Influence of co-ions in the eluent on the separation factor of lithium isotopes

The influence of co-ions in the eluent on the separation factor () of lithium isotope separation has been studied by ion exchange chromatography. A strongly acid cation exchange resin (Dowex 50W-X8) was used for the separation of lithium isotopes. The co-ions used in eluent were H⁺, K⁺, Ba²⁺, Cu²⁺, Al³⁺ and Cr³⁺ as their chlorides. From the experiments, it was found that⁶Li was enriched in the resin phase and⁷Li in solution phase. At the same distribution coefficient (K_d=30), the separation factor increased linearly with the charge of co-ion (=1.0022 to 1.0039).     

Influence of chelating agents in eluent on the separation factor of lithium isotopes

The influence of chelating agents on the separation factor, , of lithium isotopes separation was studied by ion exchange elution chromatography. Eluents contained the chelating agent having different number of coordination sites. The chelating agents used in eluent were Na-glycine (Na–Gly), 2Na-iminodiacetic acid (2Na-IDA), 3Na-nitrilotriacetic acid (3Na-NTA), and 4Na-ethylenediaminetetraacetic acid (4Na-EDTA). The ion exchanger was Dowex 50W-X8, sulfonic acid type, sodium form. As a result,⁶Li was enriched in resin phase, and⁷Li was in solution phase. The separation factor, , was gradually increased with increasing number of coordination site (=1.0022–1.0038) at the same distribution coefficient and with increasing distribution coefficients (=1.0017–1.0026) at the same concentration of chelating agents.     

Experimental and theoretical investigations of lithium isotopes separation using 10-hydroxybenzoquinoline

Journal of Radioanalytical and Nuclear Chemistry - Effective separation of lithium isotopes (6Li and 7Li) is a significant challenge in developing clean nuclear energy. In this work, 7Li was...     

Extractive separation of lithium isotopes by 4-tert-butylbenzo-15-crown-5

Based on the principle of an empirical equation, an extractive process has been developed for separating isotopes of lithium. A 2.5M aqueous solution of lithium perchlorate was contacted with twice its volume of 1.0M solution of 4-tert-butylbenzo-15-crown-5 in nitrobenzene at 25 °C to obtain a lithium isotope separation factor of 1.036 and a percent extaction of lithium reaching 45%. With 13 stages of extraction, the concentration of lithium perchlorate in the raffinate was reduced from 2.5M to 2.5×10^–4M to meet the needs of recycling cascade. With 4 stages of scrubbing by use of identical volumes of water at 60 °C, the overall recovery of lithium was found to be >99%.     

Influence of pH on distribution coefficients of lithium and impurity elements in sorption

The possibility of purifying lithium-containing solutions to remove chemical impurities by sorption in the batch mode was examined. Sulfonic (KU 2-8, Purolite C100, Resinex KW-8), carboxylic (SG-1, Purolite C104FL, Resinex KW-H), and phosphoric acid (Purolite S957) cation-exchange resins were used as sorbents. The distribution coefficients of lithium and impurity elements (sodium, potassium, magnesium, calcium, iron) at different pH values were determined experimentally. The lithium/impurity separation factors were calculated.     

The influence of potential softness on the transport coefficients of simple fluids

This study explores the effects of interaction softness on the transport properties of simple fluids. The transport coefficients of soft-sphere fluids in which the particles interact via the potential, phi(r)=epsilon(rsigma)(-n), with n in the range from 6 to 1152, have been calculated by molecular-dynamics computer simulation. The self-diffusion coefficient D shear viscosity eta(s), bulk viscosity eta(b), and thermal conductivity lambda were computed over a wide packing fraction range. It was found that the Batschinski-Hildebrand expressions, in which D, eta(s) (-1), eta(b) (-1), and lambda(-1) are assumed to have a linear dependence on the molar volume, represent the data quite well for all n, although least well for the thermal conductivity. The density for which, on extrapolation, each of these quantities is zero, increases with the softness of the interaction (or approximately n(-1)), suggesting that the effective hard-sphere diameter decreases with increasing softness in the small n limit. This treatment leads to simple empirical formulas for the effect of density and n on the effective hard-sphere diameter and packing fraction (in an intermediate range) and the four transport coefficients of these fluids.     

Dye-laser-induced separation of nitrogen and carbon isotopes

A unimolecular, laser-induced dissociation reaction of s-tetrazine (C₂H₂N₄), with a quantum yield of close to unity, was used to separate nitrogen $\text{14}\text{15}$ and carbon $\text{12}\text{13}$ isotopes. The sharp Q-branch of the 0-0 band of the 5515 Å absorption system of tetrazine was irradiated for 1 minute periods with a 10 mW cw tunable dye laser output that was monochromatic to about 0.05 Å. Each of the decomposition products, found here to be HCN and N₂, as well as the starting material, could be altered in isotopic composition, in either direction, by selection of an appropriate laser wavelength. The largest one-step enrichment ratio measured was 72. It makes possible mass separation at an efficiency of 17 moles per kWh of laser energy.     

Preparation and characterisation of synthetic mixtures of lithium isotopes

Re-certification of the absolute isotopic composition of the natural lithium isotopic reference material (IRM), IRMM-016, requires measurements calibrated by means of synthetic mixtures of highly enriched lithium isotopes. Ten such mixtures were prepared by weighing and mixing of two well characterised, isotopically enriched, Li₂CO₃ compounds. The starting materials, 99.9981% enriched ⁶Li, and 99.9937% enriched ⁷Li, were purified by ion exchange, and the purified materials converted from LiOH to Li₂CO₃ by reaction with CO₂. Ten new mixtures were prepared by mixing different weighed amounts of these dissolved Li₂CO₃ carrier compounds. The compounds had an estimated level of impurities of 100 ± 100 μg · g^–1 (expanded uncertainty with a coverage factor of 2). In the ten mixtures, the n(⁶Li)/n(⁷Li) ratio varies from 0.025 to 14 and the achieved expanded relative uncertainty on the amount ratio prepared is typically 2 · 10^–4. These mixtures were then used to determine the correction factor, K, for mass discrimination of the measurement procedure and instrument concerned. Received: 6 November 1997 / Revised: 22 December 1997 / Accepted: 24 January 1998     

Preparation and characterisation of synthetic mixtures of lithium isotopes

Re-certification of the absolute isotopic composition of the natural lithium isotopic reference material (IRM), IRMM-016, requires measurements calibrated by means of synthetic mixtures of highly enriched lithium isotopes. Ten such mixtures were prepared by weighing and mixing of two well characterised, isotopically enriched, Li₂CO₃ compounds. The starting materials, 99.9981% enriched ⁶Li, and 99.9937% enriched ⁷Li, were purified by ion exchange, and the purified materials converted from LiOH to Li₂CO₃ by reaction with CO₂. Ten new mixtures were prepared by mixing different weighed amounts of these dissolved Li₂CO₃ carrier compounds. The compounds had an estimated level of impurities of 100 ± 100 μg · g^–1 (expanded uncertainty with a coverage factor of 2). In the ten mixtures, the n(⁶Li)/n(⁷Li) ratio varies from 0.025 to 14 and the achieved expanded relative uncertainty on the amount ratio prepared is typically 2 · 10^–4. These mixtures were then used to determine the correction factor, K, for mass discrimination of the measurement procedure and instrument concerned.     

Separation of lithium isotopes by NTOE-bonded Merrifield peptide resin

A study of the elution chromatographic separation of lithium isotopes was carried out with NTOE-bonded Merrifield peptide resin. This resin had a capacity of 0.29 meq/g dry resin. Upon column chromatography [0.2 cm(I.D)×32 cm (height)] using 1.0M NH₄Cl solution as an eluent, a single separation factor of 1.026 was obtained by the Glueckauf theory. The heavier isotope, ⁷Li was concentrated in the resin phase, while the lighter isotope, ⁶Li was enriched in the solution phase.     

The influence of filler type on the separation properties of mixed-matrix membranes

Chitosan-based membranes filled with different metal oxide particles were prepared and their performance in ethanol dehydration process depending on the type of oxide and loading was discussed. For membrane preparation three oxides: TiO₂, Cr₂O₃ or Fe₃O₄ were selected. From experimental data suitable ethanol and water transport coefficients were evaluated. As shown in the results, applied fillers in different ways affect the separation properties. Presence of TiO₂ significantly affects the normalized total flux, increasing its value. On the other hand, addition of Fe₃O₄ influences most of all the separation factor, which is the among all investigated membranes. For membranes containing chromium(III) oxide as a filler, improvement in the separation properties is observed only in the case when the Cr₂O₃ content equals to 5 wt%. Above this concentration significant deterioration of separation properties is observed. The best performance has mixed-matrix membranes (MMMs) with magnetite, where the values of PSI are equal to 16.3 and 296.8 kg/m^?2 h µm for pristine and 15 wt% filler content, respectively.     

Influence of the peak height distribution on separation performances: Discrimination factor and effective peak capacity

Summary A new index of performance of the chromatographic separation between two adjacent peaks, the discrimination factor, d₀, is defined. It is normalized between 0 and 1 and is directly and easily determined from the chromatogram. It does not depend on any assumption regarding peak shape, except that the peak profiles of individual sample components have a single mode. Its value depends on the relative heights of the two peaks as well as on their separation. The separation power of a chromatographic system is classically measured by its peak capacity, defined on the basis of constant resolution between adjacent peaks. A previously developed statistical theory of the composition of mixtures makes it possible to extend the concept of peak capacity by taking into account the peak height distribution in typical average chromatograms. A new parameter, the effective peak capacity, is defined for this purpose on the basis of a constant discrimination factor between adjacent peaks. It allows to take into account the distribution of peak heights in statistical theories of the evaluation of complex chromatograms and in the measurement of the limit of determination in quantitative analysis. The characteristics of the two new parameters, the discrimination factor and effective peak capacity, are discussed and compared with those of their classical homologs, resolution and peak capacity, in the case of gaussian component peaks of equal widths.     

Precise determination of lithium isotopes in seawater using MC-ICP-MS

Li (lithium) isotope analysis using MC-ICP-MS is a very powerful tracer measurement method. This is widely used for identification of Li isotopes in many fields of study. This useful method, however, has an effect on the natural Li isotope background. This is impacted by the instrument matrix. In this study, we show that the MC-ICP-MS condition is characterized by both a low baseline background and a high-sensitivity distance at Ar plasma condition. In addition, the Li isotope ratio was measured by the use of experimental conditions that were superior to both the general plasma condition and those used in other studies. The samples were subjected to both acid leaching and a cation exchange resin (Bio-Rad AG 50 W-X8 200–400 mesh) modified for seawater samples. The isotope variations were corrected using the bracket method, the measured Li isotope ratio of sample, and the mean ratios of the L-SVEC standard (NIST L-SVEC Li₂CO₃) measured before and after the sample run. The isotope variation was presented as the deviation (per mil) of the measured ratio from that of the recommended value.     

Control strategies for laser separation of carbon isotopes

Laser isotope separation (LIS) by infrared laser chemistry of polyatomic molecules has come a long way since its discovery. The last decade has seen considerable efforts in scaling up of the process for light elements like carbon, oxygen and silicon. These efforts aim at ways to improve both the enrichment factor and the throughput. The achievement is quite significant especially for carbon isotope separation wherein macroscopic operating scales have been realized. We report our studies on the IR laser chemistry of two promising systems, viz. neat CF₂HCl and CF₃Br/Cl₂. We have investigated conditions for optimizing the dissociation yield and selectivity using natural samples containing l.l%C-13.Wealso highlight our current efforts for scaling up the process. These include the design aspects of a photochemical reactor with multipass refocusing Herriott optics for efficient photon utilization, development of a cryogenic distillation set up and a preparative gas chromatograph for large scale separation/collection of the isotopically enriched photoproduct in the post-irradiation stage.     

Enrichment of lithium isotopes by a triazacrown trimerrifield peptide resin

A study on the elution chromatographic separation of lithium isotopes was carried out with a triazacrown trimerrifield peptide resin. The capacity of the triazacrown trimerrifield peptide resin has a value of 0.08 meq/g. Upon column chromatography [0.2 cm (I.D)×35 cm (height)] using 4.0M NH₄Cl solution as an eluent, the single stage separation factor of 1.028 was obtained by the Glueckauf theory. The heavier isotope, ⁷Li, was concentrated in the resin phase, while the lighter isotope, ⁶Li, was enriched in the solution phase.     

The influence of various factors on the gas chromatographic separation of certain diastereoisomers

Conclusions Not the nature of the stationary phase, but the ratio of the vapor pressures of the diastereoisomers makes the basic contribution to the separation of 2,3-butanediol and its ester.Translated from Izvestiya Akadamii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 800–803, April, 1973.     

Separation of lithium isotopes by NDOE bonded Merrifield peptide resin

The novel NDOE (1,12,15-triaza-3,4:9,10-dibenzo-5,8-dioxacycloheptadecane) ion exchange resin was prepared. The ion exchange capacity of NDOE azacrown ion exchanger was 0.2 meq/g dry resin. A study on the separation of lithium isotopes was carried out with NDOE novel azacrown ion exchange resin. The lighter isotope,⁶Li concentrated in the solution phase, while the heavier isotope,⁷Li is enriched in the resin phase. By column chromatography (0.1 cm I.D.×32 cm height) using 2.0M NH₄Cl as an eluent, a separation factor,a=1.0201 was obtained.