Thermodynamic premises of fire refining of blister copper considering the interaction parameters of the melt

The process of fire refining of copper is based on the removal of impurities that have a high affinity for oxygen through their oxidation by gaseous oxygen. Since the main component of blister copper is copper itself, according to the law of mass action and its affinity for oxygen, during air blowing the metal primarily reacts with the oxygen in the blast. The resulting copper (I) oxide is transported from the zone of direct contact with gaseous oxygen into the region of lower oxygen concentration, where the oxidation of impurities (Mei) occurs. In practice, the actual copper melt deviates from ideal behavior; therefore, it is necessary to consider the activities of the components and the interaction parameters of the system when evaluating the thermodynamic premises of fire refining. It is known that the oxygen activity in copper melts depends on the oxygen affinity of the impurities. Impurities with a high affinity for oxygen (e.g., Al, Si, Mn) significantly reduce the oxygen activity, whereas those with a lower affinity (e.g., Zn, Fe, Sn, Co, Pb) only partially decrease it. Thermodynamic calculations were performed to estimate the final concentration of impurities in the copper melt and to theoretically evaluate the influence of impurities on oxygen activity in blister and anode copper. The calculations showed that fire refining of copper by air blowing under a weighted ideal slag has thermodynamic limitations. The final impurity concentration depends on both the oxygen activity in the melt and the activity of the impurity oxide in the slag. A decrease in the impurity oxide activity in the slag enhances refining efficiency by shifting the oxidation reaction equilibrium toward the reaction products. The theoretical effect of impurities on the oxygen activity in copper is substantiated for two melts differing in chemical compositin.