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)

In the zinc thermal process, the separation of lead can be achieved us ing the Liquid miscibility gap in the Pb-Zn system. Various impurities can be simultaneously extracted in the lead phase depending on the mu tual solubilities, well-characterised by the tie-lines inside the mult icomponent miscibility gap. This paper will describe the strategy need ed 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 n ot only to the Gibbs function and its first derivatives but also to it s second-order derivatives. A systematic exploitation of the literatur e was insufficient to realise this goal, and calorimetric measurements in the multicomponent system were needed to model the enthalpy contri bution; the entropy contribution was determined by emf experiments usi ng sealed cells and a molten-salt mixture electrolyte. Finally, a Ther mo-Gale optimisation was used to fit together all the superabundant in formation. This strategy will be described in some detail and illustra ted by some graphical results concerning our experiments and the calcu lated (Pb, Sn, Zn) miscibility gap, in spite of the fact that the data bank will remain unpublished as an industrial property. (C) 1998 Else vier Science B.V.