Isotope Separation Factor Research Articles

Selectivity of metal cations and lithium isotopes on ion exchangers in the hydrogen form prepared by thermal treatment of NH4Zr2(PO4)3

NH4Zr2(PO4)3 with different particle sizes and different specific surface areas were obtained by controlling the preparation conditions. HZr2(PO4)3, cation exchangers in the hydrogen form, were prepared by the thermal treatment of NH4Zr2(PO4)3 in the temperature range of 400 to 700°C and their ion exchange properties were investigated with the main focus on the selectivity for group I and II metal ions and lithium isotopes. Irrespective of the temperature of the thermal treatment, HZr2(PO4)3 showed especially high affinity toward the lithium ion, high affinity toward the sodium ion and had little selectivity for the rubidium and cerium ions from the group I metal ions, and showed no specific affinity toward any of group II metal ions. HZr2(PO4)3 were isotopically 6Li-specific in any conditions examined. The 6Li-to-7Li isotopic separation factor was nearly independent of temperature of the thermal treatment. It depended, however, on the pH of lithium ion-containing solution used as the solution phase in an ion exchange experiment. This pH dependence of the lithium isotope separation effect was due to the appearance of the LiZr2(PO4)3 phase and/or the hydration number of the lithium ion in the ion exchanger phase.

Lithium Isotope Selectivity of Semicrystalline Titanium Phosphates with Rapid Ion Exchange Rate

The ion exchange rate and lithium isotope selectivity of inorganic ion exchangers, semicrystalline layered titanium phosphate (Ti2O3 (H2PO4) 2⋅2H2O) prepared through the reaction in aqueous media and its thermally treated product, were investigated. Their Li+/H+ ion exchange rates were quite high; the ion exchange equilibria were attained within 3min at 25°C. The single-stage separation factor for the lithium isotopes at 25°C was 1.008-1.011 for Ti2O3 (H2PO4) 2⋅2H2O and 1.014-1.018 for its thermally treated product under weakly acidic to neutral conditions.

Lithium Isotope Effect Accompanying Chemical Insertion of Lithium into Graphite

Lithiumwas chemically intercalated from 1-methoxybutane solution of lithiumand naphthalene into graphite and vice versa, and lithium isotope fractionation accompanying those intercalation and deintercalation processes was observed. 6Li was always preferentially fractionated into the graphite phase. The single-stage lithium isotope separation factor upon intercalation was about 1.023 at 25 ºC, nearly independent of the structure of the lithium-graphite intercalation compounds formed. A much smaller separation factor was observed for the deintercalation process, suggesting the existence of lithium sites (surface areas) other than the sites between graphene layers of the host graphite. Separation factor data were consistent with the following decreasing order of the 6Li-to-7Li reduced partition function ratio (RPFR): RPFR of 1-methoxybutane solution > RPFR of surface areas > RPFR of metal lithium > RPFR of graphene interlayer sites.

Separation of Hydrogen Isotopes by Thermal Cycling Absorption Process: An Experimental Device

The separation of hydrogen isotopes is an essential element for tritium processing systems. A new process invented at the Savannah River Site, has been developed at Valduc facility: Thermal Cycling Absorption Process. This system uses palladium packed in a column to absorb a stream of hydrogen isotopes. By repeated heating and cooling cycles, the hydrogen isotopes successively desorb into a capacity and go back onto the column. The thermal cycling creates differences in the Pd separation factor for the hydrogen isotopes inducing the concentration of tritium at one end of the column and the concentration of the lighter isotopes at the other end. This paper presents experimental results obtained with a full-scale facility which has been installed in a glovebox so as to treat weakly tritiated gases. Experimental data collected on this device working with several isotopic mixtures are presented and compared to simulation results.

Hydrogen Isotope Separation Factors on Palladium Alloy Membranes

ABSTRACTThe influence of temperature and gas composition on hydrogen isotope separation factors of membrane cascade with reflux ratio of 0.9998 and different palladium alloy membranes were studied. Separation factors for H-D mixture with different palladium alloy membranes varies from 1.31 to 1.42 at different temperatures, and for H-D-T mixture with Pd-8.6%Y alloy membrane, the factors are 1.2 to 2.0 at different temperatures. The results suggest advantages of operating the cell at high temperature because the higher permeation rate and separation factor at high temperature will lead to a great decrease in the separation stages and membrane area of a separation unit.

Selectivity of Alkali Metal Ion and Lithium Isotopes on Ion Exchangers in H Form Prepared from LiTi x Zr2-x (PO4)3 (x=0, 1)

Inorganic metal (IV) phosphate-based ion exchanges in the hydrogen form, HTi x Zr2-x (PO4)3 (x =0, 1), have been prepared by leaching lithium ions from the precursors, LTi x Zr2-x (PO4)3 (x=0, 1), through ion exchange with protons. The degrees of leaching of lithium ion were more than 99%. Both ion exchangers showed high selectivity toward lithium and sodium ions and little affinity to rubidium and cesium ions among alkali metal ions. The lithium ion uptakes from aqueous solutions were monotonously increasing functions of pH. Isotopically, both ion exchangers were 6Li-specific like other inorganic ion exchangers so far examined. The 7Li-to-6Li isotopic single-stage separation factor, S, of HTiZr(PO4)3 was larger than that of HZr2(PO4)3 at a given pH-value. The relatively large S-values of 1.022 and 1.042 were found for HZr2 (PO4)3 for HTiZr(PO4)3, respectively, at 25°C when the pH of the solution phase was around 5.

Isotope Effects in Electron Exchange Reactions

It has been known that uranium chemical exchange gives relatively large isotope separation factors. The strange isotope effects of uranium gave a clue to solve the hidden isotope effects of electronic states. The present paper discusses recently observed isotope effects in two typical electron-exchange systems of amalgam formation and redox reactions in ion exchange chromatography. Attention has been placed on the temperature dependence of the isotopic fractionations. The results clearly show that the separation coefficient ε is expressed by the temperature dependence of ε=a/T 2-b/T. The unit mass separation coefficients εΔM were calculated and compared among the examined elements of Li, Rb, Mg, Ba in the amalgam system and Fe, Cu, Eu in the redox ion exchange systems.

Syntheses and separating properties of triazacrown and AM18C6 bonded Merrifield peptide resins

Separation of lithium and magnesium isotopes by cation exchange elution chromatography was carried out with a synthesized 1,13,16-trioxa-4,7,10-triazacyclooctadecane (N 3O 3)-4,7,10-trimerrifield peptide resin and with a 2 ′-aminomethyl-18-crown-6 (AM18C6) bonded Merrifield peptide resin. The resins have a capacity of 0.1 and 2.3 meq/g dry resin. A single stage separation factor of lithium isotopes, 1.018 was obtained by the Glueckauf theory from the elution curve and isotopic assays. The heavier isotope, 7Li was concentrated in the resin phase, while the lighter isotope, 6Li concentrated in the solution phase. On the other hand, the heavier isotopes of magnesium were concentrated in the solution phase, while the lighter isotopes were concentrated in the resin phase. The separation factors of 24Mg– 25Mg, 24Mg– 26Mg, and 25Mg– 26Mg isotope pair fractionations were 1.012, 1.022, and 1.012, respectively.

Chromatographic separation of lithium and magnesium isotopes by manganese(IV) oxide

Summary Separation of lithium and magnesium isotopes was investigated by chemical ion exchange with a manganese(IV) oxide using an elution chromatography. The capacity of manganese(IV) oxide was 0.5 meq/g. Two molar sodium acetate solution was used as an eluent. The heavier isotopes of lithium and magnesium were enriched in the solution phase, while the lighter isotopes were enriched in the MnO2 phase. The separation factors were determined according to the method of Glueckauf from the elution curves and isotopic assays. The separation factor of lithium isotopes was 1.026. In addition, the separation factors of 24Mg2+–25Mg2+, 24Mg2+–26Mg2+, and 25Mg2+–26Mg2+ isotope pair fractionations were 1.012, 1.022, and 1.011, respectively. The isotope separation system in this work can be explained by the fact that the hydration and isotope mass effects are more significant.

SEPARATION OF STABLE NITROGEN ISOTOPES BY ION EXCHANGE CHROMATOGRAPHY

ABSTRACT The ion exchange chromatography technique was used for the enrichment of nitrogen 15 (15N). A set of columns filled with the ion exchange resin Wofatit KPS (medium porosity type) with 5.4 cm I.D. and 1.5 m height was set up. Ammonia NH4 +/NH3 aq. was chosen as the isotopic exchange system. The ammonium bands formed in the columns were eluted by a solution of sodium hydroxide. The isotope separation factor, ϵ, was found to decrease with increasing temperature or ammonia concentration. Operational conditions of temperature and ammonium concentration were proposed as the optimum for the production of the enriched isotope by using the present process. Results showed that: (1) the rear part of the band is enriched in 15N, while the frontal part is depleted; (2) it is possible to obtain 7.6 at. % of 15N after a 60 m displacement of the ammonium band. The analytical determination of the samples was made by emission spectrometry (NOI-6E).

Isotope Effects in Electron Exchange Reactions.

It has been known that uranium chemical exchange gives relatively large isotope separation factors. The strange isotope effects of uranium gave a clue to solve the hidden isotope effects of electronic states. The present paper discusses recently observed isotope effects in two typical electron-exchange systems of amalgam formation and redox reactions in ion exchange chromatography. Attention has been placed on the temperature dependence of the isotopic fractionations. The results clearly show that the separation coefficient ε is expressed by the temperature dependence of ε=a/T 2-b/T. The unit mass separation coefficients εΔM were calculated and compared among the examined elements of Li, Rb, Mg, Ba in the amalgam system and Fe, Cu, Eu in the redox ion exchange systems.

Bipolar electrolysis for tritium recovery from weakly active tritiated water

Detritiation facilities produce low activity tritiated water from which tritium cannot be recovered. Bipolar electrolysis, based on the electrochemical permeation of hydrogen and its isotopes through Pd–Ag alloy membranes, allows tritiated water enrichment together with negligible gaseous tritium release. Our purpose is to enrich water from 500 Ci/l (1.85×10 13 Bq/l) to more than 2000 Ci/l (7.40×10 13 Bq/l). We first describe the principle of bipolar electrolysis and its application to isotopic enrichment. The experimental part of this work consists of the determination of the isotopic separation factors. From these experimental values, we simulated the working of an operational cell and we demonstrate the feasibility of the process.

QUANTUM-STATISTICAL AND PHENOMENOLOGICAL ANALYSIS OF EQUILIBRIUM ISOTOPE EFFECTS

This article discusses theoretical consequences of quantum-statistical representations of logarithm of isotopic reduced partition function ratio (ln β). Among the effects being under consideration are the localization of equilibrium isotope effect on the molecular structural elements in the vicinity of the site of isotopic substitution, distribution of increments of ln β, relationship between ln β values for the substitution of different atoms, and the influence of anharmonicity. The review also presents the phenomenological analysis of ln β for more than 2000 compounds as well as the classification of equilibrium isotope effects according to the causes of their appearance. Methods for the quantitative statistical estimation of the maximum possible isotope separation factors and criteria for the purposeful search for chemical exchange systems applicable for the practical separation of isotopes are also given.

SPECIFIC EFFECTS OF HEAVY NUCLEI IN CHEMICAL EQUILIBRIUM

The article reports the results of numerical estimations of the nuclear size equilibrium isotope effects for some medium-weight and heavy elements obtained by using the following equation: ln α fs (i,j) = (kT)−1Δρ(0)z −1 f(z)⟨r 2⟩ij, where α fs (i,j) are the equilibrium isotope separation factors corresponding to the nuclear size contribution of the nucleus field-shift for a given pair of isotopes i and j; Δρ(0) is the difference of the nucleus electron density for a pair of compounds; z −1 f(z) is the tabulated nuclear charge (z) function characterizing the nucleus of the element being the same for all isotopic nuclei; δ⟨r 2⟩ ij is the isotopic shift of the nucleus effective charge radius in square for the isotopes i and j, and k is the Boltzmann constant. The values Δρ(0) were determined from either theoretical or experimentally determined isotope field shifts and from the data of Mossbauer spectroscopy. The ⟨r 2⟩ ij values were taken from experimental measurements followed by their standardization. The values of α fs (i,j) increase from Fe to U and achieve sufficiently high level for lanthanides. For heavier elements, these specific isotope effects begin to exceed the classical chemical equilibrium isotope separation factors.

Preliminary Characterization on Li Isotope Separation with Li Ionic Conductors

Preliminary characterizations on Li isotope separation with Li ionic conductors were carried out. Three types of Li ionic conductors, which were a spinel Li4Ti5O12, a perovskite La0.55Li0.35TiO3 and a ramsdellite Li2Ti3O7 from the Li2O-TiO2 system, were selected. Electric conductivity and Li isotope separation efficiency were measured for each of the Li ionic conductors. It was shown from the results that each Li ionic conductor has sufficient electric conductivity and high Li isotope separation efficiency. Li isotope separation factors of three of the Li ionic conductors compare with that of the amalgamation process with mercury.

Isotope Separation Factor and Kinetic Isotopic Effect of the Hydrogen Evolution Reaction

The hydrogen isotope separation factor decreases with increasing overvoltage on mercury-like electrodes in acid solutions. This dependence qualitatively differs from that for the ratio between hydrogen evolution rates in light and heavy water, which increases with polarization. The reason for the difference is that the isotope separation factor depends on the kinetic isotopic effect (KIE) in two reaction stages: discharge and electrochemical desorption. Experimental data show that a decrease in KIE with potential in the latter stage outweighs the increase in KIE in the former. The KIE decreases in the desorption reaction because this process is activationless; therefore, there is no potential dependence of the relative contribution made by vibrationally excited states of the product in this case, i.e. no dependence that is responsible for the increase in KIE at the discharge stage. The same factor has no effect on KIE for a barrierless discharge, which also decreases with increasing overvoltage. Thus, all experimentally observed dependences of KIE on potential are explained in the framework of a unified approach.

Selectivity of alkali metal ion and lithium isotopes on ion exchangers prepared from MTi0.5Zr1.5(PO4)3(M = Li, Na)

Inorganic ion exchangers, H-TZP(Li) and H-TZP(Na), in the hydrogen form have been prepared by ion exchange from the precursors, LiTi0.5Zr1.5(PO4)3 and NaTi0.5Zr1.5(PO4)3, respectively. The degrees of leaching of lithium and sodium ions were 99.7% and 68%, respectively. No substantial difference in ion exchange property was observed between the two ion exchangers. Both showed high selectivity toward lithium and sodium ions, while rubidium and cesium ions showed low affinity among alkali metal ions. Isotopically, they were 6Li-specific like other inorganic ion exchangers so far examined. The 7Li-to-6Li isotopic separation factor, S, was found of 1.023 to 1.025 in acidic conditions at 25°C and nearly unity in highly basic conditions (pH 12 or higher). The latter S value was consistent with the formation of new ion exchange sites with low isotope selectivity of lithium.

Theoretical Estimation of Lithium Isotopic Reduced Partition Function Ratio for Lithium Ions in Aqueous Solution

The reduced partition function ratio for lithium ions in an aqueous solution is derived from the extrapolation of the values of the reduced partition function ratio ( ) of hydrated lithium ion clusters [Li(H2O)n]+ up to n = 6. In [Li(H2O)n]+ clusters, the values can be calculated from the normal vibration frequencies according to Bigeleisen and Mayer's theory. To obtain the values of , the normal vibration frequency calculations were carried out for optimized structures of [Li(H2O)n]+ (n = 1−6) using the RHF/6-31+G(d), RHF/6-31++G(d,p), RHF/6-311+G(d) and MP2/6-31+G(d) methods by means of the ab initio molecular orbital method. All of those structures having high symmetry were confirmed to have real harmonic frequencies at the RHF/6-31+G(d) and RHF/6-31++G(d,p) levels. For the two RHF methods, the value of increases to about 1.07 with an increase of the hydration number n, and reaches maximum at n = 4. In the most stable isomers of [Li(H2O)n]+ clusters for n = 5 and 6, respectively, the first hydration shell is saturated with the four water molecules, and the size dependence of the values converges for n ≥ 4. The converged value 1.07 can, therefore, be regarded as the reduced partition function ratio for lithium ions in aqueous solution, and gives the upper limit of the isotopic separation factor in an aqueous solution−exchanger system.

Lithium Isotopic Fractionations in the Solvent Extraction by Ion-exchange-type Extractants with Different Ion Selectivity.

Ion-exchange-type extractants showed lithium isotopic fractionations in the solvent extraction reaction, depending on their ion selectivity. The extractants having high Na+ selectivity, calix [4] arene derivative and monensin, showed high lithium isotope separation factors of 1.030 and 1.022, respectively.

Ion and lithium isotope selectivity of monoclinic antimonic acid

Antimonic acid with the monoclinic structure, M-SbA, which had a high selectivity for the lithium ion among alkali metal ions, was prepared by extracting lithium ions from LiSbO3 through ion exchange with protons and its lithium isotope selectivity has been studied. M-SbA underwent the reversible monoclinic-orthorhombic structural change upon desorption-sorption of lithium ions while it showed the irreversible monoclinic-cubic structural change upon sorption of sodium ions. Isotopically, M-SbA was a 6Li-specific ion exchanger. The 7Li-to-6Li isotopic separation factor was slightly dependent on the kinds of counterion in the solution phase of the batch experiments and the maximum S value obtained at 25°C was 1.025.