Washing enhanced electrokinetic remediation for removal zinc in contaminated soil

The main objective of this study is to evaluate the combination of electrokinetic remediation and soil washing technology in order to remove zinc from contaminated soil. Experiments were conducted on a real soil spiked with zinc 1090 mg/kg. A total of four different tests were performed to investigate the effect of different washing solutions (ethylenediaminetetraacetic acid (EDTA), sodium metabisulfite (Na2S2O5) and purging solution (acetic acid) on the electrokinetic remedial efficiency. The instrument consisted of an electrokinetic cell, two electrode compartments, two rinsing reservoirs and a power supply. The distance between the electrodes was 19 cm and a constant DC voltage gradient of 2 V/cm was applied at each test for 14 days. The electrodes were graphite discs and cylinders in order to avoid the appearance of corrosion products from the electrodes. Washing solutions helped to extract and mobile zinc followed by electrokinetic process to remove Zn out of soil. The removal of zinc from the soil using EDTA 10(-2) M as washing and purging solution was low. Also, low removal of zinc was noticed when EDTA 10-2 M was used as washing solution and acetic acid 10(-2) M was used as purging solution. Using Na2S2O5 10-2 M as washing and purging solution, 93 % of the initial zinc was removed. Maximum zinc removal (96 % was achieved when Na2S2O5 10(-2) M was used as washing solution and acetic acid 10(-2) M was used as purging solution. The results indicate that the use of Na2S2O5 as washing solution was more effective than EDTA for extraction and mobilization of zinc. The role of acetic acid seems to be negligible. During experiments pH was measured daily at three locations: 3.5, 9.5, 13.5 cm distance from anode. Due to washing and purging solutions, the soil was acidic (pH between 1 and 2), apart from the cathode compartment where it was increased.