## 1 Introduction  
During the development and utilization of coal resources, a large amount of solid waste will be discharged, mainly including coal gangue and fly ash. Among them, the annual discharge of coal gangue is about 800 million tons, accounting for 15-20% [1,2] of the coal resource output, and the annual output of fly ash has also exceeded 600 million tons [3]. Due to the large discharge of coal gangue and fly ash and the low comprehensive utilization rate, there are a series of ecological and environmental problems, such as resource waste and environmental pollution risks [4, 5, 6]. At the same time, facing the increasingly severe global climate situation, the Chinese government has proposed the dual carbon strategic goals of \"carbon peak in 2030 and carbon neutrality in 2060\" [7; 8]. In the context of the national dual carbon goals, how to reduce carbon emissions in the coal industry and achieve carbon sequestration has become a difficult problem that needs to be solved urgently. Due to the complex composition of coal gangue and fly ash, which contain a large amount of calcium and magnesium crystalline phases, they can react with CO\({}_{2}\) in solution to produce carbonates [9; 10; 11]. Therefore, coal gangue and fly ash can be used as raw materials for CO\({}_{2}\) mineralization, and their mineralization products can be comprehensively utilized, which can achieve the dual goals of large-scale disposal of coal gangue and fly ash and long-term sequestration of CO\({}_{2}\). Using coal gangue and fly ash to prepare coal gangue-based backfilling slurry (CGBS) and fill it into goat to store CO\({}_{2}\) can not only control rock movement and reduce surface subsidence but also achieve large-scale sequestration of CO\({}_{2}\) and disposal of solid waste [12; 13; 14]. However, a large number of studies have found that the rheological properties of backfilling slurry will significantly deteriorate after absorbing CO\({}_{2}\). [PERSON] et al. [9] found that after CO\({}_{2}\) gas was introduced into fly ash slurry, the slurry yield stress increased from 2.97 Pa to 36.01 Pa, and the plastic viscosity increased from 0.84 Pa-s to 57.29 Pa-s; [PERSON] et al. [15] analyzed the effects of CO\({}_{2}\) flow rate and aeration stirring time on the rheological properties of magnesium slag-based backfilling slurry. The results showed that the yield stress and plastic viscosity of the backfilling slurry were positively correlated with the CO\({}_{2}\) flow rate and aeration stirring time. [PERSON] et al. [16] studied the reaction of silicate cement with supercritical CO\({}_{2}\) at different temperatures. The results showed that after 24 h of reaction between silicate cement and supercritical CO\({}_{2}\), the carbonization of the cement slurry was basically completed, and the rheological properties deteriorated. [PERSON] et al. [17] studied the effects of stirring rate, stirring time and aeration rate on the fluidity of the magnesium-coal-based solid waste CO\({}_{2}\) backfill material. The results showed that the calcium carbonate produced by the carbonation reaction filled the voids of the slurry, increased the collision between the internal particles, and thus increased the yield stress of the slurry. In summary, research on the flow properties of backfilling slurry after carbon fixation has so far focused on factors such as material ratio, stirring time and CO\({}_{2}\) flow rate. There are few studies on the effect of carbon fixation pressure on the rheological properties of CGBS, and its change mechanism has not yet been clarified. Based on the above analysis, the effect of carbonization pressure on the rheological properties of CGBS was studied in this paper, and its rheological change mechanism was revealed by characterization by means of X-ray diffraction (XRD), a nitrogen adsorption-desorption instrument (Brunauer-Emmett-Teller Method, BET), a scanning electron microscope (SEM), etc.