Feasibility study of applying electrokinetic technology coupled with enzyme-induced carbonate precipitation treatment to Cu- and Pb-contaminated loess remediation

Inappropriate handling of smelting-and irrigation-induced copper (Cu) or lead (Pb) in soils could cause serious threats to surrounding environments and human health. Electrokinetic (EK) technology is in the spotlight due to its great maneuverability. However, the hydroxide precipitation, referred to also as the focusing effect, near the cathode degrades the removal efficiency. Although there is an upsurge in the research of enzyme-induced car-bonate precipitation (EICP) for Pb immobilization, it is criticized as urea hydrolysis is accompanied by the discharge of ammonium ions (NH4+). In the present work, a modified EK reactor was proposed where the single and multiple EICP treatments were incorporated into a permeable reactive barrier (PRB) for the first time to resolve the raised problems and also improve the removal efficiency. Results showed that the EK-PRB technology outperformed the EK technology in terms of the Cu and Pb removals. The PRB worked with the cathode elec-trolyte well to reduce the remaining Pb2+ by approximately 35%. The effect of multiple EICP treatments in-creases the potential of combining Cu2+ or Pb2+ with CO32 , which caused difficulty in performing the electromigration and electroosmosis in the EK remediation. The removal efficiency of 40% against Cu however confirms a reduction in the focusing effect. The higher cathode pH, induced by the effect of a single EICP treatment, was accompanied by the copper-ammonia complex formation to improve the fraction of Cu2+ removed by the cathode electrolyte well. The Pb removal behaved similarly to the Cu removal, although Pb2+ was more willing to combine with CO32-.