Author:

Keywords:

APC residue, Chloride, Fly ash, Lead, Solidification, Stabilization, Waste-to-Energy

Abstract:

Most of the fly ash (FA) and air pollution control residue (APC residue) of modern waste-to-energy (WtE) plants do not meet the Waste Acceptance Criteria (WAC) for hazardous waste landfills set by the EU Council decision 2003/33/EC, primarily because the leaching of lead (Pb) and/or chlorides (Cl-) is too high. In this work, the effect of selected additives on Pb leaching from APC residue was investigated. Addition of 10% by mass of FeCl3 had the highest effect on the Pb leaching from APC residue, which decreased immediately from 1694 mg.kgDM-1 to 9.7 mg.kgDM-1 and remained almost constant upon further curing. Addition of 10% by mass of Na2CO3 or Fe2(SO4)3 immediately decreased the Pb leaching by about 50% but further curing of the S/S material was needed to reach the WAC. The effect of all these additives surpassed that of the effect of the pH change they caused. A second series of leaching experiments showed that addition of cement to mixed FA and APC residue reduced the Cl- leaching by about 35%, which was not sufficient to reach the WAC. Additional experiments showed that washing of residues prior to landfilling can reduce the Cl- leaching of the washed residues by about 90% to values below the WAC. Addition of Na2CO3 , Fe2(SO4)3, FeSO4 or H3PO4 to APC residue prevented co-elution of Pb during the washing step and assured that the Pb leaching of the washed residues was well below the WAC. An economic evaluation taking into account additive and landfilling cost showed that addition of 0.2 Mg Na2CO3, 0.25 Mg FeSO4 or 0.1 Mg H3PO4 per Mg of APC residue were cheaper options than adding 0.4 Mg cement.