Experimental Study of Ferrous Calcium Silicate Slags: Phase Equilibria at $$ {\text{P}}_{{{\text{O}}_{2} }} $$ Between 1
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LAG plays an important role in the high-temperature processing of copper. Most impurities that are introduced with copper sulfide concentrates are removed chemically through the formation of the slag phase. The slag phase can then be separated physically from the immiscible product phase, i.e., matte or molten metal. The phases present in these slags and their properties can be controlled through the adjustment of slag composition by adding appropriate fluxes, and through the control of process conditions by selecting optimum temperatures and gas conditions. Industrial copper smelting processes commonly operate with slags that consist primarily of ‘‘FeOx’’-CaOSiO2 components at temperatures between 1473 K and 1573 K (1200 °C and 1300 °C) and at an oxygen partial pressure of approximately 10–8 atm, however, little information is available on the phase diagram of ferrous calcium silicate slags (‘‘FeO’’-CaO-SiO2) at these conditions. Kimura et al.[1] reported the liquidus of the ferrous calcium silicate slag at 1573 K (1300 °C) at an oxygen partial pressure of 10–7.8 atm. Eight grams of samples were used and contained in a Pt crucible. After the equilibration of samples, the samples were cooled to room temperature under an argon gas flow. The physical separation of fully liquid slag and solid crystals in the sample was carried out, and the chemical composition of the fully liquid slag was then determined by the wet chemical analysis technique. Henao et al.[2] investigated phase equilibria of ferrous calcium silicate slag at 1573 K (1300 °C) at an oxygen partial pressure of 10–8 atm. The samples in Pt foil were equilibrated for TAUFIQ HIDAYAT, Postgraduate Student, PETER C. HAYES, Xstrata Professor, and EVGUENI JAK, Professor, are with the Pyrometallurgy Research Centre, The University of Queensland, Brisbane, QLD 4072, Australia. Contact e-mail: [email protected] Manuscript submitted May 3, 2011. Article published online September 17, 2011. METALLURGICAL AND MATERIALS TRANSACTIONS B
1 day. The equilibrated samples were cooled to room temperature in argon gas stream. Electron probe X-ray microanalysis (EPMA) was used to analyze the chemical compositions of the phases in equilibrium. During the cooling of samples under argon gas flow, there is a possibility that some changes occurred in the equilibrated samples, such as the segregation of components or precipitation. Hence, the phase equilibria information provided by these studies may have uncertainties. Nikolic et al.[3] assessed critically the experimental techniques used commonly in the high-temperature equilibration of ferrous calcium silicate slag to identify possible sources of differences in liquidus measurements reported by previous researchers. They demonstrated that accurate measurement of phase equilibria of these slag systems can be achieved by a careful attention to factors such as: oxygen partial pressure and temperature, sample preparation, sample quenching method, technique for measuring the compositions of phases,[3] and importantly, confirmation of achieve
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