ACID NEUTRALIZING CAPACITY OF MUNICIPAL WASTE INCINERATOR BOTTOM ASH

One of the main concerns in relation to municipal solid waste incinerator (MSWI) bottom ash is the longterm mobility of heavy metals, which depends on leachate pH and thus on the acid neutralizing capacity of MSWI bottom ash. The acid neutralizing capacity is determined by titration. Independent of titration methodology, MSWI bottom ash appears to be predominantly buffered by Ca minerals. In alkaline conditions, calcium hydroxides/silicates and CaCO3 dominate the solution chemistry of the aqueous phase. They constitute the acid neutralizing capacity (ANC) equivalent to the titration end point at pH 7.5. Fresh samples have an ANC(7.5) Of 1.2-1.7 +/- 0.05 mequiv/g. In neutral to acid conditions, silicate dissolution becomes increasingly important. Calcium carbonate is the predominant component of ANC(7.5) in samples aged in landfills or forest track coffers. Determined ANC(7.5) values of the aged samples range between 0.6 and 1.0 +/- 0.05 mequiv/g. Intrinsic neutralization reactions with CO2 or silica are the most probable explanations for the absence of the basic calcium hydroxide/silicate components.