Activities in NaO_0.5-CO₂-AsO_2.5 slag and estimation of distribution ratio of arsenic between the slag and molten copper

A principle has been established to estimate the equilibrium distribution ratio of an impurity element X between NaO_0.5-CO₂-XO_v/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 NaO_0.5-CO₂-AsO_2.5 slag were conducted to estimate the distribution ratio of arsenic. (1) Activities of NaO_0.5 in the slag were determined by the EMF method using β″-alumina as a solid electrolyte over a wide range of the slag composition for various partial pressures of CO₂. (2) Activities of AsO_2.5 could be calculated from the activities of NaO_0.5 by integrating the Gibbs-Duhem relation. Activities of AsO_2.5 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 previously, the equilibrium distribution ratio of arsenic was successfully calculated as a function of partial pressures of CO₂ and oxygen, slag composition and temperature.