Abstract:A large amount of copper slag is produced in the pyrometallurgical process of copper smelting, and a substantial quantity of high-silica slag is produced after the recovery of valuable metals such as copper by acid leaching. In order to realize both the harmless disposal of high-silica slag and the recovery utilization of silicon, thermodynamic software Factsage 7.3 and HSC 6.0 were used to calculate and construct ΔG—T diagrams, phase equilibrium distribution diagrams, and phase diagrams of Na2O-SiO2-FeO system during the main reactions involved in the alkaline roasting process for high-silica slag. The results indicate that variations in roasting temperature and ω(Na2O)/ω(SiO2) can significantly affect the roasting transformation process and product phase composition. Theoretically, the optimization conditions for SiO2 transformation are determined to be a roasting temperature range of 800—900 ℃ with ω(Na2O)/ω(SiO2)=0.41—0.64. Furthermore, impurities such as Al and Fe were found to participate in the reaction process within high-silica slag, and insoluble impurity NaAlSiO4 being formed prior to soluble impurity Na2FeO2. According to the results of thermodynamic analysis, validation tests were carried out. The results show that the leaching rate of silicon reaches 88.56% under the conditions including excess coefficient of sodium carbonate of 0.9 times of the theoretical total amount of SiO2, Al and Fe, roasting temperature of 850 ℃, and roasting time of 2 h.