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Electrokinetics is a common and practical method for contaminant removal from fine grain soils. In spite of several researches performed on the factors affecting the application of electrokinetics method for contaminant removal from soils, there are still extensive attentions of researches on the influence of soil components on the efficiency of this method upon contaminant removal. The main objective of this research is to investigate on the impact of carbonate elimination and contaminant concentration on the Pb removal from carbonated kaolinite in electrokinetics process. To achieve this objective a natural kaolinite sample which had 4% natural carbonate and a carbonate eliminated kaolinite were laboratory contaminated with 5 and 20 cmol/kg-soil of lead nitrate. After achieving equilibrium, the laboratory contaminated samples were dried in oven at 40 centigrade temperature for 96 hours. Then, 27% water was added to samples as initial water content. To achieve homogeneous distribution of water content, the sample was kept in a plastic bag for 24 hours. Then sample was passed through #10 sieve to have a more homogeneous sample. Finally, the soil sample was compacted in five layers at dry density of 1.7 g/cm3 in the electrokinetics cell. Then, the electrokinetics method was performed on these samples for contaminant removal. Electrokinetics experiments performed for a 240 hours period. After the end of experiment, the soil sample was taken from cell and sectioned in 5 slides. Each slice was analyzed for water content, soluble and adsorbed contaminant. In addition to electrokinetics experiment, buffering capacity test was performed by titration of soil sample with nitric acid. For this purpose, the diluted nitric acid in 1:10 soil:acid solution was added to sample. The soil solution sample kept on the shaker for 96 hours. After equilibrium the pH of soil solution was measured. This experiment was performed for different concentration of nitric acid. The final type of experiment include batch equilibrium experiment in which different concentrations of 5, 10, 20, and 30 cmol/kg-soil of lead nitrate was prepared. Then 20 milligram of each solution was added to 2 grams of kaolinite sample. After the shaking period and centrifuging the sample, the pore fluid was analyzed to measure the soluble and retained heavy metal. The results of experimental study indicate that the reduction of carbonate in carbonate rich kaolinite and an increase in contaminant concentration causes a reduction in soil buffering capacity. This means that as the concentration of carbonate in soil sample decreases, one faces with a reduction in contaminant retention capacity of soil. In addition, in such a case a reduction in pH happens which consequently enhances the contaminant removal from soil. Furthermore, carbonate elimination causes an increase in contribution of electro-osmosis on soil improvement which is followed by water content variation and consolidation of soil.

Keywords: Electro-Osmosis, Electrokinetics, kaolinite, Carbonate, Contaminant Removal

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