Phase Relations and Activities of the FeO-ZnO-ZnFe₂O₄-Fe₃O₄ System

Fundamental studies of zinc extmction by the iron-reduction distillation process (9th Report)

Abstract

Phase relations in the FeO-ZnO-ZnFe2O4-Fe3O4 system at 1, 100 K have been determined by the X-ray microanalysis and X-ray diffraction studies of the quenched samples. The results indicate that magnetite (Fe₃O₄) and zinc ferrite (ZnFe₂O₄) form a complete series of solid solutions in the Fe₃O₄-ZnFe₂O₄ system, while there is a miscibility gap in the FeO-ZnO system. Lattice constants for the Ze₃O₄-ZnFe₂O₄ spinel solid solutions in equilibrium with the Fe0-ZnO system exhibit positive deviations from Vegard's law.
The partial oxygen pressures were measured by an e.m.f. method using the stabilized zirconia solid electrolytes, the activities were obtained by applying the Gibbs-Duhem relations to the oxide phases. Activity of zinc oxide in the FeO-ZnO system coexisting with the Fe₃O₄-ZnFe₂O₄ solid solutions at 1, 100 K shows a considerable positive deviation from Raoult's law except that at ZnO-rich side it exhibits a slight positive deviation from Raoult's law in the range up to the solid solubility limit. The activity coefficients at infinite dilution, reFeo and γ⁰znO, at1, 100K were estimated at 4.7 and 0.9, respectively.Both the activities of magnetite and zinc ferrite in the Fe3O4-ZnFe₂O₄ solid solutions coexisting with the FeO-ZnO system at 1, 100 K show peculiar behavior. The activity of magnetite has a finite non-zero value in pure ZnFe₂0₄. The standard Gibbs energy of the reactions at 1.100 K were also obtained as follows:
ZnO (s) + 2/3Fe₃O₄ (s)+1/602 (g)=ZnFe₂0₄ (s), -59090±47J·mol^-1 (ZnFe₂O₄) and ZnO (s)+Fe₂O₃ (s)=ZnFe₂O₄ (s), -30160J·mol-1 (ZnFe₂O₄).