The principle route for the production of copper metal from sulphide minerals and the recycling of secondary copper involve the use of high-temperature pyrometallurgical processes.
The present study involves the integration of experimental and chemical thermodynamic modeling techniques to develop new thermodynamic databases that describe the high temperature chemistries of oxide systems encountered in copper smelting and converting operations. The experimental procedures developed at Pyrometallurgy Research laboratory (Pyrosearch), the University of Queensland, which involve equilibration of mixtures at high temperatures, rapid quenching, and accurate measurement of phase compositions using electron probe X-ray microanalyses (EPMA), have been used.
Phase diagrams of ferrous calcium silicate slag (“FeO”-CaO-SiO2) at high temperatures have been characterized over a wide range of oxygen partial pressures between 10-5 atm and 10-9 atm. The pseudo-binary phase diagrams in the “Cu2O”-SiO2 system in equilibrium with air and with metallic copper have been constructed. The investigation in the “Cu2O”-SiO2 system has been extended to characterize the effects of CaO, MgO, and Al2O3 on the liquidus isotherms of tridymite in equilibrium with metallic copper at temperatures of 1473 K and 1573 K (1200 oC and 1300 oC). The phase diagrams of the “Cu2O”-“Fe2O3”-SiO2 system have been investigated in equilibrium with air atmosphere at temperatures between 1373 K and 1673 K (1100 oC and 1400 oC), and with metallic copper at temperatures between 1373 K and 1573 K (1100 oC and 1300 oC). All the systems selected in the present study are of practical importance for industrial copper production processes and have been used to improve the existing thermodynamic database of copper-containing slag systems.
The thermodynamic modeling part of the current study focuses on the improvement of thermodynamic database for the liquid slag and solid oxide phases in the Al2O3-CaO-“Cu2O”-FeO-Fe2O3-MgO-SiO2 system at conditions in equilibrium with metallic copper, which includes thermodynamic optimizations of the following sub-systems:
- CaO-“Cu2O”, “Cu2O”-SiO2, CaO-“Cu2O”-SiO2;
- Al2O3-“Cu2O”, “Cu2O”-MgO, Al2O3-“Cu2O”-SiO2, “Cu2O”-MgO-SiO2;
- “Cu2O”-FeO-Fe2O3, “Cu2O”-FeO-Fe2O3-SiO2;
- CaO-“Cu2O”-FeO-Fe2O3, CaO-“Cu2O”-FeO-Fe2O3-MgO; and
During the course of the optimization, the re-evaluation and re-optimization of copper-free systems have also been carried out, importantly these include: the FeO-Fe2O3-SiO2; CaO-FeO-Fe2O3; and CaO-FeO-Fe2O3-SiO2 systems.
The optimized thermodynamic database can be used for predictions over a wide range of process conditions in copper production processes, and for interpolation and extrapolation into the temperature and composition ranges where experimental data are not available. The predictive tools can be used to assist in improvements of industrial copper operations enabling informed decisions to be made on the selection of slag compositions, fluxing strategies and operating conditions for given feed and product requirements. Examples of industrial applications of the database for the copper metallurgical processes are presented.