Electrodes combined with permeable reaction barrier removes Cr (Ⅵ) from low permeability aquifers

Abstract

Choosing an effective means of dealing with chromium (Cr (VI)) pollution is necessary. Electrokinetic (EK) technology is widely used in low- permeability aquifers. Zero-valent iron/activated carbon (ZVI/AC) can be used as a permeable reactive barrier (PRB) filler for the removal of Cr(Ⅵ) from in low- permeability media. However, the combined effects of these two technologies on aquifers have not been studied extensively. In this study, the ratio of zero-valent iron to activated carbon was determined through a pre-experiment. A series of batch experiment was then conducted to evaluate the effectiveness of electrokinetic (EK) combined with ZVI/AC-PRB on removal of Cr (VI). The ZVI/AC mixture before and after the reaction was analyzed by scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results of the batch experiment showed that the optimum removal efficiency of Cr (VI) was 90.38 % after 1440 min at a ZVI/AC mass ratio of 1:4. During the experiment, owing to the movement of the acid and base peaks, the pH of the anode region was generally lower than that of the other regions. The current decreased as the concentration of heavy metal ions decreased. The SEM, FTIR, and XPS results show that Cr (Ⅵ) was transformed into Cr(Ⅲ) or adsorbed on the surface under the action of ZVI/AC micro-electrolysis. In the present study, these two technologies were combined to treat Cr (VI)-contaminated aquifers. The experimental results provide a theoretical basis for the field application of the EK-PRB repair technology.