Abstract:Matte smelting is the key process of pyrometallurgical copper smelting, usually using the fayalite slag system (SiO2-FeOx-MO, M represents metal). The properties, formation, dissolution, precipitation and action of ferric oxide (Fe3O4), as well as the harm and its elimination methods were systematically discussed. It is also pointed out that the previous view “in matte smelting, ferric oxide has high melting point and high viscosity, and its generation will have a serious adverse effect on matte smelting process” is not comprehensive. In matte smelting, the formation and supersaturation precipitation of Fe3O4 are related to factors such as temperature, mass ratio of Fe/SiO2 in slag, activity of FeS and Cu2S, and partial pressure of SO2. The solubility of Fe(Ⅲ) in slag is determined by the slag temperature. After the supersaturated ferric oxide precipitates into the slag, the viscosity of slag should be calculated according to Einstein-Roscoe formula. In addition, the reasons why the slag temperature and Fe/SiO2 mass ratio are different in different smelting methods were analyzed.