Objective The reutilization of solid waste such as coal gangue and steel slag is critical to green mining. Preparing solid waste-based carbon-sequestering backfill materials and then filling them into coal mine goaves emerge as an important approach to solid waste utilization, carbon emission reduction, and green coal mining.

Methods  Based on the designed mix proportions of a high-solid-waste system consisting of steel slag and coal gangue, in which steel slag was used to compensate for the insufficient carbonation reactivity of coal gangue, this study prepared solid waste-based backfill material samples composed of coal gangue, steel slag, and cement. Through mechanical and carbon-sequestration tests in the laboratory, along with a range of test methods including thermogravimetric analysis (TGA), X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and mercury intrusion porosimetry (MIP), this study explored the mechanical properties, carbon sequestration capacity, and carbonation reaction mechanisms of these solid waste-based backfill materials.

Results and Conclusions  Carbonation temperature significantly affected the mechanical properties of the backfill materials. As the carbonation temperature increased from 40 ℃ to 80 ℃, the compressive strength of the samples showed an increasing trend. Increasing the steel slag content can enhance the compressive strength of the samples during the later curing stage. With an increase in the carbonation temperature, the CO₂ absorption capacity of the samples increased initially and then decreased. Notably, the sample comprising 35% calcined coal gangue and 50% steel slags yielded a CO₂ absorption capacity reaching up to 6.9% at a carbonation temperature of 60 ℃. Carbonation reactions promoted the formation of CaCO₃ to fill material pores, while the active silico-aluminous phase accelerated the formation of calcium-silicate-hydrate ( C-S-H ) gel. Both aspects enabled the stable bonding between CaCO₃ and C-S-H and thus enhanced the material density, serving as the key mechanisms for improving the performance of solid waste-based backfill materials. The results of this study provide theoretical support for developing high-performance, multi-source solid waste-based, carbon-sequestering backfill materials, contributing to the development of carbon sequestration technology for green mine backfilling.