Simultaneous Removal of Pb, Cd, and Zn from Heavily Contaminated Mine Tailing Soil Using Enhanced Electrochemical Process

摘要

This study examined the efficacy of electrokinetic remediation of chelated mine tailing soils with mixed heavy metals. Electrokinetic experiments were conducted in a nontraditional bench-reactor that contained intermediate liquid collection interfaces within treatment zones between the electrodes. Tests were conducted using 0.05 M Na(2)EDTA as the chelating permeant. Tap water was used in control experiments. A constant direct current voltage of 20 V (electric field approximate to 0.625 V/cm) was applied across working electrodes for 48 h. Transient and spatial distribution of pH, conductivity, oxidation-reduction potential (E-h), and cumulative mass of the metal species in solution were measured. In all experiments, including controls, a larger portion of soluble metals were found in the anode reservoir, indicating transformation of the metals into complex species of negative charge, reverse electroosmotic advection toward anode, and/or colloidally assisted transport. Na(2)EDTA was expected to increase the metal extraction into the analyte as it produced negatively charged complexes with the metals. Soluble mass of the metals was markedly low in the catholyte, with heavy precipitation of metal hydroxide salts in the ensuing high pH, low E-h environment. Total removals of all three metals were either unchanged or lower, for the same duration of treatment with 0.05 M Na(2)EDTA than with tap water. Results showed that chelating agents, as was exemplified with a commonly used ligand in here, may not be advantageous in enhancing electrokinetic remediation of heavily contaminated mine tailings. In such substrates, metals' transport and removal regime (i.e., rate, sequence and preference of extraction) appeared to be influenced more so by the type of metal and transient distribution of the pH-E-h under the electric field than the solubilizing effect of a ligand within the treatment zone.