The effect of inorganic chloride on the partitioning and speciation of heavy metals during a simulated Municipal Solid Waste incineration process

A laboratory tube incinerator was used to investigate the partitioning and speciation of heavy metals, as a result of the presence of inorganic chloride in food residues in simulated Municipal Solid Wastes (MSW). The study results indicate that metal partitioning, seen from incinerator ashes and in flue gas depends on the combustion temperature and sodium chloride concentrations in the simulated MSW samples. The initial metal concentrations show little effect on this metal partitioning. Mercury was most volatile, being approximately 100% vaporized in the incinerator exhaust. Cadmium was relatively volatile, with an average of 90% or more being discharged with the fly ash. Arsenic was found in both the bottom ash and the fly ash, which indicated much less volatility than predicted. The other metals, such as lead, copper, chromium, and zinc, were relatively nonvolatile, with an average of 85% or more remaining in the bottom ash. The volatility of a metal and its compounds increased as combustion temperature and sodium chloride concentration were increased. Therefore, an increase in combustion temperature and/or sodium chloride concentration increases metal partitioning in the fly ash. The analysis of metal species in the ashes indicates that most metal compounds were formed as oxides rather than chlorides. PbO, NaCl and KCl comprised the crystalline phases observed in the fly ash samples; ZnO, Zn(OH)₂, NaCl, KCl, Pb₂O₃, as well as the elemental phases of copper, lead, and zinc were detected in the bottom ash. The presence of NaCl and KCl in both the fly ash and the bottom ash was dependent on the metals relative affinity to the spiked inorganic chloride.