Differences during the last 15years in materials' composition in Municipal Solid Waste Incineration (MSWI) regarding bottom ash (BA) were assessed as a function of particle size (>16, 8-16, 4-8, 2-4, 1-2 and 0-1mm). After sieving, fractions >2mm were carefully washed in order to separate fine particles adhering to bigger particles. The characterization took into account five types of materials: glass (primary and secondary), ceramics (natural and synthetic), non-ferrous metals, ferrous metals and unburned organic matter. The evaluation was performed through a visual (>2mm) and chemical (0-2mm) classification. Results showed that total weight of glass in the particles over 16mm has decreased with respect to 1999. Moreover, the content of glass (primary and secondary) in BA was estimated to be 60.8wt%, with 26.4wt% corresponding to primary glass in >2mm size fractions. Unlike 1999, in which glass was the predominant material, ceramics are currently the major phase in bottom ash (BA) coarse fractions. As for the metals, respect to 1999, results showed a slight increase in all size fractions. The greatest content (>22wt%) of ferromagnetic was observed for the 2-4mm size fraction while the non-ferrous type was almost non-existent in particles over 16mm, remaining below 10wt% for the rest fractions. In the finest fractions (<2mm), about 60 to 95% of non-ferrous metals corresponded to metallic aluminium. The results from the chemical characterization also indicated that the finest fractions contributed significantly to the total heavy metals content, especially for Pb, Zn, Cu, Mn and Ti.

The reuse of MgO byproducts as SO2 absorbents in a sustainable closed-loop process follows the guidelines of legislation and economic optimization. The aim of the present study was to enhance the desulfurization performance of an MgO byproduct by sieving to different size fractions and relating them with their reactivity and physical characteristics. The byproduct presented a rather irregular size distribution, with Mg presented as MgO, Mg­(OH)2, and MgCO3 and Ca as CaO, Ca­(OH)2, and CaSO4. The time of saturation (t S) was used for evaluating the desulfurization performance of each fraction with 100% removal efficiency. Thus, two different conditions for enhancing the desulfurization performance were described. A chemically established condition where the sorption capacity is improved by adding more solids and a second one dependent only on physical parameters. Accordingly, sieving to the finest size fraction could improve the desulfurization capacity close to an optimum value (2.9 kg of solids can totally neutralize 1 m3 of SO2). Taking into account that the average grinding cost to a particle size below 0.075 mm is 11.54 euro per ton, adding an extra operational unit prior to desulfurization might be a feasible alternative for attaining 100% removal efficiency. Moreover, CaSO3 and CaCO3 were the main reaction products from desulfurization, which could be reused as construction aggregates.The procedure for finding a valuable methodology for improving the SO2 removal capacity of this kind of byproduct could be extended to other wastes and residues.