Investigation into the High Temperature Phase Equilibria in the System “Cu2O”-FeO-Fe2O3-CaO-SiO2 at Metallic Copper Saturation: An Investigation of Copper Converting Slags

Stanko Nikolic (2008). Investigation into the High Temperature Phase Equilibria in the System “Cu2O”-FeO-Fe2O3-CaO-SiO2 at Metallic Copper Saturation: An Investigation of Copper Converting Slags PhD Thesis, School of Engineering, The University of Queensland.

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Author Stanko Nikolic
Thesis Title Investigation into the High Temperature Phase Equilibria in the System “Cu2O”-FeO-Fe2O3-CaO-SiO2 at Metallic Copper Saturation: An Investigation of Copper Converting Slags
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 2008-05
Thesis type PhD Thesis
Supervisor Prof. Peter C. Hayes
Prof. Eugene Jake
Total pages 256
Total black and white pages 256
Subjects 09 Engineering
Abstract/Summary The pyrometallurgical processing of copper-iron-sulphide containing concentrates typically involves initial smelting, producing a copper-iron-sulphide matte, followed by matte converting, producing blister copper. The converting stage of the process is currently undertaken, in most existing operations, using batch Peirce-Smith converters, which use silica as a flux to produce a molten iron-silicate based slag. Due to a number of issues associated with Peirce-Smith converters, including difficulties in fugitive gas capture, continuous copper converting processes have been developed. These continuous processes have identified a number of problems associated with using only silica as a fluxing material, including the formation of solid magnetite crusts within the furnaces at normal operating conditions, and that alternative fluxing practices, including the use of lime, can eliminate a number of these problems. Both the calcium ferrite system, fluxing only with lime, and the ferrous calcium silicate system, fluxing with both lime and silica, are possible alternative slag systems for use in copper converting; these slags are described by the “Cu2O”-FeO-Fe2O3-CaO-SiO2 system at copper saturation A critical review of the scientific literature available on the experimental phase equilibria on calcium ferrite and ferrous calcium silicate slags has shown that the phase equilibria in these systems are well defined only in the limiting conditions of air and metallic iron saturation, in both cases without the presence of copper oxide. There are disagreements in the literature in both systems with regards to the shape of the liquidus at fixed intermediate oxygen partial pressure conditions, and no experimental work had been found on either system at copper saturation and at fixed oxygen partial pressures. Therefore, the aim of the present study is to define the phase equilibria of both ferrous calcium silicate and calcium ferrite slag systems at conditions directly relevant to copper converting, including: • Intermediate oxygen partial pressures in the range 10-5.0 to 10-6.5atm; • Copper free slags; and • Metallic copper saturated slags. Experimental methods have been developed to investigate the phase equilibria of these complex slag systems without the presence of metallic copper involving rapid quenching of slag samples equilibrated at high temperatures in platinum crucibles with the resulting phase assemblages analysed using electron probe X-ray microanalysis (EPMA). These methods have been then further developed to allow for accurate, objective and repeatable measurements of copper saturated slags using primary phase substrate supports at both neutral and fixed oxygen partial pressures. This technique removed the limitations arising from the use of crucible/refractory materials and facilitated rapid quenching of the melt. This methodology allowed for the experimental determination of the phase equilibria in: • “FeO”-CaO-SiO2 system in the temperature range of 1200C-1350C at an oxygen partial pressure of 10-6.0atm; • “FeO”-CaO-SiO2 system at an oxygen partial pressure of 10-5.0atm at 1250C; • “Cu2O”-“FeO”-CaO-SiO2 at 1250C and 1300C and at an oxygen partial pressure of 10-6.0atm at metallic copper saturation; • “Cu2O”-“Fe2O3” and “Cu2O”-CaO systems at metallic copper saturation; • “Cu2O”-“Fe2O3”-CaO system in the temperature range of 1100C-1250C at metallic copper saturation; and • “Cu2O”-“Fe2O3”-CaO system at 1200C and 1250C at an oxygen partial pressure range of 10-5.0atm to 10-6.5atm, including the effect of SiO2 on the spinel and dicalcium ferrite liquidus. The experimental data reported in the present study were used in the verification of: • Thermodynamic computer models of the ferrous calcium silicate system; and • Empirical methods for calculating copper concentrations in calcium ferrite slags. The experimental determination of the new phase equilibria data on the calcium ferrite and ferrous calcium silicate systems has made it possible, using a mass and energy balance approach, to accurately assess the relative technical merits of using these systems in copper converting technologies. The comparison of calcium ferrite and ferrous calcium silicate slags, at the selected conditions, indicates that, in general, calcium ferrite slags have lower copper losses, lower total slag masses, reduced energy requirements and higher concentrations of SO2 in the off gas. It was shown, however, that unlike calcium ferrite slags the use of ferrous calcium silicate slags makes it possible to operate at high silica concentrations and, if the operating temperature of the process is increased, the performance approaches that of calcium ferrite slags. To enable the development of an optimised thermodynamic database for the “Cu2O”-FeO-Fe2O3-CaO-SiO2 system at metallic copper saturation further experimental studies are recommended to determine the high temperature properties of both calcium ferrite and ferrous calcium silicate slags involving the determination of the effects of: • Temperature; • Oxygen partial pressure; • Minor elements, for example MgO, Al2O3 and S, on the phase equilibria; and • Distribution of minor impurity elements between metal and slag. These data will provide further support for existing and developing copper converting operations so that informed decisions can be made regarding the optimum choice of slag compositions, fluxing strategies, and operating conditions, for given feed, product and environmental requirements.
Keyword Copper
calcium ferrite slag
ferrous calcium silicate slag
Phase Equilibria
oxygen partial pressure
“Cu2O” -FeO-Fe2O3-CaO-SiO2

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Created: Fri, 30 Jan 2009, 17:16:21 EST by Mr Stanko Nikolic on behalf of Library - Information Access Service