Valorisation of municipal solid waste incinerator fly ashes: solving problems

Municipal Solid Waste Incineration (MSWI) fly ashes constitute, together with Air Pollution Control(APC) residues, the last residues from municipal waste which are not yet recycled nor valorised. Somestudies aim to use such ashes, once treated, in cementitious materials. In this work, electrostaticprecipitator ashes have been characterised, treated and incorporated in cementitious materials. Theeffects due to the presence of chlorides, heavy metals, metallic aluminium have been identified and thetreatment has been adapted in order to solve the encountered problems. The treatment comprises threemain steps: a size-based separation is effective to decrease the heavy metal concentration in adetermined size fraction that could be further valorised; a washing (with only water) can remove up to97% of the initial chlorides; a reactive washing (with NaOH) prevents the paste from swelling.MSWI fly ash valorisation requires thus a deep treatment involving large reagent consumption.However, if the treated ashes may be valorised in cementitious materials, which may be dedicated tospecific applications, they will not be landfilled and their charge for the incineration industry, astherefore for the society, would decrease.