<p>This study investigates the stabilization performance of phosphogypsum-based supersulfated cement (PG-SSC) for four types of metallurgical slags—lead–zinc smelting slag (LZSS), secondary copper slag (CS), silicomanganese slag (SMS), and ferrochrome slag (FCS)—with particular emphasis on heavy metal immobilization, mechanical strength, and hydration behavior. Leaching tests conducted at multiple curing ages demonstrated that PG-SSC effectively immobilized Pb, Zn, Cu, and Cr as early as 3 days, indicating a rapid and robust stabilization capacity. However, substantial Mn leaching was observed in PG-SSC incorporating SMS, with the 28-day Mn concentration reaching 17.20 mg/L, attributed to the high Mn content and limited binding potential of the matrix. All slag-containing systems exhibited reduced compressive strength compared with the control; however, LZSS- and CS-based systems maintained moderate strength levels (~23 MPa), indicating potential suitability for nonstructural applications. Hydration analysis revealed that the presence of metallurgical slags variably inhibited PG-SSC hydration, as evidenced by delayed heat evolution, reduced chemically bound water, and suppressed ettringite formation, with SMS inducing the most severe suppression. Additionally, the proposed PG-SSC formulation achieved substantial reductions in CO₂ emissions, offering dual environmental benefits of heavy metal immobilization and low carbon footprint. These findings enhance the understanding of PG-SSC-based solidification systems and support their application in low-carbon hazardous waste management.</p> Graphical Abstract <p></p>