Influence of electrode placement for mobilising and removing metals during electrodialytic remediation of metals from shooting range soil.

Electrodialytic remediation was applied to a shooting range soil to investigate the influence of electrode placement on the removal and binding of metals during the treatment. The set-up was based on a 2-compartment cell, in which the cathode was separated from the soil by a cation exchange membrane and the anode was placed directly in the soil, thereby introducing protons and oxygen directly in the soil. Mobilisation of metals from less available fractions (oxidisable and residual) in the soil occurred, due to oxidation/dissolution of insoluble/soluble organic matter and possibly metal oxides in the residual fraction. The transport via electromigration out of the soil and/or re-precipitation in other fractions of the soil (oxidisable, reducible, exchangeable) depended on the metal. More than 30% of the initial content of Mn, Cd, Cu, Pb and Zn and less than 20% of the initial content of Al, Fe, K, Mg, As, Cr and Ni was transported out of the soil. By decreasing the distance between the electrodes from 3.0 to 1.5 cm, the removal of the targeted metal for remediation, Pb, was improved by more than 200%, from 14 to 31%. A similar removal could be achieved in experiments with long distance between electrodes (3.0 cm) by increasing the current intensity from 4 to 10 mA and/or the remediation time from 7 to 35 d. The experiments showed that the design and optimisation of electrodialytic remediation depends on the targeted metal and metal partitioning.