As a fundamental study of slags in metallurgical processes, liquidus lines in the FeO(wüstite)-CaO-SiO 2 and Fe 3 O 4 (spinel)-CaO-SiO 2 systems were determined at temperatures between 1573 and 1673 K and partial pressures of oxygen between 10 À4 and 36 Pa using a quenching method with a crucible of platinum foil. It was found that the two phases (solid wüstite and liquid) region in the FeO-CaO-SiO 2 system (1573 K) increased remarkably by changing the partial pressure of oxygen from 10 À4 to 10 À3 Pa. It was also found that the two phases (solid spinel and liquid) region in the Fe 3 O 4 -CaO-SiO 2 system (1573 K) at PO 2 of 10 À2 Pa was a little larger than that in the FeO-CaO-SiO 2 system at PO 2 of 10 À3 Pa but it was extended considerably when the oxygen pressure was increased to 10 À1 Pa. However, the two liquids region did no change too much in the range of oxygen pressure above 10 À1 Pa even though the liquidus line became almost parallel to the Fe 3 O 4 -CaO axis in the ternary diagram when the oxygen pressure was increased. Furthermore, it was found that the two phase region in the Fe 3 O 4 -CaO-SiO 2 system at PO 2 of 10 À1 Pa decreased remarkably with increasing temperature. On the basis of the obtained and reported data, the homogeneous liquid regions in the FeO X -CaO-SiO 2 systems (1573 K) at PO 2 of 10 À3 Pa, 10 À1 Pa and in air were compared.

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Ferrous calcium silicate slags (described by the FeO-Fe 2 O 3 -CaO-SiO 2 system) are the basis for a number of slag systems used in nonferrous smelting. Characterization of this slag system is necessary to improve the design and optimization parameters of new processes, including fluxing and operating temperatures. Particularly of interest are the phase relations at intermediate oxygen partial pressures relevant to processes such as copper converting. Experimental data on the phase equilibria of these slags at controlled oxygen partial pressures in the temperature range between 1200°C and 1350°C are discussed, differences between various data sources are analyzed, and discrepancies are resolved. An evaluation of two thermodynamic computer models is undertaken to verify the computer-aided predictions using the experimental data. New experimental data for this system are reported for the temperature condition of 1300°C, defined using the equilibration/rapid-quenching/electron probe microanalysis (EPMA) with wavelength dispersive detectors technique. This new information, combined with results from the previous study, has enabled the equilibrium liquidus compositions to be defined over a wide range of temperatures and oxygen partial pressures.

At present, there is a scarcity of data on the activities of iron oxides in the FeO-Fe 2 O 3 -CaO-SiO 2 slag system at intermediate oxygen partial pressures and temperatures relevant to sulfide smelting and nonferrous metallurgy. The present study provides relevant data at temperatures between 1573 and 1673 K and partial pressures of oxygen between 10 -9 and 10 -4 atm. The experiments were carried out by equilibrating the slag in a CO-CO 2 gas mixture in a platinum crucible, after which the phases of all the experimental samples, including the platinum foil, were analyzed by electron probe microanalysis (EPMA). Where only liquid phase or liquid phase and tridymite (SiO 2 ) were observed, wet chemical analysis was used to determine the ratio of (mass pct Fe 2+ )/(mass pct Fe 3+ ). Activity and activity coefficients for FeO (liquid) and FeO 1.33 (solid) were calculated. Tendencies of the effect of the (CaO/SiO 2 ) ratio, temperature, and oxygen partial pressure on these thermochemical quantities are discussed in this article.

Copper concentrates and fluxes can contain variable levels of SiO 2 , CaO, and MgO in addition to main components Cu, Fe, and S. Metal recovery, slag tapping, and furnace wall integrity all are dependent on phase equilibria and other properties of the phases and are functions of slag composition and operational temperature. Optimal control of the slag chemistry in the copper smelting, therefore, is essential for high recovery and productivity; this, in turn, requires detailed knowledge of the slag phase equilibria. The present work provides new phase equilibrium experimental data in the FeO-Fe 2 O 3 -SiO 2 -CaO-MgO-Al 2 O 3 system at oxygen partial pressure of 10 À8 atm within the range of temperatures and compositions directly relevant to copper smelting. For the range of conditions relevant to the Kennecott Utah Copper (South Magna, UT) smelting furnace, it was confirmed experimentally that increasing concentrations of MgO or CaO resulted in significant decreases of the tridymite liquidus temperature and in changes in the position of the tridymite liquidus in the direction of higher silica concentration; in contrast, the spinel liquidus temperatures increase significantly with the increase of MgO or CaO. Olivine and clinopyroxene precipitates appeared at high MgO concentrations in the liquid slag. The liquidus temperature in the spinel primary phase field was expressed as a linear function of 1/(wt pctFe/wt pctSiO 2 ), wt pctCaO, wt pctMgO, and wt pctAl 2 O 3 . The positions of each of the liquidus points (wt pctFe)/(wt pctSiO 2 ) at a fixed temperatures in the tridymite primary phase field were expressed as linear functions of wt pctCaO, wt pctMgO, and wt pctAl 2 O 3 .