Polysulfide as a novel chemical agent to solidify/stabilize lead in fly ash from municipal solid waste incineration

Polysulfide was produced and tested for use as an inexpensive chemical agent for the solidification/stabilization of lead in fly ash, generating little hydrogen sulfide gas. According to the equations Sn2-→S+Sn-12- and Sn2-+H+→HS-+Sn-1, this agent was expected to achieve long-term stability of disposed Pb. The leachate concentration of Pb in fly ash after sulfide treatment showed a decrease-increase-decrease trend. We also compared Pb leaching behavior from an aging/weathering experiment to thermodynamic modeling using the database from the Geochemist's Workbench software. Thermodynamic modeling indicated the tendency that when the precipitate was formed in the order of PbO, PbCO₃·PbO, and PbCO₃, the total concentration of soluble Pb will be lowered. The leaching curve of Pb in fly ash without a lime slurry injection system was close to PbO, whose activity was initially near 1, but when leaching time increased, it shifted to that of PbCO₃·PbO, before finally ending at that of PbCO₃. However, Ca(OH)₂ sprayed on fly ash interfered with the carbonation process of Pb.