Acid pond sediment and mine tailings contaminated with metals: physicochemical characterization and electrokinetic remediation

Mine tailings and acid pond sediment from a former mining area in Canakkale (Turkey) were analyzed for physical (e.g., moisture content, particle size, specific gravity and hydraulic conductivity) and chemical parameters (e.g., organic content, pH, ORP and EC) as well as metal content and sequential extraction analysis, in an attempt to evaluate their risk as a source of contaminants. Column extraction tests were conducted to investigate the leachability under model field conditions using simulated rainwater. The toxicity characteristic leaching procedure and synthetic precipitation leaching procedure (SPLP) methods were performed to evaluate the expected concentrations in the water in contact with the solid material. The column tests proved that Fe and Pb can be released to the waterbodies in contact with the solid materials. Pb was released easier than Fe due to its content in the more labile fractions in the sequential extraction analysis. SPLP-Pb in both tailings and sediment exceeded the USEPA regulatory limit, confirming the hazardousness of those materials. Electrokinetic remediation has been tested as a possible technology for the removal of metals from mine tailings and sediment. Electrokinetics removed 20% of Pb and Fe in 9 days of treatment at 1 VDC/cm. The metal removal efficiency was very affected by metal speciation. Electrokinetics could remove metal fractions I–IV [as described by Tessier et al. (Anal Chem 51(7):844–851, 1979) especially in the closest section to the anode of the solid matrix, and the metals accumulated in the following sections. The results suggested that Fe and Pb could be effectively removed from the mine tailings and sediment if the advance of the acid front was favored and the treatment time increased. However, considering the physicochemical characterization and the results from the electrokinetic treatment, other green and more sustainable remedial strategies have to be proposed for mitigation of environmental risks of former mining areas. Instead of focusing on metal removal, the results of this work suggest that the immobilization and stabilization of metals in the site are more practical solutions. Thus, phytocapping is recommended as a practical green and sustainable method to mitigate the environmental risks of former mining areas.