NaO<SUB>0.5</SUB>-CO<SUB>2</SUB>-SnO<SUB>2</SUB>系スラグの熱力学と本系スラグ-溶銅間のSnの分配比の推算

Abstract

In view of the application of sodium carbonate slag to the elimination of Sn from molten copper, the thermodynamic properties of NaO0.5-CO2-SnO2 slag have been studied by conducting the following experiments:(1) Activities of NaO0.5 in the slag were determined by the EMF method using β′′-alumina as a solid electrolyte over the composition range of 1>N≥0.795{N=nNa+(nNa⁄nSn),n:the number of moles}under the partial pressures of CO2 of 0.001∼0.08 MPa at 1423∼1523 K. It was found that the activity of NaO0.5 did not depend on the slag composition for the constant partial pressure of CO2 and the slag was saturated with Na2SnO3(s).(2) Then the solubility of Na2SnO3(s) into the sodium carbonate melt was measured under the various partial pressures of CO2 at 1523 K. With decreasing the partial pressure of CO2 the solubility increased, but the partial pressure of oxygen had no effect.(3) Activities of SnO2 were determined by the distribution equilibrium measurements for Sn between the Na2SnO3(s)-saturated slag and molten copper. From the activity of SnO2 combined with that of NaO0.5, the standard free energy change for the following reaction was determined as:(This article is not displayable. Please see full text pdf.) \ oindentThe activity of SnO2 in the homogeneous liquid region of the slag was also evaluated by the distribution equilibrium measurements.Based on the results obtained, the distribution ratios of Sn between the slag and molten copper were estimated. The ratios decrease with decreasing SnO2 content in the Na2SnO3(s)-saturated slag. The higher oxygen partial pressure and the lower CO2 partial pressure are more preferable for the removal of Sn from molten copper.