Mitigating strength degradation in high-sulfur tailings cemented paste backfills using sulfate-resistant cement and fly Ash

In modern mining, proper management of mine tailings, especially high-sulfur tailings, is crucial for environmental protection and resource utilization. When high-sulfur tailings are used for backfilling, they affect the performance of backfilling slurries, thereby influencing mining safety and efficiency. However, the underlying mechanisms and measures for improvement remain unclear. This study investigated the impact of high-sulfur tailings on the performance of cemented paste backfill (CPB) and evaluated the effectiveness of sulfate-resistant Portland cement (SR) and low-calcium fly ash (FA) in mitigating strength degradation. Tailings with sulfur contents of 5.7 wt%, 20.7 wt%, and 30.7 wt% were analyzed for their physical, chemical, and mineralogical properties. Experiments were conducted under different cement-to-tailings ratios (1:8 and 1:12) and inhibitor dosages (10 wt%–40 wt%) to test the bleeding rate, slump, rheological properties, setting time, and unconfined compressive strength (UCS). The results show that increasing the sulfur content enhances the fluidity but prolongs the initial setting time and reduces the long-term strength. Both SR and FA improved the mechanical properties of the CPB. SR was more effective in enhancing late-stage UCS, with a maximum increase of 147.5% at 150 d, and was more cost effective. FA reduced the bleeding rate at certain dosages, and a 10 wt% dosage increased the UCS and bleeding rate and prolonged the setting time. Scanning electron microscopy analysis revealed that SR and FA changed the CPB structure. The uninhibited high-sulfur CPB had a rough surface, large pores, and expansive substances, whereas the SR-added CPB had a compact structure, and the FA-added CPB had smaller pores and minerals beneficial for strength. Adding 10 wt% SR is recommended to control costs and improve backfilling performance. This study provides insights into sustainable tailings management and CPB optimization in sulfide-rich mining environments.