Ligand-enhanced electrokinetic remediation of metal-contaminated marine sediments with high acid buffering capacity

Abstract

The suitability of electrokinetic remediation for removing heavy metals from dredged marine sediments with high acid buffering capacity was investigated. Laboratory-scale electrokinetic remediation experiments were carried out by applying two different voltage gradients to the sediment (0.5 and 0.8 V/cm) while circulating water or two different chelating agents at the electrode compartments. Tap water, 0.1 M citric acid and 0.1 M ethylenediaminetetraacetic acid (EDTA) solutions were used respectively. The investigated metals were Zn, Pb, V, Ni and Cu. In the unenhanced experiment, the acid front could not propagate due to the high acid buffering capacity of the sediments; the production of OH(-) ions at the cathode resulted in a high-pH environment causing the precipitation of CaCO3 and metal hydroxides. The use of citric acid prevented the formation of precipitates, but solubilisation and mobilisation of metal species were not sufficiently achieved. Metal removal was relevant when EDTA was used as the conditioning agent, and the electric potential was raised up to 0.8 V/cm. EDTA led to the formation of negatively charged complexes with metals which migrated towards the anode compartment by electromigration. This result shows that metal removal from sediments with high acid buffering capacity may be achieved by enhancing the electrokinetic process by EDTA addition when the acidification of the medium is not economically and/or environmentally sustainable.

The influence of sediment properties and experimental variables on the efficiency of electrodialytic removal of metals from sediment

“…An initial high carbonate content results in low removal of Cu, Pb and Zn in the initial phase of EDR confirming the influence of buffer capacity as reported in literature [41,42]. Carbonate appears to have the opposite influence in the slow removal phase of Cu and Pb (figure 7) which could be related to the low difference in final concentration range, so further removal of any residual carbonate would result in relatively higher removal.…”

Medium-scale ex suit electrokinetic remediation of Cd and Zn polluted soil enhanced by EDTA, tartaric acid, citric acid and acetic acid

“…For the acetic acid test, the pH values were relatively low and changed slightly with the remediation time. The production of H + and OH -ions at the anode and cathode, respectively, resulted in polarization [13]. The pH value of the test with acetic acid was different from other tests suggesting higher acidification.…”

“…The effect of enhancement agents on heavy metal removal efficiency of EK remediation was extensively studied [8,10,12,13]. However, most studies were lab-scale, the larger scale ex suit EK remediation with enhancement agents has been rarely reported.…”

Experimental study on removing heavy metals from the municipal solid waste incineration fly ash with the modified electrokinetic remediation device

“…Under the action of electromigration and electroosmotic flow, the leached cations and anions were migrated and enriched in the anode chamber and the cathode chamber, respectively 42–45 . Moreover, insoluble or non-electric compounds were produced by cations in the cathode chamber together with OH − ions, which were eventually attached to the surface of the cathode graphite electrode to form protective oxidation film, passivation film or other insoluble corrosion materials, resulting in the increased resistance and decreased current in the sample area 31,46 .…”