Characteristic time determination for transport phenomena during the electrokinetic treatment of a porous medium (original) (raw)
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Process Safety and Environmental Protection, 2002
E lectrokinetic phenomena can be employed for a soil decontamination process generally called electroremediation. The ionic species in solution migrate through a porous medium essentially by electro-osmosis and electromigration. The aim of this work was to contribute to knowledge of this process by studying the effect of some operating conditions on the species recovery through an experimental program. The in uence of the electrical eld applied to the medium and the initial concentration of the soil solution, in particular, are studied. First, the electrokinetic transport phenomena are presented. Then, the experimental setup and procedures carried out are described. The set-up consists of a speci c electroremediation cell containing a Na-doped kaolinite medium. Chemical reactions were limited by using the sodium as a tracer. The experimental results show the important coupling existing between solution concentration and the electrical current and their in uence on both the amount and the rate of transported mass. Moreover, the dependence of the electro-osmotic coef cient on the electrical eld applied was demonstrated. The in uence of the solution concentration on the electro-osmosis is not obvious, probably due to the light modi cation of the zeta potential for the system studied.
Electrokinetic phenomena in porous media applied to soil decontamination
IEEE Transactions on Dielectrics and Electrical Insulation, 2000
The feasibility of using electrokinetic phenomena for contaminant removal from lowpermeability porous media is investigated by laboratory experiments and theoretical modeling. The main processes by which contaminant transport takes place under a dc electric field in soil are electromigration, electro-osmosis and electrophoresis. They are particularly effective in fine-grained soils, which is not the case for pressure-driven flushing. Meanwhile, although the results of various studies on a laboratory scale suggest that electrokinetics is a promising technology for water soluble contaminant removal, further research is needed at both laboratory and field scales in order to determine the effectiveness of this technology in situ and in the case of non-soluble organic matter such as heavy hydrocarbons. First, this paper describes the electrochemical processes occurring in soil under an electric field. Then the electro-osmosis phenomenon is more particularly investigated in a theoretical and experimental way. Furthermore, the main previous work on the subject is summarized, and experiments conducted in the laboratory on decontamination by electric field of clay samples polluted by motor oil, are presented.
Soil remediation using an electrokinetic method
2020
Remediation of soils contaminated by heavy metals can be accomplished by subjecting the soil to an electric DC field. The heavy metals that are dissolved will move to either the cathode (mostly) or the anode, depending on their charges. The electrical field also induces electro-osmotic flow that can carry uncharged species. Precipitated and sorbed species will dissolve as the solution is depleted. The acid that is generated at the anode can considerably enhance the dissolution. The acid moves toward the cathode and generates a region with high concentration and mobility of the cationic metals. We present the theoretical basis of the method, the results of some remediation experiments, and the results of some numerical simulations that were used to interpret the experimental results. The remediation experiments are supple mented by determinations of the acid neutralization capacity as well as the sorption capacity and sorption distribution constants for the metal ions. These are esse...
Laboratory Experiment on Electrokinetic Remediation of Soil
Journal of Chemical Education, 2011
b S Supporting Information E lectrokinetic remediation involves the application of an electric field across a volume of soil to transport contaminants to a localized area where they can be effectively extracted. 1À5 Electrokinetic remediation uses the three principles of electromigration, electroosmosis, and electrophoresis: 6 electromigration is the transportation of metallic ions by attraction to the oppositely charged electrode; 7 electroosmosis is the motion of water molecules from the anode to the cathode during electrolysis; 8 and electrophoresis is the movement of charged particles under an electrical current. 9 These factors facilitate movement of contaminant ions to the cathode where the ions can be precipitated and reclaimed. 9 Electrokinetic remediation is a proven technology for soil and water volumes and has demonstrated both promising prospects and challenges. 10À14 A laboratory experiment that introduces students to the basic principles of electrokinetic remediation of soil contaminated by heavy metals is described. This experiment best fits in an analytical chemistry laboratory or environmental chemistry laboratory that trains students in the fundamentals of electrochemistry and its application in environmental remediation. In addition, students gain experience in metal extraction from soil and complexometric titration as a method to measure ion concentration in a solution. This experiment requires two 4-h laboratory sessions. The concept of electrokinetic remediation was previously described in this Journal. 15 These experiments were focused on the destruction of organic wastes in electrochemical cell and classroom demonstration of the transport of inorganic contaminants in silica gel using an electric field based on observation of color changes. Here we discuss an electrokinetic remediation experiment with detailed quantitative analysis of ion transport, based on complexometric titration method. The concentration of Cu 2þ containment in a cell containing sand is measured along with pH variation across the cell. The role of pH gradient development on the electrokinetic remediation process is tested.
Malaysian Journal of …, 2006
Saturated soft soils can be strengthened by several methods such as dewatering or adding suitable chemicals. Introduction of chemicals through electrokinetic (EK) process to strengthen a residual soil was investigated. The results of chemical tests on an elecrokineticallytreated tropical residual soil are presented. The chemical substances used as electrolytes in the experiments were aluminum chloride (Al), calcium chloride (Ca) and phosphoric acid (PA) in addition to distilled water (DW). Four different opened-anode and opened-cathode electrokinetic systems were employed in this study, namely DW-DW, Al-DW, Ca-DW and DW-PA. A constant voltage of 30 V was applied for 168 hours to each of the opened-anode and opened-cathode configuration system. It was observed that the quantities and directions of electroosmotic flows were dependent upon the types of electrolyte. The chemical contents of the treated samples were position dependent and influenced by both the electrolyte types and electroosmotic flows.
Electrochemical remediation of the environment is gaining widespread acceptance due to the mild conditions used, the cleanliness of the electron as a reagent, the easiness for automation, its versatility, etc. In this paper three phenomena are presented at the microscale level, originating from the application of an electric field to a simulated soil sample: a) Demonstration of metal ion migration, b) Demonstration of the creation and movement of an acidic and a basic front, and c) Demonstration of water movement through soil. Keywords (Domain): Laboratory Instruction
Electrokinetics and soil decontamination: concepts and overview (Review)
Journal of Electrochemical Science and Engineering, 2014
Electrokinetic decontamination and extraction have been proven to be one of the most viable, cost effective and emerging techniques in removing contaminants, especially heavy metals from soils for about last five decades. Basic concepts and an overview of the electrokinetic extraction processes and their potential applications in geotechnical and geoenvironmental engineering have been reviewed based on the literature and presented in this paper. Primarily, theoretical and laboratory experimental studies related to electroreclamation of soils are summarised in brief with basic concepts of electrokinetic processes. The paper has been divided into different sections that include history of electrokinetics, background and concepts, modelling, parameter effects, instrumentation, contaminant extraction, field applications, and summary and recommendation. Based on the review it is obvious that the field application of electrokinetic technology to remediate heavy metal contaminated soils /sediments is very limited and site specific. Additional laboratory studies and more pilot-and full-scale information from field applications are critical to the further understanding of the technology and to customize the process in different field conditions.
Electrokinetics for removal of low-level radioactivity from soil
1993
The electrokinetic process is an emerging technology for insitu soil decontamination, in which chemical species, both ionic and nonionic are transported to an electrode site in soil. These products are subsequently removed from the ground via collection systems engineered for each specific application. Electrokinetics refer to movement of water, ions and charged particles relative to one another under the action of an applied direct current electric field. In a porous compact matrix of surface charged particles such as soil, the ion containing pore fluid may be made to flow to collection sites under the applied field. The process was demonstrated in the laboratory to show the viability of the electrokinetic treatment to move "contamination" through soil types of hydraulic conductivity as low as 1f>« cm/s to a directed location. The work presented here describes part of the effort undertaken to investigate electrokinetically enhanced transport of soil contaminants in syn...
ELECTROCHEMICAL SCIENCE Theory of Electroosmosis in Soil
This paper aims to review the electroosmosis in soils. Electroosmosis is movement of a fluid with respect to a solid wall as a result of an applied electric potential gradient. The Helmholtz-Smoluchowski model is widely to describe electroosmosis processes. The rate of elecro-osmotic flow is controlled by the coefficient of electro-osmotic permeability of the soil which is zeta potential dependent. Numbers of researchers have studied the variation of the coefficient of electro-osmotic permeability of soils. These values range from 4.91×10 -06 to 1.57×10 -05 cm 2 s -1 V -1 .