Development of Experimental Techniques for the Phase Equilibrium Study in the Pb-Fe-O-S-Si System Involving Gas, Slag, Matte, Lead Metal and Tridymite Phases

Abstract

Present society challenges, including metal scarcity, recycling, and environmental restrictions, resulted in the increased complexity and variability of metallurgical feed streams. Metallurgical processes involving complex lead and copper-containing slag and matte phases are now commonly used in response. Optimization of existing and development of new metallurgical processes require fundamental information on slag–matte phase equilibrium. Development of the experimental methodology for the characterization of slag–matte phase equilibrium is presented in the paper. Following a detailed analysis of the potential reaction pathways, experimental techniques have been developed that enable accurate measurement of slag–matte phase equilibrium in the Pb-Fe-O-S-Si system. The application of the techniques has been demonstrated for two important sets of conditions: (i) Condensed phase equilibrium for the slag–matte–metal–tridymite subsystem; and (ii) Gas–slag–matte–tridymite equilibrium at fixed oxygen and sulfur partial pressures. The experimental methodology involves high-temperature equilibration of synthetic samples, fast quenching, and microanalysis of the compositions of phases using electron probe X-ray microanalysis (EPMA). The experimental results are not affected by the changes in the bulk composition of samples during equilibration; this helps to overcome the significant barriers previously encountered in undertaking accurate measurement and characterization of these systems.