Effect of desulfurization gypsum on dissolution kinetics and phase evolution in the alkali-activated steel slag–gold tailings system

To address the issue of limited large-scale application of desulfurized gypsum (DG) due to the unclear mechanism of its action in alkali-activated systems, this study employed steel slag and gold tailings as precursors to investigate the influence of desulfurized gypsum on the dissolution kinetics, macroscopic properties, phase evolution, and reaction pathways of this alkali-activated system. The results demonstrate that an appropriate amount of desulfurized gypsum can enhance the 28-day compressive strength of the system to 22.4 MPa and shorten the initial and final setting times by more than 55 minutes. In an alkaline environment, desulfurized gypsum not only directly participates in the formation of ettringite but also maintains the Ca/Si ratio of C-(A)-S-H gel within the range of 0.8 - 1.3 and increases the Si/Al ratio to 2.0 - 3.1, thereby mitigating the mismatch in reaction rates between steel slag and gold tailings. When desulfurized gypsum is absent, the reaction pathway of the system is predominantly alkali-activated gelation, whereas with an appropriate amount of desulfurized gypsum, the reaction is primarily dominated by sulfate-activated ettringite crystallization. Furthermore, through hydration kinetics analysis, the exponential function model proposed in this study accurately describes the hydration heat release behavior of the system, reflecting the characteristic of reaction rate decay over time. This study provides a theoretical basis for the high-value utilization of desulfurized gypsum in solid waste-based cementitious materials.