Abstract
Thermodynamic properties of NaO0.5-CO2-FeO1.5 slag have been investigated for the application of sodium carbonate slag to the elimination of Fe from molten copper. The activities of NaO0.5 and Na(CO3)0.5 were measured by the EMF method, using beta′′-alumina as a solid electrolyte, for various partial pressures of CO2 at 1423 to 1523 K. There is a stable solid compound NaFeO2 in this system, and the solubility measurement of this compound into sodium carbonate melt at 1523 K revealed that the solubility is very limited and controlled by the partial pressure of CO2. The dissolution reaction seems to proceed according to the following reaction and Fe exists as FeO33− anion in the sodium carbonate-based melt.(This article is not displayable. Please see full text pdf.) \ oindentThe standard free energy change for the following reaction:(This article is not displayable. Please see full text pdf.) \ oindentwas also determined by the EMF method as:(This article is not displayable. Please see full text pdf.) \ oindentThe activity of FeO1.5 in the (solid NaFeO2+liquid) two phase region could be calculated from the activity of NaO0.5 via the above equilibrium relation. Distribution equilibrium measurements were also conducted for Fe between the slag and molten copper at 1523 K not only to confirm the calculated results but also to determine the activity of FeO1.5 in the homogeneous liquid region of the slag. The activity coefficient of FeO1.5 in the homogeneous liquid region has a constant value for a constant CO2 partial pressure, independent of the concentration.
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