Henrian Activity Coefficient of Pb in Cu-Ni Mattes

Abstract

A transpiration method was used to evaluate the Henrian activity coefficient of Pb (γoPb) in Cu-Ni mattes. Values for the activity coefficient of Pb were evaluated at 1473 K as a function of the Cu/Ni molar ratio from 0 to 1 and as a function of the sulphur deficiency (defined as SD = XS – 1/2XCu – 2/3XNi, where Xi is the mole fraction of the ith species) from – 0.1 to 0. The dependence of γoPb on both the Cu/Ni molar ratio and SD is represented by the equationsγoPb (at SD = –0.04) = 0.610 – 1.16 (Cu/Ni) + 5.08 (Cu/Ni)2andγoPb (at Cu/Ni = 0.5) = 1.97 + 42.2·SD + 636·SD2Analysis of the activity coefficient (γPb) as a function of the trace element concentration reveals that the activity coefficient is independent of Pb content at weight percents less than 0.8. Nickel in a sulphur deficient matte decreases the volatility of lead, whereas substitution of Cu for Ni significantly increases its volatility. In a matte containing both Cu and Ni, decreasing the free metal content (i.e. raising the sulphur content of the matte) first decreases the volatility of the lead and then raises it modestly. Although increasing SD decreases γPb, the increase in sulphur content of the matte leads to higher values for the vapour pressure of S2 that promotes PbS(g) formation and thus increased volatility of that species.