Abstract: A large amount of waste is generated during copper smelting. The analysis shows that the iron content in is high, predominantly present in the fayalite phase, making it difficult to recycle. In this paper, the copper slag from Baiyin Company was taken as the research object, CaO was used as the modifier, and the iron in the copper slag was recovered by the melting oxidation method. The effect of alkalinity on the migration of the iron element from the fayalite phase to the magnetite phase was studied. The thermodynamic analysis results show that the modifier CaO can promote the decomposition of fayalite phase, facilitating the formation of magnetite and pyroxene phases. When the alkalinity is 0.60, the precipitation of a stable magnetite phase is most favorable. Under these conditions, the saturation magnetization (M_s) reaches 56.34 A·m²/kg with a maximum iron recovery rate of 92.12%.