| The electrokinetic remediation of heavy metal-contaminated soils was studied through experiments and a computer model. The research addressed important issues involved within electrokinetics, such as: pH-dependent adsorption of contaminants to the soils surfaces, surface potential dependence on the aqueous phase properties, presence of reducing or oxidizing agents in the soils, presence of carbonates in the soils, presence of multiple metal contaminants in the soils, and contaminant aqueous speciation. This study was accomplished by (1) performing controlled electrokinetic bench-scale experiments on two types of clayey soils (kaolin and glacial till) contaminated with three heavy metals, namely, chromium, nickel, and cadmium, (2) performing extensive laboratory batch experiments to study surface and contaminated water interactions and modeling these interactions, (3) conducting a systematic geochemical assessment of metal transport during electrokinetic remediation, and (4) developing and validating a 1-D theoretical model for multi-component transport of reactive species under an electric field taking into consideration the geochemistry of the contaminants and the significant geochemical changes that develop during electrokinetics.; The findings revealed that during the electrokinetic remediation technique, the electroosmotic flow, and the direction and extent of contaminant removal depended on the polarity of the contaminant, the type of soil and its buffering capacity, the applied voltage gradient, and the treatment duration. This study showed that the extent of migration of the contaminants was strongly dependent on their initial speciation prior electrokinetic treatment. Higher rates of contaminant migration occurred when the contaminants initially existed in an aqueous form. It also showed that the kaolin particle zeta potential, and its surface charge influence the aqueous phase properties, consequently affecting the electroosmotic flow and contaminant adsorption.; The electrokinetic extraction model that was developed in this study was relatively successful in predicting many of the electrokinetic system relationships. Meaningful predictions for the pH profile, metal profiles, and flow were made. The program can simulate contaminant transport and chemical interactions. The main conclusion drawn from the model results was that a persistent zone of high pH was developed in the kaolin soil near the cathode during sustained electrokinetic testing. The effect of this high pH zone was to limit further migration of nickel and cadmium. Techniques that prevent the formation of this zone and the precipitation of species are essential for implementing the electrokinetic remediation of heavy metals. |
