Decoding Sulfur-Source-Dependent Mechanisms for Selective Zinc Recovery from Electric Arc Furnace Dust via Synergistic Sulfation Roasting

The selective separation of zinc from iron in electric arc furnace dust (EAFD) remains a persistent metallurgical challenge, primarily due to the stable incorporation of zinc within ferrite spinel structures. Conventional pyrometallurgical routes suffer from high carbon emissions and low product purity. This study introduces an innovative sulfation roasting approach utilizing a synergistic sulfur-source system, comprising ZnS, FeS, and FeSO4·7H2O, to fundamentally alter the reaction pathway and achieve high-fidelity zinc-iron separation. A comprehensive mechanistic investigation was undertaken to decode the sulfur-source-dependent regulation of phase transformations. Isothermal roasting with ZnS alone resulted in rapid SO2 evolution and consequently low local partial pressure, leading predominantly to direct oxidation and the formation of water-insoluble ZnO. The introduction of FeS effectively modulated the SO2 release kinetics, retarding the decomposition of ZnS and extending the temporal window for sulfation, thereby promoting the generation of partially soluble Zn3O(SO4)2. The incorporation of FeSO4·7H2O triggered an intense, early-stage SO2 evolution, which, coupled with active sulfate species, drove the complete conversion of zinc phases (ZnS, ZnO, ZnFe2O4) into water-soluble ZnSO4, while transforming iron into inert Fe2O3. Under optimal conditions (FeSO4·7H2O/(ZnS+FeS+EAFD) = 2, 675 °C, 2 h), 97.83% of zinc was recovered via simple water leaching with minimal iron co-dissolution (1.98%). This work elucidates the critical link between engineered sulfur-source combinations, controlled sulfation kinetics, and selective phase evolution, establishing a fundamental framework for the development of cleaner and more efficient hydrometallurgical pre-treatment strategies for complex zinc-laden secondary resources. Keywords: Zinc recovery; EAFD; sulfation roasting; sulfur source; selective separation; process mechanism