Abstract: Iron and steel production processes generate a large amount of CO₂ and solid wastes such as blast furnace slag.Slag mineralization for CO₂ sequestration and its injection into goaf was proposed to solve the problems of solid waste accumulation and greenhouse gas emission, which can effectively control the movement of rock layers and reduce ground surface collapse.This research investigated the mechanical properties, microstructure and phase composition of the slag-based carbon filling material (SCFM) using X-ray diffraction (XRD), scanning electron microscopy (SEM)、X-ray photoelectron spectroscopy (EDS) and thermogravimetric analysis (TG) under ambient temperature and pressure.The mechanism of CO₂ curing and UCS strengthening of SCFM were analyzed.During SCFM preparation, silicate cement, slaked lime and slag powder were first hydrated, and the hydration products (hydrated calcium silicate gel and calcium hydroxide) were then carbonized with CO₂ to produce silica gel and calcium carbonate.The results show that the strength of SCFM increased with the increase of silicate cement and slaked lime dosages, and the strength of SCFM specimens was the greatest with cement and slaked lime dosages of 20%and 7%, respectively.The strengths reached 4.41 and 16.47 MPa at the 3 d and 28 d, respectively.The maximum CO₂ sequestration of 1g SCFM is 1.83mg, which is proportional to the dosage of cement and slaked lime, and slaked lime is the controlling factor. SCFM improves solid waste and CO₂ utilization and sequestration rate, which provides theoretical supports for realizing the goal of the ″double carbon″ strategy.