DECOPPERING OF LIQUID LEAD BULLION BY ELEMENTAL SULFUR ADDITIONS .2. MECHANISM AND MODEL FOR DECOPPERING

A kinetic model has been developed that is capable of predicting the e xtent of decoppering and the growth of sulphide layers as a function o f time when liquid elemental sulphur is added to liquid lead bullion. The model assumes that the rates of sulphidation of the lead and coppe r of the bullion are controlled solely by the rates of diffusion of le ad and copper ions through the sulphide layers produced. Incorporation of experimentally measured diffusion coefficients for lead and sulphu r into the model produces good agreement with the observations of prev ious workers on lead decoppering, both in the presence and in the abse nce of silver.