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3 - Phase Equilibria in Ferrous Calcium Silicate Slags Part...

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Phase Equilibria in Ferrous Calcium Silicate Slags: Part I. Intermediate Oxygen Partial Pressures in the Temperature Range 1200 ° C to 1350 ° C STANKO NIKOLIC, PETER C. HAYES, and EVGUENI JAK Ferrous calcium silicate slags are used in primary and secondary metallurgical processes (described by the FeO-Fe 2 O 3 -CaO-SiO 2 system). Despite the industrial and scientific impor- tance of this system, the phase equilibria have not been fully investigated. Characterization of this slag system is necessary to improve the design and optimization of new and existing met- allurgical processes, particularly in relation to fluxing practice and operating temperatures. Experimental methods have been developed to investigate the phase equilibria of these slags involving the equilibration of samples at fixed oxygen partial pressures, rapid quenching, and the analysis of the compositions of solid and liquid phases using electron probe X-ray micro- analysis (EPMA) with wavelength dispersive detectors. Liquidus and solidus data are reported for the primary phase fields of spinel, pseudo-wollastonite, and tridymite in the temperature range of 1200 ° C to 1350 ° C at an oxygen partial pressure of 10 - 6 atm, and at 1250 ° C at an oxygen partial pressure of 10 - 5 atm. The resulting data have been used to construct liquidus and solidus isotherms in the ‘‘FeO’’-CaO-SiO 2 system directly relevant to industrial processes. DOI: 10.1007/s11663-008-9130-1 Ó The Minerals, Metals & Materials Society and ASM International 2008 I. INTRODUCTION F ERROUS calcium silicate slags, described by the FeO-Fe 2 O 3 -CaO-SiO 2 system, form the basis for a number of metallurgical slag systems used in nonferrous smelting. Despite the industrial importance of the phase equilibria of this system, the conditions relevant to industrial processes have not been fully investigated. The phase relations at intermediate oxygen partial pressures, relevant to such processes as copper convert- ing, are of particular interest. Characterization of this slag system at these conditions is necessary to facilitate improvements in the design, development, and optimi- zation of process conditions for existing and new metallurgical processes, such as the ISACONVERT* process. [ 1 , 2 ] The phase equilibria of the FeO-Fe 2 O 3 -CaO-SiO 2 system has been investigated experimentally in air [ 3 , 4 ] and at iron saturation. [ 5 8 ] Timucin and Morris [ 9 ] defined the liquidus and oxygen isobars in the liquid phase in the FeO-Fe 2 O 3 -CaO-SiO 2 system at fixed oxygen partial pressures by chemically analyzing the composition of liquid samples equilibrated at varying oxygen partial pressures in the range of 1 atm of oxygen to iron saturation, including the Fe 2+ /Fe 3+ ratio of the slag, with silica concentrations of 0, 5, 10, 20, and 30wt pct at 1450 ° C and 1550 ° C. Shigaki et al.
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