Reductive Extraction Process Research Articles

Determination of diffusion coefficients of uranium in liquid gallium by GITT

In the electrowinning or chemical reductive extraction process, those mass transfer kinetic parameters, for instance the diffusion coefficient in the liquid cathode or medium, have a strong impact upon the practical extraction rate and separation efficiency. This work aims to calculate the diffusion coefficient of uranium in liquid gallium with galvanostatic intermittent titration technique (GITT) and to deduce its corresponding activation energy. By analyzing the data of GITT, before U saturation in liquid gallium at the temperature range of 673-873 K, the temperature dependence of diffusion coefficients of uranium in liquid gallium was measured as ln D U Ga = − 6.90 ± 1.03 − 1.2 ± 0.8 × 10 3 T and the corresponding activation energy was determined as E a = −11.0 ± 6.7 kJ/mol. The possible source of errors to calculate the diffusion coefficients, such as reference electrode, small solubility of uranium in gallium, side reactions and geometrical approximation of cathode in the theory formula are also presented and discussed.

Reductive extraction of lanthanides (Ce,Sm) and its monitoring in LiCl[sbnd]KCl/Bi[sbnd]Li system

The reductive extraction behavior of Ln (Ce,Sm) and its on-line monitoring were explored in LiClKCl/BiLi system. According to calibration curve, the relationship of peak current and concentration of Ln (Ce,Sm) measured by square wave voltammetry, the calculated Ln (III) concentration is almost consistent with that analyzed by ICP-AES, and the relative average error is about 5.37%. The effects of Li content in BiLi alloys, temperature and stirring speed on extraction rates, efficiencies and distribution ratios for Ce and Sm were determined, and found that the extraction rates, efficiencies and distribution ratios for Ce and Sm increase with the increasing the temperature, content of Li in BiLi alloys and stirring speed. The extraction rates and efficiencies for Ln from LiClKClLnCl3 molten salts are higher than those for Ln from LiClKClCeCl3SmCl3 molten salts, and the ones for Ce are much larger than those for Sm due to the formation of Sm (II) checked using XPS and linear sweep voltammetry. The produced Sm (II) could consume some reduced Sm metal: 2Sm(III)+Sm=3Sm(II), resulting in the decrease of the extraction rate, efficiency and distribution ratios of Sm. The experimental results showed the feasibility of on-line monitoring of reductive extraction process of Ln in LiCL-KCl/BiLi system by electrochemical technique.

Novel reductive extraction process to convert the bio-oil aqueous acid fraction into fuels with the recovery of iron from wastes

In this work, bio-oil waste AAF (aqueous acid fraction) was used to recover iron from red mud (RM) waste by a reductive extraction process. In this process, extraction of iron from RM with AAF is followed by thermal treatment of AAF-Feextracted mixture, leading to the reduction of the Feextracted with the production of Fe/C composites, a valuable feedstock for the steel industry, and a gas fuel fraction. Analyses by IR, UV–vis, ESI-MS, CHN, potentiometric titration, TG, TG-MS, TOC and 1H NMR showed AAF can efficiently extract Fe3+ present in RM waste. After extraction, the mixture AAF-Feextracted was treated at 400, 600 and 800°C to decompose mainly into two fractions: solid (30–40wt%) and gas (60–70wt%). Mössbauer and XRD analyses of the solid fraction showed the presence of reduced iron phases, e.g. Fe2+, Fe0 and iron carbide, with 76% of carbon. TG-MS analyses of gas fraction showed the production of H2 (58mol%), C1–C4 (19mol%) and COx (23mol%), with potential application as a fuel.

On the use of liquid metals as cathode in molten fluorides

The aim of this article is to investigate the behaviour of liquid metallic electrodes in pyroprocesses. Thus, studies of electrochemical properties of various liquid metallic electrodes (Bi, Sb, Sn, Pb, Ga) were performed in LiF–NaF (750°C) and LiF–CaF2 (850°C). Thanks to linear sweep voltammetry technics, electroactivity domains were determined as well as a reactivity (Sb>Bi>Pb>Sn>Ga>Mo) and a nobility scale (Ga<Sn<Pb<Sb<Bi<Mo), valid in both solvent: from these data, the extraction yield of an element can be evaluated. Then the preparation of alloyed cathodes for reductive extraction process, corresponding to a spontaneous reaction between a reducing agent contained in the liquid metal and the element to be removed from the molten salt, was examined. The in situ generation of liquid Bi–Li, Na or Ca (reducing agents) reactive electrodes was performed in LiF–NaF and LiF–CaF2 solvent by galvanostatic electrolyses. Elementary analyses showed that Li+ and Ca2+ were reduced on Bi at the same reaction rate in LiF–CaF2, whereas Na was preferentially inserted into Bi, compared to Li, in LiF–NaF. Linear relationships between the electrolysis potential and the logarithm of the global mole fraction of reducing agent were found. As a consequence, by fixing the potential at the end of the electrolysis, Bi reactive cathodes with a controlled quantity of reducing agent can be produced in galvanostatic conditions.

Rapid quantification of TBP and TBP degradation product ratios by FTIR-ATR

Tri-n-butyl phosphate (TBP) is the key complexant within the plutonium and uranium reduction extraction process used to extract uranium and plutonium from used nuclear fuel. During reprocessing TBP degrades to dibutyl phosphate (DBP), butyl acid phosphate (MBP), butanol, and phosphoric acid over time. A method for rapidly monitoring TBP degradation is needed for the support of nuclear forensics. Therefore, a Fourier transform infrared spectrometry-attenuated total reflectance (FTIR-ATR) technique was developed to determine approximate peak intensity ratios of TBP and its degradation products. The technique was developed by combining variable concentrations of TBP, DBP, and MBP to simulate TBP degradation. This method is achieved by analyzing selected peak positions and peak intensity ratios of TBP and DBP at different stages of degradation. The developed technique was tested on TBP samples degraded with nitric acid. In mock degradation samples, the 1,235 cm−1 peak position shifts to 1,220 cm−1 as the concentration of TBP decreases and DBP increases. Peak intensity ratios of TBP positions at 1,279 and 1,020 cm−1 relative to DBP positions at 909 and 1,003 cm−1 demonstrate an increasing trend as the concentration of DBP increases. The same peak intensity ratios were used to analyze DBP relative to MBP whereas a decreasing trend is seen with increasing DBP concentrations. The technique developed from this study may be used as a tool to determine TBP degradation in nuclear reprocessing via a rapid FTIR-ATR measurement without gas chromatography analysis.

Promising Pyrochemical Actinide/Lanthanide Separation Processes Using Aluminum

Thermodynamic calculations have shown that aluminum is the most promising metallic solvent or support for the separation of actinides (An) from lanthanides (Ln). In molten fluoride salt, the technique of reductive extraction is under development in which the separation is based on different distributions of An and Ln between the salt and metallic Al phases. In this process molten aluminum alloy acts as both a reductant and a solvent into which the actinides are selectively extracted. It was demonstrated that a one-stage reductive extraction process, using a concentrated solution, allows a recovery of more than 99.3% of Pu and Am. In addition excellent separation factors between Pu and Ln well above 103 were obtained. In molten chloride media similar separations are developed by constant current electrorefining between a metallic alloy fuel (U60Pu20-Zr10Am2Nd3.5Y0.5Ce0.5Gd0.5) and an Al solid cathode. In a series of demonstration experiments, almost 25 g of metallic fuel was reprocessed and actinides collected as An-Al alloys on the cathode. Analysis of the An-Al deposits confirmed that an excellent An/Ln separation (An/Ln mass ratio = 2400) had been obtained. These results show that Al is a very promising material to be used in pyrochemical reprocessing of actinides.

Reductive extraction kinetics of actinide and lanthanide elements in molten chloride and liquid cadmium system

Abstract For the development of reductive extraction process, the rate of extraction of actinide and lanthanide elements was measured in a two-phase system of molten LiCl–KCl eutectic salt and liquid cadmium at 723–873 K. The mass transfer coefficient of the elements was evaluated by applying a film theory. The obtained mass transfer coefficients were found to be as high as expected in the present system. In some cases, however, it was found that the rate of reductive extraction was affected possibly by the solubility of the solute elements in the metal phase.

Extraction behavior of actinides and lanthanides in a molten fluoride/liquid aluminum system

As one of the basic investigations on the group partitioning of actinides and lanthanides by a pyrochemical reductive extraction process, the distribution ratios of Pu, Am, Ce and Sm have been experimentally determined in the binary liquid LiF–AlF 3/Al–Cu system at the temperature of 830 °C. The distribution ratios of Pu and Am are much larger than those of Ce and Sm. They would allow a high recovery yield of the actinides and good separation factors with lanthanides. The influence of the salt composition (LiF/AlF 3 ratio) on the distribution coefficients has been investigated. Coupling the obtained experimental results and literature data, a thermodynamic model that describes the extraction in terms of Gibbs enthalpies of formation and the fluorobasicity of the melt (p F) has been developed. The activity coefficients of Sm(+II) et Ce(+III) versus the p F have been infered: they clearly reveal the difference in solvation behavior between divalent and trivalent species.

Distribution of actinides and lanthanides in a molten fluoride/liquid aluminum alloy system

As one of the basic investigations on the group partitioning of actinides and lanthanides by a pyrochemical reductive extraction process, the distribution ratios of Pu, Am, Ce and Sm have been experimentally determined in the binary liquid LiF–AlF 3/Al–Cu system at the temperature of 830 °C. The distribution ratios of Pu and Am are much larger than those of Ce and Sm. They would allow a high recovery yield of the actinides and good separation factors from lanthanides. The influence of the salt composition (LiF/AlF 3 ratio) on the distribution coefficients has been studied. Coupling the obtained experimental results and literature data, a thermodynamic model that describes the extraction in terms of Gibbs enthalpies of formation and the fluoroacidity of the melt has been developed.

Feasibility of immobilizing fluorinated pyrochemical reprocessing salts in a glass-ceramic matrix

ABSTRACTSpent fuel reprocessing by an innovative reductive extraction process in a molten fluoride medium (LiF/AlF3) is now being evaluated; in this hypothesis, all the unrecoverable fission products would be conditioned as fluorides. A preliminary study was undertaken to assess the feasibility of incorporating these fluorides by melting in a glass-ceramic matrix. The containment matrix for the fluorinated waste stream was selected after examining the consequences of fluorinated compounds on the vitreous state and on the physical and chemical properties of the melt and the solidified glass. The presence of fluorinated compounds in the raw materials used to produce the vitreous material raises the problem of the volatility of some fluorides, of their solubility in the melt, and of possible crystallization of the material.

Thermodynamic assessment of systems of actinide or rare earth with Cd

A pyrometallurgical process is being developed for recycling nuclear reactor fuels. Thermodynamic information on multicomponent systems of actinides and rare earths (REs) with liquid Cd is very useful in the design of a process in which a liquid Cd electrode is used for the selective recovery of Pu and U, and a reductive extraction process using a molten salt/liquid Cd system for the recovery of minor actinides, such as Np, Pu, etc. A key issue in the design of these processes is a variation in solubility or activity of actinides or REs in multielement systems. In the present study, phase diagrams of U-Cd, Pu-Cd, Np-Cd, Y-Cd, La-Cd, Ce-Cd, Pr-Nd, Nd-Cd, and Gd-Cd were optimized by the CALPHAD method. For these systems, thermodynamic data, such as the activity of solutes in liquid Cd and the Gibbs energies of formation of the intermetallic compounds as well as the phase diagram data were available for the optimization. For optimization, the calculated primary results were entered into a database. Then, some ternary systems were preliminarily assessed through the use of the optimized data for the binary systems. Two extreme conditions were assumed: one condition was complete miscibility between the compounds that have the same mole ratio between solutes and Cd; the other condition was no solid solubility between the compounds. The results indicated the tendencies toward solubility and activity of actinides and REs in multielement systems.

The derivation of the formyl-group oxygen of chlorophyll b in higher plants from molecular oxygen. Achievement of high enrichment of the 7-formyl-group oxygen from 18O2 in greening maize leaves.

The mechanism of formation of the formyl group of chlorophyll b has long been obscure but, in this paper, the origin of the 7-formyl-group oxygen of chlorophyll b in higher plants was determined by greening etiolated maize leaves, excised from dark-grown plants, by illumination under white light in the presence of either H2(18)O or 18O2 and examining the newly synthesized chlorophylls by mass spectroscopy. To minimize the possible loss of 18O label from the 7-formyl substituent by reversible formation of chlorophyll b-7(1)-gem-diol (hydrate) with unlabelled water in the cell, the formyl group was reduced to a hydroxymethyl group during extraction with methanol containing NaBH4: chlorophyll a remained unchanged during this rapid reductive extraction process. Mass spectra of chlorophyll a and [7-hydroxymethyl]-chlorophyll b extracted from leaves greened in the presence of either H2(18)O or 18O2 revealed that 18O was incorporated only from molecular oxygen but into both chlorophylls: the mass spectra were consistent with molecular oxygen providing an oxygen atom not only for incorporation into the 7-formyl group of chlorophyll b but also for the well-documented incorporation into the 13(1)-oxo group of both chlorophylls a and b [see Walker, C. J., Mansfield, K. E., Smith, K. M. & Castelfranco, P. A. (1989) Biochem. J. 257, 599-602]. The incorporation of isotope led to as much as 77% enrichment of the 13(1)-oxo group of chlorophyll a: assuming identical incorporation into the 13(1) oxygen of chlorophyll b, then enrichment of the 7-formyl oxygen was as much as 93%. Isotope dilution by re-incorporation of photosynthetically produced oxygen from unlabelled water was negligible as shown by a greening experiment in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The high enrichment using 18O2, and the absence of labelling by H2(18)O, unequivocally demonstrates that molecular oxygen is the sole precursor of the 7-formyl oxygen of chlorophyll b in higher plants and strongly suggests a single pathway for the formation of the chlorophyll b formyl group involving the participation of an oxygenase-type enzyme.

Engineering Development of the MSBR Fuel Recycle

The molten-salt breeder reactor being developed at Oak Ridge National Laboratory (ORNL) requires continuous chemical processing of the fuel salt, 7LiF-BeF2-ThF4 (72-16-12 mole%) containing ~0.3 mole% 233UF4. The reactor and the processing plant are planned as an integral system. The main functions of the processing plant will be to isolate 233Pa from the neutron flux and to remove the rare-earth fission products. The processing method being developed involves the selective chemical reduction of the various components into liquid bismuth solutions at ~600°C, utilizing multistage counter-current extraction. Protactinium, which is easily separated from uranium, thorium, and the rare earths, would be trapped in the salt phase in a storage tank located between two extraction contactors and allowed to decay to 233U. Rare earths would be separated from thorium by a similar reductive extraction method; however, this operation will not be as simple as the protactinium isolation step because the rare-earth-thorium separation factors are only 1.3 to 3.5. The proposed process would employ electrolytic cells to simultaneously introduce reductant into the bismuth phase at the cathode and to return extracted materials to the salt phase at the anode. The practicability of the reductive extraction process depends on the successful development of salt-metal contactors, electrolytic cells, and suitable materials of construction.