# Decontamination of zinc-polluted kaolinite with electrokinetic process.

 Titre: Decontamination of zinc-polluted kaolinite with electrokinetic process. Auteur: Shariatmadari, Nader. Résumé: Electrokinetic treatment is a promising technology to remove contaminants from clayey soils. The interaction of various processes that take place simultaneously is yet to be understood, in order to better predict the efficiency of the process in a variety of soil-contaminant situations. The electrokinetic process refers to movement of water, ions, and charged particles relative to one another under the action of an applied direct current electrical field. In this research electrokinetic experiments are conducted on saturated kaolinite specimens loaded with zinc to investigate the efficiency of contaminant removal and energy expenditure during the treatment. The effect of various electrical fields on electrokinetic remediation was studied by application of constant electrical potential and current with different intensities across the specimens. The treatment duration in various tests ranged from 3 to 73 days. Electroosmotic flow, electrical gradient variation, pH, conductivity, and zinc concentration of the anolyte, catholyte and pore solution across the specimen, were measured. The calculated electroosmotic coefficients of permeability (k$\sb{\rm e}$) were within range of literature values but were not constant over time. The migration of zinc within the soil from the anode toward the cathode was significant. Almost all transported zinc was accumulated in a thin layer of soil near the cathode chamber due to high pH environment. Formation of this low conductivity layer results in higher potential drop in this region and increase in energy expenditure. In order to reduce the amount of precipitation and increase the removal of zinc in to the cathode chamber, pH enhancement technique with application of acetic acid was employed. Neutralizing the pH in the cathode chamber (pH = 6) did not lead to increase in removal efficiency of heavy metal. However, controlling the pH at lower level (pH = 4) at the cathode compartment was successful for removal of 60% zinc from soil. Effect of the position of the reference electrode on energy consumption was also studied. Experiments under controlled electrical potential field, with positioning the reference electrode close to the cathode, indicated reasonable reduction of energy expenditure during the treatment. The principal conclusions were as follows: (1) The electrokinetic technique is effective and economical for short term remediation. (2) The constant potential electrical field demonstrated lower energy consumption compared to the constant current condition, both in short term and long term remediation. (3) Controlling the pH to a value less than 4 in the cathode compartment, successfully flushed the zinc out of the sample to the catholyte. (4) Placement of the reference electrode close to the cathode (working) electrode, decreased the amount of energy expenditure significantly. Date: 1997 URI: http://hdl.handle.net/10393/4454

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