dimethyl-N,N′-dibutyltetradecyl Malonamide Research Articles

Liquid–liquid microflow patterns and mass transfer of radionuclides in the systems Eu(III)/HNO3/DMDBTDMA and U(VI)/HCl/Aliquat® 336

Two phases (liquid–liquid extraction) stratified flows in a rectangular geometry are investigated in a double-Y shape glass chip. The influence of physical properties, in particular the viscosity of the two liquids, on the velocity profiles is determined numerically. Viscosity affects the shapes of the velocity profiles of each phase. The extraction conditions (acid concentrations, contact times) in batch and in the microfluidic device were considered for a neutral extractant, N,N′-dimethyl N,N′-dibutyl tetradecylmalonamide (DMDBTDMA) and a liquid anion exchanger (Aliquat® 336), for the extraction of Eu(III) from HNO3 and U(VI) from HCl, respectively. The effects of viscosity and operating conditions on extraction performances were investigated, and the apparent rate constants were evaluated for the extraction of uranium by Aliquat® 336 k app = (0.55 ± 0.03) s−1 and for the extraction of europium by DMDBTDMA: k app = (2.9 ± 0.2) × 10−3 s−1.

Modified synthesis scheme for N,N´-dimethyl-N,N´-dioctyl-2,(2´-hexyloxyethyl) malonamide (DMDOHEMA) and its comparison with proposed solvents for actinide partitioning

Abstract N,N´-dimethyl-N,N´-dioctyl-2,(2´-hexyloxyethyl) malonamide (DMDOHEMA) has been synthesized by a relatively simpler route with a better yield than the conventional procedures for the synthesis of pentaalkyl substituted diamides. The proposed route replaces the use of acid chlorides and brominating agents (corrosive in nature) by acid diester and p-toluene sulphonyl (tosyl) chloride, respectively. The later easily replaces hydrogen from primary OH group of the 3-oxanonyl side chain and relatively less corrosive. The synthesized product has been tested for the extraction behavior of 241Am, Np, Pu as pure tracers as well as under Pressurized Heavy Water Reactor (PHWR) Simulated High-Level Waste (SHLW) conditions. The stoichiometries of extracted species of Np(IV), Pu(IV), and Am(III) from 3 M HNO3 using varying concentrations of DMDOHEMA in n-dodecane has been determined. The effect of the nature of mineral acid (viz. HCl, HNO3, and HClO4) on the extraction of Am(III) has also been investigated employing DMDOHEMA and N,N´-dimethyl-N,N´-dibutyl-tetradecyl malonamide (DMDBTDMA) as extractants and explained in terms of the aggregation behavior of diamides. The performance of DMDOHEMA has been evaluated vis-à-vis other proposed extractants for actinide partitioning under PHWR-SHLW conditions.

Solvent Extraction of Cerium(III) Using an Aliphatic Malonamide: The Role of Acid in Organic Phase Behaviors

The extraction of Ce(NO3)3 with N,N′-dimethyl N,N′-dibutyl tetradecylmalonamide (DMDBTDMA) in n-dodecane (0.5 M) from acidic (3 M HNO3) and neutral (3 M LiNO3) media was studied by varying the aqueous cerium concentration up to and beyond the point of third phase formation (defined by the Limiting Organic Concentration or LOC). The acidic system showed better Ce(III) extraction (i.e., a higher distribution ratio, DCe), increased water extraction, and also a lower LOC than the neutral system. These observations are consistent with the micellar model, suggesting that acid pre-organizes the organic phase into hydrated reverse micelles that favor Ce(NO3)3 extraction while increasing the attractive potential between aggregates so that third phase formation happens more readily. The findings in this study underline the importance of aggregation in solvent extraction systems and provide the basis for a wider structural study on the effects of acid on the supramolecular structure of the organic phase.

Redox Chemistry of Third Phases Formed in the Cerium/Nitric Acid/Malonamide‐n‐Dodecane Solvent Extraction System

AbstractUpon solvent extraction of the colorless solution 0.1 M Ce(NO3)3⋅6H2O in 3 M HNO3 with DMDBTDMA (N,N′‐dimethyl‐N,N′‐dibutyltetradecyl malonamide) at a concentration of 0.5 M in n‐dodecane (also a colorless solution), a yellow third phase is formed. In keeping with previous observations reported in the historical literature of solvent extraction, the yellow color was initially interpreted as an indication of the presence of tetravalent cerium, which is, coincidentally, yellow in aqueous HNO3. The valence quandary arising from the visual assessment led us to extract a freshly prepared solution of 0.1 M cerium(IV) nitrate, which was obtained by exhaustive bulk electrolysis of 0.1 M Ce(NO3)3⋅6H2O in 3 M HNO3. A red third phase was obtained. Under ambient light, the red third phase reverts to the yellow color of the third phase formed upon solvent extraction of CeIII. These observations, in combination with results obtained by UV/Visible and X‐ray absorption spectroscopies as well as electrochemical studies of the yellow and red third phases, demonstrate that the colors are directly correlated with changes in Ce valence, where CeIII obtains in the yellow third phase and CeIV in the red one, and the formation of coordination complexes with DMDBTDMA. By use of three‐phase electrode voltammetry and controlled potential electrolysis techniques, the one‐electron CeIII/CeIV redox chemistry in the third phases was examined in a manner not realized beforehand. These results, demonstrating reversible electrochromism, stand at the intersection of the fields of electroanalytical chemistry, on the one hand, and separations science, on the other, thus providing original insights into third phase phenomena and ion transfer across the aqueous–organic liquid interface in the extraction system.

Aqueous Partitioning of Minor Actinides by Different Processes

Actinide partitioning is a proposed strategy for effective mitigation of the long-term hazards associated with high-level waste (HLW). Octyl-(phenyl)–N,N-diisobutyl carbamoyl methyl phosphine oxide (CMPO) and diphenyl–N,N-diisobutyl carbamoyl methyl phosphine oxide (DφCMPO) are amongst the promising extractants extensively studied since the 1980s for actinide partitioning from wastes of different origin. During the last two decades, substituted malonamide extractants such as N,N'-dimethyl-N,N'-dibutyl tetradecyl malonamide (DMDBTDMA) and N,N'-dimethyl-N,N'-dioctyl hexylethoxy malonamide (DMDOHEMA) have emerged as viable green alternatives to phosphine oxides. During the last decade, diglycolamide-based extractants such as N,N,N′,N′-tetraoctyl diglycolamide (TODGA) and N,N,N′,N′-tetra-2-ethylhexyl diglycolamide (TEHDGA) have received considerable attention due to overwhelmingly favourable extraction and stripping efficiencies of minor actinides from different types of transuranium (TRU) wastes. The focus of the present review is to carry out comparative evaluation of the key physical and chemical properties of these extractants for hydrometallurgical applications. Merits of flow sheets proposed for the separation and recovery of minor actinides from high-level wastes have also been discussed.

Separation and determination of components of high level waste using IC and dynamically modified reversed-phase HPLC in ‘actinide partitioning’ studies using synthetic waste solution

Ion-chromatography (IC) as well as high performance liquid chromatography (HPLC) techniques have been used as analytical tools for the separation and estimation of some of the relevant metal ions present in the high level liquid waste (HLLW). IC was applied for the estimation of alkali and alkali earth metal ions, viz. Na, Cs, Ba and Sr using methane sulphonic acid as the eluent on a cation exchange column. On the other hand, dynamically modified (with sodium salt of n-octane sulphonic acid) reverse phase HPLC was followed for the estimation of lanthanides viz. La, Pr, Nd and Sm using α-hydroxy isobutyric acid as the eluent on a C-18 column. Sample acidity of 0.01 M HNO3 was optimized for best analytical results. The interferences of one group of metal ions on the quantification of the other group of metal ions were studied. The solvent extraction data (distribution coefficient data) of Na, Cs, Sr, Ba, La, Pr, Nd and Sm from their mixture was obtained by analyses of the aqueous samples before and after extraction with extractants used for actinide partitioning, viz., octyl(phenyl)N,N-diisobutyl carbamoyl methylene phosphine oxide (CMPO), N,N′-dimethyl-N,N′-dibutyl tetradecyl malonamide (DMDBTDMA) and N,N,N′,N′-tetraoctyl diglycolamide (TODGA). The solvent extraction data obtained by IC/HPLC techniques was compared with those obtained by ICP-AES technique. A good agreement between the results of the two techniques validated the present analytical method.

Extraction of americium(III) and europium(III) using a gamma pre-irradiated solution of N,N′-dimethyl-N,N′-dibutyltetradecyl malonamide in n-dodecane modified with N,N′-dihexyloctanamide

The extraction of Am(III) and Eu(III) using a γ-pre-irradiated N,N′-dimethyl-N,N′-dibutyltetradecyl malonamide (DMDBTDMA) modified with N,N′-dihexyloctanamide (DHOA) in n-dodecane (NDD) at 4.5M HNO3 has been studied as a function of the absorbed dose up to 2×106 Gray. The distribution ratios of Am(III) and Eu(III) were almost constant until a dose of 1×105 Gray and then they decreased gradually up to a dose of 2×106 Gray. The decrease of the distribution ratios of Am(III) and Eu(III) are due to the decreasing concentration of the DMDBTDMA by a γ-pre-irradiation and these results were supported by a determination of the DMDBTDMA concentration with a gas chromatography method. The distribution ratios of Am(III), Eu(III), Ce, Nd and Y with γ-pre-irradiated (DMDBTDMA-DHOA)/NDD have also been studied as a function of the nitric acid concentration and the extraction temperature.

N,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide impregnated magnetic particles for the uptake of lanthanides and actinides from nuclear waste streams

A novel, simple technique based on magnetically assisted chemical separation (MACS) has been developed for the uptake of lanthanides and actinides from pure nitric acid solutions as well as from Simulated Pressurized Heavy Water Reactor-High Level Waste (PHWR-SHLW). Uptake profiles of various metal ions, such as Pu(IV), U(VI), Th(IV), Am(III), Eu(III), Sr(II), Cs(I) and Fe(III) were investigated as a function of time and nitric acid concentrations usingN,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) impregnated magnetic particles and compared withN,N′-dimethyl-N,N′-dibutyl tetradecyl malonamide (DMDBTDMA) and trialkyl phosphine oxide coated magnetic particles and also with TODGA coated extraction chromatographic resins. The uptake of various metal ions follows the order Eu(III) > Am(III) > Th(IV) > Pu(IV) > U(VI) > Sr(II) > Fe(III) > Cs(I) in pure nitric acid solutions. On the other hand, distinctly high distribution coefficient (Kd) value has been observed for Pu(IV) as compared to Eu(III) and Am(III) in SHLW. Further, no significant extraction of Cs(I) or Sr(II) was observed in SHLW. Also, at any acidity theKdvalue of a given metal ion is less in the SHLW as compared to that in pure HNO3, apparently due to the co-extraction of the other metal ions present in SHLW. The loading capacity of the TODGA impregnated magnetic particles with respect to Th(IV), U(VI) and Eu(III) was determined, along with the distribution isotherms to simulate multiple contacts. The adsorption models of Langmuir and Freundlich were fitted to the experimental data and best correlations was obtained for Langmuir model suggesting monolayer adsorption is the prevalent mechanism. The stability and reusability of the TODGA coated magnetic particles was also assessed.

N, N′-dimethyl-N, N′-dibutyl tetradecyl malonamide impregnated magnetic particles for the extraction and separation of radionuclides from nuclear waste streams

Summary N, N′-dimethyl-N, N′-dibutyl tetradecyl malonamide (DMDBTDMA) coated magnetic particles are being evaluated for the possible application in the partitioning of actinides, lanthanides and fission products from pure nitric acid solutions as well as from Simulated Pressurized Heavy Water Reactor-High Level Waste (PHWR-SHLW). Uptake profiles of various metal ions, such as Pu(IV), U(VI), Am(III), Eu(III), Sr(II) and Cs(I) were obtained as a function of time and nitric acid concentration by batch studies using DMDBTDMA coated magnetic particles. The order of uptake follows the order Pu(IV)>U(VI)>Am(III)>Eu(III)>Sr(II)∼Cs(I) in both nitric acid and SHLW. The uptake of various trivalent lanthanides was also investigated as a function of nitric acid concentration and found the uptake order as Pr(III)>La(III)>Eu(III)>Tb(III)>Ho(III)>Er(III)>Yb(III)>Lu(III). The sorption capacity of the DMDBTDMA coated magnetic particles with respect to U(VI) and Eu(III) was determined, along with the sorption isotherms to simulate multiple contacts. The maximum sorption capacity of DMDBTDMA coated magnetic particles was found to be 1.58 mmol/g and 0.36 mmol/g for U(VI) and Eu(III), respectively. The adsorption models of Langmuir and Freundlich were fitted to the experimental data and best correlations were obtained for both the models. The Langmuir model predicts a loading capacity of 1.61 mmol/g and 0.37 mmol/g for U(VI) and Eu(III), respectively, which is close to the experimental values. The stability and recycling capacity of the DMDBTDMA coated magnetic particles was also assessed.

Factorial designs as tools to study the influence of thermal oxidation factors on substituted malonamide destruction

The thermal oxidation of two potential extractants for minor actinides in nuclear fuel reprocessing was investigated. These extractants were N, N′-dimethyl, N, N′-dibutyl, tetradecyl malonamide (DMDBTDMA), used as a model, and N, N′-dimethyl, N, N′-dibutyl, dodecylethoxy malonamide (DMDBDDEMA), used as a modified structure. An experimental methodology with two factorial designs was used to quantify the influence of different factors. In the first design, the factors were reaction time, temperature and oxidant type for experiments carried out on a pure solution of DMDBTDMA. The influence of temperature was clearly shown in the range of 200–250 °C. In the second design, the temperature was fixed at 250 °C, the humidity factor was introduced and experiments were carried out on a 0.5 mol l −1 solution of DMDBTDMA in n-dodecane, which represents the extractant concentration in nuclear fuel waste processing. This second series confirmed the efficiency of oxygen for destroying diamides. The results of thermal destruction were also compared with data photo-oxidation. Coupled experiments were also performed combining first photo-oxidation and secondly thermal oxidation with oxygen. This combination destroyed more than 99% of initial diamides.

Photo-oxidation of tertiary amides, main degradation products of large malonamides

Photo-oxidation of large malonamides N, N′-dimethyl, N, N′-dibutyl, tetradecyl malonamide (DMDBTDMA) and N, N′-dimethyl, N, N′-dibutyl, dodecylethoxy malonamide (DMDBDDEMA)—potential extractants for minor actinides in nuclear fuel reprocessing—leads mainly to the corresponding monoamides: N-butyl N-methyl hexadecanamide (BMHDA) and N-butyl N-methyl dodecyl oxy butanamide (BMDDOBA), respectively. The evolution of these main photoproducts was monitored during the degradation of malonamide solutions, and also pure monoamide solutions. Irradiation, for 1 h, with a low mercury pressure lamp can destroy BMHDA when diluted to 0.075 mol l −1 in n-dodecane. The two monoamides only differ by an ether bond and the weakness introduced by such a function in an alkyl chain is shown by slightly faster degradation. The relative weakness of BMDDOBA is independent of oxidant addition. Global degradation can be monitored by GC/FID or UV detection at 200 nm.

Photo-oxidation of two malonamides, extractant models for minor actinides in nuclear fuel reprocessing

The photo-oxidation of two potential extractants, the N, N′-dimethyl, N, N′-dibutyl, tetradecyl malonamide (DMDBTDMA) and the N, N′-dimethyl, N, N′-dibutyl, dodecylethoxy malonamide (DMDBDDEMA) for minor actinides in nuclear fuel reprocessing was followed. The main photoproducts, identified by coupled techniques (GC/FTIR and GC/MS) are malonamides, monoamides and carbonylate derivatives. An irradiation, for 1 h, with a low mercury pressure lamp can destroy initial diamides diluted at 0.075 mol l −1 in n-dodecane. With pure solutions of diamides (2.05 mol l −1), destruction needs several hours to be complete. Both diamides only differ by an ether bond, their reactivity under different conditions of photo-oxidation is discussed.

Development of the Diamex Process for Treating PHWR High-Level Liquid Waste

The extraction behavior of actinides like U(VI), Pu(IV), and Am(III) as well as of fission products like Tc(VII), Zr(IV), Eu(III), and structural material Fe(III) using nitric acid/simulated pressurized heavy water reactor-high-level waste solution as aqueous phase and N,N’-dimethyl-N,N’ dibutyl tetra decyl malonamide (DMDBTDMA) in n-dodecane as solvent was investigated. The present work contributes significantly toward the development of nonphosphorous (environmentally friendly) extractant capable of partitioning long-lived actinides and fission products like 99Tc from relatively short lived fission products like 90Sr and 137Cs as well as inactive components present in high-level waste. The DAm values determined in the temperature range between 15 and 45°C showed a gradual decrease with increase in temperature throughout the acidity range. The effect of N,N di-2-ethylhexyl acetamide (D2EHAA) as phase modifier on the physicochemical properties of DMDBTDMA/n-dodecane solvent was investigated and could be correlated with parameters like the limiting organic concentration value of HNO3, DAm, or phase disengagement time. Overall comparison of diamide extraction (Diamex) and transuranium extraction (Truex) solvents has been made.

Thermal oxidation of two malonamides, extractants for minor actinides in nuclear fuel reprocessing

In this study, the thermal destruction of two potential extractants — the N, N′-dimethyl, N, N′-dibutyl, tetradecyl malonamide (DMDBTDMA) and the N, N′-dimethyl, N, N′-dibutyl, dodecylethoxy malonamide (DMDBDDEMA) — for minor actinides in nuclear fuel reprocessing was compared. The thermal destruction of a main by-product, the larger monoamide formed, was also studied for each extractant. Experiments were carried out in small reactors (closed or open) with different oxidising atmospheres. The recuperation of the syrupy degradation mixture, with ethyl acetate, was the first step of analysis before separation by Gas Chromatography (GC). The quantitation of separated by-products was performed with a Flame Ionisation Detector (FID) and the identification was realized by both Fourier Transform Infrared Spectroscopy (FTIR) and Mass Spectrometry (MS). Several by-products are identified and are obtained by cleavages of covalent bond and/or oxidation. After 1 h at 250°C, under oxygen flow in an open reactor, residual levels of DMDBTDMA and DMDBDDEMA pure solutions are 10 and 12% respectively, showing that the behaviour of both diamides seems similar. However, the destruction level of initial molecule do not inform on the global degradation of such complex structures. Initial diamides can lose their methyl and/or butyl groups and then give another malonamides. Its can also lead to monoamide by cleavage of CCO malonamide bond. One of these monoamide, the major by-product, can represent 13% of conversion from initial diamide with conditions described previously. An index of degradation based on the molecular weight of residual products, was calculated so as to compare the efficiency of thermal oxidation. Behaviour of diamides was also followed by thermal differential analysis (TDA) and thermal gravimetric analysis (TGA) coupled with FTIR. These techniques has shown that carbon dioxide can be produced at temperature around 250°C.

Substituted malonamides as extractants for partitioning of actinides from nuclear waste solutions

Pentaalkyl malonamides are suggested as alternatives to organophosphorous reagents for the extraction of actinides from high level liquid waste generated during the reprocessing of irradiated fuels. With a view to study the extraction behaviour of these actinides from nitric acid medium, four diamides namely (1) N,N,N′,N′-tetrabutyl undecyl malonamide (TBUDMA), (2) N,N,N′,N′-tetrabutyl tetradecyl malonamide (TBTDMA), (3) N,N′-dimethyl- N,N′-dibutyl undecyl malonamide (DMDBUDMA) and (4) N,N′-dimethyl- N,N′-dibutyl tetradecyl malonamide (DMDBTDMA) were prepared by substitution on the basic skeletons of N,N,N′,N′-tetraalkyl-2-alkyl malonamides. The substituted diamides showed good extractability towards Am, Pu, Np and U into n-dodecane from nitric acid solutions of concentrations ranging from 3 to 8 M except for DMDBUDMA which showed third phase formation beyond 2 M HNO 3. Extraction maxima for Am with TBUDMA and TBTDMA were seen at 6–7 M whereas DMDBTDMA showed maximum extraction at 5 M nitric acid. Am(III) and Pu(IV) extracted as trisolvates whereas U(VI) was extracted as disolvate. Distribution behaviour of fission products using DMDBTDMA was also investigated. DMDBTDMA was found to be a promising alternative to the TRUEX solvent for the actinide partitioning from simulated High Level Waste (HLW).