Reuse of Phosphogypsum Pretreated with Water Washing as Aggregate for Cemented Backfill

Abstract

Phosphogypsum (PG) is reused as aggregate in the cemented backfill of the mines, which effectively improves the PG reutilization efficiency. However, the massive impurities contained in aggregate PG would adversely affect the hydration of binder, and therefore deteriorating strength development of backfill. This research starts with the feasibility study on pretreating the aggregate 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 the 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, the higher bleeding rate and the shorter setting times. Furthermore, with the pretreated aggregate PG, the strength of the backfill was significantly enhanced by more than 8 times, which was due to the removal of impurities on the surface of PG in the pretreatment. Finally, the environmental behavior of the cemented backfill was investigated. Using the pretreated PG as aggregate, concentrations of PO43−-P and F− in the bleeding water and leachates of backfill could meet the Chinese standard for integrated wastewater discharge, which significantly reduced the adverse effect of PG on the environment. The results extend the reuse of PG as aggregate in a more environmental-friendly way, meeting the needs for sustainable mines.