The Effects of Operating Parameters on Nitrogen Isotopes Separation by Displacement Band Chromatography

Abstract

The separation of nitrogen isotopes by displacement band chromatography was studied under various operating conditions, using columns packed with sulfonated polystyrene-divinyl benzene, cation exchange resins. Average resin size was varied from 10 to 113 μm, operating temperature from 23 to 70°C, displacing solution concentration from 0.3 to 0.9 N, and superficial velocity from 1.0 to 2.0 cm/min. The maximum separative power for nitrogen isotopes was directly proportional to stage velocity (band velocity/height equivalent to a theoretical stage). The effects of operating parameters on the separative power were therefore evaluated in terms of stage velocity. The results indicate that operating temperature and resin particle size have greater effects on the maximum separative power than do displacing solution concentration and flow rate.     

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.     

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 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).     

Nitrogen-15 Fractionation by Countercurrent Exchange between Liquid N2O3-N2O4 Mixtures and Their Vapor Phases under Pressured Conditions

Abstract

The nitrogen isotope exchange system for ¹⁵N-fractionation consisting of liquid mixtures of N₂O₃ and N₂O₄ and the vapor phase in equilibrium with the liquid (NO/N₂O₃ system) has been studied at temperatures between ?9 and 20°C under various pressures below 4 atm. A countercurrent isotope exchange apparatus and an associated product refluxer system are described. At 15°C the effective separation factor, α_eff, increases from 1.006 at 1 atm to 1.030 at 2.7 atm and levels off thereafter. The observed α_eff values are in good agreement with recent spectroscopic data. The height equivalent of theoretical plate (HETP) correlates well with the linear flow rate of gas phase, showing a dominant diffusion-control of the overall exchange rate. At 15°C the HETP of the NO/N₂O₃ system under 3～4 atm can be smaller by factors of 7 to 10 than that of the Nitrox (NO/HNO₃ exchange) system having the same product rate, rendering the former system a possibility for significantly smaller plant volume.     

Chromatographic Separation of Calcium Isotopes with Polymer-Bound Ligands

Abstract

Calcium isotopes were enriched in chromatography columns containing the polymer-bound ligands cryptand [2_B22], cryptand [2_B21], and 18-Crown-6. The largest equilibrium single stage separation factor, 1.0039 ± 0.0002 for the calcium 40/44 isotope pair, was found in calcium exchange with cryptand [2_B22]. The largest separation factor found for 18-Crown-6 was 1.0025 ± 0.0003 for the 40/44 isotope pair. The size of the isotope effect was found to be highly dependent on the solvent composition. An iminodiacetate resin ion exchange column yielded small enrichments of calcium isotopes. Calcium 40/44 exchange with the chelating functional group iminodiacetate yielded a small equilibrium separation factor of 1.00011 ± 0.00003, which was more typical of calcium ion exchange isotope effects.

Comparisons of the above chemical systems based on separative power showed crown chemical exchange to be an improvement over cryptand and iminodiacetate exchange. The cryptand system was rendered impractical as a consequence of a slow exchange rate and a resulting large stage residence time contribution to the separative power, on the order of 45 min. The separation factor for the iminodiacetate system was too small for practical applicability.     

Steady-State Characteristics of Lithium Isotope Separation by a Circuit of Continuous Displacement Chromatography

Abstract

Height equivalent to a theoretical plate (HETP), which is an important factor to determine separation performance, is experimentally obtained for lithium isotope separation by a circuit of continuous displacement chromatography. The values of HETP are related to the flow rates and concentrations of the displacement reagents. A new equation to estimate HETP is derived and shows good agreement with the experimental data. Diffusion in the resin is found to be the major resistance for the isotope exchange reaction, and liquid mixing in the columns also strongly influences the value of HETP.     

Isotope Separation of Nitrogen by Ion Exchange Chromatography in a Cascade System

The ion exchange chromatography technique in a cascade process was used to separate stable isotopes of nitrogen (¹⁴N/¹⁵N). For this purpose, three column systems (with different internal diameters, S1?14.5 cm; S2–9.5 cm; S3–5.2 cm) were used that contained the cationic resins DOWEX 50 WX8 (as H⁺ and equilibrated with H₂O) and measured 1.7 m in height. Isotopic fractionation of nitrogen occurs during displacement band chromatography (DBC) of the NH₃ (aq) solution with a 0.75 mol L^?1 NaOH solution. The active sites of the resin were previously saturated to form NH₄ ⁺ (RNH₄) with a 0.75 mol L^?1 solution of (NH₄)₂SO₄ at a natural isotopic abundance (0.366 at. %) in ¹⁵N. The NH₄ ⁺/NH₃ (aq) equilibrium was determined during the DBC, which enriched the rear portion of the band with ¹⁵N. In S1, enrichment of approximately 5 at. % of ¹⁵N in the last 10 cm was achieved. After four interactions (couplings) between S1–S2, an enrichment of approximately 50 at. % of ¹⁵N was obtained. During the interaction between S2–S3, after the second coupling, an isotopic enrichment of approximately 90 at. % of ¹⁵N was observed, which produced 70 g month^?1 of (¹⁵NH₄)₂SO₄.     

Synthesis of Extraction Resin Containing N,N,N′,N′-Tetraisobutyl Diglycolamide and its Application for Separation of Sr(II) from Rb(I)

Abstract

A novel Levextrel resin containing N,N,N′,N′-tetraisobutyl diglycolamide (TiBDGA) was synthesized by suspension polymerization of styrene and divinylbenzene and its performance for separation of Sr(II) from Rb(I) was investigated. The effects of crosslink degree, stirring speed, and the ratio of porogenic-agents on the resin synthesized were examined. The optimum TiBDGA resin with 40 wt.% divinylbenzene as cross linking agent and 20 wt.% of n-octanol as porogenic-agents provided excellent adsorption capacity of 22.5 mg/g. The distribution coefficient (K _d) of Sr(II) in HNO₃ media onto the resin depended heavily on the acidity in the aqueous solution. The maximum K _d for Sr(II) (7300 mL/g) was observed when the HNO₃ concentration in aqueous phase reached 2 mol/L. The difference in the Sr(II) and Rb(I) distribution coefficients of several orders of magnitude implied that ⁸⁹Sr may be separated from ⁸⁶Rb with a radionuclide purity greater than 99%. And the maximum static adsorption capacity of Sr(II) on the resin was 22.5 mg/g.     

Continuous Separation of Sugarcane Molasses with a Simulated Moving-Bed Adsorber. Adsorption Equilibria,Kinetics, and Application

Abstract

Fundamental chromatographic properties are reported that are related to the industrial separation of sugarcane molasses in a simulated moving-bed adsorber. The distribution coefficients of KCl, sucrose, glucose, and fructose on XUS-40166.00 (K⁺) cation exchanger were determined by pulse testing to be 0.00, 0.22, 0.45, and 0.50 at infinite dilution at 70°C. The adsorption isotherm of KCl is quadratic; those of the sugars only slightly nonlinear and dependent on KCl concentration. HETP was found to be independent of fluid velocity for KCl in the range of the interstitial velocity of 5 to 35 cm/min, and increasing with v for sucrose. At high fluid velocities the broadening of the sucrose band in a packed bed comes primarily from intraparticle mass transfer, with axial dispersion and film diffusion playing minor roles. The process for separation of sugarcane molasses was demonstrated on a 47-L, eight-column simulated moving-bed adsorber. A theoretical, staged model of the simulated moving-bed adsorber with one inert totally excluded and three linearly adsorbing components was found to give an excellent representation of the transient and steady-state behavior of the continuous separation of sugarcane molasses.     

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).     

Enrichment of Boron-10 by Inverse-Frontal Chromatography Using Quaternized 4-Vinylpyridine—Divinylbenzene Anion-Exchange Resin

Abstract

In order to enrich ¹⁰B, 40 meter band migration of boric acid—mannitol with hydrochloric acid solution was performed by inverse frontal chromatography on a porous, 25% crosslinked, 38% quaternized 4-vinylpyridine—divinylbenzene resin. The maximum enrichment (R _L) of ¹⁰B was 94.15%. The overall process parameters, namely slope coefficient (k) and separation coefficient (ε), were found to be 0.1282 cm^?1 and 0.02967, respectively.     

Absence of Donnan Exclusion at High‐Concentration Ion Exchange for Macroporous Anionic Resin

Abstract

High‐concentration ion exchange has been studied for an anionic macroporous resin. The mechanism of interaction of Lewatit MP‐500 (strong base resin) with several high‐concentration inorganic salts was analyzed in order to determine the effect of the Donnan potential in the process.

The systems under study were Cl^?, SO₄ ^2? as counter‐ions and K⁺, Na⁺ as co‐ions in different combinations as single electrolytes. These salts were chosen because of their interest as raw materials in the fertilizer industry. The study focuses mainly on the behavior of high‐concentration (over 1 M) counter‐ and co‐ions in the anionic resin. The results showed that Donnan exclusion does not take place completely and that electrolyte penetration inside the resin is observed. Furthermore, a certain amount of ion exchange was observed for the co‐ions (K⁺ and Na⁺) when the resin was presaturated with sulphate and chlorides that were present in the solution. Equilibrium and kinetics data were obtained under these special experimental conditions. Equilibrium constants were obtained for counter‐ions and adsorption constants for co‐ions using a constant separation factor isotherm, while diffusion coefficients were obtained using a pore diffusion model.     

Die anwendung von redoxharzen in der anorganischen chemie

Ag, Cu, Te and Se were precipitated from aqueous solutions by a redox resin containing the system anthraquinone/anthrahydroquinone. Ag, Cu and Te were dissolved in 1 N nitric acid. Se was dissolved in a solution of KCN. This resin was able to alter the valences of variable-valence ions (UO₂²⁺ → U⁴⁺; VO₂^?₂ → V³⁺). It was possible to produce H₂O₂ solutions up to a concentration of 1.3 N in a continuous process with a resin made by condensation of hydroquinone and phenol with formaldehyde.     

Kilogram-Scale Purification of Americium by Ion Exchange

Abstract

Sequential anion and cation exchange processes have been used for the final purification of ²⁴¹Am recovered during the reprocessing of aged plutonium metallurgical scrap. Plutonium was removed by absorption on Dowex 1, X-3.5 (30–50 mesh) anion exchange resin from 6.5–7.5 M HNO₃ feed solution. Following a water dilution to 0.75–1.0 M HNO₃, americium was absorbed on Dowex 50W, X-8 (50–100 mesh) cation exchange resin. Final purification was accomplished by elution of the absorbed band down 3 to 4 successive beds of the same resin, preloaded with Zn²⁺, with an NH₄OH buffered chelating agent.

The recovery of mixed ²⁴¹Am?²⁴³Am from power reactor reprocessing waste has been demonstrated. Solvent extraction was used to recover a HNO₃ solution of mixed lanthanides and actinides from waste generated by the reprocessing of 13.5 tons of Shippingport Power Reactor blanket fuel. Sequential cation exchange band-displacement processes were then used to separate americium and curium from the lanthanides and then to separate ～60 g of ²⁴⁴Cm from 1000 g of mixed ²⁴¹Am-²⁴³Am.     

Nitrogen use efficiency,floodwater properties,and nitrogen-15 balance in transplanted lowland rice as affected by liquid urea band placement

Alternative N fertilizer management practices are needed to increase productivity and N use efficiency in lowland rice (Oryza sativa L.). In 1986 dry season, a field study using¹⁵N-labeled urea evaluated the effect of time and method of fertilizer N application on grain yield and N use efficiency. Conventional fertilizer application was compared with band placement of liquid urea and point placement of urea supergranules (USG). Grain yields were significantly higher with either band or point placement than with broadcast and incorporation or surface application. Partial pressure of NH₃ (NH₃) was significantly reduced when N was deep-placed.¹⁵N balance data show that fertilizer N applied basally and incorporated gave a total¹⁵N recovery of 52% and crop (grain + straw) recovery of 30%. Band placement of liquid urea N resulted in 82–90% total and 57–65% crop¹⁵N recovery. USG point placement gave 94% total and 70% crop¹⁵N recovery. Deep placement of second N application gave only slightly higher (98%)¹⁵N recovery compared with broadcast application (89%).     

Studies of Selective Adsorption Resins. XXII. Removal and Recovery of Arsenic Ion in Geothermal Power Waste Solution with Chelating Resin Containing Mercapto Groups

Abstract

Removal and recovery of harmful arsenic ion in a geothermal power waste solution with three macroreticular chelating resins containing mercapto groups were investigated. The resin (RES), which was prepared from 2,3-epithiopropyl methacrylate-divinylbenzene copolymer beads, exhibited high affinity for arsenic(III) ion and high resistance against hot water. In the column method, arsenic(III) ion in an aqueous solution was favorably adsorbed on the RES when the sodium arsenite solution (pH 6.2) containing 3 mg/dm³ of arsenic(III) ion was passed through the RES column at a space velocity of 15 h^?1. The arsenic(III) ion adsorbed was eluted by allowing 2 mol/dm³ sodium hydroxide solution containing 5% of sodium hydrogen sulfide to pass through the column. The recycle of adsorption and elution was found to be satisfactory. The RES also exhibited high adsorption ability for arsenic ion in the geothermal power waste solution.     

Chloride-sulphate exchange on anion resins — kinetic investigation,IX. Direct,isotopic and reverse exchange

Experimental kinetics of direct, isotopic and reverse Cl^?/SO⁼₄ exchange on different anion resins are presented.At very low concentration (C = 6 × 10^?3 N) extremely high resin selectivity toward sulphates occurs (separation factors ranging from 52 to 589). Consequently chemical interaction of interdiffusing species within the resin seems to influence the rate determining step, exception made for isotopic exchange. Application of model equations from Nernst-Planck and SN₂ rate theories is discussed.     

Preparation and characterization of melamine–formaldehyde–DTPA chelating resin and its use as an adsorbent for heavy metals removal from wastewater

Melamine–formaldehyde–diethylenetriaminepentaacetic acid (MF–DTPA) resin was prepared as a new adsorbent for removing heavy metals from wastewater effluents. The resin was synthesised by anchoring the chelating agent diethylenetriaminepentaacetic acid (DTPA) to melamine via amide covalent bond during melamine–formaldehyde condensation reaction in an acidic aqueous medium. The effects of reaction parameters (temperature, acidity, and water content) on resin characteristics (water regain, rigidity, DTPA functionality, and porosity) were monitored to specify the best synthesis conditions. The resin was chemically characterized using infrared spectroscopy (FTIR), elemental analysis (EA), thermal programmed decomposition-mass spectrometry (TPD-MS), solid-state ¹³C NMR and ¹⁵N NMR, and was morphologically characterized using N₂ gas adsorption/desorption (BET analysis) and field emission-scanning electron microscopy (FE-SEM). The water regain factor was also calculated to determine hydrophilic character of the resin. The simultaneous adsorption performance of MF–DTPA resin towards selected heavy metals, Co(II), Cd(II), Zn(II), and Cu(II), was discussed. Quantitative analysis for adsorption was conducted using atomic absorption to investigate the kinetics, adsorption isotherm and thermodynamics of the removal process considering pH, initial concentration, temperature, and contact time as controlling parameters. The mechanism of adsorption was suggested based on experimental results. This work shows the potential application of the MF–DTPA resin for removing heavy metals from wastewaters.     

The effect of temperature on limiting current density and mass transfer in electrodialysis

This study focuses on a high-temperature operation in electrodialysis of salt solutions and studies the effect of temperature on limiting current density and mass transfer. Experiments were conducted under various conditions of temperature (T), varying from 15 to 90°C; of dialysate concentration (C_d), varying from 5 × 10^?3 to 3 × 10^?2M ; and of dialysate velocity (u_d), varying from 0.206 to 2.44 cm s^?1. A least squares fitting of the experimental data on limiting current density (I_lim) yields an Arrhenius equation as follows: The molar flux N? (mol cm^?2 s^?1), initial concentration (C₀; M ) and temperature (T; °C) were found to have the following relationship: N?/C₀ is slightly increased with increasing temperature ranging from 25 to 70°C.