Decoppering of Liquid Lead Bullion by Elemental Sulphur Additions -- Part 1: Sulphidation of Lead by Elemental Sulphur: sulphidation of lead by elemental sulphur

The rate of sulphidation by elemental sulphur of pure lead and of lead doped with varying amounts of silver has been measured in the temperature range 250-310°C. Sulphidation was found to follow parabolic kinetics and the measured rates of sulphidation have been analysed in terms of rate control by diffusion of lead through the lead sulphide product layer. Effective interdiffusion coefficients of lead in lead sulphide have, thus, been determined. Above a critical silver content silver doping is shown to decrease the rate of sulphidation dramatically. The critical silver content appears to correspond to that required to change the PbS from n-type to p-type.