Characterization of MSWI fly ashes along the flue gas cooling path and implications on heavy metal recovery through acid leaching. (October 2021)

• Record Type: Journal Article
• Authors: Wolffers, M.; Eggenberger, U.; Schlumberger, S.; Churakov, S.V.
• Is Part Of: Waste management. Volume 134(2021)
• Page Start: 231
• Page End: 240
• Publication Date: 2021-10
• Subjects: Mineralogy of waste incineration residues -- MSWI fly ash -- Empty pass ash -- Boiler ash -- Electrostatic precipitator ash -- Heavy metal recovery; Hazardous wastes -- Periodicals; Refuse and refuse disposal -- Periodicals; 363.728
• DOI: 10.1016/j.wasman.2021.08.022
• Languages: English
• ISSNs: 0956-053X

Abstract

Highlights: New insights into MSWI ash formation along the flue gas cooling path. Characterization with focus on heavy metal binding form and leaching behaviour. Empty pass- and boiler ash essentially composed of refractory- and glass particles. Heavy metals (Zn, Pb, Cu) predominantly enriched in electrostatic precipitator ash. Data basis for discussion on re-evaluating disposal routes of MSWI ash fractions. Abstract: This study reports on detailed chemical and mineralogical characterization of the different municipal solid waste incineration ashes forming along the flue gas path of plants with separate dust removal and neutralization. In pursuit of optimizing heavy metal recovery through acid leaching, the metal extractability from empty pass ashes (EA), boiler ashes (BOA) and the electrostatic precipitator ashes (ESPA) was evaluated and compared. The focus was laid on matrix phases affecting leachability (e.g. alkalinity, oxidation–reduction potential), as well as on distribution and concentration of recoverable heavy metals and their binding forms. The data showed, that EA and BOA are geochemically similar and are essentially composed of two different materials: the heavy metal poor airborne ash particles and the Zn- and Pb-rich sulfate deposits that condensate on heat exchanger surfaces. Variation in relative amount and chemical composition of the deposits is responsible for fluctuations in bulk composition of EA and BOA. The ESPA shows different chemical and mineralogical characteristics than EA and BOA. The ESPA is enriched in the volatile heavy metals Zn, Pb, Cu, Cd and Sn, which are mainly incorporated in chlorides and sulfates. The high content of salt-bound and thus easily soluble heavy metals together with the lower alkalinity and lower oxidation–reduction potential indicates, that ESPA has a better leachability compared to EA and BOA. The EA and BOA, on the other hand, do not show any significant differences in leachability. The data may contribute to a basis for re-evaluating disposal routes of ash fractions with poor extraction properties.