Two-stage simulation of the major heavy-metal species under various incineration conditions

A thermodynamic equilibrium model was used to determine the major species of chromium, lead, cadmium, copper, and zinc formed under various incineration conditions. The effects of temperature and oxygen, chlorine, sulfur, and hydrogen content on the speciation were established by the minimum Gibbs free energy method. Sixty-seven compounds of five metallic species were determined in this study. The simulation conditions included: 1) single metal with oxygen, chlorine, and sulfur system; 2) different chlorine and hydrogen content; and 3) comparisons of a single combustion chamber and a two-stage combustion chamber. The simulation results indicated that the oxides were the dominant forms in a single metal-oxygen system, while the metallic chlorides were the major species in a metal-chlorine-oxygen system. When sulfur was present, in the case of all metals other than Pb, the metallic sulfates were the major species at temperatures below 1000 K, and metallic oxides were the dominant species above 1000 K. Increasing the temperatures caused a decrease of lead chloride, but increased the formation of other metallic chlorides. The concentrations of metallic chlorides decreased significantly as the hydrogen moles were 2 similar to 3 orders higher than those of chlorine. The level of difference between one-stage and two-stage simulations depends on the species formed in the one-stage simulation. (C) 1998 Elsevier Science Ltd.