Enhanced Electrokinetic Removal of Heavy Metals from a Contaminated Lake Sediment for Ecological Risk Reduction

ABSTRACT

In this study, electrokinetic remediation (EKR) was performed to reduce the risk of heavy metal contaminants viz., Cd, Cu, Ni, Pb and Zn associated with different fractions of lake sediments. Firstly, batch experiments were performed to estimate the optimal concentration of enhancing agents such as EDTA, nitric acid and acetic acid for effective dissolution of heavy metals from sediments and to minimize the dissolution of earth metals (Fe and Al) to maintain good soil health. In addition to that, the effect of pH on dissolution of these heavy metals with optimized concentration was studied separately. The results from batch experiments showed that EDTA with the concentration of 0.01 M enhanced the heavy metal dissolution as 38–88% in the pH range 2–12. Nitric acid and acetic acid with the concentration of 0.05 M enhanced the heavy metal dissolution as 18–85% and 15–80%, respectively in the pH range 2–6. For enhancing agents like nitric acid and acetic acid, the increase of pH (above 6) led to the formation of metal hydroxides and carbonates, which reduced the efficiency of heavy metal dissolution. Secondly, EKR experiments were conducted in a reactor with optimal concentration of EDTA (0.01 M), nitric acid and acetic acid (0.05 M) as electrolyte and sediment saturation solution for 7–21 days of treatment time. After 21 days of EKR with 0.01 M of EDTA as enhancing agent, the average removal of heavy metals achieved about 46.4–78.8 % and associated risk with metals viz., Cd, Pb, Zn and Cu reduced from high to low risk and Ni reduced from high to medium risk, according to risk assessment category. Alternatively, the EKR treatment using nitric acid and acetic acid showed the average removal of heavy metals of about 17.2–43.60% and 24.9–57.2 %, respectively, and all heavy metals pose medium risk, except for Cd, which showed low risk to the environment.

KEYWORDS:

• Electrokinetic remediation
• heavy metals
• contaminated sediments
• EDTA
• chemical fractionation
• risk Assessment

Acknowledgments

The authors like to acknowledge the support from Frontier Areas of Science and Technology - centre of Excellence (FAST-CoE) in Sustainable Development at Indian Institute of Technology Hyderabad, funded by the Ministry of Human Resource Development, India.