Electrokinetic remediation (EKR) effects under linear and radial electric field at laboratory scale

The remediation of polluted soils by heavy metals concerns wide areas of the planet, and the electrokinetic remediation (EKR) is an alternative method to the traditional ones. Moreover, in the current technologies this technique requests high power levels, with consequent security and cost problems. To enhance the process it is possible to use hydro-silica layers properties: these layers allow to move the heavy metals, if the electrical field is applied for a long time (T > 24 hours). Previous experiences showed that a sinusoidal waveform can improve the efficiency of the process up to 70%. In this paper we show the results of the EKR experiments carried out with two different electric fields: linear and radial. The electric field was controlled both as gradient and waveform (positive sinusoidal and DC). We worked with saturated sands polluted by Cr(VI). The process was monitored and calibrated using sets of voltage electrodes, chemical analysis and complex electrical resistivity of selected sand samples. The EKR process moved the 69% of Cr(VI) applying a linear electric field, while it moved the 34% of Cr(VI), applying a radial electric field. We also observed that the local electric resistivity is an efficient and economic index of the process, and the behaviour of the resistivity versus voltage let us presume that a positive ramp up signal, with a period of 12 hours, should be more effective than the positive sinusoidal one. Moreover, these experiments show that the process electrodeposits the heavy metal on to the surface of the high current electrode, consequently the polarity inversion of the applied electric field can clean this electrode and restore his “storage capacity”.