The enhancement of the utilization rate of solid waste, along with balancing the comprehensive performance of materials, presents a significant challenge in the development of new functional building materials. This study examined the effects of high concentrations of iron tailing powder on the crystallization characteristics, pore structure, compressive strength, and water absorption of modified magnesium oxysulfate (MOS) foam cement with different dry densities. Furthermore, employing chemical foaming technology, the study characterized and analyzed the microstructure of modified MOS foam cement hydration products through scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). The results indicated that the addition of an acidic modifier effectively facilitated the hydration reaction in the MgO-MgSO₄-H₂O system, enhancing the micro-crystallization characteristics of MOS foam cement. The internal pores were uniformly round, with a dense crystal structure within the pore walls. The compressive strength of the material with 40% dry density A08 grade iron tailing powder reached 6.83 MPa, and the lowest water absorption was 5.32% at a dry density of A09.

This study investigates a sustainable alkali-activated cementitious system incorporating high-volume desulfurization gypsum (DG) with fly ash (FA) and ground granulated blast-furnace slag (GGBFS) as co-precursors. The reaction mechanism, mechanical properties, water resistance, volumetric stability, and environmental safety were systematically evaluated using XRD, FT-IR, SEM-EDS, and TG-DTG. The optimal DG content was approximately 50%, and the DG:FA:GGBFS ratio of 50:20:30 (Mix B5) exhibited the best overall performance: a 28-day compressive strength of 27.2 MPa, initial and final setting times of 90 and 180 min, water absorption of 6.2%, and a softening coefficient of 0.94. The FA/GGBFS ratio also markedly affected performance, with a ratio of 1:1.5 giving the best synergy at 50% DG. Volumetric stability tests showed that B5 underwent moderate early expansion (2.6‰–3.1‰) that stabilized at 0.40‰ at 28 days. Microstructural analysis revealed that the superior performance of B5 originated from a dense matrix of abundant C-(A)-S-H gel and well-distributed ettringite, whereas excessive DG (80%) left large amounts of unreacted gypsum and produced a porous structure with severely degraded performance. Heavy-metal leaching from the two hardened specimens (A8 and B5) remained below the GB 5085.3-2007 and GB 3838-2002 Class IV limits. This study demonstrates the feasibility of using high-volume DG as a principal raw material in alkali-activated binders, offering a promising route to low-carbon cementitious materials from industrial by-products.