Sofie Andersson

Extraction properties of 6,6'-bis-(5,6-dipentyl-[1,2,4]triazin-3-yl)-[2,2']bipyridinyl (C5-BTBP)

Abstract The extraction of americium(III) and europium(III) into a variety of organic diluents by 6,6′‐bis‐(5,6,‐dipentyl‐[1,2,4]triazin‐3‐yl)‐[2,2′]bipyridinyl (C5‐BTBP) has been investigated. In addition to determining the stoichiometry for the extraction, the dependence of extraction on contact time and temperature was also studied. The resistance of the ligand to gamma irradiation and the possibility to recycle the organic phase after stripping were tested to determine how the molecule would perform in a radiochemical process. Different organic diluents gave different extraction results, ranging from no extraction to distribution ratios of over 1000 for americium(III). In 1,1,2,2‐tetrachloroethane, the extraction and separation of americium from europium and the extraction kinetics were good; a separation factor above 60 was obtained at equilibrium, ∼5 min contact time. The extraction capabilities are adequate for C5‐BTBP to be used in a process for separating trivalent actinides from lanthanides. However, C5‐BTBP is susceptible to radiolysis (americium extraction decreases ∼80% after a dose of 17 kGy) and may not be the best choice in the processing of spent nuclear fuel. Nonetheless it is a useful starting point for further development of this type of molecule. It could also prove useful for analytical scale separations for which radiolytic instability is less important.

Determination of stability constants of lanthanide nitrate complex formation using a solvent extraction technique

Summary For lanthanides and actinides, nitrate complex formation is an important factor with respect to the reprocessing of nuclear fuels and in studies that treat partitioning and transmutation/conditioning. Different techniques, including microcalorimetry, various kinds of spectroscopy, ion-exchange and solvent extraction, can be used to determine stability constants of nitrate complex formation. However, it is uncommon that all lanthanides are studied at the same time, using the same experimental conditions and technique. The strengths of the complexes are different for lanthanides and actinides, a feature that may assist in the separation of the two groups. This paper deals with nitrate complex formation of lanthanides using a solvent extraction technique. Trace amounts of radioactive isotopes of lanthanides were produced at the TRIGA Mainz research reactor and at the Institutt for Energiteknikk in Kjeller, Norway (JEEP II reactor). The extraction of lanthanide ions into an organic phase consisting of 2,6-bis-(benzoxazolyl)-4-dodecyloxylpyridine, 2-bromodecanoic acid and tert-butyl benzene as a function of nitrate ion concentration in the aqueous phase was studied in order to estimate the stability constants of nitrate complex formation. When the nitrate ion concentration is increased in the aqueous phase, the nitrate complex formation starts to compete with the extraction of metal ions. Thus the stability constants of nitrate complex formation can be estimated by measuring the decrease in extraction and successive fitting of an appropriate model. Extraction curves for La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Dy, Ho and Er were obtained and stability constants for their nitrate complex formation were estimated. Tb, Tm, Yb and Lu were also investigated, but no stability constants could be determined. The distribution ratios for the metal ions at low nitrate ion concentration were obtained at the same time, showing the effect of lanthanide contraction resulting in decreasing extraction along the series. A clear tetrad effect in the lanthanide group was also found.

Inhibiting radiolysis of BTP molecules by addition of nitrobenzene

Summary Autoradiolysis of extraction systems sometimes occurs during reprocessing of spent fuel, which may result in a change in the extraction behaviour of the system. In the work reported here, an aromatic heterocyclic nitrogen bearing tridentate extraction agent, 2,6-di(5,6-diethyl-1,2,4-triazin-3-yl)pyridine (a BTP), was irradiated using a 60Co source. The investigation focused on the effect of changing the organic diluent in the extraction system in order to protect the extracting agent from degradation. A relationship between the distribution ratio and extracting agent concentration was determined, and it was found that the extraction efficiency decreased with increasing irradiation dose. The effect on extraction of the degradation products from the organic diluents was also considered.

Extraction behavior of the synergistic system 2,6-bis-(benzoxazolyl)-4-dodecyloxylpyridine and 2-bromodecanoic acid using Am and Eu as radioactive tracers

Abstract In this study, the extraction properties of a synergistic system consisting of 2,6‐bis‐(benzoxazolyl)‐4‐dodecyloxylpyridine (BODO) and 2‐bromodecanoic acid (HA) in tert‐butyl benzene (TBB) have been investigated as a function of ionic strength by varying the nitrate ion and perchlorate ion concentrations. The influence of the hydrogen ion concentration has also been investigated. Distribution ratios between 0.03–12 and 0.003–0.8 have been found for Am(III) and Eu(III), respectively, but there were no attempts to maximize these values. It has been shown that the distribution ratios decrease with increasing amounts of ClO4 −, NO3 −, and H+. The mechanisms, however, by which the decrease occurs, are different. In the case of increasing perchlorate ion concentration, the decrease in extraction is linear in a log–log plot of the distribution ratio vs. the ionic strength, while in the nitrate case the complexation between nitrate and Am or Eu increases at high nitrate ion concentrations and thereby decreases the distribution ratio in a non‐linear way. The decrease in extraction could be caused by changes in activity coefficients that can be explained with specific ion interaction theory (SIT); shielding of the metal ions, and by nitrate complexation with Am and Eu as competing mechanism at high ionic strengths. The separation factor between Am and Eu reaches a maximum at ∼1 M nitrate ion concentration. Thereafter the values decrease with increasing nitrate ion concentrations.

Study of nitrate complex formation with Pm, Eu, Am and Cm using a solvent extraction technique

Summary The separation of actinides and lanthanides is an important question in the treatment of spent nuclear fuel in the transmutation concept. To find an efficient and well functioning separation process it is necessary to study the chemistry of the elements in the two groups in different aqueous media. The stability constants of the nitrate complex formation with Pm, Eu, Am and Cm were determined using solvent extraction. The extraction was studied using the synergistic system of 2,6-bis-(benzoxazolyl)-4-dodecyloxylpyridine and 2-bromodecanoic acid in tert-butyl benzene. As the nitrate ion concentration in the aqueous phase was increased, a decrease in separation between actinides and lanthanides was seen owing to complex formation between the different elements and the nitrate ions.

Was natural β radioactivity of carbon-14 the origin of optical one-handedness in life?

Abstract14C labelled solid D- and L-leucine decomposes with significantly different rates by auto-radiolysis. The β-decarboxylation ratio (103xCO2%)D/(103xCO2%)L was found to be (2.3±0.2)/(1.2±0.2)= 1.9±0.5 for samples kept in evacuated tubes at room temperature for 1 year /sp. activity: 0.9 MBq g−1; β-dose: 224 Gy/. EPR indicates a 10% higher radical concentration in the stored solid D-leucine samples than in L-leucine. The relevance of these results to the question of origin of optical onehandedness in life, is discussed.

Redox Control in Solvent Extraction Studies Using a PEEK AKUFVE Unit

Abstract When studying actinides or other elements with different possible oxidation states it is important to control which state is present in solution. Earlier redox control has been done by adding some other element to the solution but this approach introduces additional uncertainties. Since the sixties the AKUFVE apparatus has been used for precise solvent extraction studies. Now this equipment has been improved with redox control facilities, additional thermal control, and all parts in contact with the liquids are made of polyetherether ketone (PEEK) to minimize sorption.

Chemical properties of 2-bromodecanoic acid

Abstract Some chemical equilibrium constants for 2‐bromodecanoic acid were investigated. The dimerization constant of 2‐bromodecanoic acid, k2 =278 M−1, in tert‐butylbenzene was first derived from IR spectroscopy measurements. Secondly, the distribution coefficient, k d =799, was found by combining the value of k2 with distribution data obtained from solvent extraction experiments evaluated with the aid of neutron activation analysis. Finally the dissociation constant, k a =3.18 *10−3 M, was estimated from two‐phase titrations. A theoretical calculation was made based on the obtained constants and this calculation was validated by a second solvent extraction experiment that gave a good correspondence between calculated and experimental values.

Berkelium nitrate complex formation using a solvent extraction technique

Summary The extraction of Bk(III) into an organic phase consisting of 2,6-bis-(benzoxazolyl)-4-dodecyloxylpyridine, 2-bromodecanoic acid and tert-butyl benzene as a function of nitrate ion concentration in the aqueous phase was studied in order to determine the stability constants of the formation of Bk nitrate complexes. Increasing the nitrate ion concentration in the aqueous phase will increase the nitrate complex formation and thus the extraction of metal ions will decrease. Measuring this decrease in distribution ratio and fitting the data points with an appropriate model gives the stability constants of the Bk nitrate complex formation.