FUNDAMENTAL FORMULATION OF ELECTROKINETIC EXTRACTION OF CONTAMINANTS FROM SOIL

Electro-osmosis and ionic migration are the basic cleanup mechanisms i n the electrokinetic extraction of contaminants from fine-grained soil s. These are coupled flows as the flows of fluid and contaminants are driven by an externally applied electrical gradient. Moreover, other e lectrochemical reactions will occur simultaneously during the process. The most pronounced effect is the generation of pH gradient in the so il. The change of pH in the pore fluid can have a significant impact o n the degree of sorption and desorption of chemicals on soil particle surfaces, complexes formation and precipitation of chemical species, a nd dissociation of organic acids; thus affecting the feasibility and e fficiency of the cleanup technique tremendously. An attempt is made to formulate the coupled flows of ionic contaminants and the resulting c hange of pH in the pore fluid during the electrokinetic extraction pro cess. The coupled flows of contaminants are formulated by the formalis m of nonequilibrium thermodynamics. The pH is determined as a function of time and space by maintaining electrical neutrality throughout the system all the times. A numerical model NEUTRAL is developed to simul ate the processes. The good agreement between computed and experimenta l results published in the literature indicates that the approach is a valid step toward a better understanding of the physics and chemistry involved during electrokinetic treatment of contaminated soils.