J. Kenneth Wittle

Electrochemical extraction and stabilization of selected inorganic species in porous media

Abstract There are metal and alkaline earth species which tend to remain ionic under a large range of pH and redox potential values. Those substances are expected to electromigrate and separate even under high pH and variable redox conditions unless they become adsorbed onto soil surfaces and clay interstices. In this study, first near complete separation of Na and Cl was accomplished in samples of drilling mud sludge recovered from a settling pond. Na recovery was invariable with the quantity of water flow through the sludge specimens of various initial degrees of water saturation. High recovery of Na and Cl was demonstrated with less than 0.5 pore volume of electroosmotic water flow. In most field situations, the contaminants are often found adsorbed onto soil surfaces. Natural buffering capacity of soil may hinder desorption and dissolution or high pH generated at the cathode site may cause insoluble hydroxide precipitates of some metal contaminants. Under such circumstances, electrochemistry may still be useful to stabilize and contain certain groups of contaminants in the ground. In this study, use of electrochemical process to deliver Fe(II) to reduce soluble species Cr(IV) to a less toxic and less soluble species Cr(III) was demonstrated in the laboratory.

Delivery and activation of nano-iron by DC electric field.

This study demonstrates that by integrating electrokinetics with nanotechnology, the transport of nano-particles can be electrokinetically enhanced for subsurface remediation of tight clay soils where transport time and process efficiency may be an issue. Polymer coated dispersed nano-iron developed at Lehigh University, were used in the experiments reported here. The particles possessed positive zeta-potential below pH 8.3 and remained suspended in solution rather than settling or agglomerating over time as it may occur with bare nano-iron. The injection of nano-iron particles in the lab tests showed a positive shift in the oxidation-reduction potential (ORP) where the effectiveness of nano-iron as an environmental catalyst was demonstrated. The presence of nano-iron and applied electric field together pushed the system ORP to higher positive values than the electrokinetic effects or nano-iron alone. The diffusion of nano-iron without the electrical field showed no activation of the iron, as indicated by little or no change in the ORP. These results showed that nano-iron was both transported and activated by the applied electrical field. The enhanced reaction was analyzed in terms of possible Faradaic processes in clay diffuse double layer, DDL, in presence of electric field.