Experimental Determination of the Phase Equilibrium in the Cu-O-ZnO-SiO2-CaO-MgO System

Abstract

Due to the intensive consumption of high quality concentrates, copper smelters are increasing portions of multi-mineral ores and secondary scraps in their feeding materials. The smelting of complex materials is always accompanied by the formation of large amount of slag. Impurities in the feeding materials will be oxidized during the smelting process, and those oxides will form the slag phase together with fluxes. Certain amount of refractory materials will be eroded by molten phases, and then merge into the slag phase. The monitoring of slag compositions and properties has significant importance. Zinc is one of the major impurity elements in copper making, and it will be oxidized to zinc oxide (ZnO) in the smelting process. Zinc content in copper scraps, for example WEEE materials and waste brass, is also quite high, and it will also be oxidized and merge into the slag phase. Currently, ZnO content in copper smelting slags is increasing. However, the thermodynamic information about high ZnO content slag is still incomplete. The thermodynamic properties of the slag can be achieved by software calculation. But there are a lot of uncertainties in applying those extrapolated information into practice. Accurate experimental data are needed in the thermodynamic assessment of those less known systems.With the guidance of calculated phase diagrams by MTDATA 5.10 and its Mtox 8.1 database, the equilibration/quenching/SEM/EDS+EPMA technique has been successfully applied in investigating the phase relationship in the Cu-O-ZnO-SiO2-CaO-MgO system and its subsystems. Phase relationships in a wide temperature range (1000 °C – 1700 °C), and at various oxygen partial pressures (pO2 = 0.21 atm, pO2 = 0.01 atm, and in pure argon) have been systematically studied. Liquidus compositions and eutectic points in the ZnO-SiO2, ZnO-CaO, Cu-O-ZnO, Cu-O-SiO2, Cu-O-ZnO-SiO2, Cu-O-ZnO-CaO, and Cu-O-ZnO-MgO systems have been investigated. Sub-solidus lines in the ZnO-CaO, ZnO-MgO binaries have also been determined. The solubility behavior of copper oxide in the other terminal phases have been carefully checked as well. The best fitted phase diagrams have been compared with the resultsfrom the literature, and with the calculated phase diagrams from MTDATA 5.10 software and Mtox 8.1 database, and the differences are significant. The thermodynamic descriptions of those systems in the database should be updated, and the Cu-O-ZnO-SiO2-CaO-MgO system and its sub-systems need re-assessments. This study provides novel data for both scientific research and industrial practices.