Comparison of Pb, Cd, Zn, and Cu chlorination during pyrolysis and incineration

- PVC can directly react with ZnO or CuO, while PbO or CdO reacts with HCl from PVC.
- PbO was more easily chloridized than other metal oxides during thermal treatment.
- NaCl alone can convert PbO to PbCl2 via a liquid-solid reaction at >801 °C.

The mechanisms of chlorination of PbO, CdO, ZnO, and CuO by poly(vinyl chloride) (PVC) and sodium chloride (NaCl), including their reaction temperatures, pathways, and products, were studied and compared. It was found that PVC can chloridize the four oxides via different mechanisms, producing corresponding chlorides. The heavy metal oxides in PVC-PbO and PVC-CdO were chloridized by gas-solid reaction with HCl, while direct chlorination by PVC occurred at 190 °C in PVC-ZnO and PVC-CuO, as their initial temperatures for weight loss were 35-44 °C lower than that of PVC decomposition. The relatively facile chlorination of PbO as compared with the other oxides might be a reason why Pb was more volatile than the other metals. NaCl had no chlorination effect on CdO, ZnO, or CuO in the absence of other media. It was found for the first time that NaCl alone could convert PbO to PbCl2 via a liquid-solid reaction when the temperature was higher than the melting point of NaCl (801 °C), and oxygen was not involved. The chlorination effect of NaCl was markedly weaker than that of PVC. Since both PVC and NaCl are the most important chlorine sources in solid waste, their chlorination effects on heavy metals cannot be ignored.