Displacement Band Chromatography of Hydrogen Sulfites for Enrichment of Sulfur Isotopes

Abstract

Experimental studies were conducted on the enrichment of sulfur isotopes by displacement band chromatography. In these studies, a band of hydrogen sulfite (bisulfite) ions from a sulfurous acid or bisulfite-salt solution was continuously displaced by bisulfate ions from a sulfuric acid or bisulfate-salt solution in a column packed with aminated polystyrene-divinyl benzene resin under varied process conditions. The sulfur isotopes were enriched through isotopic exchange between the bisulfite ions on the resin and the sulfurous acid and/or bisulfite-salt solution in contact with the resin within the moving band. During the isotopic exchange, S-34 isotope was favored in the resin phase and S-32 isotope in the liquid phase. As a result, the S-34 isotope was gradually enriched at the rear of the band, and S-32 isotope at the front. The effects of the various process conditions were evaluated on separative power, height equivalent to a theoretical plate, and operational simplicity. The highest separative power, 3.05 g S-34/cm³/yr, was achieved with an ammonium bisulfite feed displaced by a sulfuric acid displacer at 65°c operating temperature.     

Separation of Gallium and Indium Isotopes by Cation and Anion Exchange Chromatography

Ion exchange chromatography was applied to study chemical isotope effects of gallium and indium in ligand exchange reactions. A strongly acidic cation and a strongly basic anion exchange resin were used as a solid phase, and aqueous HCl as a liquid phase. On the cation exchanger, the light isotope ⁶⁹Ga was enriched at the front part of the elution band and the heavy isotope ⁷¹Ga at the end part. Instead, the light ¹¹³In isotope was enriched at the end part, and the heavy isotope ¹¹⁵In at the front part. The isotope separation factor ? is equal to 3.3?×?10^–5 for gallium and 2.0?×?10^–4 for indium. On the anion exchanger, the heavy gallium isotope was enriched at the front part, whereas the heavy indium isotope at the end part of the band, with ? equal to ～10^–3 and 1.7?×?10^–4, respectively. This pattern of enrichment is caused by stronger Ga³⁺–OH₂ than Ga³⁺–Cl^? bond, and by inverse order of bond strength for indium. In the displacement method, gallium and indium on anion exchanger also show opposite enrichment of their isotopes, but the ? values (1.5?×?10^–2 for gallium and 5?×?10^–3 for indium) are greater than those found in the elution method, probably due to much higher concentrations of the metals.     

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, ?, 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).     

Chromatographic Enrichment of 10B by Using Weak-Base Anion-Exchange Resin

Abstract

In order to enrich ¹⁰B isotope, a boron adsorption band was eluted 620 m in a reverse-breakthrough displacement manner. Thereafter the band was stopped for 10 days and then eluted again up to a total distance of 754 m. The rear boundary of the adsorption band was kept sharp throughout the elution. From monitoring of the isotope abundance during elution, the lighter isotope ¹⁰B was confirmed to be accumulated in the band end region. The maximum enrichment of ¹⁰B reached 98.43% (¹⁰B atomic fraction) at a migration distance of 620 m. The interruption in the operation caused no serious damage in isotope accumulation, but there was a slight broadening of the accumulation curve. The isotopic accumulation was examined based on theoretical equations previously proposed. The results indicate that the HETP of the system is constant, 1.8 mm, up to a migration distance of 620 m and increases slightly at the distance of 754 m. The separation coefficient shows a gradual decrease with an increase of migration distance: ε = 9 × 10^?3 (at 200 m) and 7.8 × 10^?3 (at 754 m).     

Separation of magnesium isotopes by 1-aza-12-crown-4 bonded Merrifield peptide resin

Magnesium isotope separation was investigated by chemical ion exchange with the 1-aza-12-crown-4 bonded Merrifield peptide resin using elution chromatography. The capacity of the novel azacrown ion exchanger was 1.0 meq/g dry resin. The heavier isotopes of magnesium were enriched in the resin phase, while the lighter isotopes were enriched in the solution phase. The single stage separation factor was determined according to the method of Glueckauf from the elution curve and isotopic assays. The separation factors of²⁴Mg²⁺-²⁵Mg²⁺,²⁴Mg²⁺-²⁶Mg²⁺, and²⁵Mg²⁺-²⁶Mg²⁺ isotope pairs were 1.012, 1.024, and 1.011, respectively.     

FRACTIONATION OF LITHIUM ISOTOPES IN ION EXCHANGE CHROMATOGRAPHY WITH TITANIUM PHOSPHATE EXCHANGER

ABSTRACT

Ion exchange chromatography of lithium was carried out to study the lithium isotope effect in an aqueous ion-exchange system, using titanium phosphate exchangers granulated with polyvinyl chloride or an inorganic binder. The sample granulated with PVC showed significant isotope fractionations when a 0.05 M (NH₄)₂CO₃ solution was used as an eluent. The lighter isotope ⁶Li was preferentially fractionated into the exchanger phase. The isotope separation factor was roughly evaluated as 1.007, which is smaller than that (1.017) obtained by batch experiment in a preceding paper. The smaller separation factor could be explained by the fact that the number of sites effective for Li⁺ exchange is less than the number evaluated from the ion exchange capacity. The exchanger granulated with an inorganic binder did not show lithium isotope fractionation in spite of its large capacity for retention of lithium.     

NUCLEAR SIZE AND SHAPE EFFECT IN CHEMICAL ISOTOPE EFFECT OF GADOLINIUM USING DICYCLOHEXANO-18-CROWN-6

ABSTRACT

Gadolinium isotopes were fractionated in a liquid-liquid extraction system using dicyclohexano-18-crown-6. The isotope enrichment factors showed breakdowns of the conventional Bigeleisen-Mayer approximation for every condition of the initial phases; the concentrations of gadolinium and hydrochloric acid and the type of organic solvents. The nuclear mass effect and the field shift effect were estimated by use of the isotope pairs ¹⁵²Gd-¹⁶⁰Gd and ¹⁵⁴Gd-¹⁶⁰Gd. Since both isotopes, ¹⁵²Gd and ¹⁵⁴Gd, have the unique characteristics of the nuclear charge radii, <r²>'s, the unusual isotope effects due to the field shifts took place, while the mass effects of the other isotopes canceled the field shift effects. The maximum isotope effect was observed to be ε_160,152 =0·0252 ± 0·0024 whose initial aqueous phase was 0·023 M GdCl₃ in 12 M HC1, and its organic phase was 0·2 M DC18C6 in chloroform: this was 0·00315 ± 0·00030 in terms of the enrichment factor for unit mass.     

Energy Consumption of Chemical Uranium Enrichment

Abstract

A quantitative study of chemical separation energy for enriching uranium-235 by the redox chromatography was conducted. Isotope exchange reactions between U⁴⁺-UO₂ ²⁺ ions in the enrichment column are maintained by the redox reactions. The chemical separation energy is ultimately supplied by hydrogen and oxygen gas for regenerating redox agents. The redox energy for the isotope separation is theoretically predicted as a function of the dynamic enrichment factor observed in the chromatographic development of uranium adsorption band. Thermodynamic treatments of the equilibrium reactions implies an “inverse redox reaction” which can be enhanced by the chemical potential of the ion-exchange reaction of oxidant. Experimental results showed 30 to 90% recovery of the redox energy by the inverse reaction. These results will devise a simplified redox chromatography process where a number of columns in one module is reduced.     

Ethylenediamine tetraacetic acid modification of crosslinked chitosan designed for a novel metal‐ion adsorbent

Novel chitosan‐based adsorbent materials were synthesized with a higher fatty diacid diglycidyl as a crosslinking agent, and the adsorption ability of the resulting polymers for several metal ions was evaluated. Selective adsorption for Cu²⁺ in comparison with other divalent metal ions, such as Ni²⁺, Pb²⁺, Cd²⁺, and Ca²⁺, was observed with the crosslinked chitosan sorbent at pH 6; however, the adsorption power decreased abruptly as the pH value of the solution decreased. The addition of ethylenediamine tetraacetic acid (EDTA) residues to crosslinked chitosan significantly enhanced the adsorption power for metal ions, especially for Ca²⁺. The adsorptivity of Ca²⁺ was dramatically improved with the introduction of EDTA residues, and the value was greater than that obtained with a commercial chelate resin (CR11). Although the adsorption power of the EDTA‐derivatized sorbent for other metal ions was just comparable to that of the CR11 material, the newly synthesized adsorbent could be used for the recovery of metal ions from industrial waste solutions with a relatively wide range of pHs, from 4.0 to 6.0. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2758–2764, 2004     

The conditions of cationic exchange with the use of recycling polystyrene derivative,the product of sulfonation by silica sulfuric acid

Growing amount of waste plastics has become an environmental problem on a global scale. This study presents an investigation of the conditions of cleaning water from heavy metal ions using chemically recycled polystyrene. To get effective ion exchangers, the sulfonation of virgin polystyrene and expanded polystyrene wastes were obtained using silica sulfuric acid. As it turned out, the use of this solid sulfonating agent simplifies the separation of the polymeric product from the acid and the solvent in comparison to conventional sulfonation methods. The ion exchange behavior of copper and zinc cations in the yielded sulfonated derivatives of polystyrene was studied. Batch shaking adsorption experiments depending on contact time, pH, temperature, and dosage of adsorbate were carried out. The stability of resin to cyclical adsorption and regeneration (column experiment) was also investigated. We report that resins have a high adsorption efficiency with total ion exchange capacity (IEC) about 2.6 meq g^?1, which drops with decreasing pH owing to competition between protons H⁺ and metal cations, whereas with the increasing resin doses the removal of cations rises for a constant initial metal concentration. The speed of cation exchange for yielded adsorbents was even better than for commercial resins. After 360 cyclical adsorption and regeneration in column, resin had working IEC of about 2.3 meq g^?1. The study shows that cation exchange resin from polystyrene wastes can be used as an efficient adsorbent for the removal of heavy metal ions from water. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The Adsorption and Desorption Characteristics of EDTA-Chelated Copper Ion by Activated Carbon

Abstract

This paper addresses the effect of EDTA, a strong agent, on the removal of copper ion from solutions using activated carbon adsorption. Experimental studies indicate the presence of EDTA significantly altered the adsorption behavior of copper on the activated carbon due to the formation of copper chelate species in the solution. The adsorption isotherms and kinetics were found to be strong functions of solution pH and the ratio of copper ion and EDTA concentrations. Adsorption of EDTA-Cu chelates was found to be more favorable than those of free copper ion and unbound EDTA species in the solution. Experimental results indicated that the desorption of chelated copper ion from activated carbon by NaOH and HClO⁴ solutions was influenced by the initial adsorption conditions. A significantly higher quantity of copper ion was recovered with HClO⁴ than with NaOH. Combining the adsorption and desorption data of copper and EDTA, and an understanding of the species distribution of copper in the presence of EDTA, the behavior of the adsorption of EDTA-chelated copper on the activated carbon was described. The predominant adsorbed copper species was the chelated form, CuEDTA^2-, which can be adsorbed on activated carbon surfaces with either the Cu end or the EDTA end bonding directly to the surface.     

Analysis of 235U Enrichment by Chemical Exchange in U(IV)‐U(VI) System on Anionite

Abstract

A theoretical study about ²³⁵U enrichment by the chemical exchange method in U(IV)‐U(VI) system on anion‐exchange resins is presented. The ²³⁵U isotope concentration profiles along the band were numerically calculated using an accurate mathematical model and simulations were carried out for the situation of product and waste withdrawal and feed supply. By means of numerical simulation, an estimation of the migration time, necessary for a desired enrichment degree, was obtained. The required migration distance, the production of uranium 3 at.% ²³⁵U per year and the plant configuration are calculated for different operating conditions. An analysis of the process scale for various experimental conditions is also presented.     

Theoretical Study of Lithium Isotope Separation by Displacement Chromatography

Abstract

Lithium isotope separation by displacement chromatography is studied using fundamental principles; the equations are derived assuming theoretical stages in lithium adsorption bands. The concentration profiles in the band are calculated numerically under unsteady state.     

Nitrogen Isotope Separation Using Porous Microreticular Cation-Exchange Resin

A long-distance chromatographic operation was carried out in order to study the isotope accumulation of ¹⁵N in the ion-exchange enrichment process by using a porous microreticular cation-exchange resin. Combined bands of ammonium and lithium ions were eluted up to 20 m, and thereafter the ammonium band was eluted up to a total migration distance of 60 m. The constant lengths of the adsorbed bands were maintained throughout the elution, and a sharp boundary at the rear end of the ammonium band was monitored by an electric conductivity meter. The enrichment of both ¹⁵N at the rear end of the ammonium band and ⁶Li at the rear end of the lithium band were confirmed in the experiment. The values of HETP in the system were kept almost constant, 49 mm, throughout the migration up to a distance of 60 m. Previously reported works on the same process are analyzed, and an empirical relation for HETP in terms of resin diameter and band velocity has been obtained as HETP = c(d_pμ_B)⁸⁴.     

The Potential Use of Low‐Grade Phosphate Rocks as Adsorbent

This study evaluates the suitability of using low‐grade phosphate for Cu²⁺ removal. The study also investigates the effects of the presence of ethylene‐diamine‐tetra‐acetic acid (EDTA), citric acid, tartaric acid and sodium chloride in a solution containing Cu²⁺ on the adsorption capacity of Cu²⁺ onto low‐grade phosphate. For aqueous solutions with 100 ppm Cu²⁺, the percentage removal of Cu²⁺ at pH 4 onto 0.2 g of 0.063 mm low‐grade phosphate was found to be 96.6 % after one hour. Using one mmol of either Cu²⁺, Cu‐NaCl, Cu‐tartaric acid, Cu‐EDTA, or Cu‐citric acid aqueous solutions, the present work shows trend of the percentage removal of Cu²⁺ at equilibrium time: Cu²⁺ > Cu‐NaCl > Cu‐tartaric acid > Cu‐EDTA > Cu‐citric acid. It is also found that increasing the concentration of ligand to copper ratio decreases the percentage removal of Cu²⁺ significantly. This means that the adsorption capacity is ligand type and concentration dependent.     

Effect of Complexation on the Adsorption of Cadmium by Activated Carbon

Abstract

The adsorption of Cd²⁺ in the absence and presence of two chelating agents was examined as a function of pH. Fits of the data to the Freundlich and Langmuir equations were compared as were results with Zn and Pb using four different activated carbons. In general, adsorption increased with increasing pH and was not extensive, particularly for Cd. At low cadmium to carbon ratios, EDTA appeared to enhance adsorption. With more realistic loadings, when competition for surface sites is greatest, the presence of EDTA is shown to be detrimental to the process. 1,10-Phenanthroline, the second chelating agent studied, was more effective for promoting the removal of Cd. The uncomplexed Cd and Cd-EDTA systems were best described by the simple Langmuir adsorption isotherm. The adsorption of 1,10-phenanthroline and its Cd complex were modeled using a modified form of the Langmuir equation.     

Removal of cobalt ions from aqueous solutions by using poly(N,N‐dimethylaminopropyl methacrylamide/itaconic acid) hydrogels

In this study, N,N‐dimethylaminopropyl methacrylamide (DMAPMAm) homopolymer and DMAPMAm/itaconic acid (DMAPMAm/IA) copolymers were obtained from ⁶⁰Co‐γ radiation polymerization. Gel fraction and percentage of swelling values were calculated through gravimetrical calculations. In order to increase the swelling of the hydrogel, the amount of IA in initial copolymer composition was gradually increased, but it was observed that gelation values were low. The structural and morphological assessments of homopolymer and copolymers were made by means of several techniques including Fourier Transform Infrared Spectroscopy (FT‐IR), Scanning Electron Microscopy (SEM), and Energy‐Dispersive X‐ray Spectroscopy (EDS). The cobalt ion (Co²⁺) removal capacities of hydrogel were investigated by taking into account of the initial metal ion concentration and pH of aqueous medium. When it came to the maximum capacity of values obtained from adsorption experiments by using Co²⁺ solutions at pH 5, they changed between 220 and 245 mg Co²⁺/g dry hydrogel. FT‐IR, SEM, EDS, and XRD analyses were carried out for enlightening the mechanism of Co²⁺ removal by hydrogels after the completion of adsorption. Also, desorption studies were conducted using ethylenediaminetetraacetic acid (EDTA). Finally, within approximately 5 days, all adsorbed Co²⁺ ions were released from hydrogels at pH 5 using 0.1M EDTA solution. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39569.     

Transient Behavior of Lithium Isotope Separation by Displacement Chromatography

Abstract

Lithium isotope concentration profiles at the steady and unsteady states are obtained using the circuit for continuous displacement chromatography, which is composed of 2 cm i.d. columns packed with the strong-acid cation exchange resin, Diaion SK116 (100 μm). These profiles agree well with the results calculated assuming lithium adsorption bands to be square cascades in total reflux operation.     

Fractionation of Calcium Isotopes in Cation-Exchange Chromatography

Abstract

Ion-exchange displacement chromatography of calcium has been carried out successfully for the purpose of observing calcium isotope fractionation effects. Small but definite accumulation of the heavier isotopes has been observed at the front parts of the calcium adsorption bands, which means they are preferentially fractionated into the solution phase. The average values of the single-stage separation factor minus one per unit mass difference between isotopes (ε/Δ M) have been 2.0 × 10^?5 for the calcium chloride system, 5.2 × 10^?5 for the calcium lactate system, and 2.3 × 10^?5 for the calcium acetate system at 25°C. The reduced partition function ratios of the calcium species involved in the present study have been estimated by using separation factor data and available data on calcium hydration under appropriate assumptions. The reduced partition function ratios of the complex species have been found to be larger than that of the simple hydrated calcium ion, which is a cause of the experimental results that the separation factor values of the calcium lactate and acetate systems are larger than that of the calcium chloride system. It has also been found that, for the alkali and alkaline earth metals, the magnitude of isotope effect per unit mass difference between isotopes accompanying pure ion exchange is nearly inversely proportional to the square of the atomic mass.