Bismuth, Arsenic and Antimony Removal From Anode Copper via Vacuum Distillation

Abstract

Experiments determined rates of removal of bismuth, arsenic and antimony by vacuum refining 35–kg melts of impure copper anode at temperatures in the range 1170–1300°C and chamber pressures in the range 3–25 Pa. In 40–60 min of treatment, bismuth elimination was in the range from 41 to 88% and arsenic elimination was in the range from 2 to 25%. Antimony removal rates were found to be negligible, due to a combination of the effects of a low antimony activity coefficient and the low vapour pressure of pure antimony. It was found that bismuth removal was gas phase mass transport controlled except when the ratio of the melt vapour pressure to the chamber pressure (defined here as the Over Pressure Ratio (OPR)) exceeded a value of two. At OPR's greater than two, there was mixed control from gas phase and liquid phase kinetics. Arsenic removal rates were evaporation controlled except when OPR was less than about 0.3, when gas phase control came into consideration.