Recovery of lead and zinc from fly ash generated from municipal incineration plants by means of acid and/or alkaline leaching

Fly ash fi om municipal waste incineration (MWI) is regulated as a hazardou s waste because it contains considerable amounts of heavy metals and hazard ous organic materials such as dioxin. Primary fly ash contains 0.8 wt.% Zn and 0.12 wt.% Ph, 1.37 wt.% Fe while secondary fly ash contains 40.18 wt.% Zn, 10.7 wt.% Pb and 2.12 wt.% Fe in addition to large amount of sodium chl oride and potassium chloride. Therefore, it should be treated for detoxific ation or for the recovery of these metals as secondary resources. The recov ery of these heavy metals by acid leaching using different acids such as su lfuric, hydrochloric and acetic acid was carried out, it was found that sul furic acid leaching is effective where most of Zn was dissolved and also hy drochloric or acetic acid leaching was effective where most of Pb and Zn we re dissolved. However, the acids dissolve also some impurities together wit h Pb and Zn from the fly ash. Therefore, alkaline leaching using NaOH as le achate was carried out. It was found that alkaline leaching suffers from lo w solubility of Zn. In order to improve Zn solubility, washing the solid re sidue using 2 or 5 wt.% HCl was carried out. It was found that almost all P h (more than 97 wt.%) and about 68 wt.% Zn were leached from secondary fly ash by this method. This investigation has shown that hydrometallurgical tr eatment of fly ash by means of alkaline leaching followed by dilute acid wa shing is a potentially feasible method. A recommended flow sheet for alkali ne leaching is proposed. (C) 2000 Elsevier Science B.V. All rights reserved .