Efficient Isotope Separation Research Articles

Liquid solution centrifugation for safe, scalable, and efficient isotope separation

A general method of separating isotopes by centrifuging dissolved chemical compounds in a liquid is introduced. This technique can be applied to almost all elements and leads to large separation factors. The method has been demonstrated in several isotopic systems including Ca, Mo, O, and Li with single-stage selectivities of 1.046 to 1.067 per neutron mass difference (e.g., 1.43 in 40 Ca/ 48 Ca), which are beyond the capabilities of various conventional methods. Equations are derived to model the process, and the results agree with those of the experiments. The scalability of the technique has been demonstrated by a three-stage enrichment of 48 Ca with a total 40 Ca/ 48 Ca selectivity of 2.43, and the scalability is more broadly supported through analogies to gas centrifuge, whereby countercurrent centrifugation can further multiply the separation factor by 5 to 10 times per stage in a continuous process. Optimal centrifuge conditions and solutions can achieve both high-throughput and highly efficient isotope separation.

(Invited) Pd Monolayer Catalyst As Transformative Concept for Electrolytic Hydrogen Isotope Separation

The effect of strain in Pd monolayer catalyst is explored for electrolytic hydrogen isotope separation. Positive/negative strain increases/decreases strength of adsorbed hydrogen bond in overpotential region where recombination of hydrogen atoms is the rate determining step in hydrogen evolution reaction. As a result, the increased/decreased hydrogen isotope separation efficiency of Pd monolayers is expected as compared to bulk Pd. The positive/negative strain rises/lowers diffusion barrier for adsorbed hydrogen atoms. This effect favors/retards recombination of isotopes with smaller mass. As the surface is stretched/compressed, the neighboring adsorption sites separate/approach each other which affects heavier hydrogen isotopes more/less and result in their lower/higher probability for recombination. All these fundamental consideration indicate that Pd monolayers with different level of strain should have much different separation factors than corresponding bulk electrodes. To study described effects, Pd monolayers we synthesized electrochemically on Au(111) and Ru(0001) electrodes each yielding qualitatively different strain levels (Au-positive, Ru-negative). The adsorption strength of hydrogen isotopes is studied by infra-red spectroscopy. These results are input in classical models for isotope separation[1] T calculations. The calculated ratio between the rates of hydrogen and deuterium recombination and separation factors for Pd monolayers and corresponding bulk electrodes are compared to experimentally measured ones. The following discussion focuses on understanding and quantification of strain effects on separation efficiency of Pd monolayers. [1] B. E. Conway, Proceedings of The Royal Society of London, A. Mathematical and Physical Sciences, 247, 400 (1958).

High Hydrogen Isotope Separation Efficiency: Graphene or Catalyst?

Single-layer graphene has been demonstrated to be a high-efficiency hydrogen isotope sieving membrane in the electrochemical hydrogen pumping system. In this work, we transferred this membrane to proton exchange membrane water electrolysis (PEMWE), which has wide industrial applications. Two membrane electrode assemblies with decorated Pt and ink-coated Pt were investigated. The graphene with the decorated Pt scheme acquired the reported highest proton-to-tritium separation factor of 19.50 in PEMWE. However, rather than graphene, the decorated catalyst was demonstrated to be responsible for this remarkable separation efficiency. Previous studies from Geim's group underestimated the enhanced separation efficiency of decorated Pt over ink-coated Pt, resulting in an exaggerated separation efficiency for graphene. The behavior of proton transfer with hydrogen isotope separation through graphene was interpreted by a serial-parallel circuit model, which suggested that hydrogen isotope separation occurs at defect sites. The limited separation efficiency for graphene was also well understood by a density functional theory (DFT) calculation using an SW 55-77 model and the transition state theory for the kinetic isotope effect. This research provides a thorough understanding of proton transfer with hydrogen isotope separation through graphene.

Gold as an efficient hydrogen isotope separation catalyst in proton exchange membrane water electrolysis

The development of proton exchange membrane water electrolysis (PEMWE) offers an updating potential for electrolytic hydrogen isotope separation. However, it has a significantly lower separation factor than the traditional alkaline water electrolysis. In this study, we propose gold as a promising cathodic catalyst for efficient hydrogen isotope separation in PEMWE. Au/C has a protium-to-deuterium (H/D) separation factor of 7.47 in PEMWE, about twice that of Pt/C. In addition, the full cell's electrochemical performance is comparable to that of its Pt/C counterpart. The separation mechanism in PEMWE is explained by the transitional hydrogen evolution reaction mechanism from Heyrovsky to Tafel for Pt and the unchangeable Volmer mechanism for Au. The high separation factor for Au is also calculated by the H/D zero-point vibrational energy difference between transition state and reaction state through a simple density functional theory calculation. This work offers an effective strategy to improve hydrogen isotope separation efficiency in PEMWE.

Elucidation of Diffusivity of Hydrogen Isotopes in Flexible MOFs by Quasi-Elastic Neutron Scattering.

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.

Highly effective H2/D2 separation in a stable Cu-based metal-organic framework

A three-dimensional copper metal—organic framework with the rare chabazite (CHA) topology namely FJI-Y11 has been constructed with flexibly carboxylic ligand 5,5′-[(1,4-phenylenebis(methylene))bis(oxy)]diisophthalic acid (H4L). FJI-Y11 exhibits high water stability with the pH range from 2 to 12 at temperature as high as 373 K. Importantly, FJI-Y11 also shows high efficiency of hydrogen isotope separation using dynamic column breakthrough experiments under atmospheric pressure at 77 K. Attributed to its excellent structural stability, FJI-Y11 possesses good regenerated performance and maintains high separation efficiency after three cycles of breakthrough experiments.

A multi E x B filter system for isotope enrichment application

The design of a special type E x B (or “Wien”) filter for efficient isotope separation is described. Computation results demonstrated that an optimized E x B filter can produce highly enriched isotopes such as 10B, 98Mo, and 100Mo which are useful for the manufacturing of radioactive isotopes for medical diagnostic imaging studies and therapeutic applications. Using the ion beams generated by a large area RF-driven plasma source, it is shown that a multi E x B filter system can greatly enhance the yield of a range of commercially desirable isotopes.

Strain Effect on Electrolytic Hydrogen Isotope Separation

The effect of strain in Pt and Pd monolayer catalyst is explored for electrolytic hydrogen isotope separation. Positive/negative strain increases/decreases strength of adsorbed hydrogen bond in overpotential region where recombination of hydrogen atoms is the rate determining step in hydrogen evolution reaction. As a result, the increased/decreased hydrogen isotope separation efficiency of Pt and Pd monolayers is expected as compared to bulk Pt and Pd. The positive/negative strain rises/lowers diffusion barrier for adsorbed hydrogen atoms. This effect favors/retards recombination of isotopes with smaller mass. As the surface is stretched/compressed, the neighboring adsorption sites separate/approach each other which affects heavier hydrogen isotopes more/less and results in their lower/higher probability for recombination. All these fundamental consideration indicate that Pt and Pd monolayers with different level of strain should have much different separation factors than corresponding bulk electrodes. To study described effects, Pt and Pd monolayers we synthesized electrochemically on Au(111) and Ru(0001) electrodes each yielding qualitatively different strain levels (Au-positive, Ru-negative). Pd monolayers are synthesized using electrodeposition[1] while Pt monolayers were synthesized using deposition via surface limited redox replacement reaction[2]. The adsorption strength of hydrogen isotopes is studied by infra-red spectroscopy. These results will are input in our classical models for isotope separation[3] and to our DFT calculations. The calculated ratio between the rates of hydrogen and deuterium recombination and separation factors for Pt and Pd monolayers and corresponding bulk electrodes are compared to experimentally measured ones. The following discussion is focused on understanding and quantification of strain effects on separation efficiency of Pt and Pd monolayers. [1] H. –F. Waibel, M. Kleinert, L. A. Kibler, and D. M. Kolb, Electrochim. Acta, 47, 1461 (2002). [2] S. R. Brankovic, J. X. Wang and R.R. Adzic, Surface Science, 474, L173 (2001). [3] B. E. Conway, Proceedings of The Royal Society of London, A. Mathematical and Physical Sciences, 247, 400 (1958).

Hyperfine structure and isotope shift measurements on spin-forbidden transitions of atomic gadolinium

We present the first measurements of the [Xe]4f75d16s6p$\;^{11}{F_J}$11FJ excited state hyperfine coefficients and isotope shifts of spin-forbidden transitions of atomic gadolinium (Gd) at 726 and 743 nm in a hollow cathode gas discharge. In addition, we performed a King Plot analysis to determine specific mass shift and field shift constants for these lines. Moreover, we observed King Plot nonlinearity for the 743 nm transition, which is an effect recently proposed to aid in searches for hypothetical new light bosons. Spectroscopic results obtained from this study will facilitate the development of more efficient isotope separation techniques, enable narrowband laser cooling of Gd for novel dipolar physics investigations, and foster technological advances in high precision atomic clocks and quantum enhanced metrology.

Response to Criticism of: “Effects of various factors on the hydrogen isotope separation efficiency of a novel hydrophobic platinum-polytetrafluoroethylene catalyst”, author Feng Huang (International Journal of Hydrogen Energy, V. 43 (2018), p. 1718–1724)

Response to Criticism of: “Effects of various factors on the hydrogen isotope separation efficiency of a novel hydrophobic platinum-polytetrafluoroethylene catalyst”, author Feng Huang (International Journal of Hydrogen Energy, V. 43 (2018), p. 1718–1724)

Criticism of: “Effects of various factors on the hydrogen isotope separation efficiency of a novel hydrophobic platinum-polytetrafluoroethylene catalyst”, author Feng Huang (International Journal of Hydrogen Energy, V. 43 (2018), p. 1718–1724)

Criticism of: “Effects of various factors on the hydrogen isotope separation efficiency of a novel hydrophobic platinum-polytetrafluoroethylene catalyst”, author Feng Huang (International Journal of Hydrogen Energy, V. 43 (2018), p. 1718–1724)

Effects of various factors on the hydrogen isotope separation efficiency of a novel hydrophobic platinum-polytetrafluoroethylene catalyst

The application of platinum supported on polytetrafluoroethylene (Pt/PTFE) as a composite catalyst for the separation of hydrogen isotopes holds much promise but warrants further refinement for improved performance. The objective of the present study was to examine the performance of a new hydrophobic Pt/PTFE catalyst during hydrogen-water exchange-based deuterium separation. The influence of diverse factors such as flow rate, column height, temperature, the volume ratio of filler to catalyst, and flow mode (co-current or counter-current), and so on, on catalytic performance was investigated. The deuterium conversion rate from co-current exchange was superior to that from counter-current exchange. Decreasing the hydrogen flow rate, increasing the feed water flow rate, and decreasing the molar flow ratio of hydrogen to water improved the deuterium conversion rate. In terms of layered filling of the catalyst column, adding more hydrophilic fillers improved the deuterium conversion rate. The characterization results highlight the high catalytic activity of the Pt/PTFE catalyst for hydrogen-water exchange, as well as its high stability in water.

A Fast Separation Method for Isotope Analysis Based on Compressed Nitrogen Gas and Ion-Exchange Chromatography Technique—A Case Study of Sr-Nd Isotope Measurement

High-purity N2 was used to increase the mobile phase flow rate during ion purification of ion-exchange resin. This was performed to improve the efficiency of isotope separation and purification, and to meet the efficiency requirements of rapid multiple-collector-inductively coupled plasma mass spectrometry (MC-ICPMS) analysis. For Cu isotope separation, our results indicated that at a gas flow rate >60 mL/min, the separation chromatographic peaks broadened and the recovery rate decreased to 99.9%. The Cu isotope ratio, measured by the standard-sample bracketing method, agreed with reference data within a ±2 SD error range. The separation time was reduced from the traditional 10 h (without N2) to 4 h (with N2), indicating that the efficiency was more than doubled. Moreover, Sr and Nd isotope separation in AGV-2 (US Geological Survey andesite standard sample) accelerated with a 20 mL/min gas flow, demonstrating that with the passage of N2, the purified liquid comprised Rb/Sr and Sm/Nd ratios of <0.000 049 and <0.000 001 5, respectively. This indicated an effective separation of Rb from Sr and Sm from Nd. MC-ICPMS could therefore be applied to accurately determine Sr and Nd isotope ratios. The results afforded were consistent with the reference data within a ±2 SD error range and the total separation time was shortened from 2 d to <10 h.

Innovative Separation Technology for Lithium-6 Enrichment Using Electrodialysis with Lithium Ionic Superconductor

Tritium needed as a fuel for fusion reactors is produced via neutron capture by lithium-6 (6Li). However, natural Li contains only about 7.8% 6Li, and enrichment of 6Li up to 90% is required for adequate tritium breeding in fusion reactors. The mercury amalgam method is superior to some of the lithium isotope enrichment methods. In Japan, lithium isotope enrichment methods have been developed to avoid the environmental hazards of using mercury. However, the isotope separation coefficient and efficiency is too low to meet the practical need of large mass production of 6Li. Therefore, new Li isotope separation technique using a Li ionic superconductor functioning as a Li isotope separation membrane (LISM) have been developed [1]. Li ions move by electrodialysis through LISM between the cathode and the anode in lithium solutions. Because the mobility of 6Li ions is higher than that of 7Li ions, 6Li can be enriched on the cathode side of a cell. It has been reported that the difference in the mobility between 6Li and 7Li become large in ionic superconductor. The isotope effect in ionic superconductor is expected to be applicable to isotope separation membrane. In this research, we numerically investigated the ionic mobility of Li isotopes in ionic superconductor. Combing the first principle and the kinetics Monte Calro simulation, we calculate the diffusion constant of 6Li and 7Li. I show the two important effects for the difference in the mobility between isotope of Li. The first is the quantum effect, which decrease the diffusion barrier for Li ion and increase the ratio of the diffusion constant of Li isotopes. The second is the correlation effect between 6Li, 7Li and vacancy. Using Li0.29La0.57TiO3 (LLTO) as the Li ionic superconductor was prepared, and the relationship between the 6Li separation coefficient and the electrodialysis time was investigated. After electrodialysis, we obtained a maximum of 1.04 for the 6Li isotope separation coefficient. This result showed that the 6Li isotope separation coefficient of this method is the same as that of the amalgamation process using mercury (1.06). Thus, this method has the potential to be a superior 6Li enrichment method to produce 90% enriched tritium breeder for fusion reactors. Figure 1

Adsorption dynamics of hydrogen and deuterium in a carbon molecular sieve bed at 77 K

The adsorption equilibrium and rate of H2 and D2 on a Carbon Molecular Sieve (CMS) with wide pore size distribution were measured at 77K using a volumetric method. The adsorption equilibrium or kinetic ratios for D2 to H2 decreased with increasing pressure. The adsorption uptake curve showed a slow adsorption rate with time after displaying a fast adsorption rate in the initial period. Adsorption rate constants of D2 were larger than those of H2 at low pressure, and the ratio of D2 to H2 decreased with an increase in pressure. However, in breakthrough experiments for dynamic separation efficiency of hydrogen isotope separation, the CMS showed higher breakthrough separation factors than the corresponding adsorption equilibrium or kinetic ratios. The breakthrough separation factor reached 1.53 at a total gas pressure of 400.0kPa and a flow rate of 129.8cm3/min in the adsorption bed length of 1.0m. In addition, the shape of D2 breakthrough curve was slightly affected by the change of flow rate, but that of H2 breakthrough curve showed almost constant pattern. And meso and macropores of the CMS gave a negative effect on the separation of H2 and D2. Therefore, the key factor in separating H2 and D2 from the mixture depended not only on their equilibrium selectivity but also on their dynamic diffusional difference in the CMS bed due to the quantum molecular sieving effect in space-limited pore at low temperature.

Optical Frequency Comb Opens up Highly Efficient Isotope Separation of Long-lived Fission Products

日本原子力研究開発機構の量子ビーム応用研究センターでは，パルス中性子線や放射線，放射光など量子ビームテクノロジーを駆使した研究を展開している。その中で関西光科学研究所では，最先端のレーザー技術を利用して重元素の精密な同位体分離技術の創出に取り組んでいる。つまりシーズ側の立場から始められている。しかし，重元素の同位体を精密に分別できれば，われわれの社会が核反応を利用する限りどこかでニーズが生まれるであろう。もちろん，現時点で知られている要請だけでも，実現すれば原子力エネルギーシステムに新しい展開をもたらす。本稿でとりあげるCs-135など長寿命核分裂生成物の核変換の前処理や使用済み燃料中に含まれるPdなど有用元素の精製などである。すぐにすべてを実現できる見通しがあるわけではないが，今の研究を続けることで技術のステップを一段登ることができると信じたい。

Theoretical study on isotope separation of an ytterbium atomic beam by laser deflection

Isotope separation by laser deflecting an atomic beam is analyzed theoretically. Interacting with a tilted one-dimensional optical molasses, an ytterbium atomic beam is split into multi-beams with different isotopes like 172Yb,173Yb, and 174Yb. By using the numerical calculation, the dependences of the splitting angle on the molasses laser intensity and detuning are studied, and the optimal parameters for the isotope separation are also investigated. Furthermore, the isotope separation efficiency and purity are estimated. Finally a new scheme for the efficient isotope separation is proposed. These findings will give a guideline for simply obtaining pure isotopes of various elements.

Magnetically activated and guided isotope separation

We propose a general method for efficient isotope separation. The principle of operation is based on an irreversible change of the mass-to-magnetic moment ratio of a particular isotope in an effusive atomic beam, followed by magnetic guiding. We show that scalability is feasible with this method. The application of this method towards production of highly enriched Li-7 for the nuclear industry is analyzed in detail, and extension to other elements is discussed.

High-efficiency technology for lithium isotope separation using an ionic-liquid impregnated organic membrane

The tritium needed as a fuel for fusion reactors is produced by the neutron capture reaction of lithium-6 ( 6Li) in tritium breeding materials. New lithium isotope separation technique using ionic-liquid impregnated organic membranes (Ionic-Liquid-i-OMs) have been developed. Lithium ions are able to move by electrodialysis through certain Ionic-Liquid-i-OMs between the cathode and the anode in lithium solutions. In this report, the effects of protection cover and membrane thickness on the durability of membrane and the efficiency of isotope separation were evaluated. In order to improve the durability of the Ionic-Liquid-i-OM, we developed highly-durable Ionic-Liquid-i-OM. Both surfaces of the Ionic-Liquid-i-OM were covered by a nafion 324 overcoat or a cation exchange membrane (SELEMION™ CMD) to prevent the outflow of the ionic liquid. It was observed that the durability of the Ionic-Liquid-i-OM was improved by a nafion 324 overcoat. On the other hand, the organic membrane selected was 1, 2 or 3 mm highly-porous Teflon film, in order to efficiently impregnate the ionic liquid. The 6Li isotope separation factor by electrodialysis using highly-porous Teflon film of 3 mm thickness was larger than using that of 1 or 2 mm thickness.

Influence of liquid structure on diffusive isotope separation in molten silicates and aqueous solutions

Molecular diffusion in natural volcanic liquids discriminates between isotopes of major ions (e.g., Fe, Mg, Ca, and Li). Although isotope separation by diffusion is expected on theoretical grounds, the dependence on mass is highly variable for different elements and in different media. Silicate liquid diffusion experiments using simple liquid compositions were carried out to further probe the compositional dependence of diffusive isotopic discrimination and its relationship to liquid structure. Two diffusion couples consisting of the mineral constituents anorthite (CaAl 2Si 2O 8; denoted AN), albite (NaAlSi 3O 8; denoted AB), and diopside (CaMgSi 2O 6; denoted DI) were held at 1450 °C for 2 h and then quenched to ambient pressure and temperature. Major-element as well as Ca and Mg isotope profiles were measured on the recovered quenched glasses. In both experiments, Ca diffuses rapidly with respect to Si. In the AB–AN experiment, D Ca / D Si ≈ 20 and the efficiency of isotope separation for Ca is much greater than in natural liquid experiments where D Ca / D Si ≈ 1. In the AB–DI experiment, D Ca / D Si ≈ 6 and the efficiency of isotope separation is between that of the natural liquid experiments and the AB–AN experiment. In the AB–DI experiment, D Mg / D Si ≈ 1 and the efficiency of isotope separation for Mg is smaller than it is for Ca yet similar to that observed for Mg in natural liquids. The results from the experiments reported here, in combination with results from natural volcanic liquids, show clearly that the efficiency of diffusive separation of Ca isotopes is systematically related to the solvent-normalized diffusivity – the ratio of the diffusivity of the cation ( D Ca ) to the diffusivity of silicon ( D Si ). The results on Ca isotopes are consistent with available data on Fe, Li, and Mg isotopes in silicate liquids, when considered in terms of the parameter D cation / D Si . Cations diffusing in aqueous solutions display a similar relationship between isotopic separation efficiency and D cation / D H 2 O , although the efficiencies are smaller than in silicate liquids. Our empirical relationship provides a tool for predicting the magnitude of diffusive isotopic effects in many geologic environments and a basis for a more comprehensive theory of isotope separation in liquid solutions. We present a conceptual model for the relationship between diffusivity and liquid structure that is consistent with available data.