Vapor Pressure Measurements of heavy Metal Component in Molten Slag and Incinerator Residue by Transpiration Method Using Vertical Volatilization Chamber

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As fundamentals for developing an efficient process to eliminate detrimental components such as lead, arsenic and antimony in the molten slag and incinerator residue by means of volatilization, the data on vapor pressure and activity coefficient of these components are of practical importance. Hence, in the present study, a transpiration method using a vertical volatilization chamber was developed and the vapor pressure of PbO in the liquid PbO-FeO_<1.5>-CaO-SiO_2 and PbO-ZnO-FeO_<1.5>-CaO-SiO_2 slags and those of SbO_<1.5>, SbO_<2.5> and AsO_<2.5> in the liquid CaO-SiO_2-FeO_<1.5> slags were determined at 1150-1300℃. On the basis of these data, the activity coefficients of these components in the slag were derived.For any slag investigated, the activity of PbO was found to present a negative deviation from the Raoultian behavior and the activity coefficient of PbO showed a minimum value at the mole fraction of PbO in the slag with about 0.5. It was found that the activity coefficient of PbO increased with increasing basicity of slag. It was also clarified that the activity coefficient of PbO in the slag with ZnO was smaller than that in the slag without ZnO.The gas species evaporated from the slags were evaluated using the obtained thermodynamic data and it was suggested that the PbO monomer is prevailing in the gas phase while As_4O_6 and Sb_4O_6 prevail for arsenic oxide and antimony oxide, respectively. Thus, the volatilization behavior of these heavy metal components in the slag and incinerator residue was discussed on the basis of the obtained data.