Electrokinetic Enhancement: Effect of Sample Stacking on Strengthening Heavy Metal Removal in Electrokinetic Remediation of Municipal Solid Waste Incineration Fly Ash

Abstract

Municipal solid waste incineration (MSWI) fly ash is internationally categorized into a hazardous waste due to its high content of heavy metals (HMs) and dioxins. A traditional electrochemical platform was intrinsically modified by changing stackings of samples in the electrolyzer to solve a near-anode concentration focusing (NA-CF) phenomenon during the electrokinetic remediation (EKR) and to improve electrokinetic performance to the HM removals from MSWI fly ashes. The effect of sample stacking in the electrolyzer on the removal performance of the electrokinetics was comprehensively investigated. Summarily, the stacking styles profoundly affected the electrochemical environment. The excavation of specimen near the anode chamber facilitated the diffusion of H+ ions in the electrolyte and effectively avoided the generation of NA-CF phenomenon. The best removal efficiencies for all four HM elements were achieved through simultaneously moving the ash samples out near the two electrodes. The influence of voltage gradient (V/cm) on the HM removals was proved to be more significant than the remediation time. The voltage gradient of 1.5–2.0 V/cm and the remediation time of 18–21 days were determined as the optimal ranges for the remediation of MSWI fly ashes. The environmental toxicities of HMs were noticeably decreased using the adjusted EKR system. The average leaching toxicities of Zn, Pb, Cu, and Cd were reduced by approximately 60%, 83%, 58%, and 77%, respectively. The SD-EKR process significantly reduced the environmental activity of MSWI fly ashes. The excavation of samples from subregions of S2 and S5 at the third day of EKR process increased HM dissolution, decreased ion-migration resistances, and facilitated HM removals from fly ashes.