Phase equilibrium study of ZnO-'FeO'-SiO2 System at Fixed Po2 10-8 atm

Analysis of quenched copper smelting slag from the bottom blown furnace at Dongying Fangyuan Nonferrous Metals Co., Ltd. (Fangyuan) shows that significant ZnO is present in both liquid and spinel phases. Phase equilibria have been investigated in the system ZnO-Fe2O3-SiO2 in air and system ZnO-'FeO'-SiO2 in equilibrium with metallic iron. These conditions cannot represent copper smelting process in which oxygen partial pressure is around 10-8 atm. In the present study phase equilibria in the system ZnO-'FeO'-SiO2 have been carried out at Po2 10-8 atm. A series of experimental difficulties have been overcome to enable the ZnO-containing system to be investigated under reducing conditions controlled by CO-CO2 gas mixture. The experimental approach includes master slag preparation, high-temperature equilibration, quench and electron probe X-ray microanalysis (EPMA). Phase compositions in the quenched samples were measured by EPMA and used for construction of phase diagram. It was found that the isotherms of the system ZnO-'FeO'-SiO2 at Po2 10-8 atm are significantly different from those in air or in equilibrium with metallic iron. Presence of ZnO in copper smelting slag significantly increases the liquidus temperature in spinel primary phase field. The partitioning of ZnO in liquid and spinel is also reported in this paper.