Carrier-in-Pulp Method as a New Hydrometallurgical Route to Reject and Recover Heavy Metals from MSW Melting Fly Ash

摘要

MSW melting fly ash is classified as a hazardous waste because it contains considerable amount of heavy metals which pose environmental concern due to their leaching potential in landfill environments. This study proposes Carrier-in-Pulp (CIP) method as a new hydrometallurgical route to reject and recover Pb, Zn, Cu, and Cd from melting fly ash before landfilling. In this method, a carrier material which recovers the extracted metals is added simultaneously with fly ash to leaching solutions and is harvested from the pulp by physical separation method such as magnetic separation or sieving. To demonstrate the effect of CIP method, shaking flask experiments were conducted under various conditions using NaCl solution, iron powder as carrier, and melting fly ash. More than 99 wt percent Pb, Zn, and Cd, and 97 wt percent Cu were rejected from the ash. However, only Pb and Cu were recovered (96.3 wt percent Pb and 94.3 wt percent Cu) by the iron powder through cementation, leaving behind Zn and Cd ions in the solution phase. The leaching test conducted on the treated fly ash residue revealed that the CIP method suppressed the extraction of heavy metals, especially Pb and Cd, to values below the landfill disposal guideline.