Electrodialytic soil remediation is a newly developed method for removal of heavy metal from polluted soil. The method is based on a combination of the electrokinetic movement of ions in soil with the principle of electrodialysis. The principle was tested in six experiments using laboratory cells on a copper-polluted Danish loamy sand. The duration of the experiments was varied, and the development of concentration profiles in the soil after the remediation was investigated for two different dc currents (0.1 and 0.2 mA/ cm 2 of soil). The rate of Cu removal was about doubled when doubling the current. It was found that Cu content was reduced to a level below 100 mg of Cu/kg of dry soil in the section closest to the anode and that the Cu removed was accumulated in the next section in the direction of the cathode. The accumulation zone was moving in the direction of the cathode during the application of an electric current. When the remediation ended, all Cu could be found in the cathode compartment, and results showed that it was possible to decontaminate the soil from 1360 to below 40 mg of Cu/kg of dry soil.

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Electrodialytic remediation of heavy metal polluted soil is a method which combines the technique of electrodialysis with the electromigration of ions in the polluted soil. Results from laboratory-scale remediation experiments of soil samples from three real contaminated sites with di †erent heavy metals are presented. In the three cases it was possible to mobilize and reduce the amount of the pollutants in the soil. The pollutants were (1) copper and chromium, (2) mercury and (3) copper, lead and zinc. For a loamy sand polluted with copper and chromium it was possible to decontaminate the soil to an extent lower than the recommended critical values for metal concentration in soil. Parameters that were identiÐed as important for the efficiency of the electrodialytic remediation method were pH in the soil, lime content and speciation of the heavy metal.

In this study a pilot plant for electrodialytic treatment of municipal solid waste incineration (MSWI) air pollution control (APC) residue was tested and proposed as a treatment method which can lead to reuse of this otherwise hazardous waste. The pilot plant was developed based on a design that is adapted from conventional electrodialysis, e.g. used in desalination of solutions. The APC residue was treated in a suspension (8 kg APC residue and 80 L tap water) and circulated through an electrodialytic (ED) stack consisting of 50 cell pairs separated by ion exchange membranes. A direct current was applied to the ED stack for removal of heavy metals (As, Ba, Cd, Cr, Cu, Mn, Ni, Pb, Zn) and salts (Cl, Na, SO 4 ) from the APC residue suspension. Different tank designs for mixing the APC residue suspension were tested as well as changing experimental conditions. A part of the raw experimental APC residue was carbonated by reaction with CO 2 under moist conditions prior to electrodialytic treatment. The carbonation alone reduced the leaching of some heavy metals. However, it was not sufficient to reduce the heavy metal or salt leaching to meet the Danish Category 3 guideline levels for waste material reuse and could not stand as a treatment method alone. Leaching of both heavy metals and salts were significantly reduced by the electrodialytic treatment for both the raw and carbonated APC residue. In the electrodialytically treated carbonated APC residue only Cr exceeded the Category 3 levels while in the electrodialytically treated raw APC residue both Pb and Zn leaching exceeded the Category 3. Optimization of the electrodialytic upgrading method is necessary to meet the Category 3 levels for all heavy metals. Removal of Na and SO 4 to below the Category 3 leaching levels were obtained in all the experiments. Cl removal was not sufficient in all experiments even if up to 1 kg of Cl was removed, the optimal conditions for Cl removal was a constant current of 5 A over the ED stack. The results of this study suggest that, with some optimization, electrodialytic upgrading, possibly in combination with carbonation, could be used as a treatment method for MSWI APC residue.

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Electrodialytic remediation (EDR) was used to remove Cu, Zn, Pb, and Cd from contaminated harbor sediment. Extraction experiments were made prior to EDR, and the metal desorption was pH dependent but not liquid-to-solid ratio (L/S) dependent. The desorption order was Cd > Zn > Pb > Cu. Electrodialytic experiments were made with HCl as desorbing agent in a sediment suspension, which was stirred during EDR. Effects of different current strengths and L/S ratios on the heavy metal removal were investigated on wet and air-dried sediment. The effects of drying the sediment were negligible for the removal of Cu, Zn, and Pb, probably due to oxidation of the sediments during stirring. Contrary, Cd removal was lower in the wet sediment as compared to the air-dried. The heavy metal removal was influenced by higher current strengths and varying L/S ratios. The highest removal obtained was in an experiment with dry sediment (L/S 8) and a 70 mA applied current that lasted 14 days. These experimental conditions were thereafter used to remediate more strongly contaminated sediments. Regardless of the initial heavy metal concentrations in the sediments, 67-87% Cu, 79-98% Cd, 90-97% Zn, and 91-96% Pb were removed.

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