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To address the issues of corrosion weakening of solid-waste-based backfill material caused by mine water, a novel hydrophobic solid waste backfill (HSBF) material was developed using polydimethylsiloxane (PDMS) and a silane coupling agent (SCA) as hydrophobic modification additives, and NaOH (SH) and sodium silicate (SS) as alkali activators. Fly ash and slag were chosen as the primary raw solid waste materials. The rheological properties of the hydrophobic-treated backfill slurries were measured, and the resulting physicochemical properties were compared with the unmodified reference group. This study reveals that the fresh HSBF slurry follows a Modified Bingham (M-B) model with shear-thinning characteristics. The addition of PDMS causes an increase in the water contact angle of the hardened HSBF material with F8S2 to up to 134.9°, indicating high hydrophobicity. Morphological observations indicated that PDMS mainly attaches to the inorganic particles' surface through the bridging action of SCA for the hydrophobic modification of the backfill material. The overall strength of the HSBF materials was further ensured via fly ash–slag ratio optimization, and was found to be enhanced up to 98% by increasing slag content from 20% to 50%. This is mainly attributed to the hydration of slag, forming C-S(A)-H gel, which contributes to the increased strength. The novel HSBF material enables the elimination of cement in mine backfilling applications, demonstrating good economic benefits. Its excellent mechanical and hydrophobic properties can not only prevent overburden displacement in goaf areas, but can also mitigate water resource loss from overlying strata and simultaneously reduce the safety risks associated with long-term mine water deterioration. [ABSTRACT FROM AUTHOR]

Underground backfilling stands out as a crucial technological strategy for the eco-friendly and effective management of solid waste in mining operations. However, existing backfilling techniques have led to increased production processes at the working face, resulting in a reduction in coal extraction efficiency. Addressing the temporal and spatial interference between mine solid waste backfilling and coal mining is essential. To overcome this challenge, this study introduces a novel post-mining spatial gangue slurry backfilling method. Radar detection was employed to ascertain the typical characteristics of the subsequent space collapse roof shape. Stress monitoring and compaction experiments were conducted to establish the relationship between stress and the bulking coefficient of the overlying rock mass, identifying subsequent spatial void structure characteristics. The development of a CO2 mineralized coal-based solid waste filling material, utilizing conventional low-calcium fly ash under normal temperature and pressure conditions, was presented. This paper provides a comprehensive understanding of the post-mining spatial gangue slurry backfilling method, outlines the spatial layout approach for the corresponding system, and analyzes research challenges associated with gangue slurry backfilling materials and the technology of slurry injection borehole layout. The research aims to innovate an efficient underground disposal model for gangue, contributing to the refinement of the technical system for the comprehensive disposal and utilization of gangue. [ABSTRACT FROM AUTHOR]

Static segregation of coal gangue-fly ash backfill (CGFB) material presents a significant impact on its mechanical performance for underground support. To resolve, a novel formulation was addressed using sodium silicate (SS) and CO2 as co-activator. Its setting behaviors and mechanical properties were investigated with respect to the coal gangue content, CO2 influx and the concentration of sodium silicate solution. The microstructure was characterized by SEM, EDX, XRD, and FTIR. The present method lowered the initial and final setting times to approximately 90% and 74% comparing to which of conventional activator. The compressive strength increased from 2.06 to 10.23 MPa with coal gangue ratio of 3.2 after 56 days curing. This mainly results from the mitigation of the effect of segregation through the generation of silica gel, which precipitated on the grain surface. The silica gel promoted the interparticle binding and rapid consistency, thus preventing gangue from settlement. Incorporating the microscale crystalline phase characterization, the carbonate products work as the filling particle and the coal gangue presents as the reinforcement after hardening, leading to the significant increase in material strength. This method not only ensures safe disposal of coal gangue and fly ash from segregation, but also mitigates overburden deformation and promotes CO2 utilization. Therefore, the coordinated development of coal resource development, environmental protection, and carbon footprint reduction is realized. [ABSTRACT FROM AUTHOR]

The consumption of coal resources has caused an increase in CO2 emissions. A scientific concept that can realize CO2 sequestration, the harmless treatment of solid wastes, and coal extraction under buildings, railways, and water bodies (BRW) is proposed. First, a novel CO2 mineralized filling body (CMFB) is developed by employing CO2 gas, fly ash, silicate additives, and cement. It is then injected into the mined-out mining roadways (MRs) of the continuous extracting and continuous backfill (CECB) mining method to ameliorate the overburden migration and thus extract the coal body under the BRW. The AHP-fuzzy comprehensive evaluation method was employed to construct a prediction model for the suitability of this concept. Subsequently, the evaluation model is generalized and applied to the Yu-Shen mining area. Each indicator affecting adaptability is plotted on a thematic map, and the corresponding membership degree is determined. The aptness for 400 boreholes distributed in the entire area was determined and a zoning map which divides the whole area into good, moderate, slightly poor, and extremely poor suitability was drawn. This paper puts forward a mathematical model for predicting the suitability of using CECB and CMFB to sequestrate CO2. Research results can provide references for determining the site of CO2 sequestration under the premise of maximizing the economic and ecological benefits, which is conducive to constructing ecological, green, and sustainable coal mines. [ABSTRACT FROM AUTHOR]

The exploitation and utilization of coal resources are not only prone to causing water table lowering, but also produce a large amount of CO2 and coal-based solid waste. A scientific concept that employs the CO2 and solid wastes to develop filling bodies and inject them into the mined-out area, to sequestrate CO2 and mitigate the overburden migration and thus preserve the overlying aquifer, is proposed. Continuous extraction and continuous backfill (CECB) mining was selected as the mining method to meet the aforementioned objectives. Additionally, carbon dioxide mineralized filling body (CMFB) under ambient temperature and pressure was developed, with fly ash as aggregate, and CO2 gas, silicate additives and cement as accessories. The uniaxial compressive strength (UCS) and tensile strength of CMFB with various curing times and fly ash contents were tested indoors. A physical analogue simulation and FLAC3D numerical calculation were then successively implemented on the premise of determining a similar material ratio of CMFB in analogue simulation and calibrating the parameters of the CMFB in numerical simulation. The deformation of aquifuge and water level lowering while using CECB and CMFB with various proportion of fly ash were obtained. When using the CMFB with 75% fly ash content and 28 d curing time, the maximum values of vertical displacement, horizontal displacement, inclination, horizontal deformation and curvature of aquiclude were 26 mm, 6.5 mm, 0.12 mm/m, 0.08 mm/m and 0.0015 mm/m2, respectively, and the water table decreased 0.47 m. The results show that the CMFB with 75% fly ash is the most appropriate ratio to realize water preservation mining, CO2 sequestration and harmless treatment of solid wastes, contributing to the green and sustainable development of coal areas. [ABSTRACT FROM AUTHOR]

CO 2 mineral carbonation is a promising strategy to sequestrate CO 2. Whereas, its industrial applications were still limited owing to high temperature and high pressure. A Trinity green mining (TGM) concept is proposed for CO 2 sequestration, solid waste treatment, and overburden movement mitigation. The samples of CO 2 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 CO 2 mineralization rate decreases from 1.34 to 1.13 mg CO 2 /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 CO 2 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. [ABSTRACT FROM AUTHOR]