Preparation of new copper smelting slag-based mine backfill material and investigation of its mechanical properties.

• Composite activation can effectively stimulate the activity of copper smelting slag (CSS). • The orthogonal experimental method was used to optimize the experimental ratio. • The microstructure and hydration mechanism were studied by XRD, SEM and EDS. • A new type of CSS based composite mine backfill cementitious material was developed. The stockpiling of copper smelting slag (CSS) has broken the ecological environment of the mining area, and the resource utilization of CSS is an urgent requirement to promote ecological sustainable development. The optimal cementitious material ratio determines as 69:15:6:2:8 for CSS: cement clinker (CC): gypsum powder (GP):NaOH: slaked lime (SL) by analyzing the physical and chemical properties of CSS and the uniaxial compressive strengths (UCS) at 3d, 7d and 28d curing ages investigate. The uniaxial compressive strengths reached 3.55 MPa, 9.48 MPa, and 32.43 MPa. In the meantime, XRF, XRD, EDS, and SEM microscopic analysis of the prepared gelling material specimens explored the hydration products and microstructural changes of the backfill gelling system and revealed the hydration mechanism of the gelling system and the strength formation mechanism of the specimens. The results of the experimental study showed that the strength of the specimens at different maintenance ages was subject to different significance arrangements of the factors. Based on the optimized ratio of composite cementitious materials, the 28d UCS of the filler prepared by synergistic tailing sand reaches 3.88 MPa, which can meet the jksg of partial mine filler mining. Applying copper smelting slag-based gelling backfill materials (CSSM) at mine sites reduces backfill costs while effectively reducing solid waste emissions, thereby protecting the environment and promoting the realization of waste-free mines and green mining. [ABSTRACT FROM AUTHOR]