Mark Foreman

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.

An overview and historical look back at the solvent extraction using nitrogen donor ligands to extract and separate An(III) from Ln(III)

The partitioning of minor trivalent actinides (An) from lanthanides (Ln) is one of the challenges in the chemical treatment of nuclear waste. The optimal ligand to carry out the separation of An(III) and Ln(III) using solvent extraction has to meet several important criteria: high selectivity towards the solute, chemical and radiolytic stability, stripping possibilities and recycling of the organic phase, high separation factors and good distribution ratio, to name just a few of them. A chronological line can be drawn along the development of each extraction ligand family and some milestones are emphasized in this overview. Further developments in organic synthesis of extracting ligands are expected.

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.

A TBP/BTBP-based GANEX Separation Process. Part 1: Feasibility

Abstract A GANEX (Group ActiNide EXtraction) separation system for transmutation has been developed. In this separation process the actinides should be extracted as a group from the lanthanides and the fission and corrosion/activation products. This can be achieved by combining BTBP (bis-triazine-bipyridine) with TBP (tri-butyl phosphate) in cyclohexanone. From 4M nitric acid this organic system extracts the actinides (log(DAm) = 2.19, log(DPu) = 2.31, log(DU) = 1.03, log(DNp) = 0.53) and also separates them from the lanthanides (log(DLa) = −2.0, log(DCe) = −1.72, log(DNd) = −1.05, log(DSm) = −0.18, log(DEu) = −0.02). One problem encountered is that some of the fission and corrosion products are also extracted. The new system however still looks feasible.

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).

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.

Separation of Actinides(III) from Lanthanides(III) in Simulated Nuclear Waste Streams using 6,6′‐Bis‐(5,6‐dipentyl‐[1,2,4]triazin‐3‐yl)‐[2,2′]bipyridinyl (C5‐BTBP) in Cyclohexanone

Abstract An extraction system comprising 6,6′‐bis‐(5,6‐dipentyl‐[1,2,4]triazin‐3‐yl)‐[2,2′]bipyridinyl (C5‐BTBP) dissolved in cyclohexanone was investigated. The main purpose of this investigation was to extract and separate actinides(III) from lanthanides(III), both of which are present in the waste from the reprocessing of spent nuclear fuel. The system studied showed high distribution ratios for the actinides(III) and a high separation factor between actinides and lanthanides (SFAm/Eu around 150). The extraction kinetics were fast with equilibrium being reached in 5 minutes. The effects of temperature on the extraction and the stoichiometry of the extracted complex were investigated. The extraction of californium(III) was studied and it was found that the BTBP molecule has a higher affinity for californium than for americium (SFCf/Am around 4). This system could be used to separate actinides(III) from lanthanide fission products with high efficiency, if used in conjunction with a pre‐equilibrium step.

A TBP/BTBP-based GANEX Separation ProcessPart 2: Ageing, Hydrolytic, and Radiolytic Stability

Abstract The waste from nuclear power plants worldwide has to be isolated from man and his environment for about 100,000 years to equal the levels of natural uranium. If, however, the long-lived actinides could be separated from the spent fuel and transmuted, then the isolation time could be shortened to about 1,000 years. This does, however, require the selective separation of the actinides from the rest of the waste. Several processes exist for such a separation, of which one is the Group ActiNide Extraction (GANEX) process. A novel GANEX process has been developed at the Chalmers University of Technology utilizing the properties of already well known extractants by combining BTBP and TBP into one solvent. The stability provided by this GANEX solvent towards ageing, hydrolysis, and radiolysis has been investigated. The results show that the actinide distribution ratios are maintained after a long duration of contact with strong nitric acid. The solvent has also been found to be stable towards radiolysis up to 200 kGy in contact with 4 M nitric acid.

An analysis of the composition and metal contamination of plastics from waste electrical and electronic equipment (WEEE)

The compositions of three WEEE plastic batches of different origin were investigated using infrared spectroscopy, and the metal content was determined with inductively coupled plasma. The composition analysis of the plastics was based mainly on 14 samples collected from a real waste stream, and showed that the major constituents were high impact polystyrene (42 wt%), acrylonitrile-butadiene-styrene copolymer (38 wt%) and polypropylene (10 wt%). Their respective standard deviations were 21.4%, 16.5% and 60.7%, indicating a considerable variation even within a single batch. The level of metal particle contamination was found to be low in all samples, whereas wood contamination and rubber contamination were found to be about 1 wt% each in most samples. In the metal content analysis, iron was detected at levels up to 700 ppm in the recyclable waste plastics fraction, which is of concern due to its potential to catalyse redox reactions during melt processing and thus accelerate the degradation of plastics during recycling. Toxic metals were found only at very low concentrations, with the exception of lead and cadmium which could be detected at 200 ppm and 70 ppm levels, respectively, but these values are below the current threshold limits of 1000 ppm and 100 ppm set by the Restriction of Hazardous Substances directive.

Influence of dose rate on the radiolytic stability of a BTBP solvent for actinide(III)/lanthanide(III) separation

Abstract The recently developed ligand MF2-BTBP dissolved in cyclohexanone is a promising solvent for the group separation of trivalent actinides(III) from the lanthanides(III). Its high stability against nitric acid has been demonstrated recently. Since the solvent is also exposed to a continuously high radiation level in the counter current process, the radiolytic stability of the solvent was examined in this study. Irradiation experiments were carried out up to an absorbed dose of 100 kGy and the effect of the dose rate was investigated. The extraction behaviour for An(III)/Ln(III) separation was studied after radiolysis for evaluation. It was found that during high dose rate irradiation the extraction efficiency for both Am(III) and Eu(III) decreased significantly with increasing absorbed dose, whereas during the low dose rate irradiation the extraction efficiencies remained more or less at the same level.