REDOX CONDITIONS DURING ELECTRODIALYTIC SOIL REMEDIATION OF HEAVY METALS

Key words: electrokinetic treatment, heavy metals, redox potential, pH

During the electrodialytic remediation (EDR) of soil polluted with heavy metal, the heavy metals change their type of binding (Ottosen et al., 1997). This happens as a result of changes in soil conditions caused by the applied dc current. Important roles are played by the heavy metals involved, changes in pH, and ion concentra- tion, but also the amount of the Fe-oxides, sizes of the clay fraction, organic mate- rial, and carbonates, and possible changes in oxidation state and temperature play important roles. The principle of electrodialytic soil remediation is shown in Fig. 1, where Cu2+, moving towards the cathode, and Cr042", moving towards the anode, indicate the polluting heavy metals. An anion-exchange membrane at the anode compartment (I) and a cation-exchange membrane at the cathode compartment (V) separate the soil (III) from the electrodes. Protones and oxygen are produced at the anode, and hydroxide ions and hydrogen are produced at the cathode, due to the electrode processes. A more detailed description is found in Kliem et al. 1999.