Electrokinetic Remediation Using Surfactant-Coated Ceramic Casings

Electrokinetic remediation is an emerging technique that can be used to remove metals from saturated or unsaturated soils. In unsaturated soils, control of the medium's water content is essential. Previously used electrode designs have caused detrimental soil wetting due to excess electroosmotic flow out of ceramic-encased anodes. We tested a method to reverse the electroosmotic flow at the anode by treating the ceramic casing with the cationic surfactant hexadecyltrimethylammonium (HDTMA). Laboratory tests showed the untreated ceramic had an electroosmotic permeability of 2.4 × 10−5 cm2 V−1 s−1. Ceramic treated with HDTMA had an electroosmotic permeability of −1.3 × 10−5 cm2 V−1 s−1. Under an applied electric potential, electroosmotic flow was reversed in the HDTMA-treated ceramic, indicating a reversed zeta potential due to formation of an HDTMA bilayer on the ceramic surface. Field tests conducted over a 6-month period showed negligible water loss from HDTMA-treated ceramic (0.03 L h−1) compared to untreated ceramics (up to 6 L h−1). The results indicated that a surfactant treatment to the anode ceramic casing can greatly improve the application of electrokinetics in unsaturated environments.