2004 Volume 30 Issue 6 Pages 778-785
The effects of NaCl, KCl and CaCl2 on chloride volatilization of Pb, Zn and Cu from three different molten fly ashes and model fly ashes were investigated in the temperature range of 873-1173 K and under N2 atmosphere.
Results showed that when the model ashes containing PbO, ZnO and CuO were heated at 1023 K after mixing with NaCl, KCl and CaCl2, the effectiveness of inorganic chloride for volatilization of PbO, ZnO and CuO was in the order of CaCl2>NaCl>KCl. The volatilization behavior of Pb in the molten fly ashes showed the same trend as that in the model fly ashes, and the volatilization ratio of Pb increased with heating temperature above 873 K. Also, the chlorination of Pb was favored in the presence of NaCl, KCl and CaCl2, which formed a low temperature eutectic mixture below 923 K. On the other hand, volatilization behavior of Zn from the model fly ash was greatly different from that from the molten fly ash. ZnO in the molten fly ash was thought to be reduced to Zn by unburned carbon or Fe contained in the ash, and the Zn was volatilized at a lower temperature than melting temperature of ZnO. Volatilization ratio of Cu from the model fly ash was low even at 1173 K, and no volatilization of Cu was observed for the molten fly ash. As in the case of Zn, CuO in the molten fly ash was thought to be reduced to Cu by unburned carbon and Fe, and the Cu was hardly chlorinated to form CuCl.
