Reuse of phosphogypsum pretreated with water washing as aggregate for cemented backfill

Phosphogypsum (PG) is reused as aggregate in the cemented backfill, which effectively improves the PG reutilization efficiency. However, the massive impurities contained in aggregate PG would adversely affect the hydration of binder, and therefore deteriorate the strength development of backfill. This research starts with the feasibility study on pretreating PG with the water washing method. Based on the most economical principle of the water demand, the optimal conditions for washing PG were determined at a stirring time of 5 min and a solid-liquid ratio of 1:0.5. Then, the original and pretreated PG were made into the backfill. Compared to using the original PG, the backfill slurry using the pretreated PG had better fluidity performance, such as the lower slurry viscosity and the higher bleeding rate. Furthermore, with the pretreated aggregate PG, the backfill strength was significantly enhanced by more than 8 times. Finally, the environmental behavior of the cemented backfill was investigated. Using the pretreated PG as aggregate, concentrations of PO₄^3- and F^- in the bleeding water and backfill leachates could meet the Chinese standard for integrated wastewater discharge. The results extend the reuse of PG as aggregate in a more environmental-friendly way, meeting the needs for sustainable mines.