Electrokinetic Barriers Research Articles

Performance evaluation of one dimensional electrokinetic barrier subjected to saltwater intrusion: A laboratory scale study

Performance evaluation of one dimensional electrokinetic barrier subjected to saltwater intrusion: A laboratory scale study

Analytical solutions for one-dimensional contaminant ion transport through electro-kinetic barriers

To prevent contaminant ions from spreading over the adjacent environment, it is of great interest to consider using electro-kinetic barriers to counteract contaminant transport through the combined effects of electro-osmosis and electro-migration. In this study, considering the bottom surface as a Cauchy boundary or a Drichlet boundary condition, two analytical solutions are proposed to predict the contaminant ion transport in the electro-kinetic barrier. Analytical solutions are verified against experimental data and numerical solutions from the previous literature. Subsequently, the proposed analytical solutions are used to investigate the effects of average applied voltage gradient, barrier thickness, diffusion coefficient, retardation factor and electro-osmotic conductivity on the transport of contaminant through the electro-kinetic barrier. The results show that the steady state base contaminant concentration decreases with the increase in average voltage gradient and barrier thickness. Additionally, the logarithm of the final stable base contaminant concentration changes linearly with the average applied voltage gradient and barrier thickness. For the contaminants with a high diffusion coefficient, a larger average voltage gradient should be applied to improve the electro-kinetic effects. Clayey soils with high sorption capacity and relatively high electro-osmotic conductivity are the suggested material choice for constructing compacted soil liners within the electro-kinetic barrier, due to distinct advantages in contaminant migration prevention. Finally, a dimensionless factor is introduced to uniformly describe influences on the base relative concentration, and it can be used as an important parameter for the design of an electro-kinetic barrier.

Regulation of clay particles charge for design of protective electrokinetic barriers

Coupled electrokinetic protective reactive barriers (PRB) are considered as a perspective technology for the treatment of contaminated groundwater. Design of PRB is directly connected with a problem of barrier material choice. Clays can be considered as an appropriate material due to high adsorptive properties and relative cheapness. The barrier internals are formed by clay surface charge properties. We revealed that acidic and alkaline treatment of clay is an effective way to affect its protective properties so that clay can be used to treat various pollutants. Surface charge and electrokinetic properties of clays were characterized by point of zero charge (p.z.c.), point of zero net proton charge (p.z.n.p.c.) and ζ-potential at different pH. Suspensions of 3 main clay types were studied by microelectrophoresis and potentiometric titration methods. At pH > p.z.n.p.c. clayey barrier adsorbs predominantly cationic toxicants and at pH < p.z.c. – anionic ones. The barrier is seemed to be the least effective in pH range between p.z.c. and p.z.n.p.c. Given the physicochemical and electrokinetic parameters, the most efficient clays for barrier design are Cambrian illite and all montmorillonite clays.

A model for coupled electro-hydro-mechanical processes in fine grained soils accounting for gas generation and transport

A theoretical and numerical model is developed for the quantitative analysis of coupled processes taking place in active waste containment systems, such as electrokinetic barriers or fences, in which a low intensity DC current is circulated across the clay barrier to move polar and non-polar contaminants. A novel feature of the proposed approach is the allowance for the presence of air in the pore space. Under unsaturated conditions, all transport coefficients involved in the electrokinetic process are strongly dependent on the degree of saturation of pore liquid. In order to assess the predictive capability of the proposed theory and to appreciate the impact of gas production at the electrodes, a series of numerical simulations of simple one-dimensional electrokinetic tests have been performed. The results of the simulations compare reasonably well with data obtained from laboratory experiments performed on an illitic clayey silt. The numerical results indicate that the impact of gas production at the electrodes can be significant, even in low-intensity and short-duration treatments.

Preliminary tests of an electrokinetic barrier to prevent heavy metal pollution of soils

Sardinia has to deal with significant environmental problems related to heavy-metal contamination, mainly located at its abandoned mining districts. In particular, acid mine drainage management and groundwater pollution are typical problems associated with mining activities which constitute a serious threat to human health. To prevent contaminant spread over the adjacent environment, it is of great interest to consider using an electric field as a containment fence to counteract pollutant transport. In this application, contaminant transport due to a hydraulic gradient driving force is prevented by the combined effect of electro-osmosis and electro-migration. Although there are other alternative containment technologies, the electrokinetic fence offers many advantages, as it is easy to operate, there is a minimal exposure to the operating personnel and it is likely to be effective for a wide range of contaminants. In this work, both one-dimensional (1D) and two-dimensional (2D) tests have been carried out. In the 1D tests, the efficiency of an electrokinetic barrier to prevent cadmium from polluting an uncontaminated sample was investigated; soil pH, metal concentration and current intensity have been monitored; results indicate that the barrier can prevent or significantly reduce heavy-metal contamination from spreading against a hydraulic gradient of 7. In 2D tests, two rows of electrodes inserted in a horizontally flat soil tank were used to generate an electric field. It was found that an electric field of 125 V m −1 was sufficient to prevent significant copper incursion from a contaminant flow under a hydraulic gradient of 1.3.

Electrokinetic barrier to prevent subsurface contaminant migration: theoretical model development and validation

The application of a DC electric field down gradient to the contaminated zone in the subsurface can create an electrokinetic barrier. The electrical potential gradient causes the movement of ions which in turn imposes a viscous drag on the pore water. In clayey soils, this viscous drag can generate a high enough pore water pressure capable of counteracting the ground water gradient. This phenomenon can be used effectively as a barrier to prevent contaminant migration. A finite element model was developed to simulate the contaminant migration in soil under coupled hydraulic, electrical and chemical gradients. The model is also capable of predicting the associated changes in the soil like the pore water pressure, pH and voltage gradient as a function of time and distance from the electrode. This model was validated using the experimental data presented by Yeung [Yeung, A.T., 1990. Electro-kinetic barrier to contaminant transport through compacted clay. PhD Thesis, University of California, Berkeley, 260 pp.]. The results indicate very good agreement between the experimental and simulated results. The model predications show that when the anode is placed down gradient of the cathode, the cation migration could be completely arrested. However, the anions were found to move faster in the direction of the ground water flow and reduce the effectiveness of the barrier. This could be avoided by carefully designing the placement of the electrodes. If the contaminant of interest is either a cation or an anion, a simple double row of anode and cathode electrode arrangement could serve as an effective barrier. On the other hand, if the contaminant includes both anions and cations, then a triple-row configuration of electrodes need to be implemented. The model simulations could be used to assess different electrode configurations and current application strategies.

A New Apparatus for the Evaluation of Electro-Kinetic Processes in Hazardous Waste Management

Abstract Possible uses of electro-kinetics for hazardous waste site remediation are being investigated. This paper describes a new apparatus which has been specifically designed, fabricated, and assembled to evaluate the viability, feasibility, practicality, and potential costs of these conceivable techniques experimentally. Results of studies on the existence of electro-osmotic flow in compacted clay and the electro-kinetic barrier to contaminant transport are used to illustrate the types of information that can be obtained by the apparatus.