Electroosmotic Permeability Research Articles

Experimental study of electroosmosis and (Cl-) diffusion in fired-clay bricks

Electroosmosis (EO) is considered as a base for methods in drying moist masonry. EO and the other transport mechanisms, namely electromigration and diffusion, that can influence EO in the bricks, were studied in four Danish bricks with different manufacturing years and locations. Brick cubes were cut from each brick type and then saturated in NaCl 0.1 M solution. A cell with four electrodes was used to measure the electroosmotic permeability coefficient using a phenomenological approach based on non-equilibrium thermodynamics. The effective diffusion coefficient for chloride and electromigration coefficient were calculated. Results showed that the EO flux obtained in the bricks did not follow either the magnitude of zeta potential or ionic content present in the bricks. It was observed that there was a correlation between the EO coefficient and the porous structure of the brick, especially with the pore connectivity, since the bricks with higher pore connectivity and, therefore, with higher effective diffusion coefficient had a higher electroosmotic coefficient.

Experimental investigation of dewatering silty tailings using electrokinetic method

Mining and using underground resources demand high water usage, producing significant waste with environmental risks. Methods like electrokinetics prove effective in accelerating dewatering and stabilizing structures. This research provides the results of experimental investigation on dewatering silty tailings obtained from Sungun Tailings Dam (East Azerbaijan, Iran) using the electrokinetic water recovery method. Previous studies primarily examined the electrokinetic process in steady-state flow and saturated soil, with limited exploration of unsaturated soil parameters. In this research, the electrokinetic process in steady-state flow was initially investigated, and the saturated electro-osmotic permeability was determined. Subsequently, experiments were conducted in non-steady-state flow and unsaturated conditions, measuring the influential parameters with soil moisture sensors and tensiometers. Results show that decreasing sample moisture through electro-osmotic flow increases negative pore water pressure. Tailings' electrical conductivity is more influenced by moisture content, with a steeper reduction slope concerning volumetric moisture reduction over time. pH assessments show soil acidity at anode side and alkalinity on the cathode side. Higher applied voltage increasing maximum power consumption. Importantly, the results caution against assuming that higher applied voltage improves the electro-osmotic process, as it may lead to issues such as deep sample cracking; void space creation, interrupted electrical flow, and energy loss.

Electroosmotic permeability in kaolinite and CaCO3 poultice mixtures

Electrokinetic treatment of masonry for desalination or electroosmotic dewatering depends on a poultice, in which the electrodes are placed, which fulfills several purposes. Poultice composed of kaolinite and CaCO3 have been shown to have good workability and high pH buffering capacity. In this work, the electroosmotic (EO) permeability is studied in different kaolinite - CaCO3 mixtures. In addition, the effect on EO of using NaCl as a mixing solution is investigated. A special cell is used to test the EO in the specimens. A phenomenological approach, based on the potential gradient and the flux of solution, was used to calculate the EO flow rate and EO permeability coefficient. Results showed that by increasing the concentration of CaCO3 in the poultice mixture, the EO flow rate decreased and the poultice with 80 % CaCO3 and more did not have any EO flow. Furthermore, the ionic strength in the mixing solution decreases the EO flow rate.

Influence of composite flocculants on electrokinetic properties and electroosmotic vacuum preloading behavior of sludge

In recent years, dredging projects in rivers and lakes have generated large volumes of sludge that exhibit high water content and low permeability. This dredged sludge needs to be treated quickly to reduce its volume, thus reducing transportation costs and environmental impacts. Flocculation combined with electroosmotic vacuum preloading is a new technology for dewatering sludge. At present, the influence of flocculants on the electrokinetic properties of sludge has not been thoroughly studied, and composite forms of these have not been applied in electroosmotic vacuum precompression. Therefore, inorganic flocculant and organic flocculant were combined to form a composite flocculant, which was used in electroosmosis vacuum preloading to increase the water discharge effect of dredged sludge. Based on analyzing the mechanism of flocculants, two kinds of composite flocculants, PAC-APAM and FeCl3-APAM, were configured, and the optimal ratio of inorganic flocculant and organic flocculant in the composite flocculant was determined with a settling column test. The properties, including pore size distribution, electric conductivity, and electroosmotic permeability coefficient, of the sludge mixed with flocculants PAC, FeCl3, APAM, PAC-APAM, and FeCl3-APAM were analyzed by NMR tests and Miler Soil Box tests. In addition, a model test of electroosmotic vacuum preloading treatment of dredged sludge was conducted, and the influences of different types of flocculants on the surface settlement, water discharge, current, pore water pressure, and shear strength of the sludge were compared and analyzed. The results showed that the composite flocculants suggested in this study were able to increase the electroosmotic permeability coefficient of sludge more significantly than single-type flocculants. In situations where electroosmotic vacuum preloading combined with composite flocculants was used to treat sludge, water discharge, and consolidation settlement were larger, and the shear strength of the treated sludge was higher. Compared with FeCl3-APAM, PAC-APAM showed better performance in electroosmotic vacuum preloading.

Mathematical model and experiment investigation on electrodialysis separation process of LiBr from NH3-H2O-LiBr ternary solution in ammonia absorption refrigeration system

The utilization of NH3-H2O-LiBr ternary working fluid is effective to improve the COP of the ammonia absorption refrigeration system (AARS). However, LiBr impairs the absorption of NH3 in the absorber and consequently limits the COP promotion. To address this limitation, electrodialysis (ED) is introduced into AARS to reduce the LiBr concentration in the absorber because it has been widely applied in ion separation from industrial waste solutions. In this study, a simulation model for the NH3-H2O-LiBr ternary solution ED separation process was developed based on the overall mass transfer equation. Experiments were conducted to measure and verify the coefficients in the model. The results showed that the NH3 transport was hard to be separated by ED. For the LiBr, the overall transport number and the overall electro-osmotic permeability were −3.49 × 10−3 kg min−1 A−1 and -1.33 × 10−4 L min−1 A−1. The overall diffusion permeability, overall osmosis permeability, and average resistance were dependent on the LiBr concentrations in the solutions. Moreover, the influences of ED parameters on the LiBr separation were studied using the model and the energy efficiency was applied to evaluate the separation performance. The energy efficiencies were 0.0325 and 0.323 when the membrane pair exceeded 10 and the membrane effective area (Aeff) surpassed 0.0325 m2. The energy efficiency increased with the decrease of current density and the increase of LiBr concentration difference between the two solutions. Moreover, an effective method was built to obtain a set of suitable ED parameters that meet high ED energy efficiency and the LiBr separation requirements in AARS.

The Influence of Inert Fluoropolymer on Equilibrium and Dynamic Hydration Characteristics of MF-4SC Membrane

The influence of the type and amount of an inert component in perfluorinated MF-4SC sulfonic cation-exchange membrane on its equilibrium physicochemical and transport properties has been studied. The exchange capacity, water content, specific conductivity, and diffusion and electroosmotic permeability of two series of MF-4SC membranes obtained by casting from polymer solutions in dimethylformamide with variable contents of inert fluoropolymers have been investigated. A relationship between the equilibrium and dynamic hydration characteristics of the samples has been found as a result of studying water distribution over water binding energies and effective pore radii and the numbers of water transport in an external electric field. The type and content of an inert component in the perfluorinated membrane have been found to affect more significantly the state of water under equilibrium conditions than the electroosmotic water transport.

Evaluation of Electroosmotic Permeability Using Different Models and Investigation of Its Effect on Chromium Removal

Electroosmotic permeability is an important parameter in the electrokinetic remediation (EKR) of heavy-metal-contaminated soil. This study focuses on the applicability of electroosmotic permeability models and the relationship between electroosmotic permeability and heavy metal removal efficiency. The electroosmotic permeability models of ion hydration and the ion hydration–friction model were developed and investigated. Moreover, 11 EKR experiments were conducted in the laboratory to remediate Cr6+-contaminated soil. The results showed that the electroosmotic permeability calculated by the H-S model was 3–7 times larger than the measured value, and it was 65–90% of the measured value as calculated by the ion hydration model. However, the ion hydration–friction model, which combined the ion hydration and Spiegler friction theories, predicted the electroosmotic permeability more accurately compared to the H-S and ion hydration models. In addition, the parameters in the ion hydration–friction model were determined easily, meaning that the ion hydration–friction model is of good applicability. The experimental results showed that the soil properties changed and the electroosmotic flow rate decreased when acid was added to the soil, and the Cr6+ removal efficiency improved.

A new method for assessment of electro-osmotic permeability through the integration of theoretical and experimental ion flux in electrokinetic processes

Electrokinetic (EK) technology is promising for removing heavy metals from contaminated unsaturated soils. It is crucial to accurately determine the unsaturated electro-osmotic permeability for predicting the efficiency of EK treatment, optimizing treatment strategies, and accurately predicting the distribution of contaminant concentrations. However, the current approach of estimating unsaturated electro-osmotic permeability, which involves measuring effective voltage, drainage volume, and performing exponential fitting, fails to address the issue of uneven voltage gradient distribution during EK treatment. Herein, a novel method was presented for estimating the electro-osmotic permeability of unsaturated porous media. This method quantifies the electro-osmotic flow in an unsaturated porous medium by considering the difference in mass-transfer efficiency (MTE) between real (with electro-osmotic flow) and hypothetical cases (without electro-osmotic flow). This difference serves as a metric for estimating the electro-osmotic permeability. Results revealed a linear relationship between the electro-osmotic permeability and the product of volumetric moisture content and tortuosity, with the slope related to the ionic mobility of target ions, hypothetical and actual MTE. To validate this method, hexavalent Cr (Cr(VI)) was selected as the target contaminant and six EK experiments were conducted with varying initial volumetric moisture content. The feasibility of the method was evaluated by fitting the results of these experiments to obtain the specific slope of the porous medium used. Compared to the existing effective voltage–drainage volume–exponential fitting method, the proposed method offers several advantages. First, it effectively addressed the issue of nonuniform voltage distribution during EK treatment in the unsaturated porous medium. Second, it overcame the problem of a nonzero electro-osmotic permeability at zero volumetric moisture content in the exponential empirical formula. Third, the proposed method was based on theoretical derivations instead of relying solely on empirical fitting. Finally, the proposed method does not require a prior estimate of the saturated electro-osmotic permeability of the porous medium.

A Pore-Scale Physical Model for Electric Dewatering of Municipal Sludge Based on Fractal Geometry

Water in municipal sludge has an electric double layer (EDL), and can be rapidly removed via electroosmosis. However, the understanding of the physical mechanisms of electroosmosis is limited owing to the complex pore structure of sludge porous media, which may restrict the development of electric dewatering (EDW) technology. In this study, the sludge microstructure was measured using the computerized tomography technique and quantitatively characterized using fractal geometry. A new pore-scale physical model for the electroosmotic flow through sludge porous media was developed based on the EDL theory, and the analytical expressions for the electroosmotic flow rate and permeability coefficient were determined. The proposed fractal pore-scale model for electroosmotic flow was validated by comparing it with the measured electroosmotic flow rate using a self-designed EDW device for municipal sludge composed of a hydraulic system and applied electric field. The results show that the electroosmotic flow rate of sludge porous media depends not only on the applied electric field, but also on the sludge microstructure including porosity, maximum pore size, and pore and tortuosity fractal dimensions. However, the correlation between the electroosmotic flow rate and the voltage gradient was usually nonlinear, and became linear only if the tortuosity fractal dimension equaled to one (straight flow path). The electroosmotic permeability coefficient increases with an increase in porosity; however, it is lowered by the increased pore and tortuosity fractal dimensions under a certain porosity. The electroosmosis phenomenon can effectively remove part of the interstitial water and surface water in sludge porous media, and the proposed electroosmotic physical model provides a useful theoretical basis for the development of EDW technology for municipal sludge.

Theoretical and Experimental Study of Joint Osmotic and Electroosmotic Water Transfer through a Cation-Exchange Membrane.

Using the previously developed cell model of a charged membrane and the principles of linear thermodynamics of irreversible processes (the Onsager approach), exact and approximate (in the case of an ideally selective membrane) analytical formulae for calculating the osmotic and electroosmotic permeability of the membrane in aqueous solutions of 1:1 electrolyte at constant electric current density and concentration gradient were suggested. The formulae have been successfully verified by our own experimental data for the extrusion cation-exchange membrane MF-4SC p.29 in NaCl solution up to concentrations of 3 M. The contribution of electroosmotic and osmotic water fluxes to the total water transport through the mentioned individual perfluorinated ion-exchange membrane under conditions close to the process of electrodialysis concentrating was experimentally estimated. The cases of co- and counter-directed osmotic and electroosmotic water fluxes are studied. A good correspondence between theoretical and experimental results was obtained, which made it possible to determine the physicochemical parameters of the electromembrane system (the diffusion coefficients of individual ions and the coefficient of equilibrium distribution of electrolyte molecules in the membrane matrix, the characteristic exchange capacity of the cell model). The achieved results make it possible to fully characterize existing and promising types of ion-exchange membranes based on the developed cell model of a charged membrane.

Stabilisation of a clay soil by injection of different ions

In this research study the effects of calcium and magnesium ions on stabilisation of a clay soil were studied by conducting a set of laboratory tests. A special apparatus was employed for carrying out the tests under constant voltage and time. During the tests, solutions of calcium chloride (CaCl2) or magnesium chloride (MgCl2) with different concentrations were injected into the soil samples. The electro-osmotic and electrokinetics methods were used for stabilisation of the soil and the results were compared with each other. In the electro-osmotic technique, distilled water was used as pore fluid, but in the electrokinetic method, calcium chloride or magnesium chloride solutions with various concentrations were injected into the pores of soil samples. The results revealed an increase in strength of the soil in both methods. In the electrokinetic method, the amount of increase in strength was a function of concentration of the solution that was used. The results also indicated that a solution of calcium chloride is more effective in increasing the strength, discharge flow and electro-osmotic permeability than a magnesium chloride solution at various concentrations. In addition, the variations of these properties are a function of the concentration of the given solution.

Comparative Study of Electroosmotic Permeability of Ion Exchange Membrane by Volumetric and Gravimetric Methods

Comparative Study of Electroosmotic Permeability of Ion Exchange Membrane by Volumetric and Gravimetric Methods

Electro-osmotic permeability model based on ions migration

Electro-osmotic permeability model based on ions migration

Moisture migration and electric distribution of unsaturated clay under electro-osmosis with carbon fiber tape as electrode

Electro-osmosis is a promising technique for controlling the moisture content of a subgrade. The moisture content increases when subjected to groundwater, rainfall, winter freeze, and spring thaw, decreasing the modulus and pavement life. In this study, laboratory experiments were conducted to investigate the effect of electro-osmosis on moisture control of compacted subgrade. A special apparatus was constructed to perform one-dimensional electro-osmosis experiments based on two types of electrode materials, three levels of supply voltages, and three types of dry densities. The feasibility of electro-osmosis on moisture control of subgrade and other influential factors was investigated. The experimental results show that electro-osmosis reduced the moisture content of compacted subgrade clay by 9.7–15.6%, ensuring that the saturation degree of subgrade was close to the optimum value. The moisture migration rate in unsaturated soil decreased significantly during electro-osmosis, and the relationship between electro-osmotic permeability and moisture content could be described by an exponential function. The two types of electrodes used are copper and carbon fiber tape (CFT). It was observed that the CFT electrode has a better contact performance with soil compared to the copper electrode, exhibits electrochemical corrosion resistance, and provides a voltage loss of 9.3–34.2%. However, an increase in supply voltage doesn't necessarily improve the performance of electro-osmosis because of serious voltage loss at the anode electrode-soil interface; hence, proper voltage is more effective and energy-saving. For future research, the electrode-soil contact can be improved to reduce the wastage of energy.

Experimental investigation of influence of calcium ion (Ca2+) and pH on the shear strength of Taipei silty clay

ABSTRACT Electroosmotic chemical treatment is a technique for improving the strength of soft soil. This study examined the effects of injection duration, Ca2+ions concentration, and pH distribution on the shear strength of Taipei silty clay. Experimental tests were conducted by injecting calcium chloride (CaCl2) solution into Taipei silty clay during electroosmosis for various durations. After testing, the water content, pH, Ca2+ ions concentration, injection volume, drainage volume, and cone resistance were measured. The results indicated that the injection volume, drainage volume, Ca2+ ions concentration, and strength of the silty clay were low compared with the same measurements for kaolinite because Taipei silty clay consists mainly of illite, which results in the soil having a lower coefficient of electroosmotic permeability. The treatments of 12–48 h were insufficient for improving soil strength. However, the 120-h 1.5 M C120 injection treatment resulted in a moderate increase in soil strength due to consolidation and Ca2+ ions precipitation. By comparing our results with those of studies on kaolinite, we established a suitable injection procedure, which includes solutions for treatment duration and concentration of CaCl2 solution (i.e. 1.5 M C48, 0.2 M C120, and 0.75 M C120).

A hydro-mechanical coupled solution for electro-osmotic consolidation in unsaturated soils considering the decrease in effective voltage with time

For electro-osmotic consolidation in unsaturated soils, coupled deformation, inconsistent changes in hydraulic conductivity and electro-osmotic permeability with matric suction, and a decrease in effective voltage with time occur simultaneously. To consider all of these processes, an analytical solution was proposed. The time-stepping method was adopted in the calculation of the solution to depict the nonlinear change in shrinkage deformation with matric suction. The accuracy of the proposed analytical solution was validated by comparison with results from laboratory tests and from a previously presented solution without considering coupled deformation. Then, a parametric study was conducted. The results indicate that the dissipation of the pore water pressure is slow when considering coupled deformation, but a large volume of water is discharged in the end, especially for soils with a large volumetric shrinkage index Cm. A larger final negative pore water pressure and discharged water can be predicted by considering the inconsistent changes in hydraulic conductivity and electro-osmotic permeability. Finally, with the consideration of the decrease in effective voltage over time, both the maximum negative pore water pressure and final drainage decrease, which is consistent with field observations.

Donnan-ion hydration model to estimate the electroosmotic permeability of clays

Electroosmotic permeability is a soil parameter that is fundamental for designing and implementing environmental remediation, dewatering, or soil stabilization processes. It presents a narrow range of variation compared to hydraulic permeability, so that in many occasions no experimental tests are carried out to determine it. Traditionally, the Helmholtz–Smoluchowski equation has been used to estimate electroosmotic permeability, despite having several drawbacks that make it difficult to apply, as it was deduced for large capillaries (unusual in clays) and its dependence on the zeta potential of the soil, difficult to measure and dependent on a wide variety of factors. The present work describes a semi-empirical formulation that allows the estimation of the electroosmotic permeability as a function of the specific surface area and the total void ratio and is based on the Donnan equilibrium and the ion hydration models. The parameters for modeling are calibrated and validated with experimental data, obtaining better results than those given by the Helmholtz–Smoluchowski model. In addition, the expected trends in the behavior of clays that can be found in the literature are obtained in a quantitative and consistent manner for different types of clays with variable water content and pore water salinity.

Electro-Osmotic Behavior of Polymeric Cation-Exchange Membranes in Ethanol-Water Solutions.

The aim of this work is to apply linear non-equilibrium thermodynamics to study the electrokinetic properties of three cation-exchange membranes of different structures in ethanol-water electrolyte solutions. To this end, liquid uptake and electro-osmotic permeability were estimated with potassium chloride ethanol-water solutions with different ethanol proportions as solvent. Current–voltage curves were also measured for each membrane system to estimate the energy dissipation due to the Joule effect. Considering the Onsager reciprocity relations, the streaming potential coefficient was discussed in terms of ethanol content of the solutions and the membrane structure. The results showed that more porous heterogeneous membrane presented lower values of liquid uptake and streaming potential coefficient with increasing ethanol content. Denser homogeneous membrane showed higher values for both, solvent uptake and streaming coefficient for intermediate content of ethanol.

Feasibility of Ion Exchange Membranes to Control pH during Electro-Osmotic Consolidation

Abstract Electro-osmosis is an established method of consolidating soft fine-grained soils. Its efficiency is controlled by the electrical resistance of the soil-electrode system. Because of an increase in soil electrical resistance during treatment, its cost efficiency is reduced, limiting the widespread use of this technique, especially in developed nations. One of the main causes of electrical resistance is hydrolysis of water molecules around the electrodes. The acidification of the anode, in particular, reduces the negative surface charge of clay particles and, thus, the zeta potential. According to the Helmholtz-Smoluchowski model, the zeta potential is directly proportional to the electro-osmotic permeability. This article studies the use of ion exchange membranes to assess their ability to prevent flow of hydrogen ions into the soil. The test with an anion exchange membrane showed minimal change of the pH in the soil around the anode compared to a control, which is better for electro-osmotic consolidation.

Stabilisation of a clay soil by ion injection using an electrical field

A programme of experiments was conducted to study the use of the electro-kinetic technique to transport a stabilising chemical agent through a clay soil. The experimental tests were undertaken on a clay soil in a special apparatus by applying a constant voltage gradient across the sample to introduce a solution of calcium chloride (CaCl2) with different concentrations in the soil. The variations of shear strength across the sample resulting from the electro-kinetic process were determined. The experiments were conducted in two groups. In the first group, the electro-osmosis method was used for soil samples with distilled water. In the second group, the electro-kinetic technique was applied to the soil to transport the solution of calcium chloride with varying concentrations through the pores in the soil. The results showed that the strength of soil increased for both groups and the amount of increase in the second group was dependent on the concentration of calcium chloride injected into the soil. The injection of this stabiliser also increased the electric current and electro-osmotic permeability.