Phase Separation and Silver and Gold Distribution in the Pb-Fe-Sb and Pb-Cu-Sb Systems at 1200°C

Abstract

The miscibility gap between speiss and metallic lead as well as silver and gold distribution were determined at 1200°C in the Pb-Fe-Sb and Pb-Cu-Sb ternary systems.
Phase separation between speiss and metallic lead occurs in the 37-53 mass% antimony range in speiss of the Pb-Fe-Sb system. Below this composition, solid iron precipitates to form a three phase equilibrium region. Mutual solubility between the speiss and the lead phases is relatively small and minimum lead solubility in speiss is about 5 mass%. However, antimony is not entirely concentrated in speiss since antimony content in metallic lead is one-half the content in speiss. The miscibility gap in the Pb-Fe-Sb system is narrower than in the Pb-Fe-As system, while the two phase region in the Pb-Cu-Sb system plotted in atomic percent depicts a nearly identical miscibility gap as in the Pb-Cu-As system at 1200°C.
In the Pb-Fe-Sb system, a decrease in the iron distribution coefficient between speiss and metallic lead, defined as L_FesP/Pb (mass% Fe in speiss)/(mass% Fe in lead), results in an increase in the silver distribution coefficient from 0.1 to 0.8, suggesting an intimate relationship between silver distribution and iron activity. The distribution coefficient of silver in the Pb-Cu-Sb system is about unity.
The distribution coefficient of gold in the Pb-Fe-Sb system is approximately 0.8, whereas in the Pb-Cu-Sb system it is about 5, demonstrating a capacity for speiss to absorb an appreciable amount of gold. Therefore, a potential exists for utilizing speiss as an extractive medium to collect, for example, copper and precious metals dissolved in slag.