brown et al. (1999). Specihc recent applications of the spectroscopic techniques to radionuclides are described by Runde et al. (2002b). Rai and co-workers have carried out a number of experimental studies of the solubility and speciation of plutonium, neptunium, americium, and uranium that illustrate combinations of various solution and spectroscopic techniques (Rai et al, 1980, 1997, 1998 Felmy et al, 1989, 1990 Xia et al., 2001). 

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