A strategy to establish an industrial thermodynamic data bank. The ternary (Pb, Sn, Zn) liquid phase in the zinc purification process. Extension to any quaternary system (M, Pb, Sn, Zn)

摘要

In the zinc thermal process, the separation of lead can be achieved using the Liquid miscibility gap in the Pb-Zn system. Various impurities can be simultaneously extracted in the lead phase depending on the mutual solubilities, well-characterised by the tie-lines inside the multicomponent miscibility gap. This paper will describe the strategy needed to establish a thermodynamic (M, Pb, Sn, Zn) data bank suitable to accurately calculate this particular phase diagram: a miscibility gap is especially difficult to fit because its shape is strongly related not only to the Gibbs function and its first derivatives but also to its second-order derivatives. A systematic exploitation of the literature was insufficient to realise this goal, and calorimetric measurements in the multicomponent system were needed to model the enthalpy contribution; the entropy contribution was determined by emf experiments using sealed cells and a molten-salt mixture electrolyte. Finally, a Thermo-Gale optimisation was used to fit together all the superabundant information. This strategy will be described in some detail and illustrated by some graphical results concerning our experiments and the calculated (Pb, Sn, Zn) miscibility gap, in spite of the fact that the data bank will remain unpublished as an industrial property. (C) 1998 Elsevier Science B.V. [References: 14]