Accelerating Solid/Liquid Chemical Exchange-Based Isotope Separation by the Dissolution/Precipitation Mechanism.

This study focuses on the spatial patterns of transpiration-driven water isotope enrichment (Delta(lw)) along monocot leaves. It has been suggested that these spatial patterns are the result of competing effects of advection and (back-)diffusion of water isotopes along leaf veins and in the mesophyll, but also reflect leaf geometry (e.g. leaf length, interveinal distance) and non-uniform gas-exchange parameters. We therefore developed a two-dimensional model of isotopic leaf water enrichment that incorporates new features, compared with previous models, such as radial diffusion in the xylem, longitudinal diffusion in the mesophyll, non-uniform gas-exchange parameters and non-steady-state effects. The model reproduces well all published measurements of Delta(lw) along monocot leaf blades, except at the leaf tip and given the uncertainties on measurements and model parameters. We show that the longitudinal diffusion in the mesophyll cannot explain the observed reduction in the isotope gradient at the leaf tip. Our results also suggest that the observed differences in Delta(lw) between C(3) and C(4) plants reflect more differences in mesophyll tortuosity rather than in leaf length or interveinal distance. Mesophyll tortuosity is by far the most sensitive parameter and different values are required for different experiments on the same plant species. Finally, using new measurements of non-steady-state, spatially varying leaf water enrichment we show that spatial patterns are in steady state around midday only, just as observed for bulk leaf water enrichment, but can be easily upscaled to the whole leaf level, regardless of their degree of heterogeneity along the leaf.

Liquid-liquid extraction separation of lithium isotopes by using room-temperature ionic liquids-chloroform mixed solvent system contained benzo-15-crown-5

Kinetic-quantum-sieving-assisted H2 :D2 separation in flexible porous materials is more effective than the currently used energy-intensive cryogenic distillation and girdle-sulfide processes for isotope separation. It is believed that material flexibility results in a pore-breathing phenomenon under the influence of external stimuli, which helps in adjusting the pore size and gives rise to the optimum quantum-sieving phenomenon at each stage of gas separation. However, only a few studies have investigated kinetic-quantum-sieving-assisted isotope separation using flexible porous materials. In addition, no reports are available on the microscopic observation of isotopic molecular transportation during the separation process under dynamic transition. Here, the experimental observation of a significantly faster diffusion of deuterium than hydrogen in a flexible pore structure, even at high temperatures, through quasi-elastic neutron scattering, is reported. Unlike rigid structures, the extracted diffusion dynamics of hydrogen isotopes within flexible frameworks show that the diffusion difference between the isotopes increases with an increase in temperature. Owing to this unique inverse trend, a new strategy is suggested for achieving higher operating temperatures for efficient isotope separation utilizing a flexible metal-organic framework system.

High-efficiency lithium isotope separation in an electrochemical system with 1-butyl-3-methylimidazolium dicyanamide, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and diethyl carbonate as the solvents

In the previous chapter we have seen how tunable lasers can be used in a multitude of ways to gain basic information on atomic and molecular systems. Thus, the laser has had a considerable impact on basic research, and its utility within the applied spectroscopic field is not smaller. We shall here discuss some applications of considerable interest. Previously, we have mainly chosen atomic spectroscopic examples rather than molecular ones, but in this chapter we shall mainly discuss applied molecular spectroscopy. First we will describe diagnostics of combustion processes and then discuss atmospheric monitoring by laser techniques. Different aspects of laser-induced fluorescence in liquids and solids will be considered with examples from the environmental, industrial and medical fields. We will also describe laser-induced chemical processes and isotope separation with lasers. Finally, spectroscopic aspects of lasers in medicine will be discussed. Applied aspects of laser spectroscopy have been covered in [10.1,2].

A method is described for the electromagnetic separation of germanium and magnesium isotopes in a small electromagnetic separator with a focusing angle of 180 °. The construction of an ion source and an ion collecter (isotope receiver) is considered. The ion source, which maintains a discharge in the vapor of the element to be separated, operates satisfactorily in a temperature range up to 1500 °C. The construction of the receiver permits the simultaneous collection of all the isotopes of the element to be separated. The relation of the size of the ion current, focused on the receiver, to the method of discharge in the source was investigated. During the separation of germanium isotopes the ionic current at the receiver reached 15–20 ma; during magnesium separation it was 35–40 ma. Every hour ∼ 40 mg of enriched germarilum isotopes (or ∼ 25 mg of enriched magnesium isotopes) was collected in the receiver's containers. The coefficient of material recovery was 2–6%. Mass-spectrometric analyses were carried out on metal samples for the enriched germanium isotopes and the compound Mgl2 for the magnesfurn isotopes. The enrichment coefficient for germanium and magnesium lay within the limits 17–175 depending on natural diffusion and mass of the isotopes.

The status of the following programs is reported: isotope separation of carbon, argon, helium, krypton, neon, xenon, oxygen, and sulfur; metal hydride research; separation chemistry; and separation research. (LK)

The calcium isotope separation at a strongly acidic exchanger resin as a function of the concentration of a LiCl solution is investigated in column experiments. Whereas an enrichment of the heavier calcium isotopes in the solution phase is found with a 3 M LiCl solution, an inverse effect is obtained with 8 M and 12 M LiCl solutions. The separation effect e for the 12 M solution is found to be the highest calcium enrichment in a system without a complexing agent. The results are compared with those for other electrolyte solutions and can be explained by the anion/cation interactions.

Liquid-phase water isotope separation using graphene-oxide membranes

Evidence of Zn isotopic fractionation in a soil–plant system of a pristine tropical watershed (Nsimi, Cameroon)

This present study investigates a three-step laser isotope separation method for the enrichment of 168Er isotope using 631.052 nm – 586.912 nm – 566.003 nm three-step photoionization scheme. The lineshape contours observed in three-step photoionization process have been investigated in detail. This study shows that enrichment of 168Er isotope can be achieved with a relatively simple experimental configuration. With the derived system configuration, it has been shown that it is possible to produce 18 g/day of 90% enriched 168Er. Using the enriched 168Er isotope obtained from the laser isotope separation process, irradiation in low, medium, and high flux reactors can produce 180, 1800, and 18,000 doses per day (each with an activity of 7.4 GBq) respectively. After 24 h of irradiation and chemical separation, the radioisotopic purity of the medical isotope reaches to > 99% making it suitable for the medical applications. This is the first ever study on the laser isotope separation of 168Er isotope.

In terms of isotopic technologies, it is essential to be able to produce materials with an enriched isotopic abundance (i.e., a compound isotopic labelled with 2H, 13C, 6Li, 18O or 37Cl), which is one that differs from natural abundance. The isotopic-labelled compounds can be used to study different natural processes (like compounds labelled with 2H, 13C, or 18O), or they can be used to produce other isotopes as in the case of 6Li, which can be used to produce 3H, or to produce LiH that acts like a protection shield against fast neutrons. At the same time, 7Li isotope can be used as a pH controller in nuclear reactors. The COLEX process, which is currently the only technology available to produce 6Li at industrial scale, has environmental drawbacks due to generation of Hg waste and vapours. Therefore, there is a need for new eco-friendly technologies for separation of 6Li. The separation factor of 6Li/7Li with chemical extraction methods in two liquid phases using crown ethers is comparable to that of COLEX method, but has the disadvantages of low distribution coefficient of Li and the loss of crown ethers during the extraction. Electrochemical separation of lithium isotopes through the difference in migration rates between 6Li and 7Li is one of the green and promising alternatives for the separation of lithium isotopes, but this methodology requires complicated experimental setup and optimisation. Displacement chromatography methods like ion exchange in different experimental configurations have been also applied to enrich 6Li with promising results. Besides separation methods, there is also a need for development of new analysis methods (ICP-MS, MC-ICP-MS, TIMS) for reliable determination of Li isotope ratios upon enrichment. Considering all the above-mentioned facts, this paper will try to emphasize the current trends in separation techniques of lithium isotopes by exposing all the chemical separation and spectrometric analysis methods, and highlighting their advantages and disadvantages.

Enriched stable isotopes of many elements have been widely used in many aspects and such isotopes have been primarily used as the tracer for agricultural and biochemical studies and the availability of the isotopically labeled compounds have been now extensively increasing. Chemical exchange separation of isotopes is based on the equilibrium fractionation of isotopes between two phases, ion exchange isotope separation which is one of the chemical exchange methods, is based on the chemical equilibrium between a stationary phase and a mobile fluid phase. Displacement always results in a sharp boundary between the bands of eluted solute and displacing solute in this method. Displacement chromatographic ion exchange technology for isotope separation is described in this chapter. This chapter mainly divided into two sections. Ion exchange system, ion exchange separation and analysis are introduced in the former section as the basic theory and concept for ion exchange separation. The second section is about the experiment parts of nitrogen isotope separation which include nitrogen isotope application, nitrogen isotope separation process, nitrogen isotopic analysis with mass spectrometry and the obtained results and discussion which were performed by our recent experiments.

Only gas graphite reactors and heavy water reactors can operate with natural uranium (\({\sim }0.7\%\) U-235). However, the burnup of their fuel is limited. Present light water reactors operating with a fuel burnup of about 55–60 \(\text{ GW}_\mathrm{ th}/\text{ t}\) need their uranium fuel enriched to 4–5% U-235 content. Uranium enrichment is performed almost exclusively by the gaseous diffusion and gas centrifuge process. The gaseous diffusion enrichment plants in the USA and France provide about 42% of the worldwide enrichment capacity. Gaseous diffusion plants will phase out in the near future as more economic gas centrifuge plants will be built which provide already about 58% of the world wide enrichment capacity. The separative work unit (SWU) which is a measure of the amount of energy necessary to produce a certain unit (amount) of enriched uranium is by an order of magnitude lower (in e.g. SWU/kg U) for centrifuge enrichment than for gaseous diffusion enrichment. Laser isotope separation, chemical isotope separation and plasma isotope separation were scientifically studied. Only one laser isotope separation (SILEX) plant is being built in the USA.KeywordsFuel ElementNatural UraniumUranium DioxideCounter Current FlowUranium HexafluorideThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

A theoretical analysis is made of an isotope separation method based on chemical reactions stimulated by infrared laser radiation. It is shown that the anharmonicity of the molecular vibrations has practically no effect on the isotope separation coefficient. A description is given of an experiment in which the nitrogen isotopes were separated by the laser-stimulated reaction N2+O2→2NO. This reaction was stimulated in a cell containing air which was subjected simultaneously to ruby laser radiation and to a strong Stokes component generated separately by stimulated Raman scattering in liquid nitrogen.