Henrian activity coefficient of Pb in Cu-Fe mattes and white metal

Abstract

A transpiration method was used to evaluate the Henrian activity coefficient of Pb (γ°_Pb) in Cu-Fe mattes and white metal. Values for the activity coefficient of Pb (γ _Pb) have been evaluated as a function of the Cu/Fe molar ratio from 1 to ∞, as a function of the sulfur deficiency (defined as SD=X _S−1/2X _Cu−X _Fe, where X ₁ is the mole fraction of the ith species) from −0.02 to +0.02, and at temperatures between 1493 and 1573 K. Analysis of γ _Pb as a function of the trace element concentration reveals that the activity coefficient is independent of Pb content at weight percents less than 0.2. Dependence of γ _Pb on temperature was found to be slight, and as such, comparison of data obtained by other investigators at 1473 K was possible. Agreement in the data is excellent, and all the data have been used to generate the empirical equation

$$\log \gamma _{Pb}^o = 0.609 - 40.0SD - \frac{{0.556}}{{(Cu/Fe)}} - 12.9SD^2 + \frac{{0.574}}{{(Cu/Fe)^2 }} + 25.0\frac{{SD}}{{(Cu/Fe)}}$$

that is valid over the temperature range from 1473 to 1573 K. The experimental results suggest that in high sulfur content melts, lead is stabilized as PbS. The results also reveal that free copper, in sulfur deficient mattes, tends to stabilize Pb, but to a lesser extent than that experienced with excess sulfur in high sulfur melts. Failure to account for sulfur loss can lead to a significant error. This article also presents a method whereby sulfur loss during experiments can be accounted for in computing activity coefficients.