Mineralogy and pore water chemistry of a boiler ash from a MSW fluidized-bed incinerator

摘要

This paper presents an investigation of the mineralogy and pore water chemistry of a boiler ash sampled from a municipal solid waste fluidized-bed incinerator, subject to 18 months of dynamic leaching in a large percolation column experiment. A particular focus is on the redox behaviour of Cr(Ⅵ) in relation to metal aluminium AI~0, as chromium may represent an environmental or health hazard. The leaching behaviour and interaction between Cr(Ⅵ) and AI~0 are interpreted on the basis of mineralogical evolutions observed over the 18-month period and of saturation indices calculated with the geochemicai code Phre-eqC and reviewed thermodynamic data. Results of mineralogical analyses show in particular the alteration of mineral phases during leaching (e.g. quartz and metal aluminium grains), while geochemicai calculations suggest equilibria of percolating fluids with respect to specific mineral phases (e.g. mono-hydrocalcite and aluminium hydroxide). The combination of leaching data on a large scale and mineralogical analyses document the coupled leaching behaviour of aluminium and chromium, with chromium appearing in the pore fluids in its hexavalent and mobile state once metal aluminium is no longer available for chromium reduction.