Influence of H 2 O/HCl/H 2 S containing gas mixtures on condensation behavior of the trace metals lead and cadmium under gasification-like conditions

In order to achieve an environmentally friendly treatment of growing municipal solid waste, gasification technology as a good candidate gains increasing attention and will play a vital role in the processes of waste-to-energy. In this study, the condensation behavior of trace metals Pb and Cd, especially in HCl/H 2 S containing gas mixtures was investigated under lab-scale gasification conditions. It was found that PbO was a completely predominant condensation species in atmospheres containing H 2 O or HCl while regarding Cd condensation under identical conditions metallic Cd prevails. It was also observed that the presence of 125 ppm v HCl caused a significant shift of the condensation of PbO from 790 to 670 °C. In the presence of H 2 S, the condensation as sulfides, i.e. PbS and CdS occurred overwhelmingly. A mechanism for the condensation of PbS was proposed, with which an interesting phenomenon was illuminated that the condensation of PbS moves to higher temperatures as the H 2 S concentration increases from 125 to 250 ppm v, while it shifts towards lower temperatures with a further concentration increase to 500 ppm v. In addition, the difference in condensation mechanism for Cd and Pb was compared and discussed.