Enhanced reduction of Cr(VI) by direct electric current in a contaminated clay.
The probable relation between diffuse double-layer processes and redox reactions that enhance degradation or conversion of contaminants under an applied electric field were examined in a clay medium. Kaolinite clay, precontaminated with hexavalent chromium, was the test soil medium. Analyte, containing ferrous iron, was transported through the kaolinite clay using direct electric current. The Cr(VI) reduction to Cr(III) was followed by measuring the soil redox potential and pH at discrete locations in the clay bed. The post-test distribution of Cr showed significantly more Cr(III) than Cr(VI) at low to slightly acidic pH distribution (2 < pH < 6) in clay. The stoichiometric analyses of measured chromium and iron species concentrations versus the measured redox potentials were compared to Nernst equation predictions of an equivalent aqueous system. An average of +0.37 V shift was measured from the linear Nernstian prediction of cell potential. The applied electric field appeared to provide additional "cathodic current" to drive forth the redox reactions. The redox potential shift was explained by possible overpotential development at the clay-water interfaces due to double-layer polarization under the applied field.
Pamukcu
Sibel
S
Department of Civil and Environmental Engineering, 13 East Packer Avenue, Fritz Engineering Laboratory, Lehigh University, Bethlehem, Pennsylvania 18015, USA. sp01@lehigh.edu
Weeks
Antoinette
A
Wittle
J Kenneth
JK
D000538:Aluminum Silicates / Q000737:chemistry; D002274:Carcinogens, Environmental / Q000737:chemistry*; D002857:Chromium / Q000737:chemistry*; D000077215:Clay; D004058:Diffusion; D004560:Electricity; D004787:Environmental Pollution / Q000517:prevention & control*; D010084:Oxidation-Reduction; D012989:Soil Pollutants
D000538:Aluminum Silicates; D002274:Carcinogens, Environmental; D012989:Soil Pollutants; D002857:Chromium; C074702:chromium hexavalent ion; D000077215:Clay