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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.

Carbon dioxide increase in the atmosphere is a relentless rise process. Many mitigation measures aimed at the reduction of carbon dioxide emissions coupled with capture in variously stable sequestration systems have been proposed over time. In a previous paper (Pastero, 2019), we proposed a new and green method to capture carbon dioxide avoiding the usage of hazardous reagents and the production of harmful compounds. The method involves the application of an aqueous solution of calcium ascorbate (vitamin C) as the only reagent and the precipitation of calcium oxalate as the main reaction product. The role of the chemical and physical process variables controlling the reaction has been investigated in order to increase significantly and stabilize the reaction yield in terms of CO2-sequestration capacity. In the present paper, we evaluated the performance of our method quantitatively, referring to two simple experimental setups: the maximum carbon dioxide yield exceeded 60 %, meaning that every 100 mol of carbon dioxide fed to the capturing system, 60 mol are removed and stored into a stable solid phase. This boost in the method’s performance was obtained optimizing the key-parameters of the reaction and increasing the exchange surface.

Treatments to reduce the leaching of contaminants (chloride, sulfate, heavy metals) into the environment from bottom ash (BA) are investigated, as a function of the ash&rsquo, s particle size (s). The aim is to make BA suitable for reuse as secondary raw material, in accordance with the legal requirements. Such treatments must be economically feasible and, possibly, have to use by-products of the plant (in this case, steam in excess from the turbine). For the sake of completeness and comparison, carbonation is performed on those BA particle size classes that are not positively responsive to steam washing. BA is partitioned into four different particle size classes (s &ge, 4.75, 4.75 &gt, s &ge, 2, 2 &gt, 1 and s &lt, 1 mm, corresponding to 36, 24, 13 and 27 wt%, respectively). In the case of s &ge, 2 mm (60 wt%), steam washing is effective in reducing to under the legal limits the leaching of chlorides, sulfate and heavy metals (Zn, Cu, Cd, Pb). It has been observed that steam washing causes both removal and dissolution of thin dust adherent to the BA&rsquo, s surface. BA with 2 &gt, 1 (~13 wt% of total BA) requires a combination of steam washing and carbonation to achieve a leaching below the legal limits. The finest BA fraction, s &lt, 1 mm (~27 wt% of total BA), is treated by carbonation, which reduces heavy metals leaching by 85%, but it fails to sufficiently curb chlorides and sulfates.

The aim of this study is twofold: (i) characterization of the bottom ashes from the Incinerator plant of the city of Turin (northern Italy), in terms of their chemical/phase compositions and capacity to release heavy metals in leachates, as a function of particle size; (ii) investigation of thermal treatments' efficacy to promote inertization of the same bottom ashes, exploring time-temperature ranges with t ≤ 6 h and T ≤ 1000 °C. Special attention is paid to macro-sampling techniques in order to have samples that are representative of the average bottom ashes production. Micro-XRF, ICP-OES, SEM-EDS, Ion Chromatography and X-ray powder diffraction were used to investigate bottom ashes and leachates. Bottom ashes are mainly constituted by an amorphous phase, ∼66-97 wt%, regardless of particle size; the remaining phases are quartz, calcite, Fe-oxides, melilite and other minor crystalline materials. The amorphous phase exhibits a relevant dependence on particle size, and undergoes dissolution in water up to 20 wt%, thus being the most important component in affecting chemical species release. The smaller the bottom ashes' particle size, the more the heavy metals (major species: Zn, Cu, Ti, Pb) and calcium contents increase, whereas silicon's decreases. Electrolytic current observations in combination with phase/chemical composition and metals release as a function of particle size, suggest that bottom ashes partition into two classes, i.e. ≥1 and1 mm, for inertization purposes. Thermal treatments exhibit partial efficacy to curb heavy metals mobility: whilst they reduce Cu release, they lead to a inverse effect in the case of Cr.