f Electrokinetic treatment of cadmium spiked clays. influence of the heterogeneities.

Recently, attention has focused on electrokinetic techniques that make it possible to move and extract contaminants from fine-grained soil under an electric field (Figure 1). The application of a constant electric current has several effects: (1) electrolysis of water, plating reactions and gas formation occur at the electrodes. H+ is produced at the anode, and OH- at the cathode (2) the electric potential difference leads to electroosmosis , the pore water flow is toward the cathode, since most soils have a negative surface charge (3) the electric field initiates electromigration of species available in the pore fluid and of those introduced at the electrolytes. These phenomena change the chemical pore fluid composition and induce sorption reactions in the soil. Bench scale studies showed that inorganic species and heavy metals such as arsenic, cadmium, chrome, copper, iron, lead, mercury, nickel and zinc can be efficiently extracted from polluted or spiked soils (Pamucku and Wittle, 1992; Acar and al., 1995; Cox and al., 1996; Reed and al., 1995; Li and al., 1996; Acar and Alshawabkeh, 1996; Marceau and al., 1999). Extraction rates of over 90 % are reported. But species seem to precipitate with OH- near the catholyte. Organic species such as benzene, phenol and acetic acid can also be removed (de Marsily and al., 1992; Bruell and al., 1992; Acar and al., 1992).