Full Scale Tests of Short-Term Municipal Solid Waste Incineration Bottom Ash Weathering Before Landfill Disposal

Abstract

Problem statement: Natural weathering is the most economic method of treatment in order to reduce the release of heavy metals present in the residue. Approach: The aim of the study was to optimize the minimum weathering times that were useful to reduce the lead release to within the Italian limits for landfill disposal. The mechanism of short-term weathering of MSWI bottom ash had been studied and its effect on the leaching of lead had been evaluated. Two bottom ash heaps had been realized for the experimental assessment: In one case an open-air situation was used, in the other, a heap placed under shelter was not exposed to rain. Results: The weathering course was monitored through the results of a leaching test that was carried out at different ageing times (EN 12457-2:2002). The total carbonates were also measured, at the same time, on the fine fraction of the weathered bottom ash (<1 mm). A fast decrease in lead release was observed in the analysis of the leachates and, at the same time, a decrease in pH and calcium concentration. The pH and leachate lead concentration control mechanisms were investigated and individuated. It had been possible to observe that the lead concentration was fundamentally a function of the pH. The Calcite precipitation that occurred from calcium hydroxide carbonation was the main reason for the decrease above all during the first days of the process, when the maximum quantity of CO 2 was fixed by air. The pH value was controlled by Portlandite dissolution only at the beginning, after the pH control seems to be due to aluminum hydroxides. Conclusion: The most significant changes in the bottom ash were found to occur in the first 60 days. It had been possible to verify the limited influence of washing phenomena while it was confirmed that carbonation was the most important process in short-term weathering and that it had an important rule on limiting lead release.

Effect of leaching behaviour by quenching of bottom ash from MSW incineration

“…The pH-Ca correlation confirms that the pH for BA3 was controlled by the dissolution of Ca(OH) 2 . The equilibrium considerations in the aqueous phase (Perkins & Palmer 1999) for BA1 and BA2, taking into account the aluminium, calcium and sulfates concentrations, should be an indication of the fact that the pH was controlled by the precipitation/solubility equilibrium of micro-crystalline gibbsite (Marchese & Genon 2009) and ettringite. This hypothesis, which is in agreement with other authors' observations (Meima & Comans 1997, Speiser et al 2000, Chimenos et al 2008, is consistent with the presence of hydrated phases in BA1.…”

Occurrence and Significance of Secondary Iron-rich Products in Landfilled MSWI Bottom Ash

“…Among different treatment techniques, natural ageing and weathering has been considered as one of the most costeffective methods of treatment for the chemical stabilization of MSWI bottom ash. Many researchers have been investigating the natural or accelerated aging of bottom ash, a process which could also be applied to fly ash disposal [7][8][9][10].…”