FactSage database for the pyrometallurgy of lead (Pb) processing systems
A research program is under way to create an accurate and comprehensive self-consistent thermodynamic database describing the complex non-ferrous pyrometallurgical systems encountered in lead-copper-zinc extraction and recylcling processes. The major components, Cu-Pb-Fe-Zn-Ca-Si-O-S form liquid slag, matte and metal phases. Al and Mg are present principally in the slag solution. As, Sb, Bi, Sn, Ni, Ag, Au are minor elements that distribute among all liquid phases and may form liquid speiss. The database includes solid solutions and stoichiometric phases: oxides (spinel, melilite, zincite, olivine, etc.), sulfides, sulfates, metallic alloys, and speiss-forming compounds. The gas phase includes volatile metal-containing species. Thermodynamic modelling is integrated with the experimental program conducted in PYROSEARCH. The CALPHAD methodology for the thermodynamic optimization of database parameters is applied, which imposes strict requirement for the self-consistency among the solution models and within the sub-systems.
This is illustrated by the analysis of self-consistency between PbO-SiO2 slag and Pb-S matte. The slag solution is constructed using the Modified Quasichemical Formalism in Quadruplet approximation: (Pb2+, Si4+, …)(O2-, S2-). An experimental study of the solubility of solid PbS in slag is used to improve the thermodynamic description of the Pb-S first-nearest-neighbor short-range-bonding in slag. This in turn is necessary for accurate prediction of the distribution of lead (Pb) and minor elements among liquid phases. Examples of calculations of slag/matte/metal equilibria in higher-order systems close to the industrial lead smelting conditions and lead refining example with the formation of solid or liquid speiss are provided. The thermodynamic database developed in the present study is compatible with the FactSageTM-family of software products (ChemSheetTM, SimuSageTM, ChemAppTM).