Hydrophilic Actinide Complexation Studied By Solvent Extraction Radiotracer Technique
Titel:
Hydrophilic Actinide Complexation Studied By Solvent Extraction Radiotracer Technique
Auteur:
Rydberg, Jan
Verschenen in:
Mineral processing & extractive metallurgy review
Paginering:
Jaargang 21 (2000) nr. 1-5 pagina's 167-215
Jaar:
2000-09-01
Inhoud:
Actinide migration in the ground is enhanced by the formation of water soluble complexes between the actinide ions ( central atoms) and inorganic and/or organic complex formers ( ligands) dissolved in the ground water. It is essentia! to risk analysis of a wet repository to know the concentration of the central atoms and the ligands in the ground water, and the stability of the complexes formed between them (the complex formation constant) from such data the concentration of all dissolved actinide species can be calculated, and-using additional data on sorption, diffusion, and ground water flow rate-the migration rate of the actinides in the ground can be predicted. The important actinides in nuclear waste are U, Np, Pu and Am, all radioactive and with half-lives long enough to allow the determination of their macroscopic properties, usually at> 10ninus7M. However, when dissolved in nature, their concentrations are hardly macroscopic; typical concentration values are<10ninus7 M ( trace concentrations) Because the chemical behavior at trace concentrations often differ from that at macro concentrations (for example polynuclear complex formation), it is important to know the chemical behavior of actinides at trace concentrations in the ground water. One method commonly used for such investigations is the solvent extraction radiotracer ( SXRT) technique, by which the radioactive properties of the actinides are used for their detection. This report describes the SXRT technique in some detail. A particular reason for this analysis is the claim that complex formation constants obtained by the SXRT technique differs even at same actinide concentration, or are less reliable than results obtained by alternative techniques. It is true that several difficulties are encountered in the application of the SXRT technique to actinide solutions, as for example redox instability, hydrophilic complexation by side reactions and sorption, but it is also shown that a careful application of the SXRT technique yields results as reliable as by any other technique. The report contains a literature survey on solvent extraction studies of actinide complexes formed in aqueous solutions, particularly by using the organic reagent thenoyltrifluoroacetone (TTA) dissolved in benzene or chloroform (Tab. I). Hydrolysis constants obtained by solvent extraction are listed in Table IX. The last two tables contain all actinide complexes studied by SX with inorganic ligands (Tab. XI) and with organic ligands (Tab. XII).
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