Research on a closed-loop method that enhances the electrokinetic removal of heavy metals from municipal solid waste incineration fly ashes

The high leachability of heavy metals and toxic organic components has severely discouraged the broader resource recycling of municipal solid waste incineration fly ashes. In this study, a recycling system combining water washing treatment, cationic buffer solution recovery, and electrokinetic remediation was designed based on pH controls and comprehensively explored in terms of strengthening the removal of heavy metals from samples and reducing the risk of environmental leaching of heavy metals in fly ashes. The water washing pretreatment removed a considerable amount of soluble minerals from the fly ash and lowered the initial pH of the electrochemical system to below 10. The dosing of buffer cations decreased the thickness of the diffuse double layer and ameliorated the mobility of the heavy metal species in the pore fluid. Cu was most sensitive to the changes in the operating factors during electrokinetics. The effects of the remediation times and voltage gradients were more significant on heavy metal removal than those of the nitric acid concentration in the electrokinetic optimization system. The leaching toxicities of zinc, lead, copper, and cadmium were reduced by 82.59%, 73.64%, 67.07%, and 93.13%, respectively. Generally, the recovery of the water washing leachate not only enhanced the performance of the electrokinetic remediation for the municipal solid waste incineration fly ash but also avoided downstream disposal of the effluent.