The separation of halogens and recovery of heavy metals from secondary copper smelting (SCS) dust using a sulfating roasting-water leaching process were investigated. The thermodynamic analysis results confirm the feasibility of the phase transformation to metal sulfates and to gaseous HF and HCl. Under the sulfating roasting conditions of the roasting temperature of 250 °C and the sulfuric acid excess coefficient of 1.8, over 74 wt.% of F and 98 wt.% of Cl were volatilized into flue gas. Approximately 98.6 wt.% of Zn and 96.5 wt.% of Cu in the roasting product were dissolved into the leaching solution after the water leaching process, while the leaching efficiencies of Pb and Sn were only 0.12% and 0.22%, respectively. The mechanism studies indicate the pivotal effect of roasting temperature on the sulphation reactions from various metal species to metal sulfates and the salting out reactions from various metal halides to gaseous hydrogen halides.