Zinc reoxidation in the shaft of a zinc–lead Imperial Smelting Furnace—2: zinc–carbon–oxygen system in combination with sinter and coke substrates

Abstract

The effects of sinter and coke substrates on the chemistry and kinetics of zinc vapour reoxidation in the system ZnO-Zn-CO-CO₂(-H-H₂O) were investigated. Zinc oxide was observed to deposit preferentially on to sinter and coke rather than the walls of the quartz tube. The multi-faceted surface of the sinter probably provided many nucleation sites, accounting for the threefold increase in deposition rate. On coke, how-ever, the rate was 30 times greater between 800 and 900°C and 300 times greater at 700°C. This was attributed in the main to the very high surface area offered by the deeply penetrating pores of the coke. The highly reactive carbon surface with its abundant nucleation sites probably also contributed. An addition of 5 vol% hydrogen to the gas stream did not increase the deposition rate on to the sinter and coke significantly. Zinc droplets were observed to condense on to sinter in the pre-condenser zone, subsequently oxidizing to zinc oxide and forming a crust. Lead was observed as an immiscible phase with the zinc. Zinc sulphide was also observed in the pre-condenser zone, propagating from a base zinc oxide crust. The quantity of zinc sulphide produced is determined by the sulphur and sulphide activities in the coke and sinter, respectively.