Mineralogical evolution and leaching behavior of a heap of bottom ash as a function of time – influence on its valorization.

International audienceMSWI BA in France is reused as a substitute for natural aggregates in building material for road constructions. Before MSWI BA reuse, treatment operations are generally necessary such as ferrous and non-ferrous metals removal, ageing process, and particle size separation. BA valorization depends on the leaching behavior of the main MTE, which depends on pH. It’s well known that ageing process influence the naturel pH of the BA. Initial pH of fresh BA (around 12 – 13) may decrease until the pH value 8 reached for weathered BA. Ageing process is influenced by different parameters, for example the presence of ferrous metals because of their oxidation and the CO2 content of the gaseous phase in the porosity of BA. Then, as the ferrous removal is more and more efficient and as the MSWI BA are stored in heaps, limiting the atmospheric exchange, the efficiency of ageing process is no longer certain. The main objective of this study was to measure the efficiency of the ageing process when BA are stored in heap. The mineralogical evolution and the leaching behavior of BA were observed during 7 months. To compare, two artificial ageing processes were carried out on the final sample. All the results showed that when the BA were stored in heap, the ageing process was not efficient. The evolution of pH was very low, showing that the carbonation didn’t occur. On the contrary, ‘artificial’ ageing processes permit to diminish the pH value. Mineralogical characterization showed differences between all the samples. These differences permitted to explain the MTE leaching, especially for lead or antimony