Transport phenomena in soils submitted to an electric field are the basis of a soil decontamination technique called electromigration or more generally electrokinetic remediation. An experimental study was carried out in order to determine the influence of the applied electric potential on the most important variables for the treatment: the amount of pollutant removed and the current intensity produced. Physicochemical and transport aspects of the process are taken into account in order to prove the feasibility and the efficiency of the technique to treat a fluorine contaminated soil.

Electroremediation is a soil decontamination technique. The electric field applied to a porous medium induces the migration of ionic species in solution. The different phenomena appearing in soil are presented. A new methodological approach is carried out in order to determine if preponderant and/or limiting phenomena can be considered. The theoretical study, using dimensional analysis, showed that transport of ionic species in solution could be described only by electro-osmosis and electromigration phenomena. But, other phenomena, such as heterogeneous reactions, can restrict the migration of ionic species which is only possible for chemical species in solution. Then, an experimental study was carried out with a tracer, in order to verify the theoretical characteristic times for transport phenomena, obtained by dimensional analysis and calculated in a synthetic medium. Rigorous experimental procedures were followed to realise well-controlled electroremediation experiments. The experimental results obtained have allowed the measurement of characteristic times of electrokinetic transport and the theoretical times have been validated. In addition, the application of a simple mass balance equation to the soil and an electrolytic compartment has allowed the verification of the migration behaviour of the mass flux as a front advance.

a b s t r a c tThe influence of the ion-exchange solid/liquid reaction on electrokinetic transport phenomena was studied and modelled for a non-permeable porous medium composed of kaolin. Kaolin was selected to model a low-permeable medium, even though it is usually considered to have low ion-exchange capacity and weak selectivity. The influence of this reaction on the characteristic time of the process was demonstrated by studying the lithium (Li + ) electrokinetic transport on a sodium (Na + ) pre-saturated kaolin. Experimental results were obtained using apparatus developed specifically for the study of the electrokinetic transport and which has been well characterized in previous works. The tests were performed by introducing a solution containing Li + at the anode, and measuring the Na + and Li + concentrations at the cathode outlet. Under operating conditions, local equilibrium is assumed in the medium. The equilibrium isotherm of Li + /Na + exchange was determined by independent experiments on a laboratory column. Ion-exchange equilibrium can be satisfactorily described by a linear isotherm. A theoretical model based on the tanksin-series model was used for modeling the experimental results of the Li + electrokinetic transport. This model considers electro-migration and electro-osmosis as the only transport mechanisms, and takes into account the solid/liquid reaction by a retardation factor, as is usually the case for linear equilibrium models. The comparison between experimental and theoretical results shows that the chemical solid/liquid reaction at least doubles the characteristic time of the transport.

E lectrokinetic phenomena can be employed for a soil decontamination process generally called electroremediation. The ionic species in solution migrate through a porous medium essentially by electro-osmosis and electromigration. The aim of this work was to contribute to knowledge of this process by studying the effect of some operating conditions on the species recovery through an experimental program. The in uence of the electrical eld applied to the medium and the initial concentration of the soil solution, in particular, are studied. First, the electrokinetic transport phenomena are presented. Then, the experimental setup and procedures carried out are described. The setup consists of a speci c electroremediation cell containing a Na-doped kaolinite medium. Chemical reactions were limited by using the sodium as a tracer. The experimental results show the important coupling existing between solution concentration and the electrical current and their in uence on both the amount and the rate of transported mass. Moreover, the dependence of the electro-osmotic coef cient on the electrical eld applied was demonstrated. The in uence of the solution concentration on the electro-osmosis is not obvious, probably due to the light modi cation of the zeta potential for the system studied.