Improvement of the Removal of Heavy Metals from Porous Media by Modified Electrokinetic Remediation

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Throughout this work several aspects of soil electrokinetic remediation (EKR) were explored. In this dissertation several technical aspects of EKR were evaluated. The first one was the effect ofelectrode configuration on the migration of heavy metals, the second was the optimization of pH control during EKR, the third was the use of rotating and reciprocation electrodes in EKR, and finally an estimation of the gas production at the electrodes during EKR was described. The increasing in the amount ofmigrated ions with the angle between the cathodes verified that electrode configuration has a direct impact in the migration of Cu ions. With a 600 angle between the two cathodes, the amount of Cu migrated ions was the highest. This was because the lower pH distribution allowed Cu ions to migrate not only from the anode towards the cathodes but also in the opposite direction. By optimizing pH control during EKR it was possible to extract cadmium from kaolin (98% recovery) and partially precipitate it at the catholyte (63% recovery). The pH level in the catholyte was a function of the relationship between the HN03 concentration, the electrolyte conductivity, and time. It was also proven that reducing the quantity of acid used to control the pH substantially reduced energy consumption. The experiment with the rotating electrodes showed a clear relationship between the cathode rotation speed and the extraction rate of Cd, Cu, Ni and Zn. The highest rates of extraction rate were observed at 1.25 rpm when pH was not controlled and at 0.6 rpm when pH was controlled; by rotating the cathode at 0.6 rpm the extraction rate was increased l.4 times for Cd, 3.2 times for Cu, 2.2 times for Ni, and 2.0 times for Zn. The experiment with the reciprocating electrodes did not show significant changes in the migration of heavy metals in the soil as the experiment with rotating electrodes did. A wide deflection angle of the orientation of the electric field diminished the effect of the reorientation of the electric field on the electromigration of heavy metals in kaolin. A conceptual model was proposed to explain the migration of heavy metals under reoriented electrical field. Regarding the production of H2 and 02 at the membranes it was found a strong dependence on the type of soil. The presence of N03- and S04- in the soil hindered the production of oxygen at the anode. This problem could be solved by the use of a cationic exchange membrane. An estimated maximum of 14.2 m3/month of H2 and 6.1 m3/month of O2 were produced with a silty clayey soil with the use of ion exchange membranes.
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