A new strategy for preparing cemented paste backfill using red mud neutralized by phosphogypsum: Mechanical properties, hydration mechanism and production cost.

Abstract

Red mud (RM) and phosphogypsum (PG) are hazardous wastes that are difficult to utilize extensively due to their high alkalinity and acidity. In this study, a new strategy for using RM neutralized by PG (P&R-composites) is proposed to prepare cemented paste backfill (PR-CPB), representing an environmental-friendly technology to place solid wastes into underground goafs. The corresponding effects of P&R-composites contents on the properties of PR-CPB were investigated by macroscopic and microscopic experiments. The results showed that the unconfined compressive strength (UCS) of PR-1 specimens cured for 14d and 28d could reach 2.60 MPa and 4.02 MPa, respectively, while the corresponding pH dropped rapidly to about 11.0. However, the UCS increased significantly across all groups during the initial stages of hydration. The mineral phases analysis also revealed that amorphous content decreased slightly in PR-CPB specimens with increasing P&R-composites contents. The microstructural investigation confirmed hydration products interwoven with unreacted RM and PG particles, forming denser structures that enhanced mechanical performance and stability. Further, the cost analysis showed total savings of 9.45e+5 CNY based on PR-CPB preparation consuming 1000 t of OPC. This study provides theoretical support for the practical application of PR-CPB specimens, contributing to cost-efficient and environmentally-friendly industrial practices.