Electrokinetic stabilization as a reclamation tool for waste materials polluted by both salts and heavy metals

A method for detoxifying industrial wastes is presented, aiming at a safer management and reuse. Focusing, in particular, on bottom ashes from a municipal solid waste incinerator, the proposed ‘‘ElectroKinetic Stabilization” (EKS) technique requires a relatively short treatment time and improves the remediation of ashes by combining a fast extraction of chlorides by electromigration, together with a stabilization of metals through their reaction with phosphate anions, which migrate through the ash under the influence of the electric field. Heavy metals react with the phosphate anions, leading to the precipitation of metal hydroxy-apatite or chloro-apatite (for Pb and Ba), or to their trapping in a calcium-apatite mineral, that formed during the process. Along with precipitation, metal immobilization is allowed by the decrease of ash pH to 9–11 by means of H+ produced at the anode from the electrolysis of water. The migration of salts through the wet ashes is very fast and the treatment time could be decreased to 24 h. After EKS, Ba, Pb and F- leaching was reduced by 97%, 92% and 92%, respectively, below the allowed limits. In contrast, the final leaching of Cu and chlorides was reduced by 90% and 80%, respectively, still above the allowed limits.