Zinc reoxidation in the shaft of a zinc-lead Imperial Smelting Furnace-1: zinc-carbon-oxygen system with deposition initiated on a quartz substrate and subequent propagation on zinc oxide

摘要

The kinetics of zinc vapour reoxidation in the Imperial Smelting Process was investigated in the system ZN-ZnO-CO-CO_2(-H_2-H_2O) by passing the gases through a heated quartz reactor tube containing zinc oxide pellets. The temperature profile could be controlled accurately and a mass balance was subsequently performed on the system. The morphological features of the zinc oxide deposit were investigated by scanning electron microscopy. The basic reoxidation reaction isZn(v) + CO_2(g) = ZnO + CO(g)At temperatures, T, less than 750 deg C a distinct correlation was found between the deposition rate, R, excess zinc partial pressure (P_(Zn)- P~e_(Zn)) and zinc oxide morphology. Furthermore, the deposition rate at >850 deg C was significantly greater than that at <750 deg C, the greater thermodynamic driving force losing out to the reduced temperature kinetic effect. Two distinct types of crystals were produced for the two temperature ranges, indicating two different mechanisms of formation. At 750 deg C < T < 850 deg C a complex mixed morphology was observed. At >800 deg C 5 vol percent hydrogen added to the gas stream increased the deposition rate by one order of magnitude-an effect that is attributed to the alternative reoxidation reactionZn(v) + H_2O(v)=ZnO + H_2(g)At <760 deg C the increase is much less pronounced and is thought to be due to elevated CO_2 levels arising from the reactionCO (g) + H_2O(g) = H_2(g) + CO_2(g)Carbon deposition was observed separately in the presence of furnace sinter and sulphuric acid. This was most probably caused by sulphur from these two sources. When they were absent carbon deposition via the reactionZn(v)+CO(g)=ZnO+Cwas not observed, indicating that CO is not a viable oxidizing species in the process.