Enhancement of Hexavalent Chromium [Cr(VI)] Remediation from Clayey Soils by Electrokinetics Coupled with a Nano-Sized Zero-Valent Iron Barrier

Environmental Engineering Science (Impact Factor: 0.99). 06/2009; 26(6):1071-1079. DOI: 10.1089/ees.2008.0257


The effectiveness of coupling electrokinetics (EK) with a permeable reactive barrier (PRB) to remediate hexavalent chromium [Cr(VI)]-contaminated clayey soil (100mg/kg) was evaluated. Nano-sized zero-valent iron (nZVI) was used as reactive material in a PRB. The experimental setup consisted of an 8 cm-long soil chamber with a 4-cm diameter, which had two chambers on either side acting as the anode and cathode. A constant electrical gradient of 2V/cm was applied in all tests for 24 h. Cr(VI) removal for the base experiment (only applying EK) was found to be 14.78%. When the soil was treated by the coupled EK/PRB process, the Cr(VI) reduction and total Cr removal efficiencies were increased to 88 and 19%, respectively. In another attempt, the reservoir pH was maintained constant at 6.3 with PRB near the anode; this improved the total Cr removal efficiency to 42% by increasing the current intensity that passed through the soil specimen. Data suggest that redox and adsorption/desorption reactions were taking place during the EK/PRB process, resulting in significant reduction of Cr(VI) to the less toxic Cr(III). These findings indicate that this EK/PRB process is capable of removing Cr(VI) from clayey soils.

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    • "). This phenomenon was in line with many previous studies, which concluded that Cr(III) often coexists with ferric oxides or hydroxides (Shariatmadari et al., 2009). In contrast, a considerable amount of "
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    ABSTRACT: Cr(VI) was often reported to oxidize soil organic matter at acidic environments due to its high ORP, probably thus changing cationic metal species bound to soil organic matter, and influencing their electro-migration patterns. However, such an effect on the electro-migration was not confirmed in most previous studies. Therefore, this study applied a fixed voltage direct current field on an aged electroplating contaminated clayed soil, with a special interest in the direct or indirect influence of Cr(VI) on the electro-migration of other coexisting metals. After 353 h electrokinetic process, 81% of Zn, 53% of Ni and 22% of Cu in the original soil were electro-migrated into the electrolyte, and most of the remaining concentrated near the cathode. The Cr(VI) oxidized some soil organic matter along its migration pathway, with a pronounced reaction occurred near the anode at low pHs. The resulting Cr(III) reversed its original movement, and migrated towards the cathode, leading to the occurrence of a second Cr concentration peak in the soil. Metal species analyses showed that the amount of metals bound to soil organic matter significantly decreased, while a substantial increase in the Cr species bound to Fe/Mn (hydro-)oxides was observed, suggesting an enhancement of cationic metal electro-migration by the reduction of Cr(VI) into Cr(III). However, the Cr(VI) may form some stable lead chromate precipitates, and in turn demobilize Pb in the soil, as the results showed a low Pb removal and an increase in its acid-extractable and residual fractions after electrokinetic remediation.
    Full-text · Article · Dec 2011 · Chemosphere
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    ABSTRACT: Electrokinetics (EK) has been used extensively to remove heavy metals from low permeability porous media. Electrokinetics (EK) or more specifically electrophoresis (EP) has also been proposed to enhance transport of nanoscale zero valent iron (NZVI) in fine grained porous media in the subsurface. However, increased dissolved oxygen and lower pH, due to electrolysis of water at the anode oxidizes NZVI particles and thus affects the remediation potential of EP with NZVI. This study focuses on minimization of NZVI oxidation and quantification of NZVI migration enhancement through the application of EP. Application of 50 and 100 mA currents under constant current conditions with an oxygen scavenger enhanced NZVI transport from the cathode to the anode. The enhancement in transport compared to diffusion was proportional to the applied current. Predictions of a numerical model, based on traditional colloidal filtration theory (CFT), were consistent with experimental results. In developing the model, the traditional CFT based mass balance equation was modified for the case of no advection. This study suggests that EP has the potential to deliver NZVI in low permeability porous media and that the numerical simulator can be used to predict NZVI mobility with EP.
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