Activities in NaO0.5-CO2-AsO2.5 Slag and Estimation of Distribution Ratio of As between the Slag and Molten Copper

A principle was established to estimate the equilibrium distribution ratio of the impurity element X between NaO0.5-CO2-XOv/2 slag (v: the valence of X) and molten copper defined by {(mass% of X in slag)/[mass% of X in metal]}, over a wide range of the slag composition as a function of partial pressures of CO2 and oxygen. Based on the principle, the following measurements on NaO0.5-CO2-AsO2.5 slag were conducted to estimate the distribution ratio of arsenic. (1) Activity measurement of NaO0.5; 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>0.8{N=nNaO0.5/(nNaO0.5+nAsO2.5), n: the number of moles} under the partial pressures of CO2 of 0.001-0.08 MPa at 1, 423-1, 523 K. (2) Activity measurement of AsO2.5; Activities of AsO2.5 could be calculated from the activities of NaO0.5 by integrating the Gibbs-Duhem relation. Activities of AsO2.5 as the initial values of the integration were determined by the distribution equilibrium measurements of arsenic between the slag and molten copper. From the obtained results, together with the solubility data of CO2 in the slag reported in the previous study, the equilibrium distribution ratio of arsenic was successfully calculated over the composition range of 1>N>0.8 as a function of partial pressures of CO2 and oxygen at the temperatures of 1, 423 and 1, 523 K. The calculated distribution ratio of arsenic has a considerably large value and increases with increasing the value of N. The higher oxygen partial pressure and the lower CO2 partial pressure and the lower temperature are more preferable for the removal of arsenic from molten copper.