Effects of Electro-Osmosis on the Physical and Chemical Properties of Bentonite

Electro-osmosis is a process coupling electrolyte flow and associated hydraulic flow under an external electrical field, resulting in the permeation of both electrolyte and pore fluid in porous media. One-dimensional column experiments were conducted to comprehend the effects of electro-osmosis treatment on the physical and chemical properties of a Na-bentonite by varying the electrode materials, including copper and iron as reactive electrodes and graphite and stainless steel as inert ones. Soil plasticity, free swelling ratio, zeta potential, and cation exchange capacity decrease after electro-osmosis, especially for the reactive electrodes. Moreover, soil microfabric is converted from the flocculated microplatelets to smectite aggregates of 10–30 μm in size. The original ${\mathrm{Na}}^{+}$ cations absorbed into smectite interlayer and adsorbed onto smectite external surfaces are exchanged with the released ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ for copper and iron electrodes, and the pre-existing multivalent cations such as ${\mathrm{Ca}}^{2+}$ for graphite and stainless steel electrodes. The resulting change in soil microfabric and chemical compositions decreases the water adsorption and holding capacity and also affects the physical and chemical properties of the Na-bentonite.