Electrokinetic extraction of heavy metals from dredged marine sediment

This study investigates the suitability of the electrokinetic process for extracting heavy metals from dredged marine sediment. Marine sediments have unique characteristics such as high alkalinity, high buffering capacity, and a large fraction of fine particles and organic contents. The target heavy metals were nickel (Ni), copper (Cu), zinc (Zn), and lead (Pb). Tap water was circulated in the anode and various processing fluids such as 0.1 M of ethylenediamine tetraacetic acid (EDTA), citric acid (CA), HNO3, and HCl were circulated in the cathode under a constant voltage gradient of 1 V/cm for 15 days. Heavy metals were most efficiently extracted from the marine sediment with HCl, and the extraction efficiencies of Ni, Cu, Zn, and Pb were 71.5%, 68.6%, 62.4%, and 65.3%, respectively. In the case of citric acid, the extraction efficiencies of Ni, Cu, Zn, and Pb were 56.3%, 71.3%, 60.3%, and 54%, respectively. Even though HNO3 is a strong inorganic acid like HCl, extraction efficiency was lower than of HCl because chloride forms a metal–chloride complex and the complex formation enhances desorption from sediment surface or ionization at alkaline pH. On the basis of the experimental results, we conclude that the electrokinetic process, using citric acid or HCl, is suitable for extracting heavy metals from dredged marine sediment.

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► HCl and citric acid were effective electrolyte-conditioning agents to remove heavy metals from dredged marine sediment.
► Chloride-metal and citrate-metal complexes enhanced the removal of metals from sediment.
► The amount of heavy metal extracted from the marine sediment was in the order Zn ∼ Cu ≫ Pb > Ni and the order was consistent with the amount of residual fraction in the sequential extraction of metals.