Electrokinetic remediation of heavy metal-contaminated soils: performance comparison between one- and two-dimensional electrode configurations

Abstract

Purpose Electrokinetic (EK) soil remediation is significantly affected by the electrode configurations. Therefore, this study was conducted to compare the performance of one-dimensional (1D) and two-dimensional (2D) arrays with respect to the remediation of heavy metal-contaminated soils. Materials and methods A series of laboratory-scale experiments were carried out using two types of soils: kaolinite soil (KS) artificially spiked with heavy metals (Cd, Cu, Pb, Ni, and Zn) and smelter soil (SS) contaminated with Cu and Pb, obtained near a closed smelting factory. First, stepwise experiments on the KS were conducted to compare the EK performance between the 1D and 2D electrode arrays. More specifically, the effect of the number of anode-cathode pairs was investigated in the experiments on the 1D electrode configuration, and trigonal and hexagonal arrangements were compared in the 2D EK experiments. Additionally, the performance of the trigonal array was evaluated according to changes in the anode positions, to switch the areas of effective and ineffective electric field. Results and discussion The removal efficiencies of the 1D electrode configuration with four anode-cathode pairs (eight electrodes in total) were 69.1% for Cd, 69.2% for Cu, 74.7% for Ni, 28.3% for Pb, and 71.3% for Zn. The removal efficiencies of the 2D hexagonal electrode array, with a similar number of electrodes (six anodes and one cathode for seven electrodes in total), were 79.8% (Cd), 82.6% (Cu), 83.7% (Ni), 34.3% (Pb), and 81.1% (Zn). The total electric power consumptions for the two types of electrode configurations were investigated to be 15.6 and 22.0 kWh/ton, respectively. Despite the increase in electric power consumption in the 2D electrode configuration, it was more efficient than the 1D configuration due to the increased area of effective (active) electric field and subsequently higher removal efficiency. As a result of changing the positions of anodes in the trigonal 2D arrangement, the removal efficiencies of Cu and Pb were increased to a level similar to that obtained with the hexagonal configuration. Conclusions This study demonstrated that a 2D electrode configuration increased the EK removal efficiency of contaminants compared with a 1D array. However, cost-effectiveness should be taken into account when optimizing electrode design. Furthermore, the performance of the trigonal 2D EK process was improved by changing the positions of anodes, as a result of the increase in the removal efficiency and decrease in the electrode cost and energy consumption.