Andreas Geist

6,6′‐Bis(5,5,8,8‐tetramethyl‐5,6,7,8‐tetrahydro‐benzo[1,2,4]triazin‐3‐yl) [2,2′]bipyridine, an Effective Extracting Agent for the Separation of Americium(III) and Curium(III) from the Lanthanides

Abstract The extraction of americium(III), curium(III), and the lanthanides(III) from nitric acid by 6,6′‐bis(5,5,8,8‐tetramethyl‐5,6,7,8‐tetrahydro‐benzo[1,2,4]triazin‐3‐yl)‐[2,2′]bipyridine (CyMe4‐BTBP) has been studied. Since the extraction kinetics were slow, N,N′‐dimethyl‐N,N′‐dioctyl‐2‐(2‐hexyloxy‐ethyl)malonamide (DMDOHEMA) was added as a phase transfer reagent. With a mixture of 0.01 M CyMe4‐BTBP+0.25 M DMDOHEMA in n‐octanol, extraction equilibrium was reached within 5 min of mixing. At a nitric acid concentration of 1 M, an americium(III) distribution ratio of approx. 10 was achieved. Americium(III)/lanthanide(III) separation factors between 50 (dysprosium) and 1500 (lanthanum) were obtained. Whereas americium(III) and curium(III) were extracted as disolvates, the stoichiometries of the lanthanide(III) complexes were not identified unambiguously, owing to the presence of DMDOHEMA. In the absence of DMDOHEMA, both americium(III) and europium(III) were extracted as disolvates. Back‐extraction with 0.1 M nitric acid was thermodynamically possible but rather slow. Using a buffered glycolate solution of pH=4, an americium(III) distribution ratio of 0.01 was obtained within 5 min of mixing. There was no evidence of degradation of the extractant, for example, the extraction performance of CyMe4‐BTBP during hydrolylsis with 1 M nitric acid did not change over a two month contact.

Demonstration of a SANEX Process in Centrifugal Contactors using the CyMe4‐BTBP Molecule on a Genuine Fuel Solution

Efficient recovery of minor actinides from a genuine spent fuel solution has been successfully demonstrated by the CyMe4‐BTBP/DMDOHEMA extractant mixture dissolved in octanol. The continuous countercurrent process, in which actinides(III) were separated from lanthanides(III), was carried out in laboratory centrifugal contactors using an optimized flow‐sheet involving a total of 16 stages. The process was divided into 9 stages for extraction from a 2 M nitric acid feed solution, 3 stages for lanthanide scrubbing, and 4 stages for actinide back‐extraction. Excellent feed decontamination factors for Am (7000) and Cm (1000) were obtained and the recoveries of these elements were higher than 99.9%. More than 99.9% of the lanthanides were directed to the raffinate except Gd for which 0.32% was recovered in the product.

An Investigation into the Extraction of Americium(III), Lanthanides and D‐Block Metals by 6,6′‐Bis‐(5,6‐dipentyl‐[1,2,4]triazin‐3‐yl)‐[2,2′]bipyridinyl (C5‐BTBP)

Abstract The tetradentate ligand (C5‐BTBP) was able to extract americium(III) selectively from nitric acid. In octanol/kerosene the distribution ratios suggest that stripping will be possible. C5‐BTBP has unusual properties and potentially offers a means of separating metals, which otherwise are difficult to separate. For example C5‐BTBP has the potential to separate palladium(II) from a mixture containing rhodium(III) and ruthenium(II) nitrosyl. In addition, C5‐BTBP has the potential to remove traces of cadmium from effluent or from solutions of other metals contaminated with cadmium. C5‐BTBP has potential as a reagent for the separation of americium(III) from solutions contaminated with iron(III) and nickel(II), hence offering a means of concentrating americium(III) for analytical purposes from nitric acid solutions containing high concentrations of iron(III) or nickel(II).

An Improved Hydrolytically-Stable Bis-Triazinyl-Pyridine (BTP) for Selective Actinide Extraction

Abstract Bis-2,6-(5,6,7,8-tetrahydro-5,9,9-trimethyl-5,8-methano-1,2,4-benzotriazin-3-yl)pyridine (CA-BTP) is presented as a novel optimized extracting agent for the separation of americium(III) and curium(III) from lanthanides(III). CA-BTP is synthesized and studied concerning its extraction properties under conditions relevant to the SANEX process. It is demonstrated that CA-BTP is the first relevant molecule to show both high stability towards highly-acidic process solutions and satisfactory extraction kinetics. Its high solubility in 1-octanol adds to CA-BTPs favorable properties. Furthermore, CA-BTP is synthesized from a commercially available and moderately priced precursor molecule, reducing extracting-agent production costs.

Actinide(III)/Lanthanide(III) Separation Via Selective Aqueous Complexation of Actinides(III) using a Hydrophilic 2,6-Bis(1,2,4-Triazin-3-Yl)-Pyridine in Nitric Acid

i-SANEX is a process for separating actinides(III) from used nuclear fuels by solvent extraction: Actinides(III) and lanthanides(III) are co-extracted from a PUREX raffinate followed by selective back extraction of actinides(III) from the loaded organic phase. This step requires a complexing agent selective for actinides(III). A hydrophilic sulfonated bis triazinyl pyridine (SO3-Ph-BTP) was synthesized and tested for selective complexation of actinides(III) in nitric acid solution. When co-extracting Am(III) and Eu(III) from nitric acid into TODGA, adding SO3-Ph-BTP to the aqueous phase suppresses Am(III) extraction while Eu(III) is extracted. Separation factors in the range of 1000 are achieved. SO3-Ph-BTP remains active in nitric acid up to 2 mol/L. As a result of this performance, buffering or salting-out agents are not needed in the aqueous phase; nitric acid is used to keep the lanthanides(III) in the TODGA solvent. These properties make SO3-Ph-BTP a suitable candidate for i-SANEX process development.

A review of the demonstration of innovative solvent extraction processes for the recovery of trivalent minor actinides from PUREX raffinate

Abstract The selective partitioning (P) of long-lived minor actinides fromhighly active waste solutions and their transmutation (T) to short-lived or stable isotopes by nuclear reactions will reduce the long-term hazard of the high-level waste and significantly shorten the time needed to ensure their safe confinement in a repository. The present paper summarizes the on-going research activities at Forschungszentrum Jülich (FZJ), Karlsruher Institut für Technologie (KIT) and Institute for Transuranium Elements (ITU) in the field of actinide partitioning using innovative solvent extraction processes. European research over the last few decades, i.e. in the NEWPART, PARTNEW and EUROPART programmes, has resulted in the development of multi-cycle processes for minor actinide partitioning. These multi-cycle processes are based on the co-separation of trivalent actinides and lanthanides (e.g. by the DIAMEX process), followed by the subsequent actinide(III)/lanthanide(III) group separation in the SANEX process. The current direction of research for the development of innovative processes within the recent European ACSEPT project is discussed additionally. This paper is focused on the development of flow-sheets for recovery of americium and curium from highly active waste solutions. The flow-sheets are verified by demonstration processes, in centrifugal contactors, using synthetic or genuine fuel solutions. The feasibility of the processes is also discussed.

Demonstration of the LUCA process for the separation of americium(III) from curium(III), californium(III), and lanthanides(III) in acidic solution using a synergistic mixture of bis(chlorophenyl)dithiophosphinic acid and tris(2-ethylhexyl)phosphate

Abstract The LUCA process was developed at Forschungszentrum Jülich for the selective separation of Am(III) from an acidic solution containing the trivalent actinides Am(III), Cm(III), and Cf(III) as well as lanthanides. A mixture of 0.4 mol/L bis(chlorophenyl)dithiophosphinic acid and 0.15 mol/L tris(2-ethylhexyl)phosphate dissolved in 20% isooctane/80% tert-butyl benzene was used as the extractant. The process was carried out in centrifugal contactors using an optimized flowsheet involving 7 stages for extraction, 9 stages for scrubbing and 8 stages for back-extraction. Very encouraging results were obtained. A high feed decontamination factor was obtained for Am(III) (>1000), and recovery in the product after stripping was higher than 99.8%. The Am(III) product was contaminated with 0.47% Cm(III). More than 99.9% Cf(III), Eu(III) and >99.5% Cm(III) inventories were directed to the raffinate and the contamination with Am(III) (<0.08%) was low. The experimental results were in good agreement with the predictions of a computer code.

Kinetics of Americium(III) Extraction and Back Extraction with BTP

Abstract 2,6‐Di(5,6‐dipropyl‐1,2,4‐triazin‐3‐yl)pyridine (BTP) extracts trivalent actinides from nitric acid with high separation factors over the lanthanides. The kinetics of americium(III) extraction and back extraction of this extraction system was studied in a constant‐interface stirred cell. The americium(III) extraction rate was found to be independent of the stirring speed. This means that the rate of mass transfer is limited by a slow chemical complexation reaction (“chemical regime”). The americium(III) extraction rate was found to increase linearly with BTP concentration. Nitric acid concentration had a strong influence on the rate of the americium(III) extraction, due to its influence on the free extractant concentration. The addition of ammonium nitrate did not affect the rate of americium(III) extraction. By investigating the influence of the interfacial area on the americium(III) extraction rate, the interface was identified as the site of the chemical reaction. The americium(III) back extraction rate increased linearly with the stirring speed, indicating that the back extraction is limited by diffusion. The extraction and the back extraction rates could be calculated by a simple model based on equilibrium data for the co‐extraction of americium(III) and nitric acid.

Complexation of Europium(III) by Bis(dialkyltriazinyl)bipyridines in 1-Octanol

The present work focuses on highly selective ligands for An(III)/Ln(III) separation: bis(triazinyl)bipyridines (BTBPs). By combining time-resolved laser-induced fluorescence spectroscopy, nanoelectrospray ionization mass spectrometry, vibronic sideband spectroscopy, and X-ray diffraction, we obtain a detailed picture of the structure and stoichiometry of the first coordination sphere of Eu(III)-BTBP complexes in an octanolic solution. The main focus is on the 1:2 complexes because extraction studies revealed that those are the species extracted into the organic phase. The investigations on europium(III) complexes of BTBP with different triazin alkylation revealed differences in the formed complexes due to the bulkiness of the ligands. Because of the vibronic sidebands in the fluorescence spectra, we were able to detect whether or not nitrate ligands are coordinated in the first coordination sphere of the Eu-BTBP complexes. In solution, less sterically demanding BTBP offers enough space for additional coordination of anions and/or solvent molecules to form 9-coordinated Eu-BTBP 1:2 complexes, while bulkier ligands tend to form 8-fold-coordinated structures. We also report the first crystal structure of a Ln-BTBP 1:2 complex and that of its 1:1 complex, both of which are 10-coordinated.

2,6-Bis(5-(2,2-dimethylpropyl)-1H-pyrazol-3-yl)pyridine as a Ligand for Efficient Actinide(III)/Lanthanide(III) Separation

The N-donor complexing ligand 2,6-bis(5-(2,2-dimethylpropyl)-1H-pyrazol-3-yl)pyridine (C5-BPP) was synthesized and screened as an extracting agent selective for trivalent actinide cations over lanthanides. C5-BPP extracts Am(III) from up to 1 mol/L HNO(3) with a separation factor over Eu(III) of approximately 100. Due to its good performance as an extracting agent, the complexation of trivalent actinides and lanthanides with C5-BPP was studied. The solid-state compounds [Ln(C5-BPP)(NO(3))(3)(DMF)] (Ln = Sm(III), Eu(III)) were synthesized, fully characterized, and compared to the solution structure of the Am(III) 1:1 complex [Am(C5-BPP)(NO(3))(3)]. The high stability constant of log β(3) = 14.8 ± 0.4 determined for the Cm(III) 1:3 complex is in line with C5-BPPs high distribution ratios for Am(III) observed in extraction experiments.