Lithium Isotope Separation Research Articles

Lithium isotope separation by electromigration

Lithium-6 and lithium-7 with high abundance can be used in fusion (6Li > 30%) and fission (7Li > 99.9%) respectively. Lithium isotope separation with nature abundance always inspires people's interest. In this work, lithium isotope separation by electromigration from lithium-loaded organic phase to aqueous solution was investigated. It was found that immigrant lithium ions in aqueous solution enriched lithium-7 at 1.5 V and enriched lithium-6 at 20 V. After electromigration, the lithium isotope value in aqueous solutions could reach −21.5. The results confirmed the isotopic separation effect of lithium ions electromigration which attributed to dissociating difference of lithium isotopic ions-crown ethers complex.

Lithium isotope separation using 4′-acetylbenzo-15-crown-5 and 1-butyl-3-methylimidazolium bis[(trifluoromethyl) sulfonyl] imide in the synergistic extraction system

A novel synergistic extraction system was studied for the separation of lithium isotopes using lithium salts solution as aqueous phase and dichloromethane containing 4′-acetylbenzo-15-crown-5 and [BMIm][NTf2] as organic phase with solvent extraction method. The key factors such as anions of lithium salts, concentrations of LiNTf2, initial pH values of aqueous phase, solvents, volume ratio of dichloromethane and [BMIm][NTf2] were investigated in this study. Results showed that the maximum extraction rate of lithium was 68.36% and the maximum single stage separation factor of 6Li and 7Li was 1.056 ± 0.002. The formed complex in organic phase was studied by the slope analysis method, which indicated that the complex was composed of Li-ion and 4′-actylbenzo-15-crown-5 by 1:1. The thermodynamic parameters of the 6Li and 7Li exchange reaction were calculated by data obtained on temperature during experiments, which explained that the exchange behavior of 6Li and 7Li in this system was a spontaneous exothermic reaction. In addition, this system was able to efficiently separate lithium isotopes at lower temperature.

Automated Analyte Separation by Ion Chromatography Using a Cobot Applied to Geological Reference Materials for Li Isotope Composition

The demand for large and reliable data sets on isotopic composition has increased in geochemistry and environmental sciences over recent years. We present an automated ion chromatographic separation method using a robotic pipetting arm, termed ‘ChemCobOne’, to reduce sample separation time. Its performance was tested for lithium isotope separation in geological reference materials using a single‐step separation with HCl (0.2 mol l−1) and a 2 ml resin volume. This refined lithium purification method does not forfeit precision, accuracy or purity compared with manual sample processing. In addition, a δ7Li value for NASS‐6 of 30.99 ± 0.50‰ (2s) (95% CI = 0.14‰, n = 44) was determined and the first δ7Li values for the granite rock reference material GS‐N (−0.57 ± 0.25‰ (2s), 95% CI = 0.15‰, n = 15), and for the soil reference material NIST SRM 2709a (−0.37 ± 0.67‰ (2s), 95% CI = 0.15‰, n = 63) are proposed.

An Experimental Technique for Separating Lithium Isotopes in Plasma Using the Ion Cyclotron Resonance Method

An experimental facility designed for separating lithium isotopes in plasma using the ion cyclotron resonance (ICR) method is described. High values of the lithium-isotope separation factor (α > 50) are attainable at the facility. A lithium-plasma source, the layout of cyclotron ion heating, and a collector system for lithium enriched and depleted with the 6Li isotope are described in detail. The methods used for measuring the parameters of the lithium plasma and the separation characteristics of the facility are also presented. The use of a “shadow,” i.e., a strip from the enriched-lithium collector without the lithium deposit on the depleted-lithium collector, for diagnostics of the plasma column rotation is noted. The projects for ICR facilities developed with our participation for separating isotopes of other chemical elements are briefly reported.

Development of a viable route for lithium-6 supply of DEMO and future fusion power plants

In the European DEMO program, the design development of a demonstration power plant (DEMO) is currently in its pre-conceptual phase. In DEMO, breeding blankets will use large quantities of lithium, enriched in the isotope lithium-6 (6Li), for breeding the tritium needed to feed the DT fusion reaction. Unfortunately, enriched lithium is commercially not available in the required quantities, which is threatening the success of future power plant applications of nuclear fusion. Even if the manufacturing of the breeding blankets is still two decades ahead of us, it is now mandatory to address the topic of lithium-6 supply and to make sure that a viable supply (and reprocessing) route is available when needed.This paper presents an unbiased systems engineering approach assessing a number of available lithium isotope separation methods by defining requirements, rating them systematically and finally calculating a ranking number expressing the value of different methods. As a result, we suggest using a chemical exchange method based on a lithium amalgam system, but including some important improvements leading to a more efficient and ‘clean’ process (the ICOMAX process) in comparison with the formerly used COLEX process. Furthermore, by modelling activities and experiments in the KIT mercury laboratory (HgLab Karlsruhe), it is shown which work has to be done in the next years to make sure that the technical-scale process is available in time to supply DEMO and future fusion power plants by middle of the 21st century.

Separation of lithium isotopes by using solvent extraction system of crown ether-ionic liquid

A solvent extraction system was selected to separate lithium isotopes by using 1-Ethyl-3-methyl-imidazolium-bis(trifluoromethysulfonyl)-imide ([EMIm][NTf2]) as extraction solvent, Dibenzo-15-crown-5 (DB15C5) as extracting agent and a traditional organic solvent as diluent. The effect of kinds of diluent, the content of ionic liquid in organic solvent, extraction time, extractant concentration and counter anions of lithium salt on the separation of lithium isotopes was studied. The single-stage separation factor α can reach up to 1.031 ± 0.001 and the abundance of the light isotope 6Li in organic phase can reach 7.76%. The exchange mechanism between the lithium salt and the ionic liquid is cation exchange. Lithium ions and ionic liquid cations are 1:1 exchange in the extraction system. Multistage experiment for separation of lithium isotope was also developed for enrichment of 6Li as much as possible. The abundance of 6Li in organic phase can reach 7.80% after 5 stages extraction experiment. Lithium of organic phase was stripped into the aqueous phase by 1 mol L−1 HCl solution.

Novel Functionalized Cellulose Microspheres for Efficient Separation of Lithium Ion and Its Isotopes: Synthesis and Adsorption Performance.

The adsorption of lithium ions(Li+) and the separation of lithium isotopes have attracted interests due to their important role in energy storage and nuclear energy, respectively. However, it is still challenging to separate the Li+ and its isotopes with high efficiency and selectivity. A novel cellulose-based microsphere containing crown ethers groups (named as MCM-g-AB15C5) was successfully synthesized by pre-irradiation-induced emulsion grafting of glycidyl methacrylate (GMA) and followed by the chemical reaction between the epoxy group of grafted polymer and 4′-aminobenzo-15-crown-5 (AB15C5). By using MCM-g-AB15C5 as adsorbent, the effects of solvent, metal ions, and adsorption temperature on the adsorption uptake of Li+ and separation factor of 6Li/7Li were investigated in detail. Solvent with low polarity, high adsorption temperature in acetonitrile could improve the uptake of Li+ and separation factor of lithium isotopes. The MCM-g-AB15C5 exhibited the strongest adsorption affinity to Li+ with a separation factor of 1.022 ± 0.002 for 6Li/7Li in acetonitrile. The adsorption isotherms in acetonitrile is fitted well with the Langmuir model with an ultrahigh adsorption capacity up to 12.9 mg·g−1, indicating the unexpected complexation ratio of 1:2 between MCM-g-AB15C5 and Li+. The thermodynamics study confirmed the adsorption process is the endothermic, spontaneous, and chemisorption adsorption. As-prepared novel cellulose-based adsorbents are promising materials for the efficient and selective separation of Li+ and its isotopes.

Measurements and simulations of Li isotope enrichment by diffusion and electrochemical migration using gel-based electrolyte

Due to the variety of applications of the isotopes in science and engineering as well as their strategic importance in national security, efficient and purity production is essential. 6Li and 7Li have a natural abundance of ~7.5% and 92.5%, respectively. Many of the ongoing lithium isotope separation processes have environmental issues, and the use of mercury is one of them and as part of the development of a new lithium isotope separation process, a model based on diffusion and migration processes on the influence of cell lengths and electrode materials, was used to simulate and predict the subtle differences in the concentration and the isotope ratio distribution with time. The three cell lengths used in the model simulation were 2 cm, 5 cm, and 10 cm, all with the two-compartments and two-electrodes configuration to study the influence of cell length on the separation process while the effect of electrode material on 7Li enrichment was investigated using graphite and LiCoO2 coated aluminum foil. The model predicted a higher maximum 6Li/7Li isotope ratio using LiCoO2 coated aluminum electrode and the time it takes for the Li ions to reach the cathode surface increases with the cell length under a second-order polynomial regression. The longer cell of 10 cm gives a better maximum separation factor and a larger volume of higher 6Li/7Li isotope ratio solution at the cost of the time it takes. Experimental tests were conducted in a 2 cm horizontal cell to investigate the influence of electrode materials and also the influence of alternating voltage on the lithium isotope separation. The obtained 7Li/6Li separation factor tests were: 1.010 and 1.008, respectively for the LiCoO2 anode and graphite anode material in the 3-hour long test while the shorter duration tests of 10 and 20 min yielded a high 7Li/6Li separation factor of 1.023 and 1.031, respectively. In addition, multi-stage tests were conducted in a vertical compartment cell for effective 7Li enrichment.

Polysulfone-graft-4′- aminobenzo-15-crown-5-ether based tandem membrane chromatography for efficient adsorptive separation of lithium isotopes

Adsorptive membrane-based chromatography can provide the high separation efficiency common to column chromatography but at a lower working pressure. Herein, a novel membrane chromatography system for lithium isotope adsorptive separation is reported. It uses polysulfone-graft-4′-aminobenzo-15-crown-5-ether (PSf-g-AB15C5) porous membranes (0.52 mmol/g of immobilization crown ether, average pore size of 62.7 nm, porosity of 80.4%) as a stationary phase packed in a chromatography column (Ø 25 × 100 mm). Furthermore, a four-stage tandem membrane chromatography system was designed to enhance lithium isotope separation performance. The partial eluate from the former column was used as the feed solution for the next stage. Results show that the flow rate of the eluent could reach 18 mL/h owing to the lower internal diffusion resistance of membranes. Meanwhile, adsorption isotherms and adsorption kinetics show that Li+ adsorption was an exothermic and spontaneous process. The surface diffusion, multilayer adsorption and ion–pore electrostatic interaction between Li+ and the crown ether groups on the membranes played a key role in the separation of 7Li+ and 6Li+ by membrane chromatography. The separation factor obtained from the single-stage membrane chromatography was up to 1.0232. The abundances of 7Li+ and 6Li+ gradually increased with an increase in the elution stages. The relative abundances of 7Li+ and 6Li+ obtained from the four-stage tandem membrane chromatography increased by 0.26% (from 92.40 to 92.66%) and 0.2% (from 7.60 to 7.80%), respectively. In conclusion, our current research opens a new avenue for the simultaneous enrichment of 7Li+ and 6Li+ during lithium isotope adsorptive separation.

Simultaneous selective laser pumping of lithium

Recently, studies of isotope separation using low-power laser are progressed in high key including Magnetically Activated and Guided Isotope Separation. In this paper, possibility of more effective isotope separation by simultaneous pumping of two isotopes is considered against usual method that pumps only one isotope for lithium isotope separation. It gets to obtain two enriched materials without depleted material by a single optical pumping.

Behavior of Na and K in the extraction process of lithium isotope separation

The extraction behavior of Na and K during lithium isotope separation using benzo-15-crown-5 (B15C5) in chloroform as the extractant was investigated. It was found that potassium was extracted better than sodium and lithium, the metal: B15C5 ratio in the extracted compound was 1: 1 for all metals. It was shown that in the extraction systems with a LiCl concentration higher than 5 mol L-1, B15C5 was noticeably transferred into aqueous solutions, while concentrated LiCl solutions had a salting-out effect with respect to Na and K.

LITHIUM ENRICHING BY ISOTOPE 7Li WITH ELECTROMEMBRANE METHOD

The need for using isotopes in the nuclear power engineering, medicine, as well as in the sphere of control of engineering and construction facilities is increasing annually. However, the isotope separation methods do not allow to meet the need for production of a significant list of isotopes, including the purity of lithium isotopes. The process of amalgamation to date is the main technology of enrichment of 7Li in practical use. Other methods have very low separation efficiency and are not suitable for mass production. The present work is devoted to a new method for enriching the isotope 7Li, in parallel, the work presents the method of separating lithium isotopes by amalgamation modified by authors. The study relates to physical chemistry, in particular to electromigration processes and methods for separating lithium isotopes. A new promising approach for separating Li isotopes is the electrodialysis process using an ionic liquid as an electrolyte. Data on the relevance and uses of 7Li isotopes are given, the existing methods and criteria for the separation of lithium isotopes are considered. The article briefly describes the principle of the new technology, the regimes of enrichment experiments and the details of analysis of products obtained. Moreover, the new technology demonstrates the good environmental characteristics, it is amenable to mass production and has very low power consumption. However, it should be also emphasized that ionic liquids are very sensitive to impurities which inevitably appear in the electrolyte during separation process. One of the most important characteristics of isotope separation methods and technologies is the specific energy consumption, so currently the problem of reducing energy consumption is acute, for which it is necessary to create new methods for separation and purification of isotope systems and modernization of technologies already introduced in industry. The proposed method for enriching the 7Li isotope is carried out by controlling the process of electromigration of lithium ions through ion-exchange membranes in the electrolytic cell compartments. The work in the long-term future can ensure an increase in the efficiency of enrichment process for the 7Li isotope and a decrease in specific energy costs.

Theoretical prediction of 6Li/7Li separation in solvent extraction system using Urey model

Separation of lithium isotopes (6Li, 7Li) is a key technology to the development and utilization of nuclear energy. In this work, we present an efficient method to theoretically estimate the separation factors of 6Li/7Li in solvent extraction system based on Urey model. The approach was implemented by calculating the equilibrium separation factor of 6Li/7Li in the crown ether/Li aqueous solution [15-crown-5 (15C5), Benzo-15-crown-5 (B15C5), 12-crown-4 (12C4), Dicyclohexyl-18-Crown-6 (DH18C6)/LiX-H2O, X = Cl/I] exchange system utilizing the calculated harmonic vibration frequencies obtained by Density Functional Theory (DFT). The results showed that Urey model can correctly predict the direction of the 6Li/7Li separation as observed in the experiments. With this model, the underlying mechanisms driving the equilibrium isotope separation were elucidated further. The coordination structure of the Li complex played a dominant role in the separation of 6Li/7Li. For the solvent extraction system comprising crown ether phase and LiX aqueous solution, the crown ether with strong ability of excluding the hydrated water of Li gives a higher separation factor. The ways by which Li–O bonding of the Li-crown ether complex can be weakened, such as reducing the coordinated water molecules, applying high polar solvents, performing separation from Li salt with a softer anion, are helpful to improve the separation factor of 6Li/7Li at a fixed temperature. The lithium isotopic exchange is an exothermic reaction. Decreasing temperature favors the exchange reaction. This work is expected to provide guidance for the design of the exchanger and screening of the chemical exchange system for the separation of 6Li/7Li.

Lithium isotope separation by crown ethers of different nitrogen-containing derivatives in the ionic liquid-anisole system

A green and efficient ionic liquid-anisole extraction system was employed for the separation of lithium isotopes by comparing 4‑aminobenzo‑15‑crown‑5 (4‑NH2‑B15C5), 4‑nitrobenzo‑15‑crown‑5 (4‑NO2‑B15C5) and benzo‑15‑crown‑5 (B15C5) extraction agents. The results of the effects of crown ether substituents, crown ether concentration and lithium salt anion on solvent extraction indicated that the molar ratio of crown ether and lithium ion complex is 2:1 and the order of the extraction efficiency in three extraction agents was 4‑NH2‑B15C5 > B15C5 > 4‑NO2‑B15C5. Furthermore, the single-stage separation factor α for 6Li/7Li obtained in present work was 1.032 and maximum abundance of 6Li in organic phase was reached 7.762% in the extraction system of LiI/4‑NO2‑B15C5‑ILs.

Laser assisted isotope separation of lithium by two-step photoionization using time of flight mass-spectrometer

Laser assisted isotope separation of lithium is carried out by isotope-selective two-step photoionization method using time of flight mass-spectrometer. The isotopes of lithium are important for nuclear industry. A narrowband tunable dye laser in combination with mass-spectrometer on tuning with 6Li (2S1/2 → 2P1/2) and 7Li (2S1/2 → 2P3/2) resonance levels confirms high degree of isotope selectivity (∼32). Both the dye laser (∼0.2 cm−1, 6 ns, 640–680 nm) and the mass-spectrometer are developed in-house and optimized. Measured relative isotopic abundance (6Li/7Li ≈ 0.080) is found in close agreement with literature. It is also found that concentration of naturally less abundant (6Li) isotope get enhanced remarkably from 7.5% up to over 72% upon precise tuning of the dye laser to 6Li (2S1/2 → 2P1/2) resonance level. Photoionization cross-sections of both the isotopes are measured as 6Li (15.53 ± 2.1 Mb) and 7Li (18.62 ± 2.4 Mb) for 2p excited state using more popular and accurate saturation technique, whereas number density are determined as N0 ≈ 5.9 × 109 and 5.62 × 1010 atoms/cm3 respectively. It is inferred that selected energy pathway [2S1/2 → ∼671 nm → 2P1/2, 3/2 → ∼337 nm → 1S0 (Li+)] gives high photoionization yield and the large (∼10 folds) isotope enrichment.

Preparation of PSf-g-BN15C5/NWF composite membrane with sponge-like pore structure for lithium isotopes adsorptive separation

Polysulfone-graft-monoazabenzo-15-crown-5 ether (PSf-g-BN15C5) was synthesized via nucleophilic substitution reaction and used to prepare PSf-g-BN15C5/non-woven fabrics (NWF) composite membrane for lithium isotopes adsorptive separation by non-induced phase separation (NIPS). The influences of polymer concentration, additive and coagulation bath temperature on membrane properties were systematically explored. A solid–liquid dynamic extraction method was employed to investigate the lithium isotopes separation of the composite membrane. Results showed that the PSf-g-BN15C5/NWF composite membrane with a sponge-like pore structure, the porosity of 69% and the pure water flux of 1433 L/m2/h were obtained under the conditions: PSf-g-BN15C5 polymer concentration of 14 wt%, DMF as solvent and water as a non-solvent in coagulation bath at 60 °C. Moreover, it was found that the lithium isotopes equilibrium separation factor obtained from the membrane with immobilization amount (IA) of 0.81 mmol/g was up to 1.052 ± 0.002, which was much higher than that obtained from the traditional liquid–liquid extraction system of H2O-LiI/BN15C5-CHCl3 (1.007 ± 0.002) and the solid–liquid static extraction using PSf-g-BN15C5 polymer (1.014 ± 0.002) as extractant. In brief, the composite membrane has a great potential application in the development of a green-friendly adsorptive separation method for lithium isotopes.

Preparation of polysulfone-graft-monoazabenzo-15-crown-5 ether porous membrane for lithium isotope separation

A novel polysulfone-graft-monoazabenzo-15-crown-5 ether (PSF-g-BN15C5) polymer was prepared via nucleophilic substitution reaction and characterized by FT-IR, 1H NMR, TGA, and XPS. The non-induced phase separation was employed to fabricate PSF-g-BN15C5 porous membrane with sponge-like structure for lithium isotope separation. The effects of lithium salt, temperature and immobilization amount of crown ether on distribution coefficient and separation factor were explored. Results showed that a maximum separation factor obtained from the solid–liquid extraction system of H2O-LiI/PSF-g-BN15C5 was up to 1.049 ± 0.002. Furthermore, the light isotope 6Li was enriched in the membrane phase owing to the stronger bonding environment.

Measurements and Simulations of Lithium Isotopes Concentration Fluxes during Electrolytic Lithium -7 Enrichment

Isotopes are utilized in many applications, including physical science analyses, food preservation, archaeology, biology, medicine, pharmaceuticals, national security, and agriculture. The purity is a key requirement for the isotope use. Many different technologies have been used to enrich and separate isotopes. Lithium isotope separation techniques are not very efficient and hence the supply of 7Li is limited. Natural lithium contains a mixture of the two isotopes 6Li and 7Li with abundances of ~ 7.5% and 92.5%, respectively. 7LiOH is often utilized for pH control in pressurized water reactors in the nuclear power industry. The effective separation can be improved to produce purified 7Li or 7Li enriched salt by careful control of diffusion and migration of these isotopes that differ due to their different atomic mass. A systematic study was conducted using computational and experimental techniques for achieving enhanced, environmentally friendly, and reliable 7Li production techniques.

Measurements and Simulations of Lithium Isotopes Concentration Fluxes during Electrolytic Lithium -7 Enrichment

High purity lithium isotopes have significant applications in nuclear industry and other related fields. Many of the ongoing lithium isotope separation processes have environmental issues, and the use of mercury is one of them. As part of the development of a new lithium isotope separation process, the effect of the concentration gradient and electric field were studied using experimental electrochemical cells and a recently built numerical model. Samples from the experimental test were collected and then purified by the ion exchange chromatography for ICP-MS analysis. The concentration and isotopes ratio measured with ICP-MS indicated reasonable time dependence behavior. The data confirmed that the difference in the diffusion and migration rate of the isotopes facilitates Li isotope separations. Furthermore, the potentiostatic scanning tests were conducted, and they revealed the time it takes to achieve separation with diffusion and migration. Finally, the electrochemical model with mass transfer predicted the isotopes ratio distribution for comparison with the experimental results. The mass transfer of Li isotopes confirmed the excellent separation potential using the electrochemical approach.

Distribution of benzo-substituted crown-ethers between chloroform and water: effects of macrocycle ring size and lithium chloride

Small size benzo-substituted crown ethers are attractive complexing agents for lithium isotope separation by solvent extraction. Low transfer of the crown ethers from solvent to water is a key point for applicability of the extractants. In the present study, 9- and 12-membered crown ethers were synthesized, and their distribution between chloroform and water was studied. Polyether ring size, benzene substituents and addition of LiCl to water were found to effect on distribution constants. Low losses of the macrocycles were observed at single-stage contact with aqueous phase. However, these losses should be taken into account in the design of multistage processes for the preparation of highly enriched lithium isotopes.