Efficient electrokinetic remediation of heavy metals from MSWI fly ash using approaching anode integrated with permeable reactive barrier

During electrokinetic remediation (EKR) of heavy metals (HMs) (Pb, Zn, Cu, and Cd) from municipal solid waste incineration (MSWI) fly ash enhanced by a permeable reactive barrier (PRB), the nearer to the anode, the higher the concentration of H+ ions and the greater the remediation effect. Therefore, a potentially new method of PRB-enhanced EKR using an approaching anode (A-EKR + PRB) was studied to help H+ ions to quickly migrate to the sample near the cathode. Consequently, the HM leaching and total concentrations were reduced, while an energy reduction of nearly 40% was achieved. The results showed that the best remediation ability was obtained when MSWI fly ash was treated for 16 days at a voltage gradient of 2.5 V/cm, the approaching anode was moved after 4 days, and the PRB contained 10 g of activated carbon. After remediation, the environmental risk analysis showed that A-EKR + PRB reduced all the fractions of HMs, especially the acid extractable and oxidizable fractions, which might have been due to the enhancement of acid dissolution and oxidation by the approaching anode. In addition, the environmental risks of the remaining HMs were reduced, and the results indicated that A-EKR + PRB is an advisable choice for remediation of MSWI fly ash.