Abstract
A kinetic study on the volatilization of PbO from CaO-SiO2-Al2O3 molten slag, which simulated the volatilization of PbO in municipal solid waste melting, was conducted at a temperature range of 1673 to 1773 K in an 80% N2, 20% O2 atmosphere with a space velocity of N2-O2 mixed gas of 1.50×10−4~3.01×10−3 m·s−1 in the melting furnace. The composition of the employed slag was varied by changing the weight ratio of CaO, SiO2 and Al2O3 from 10 to 60wt%. The rate of volatilization of PbO was determined based on the film theory, with the assumption that the kinetic model might be applicable to the transportation of PbO from CaO-SiO2-Al2O3 molten slag to the gas phase. The rate of volatilization of PbO from CaO-SiO2-Al2O3 molten slag in an N2-O2 atmosphere was estimated by taking into consideration the rate of vaporization of Mn from iron melting in an argon gas flow condition at atmospheric pressure. In the present study, the overall mass transfer coefficient was determined as a function of slag composition and temperature, and the rate of volatilization of PbO from CaO-SiO2-Al2O3 molten slag was estimated.
As a result, it was apparent that the rate of volatilization of PbO from CaO-SiO2-Al2O3 molten slag in the N2-O2 gas flow condition was influenced by both the rate of vaporization of PbO from the interface of gas-molten slag and the mass transfer rate of PbO in the liquid phase, when the flow rate of 80% N2, 20% O2 mixed gas was higher than 9.02×10−4 m·s−1. The calculated results on the volatilization of PbO predicted by the present kinetic study were in fairly good agreement with the experimental results for a low viscous CaO-SiO2-Al2O3 molten slag with 0.40 to 1.4Pa·s viscosity under the present experimental conditions.
