Optimizing large-scale ageing of municipal solid waste incinerator bottom ash prior to the advanced metal recovery: Phase I: Monitoring of temperature, moisture content, and CO 2 level.

Development of temperature, CO2 level, and moisture was followed during several months of outdoor ageing of municipal solid waste incineration bottom ash (IBA) in seventeen 5000-ton piles, in order to obtain input data for possible optimization of the ageing process in terms of faster/better drying prior to the metal recovery operation. In addition, measured thermal conductivity and specific heat capacity of IBA were combined with calculated thermal output and used as input to a model originally developed for accessing temperature development in hardening concrete structures. The results show that the temperature in pile's core increased to 90-94 °C in two-three weeks and remained stable for at least another month. The temperatures in the outer 80 cm of the pile were shown to be affected by outside temperatures while effects of precipitation on temperature development were shown in the upper 50 cm. The used thermal model described the observed temperatures in large part of the pile well; however, it failed to describe the temperature level observed towards the top of the pile. This may be caused by an unaccounted transport process. The CO2 measured inside the pile was constantly at "zero-level" thus indicating an incomplete carbonation. The moisture content was found to decrease during the ageing; however, significantly better data needs to be gathered especially for the period after the quenching, where the largest variation seemed to take place. The leaching of chloride, sulfate, Na, As, Ba, Cd, Cr, Cu, Hg, Ni, Pb, Se, Zn and dissolved organic carbon (DOC) from all IBA samples was shown to comply with the leaching limit values for Category 3; i.e. the IBA was found suitable for utilization in e.g. an unbound subbase of a road or a parking space. For the next phase of this project an optimized treatment was proposed which is based on using a telescopic radial stacker allowing construction of a less-compacted, higher/steeper pile with a smaller footprint which may further improve air transport through the pile, prevent excessive infiltration of precipitation, and save facility space. In addition, all ferrous material will be purposely left inside the aging piles in order to facilitate the temperature increase and to shorten the total drying time prior to the advanced metal recovery.