Clays as Micro-Electrodes in Environmental Detoxification

Abstract In-situ reduction of contamination in soil and groundwater is an ongoing challenge that often requires a multi-pronged approach for effective and efficient clean-up. Spontaneous or assisted electrochemical reactions that break down certain pollutants held on clay surfaces can render natural clays a unique and powerful ally in environmental mitigation of contaminated soils. Application of a low-level DC electric field (mV/cm) has been shown to facilitate transformation of some compounds and ionic species through redox reactions in addition to transporting them through the pores in wet clay soils. Results from previous tests suggest that the natural electrochemical processes that promote pollutant sloughing or chemical breakdown can be enhanced for targeted treatment by applying low-level electric field to the contaminated soil with clay content. The central idea of this hypothesis is that clay, due to its surface charge and electrostatic interaction with adjacent pore fluid, acts as a “micro-electrode” through the diffused double layer (DDL) interactions when subjected to an external electric field. This hypothesis, proven viable, may unlock potential ability of natural clays to generate beneficial reactions for detoxification of contaminated sub-surfaces. Evidence from past laboratory experiments accompanied by a proposed electrical model of clay behaving as a micro-electrode are presented in this paper. The laboratory experiment results support the proposed electrical model.