Transport and Exchange Behavior of Ions in Bentonite During Electro-Osmotic Consolidation

Electro-osmotic consolidation is considered to be an efficient technique for dewatering and consolidation of soft soil. In the present study, four experiments were conducted on a Na-rich bentonite using two reactive electrodes (copper and iron) and two inert electrodes (graphite and stainless steel) to study the transport and exchange behavior of ions during electro-osmotic consolidation. The results showed that the changes in pH and ion contents were limited to the zone close to the electrode due to the buffering capacity of bentonite and the significant reduction in electric current density. The ion concentration profiles indicated that Na+ ions were largely responsible for carrying the pore water to the cathode. The reactive electrodes are better at transporting Na+ ions and therefore induce better drainage than inert electrodes. Ion-exchange reactions occurred between the Cu2+ and Fe2+/Fe3+ ions released and pre-existing Na+ ions in the electrical double layer, causing decreased water adsorption capacity and plasticity index. The swelling and shrinkage characteristics of the bentonite were thus reduced, and electroosmotic consolidation may therefore provide a new way to improve the stability of expansive soils and slopes.