Udo Müllich

Selective extraction of Am(III) over Eu(III) by 2,6-ditriazolyl- and 2,6,-ditriazinylpyridines

ABSTRACT 2,6-Di(5-alkyl-1,2,4-triazol-3-yl)-pyridine and 2,6-di(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine type compounds extract Am(III) 2-bromohexanoate and nitrate from acidic solutions (≤1 M HNO3) with an appreciable efficiency and selectivity, yielding Am(III)/Eu(III) separation factors of ≤150.

EXTRACTION OF Am(lll) AND Eu(lll) NITRATES BY 2-6-DI-(5,6-DIPROPYL-1,2,4-TRIAZIN-3-YL)PYRIDINES 1

ABSTRACT The extraction of Am(lll) and Eu(lll) by 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)-pyridines from mostly 1·9 M (HNO3 + NH4NO3) was studied. The compound with n-propyl (DPTP) forms dimers and trimers in mixed branched alkanes modified with 2-ethyl-1-hexanol. The self-association is supported by enhancing the HNO3 concentration from 0·3 to 0·9 M. In the above modified diluent, DPTP extracts Am(lll) and Eu(lll) nitrates as the complexes Am(NO3)3HNO3-3B and Eu(NO3)3HN033B. The Am(lll)/Eu(lll) separation factor is typically 100 -120. The extraction and separation efficiency of DPTP strongly decreases in the order of diluents (each modified with 2-ethyl-1-hexanol) branched alkanes > cyclohexane > 2-methyl-4-pentanone > 2-ethylhexyl acetate > benzene > chlorobenzene > xylene. 1-Octanol and 2-ethyl-1-hexanol modifiers support appropriately the solubility of protonated forms of DPTP in branched alkanes, and moderately enhance the extraction of Am(lll) and Eu(lll). 1-Butanol modifier allows a higher extracti...

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.

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.

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.

Development of a New Flowsheet for Co-Separating the Transuranic Actinides: The "Euro-GANEX" Process

A flowsheet for a novel GANEX (Grouped ActiNide EXtraction) process has been tested in a spiked flowsheet trial in a 32 stage plutonium-active centrifugal contactor rig with a simulant feed that contained 10 g/L plutonium as well as some fission products and other transuranic actinides. The solvent system used was a combination of 0.2 mol/L N,N,N’,N’-tetraoctyl diglycolamide (TODGA) and 0.5 mol/L N,N’-(dimethyl-N,N’-dioctylhexylethoxy-malonamide (DMDOHEMA) in a kerosene diluent that co-extracted actinides and lanthanides. Actinides were subsequently selectively co-stripped away from the lanthanides using a sulphonated and, therefore, hydrophilic bis-triazinyl pyridine (BTP) complexant in conjunction with acetohydroxamic acid (AHA). Plutonium and americium recoveries were high with decontamination factors across the strip contactors of ˜14,000 and ˜390, respectively. However, approximately 30% of neptunium was lost to the aqueous raffinate which was due to recycling within the first extract-scrub section causing a large build-up of neptunium. Some accumulation of strontium was also observed but in this case it was fully directed to the raffinate stream. In the stripping section, a small fraction of europium (taken as a model lanthanide ion), ca. 7%, was found in the actinide product stream. Modelling of selected data using the PAREX code has shown that even with a relatively simplistic treatment, reasonable agreement between modelling and experiment can be obtained, giving confidence in the use of modelling to refine the GANEX flowsheet design prior to further testing with irradiated fast reactor fuel.

Evidence for covalence in a N-donor complex of americium(III)

The molecular origin of the selectivity of N-donor ligands, such as alkylated bis-triazinyl pyridines (BTPs), for actinide complexation in the presence of lanthanides is still largely unclear. NMR investigations of an Am(nPrBTP)3(3+) complex with a (15)N labelled ligand showed that it exhibits large differences in (15)N chemical shift for coordinating N-atoms in comparison to both lanthanide(III) complexes and the free ligand. The temperature dependence of NMR chemical shifts observed for this complex indicates a weak paramagnetism. This fact and the observed large chemical shift for bound nitrogen atoms allow us to conclude that metal-ligand bonding in the reported Am(III) N-donor complex has a larger share of covalence than in lanthanide complexes. This may account for the observed selectivity.

Laboratory-Scale Counter-Current Centrifugal Contactor Demonstration of an Innovative-SANEX Process Using a Water Soluble BTP

In this paper the development and laboratory-scale demonstration of a novel “innovative-SANEX” (Selective Actinide Extraction) process using annular centrifugal contactors is presented. In this strategy, a solvent comprising the N,N,N’,N’-tetraoctyldiglycolamide (TODGA) extractant with addition of 5 vol.-% 1-octanol showed very good extraction efficiency of Am(III) and Cm(III) together with the trivalent lanthanides (Ln(III)) from simulated Plutonium Uranium Refining by Extraction (PUREX) raffinate solution without 3rd phase formation. Cyclohexanediaminetetraacetic acid (CDTA) was used as masking agent to prevent the co-extraction of Zr and Pd. An(III) and Ln(III) were co-extracted from simulated PUREX raffinate, and the loaded solvent was subjected to several stripping steps. The An(III) were selectively stripped using the hydrophilic complexing agent SO3-Ph-BTP (2,6-bis(5,6-di(sulfophenyl)-1,2,4-triazin-3-yl)pyridine). For the subsequent stripping of the Ln(III), a citric acid based solution was used. A 32-stage process flow-sheet was designed using computer-code calculations and tested in annular miniature centrifugal contactors in counter-current mode. The innovative SANEX process showed excellent performance for the recovery of An(III) from simulated High Active Raffinate (HAR) solution and separation from the fission and activation products. ≥ 99.8% An(III) were recovered with only low impurities (0.4% Ru, 0.3% Sr, 0.1% Ln(III)). The separation from the Ln(III) was excellent and the Ln(III) were efficiently stripped by the citrate-based stripping solution. The only major contaminant in the spent solvent was Ru, with 14.7% of the initial amount being found in the spent solvent. Solvent cleaning and recycling therefore has to be further investigated. This successful spiked test demonstrated the possibility of separating An(III) directly from HAR solution in a single cycle which is a great improvement over the former multi-cycle strategy. The results of this test are presented and discussed.

Application of novel extractants for actinide(III)/ lanthanide(III) separation in hollow-fibre modules

Abstract Separation tests using hollow-fibre modules were performed for the difficult selective extraction of trivalent actinides over fission lanthanides from acidic media. This article shows that with 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine as the extractant, up to 94% americium could be extracted from 1.0 kmol/m 3 HNO 3 , with minimal lanthanide co-extraction. Using a synergistic mixture of bis(chlorophenyl)dithiophosphinic acid and tri- n -octyl phosphine oxide, tests were performed on extraction, lanthanide scrubbing and stripping. In the extraction test, up to 99.99% americium could be extracted from 0.5 kmol/m 3 HNO 3 , with approximately one third of the lanthanides being co-extracted. Mass transfer calculations using a consistent set of input data showed good agreement with the experiments.

Selective Extraction of Am(III) from PUREX Raffinate: The AmSel System

ABSTRACT The separation of actinides(III) from used nuclear fuel is a key step for the recycling of used nuclear fuel in innovative fuel cycles. However, high neutron dose rates and heat load of short-lived curium isotopes complicate the production and handling of new nuclear fuel containing curium(III) and americium(III). Therefore, new processes have to be developed separating only americium(III) from PUREX (Plutonium-Uranium Recovery by Extraction) raffinate. This is achieved by coextracting An(III) and Ln(III) from PUREX raffinate using N,N,N’,N’-tetraoctyl-diglycolamide (TODGA), followed by the subsequent selective stripping of Am(III) by a water-soluble bis-triazinyl-bipyridin (sodium 3,3’,3’’,3’’’-([2,2’-bipyridine]-6,6’-diylbis(1,2,4-triazine-3,5,6-triyl))tetrabenzenesulfonate, SO3-Ph-BTBP). The selectivity for Am(III) over Cm(III) is SFCm(III)/Am(III) ≈ 2.5, due to the inverse selectivity of TODGA and SO3-Ph-BTBP. Additionally, a separation factor up to 1200 is achieved for the separation of Eu(III) from Am(III). The results demonstrate that the presented system works very well even at acidic conditions using nitric acid as the aqueous phase and does not require additional salting out agents.