Electrokinetic enhanced transport of zero valent iron nanoparticles for chromium(VI) reduction in soils

Zero valent iron nanoparticles (nZVI) are a promising technology that could provide cost-effective solutions to soil and groundwater remediation. However, transport of nZVI is normally limited by their aggregation and settling, and with mobility being normally less than a few meters.The main research objective of this study is to find out if coupling electrokinetics and reactive iron nanoparticles can be an effective method for treating chromium contaminated clay soils. Direct current was used to enhance poly(acrylic acid), sodium salt (PAA) coated iron nanoparticles (PAA-nZVI) mobility in Cr(VI) spiked kaolin.A commercially available electrophoretic cell was modified for these experiments and equipped with internal auxiliary electrodes that allow to measure the redox potential directly in the clay. A constant potential of 5.0 V wasapplied across the test bed. Experimental results show that electrokinetics can enhance the delivery of nanoscale iron particles for the reduction of hexavalent chromium to the less toxic trivalent chromium. Direct current enhanced nZVI transport up to 74 % when compared with diffusion, maximum value found when comparing iron concentrations ratios. Activation of nZVI was also observed with a decrease in the redox potential of 531 mV, in average, after the injection point.This work has been funded by the European Regional Development Fund (ERDF) through COMPETE – Operational Programme for Competitiveness Factors (OPCF), by Portuguese National funds through “FCT - Fundaçãopara a Ciência e a Tecnologia” under project «PTDC/AGR AAM/101643/2008 NanoDC», by the research grant SFRH/BD/76070/2011 and by FP7-PEOPLE-IRSES-2010-269289- ELECTROACROSS. DanZerokais kindly acknowledged for the electrophoretic cell modification and the construction of the device to increase resistance.