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Showing papers in "Separation Science and Technology in 1991"


Journal ArticleDOI
TL;DR: In this article, a new class of extractants, pentaalkylpropane diamides, was investigated and the results of a bench-scale experiment performed in a mixer-settler battery were presented.
Abstract: A new class of extractants has been investigated: pentaalkylpropane diamides. Due to their chelating effect on metallic cations, they extract trivalent actinides such as Am3+ and Cm3+ from acidic nitrate nuclear waste solutions. These solvents are completely incinerable and do not generate large amounts of waste. A review is provided of their chemical properties, leading to the choice of the proper molecule. The results of a bench-scale experiment performed in a mixer-settler battery are presented.

207 citations


Journal ArticleDOI
TL;DR: The recent status of pressure swing adsorption (PSA) as a process for separating multicomponent gas mixtures is reviewed in this article, where applications of a new generation of adsorbents, such as zeolites, carbon molecular sieves, and pore engineered molecular sizers, are described in detail.
Abstract: The recent status of pressure swing adsorption (PSA) as a process for separating multicomponent gas mixtures is reviewed. The applications of a new generation of adsorbents, such as zeolites, carbon molecular sieves, and, more recently, pore engineered molecular sieves, are described in detail. The more important theories of adsorption from gas mixtures as well as those of the PSA process are described briefly. The commercial applications of PSA the process-present and potential-are discussed at length.

108 citations


Journal ArticleDOI
Takao Oi1, Norio Morioka1, Hideki Ogino1, Hidetake Kakihana1, Morikazu Hosoe 
TL;DR: In this paper, 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.
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 (∊/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 r...

89 citations


Journal ArticleDOI
TL;DR: In this article, an experimental investigation of a new method for heating adsorbent beds in the desorption step owing to Joule's heat generated inside the adorbent particles by passing an electric current through them is presented.
Abstract: Results of an experimental investigation of a new method for heating adsorbent beds in the desorption step owing to Joule's heat generated inside the adsorbent particles by passing an electric current through them are presented. Desorption of a previously saturated bed and cyclic separation with the electric potential applied to a fibrous activated carbon bed was performed.

72 citations


Journal ArticleDOI
TL;DR: In this article, a resistance model was developed to describe the increased pervaporation flux and selectivity for the separation of ethanol/water mixtures with silicalite-filled silicone rubber (SR) membranes as compared to unfilled SR membranes.
Abstract: A resistance model has been developed to describe the increased pervaporation flux and selectivity for the separation of ethanol/water mixtures with silicalite-filled silicone rubber (SR) membranes as compared to unfilled SR membranes. The model interprets the increased component flux for ethanol in terms of an increasing ethanol permeability of the membrane. Membrane permeability is given as a function of rubber and silicalite permeabilities and of the silicalite content of the membrane. It is shown that silicalite permeability varies with the type of alcohol and the alcohol concentration in the feed mixture. In the series methanol, ethanol, propanol, and butanol, the alcohol permeability of silicalite varies with the length of the alcohol molecule, the lowest permeability being found for butanol. In the presence of propanol and butanol, the silicalite particles are impermeable to water and obstruct water transport through the membrane.

59 citations


Journal ArticleDOI
TL;DR: Ligand-modified micellar-enhanced ultrafiltration (LM-MEUF) is a membranebased separation technique which can selectively remove specific ions from an aqueous solution containing several ions of like charge.
Abstract: Ligand-modified micellar-enhanced ultrafiltration (LM-MEUF) is a membranebased separation technique which can selectively remove specific ions from an aqueous solution containing several ions of like charge. In LM-MEUF, surfactant and amphiphilic ligand are added to the contaminated water. The surfactant forms aggregates called micelles, and the ligand is selected to complex the ion of interest and to solubilize strongly in the micelles. The result is micelles containing a high fraction of the ligand and the target ion. If the surfactant is chosen to have the same charge as the target ion, other ions in solution with this same charge will not associate with the micelles, making the retention of ions by the micelles very selective. The solution is then passed through an ultrafiltration membrane with pore sizes small enough to block the passage of micelles. In this study, divalent copper is the target ion in a solution also containing divalent calcium. A cationic surfactant is used with N-n-dodecyl...

48 citations


Journal ArticleDOI
TL;DR: In this article, the authors assess the accuracy of using selectivity as a basis for solvent screening in extractive distillation processes and assess the total annual costs for each of the chosen mixtures and for various solvents.
Abstract: An important parameter for consideration in the screening of solvents for an extractive distillation process is selectivity at infinite dilution. The higher the selectivity, the better the solvent. This paper assesses the accuracy of using selectivity as a basis for solvent screening in extractive distillation processes. Three types of binary mixtures that are usually separated by an extractive distillation process are chosen for investigation. Having determined the optimum solvent feed rate to be two times the feed rate of the binary mixture, the total annual costs of extractive distillation processes for each of the chosen mixtures and for various solvents are carried out. The solvents are ranked on the basis of the total annual cost (obtained by design and costing equations) for the extractive distillation processes, and this ranking order is compared with that of selectivity at infinite dilution as determined by the UNIFAC method. This matching of selectivity with total annual cost does not p...

47 citations


Journal ArticleDOI
TL;DR: Sodium borohydride can be used as an efficient agent for reducing gold and silver in acidic solutions of thiourea, thiocyanate, thiosulfate, acid chloride, and acid nitrate.
Abstract: Sodium borohydride can be used as an efficient agent for reducing gold and silver in acidic solutions of thiourea, thiocyanate, thiosulfate, acid chloride, and acid nitrate. The Au(I) ion is reduced to metallic gold in the form of very fine crystals, as indicated by XRD and SEM analysis. The reduction reaction is carried out at ambient temperature for a very short period of time (30 s). The reduction of Au(I) in such solutions can be performed for a wide range of gold concentrations (2 mg/L-2 g/L). Different parameters controlling the rate of the reaction and the efficiency of borohydride were studied, namely: acidity, stoichiometry, thiourea concentration, the presence of foreign ions, and temperature. Gold reduction by sodium borohydride is more favorable in the presence of Ag+ and/or Zn2+ ions, while the presence of Fe2+, Co2+, Ni2+, and Cu2+ ions decreases the efficiency of borohydride. The reduction reaction is selective for gold and silver over base metals in a solution mixture since the re...

46 citations


Journal ArticleDOI
TL;DR: In the present investigation, isolation of proteins from human placental extract by using the continuous foam fractionation technique is studied and the effect of different physicochemical parameters on the separation of proteins and purification of proteolytic enzymes is reported.
Abstract: The recovery of valuable proteins (like proteolytic enzymes) from nonconventional biological sources by using modern separation techniques is becoming increasingly important because of their high commercial potential. In the present investigation, isolation of proteins from human placental extract by using the continuous foam fractionation technique is studied. The effect of different physicochemical parameters on the separation of proteins and purification of proteolytic enzymes are reported. A method for finding a quasi-equilibrium relationship between the solute concentration in the foamate and in the effluent by using the same system is described. The quasi-equilibrium curve is also presented.

40 citations


Journal ArticleDOI
TL;DR: In this paper, the removal of weathered-in PCBs from clayey soil by surfactant washing is demonstrated at bench scale by using mathematical models for batch-batch, batch-continuous flow, and countercurrent flow.
Abstract: The removal of weathered-in PCBs from clayey soil by surfactant washing is demonstrated at bench scale. Spent surfactant solution was treated for recycle at bench scale by countercurrent liquid-liquid extraction for the removal of nonvolatile contaminants, and by thin film aeration in packed columns for removal of volatile organics. A correlation of micelle/water partition coefficients with octanol/ water partition coefficients reported earlier by Valsaraj et al. is extended to several additional compounds. Mathematical models for batch–batch, batch–continuous flow, and countercurrent flow surfactant soil washing are described, and the effects of the model parameters are discussed.

40 citations


Journal ArticleDOI
TL;DR: In this article, the efficiency and stability of flat-sheet supported liquid membranes (SLMs) were studied in the case of the active transport of an amino acid, L-valine, and the experimental efficiency was modeled by a mathematical expression involving the distribution coefficient of the solute and the viscosity of the organic solution.
Abstract: The efficiency and the stability of flat-sheet supported liquid membranes (SLMs) were studied in the case of the active transport of an amino acid, L-valine. Independent measurements on the organic phase (valine distribution, water concentration and viscosity) combined with the determination of some surface properties (interfacial tension and drop point) permit the description and prediction of the experimental permeability and stability of SLMs. The lifetime of the SLM was explained by taking into account diluent solubility in the aqueous phase, water concentration in the organic phase, interfacial tension between organic and feed phases, and drop point of the SLM. The experimental efficiency could be modeled by a mathematical expression involving the distribution coefficient of the solute and the viscosity of the organic solution.

Journal ArticleDOI
TL;DR: In this paper, a new and useful method has been developed for analytical evaluation of the distribution coefficient (Kd ) at an infinitesimal exchange, based on the extrapolation of the Kielland plot from an ion-exchange isotherm to zero loading.
Abstract: A new and useful method has been developed for analytical evaluation of the distribution coefficient (Kd ) at an infinitesimal exchange. Kd values have an important role for the chromatographic separation of ions. This method is based on the extrapolation of the Kielland plot from an ion-exchange isotherm to zero loading. The usefulness of this method is exemplified by evaluation of Kd values for Cs+ on Al3+−substituted tobermorite which is known to exhibit high selectivity toward Cs+.

Journal ArticleDOI
TL;DR: In this article, the effects of such parameters as temperature (200-600°C), duration of roasting (15-120 min), and amount of ammonium sulfate (0.5-2.5 times stoichiometric) have been studied.
Abstract: Copper converter slag, provided by Ergani Copper Co. of Etibank and containing 2.56% copper and 0.22% cobalt, was roasted with ammonium sulfate. The effects of such parameters as temperature (200–600°C), duration of roasting (15–120 min), and amount of ammonium sulfate (0.5–2.5 times stoichiometric) have been studied. Under optimum conditions (slag size, − 100 mesh; stoichiometric requirement of ammonium sulfate; roasting temperature of 400°C for 60 min), we obtained 88% Cu and 67% Co by extraction. Similar studies were carried out with concentrated sulfuric acid. The influence of experimental variables such as roasting temperature (25–300°C), roasting period (30–120 min), and amount of sulfuric acid (0.5–2 times stoichiometric) has been studied. Under atmospheric conditions, i.e., at 200°C and a roasting period of 60 min with 1.5 times the stoichiometric amount of sulfuric acid, recoveries of copper and cobalt were 82 and 96%, respectively.

Journal ArticleDOI
TL;DR: In this article, the adsorption equilibrium data for adsorbates such as phenol, aniline, benzoic acid, o−cresol, and p−methoxyphenol on six grades of granular activated carbons were analyzed for their adherence to Freundlich or Langmuir adaption isotherms, and the results are discussed.
Abstract: Adsorption equilibrium studies of some aromatic organic pollutants in water with some commercially available standard grades of granular activated carbons have been carried out at 35°C. The adsorption equilibrium data for adsorbates such as phenol, aniline, benzoic acid, o−cresol, and p−methoxyphenol on six grades of granular activated carbons were analyzed for their adherence to Freundlich or Langmuir adsorption isotherms, and the results are discussed.

Journal ArticleDOI
TL;DR: In this paper, a complete model incorporating all known transport mechanisms for solutes between aqueous and organic solvent phases in solvent sublation is proposed, and the predictions from the model with respect to the different transport mechanisms are substantiated with experiments on the solvent sublations of neutral pentachloro-phenol (PCP) molecules (pH = 3.0) and ionic PCP molecules as PCP + hexadecyl trimethyl ammonium bromide complex (pP = 8.9) into different solvents.
Abstract: A complete model incorporating all known transport mechanisms for solutes between aqueous and organic solvent phases in solvent sublation is proposed. The predictions from the model with respect to the different transport mechanisms were substantiated with experiments on the solvent sublation of neutral pentachloro-phenol (PCP) molecules (pH = 3.0) and ionic PCP molecules as PCP + hexadecyl trimethyl ammonium bromide complex (pH = 8.9) into different solvents—mineral oil (a nonionic solvent) and decyl alcohol (a partly ionic solvent). Effects of inorganic salts on the sublation of both types of PCP molecules were investigated.

Journal ArticleDOI
TL;DR: In this article, a preliminary study was initiated to determine the feasibility of using ultrafiltration to remove dyes and other contaminants from industrial textile plant waste streams, which was conducted on samples of the waste stream by using a lab-scale UF unit fitted with a polysulfone XM50 hollow fiber membrane.
Abstract: This preliminary study was initiated to determine the feasibility of using ultrafiltration to remove dyes and other contaminants from industrial textile plant waste streams. Various runs were conducted on samples of the waste stream by using a lab-scale UF unit fitted with a polysulfone XM50 hollow fiber membrane. The effects of temperature and pressure on permeate flow rate and rejection coefficient were investigated. Spectrophotometric analysis was used to determine the rejection coefficients. The average rejection coefficients ranged from 30 to 90%. The permeate-to-feed ratios ranged from 1.4 to 15.2%. Increasing the pressure increased the permeate flow rate, but also decreased the rejection coefficient. The effect of temperature was inconclusive. Fouling varied with the waste solutions, but could be enough to clog the whole unit. The pH remained at the same value of 10 for the permeate, retentate, and feed in all the runs.

Journal ArticleDOI
TL;DR: In this article, the solid/liquid separation of a NaY zeolite, a known cation exchanger, was investigated in the laboratory by foam flotation from aqueous suspensions.
Abstract: In this paper the solid/liquid separation of a NaY zeolite, a known cation exchanger, was investigated in the laboratory by foam flotation from aqueous suspensions. The main parameters affecting the process in batch experiments, such as the pH of the suspension, the type of collector, the cationic collector concentration, the zeolite concentration, and the ionic strength were examined. The optimum conditions for removal (flotation) of more than 95% of the zeolite were determined. Following flotation of the zeolite in the Na form, zinc ions were chosen to serve as an application for ion exchange by the zeolite (for metal recovery), followed by foam floatation of the exchanged form of the zeolite from solution.

Journal ArticleDOI
TL;DR: In this paper, a PAN ultrafiltration membrane is optimized with respect to the fatty acid/water/isopropanol ratio, and it appears that a 1:6.5:3 (v/v) ratio gives the highest flux [95 L/(m2−h-bar).
Abstract: Fatty acids can be extracted from an oil phase by forming a dispersed phase of saponified fatty acids/water/isopropanol in oil. This dispersion can be separated in the two phases by two membranes of opposite polarity in series. In this study the separation of the water phase from the dispersion by a hydrophilic membrane and the mechanisms underlying the flux characteristics are investigated. The permeation flux through a PAN ultrafiltration membrane is optimized with respect to the fatty acid/water/isopropanol ratio. It appears that a 1:6.5:3 (v/v) ratio gives the highest flux [95 L/(m2−h-bar)]. The dispersion at these conditions consists of a continuous oil phase as well as a continuous water phase between 20 and 65% water phase hold up. The flux/pressure curve shows a linear increase of the flux with pressure at low pressures (determined by the membrane resistance), followed by a maximum flux value for the case where the volume of the water phase present in the inflow is limiting. It is not pos...

Journal ArticleDOI
TL;DR: In this paper, an experimental investigation of batch ion flotation of the transition metal cations Cr3-, Fe3+, Mn2+, Co2+, Zn2+, Ag+, Cd2+, and In3+ was presented.
Abstract: An experimental investigation is presented of the batch ion flotation of the transition metal cations Cr3-, Fe3+, Mn2+, Co2+, Zn2+, Ag+, Cd2+, and In3+ from acidic aqueous solutions with sodium dodecylsulfonate and sodium dodecylben-zenesulfonate as anionic surfactants. The selectivity sequences Mn2+ < Zn2+ < Co2+ < Fe3+ < Cr3+ and Ag+ < Cd2+ < In3+ are established, both from data for single and multi-ion metal cations solutions, where sublate was not formed in the bulk solution. Good agreement between the selectivity sequences and the values of ionic potential of metal cations was found. An experimental investigation was also performed on the solubility of sublates. The sublates solubility values are discussed in terms of ionic potentials of metal cations as well as of the surfactant size.

Journal ArticleDOI
TL;DR: In this paper, a template procedure was performed with Ni2+ and Cu2- ions, and comparisons were made of exchange capacities and equilibrium constants for templated and untemplated resins.
Abstract: Ion-exchange resins were prepared by copolymerization of styrenic monomers with metal ion complex compounds bearing polymerizable ligands. Removal of the metal ions by acid washing produced sites in the resins which contained ligands configured to match the bonding characteristics of the ions used in their construction. This template procedure was performed with Ni2+ and Cu2- ions, and comparisons were made of exchange capacities and equilibrium constants for templated and untemplated resins. Templated resins showed order of magnitude capacity preferences for the ion used in their preparation. Equilibrium constants were found to be inversely related to capacities.

Journal ArticleDOI
TL;DR: In this article, the active transport of cadmium ions across a supported liquid membrane (SLM) containing a ligand based on a driving force supplied by the concentration gradient of the chloride ion is described.
Abstract: The active transport of cadmium ions across a supported liquid membrane (SLM) containing a ligand based on a driving force supplied by the concentration gradient of the chloride ion is described. The SLM used is a microporous polypropylene membrane impregnated with a bathocuproine (4,7-diphenyl-2.9-dimethyl-1,10-phenanthroline) solution in dibenzyl ether as a carrier. The characteristics of the cadmium ion transport system are examined under various experimental conditions. The active transport of cadmium ions through an SLM is dependent on the concentrations of the cadmium ion, ligand, and chloride ion. An equation for the permeation velocity of cadmium ions, consisting of three important factors for this transport system, is proposed.

Journal ArticleDOI
TL;DR: In this article, a two-dimensional mathematical model is developed for in-situ surfactant flushing of contaminants from an aquifer by means of injection and recovery wells.
Abstract: A two-dimensional mathematical model is developed for in-situ surfactant flushing of contaminants from an aquifer by means of injection and recovery wells. The model tracks both surfactant concentration and contaminant concentration, and permits the use of the Langmuir, Freundlich, BET, or other adsorption isotherms for the contaminant-soil binding. The permeability of the aquifer is assumed to be constant and isotropic, and local equilibrium is assumed between adsorbed and solubilized contaminant.

Journal ArticleDOI
TL;DR: In this article, a solution-diffusion mechanism for pervaporation is described, where the permeation rate is a function of solubility and diffusivity, and two aspects are distinguished with respect to selective transport: flow coupling and thermodynamic interaction.
Abstract: Transport in pervaporation takes place in a three-step sequence: 1) (selective) sorption into the membrane, 2) diffusion through the membrane, and 3) desorption into a vapor phase. Diffusion through the membrane is the rate-determinating step. The transport can be described by a solution-diffusion mechanism where the permeation rate is a function of solubility and diffusivity. The basic principles of this model are described. In the case of a liquid mixture, two aspects have to be distinguished with respect to selective transport: flow coupling and thermodynamic interaction. Both aspects are discussed.

Journal ArticleDOI
TL;DR: In this paper, a high-pressure mercury lamp was used as the light source for photoreduction to separate Eu from the Sm, Eu, and Gd concentrate in a mixed alcohol (ethanol and isopropanol) system.
Abstract: Eu can be separated by photoreduction from the Sm, Eu, and Gd concentrate in a mixed alcohol (ethanol and isopropanol) system by using a high-pressure mercury lamp as the light source. The influencing factors, such as the concentration of EtOH-isopropanol, irradiation time, and the lamp power, on the photoreduction were investigated in detaii in this research, and the optimum technological conditions were determined. The separation coefficients were βGd/Eu > βSm/Eu = 960, and the yield of Eu(II) is 95%. The purity of Eu obtained is 92%.

Journal ArticleDOI
TL;DR: In this article, Carboxylic and sulfonic ion exchange membranes were used with hydrogen counterion and additionally with trimethylammonium, triethylammmonium and tributylammium counterions.
Abstract: Several ion-exchange and neutral membranes were examined in the pervaporation of water-pyridine mixtures. Carboxylic and sulfonic ion-exchange membranes were used with hydrogen counterion and additionally with trimethylammonium, triethylammonium, and tributylammonium counterions. All membranes were selective to water, but the transport mode and selectivity properties of membranes were dependent on both the character of the ion-exchange group and the ionic form of the membrane. The results obtained suggest that pervaporation of waterpyridine mixtures could be used with standard distillation in the large-scale dehydration process of pyridine.

Journal ArticleDOI
TL;DR: In this article, the characterization of microfiltration membranes by porosimetric measurements has been studied and liquid displacement porometry has been proven to be the only method applicable for proper characterization of the membranes.
Abstract: This paper deals with the characterization of microfiltration membranes by porosimetric measurements. Different methods have been used to test the membranes: the Poiseuille-Knudsen method, the mercury intrusion method, and liquid displacement porometry. Membranes were also examined with the aid of a scanning electron microscope. On the basis of the results obtained, liquid displacement porometry was proven the only method applicable for a proper characterization of the membranes.

Journal ArticleDOI
TL;DR: In this paper, a continuous rotating annular chromatograph was developed for preparative multicomponents separations, where an annular bed was fixed while a nozzle of feed and collectors of products were rotated at the same speed.
Abstract: A continuous rotating annular chromatograph was developed for preparative multicomponents separations. An annular bed was fixed while a nozzle of feed and collectors of products were rotated at the same speed. To evaluate the performance of this device, three kinds of amino acids were separated by an ion-exchange resin. Rotation speeds, feed rates, and feed concentrations were varied. Experimental concentration profiles were compared with results calculated by using a model with interactions of amino acids. This system was found to be promising for continuous preparative chromatographic separations.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a dispersion-free solvent extraction process, which uses microporous membranes, overcomes such shortcomings of conventional liquid extraction as flooding and loadings.
Abstract: The high energy requirements of the traditional separation of ethanol from fermentation liquors by distillation led us to seek a new energy-efficient separation method. Several alternatives, including absorption, molecular sieves, membrane separation processes, and liquid-liquid extraction processes, have been proposed and investigated (I). One of the most investigated separation techniques during the past few years has been membrane-aided solvent extraction (2–5). This dispersion-free solvent extraction process, which uses microporous membranes, overcomes such shortcomings of conventional liquid extraction as flooding and loadings. On the other hand, a technique with microporous hollow fibers may provide high mass transfer per unit volume since hollow-fiber modules contain an enormous surface area.

Journal ArticleDOI
TL;DR: In this article, an experimental study was performed by using a device that provides visualization of the sample stream inside the separation chamber by working with an alternating current which enables only the influence of electrohydrodynamic effects to be studied without any interference from the other transport phenomena, such as electroosmosis and electrophoretic migration.
Abstract: Continuous flow electrophoresis is a process that enables one to purify or to separate proteins on a preparative scale. Its performance depends on a number of transport phenomena that act together to spread the protein stream, which may cause a loss of resolution. This paper is devoted to the study of one of them, called electrohydrodynamics, which is due to the difference existing between the electrical properties of the protein sample and those of its surrounding fluid. An experimental study was performed by using a device that provides visualization of the sample stream inside the separation chamber by working with an alternating current which enables only the influence of electrohydrodynamic effects to be studied without any interference from the other transport phenomena, such as electroosmosis and electrophoretic migration. The experimental results are found to be in very good agreement with the theoretical predictions, which give the sample elongation under different operating conditions, ...

Journal ArticleDOI
TL;DR: In this paper, a mathematical model for in-situ soil vapor stripping (vacuum extraction) is developed and used to examine the effects of a spatially variable pneumatic permeability tensor on the rate of clean-up of a site contaminated with volatile organic compounds.
Abstract: A mathematical model for in-situ soil vapor stripping (vacuum extraction) is developed and used to examine the effects of a spatially variable pneumatic permeability tensor on the rate of clean-up of a site contaminated with volatile organic compounds. Runs are made with low-permeability clay lenses placed at various locations in the domain of interest; also the effect of soil moisture distribution on the soil gas flow field is examined. The model permits one to carry out a sensitivity analysis of the effects of heterogeneity in the permeability, and to develop strategies for minimizing the damaging effects of domains of low permeability.