Characteristics of overburden migration under continuous extraction and continuous backfill mining method with CO2 mineralized filling materials

CO2 mineral carbonation is a promising strategy to sequestrate CO2. Whereas, its industrial applications were still limited owing to high temperature and high pressure. A Trinity green mining (TGM) concept is proposed for CO2 sequestration, solid waste treatment, and overburden movement mitigation. The samples of CO2 mineralized filling materials (CMFM) were developed at ambient temperature and pressure and its feasibility of field application was verified. The results show that: (1) As the fly ash (FA) proportion increases from 55 % to 85 %, the UCS ascends first and then decreases, reaching a peak at 75 % since the dosage of FA exceeds the cementation ability of the gel. The gel can be characterized as C–S(A)-H and silicon-based gel. (2) The maximum yield stress is 88 MPa and the mini-slump is 109 mm. The 75 % and 85 % CMFM has good transportability while the 55 CMFM is unsuitable due to its shorter initial setting time. The CO2 mineralization rate decreases from 1.34 to 1.13 mg CO2/g-CMFM with the rising FA content. The parameters of fresh slurry transportation pipeline were also determined. The velocity of slurry injection is 1.5 m/s. The filling capacity and the pipeline diameter is 192 m/h and 213 mm, respectively. The maximum working pressures of the pump are 10.02, 8.81, 4.11, and 3.91 MPa and the pipeline thicknesses are 8.4, 7.7, 5.2, and 5.1 mm corresponding to four different ratios of CMFM. Additionally, as the FA proportion rises from 55 % to 85 %, the processing capacity of FA grows from 54 E3 t to 80 E3 t. In contrast, the CO2 storage capacity drops from 188 t to 152 t. Moreover, the surface deformation under TGM were illustrated using analogue simulation and mechanical modeling. The results show that: the maximum subsidence of the latter is 23 mm, which is 15 % greater than that of the former. The maximum tilt is 0.15 mm/m and 0.13 mm/m, respectively. The maximum curvature is 0.375 E-2 and 0.152 E−2 mm/m2, respectively. The tilt and curvature of surface from two approaches meet the grade Ⅰ damage standard for buildings released by state, indicating TGM can ameliorate strata migration and thus protect surface buildings effectively.