Chromate adsorption in a transformed red mud permeable reactive barrier using electrokinesis

Abstract

Electrokinetic removal of chromium from artificially contaminated clayey soil in a bench-scale cell was enhanced by a reactive barrier (RB) of transformed Red Mud (TRM, BAUXSOL) fitted near the anode. When using 0.75 wt% of TRM in a soil spiked up to a Cr (VI) concentration of 1000 mg/kg dry weight, about 54 wt% of total Cr was removed after 6 days, as compared to only 36 wt% from the control cell without TRM RB. Increasing the duration of the treatment up to 12 days and using 1.5 wt% of TRM resulted in the increase of the above mentioned removal efficiencies up to 93 wt% and 57 wt%, respectively. The reduction of Cr (VI) into less mobile Cr (III) was limited by the TRM RB; in fact, lower reduction percentages for the tests with TRM RB as compared to the tests without were observed (respectively, 42% versus 72% for 6 days test, and 60% versus 93% for 12 days test). The obtained results show that Cr (VI) removal efficiency is proportional to the duration of the treatment and enhanced by the development of favorable pH conditions caused by the activity of the anodic TRM RB. It is suggested that electrokinesis may increase the efficiency of metal-oxyanion adsorption on TRM, as well as that the use of a TRM RB may improve the efficiency of contaminated soil remediation by means of electrokinesis.

Keywords:

• Chromate soil contamination
• electrokinetic remediation
• reactive barrier
• transformed Red Mud
• BAUXSOL

Acknowledgments

The authors wish to thank Matteo Floris, Orietta Masala and the IGAG - CNR (Environmental Geology and Geoengineering Institute of the National Research Council, Italy) of Cagliari and Dott. Piero Mulas, Angelina Cabras, Lorenzo Cau and Stefano Farci of Sardinia Service laboratory for the precious cooperation to the chemical-physical analyses.