Application of surface complexation precipitation modeling to contaminant leaching from weathered municipal solid waste incinerator bottom ash

In this paper, we have successfully applied surface complexation/precipitation modeling to describe the leaching of contaminants from weathered municipal solid waste incinerator (MSWI) bottom ash. A combination of 'selective' chemical extractions and leaching at pH values unfavorable for sorption has been shown to be useful for obtaining sorbent mineral and sorbate concentrations. Model calculations are based on the Diffuse Layer Model and a database of sorption constants for hydrous ferric oxide (HFO), both of which are incorporated in the computer code MINT-EQA2. This approach to sorption modeling shows that the leaching of Mb, Pb, and Cu from weathered MSWI bottom ash is well described by surface complexation, whereas the surface precipitation model is needed to describe the leaching data of Zn. The leaching of Cd cannot be explained with these models since the affinity of Cd for HFO is too low. Our results suggest that Mo and Zn are bound mainly to HFO. Additional sorbent minerals, e.g., amorphous aluminum (hydr)oxides, are required to describe the leaching of Cu and Pb.