Enhanced electrokinetic treatment of different marine sediments contaminated by heavy metals

Abstract

In the present work, the application of an assisted electrokinetic process for the removal of heavy metals from real contaminated sediments was investigated. The process made use of both chemical and physical methods, including addition of chelating and acid agents, as well as application of a hydraulic gradient. Lab-scale electrokinetic runs were applied on two different dredged sediments varying the applied voltage gradient and the treatment duration. The use of EDTA significantly improved the overall performance of the electrokinetic treatment for sediment V (more than 60% mobilized for each metal), while only aggressive acid conditioning with nitric acid was able to remove significant amounts of heavy metals (up to 40.5% for Pb) from sediment S due to the strong buffering capacity of this material. This clearly assesses that the specific characteristics of the materials under concern and the reactions occurring at the electrodes must be carefully evaluated when applying an electroremediation process.

Keywords:

• Marine sediments
• electrokinetic
• enhancing agents
• heavy metals

Acknowledgments

The financial support for this study was provided by the Italian Ministry for University and Research in the framework of the PRIN Projects (2005–2007). The authors wish to thanks Orietta Masala and the IGAG - CNR (Environmental Geology and Geoengineering Institute of the National Research Council, Italy) of Cagliari for the precious cooperation to the chemical-physical analyses. The valuable contribution given by Elisa Becce, Daniela Spiga, Patrizia Olla and Elpidio Serangeli is also gratefully acknowledged.

Notes

⁽¹⁾ HNO₃ was added periodically to maintain the pH at around 3 units.

⁽²⁾ A hydraulic gradient of 8.3 m/m was applied in the direction cathode to anode.

⁽³⁾ HNO₃ was added periodically to maintain the pH at around 3 units.

⁽⁴⁾ Sieving was performed before the electrokinetic treatment in order to remove particles > 500 μ m.