Putting accelerated carbonation of bottom ash into practice: operation of a semi full scale continuously fed rotating drum reactor

Bottom ash is the dominant residue from municipal solid waste or refuse-derived fuel incineration. Disposal costs chiefly depend on the leachability of trace metals and salts. The mobility of these constituents is classically minimized by ageing the material for several months. Ageing involves the oxidation of metals, dissolution and precipitation of hydroxides and salts, and most importantly, carbonation of the bottom induced by the uptake of atmospheric carbon dioxide. Technically enhanced exposure to carbon dioxide sources has been referred to as accelerated carbonation. Here we report on the successful implementation of the accelerated carbonation of bottom ash in a continuous pilot-scale rotating drum reactor operated with the flue gas of a cogeneration plant. The system was tested in 20 field trials that aimed at stabilizing the ash such as to comply with the regulatory standards for disposal on a lower landfill class or for its geotechnical re-use. Performance and process efficiency were addressed by maximizing reactor loading and minimizing the residence time of bottom ash. While leachtate values of the fresh bottom ash were indicative of a hazardous waste pertaining to a class III landfill, the carbonated material fulfilled the regulatory standards for a class I landfill and was, in addition, complied with the standards for geotechnical re-use. In the field trials bottom ash residence times could be cut to 30 minutes thus allowing for an on-line integration of the accelerated carbonation process.