Dynamic studies on lead volatilization from CaO–SiO2–Al2O3 molten slag under N2–CO–CO2, N2–HCl and N2–H2S gas atmospheres

Abstract

Dynamic studies on the volatilization of lead from CaO–SiO2–Al2O3 molten slags were conducted in a lab-scale melting furnace from 1623 to 1773 K under different mixed gas atmospheres of CO 0.05–0.3 atm to CO2 0–0.3 atm to N2 (balance), HCl 1.7 × 10−3–6.7 × 10−3 atm to N2 (balance), and H2S 3.0 × 10−4 to 1.7 × 10−3 atm to N2 (balance). The slag samples consisted of the mixed powders of 20–50 wt% CaO, 30–60 wt% SiO2, and 10–40 wt% Al2O3, containing 2000 ppm PbO.Results showed that the rates of volatilization of lead from the CaO–SiO2–Al2O3 molten slags under the N2–CO–CO2, N2–HCl, and N2–H2S gas atmospheres were higher than those under the simulated air (N2–O2), which increased with CO, HCl, and H2S partial pressures. At $$p_{{HCl}}$$ = $$p_{H_{2}S}$$ = 1.7 × 10−3 atm, the apparent rate constants for the volatilization of lead under the N2–H2S and N2–HCl gas atmospheres were nearly equal, which increased with a rise in temperature. Results also showed that the rate of volatilization of lead from the molten slag decreased drastically with the increasing viscosity of the molten slag, in the viscosity range lower than 3 Pa s. Consequently, the volatilization of lead from the CaO–SiO2–Al2O3 molten slag was significantly influenced by CO, HCl, and H2S partial pressures and by the viscosity of the molten slag.