Decontamination of Heavy Metals from Soil by Electrokinetic Combined with Reactive Filter Media from Industrial Wastes

Abstract

The electrokinetic (EK) is an in-situ method for soil remediation, aiming to reduce extensive excavation and mitigate risks associated with exposure to hazardous substances. However, heavy metal precipitation near the cathode under alkaline pH remains challenging. This study employed recyclable waste materials of sawdust crosslinked by glutaraldehyde with iron slag as a reactive filter media (RFM) for single and mixed heavy metals from kaolinite and natural soils. Experiments were conducted over two and three weeks, employing 20 to 30 mA electric currents. Incorporating iron slag RFM into the EK process resulted in a notable enhancement in copper removal from 3.21% to 23.76%. Mixing sawdust with iron slag in the RFM further improved the efficiency of copper extraction from the soil, reaching 71.80%. Also, copper removal improved as the electric current increased from 20 to 25 mA, reaching 88.10% in a three-week experiment. A slight improvement in copper removal was recorded due to the electric current increasing to 30 mA, indicating that copper removal is not linear with the applied electric current. However, sawdust treatment with HCl lowered the RFM pH, resulting in a total copper removal of 90.30% at electrical currents of 25 mA. Crosslinking sawdust with iron slag by 2% glutaraldehyde achieved a remarkable 97.92% copper removal at 0.18 kWh/kg specific energy from kaolinite soil, while in natural soil, the removal rates for copper, nickel, and zinc reached 26.72%, 54.36%, and 56.44%, respectively after 5 weeks. The discrepancy in heavy metals removal between kaolinite and natural soils reflects the complicated environmental conditions in natural soils on the efficiency of the electrokinetic process when laboratory tests are applied to the field.