Influence of speciation distribution and particle size on heavy metal leaching from MSWI fly ash. (1st February 2022)

• Record Type: Journal Article
• Authors: Bernasconi, Davide; Caviglia, Caterina; Destefanis, Enrico; Agostino, Angelo; Boero, Renato; Marinoni, Nicoletta; Bonadiman, Costanza; Pavese, Alessandro
• Is Part Of: Waste management. Volume 138(2022)
• Page Start: 318
• Page End: 327
• Publication Date: 2022-02-01
• Subjects: MSWI fly ash -- Particle size -- Heavy metal leaching -- Speciation; Hazardous wastes -- Periodicals; Refuse and refuse disposal -- Periodicals; 363.728
• DOI: 10.1016/j.wasman.2021.12.008
• Languages: English
• ISSNs: 0956-053X

Abstract

Highlights: Municipal fly ash heavy metal leaching is mainly affected by speciation distribution. Particle size and heavy metal content do not show a major correlation with leaching. pH-dependent leaching tests are well simulated by thermodynamic geochemical modelling. F1-speciation should be implemented as a reference check of leaching behaviour. Particle size separation strategies have modest efficiency in managing leaching. Abstract: Fly ash from municipal solid waste incineration (MSWI-FA) contains leachable heavy metals. In the present study the correlations between heavy metal content, particle size, speciation distribution with respect to water leaching are investigated, using a combination of solid-state bulk analytical techniques, leaching treatments, sequential extractions and thermodynamic geochemical modelling. Among the analyzed heavy metals, Zn and Pb are the most abundant in any grain size class, followed by Cu, Cr, Cd and Ni, with concentration that tends to increase with a decrease of the grain size. The phase composition is constituted of salt (halite, sylvite, anhydrite and syngenite), which provide the main minerals regardless of the particle size class; calcite, quartz and gehlenite occur in comparatively lower amounts, while 50% wt is composed of amorphous fraction. Heavy metal leaching is strongly correlated to speciation distribution, and in particular to the fraction (F1) associated with salt, carbonate and weak surface sorption. Leaching from speciation due to surface complexation on Al/Fe (hydr)oxide becomes relevant at acidic regime. Particle size and heavy metal content, in turn, moderately correlate with leaching. The F1-speciation as a function of particle size does not exhibit a definite trend shared by all heavy metals under investigation. This suggests that i) differences in speciation distribution, rather than bare heavy metal content or particle size, govern leaching from MSWI-FA; ii) F1 can be regarded as a marker of the potential heavy metal leaching; iii) a comparatively modest efficiency in managing MSWI-FA is expected from grain size separation strategies.