Pre-treatment of municipal solid waste incineration (MSWI) bottom ash for utilisation in road construction

Sammanfattning: Municipal solid waste incineration (MSWI) bottom ash has the potential for utilisation in construction, e.g. as a road base material. Such an utilisation would decrease the amount of bottom ash to be landfilled. However, leachates generated from bottom ash could be concentrated with respect to salts and metals, causing environmental problems. The use of carbonation of as a method to decrease the leaching of inorganic pollutants from MSWI bottom ash has been studied. Field investigations and laboratory leaching experiments enabled the identification of inorganic pollutants whose leaching might be critical during such an utilisation. Treatment methods by carbonation and water extraction were evaluated regarding the mobility of seven critical pollutants (Al, Cl, Cr, Cu, Mo, Sb and SO4). The stabilising effect of carbonation to a moderate alkaline level (~pH 8.3) was evaluated and compared to the mobilising effect of carbonation in excess (~pH 6.4). Carbonation to a moderate alkaline level demobilised four (Al, Cr, Cu and Sb) of seven critical components. Washing to remove easily soluble salts was recommended in addition to moderate carbonation. Carbonation in excess had the highest mobilising effect on Cr, Cu and Sb when interacted with other factors, mostly pH. Carbonation in excess was therefore proven to be a key factor enhancing the effectiveness of MSWI bottom ash treatment by wet extraction.