Reduction kinetics of lead-rich slag with carbon in the temperature range of 1073 to 1473K

The use of the ISASMELT furnace results in a greatly simplified operation with more efficient capture of SO2, and lead fugitive emissions. In addition, the high lead slag product is low in sulfur (<0.5%) compared to sinter, reducing the environmental problems with the blast furnace operation. Therefore, the ISASMELT furnace has a promising application in the filed of lead production and has replaced the conventional sinter plant in modern lead production. Lead-rich slag produced from the IsaSmelt furnace is used as feedstock to a lead blast furnace for the production of lead metal. To assist in the optimization of the lead blast furnace operations, it is essential to obtain a fundamental understanding of the reaction and kinetics occurring during the reduction of the lead slag in the blast furnace. In this study, extensive experiments have been carried out on the reduction of lead sinters in carbon crucibles at temperature range from 1073 to 1473K. A comprehensive study has been carried out on industrial sinters and synthetic slags to compare the reduction kinetics. The extent of reaction for each sample is measured by measuring the volume of gas produced at a given temperature and time. For all slag investigated at fixed temperature, the reaction rate between the slag and carbon is initially fast and then the rate becomes slower as the extent of reaction increases. Only limited reaction between slag and carbon occurs at temperatures below 1173K. At temperatures above 1173K, the reaction rate increases significantly with increasing temperature. For industrial sinters slag, it was found that a layer of metallic lead was formed at the interface between the sinter sample and carbon at the temperature of 1473K, indicating that the metallic lead layer reduces the contact area between the sinter and carbon thereby reducing the overall rate of reaction. For the slag compositions investigated liquid starts to form at approximately 1073K. Proportion of liquid phases increases with temperature increasing. The reduction reaction belongs to liquid-solid reaction. The reaction kinetics was chemical reaction controlled at initial stage and diffusion controlled at longer time interval. The apparent activation energy was calculated to be 83.8 kJ/mol (chemical controlled) and 224.9 kJ/mol (diffusion controlled) for reduction of sinter slag. For the synthetic slag, the reaction activation energy was 102.9 kJ/mol at initial stage and 259.4 kJ/mol at diffusion controlled stage.