Activity of lead in copper matte at very low lead concentration

摘要

The thermodynamic behavior of lead in Cu-Fe matte was investigated using a transportation technique where argon gas was bubbled into a bath of copper matte containing approximately 100 ppm lead at temperatures between 1300 and 1400°C. The effect of flow rate, temperature and matte grade were investigated on the lead transport from a bath containing 100 grams of synthetic copper matte to the gas phase. The concentration of lead in the bath was followed with time. At argon flow rates between 3 l h-1 and 18 l h-1, it was observed that the concentration change of lead in the matte was found to follow a first order relationship where the calculated concentration at time t ,is of the form: [ Pb ]= a.e-b.t where a is equal to the initial lead content in ppm, [ Pb ]i, and b is an exponential term and t is time in minutes. The partial pressure of lead species in the gas phase was calculated from the concentration changes in the matte and from the bubbling gas rate. At gas flow rates between 3 and 9 l h-1, the lead removal appeared to be under equilibrium conditions. At higher gas flow rates, the apparent rate decreased, mainly due to splashing of matte into the cold zone of the furnace. In these experiments with Ar as the carrier gas, the sulphur and oxygen partial pressures of the melt were not controlled. Chemical analysis of the major components in the matte showed only random variation with bubbling time, and so a thermodynamic solution model for copper matte was used to calculate the equilibrium sulphur pressure expected. From this approach the proportion of Pb, PbS and Pb2 species in the gas could be calculated knowing the relevant reaction constants, e.g.: PbS(g) = Pb(g) + 1/2S2(g) From the proportions of the lead species in the gas, the value of the lead activity coefficient with respect to the gas state could be determined. For a 50% copper matte, it was found that the activity coefficient increased with temperature, from a value of 0.8 at 1300°C to 1.4 at 1400°C. At the white metal composition, this value was 0.28 at 1300°C. These results are compared with other relevant studies in the literature.