Electrokinetic Soil Processing Research Articles

Removal of Cadmium from Red Soil by Electrokinetic Method

A constant direct current density of 0.5 mA/cm2 was applied in a laboratory experiment for studing the feasibility of electrokinetic treatment on the removal of Cd from red soils. The result shows that the removal efficiency of Cd was remarkably pH-dependent. The initial Cd concentration was1490 mg/kg and over 79% of Cd was removed from the red soils after 96 hours’ treatment. The energy expenditure was about 77.6 kW.h/m3 and the cost was 42.6 RMB Yuan/m3, which suggest that electrokinetic soil processing is a promising technology for remedying cd-contaminated red soils.

Desorption characteristics of kaolin clay contaminated with zinc from electrokinetic soil processing

A number of bench scale laboratory column tests were carried out using a newly designed and developed electrokinetic cell to investigate the fundamental behavior of zinc-spiked kaolin clay subjected to an electric field. Laboratory investigations focused on (i) zinc migration by the combined effects of electromigration and electro-osmosis and (ii) the electrically induced desorption characteristics of zinc-contaminated kaolin that occurred during processing. The correlations of the applied voltage gradient, electro-osmotic flow rate, and the development of a pH gradient were examined and evaluated. The results showed that the removal efficiency was high during the early stage of processing due to rapid desorption by electrokinetic effects in the cathode region. However, the majority of zinc migrating from the anode was precipitated due to the high pH environment in the cathode region.

Modelling of electro-osmosis in clayey materials including pH effects

A multiscale approach (periodic homogenization) is carried out to model clayey materials behaviour, and especially the coupled phenomena that govern electro-osmotic process. Clays are composed of a charged solid phase saturated by an aqueous electrolyte containing four ionic species Na +, Cl −, H + and OH −. The novelty of this approach consists in the integration of chemical reactions in our description. Thus influence of ionic exchanges that occur at the platelet’s scale can be propagated at the macroscale. In particular, suction effects observed in electrokinetic soil processing can be explained by this approach.

Numerical analysis for electrokinetic soil processing enhanced by chemical conditioning of the electrode reservoirs

A numerical analysis was undertaken for enhanced electrokinetic soil processing. To perform chemical conditioning of the electrode reservoirs, the electrokinetic soil process employed a membrane as a barrier between the electrode reservoirs and the contaminated soil. An alkaline solution was purged in the anode reservoir that was bounded by the membrane. A mathematical model was used for demonstration of pH change and phenol removal from a kaolinite soil bed, the prediction of pH variations in both electrode reservoirs, and the determination of an optimized injection time of the anode-purging solution. The time-dependent dispersion coefficient was employed in consideration of the averaging effect of the velocity profile on a one-dimensional transport. The estimation of pH and phenol profiles in the soil bed reasonably agreed with the experimental data. The simulation revealed that the removal efficiency of phenol from the kaolinite soil could be improved by maintaining pH of the anode solution.

Removal of Heavy Metals from Soils using Enhanced Electrokinetic Soil Processing

In order to remediate contaminated land, a new process of electrokinetic purging of heavy metals from saturated soil is examined by laboratory experiments. Electrokinetic soil remediation is one of the most promising soil decontamination processes as it has high removal efficiency and time-effectiveness in low permeability soils such as clay. Being combined with several mechanisms-electromigration, electroosmosis, diffusion and electrolysis of water, electrokinetic soil processing can remove non-polar organics as well as ionic contaminants. This study suggests that the removal efficiencies for Pb and Cd are significantly influencedby applied voltage and current, type of purging solutions, soilpH, permeability and zeta potential of soil. The removal efficiencies for Pb and Cd were 75–85% for the kaolinite soil and 50–70% for the tailing soil over the duration of 4 days. For heavy metals, their adsorption capacities on the soil surface and mobilities in soil have significant effects on the removal efficiency.

Enhanced Electrokinetic Soil Remediation for Removal of Organic Contaminants

Organic contamination in soil is a common problem at hazardous waste sites. This study investigates the application of enhanced electrokinetic soil processing to remediate soils contaminated with phenol (C6H5OH) and PCP (pentachlorophenol: Cl5C6OH). Electrokinetic soil remediation has high removal efficiency and time-effectiveness in low permeability soils such as clay. This experimental study examined the enhanced process of electrokinetically purging chemicals from saturated soils. Electrokinetic soil processing can significantly remove non-polar organic contaminants with electromigration, electroosmosis, diffusion and electrolysis of water. The removal efficiency is significantly influenced by applied voltage and current, type of purging solutions, soil pH, permeability and zeta potentials of soil. Depending on the original level or load of pollutants and the duration of the removal process, the removal efficiencies of phenol and PCP were higher than 85% over the duration of 4 days and mainly dependent on the electroosmotic flow.

Temperature effect on ionic transport during soil electrokinetic treatment at constant pH

Laboratory experiments and theoretical modelling generally proposed for electrokinetic soil processing consider isothermal conditions at room temperature. Important increases of the soil temperature, due to the Joule effect, have been observed during pilot or field-scale tests. The temperature effect on the transport of ionic species present in the pore solution is investigated when an electric field is applied through the soil mass. Laboratory experiments are run at 20 and 40°C using kaolinite as soil model and one anion and one cation as model pollutants. An adapted methodology (pH control, steady state conditions) allows the measurement and the comparison of the ionic electrokinetic velocities at the two temperatures. Under the conditions developed, the temperature mainly influences the ionic velocities, which increase, for the two ions of interest, when the temperature rises.

Copper Removal from Kaolinite Using Enhanced Electrokinetic Soil Processing

ABSTRACT Recently electrokinetic soil remediation has become one of the most promising soil decontamination process that has high removal efficiencies and time-effectiveness in low-permeability soils such as clay. It is a method that can remove not only ionic contaminants by electromigration but also non-polar organics by electroosmosis. The purposes of this study were to investigate the effects of pH on transport phenomena in soil while removing copper from kaolinite by electrokinetic remediation, and to examine the removal efficiencies under various experimental conditions. The results showed that electrokinetic soil remediation lead to high removal efficiency. Under a direct current density of 1.24 mA/cm2 for 4 days, 87.5% of copper was removed from kaolinite where the pH of the anode electrolyte solution was controlled at 2.5. At a higher pH of anode electrolyte solution, the removal efficiency decreased significantly. The results indicated that the copper removal efficiency was dependent on the amount of hydronium ions transported through soil, and the maximum electroosmotic flow was observed to be 6.79 cm/day. It was concluded that both electromigration and electroosmosis affected the removal efficiency of copper in soils.

Modelling of Decontamination Rate in an Electrokinetic Soil Processing

Modelling of the soil decontamination rate is developed for the case of an electrokinetic remediation run under controlled pH conditions. This model is based on a simple expression of the electrokinetic velocity of ionic species, including some parameters depending on the soil and pollutant species. Laboratory experiments run on kaolinite, using some cations as contaminant models fit well the theoretical calculations.

ELECTROKINETIC SOIL PROCESSING COMPLICATING FEATURES OF ELECTROKINETIC REMEDIATION OF SOILS AND SLURRIES: SATURATION EFFECTS AND THE ROLE OF THE CATHODE ELECTROLYSIS.

Abstract Electrokinetic soil processing is an emerging technology for decontamination of certain radionuclides, heavy metals, or organic species from soils or slurries. Tests reveal that the process efficiencies in partially saturated kaolinite samples (without contaminants) are high, since water supplied at the anode eventually flushed across the specimens and saturated the deposits. Consolidation settlements are expected in the vicinity of anodes in fine-grained soils, even when both electrodes allow ingess or egress of the water. Uranyl ion at 1000 pCi/g could be effectively removed from kaolinite but the removal efficiency decreased close to the cathode due to the high pH in this region. A yellow uranium hydroxide precipitate was collected at the cathode. Thorium ion, even at 300 pCi/g, could not be efficiently removed throughout the cell because of its high adsorptive capacity, facile hydrolysis, and the precipitation of insoluble hydroxide. Methods are required to prevent hydroxide ion formation by the cathode reduction of water and thus enable extraction of these metal species in soluble forms.

Removal of contaminants from soils by electrokinetics: A theoretical treatise

Abstract Feasibility and cost‐effectiveness of electrokinetic soil processing in the remediation of contaminated clayey soils has been demonstrated by bench‐scale studies and limited pilot‐scale studies. A review of the fundamentals controlling the process demonstrates that contaminant transport and removal by electrokinetics are dependent on several factors including electrode reactions, pH and surface chemistry of the soil, equilibrium chemistry of the aqueous system, electrochemical properties of the contaminants and hydrological properties of the soil medium. Chemical, hydraulic and electrical fluxes in electrokinetic processing are formalized. A theoretical model describing reactive solute transport is developed in a coupled system of differential/algebraic equations. Considerations for solutions are discussed. An important factor in the removal of contaminants is the transport of the acid front developed by the anode reaction. The basic equation describing the pH distribution resulting from electrod...