Phase equilibria and thermodynamic properties of the Cu 2 O-CaO-Na 2 O system in equilibrium with copper
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8/28/03
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Phase Equilibria and Thermodynamic Properties of the Cu2O-CaO-Na2O System in Equilibrium with Copper PASCAL COURSOL, ARTHUR D. PELTON, and MANUEL ZAMALLOA The liquidus surfaces of the Cu2O-CaO, Cu2O-Na2O, and Cu2O-CaO-Na2O phase diagrams in equilibrium with metallic Cu were measured by thermal analysis at compositions varying from approximately 0 to 35 wt pct Na2O and 0 to 15 wt pct CaO. Solubilities in the solid binary terminal solutions were also measured by wavelength dispersive X-ray spectrometer analysis. Copper oxide activities in binary liquid slags were determined from the measured oxygen content of the metallic copper equilibrated with the slags. The ternary system is a simple eutectic system. No ternary compounds were observed. The Cu2O-CaO binary eutectic was measured at 1140 °C 10 °C at 10 1 wt pct CaO and the Cu2O-Na2O binary eutectic was measured at 803 °C 15 °C at 28 2 wt pct Na2O. The liquid slag was thermodynamically modeled with the modified quasi-chemical model, while the solid Cu2O-rich solution was treated as Henrian ideal. All data from the present work and from the literature (phase diagrams and activities) for the binary systems were evaluated simultaneously by least-squares optimization in order to obtain the best model parameters. With only these binary parameters, the calculated ternary liquidus surface is in very good agreement with the measurements. Finally, using the model, the liquidus projection of the Cu2O-CaO-Na2O system in equilibrium with Cu was calculated as well as the oxygen content of the equilibrated Cu as a function of slag composition.
I. INTRODUCTION
BASIC fluxes are commonly used to reduce the concentrations of certain minor elements in blister copper. Despite the proven effectiveness of Na2CO3-CaO fluxes in removing As and Sb,[1–4] various thermochemical aspects of the slag produced industrially are not fully understood. As described by Riveros et al.[5], Na2CO3 and Cu2O are not fully miscible. Depending upon the overall composition and the oxygen content of the copper, the slag formed during fluxing may consist of two liquid phases, one rich in Na2CO3 and one rich in Cu2O. An understanding of the phase equilibria and thermodynamics of this system is essential for process simulation and control. Kuxmann and Kurre[6] studied the solubility of CaO in liquid Cu2O in the presence of metallic copper. Oishi et al.[7] have studied the partial pressure of O2 in equilibrium with liquid copper and CaO-Cu2O liquid solutions at 1300 °C. Thermodynamic modeling of the Cu-CuO-Cu2O-CaO subsystem was done by Ranniko[8] using the association model. No other literature data were found. In the present article, we report our measurements and thermodynamic modeling of the Cu2O-CaO-Na2O system in equilibrium with copper. II. EXPERIMENTAL A. Thermal Analysis and Differential Thermal Analysis The DTA apparatus is shown in Figure 1. Recrystallized Al2O3 crucibles of 99.8 pct purity (Vesuvius McDanel) were PASCAL COURSOL, Process Scientist, is with the Alcan
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