Dual-Temperature Ion-Exchange Separation of Copper and Zinc by Different Techniques

Abstract

Separation of copper from zinc-containing acidic solutions has been advanced by different techniques of dual-temperature ionexchange fractionation on iminodiacetic resin Amberlite IRC 718. Cycling-zone adsorption and parametric pumping (using single-column as well as double-column set-ups) experiments have been carried out in fixed-bed ion-exchange column. Measurement of equilibrium characteristics of the resin-solution system has shown that separation results from the variation of the ions sorbability with temperature. It has been found that temperature variation leads to reverse of selectivity between copper and hydrogen ions. Cycling-zone adsorption technique has allowed the copper content to be decreased up to 4 times in the resin phase and increased up to 1.7 times in the effluent when carrying out the process at 80 and 20 °C, respectively. The copper concentration has been decreased 4.4 fold after 9 treatment cycles of solution aliquot (15 BV) by single-column mode of the parametric pumping method. Two steps of the fractionation process (loading and elution) have been performed by continuous mode of operation in two counter-current columns. Continuous separation is preferred over fixed-bed column techniques. The steady-state sorption fronts have been formed on both stages of the process due to the reverse of selectivity mentioned above.     

Modeling of Size Exclusion Parametric Pumping

Abstract

Sephadex G and Biogel P, well-known gels in size exclusion chromatography, show a large change in their elution behaviors as temperature changes. These phenomena were exploited to separate the binary model solutes Blue Dextran 2000 and nickel nitrate. A series of batch size exclusion parametric pumping experiments in the direct thermal mode was carried out previously to separate binary mixtures. In this paper the experimental separations in batch size exclusion parametric pumping are compared with the predictions of both a local equilibrium model and a dispersion model. The dispersion model, which includes an axial dispersion term, gives a better fit of the experimental data. Experimentally obtained adsorption isotherms are used in the dispersion model to predict the separation performance of nickel nitrate in the Sephadex gel column. The resulting simultaneous partial differential equations are solved by quasilinearization of the equations followed by numerical integration. For both models, all parameters were estimated independently.     

Water desalting by means of electrochemical parametric pumping. II. Separation properties of a multistage column

Multistage electrochemical parametric pumping has been successfully carried out for water desalination. Separation was effected by electroadsorption-desorption cycles of the ions into and from the electrical double layer of high surface carbon electrodes. At steady state and total reflux, the concentration ratio between the upper and lower heads of the electrochemical column was as high as 150. Two models for the build up of the concentration profile within the column are presented. The first is based on a solution of the two-phase mass transport equation using the proper boundary and initial conditions. The second treatment is based on the mixed cells assumptions. In both treatments, interphase equilibrium is assumed using the isopotentiograms as the specific equilibrium curves. Use is also made of a fast computer for the simulation of the electrochemical paramatric pumping cycles. The two models are in good agreement with the experimental results particularly in the cases where the initial concentration is high and interphase equilibrium is maintained.     

Cyclic Separation Processes

Abstract

This review covers cyclic separation methods used for adsorption, ion exchange, and chromatographic separation processes where the cyclic parameter is a thermodynamic variable which changes the equilibrium distribution coefficients of the solutes. The cyclic methods reviewed include heatless or pressure-swing adsorption, parametric pumping, and cycling zone adsorption. These cyclic techniques have been studied as a possible preparative chromatographic separation method or for continuous production from adsorption or ion exchange columns.     

A Generalized Computer Model of the Transient Behavior of Multicomponent Isotope Separation Cascades

Abstract

The time dependent performance of large separation systems is a major consideration in the enrichment of the isotopes of elements that have a direct role in nuclear fuel cycles. The transient behavior of multicomponent separation cascades is described by a set of nonlinear partial differential equations that are similar in form for chemical exchange, distillation, gaseous diffusion, thermal diffusion, and other countercurrent processes. The Mound computer model is set up to solve the differential equations by a fast, implicit forward difference technique. Systems of up to 10 components can be handled with a wide variety of multiple input and output streams. With modifications, the program can be used to model systems of two or more cascades. It has been applied to the separation of the isotopes of uranium, the noble gases, carbon, oxygen, nitrogen, chlorine, sulfur and calcium. A neon isotope separation problem is given as an example of the precision with which performance can be predicted for multicomponent systems.     

A Comparison of Static Bed and Moving Bed Chromatography

Abstract

An analysis of static and moving bed perfect column chromatography is carried out for the separation of a binary mixture having constant separation factor isotherms. It is shown that the carrier requirements are identical for both methods of operation. The model does not provide information on the length of the moving bed column, but shows that the length of the static bed column can be made vanishingly small by reducing the duration of feed intervals. Furthermore, separating the feed bands only partially can - lead to a substantial reduction in the length of the static column at fixed separation rates.     

Thermal Parametric Pumping of Air–-SO2

Abstract

The separation of air-SO₂ mixtures in a specially prepared silica gel column has been accomplished using a direct mode thermal parapump. The effect of the number of cycles, pumping cycle time, and operating temperature range and level on the extent of separation has been studied over a wide range of operating conditions. The separation factors obtained were several orders of magnitude greater than those typically reported in the literature for gas-solid systems, and compare favorably with those obtained in liquid-solid systems.     

ION EXCHANGE CHROMATOGRAPHIC SEPARATION AND MS ANALYSIS OF ISOTOPES OF BORON

ABSTRACT

Using electrochemical techniques sch as pH-metry and conductimetry, the choice of a suitable complexrng reagent was made amongst ethylene glycol, propylene glycol, dextrose and mannitol for cost-effective separation of isotopes of boron by ion 'exchange chromatography. Quantitative relationships between pH and concentration; pK_a and concentration of each of these complexing reagents were determined by least square polynomial curve fitting and an attempt was made to determine the formation constants of mannitol - borate complexes. The results of experiments carried out for selection and regeneration of a resin; separation factor determinations using batch as well as column techniques, and monitoring of band movements using these electrochemical techniques are discussed.     

Effect of Feed Concentration in Equilibrium Parametric Pumps

Abstract

The effect of high initial feed concentration in batch equilibrium parametric pumping was experimentally investigated at different bed temperatures and cycle times. The system studied was benzene-n-hexane over a silica gel bed. It was observed that the initial feed concentration which leads to the best separation is dictated by the shape of the equilibrium isotherms of the system. An increase in the temperature difference between hot and cold cycles was shown to improve the separation because it led to a more favorable equilibrium relationship. Experiments also indicated that a long enough cycle time must be selected for true equilibrium to be established within the system, otherwise maximum separation cannot be obtained. In mathematical modeling studies the effect of nonlineariry of equilibrium isotherms at high feed concentrations was shown to be very effective for predictions of the model.     

The Use of Powell's Conjugate Gradient Minimization Method for Computing Concentration Profiles in Multicomponent and Multistage Separation Systems

Abstract

Concentration profiles in multicomponent and multistage separation systems can be computed by using a continuous or a stagewise model. The numerical calculations are iterative, and fast convergence is achieved when Powell's conjugate gradient minimization method is used. The procedure developed in the present work was implemented on thermal diffusion separation systems for oxygen and krypton isotopes. Although the technique was developed with special emphasis on isotope separation problems, it is also applicable to other multicomponent and multistage separation processes     

Isotope Separation by Distillation: Design of a Carbon-13 Plant

Abstract

This isotope separating plant has a great height with many long columns in parallel, low process flows compared with its boil-up, and a long time response. All these features result from dealing with a mixture whose separation factor is near unity, the carbon monoxide system. Considering that there are three isotopes of oxygen involved, six molecular species are being separated. Although CO molecules are unreacting within the columns, an exchange reactor is used when the separation is partially complete to assist in obtaining high quality product. These considerations have been formulated in a good theoretical design procedure along with excellent mechanical design, fabrication and assembly to yield a plant of high performance for carbon-13 production.     

Study of Controlled Cyclic Distillation: II. Analytical Transient Solution and Asymptotic Plate Efficiencies

Abstract

The dynamic equations of the composition variables of a controlled cycling distillation column are solved to obtain the transient solutions for the vapor-flow period. These solutions are then used to establish asymptotic expressions for the compositions at the pseudo-steady-state condition of the cycling column. Analytical expressions for the asymptotic plate efficiencies in terms of the operating conditions, equilibrium data, and local point efficiencies are derived to show quantitatively the amount of improvement in the separating ability that can be achieved in an ideal cycling column. A method of numerical iterative solution for a nonlinear equilibrium relationship is demonstrated, and a simplified graphical method for calculating the number of stages required for a given separation is presented.     

热循环吸附装置的初步氢同位素分离

设计建立了热循环吸附法(TCAP)氢同位素分离实验装置,并通过初步实验验证其分离性能。分离柱为双排圆形排列钻孔管结构,总长度约16 m,封装涂钯氧化铝1 558 g。全回流模式的初步实验结果显示,该分离实验装置可有效实现氢同位素分离,全回流模式下,分离柱热/冷循环温度为150℃/10℃,体积分数50.7%H2—49.3%D2的混合气体经30个循环后,柱底部的氘丰度达到98.8%,顶部氕丰度达到98.4%。初步实验结果表明,该分离装置可有效实现氢同位素分离。     

A Study of the Separation Efficiency in the Concentric-Tube Countercurrent Separation Process under Generalized Linear Applied Fields and with Recycles at Both Ends

Abstract

The mathematical model for the separation of binary mixtures has been extended to a concentric-tube continuous-contact countercurrent column under generalized linear external fields and with recycles at both ends. An analytical solution is obtained by use of the orthogonal expansion method. Numerical results for separation in a thermal diffusion column are also illustrated.     

Groundwater Cleanup by In-Situ Sparging. X. Air Channeling Model for Biosparging of Nonaqueous Phase Liquid

Abstract

A column model is developed to simulate the removal and biodegradation of dissolved and nonaqueous phase liquid (NAPL) volatile organic compounds (VOCs) from contaminated aquifers by biosparging. The model assumes that the injected air moves through the aquifer in persistent channels and that NAPL must dissolve and move to these channels by diffusion and dispersion. The dependence of model results on several of the parameters of the model is investigated, and suggestions for optimizing biosparging system operations are made. The removal of NAPL VOCs of quite low solubility (such as alkanes) from smear zones below the water is modeled, and is found to be an extremely slow process. Drawing down the water table to below the smear zone by pumping is suggested as a possible solution.     

Combined mode of operation for thermal parametric pumping

In thermal parametric pumping, the temperature change can be imposed through the bed jacket (direct mode) or through temperature change of the fluid stream (recuperative mode). The process to be addressed here is thermal parametric pumping operating in a combined mode of operation by changing the temperature of the fluid stream before entering the packed bed through a heat exchanger (recuperative mode) at the same time as imposing a temperature change through the bed jacket (direct mode). Axial dispersion and the general non‐linear form of the equilibrium isotherm were taken into account in the mathematical model used to verify the experimental results of separating a binary liquid mixture of a benzene/n‐hexane/silica gel system. Copyright © 2003 Society of Chemical Industry     

Separation of silicon isotopes by chemical exchange between silicon tetrafluoride and its complex compounds with aliphatic alcohols

Silicon tetrafluoride SiF₄ reacted with aliphatic alcohols ROH to form liquid complex compounds SiF₄ · 2ROH. The gas-liquid SiF_4(g) -SiF₄ · 2ROH_(l) systems can be used for separating silicon isotopes. The hydrodynamics and mass transfer of the separation of silicon isotopes in a countercurrent column were studied using SiF₄-SiF₄ · 2ROH systems based on butanol-1, pentanol-1, and hexanol-1 at 293 K. Corrections were applied to the empirical coefficients in the equations of the dependence of the total holdup of a helical prismatic packing (HPP) and its specific pressure drop on a load in an isotope exchange column. The height equivalent to the theoretical plate (HETP) increased more than twofold in the butanol-1-hexanol-1 homologous series (the flow rate in the column was (3.4 ± 0.2) mmol SiF₄/(cm² min) for the working gas). It was shown using pentanol-1 as a complex-forming agent that the limiting stage of mass transfer during the separation of silicon isotopes was the isotope exchange between SiF₄ and the SiF₄ · 2ROH complex.     

Extractive Separation of Lithium Isotopes Using Benzo-15-Crown-5. Effect of Salt Concentration

Abstract

In an extractive separation of lithium isotopes with benzo-15-crown-5, the greater separation factor is obtained from more concentrated LiCl solution. The intrinsic separation factor of benzo-15-crown-5 is determined to be α = 1.045 at 20°C.     

Laser Isotope Separation

Abstract

A brief background on the history and motivation of laser isotope separation is presented. Methods of molecular laser isotope separation are reviewed, and the Los Alamos process for separation of uranium isotopes as well as the general problems with this approach are covered. A short summary on critical uv cross-section-enhancement results is given and the implications of infrared cross-section dependence on laser fluence is discussed. The laser requirements for the LASL process and the projected economics for this process are presented. The future prospects for molecular laser isotope separation as well as some speculation on general advances in photochemistry are presented.     

Continuous Isotope Separation in Systems with Solid Phase. I. Gas-Phase Separation of Isotopes of the Light Elements

Abstract

A continuous countercurrent process for separation of isotopes of the light elements in gas-solid systems is reported. To separate hydrogen isotopes a hydrideforming palladium adsorbent and a zeolite 13A were used as a solid phase. The molecular sieve was also used to separate oxygen, nitrogen, and argon isotopes. The simulated moving-bed technique (SMB) was employed to organize a countercurrency between gas and solid phases without actual movement of the latter phase. Details of the experimental SMB unit operating in the gas phase are presented, and the results of the separation tests are discussed. A multichannel disk rotary valve was used to switch the flows. It is shown that the process takes advantage of a continuous operation and possesses very high separation efficiency with HETP values comparable to those for the equivalent conventional chromatographic process. It appears that the process proposed is ideally suited for processing tritium-containing streams to produce commodity-grade tritium and may be effectively used to separate isotopes of other light elements.