Search

The AKUFVE techniques were developed by Rydberg and co-workers in the 1960s. The main aim was to be able to perform a series of liquid-liquid extraction data varying one or more parameters and at the same time achieve very pure phases. As such, this technique was later used for short-lived isotope studies in the SISAK system, but also as a standalone unit for a large number of thermodynamic studies of extraction systems both for fundamental understanding as well as more applied investigations. In this paper, the apparatus with modifications made over the decades is described. In addition, studies with stability constant determinations for the zirconium-water-acetylacetone system as well as lanthanide extraction using bromodecanoic acid are exemplified to demonstrate the potential use of the technique. The results shown clearly demonstrate the versatility and ability of the AKUFVE system. [ABSTRACT FROM AUTHOR]

The extractability and coordination chemistry for lanthanides in a binary extraction system containing aerosol OT (AOT) and a phosphine oxide (CMPO) have been investigated by means of UV-Vis and X-ray absorption fine structure (XAFS) techniques over a range of extractant concentrations. In addition to the Fourier transform EXAFS analysis, the application of wavelet transform (WT) to the Fourier transform was adapted to the Ho L-III edge to provide a better contrast between the heavier and lighter backscattering atoms at higher coordination shells in the mixed extractant system. Through the variation of the ratio of AOT and CMPO and the acid concentration of the aqueous phase, a synergistic effect appeared at a 1 : 1 ratio of AOT and CMPO using a moderate acid concentration (0.5 M HNO3). It was also found that CMPO itself is directly coordinated with the metal ions by forming the bond with P=O and C=O, while AOT extracts the lanthanide as a hydrated form through reverse micelle formation. However, the complex of CMPO (C=O–M and P=O–M) to metal becomes weaker as it is mixed with AOT. Our results indicate that complexation from the CMPO is aiding the control of water extraction through reverse micelles from AOT, which results in the cooperative effect of certain mixtures of AOT–CMPO. The information from this coordination environment offers insight into the role of reverse micelle formation in a mixed-extractant solvent extraction system. [ABSTRACT FROM AUTHOR]

In this work, we propose a new transport mechanism for metal ions relevant for used nuclear fuel separation processes by a supported liquid membrane (SLM). Two SLM extraction systems were investigated where the membrane was impregnated with either di-(2-ethylhexyl)phosphoric acid (HDEHP) or tributyl phosphate (TBP). A HDEHP impregnated membrane was used to extract neodymium (III), representative of a typical trivalent lanthanide. Cerium, which was oxidized by sodium bismuthate from trivalent to tetravalent state, was extracted by TBP. Oxidized cerium was used as a surrogate for oxidized americium to investigate the kinetics and possibility of americium and curium separation by membrane extraction. Both extraction systems were operated at varying nitric acid concentrations, and changes in the kinetics and extraction efficiency of metal ions were investigated. The proposed transport mechanism that was chosen for our studies was modified from the previous works by Danesi et al.[1,2]and Cussler et al.[3]The mechanism was selected due to the ability to accommodate and describe transport phenomena across a SLM when formation of extractant nano-channels in the membrane may exist. We were able to obtain acceptable fit of the models to our overall data trends although chemical and physical conditions must be well established and purity and homogeneity of the membrane are critical. A reverse transport of metal ions was observed when leaving the system for longer times which agrees with our model. The membrane was investigated for degradation and shown to be stable after contact with up to 7 M nitric acid for over 2000 minutes. Finally, we examined the possibility of partitioning americium from curium using a SLM impregnated by TBP. Separation of americium from curium was observed although not to a degree that was expected based on the Ce(IV) transport. Incomplete oxidation of Am(III) to Am(V) and reduction of Am(VI) on the membrane surface are possible causes for this observed discrepancy. Our model was, however, able to accurately predict Cm(III) transport through the membrane. [ABSTRACT FROM AUTHOR]

Radioactive lanthanides have become an important imaging, diagnostic and therapeutic tool in the medical field. The objective of our research was to investigate the feasibility of producing radioactive lanthanides with high specific activity in a small-scale research reactor using the Szilard-Chalmers method. The results indicate that the activated nuclides recoil out of the target after neutron capture and we obtain enrichment of the radionuclide compared to the bulk irradiation. These first attempts, result in enrichment factors and yields that are low but indicates a possibility of using this technique if the method is further optimized. [ABSTRACT FROM AUTHOR]

During treatment of nuclear fuel in the Plutonium/URanium EXtraction (PUREX) process, the extractant tri-n-butyl phosphate (TBP) is known to degrade to dibutylphosphoric acid (HDBP), which increases the extraction of metal ions, thereby inhibiting their stripping from the organic phase. To better understand this phenomenon, we investigated how mixtures of TBP and HDBP influenced the extraction of metal, nitric acid, and water, and correlated the results to aggregated structures in the organic phase. The mole ratios of TBP-HDBP mixtures had a non-linear effect on the extraction of Dy3+and water from 0.2 M HNO3, indicating synergism. In 2 M HNO3, the TBP:HDBP mole ratio had a more linear relation to Dy3+and water extraction, so the synergistic effect was less pronounced than in the low acid system. The extraction of nitric acid showed no synergistic effect and follows closely what would be expected in a system using TBP only. The small-angle X-ray scattering (SAXS) data of the 0.2 M acid system showed maximum contrast at a TBP:HDBP mole ratio of 0.25, so that the synergistic mixture is also the most aggregated at 0.2 M acid. The 2 M acid system also showed that the mixed system is more aggregated than the end members, although this does not result in peak extraction. Previous studies of synergistic extraction of metal cations explain the enhanced extraction by increased dehydration of the metal ion. Although our data do not rule out the formation of mixed complexes according to the classical mechanism of synergism, our evidence of increased water extraction and aggregate formation in systems combining TBP and HDBP are complementary to the metal-centric dehydration aspects of the process. The findings in this study give insights into the complex chemistry of solvent extraction, providing a possible link between formation of aggregates in the organic phase and synergistic extraction. [ABSTRACT FROM AUTHOR]

The TALSPEAK process, developed in the 1960s at the Oak Ridge National Laboratory and demonstrated in various forms up to pilot scale elsewhere, has emerged as a primary method for partitioning of trivalent transplutonium actinides from fission product lanthanides in advanced nuclear fuel cycles. The baseline process relies on the monoacidic dialkyl phosphoric acid extractant bis-(2-ethylhexyl)phosphoric acid (HDEHP), the aqueous complexant diethylenetriamine-N,N,N',N'',N''-pentaacetic acid (DTPA), and high concentrations of a pH 3.5 buffer, usually 1-2 M lactic acid (HL). Previous reports have established that HL not only buffers the pH, but also increases phase transfer kinetics, improves the radiation stability of DTPA, and has been implicated as a possible participant in the formation of ternary complexes in both the aqueous and organic phases. One feature central to the interpretation of these results is the extent of partitioning of HL between the phases. In this study, 14C-labeled HL has been used to examine the details of its partitioning between aqueous solutions and organic solutions relevant to the possible deployment of TALSPEAK. It is found that, contrary to previous reports, HL partitions into the organic phase independently of the amount and identity of the metal ions that are present. [ABSTRACT FROM AUTHOR]

A recent review of the TALSPEAK (Trivalent Actinide - Lanthanide Separation by Phosphorous reagent Extraction from Aqueous Komplexes) process summarized previous research characterizing the performance of this system. Attempts were made in that report to develop correlations between the previous separations data and the thermodynamic data that describes the interactions among the components of the separation system. However, the diversity of observations and the breadth of conditions employed in the many studies from the literature make comparisons between the TALSPEAK system performance and existing thermodynamic data challenging. To better test the adequacy of the available thermodynamic database for modeling this system, an internally consistent set of observations of lanthanide extraction under TALSPEAK conditions is offered in this report. The extraction of the lanthanides from La through Lu (excluding Pm) plus Y, and that of Am3+ from buffered lactic acid solutions containing diethylenetriamine-N,N,N',N'',N''-pentaacetic acid (DTPA) into organic solutions of bis-(2-ethylhexyl)phosphoric acid (HDEHP) solutions in 1,4-diisopropylbenzene has been investigated as a function of temperature, pH, and ionic strength. Extraction of both lanthanides and Am3+ decreases with increasing pH and with temperature. At the same time, separation factors remain approximately constant. Calculations based on an internally consistent thermodynamic data set confirm the prior conclusion that the existing thermodynamic data do not predict the observed decline in partitioning with increased pH, though the data do support the constancy of the separation factors. The relationship between the basic thermodynamic data, calculated speciation, and the performance of the separation system is discussed. [ABSTRACT FROM AUTHOR]

The separation of trivalent transplutonium actinides from fission product lanthanide ions represents arguably the most challenging aspect of advanced nuclear fuel partitioning schemes. A considerable amount of effort has been dedicated to the development of effective methods for accomplishing this separation, essential for transmutation of the actinides heavier than Pu. Among the methods currently considered to be ready for technological deployment is the TALSPEAK (Trivalent Actinide - Lanthanide Separation by Phosphorus reagent Extraction from Aqueous Komplexes) Process, developed in the late 1960s at Oak Ridge National Laboratory. This process is based on the partitioning of lanthanides and actinides between an acidic organophosphorus extractant ((RO)2PO2H) solution and an aqueous phase containing a high concentration of a carboxylic acid buffer and a polyaminopolycarboxylate complexant. The latter reagent is principally responsible for holding back the trivalent actinides, allowing the selective transfer of the lanthanides into the organic phase. Several combinations of different extractants and aqueous complexants have been investigated, as have the effect of diluent, temperature and p[H+] on separation efficiency. In this report, the prior literature is examined to help provide guidance for potential deployment of the technology in advanced nuclear fuel cycles and to identify opportunities for fine-tuning the process. [ABSTRACT FROM AUTHOR]