Corecycling of Granular Steel Slag and Phosphogypsum for Preparing Sustainable Cement Clinker via Fusion Adhering Calcined Technique

Abstract

The large-scale stockpiling of steel slag and phosphogypsum (PG) is a global challenge in industrial solid waste management. Direct utilization of granular steel slag for preparing steel slag fusion adhering calcined (SFAC) cement clinker is effective for carbon emission reduction and conserving resources. Nevertheless, SFAC cement clinker synthesized by high-proportion moderate-alkalinity steel slag inherently suffers from poor mechanical properties. In this study, PG was innovatively employed as a mineralizer within the SFAC clinker system to systematically evaluate its influences on the chemical composition, mineralogical evolution, microstructural characteristics, and mechanical properties of the SFAC clinker. The results demonstrate that PG significantly promoted the decomposition of carbonate and improved the burnability of the cement raw meal. Petrographically, small-sized irregular C2S crystals with high hydration activity formed in the high-ferrite (HF) zone due to the decomposition of C3S. Therefore, the PG mineralized SFAC clinker exhibited a relatively low content of C3S while presenting a high content of C3A and amorphous phase. Residual SO3 persisted predominantly as CaSO4 and (Ca2K2)(SO4)3, which scarcely evaporated into the air during the sintering process and promoted the early-stage hydration of C3S and C3A. Benefiting from synergistically elevated crystalline imperfections in C3S and β-C2S, enhanced hydration degree, and refinement of the hardened paste microstructure, the 3d and 28d compressive strengths of PG mineralized SFAC clinker increased by 16.93 and 18.72%, respectively, compared with the control sample without PG. This study proposes a sustainable low-carbon production way of mechanical enhanced SFAC clinker for the corecycling of original granular steel slag and PG in cement industry.