Material characterization of the MSWI bottom ash as a function of particle size. Effects of glass recycling over time

Differences during the last 15 years 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 - 1 mm). After sieving, fractions greater than 2 mm 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 (> 2 mm) and chemical (0 - 2 mm) classification. Results showed that total weight of glass in the particles over 16 mm has decreased with respect to 1999. Moreover, the content of glass (primary and secondary) in BA was estimated to be 60.8 wt%, with 26.4 wt% corresponding to primary glass in > 2 mm 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 (> 22 wt%) of ferromagnetic was observed for the 2 - 4 mm size fraction while the non-ferrous type was almost non-existent in particles over 16 mm, remaining below 10 wt% for the rest fractions. In the finest fractions (< 2 mm), 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