Durung the second half of the 20th century solvent extraction, i.e., the partition of a species between two immiscible phases, has become one of the major techniques for separation of short-lived radionuclides from complex nuclear reaction product mixtures. It is used in nuclear spectroscopy as well as to study chemical properties of the heaviest elements. Here three of the most successful techniques will be presented. Two of them are automatized batch techniques and the third one is fully continuous. Possible future developments will be discussed, especially with respect to continuous solvent extraction.
The extraction of polonium from lactic acid (HLac) solutions has been studied with di-n-octyl sulphide (DOS), Cyanex 272, Cyanex 301 and Cyanex 302 extractants dissolved in toluene. For the extraction with DOS, the extracted species is most likely PoO(Lac)2·3DOS. The results for Cyanex 272 also indicate extraction via a solvation mechanism rather than cation exchange. The extracted species is probably PoO(Lac)2·2HA. The major species extracted with Cyanex 301 or Cyanex 302 do not contain any lactate molecules. The extracted species is most likely PoOA2 at low extractant concentrations, while at higher concentrations an adduct complex of the type PoOA2·2HA is formed. The extraction of polonium increases in the order Cyanex 272 < Cyanex 302 < DOS < Cyanex 301, which is the same order as the increase of the number of sulphur atoms in the reagents.
Three independent speciation techniques, the free liquid/moving boundary electrophoresis, ultrafiltration, and equilibrium dialysis, combined with the radiotracer method (using 152Eu) have been compared at the study of Eu interaction with humic acid (HA). The degree of complexation of Eu in 10 mg/l Aldrich HA solutions was determined within a broad range of metal loading (Eu total concentration 10-8-10-4 mol . l-1), at pH 4 and 6, ionic strength of 0.01 and 0.1 (NaClO4). From the anodic electrophoretic mobilities determined, additional information on the charge of the Eu-HA complexes was obtained. Uncertainty of the determination given by sorption losses of Eu on the walls and membranes of the experimental devices, and the effect of kinetic lability of the Eu-HA complexes are estimated. Based on the ultrafiltration experiments, the existence of an unknown, labile, high-molecular non-humic Eu species is discussed.
The extraction properties of Th/IV/, Pa/V/, U/VI/ and Np from nitric acid solutions into 1-phenyl-3-methyl-4-benzoylpyrazolone-5 /PMBP/ in toluene were studied, using singlestep batch and continuous H-centrifuge methods. The effects of acid and extractant concentration, temperature and phase contact time on the extraction were investigated.
A new epithermal neutron activation technique is described. The technetium is based on the existence of non-overlapping resonance peaks in the neutron absorption cross-section spectra for the nuclides present in the sample to be analyzed. By this method it is possible to reduce some of the interfering activities with respect to the sought activity by using appropriàte filters. An experiment has been carried out to demonstrate the validity of the technique.
A solvent extraction procedure for rapid separation of uranium from complex nuclear reaction product mixtures is suggested. The procedure has been tested in batch experiments with tracer amounts of representative elements. It has also been tested with fission products and uranium tracer using the continuous chemical separation system SISAK at the Mainz TRIGA reactor.
Authors:J. Byegård, G. Skarnemark, and M. Skålberg
Studies of the stability of various metal EDTA, DTPA and DOTA complexes in order to evaluate their applicability as non-sorbing
tracers have been performed. In laboratory tests, the stability generally increases for the individual metal ions in the EDTA<DTPA<DOTA
order. For most metal ions, the same trend can be observed for the thermodynamic stability constants. In the in situ experiment,
various metal EDTA tracers were used in very low concentrations; YbEDTA−, for example had a breakthrough and recovery which were very similar to the non-sorbing tracers used. According to the extremely
low tracers concentrations used, thermodynamic data indicate that all metal EDTA tracers should have been decomplexed as a
result of the competition with the naturally occurring cations in the groundwater. This was not found, which indicates that
the decomplexation rate and sorption mechanism are important in estimating the applicability of the metal complexes as tracers.
The DOTA complexes of elements in the middle of the lanthanide series have indicated high stability in the laboratory tests
and therefore appear to be good candidates as non-sorbing tracers. However, in contrary to the metal EDTA, tracers, the DOTA
complexes of La3+ and Lu3+ seemed to be slightly delayed in the in situ experiment.
Authors:M. Johansson, R. Malmbeck, B. Wierczinski, and G. Skarnemark
A study of the extraction of polonium from aqueous solutions containing -hydroxyisobutyric acid (-HIBA) was performed with four different extractants, di-n-octyl sulphide (DOS), Cyanex 272, Cyanex 301 and Cyanex 302, dissolved in toluene. The extracted complex for DOS at low -HIBA concentrations is most likely PoO(-HIB)2·2DOS, while at higher -HIBA concentrations there seems to be a solvating effect implicating an extracted complex of the type PoO(-HIB)2(-HIBA)2·2DOS. For the extraction of polonium with Cyanex 272 the results are inconclusive. The extracted complex is either PoOA2 or PoO(-HIB)2·2HA. For extraction with Cyanex 301 or Cyanex 302 the major extracted species does not contain any -HIBA molecules. The neutral species in both cases is PoOA2, extracted at low extractant concentrations, while at higher extractant concentrations a complex of the type PoOA2·xHA is extracted. The extraction of polonium increases in the order Cyanex 272 < DOS < Cyanex 302 < Cyanex 301.
Authors:G. Skarnemark, J. Alstad, N. Kaffrell, and N. Trautmann
The multistage solvent extraction system SISAK is described. The system is used for online studies of nuclides with half-lives down to 1 s. Some of the chemical separation procedures are presented, and a survey is given on the results obtained so far. The possiblity to gain access to nuclides with even shorter half-lives is also discussed.
Authors:B. Bartoś, E. Kowalska, A. Bilewicz, and G. Skarnemark
103mRh is a very promising radionuclide for Auger electron therapy due to its very low photon/electron ratio. The goal of the
present work was the elaboration a method for production of large quantities of 103mRh for generator system. It was found that the combination of solvent extraction with evaporation of 103RuO4 followed by decomposition of H5IO6 makes it possible to produce 103mRh of high radionuclidic and chemical purity.