Electro-Kinetic Remediation Processes - A Brief Overview and Selected Applications

The basic electro-kinetic process is defined by forced/induced movement of target pollutants in soil/sand medium under applied electric field low strength between electrodes of opposite polarities. There are several specific mechanisms that contribute to this movement of pollutants. However, one study suggested that the most important ones are electro-osmosis, electro migration, and electrophoresis [2]. The electro-osmosis is the movement of pore water from the anode to the cathode in a fluid conduit of small size. The small size of conduits enables electrical double layers of small sizes to be effective in inducing the motion. As the conduit size gets bigger the effectiveness of electro-osmosis rapidly decreases. It is the most effective in pores and capillary tubes. The electro migration is the transport of ions and any other charged species occurring in the applied electric field due to the induced attraction and repulsion forces acting in the electric field. The electro migration is utilized for supply or extraction of ions from various porous materials within both civil and environmental engineering. In civil engineering, most research has been conducted on the removal of chlorides from concrete to hinder reinforcement corrosion [3] and in many other cases in making concrete denser and stronger [4], while in environmental engineering it has been mainly used for remediation of soil contaminated with heavy metals. Whereas, the electrophoresis is the transport of charged particles of colloidal size and bound contaminants due to the application of a low direct current or voltage gradient relative to the stationary pore fluid. Compared to electro migration and electro-osmosis, mass transport by electrophoresis is negligible in soil systems of low permeability such as clay, silty-clay and clay-loam. However, mass transport by electrophoresis may become significant in soil suspension systems and it is the mechanism for the transportation of colloids (including bacteria) and micelles. Electro-osmosis and electromigration mainly depends on the pH, electric potential applied, and ionic strength.