Thermodynamic studies of ZnO in solid zinc silicate. Fundamental studies of zinc extraction by the iron-reduction distillation process (4th report)

Phase relations of solid ZnO-SiO₂, ZnO-SiO₂-CaO, ZnO-SiO₂-Al₂O₃ and ZnO-SiO₂-MgO systems at 1073 K have been determined by X-ray diffraction and X-ray microanalysis studies of quenched samples. e.m.f. measurements using stabilized zirconia solid electrolytes have been carried out to determine the activities of zinc oxide in solid ZnO-SiO₂ and ZnO-SiO₂-CaO systems, the activities of zinc in liquid Au-Zn alloys and the standard free energy of formation of Cu₂O and ZnO. In the ZnO-SiO₂ system, the activities of zinc oxide are represented by a single value of a_ZnO = 1.0 over the range N_ZnO = 0.67 - 1.0, while at N_SiO(2) = 0.33 - 1.0 they showed a single value of around 0.2 at 973 and 1073 K. In the ZnO-SiO₂-CaO system, the activities of zinc oxide showed a single value of a_ZnO = 1.0 in the compositions near pure ZnO at 973 - 1073 K. In the ZnO-SiO₂-Al₂O₃ and ZnO-SiO₂-MgO systems, solid solubilities of SiO₂, Al₂O₃, MgO in ZnO phase were small. The activities of zinc oxide showed a single value of a_ZnO = 1.0 in the compositions near pure ZnO. In liquid Au-Zn alloys, the activities of zinc showed considerable negative deviation from Raoult's law at 1023, 1073 K and agreed with published data. The standard free energies of formation of Cu₂O and ZnO were determined.