This paper proposes a technique for producing underground backfilling materials using enzyme-induced calcium carbonate precipitation (EICP) technology to address the growing ecological security concerns caused by coal mining. To augment the mineralization impact of EICP, diverse levels of organic substances, including yeast extract, peptone, and skimmed milk powder, were incorporated into the cementing solution to offer a greater number of nucleation sites for the precipitation of calcium carbonate. The results indicate that (1) based on visual observations, all the sand columns remained intact after cementation, demonstrating a good cementation effect; (2) unconfined compressive strength (UCS) test findings demonstrated that the introduction of organic components effectively augmented the strength of EICP. Among these materials, skimmed milk powder exhibited the most significant effect, resulting in a 66.01% increase in the UCS of EICP at a concentration of 6 g/L. Peptone also showed a positive impact, albeit to a lesser extent, while yeast powder had a relatively lower effect; (3) The utilization of scanning electron microscopy (SEM) revealed a significant diversification in the crystal morphology of calcium carbonate when combined with organic materials through the EICP process. An X-ray diffraction (XRD) test confirmed the presence of calcite and vaterite. This finding implies that the molecular structure of calcium carbonate is enhanced by the inclusion of organic materials.

The utilization of CO₂ mineralization fly ash (F) and coal gangue (G) technology is proposed in this research work to prepare underground backfilling materials. The test process can be divided into pre-treatment and post-treatment stages. In the pre-treatment stage, a sealed stirring vessel is used to conduct CO₂ wet mineralization. The ratios of F and G were selected as follows: 20%:60% (F2G6), 30%:50% (F3G5), 40%:40% (F4G4), 50%:30% (F5G3), and 60%:20% (F6G2). The ratios were prepared into Φ50 mm × 100 mm cylindrical samples, with curing durations of 3 d, 7 d, 14 d, and 28 d. In the post-processing stage, the SANS microcomputer-controlled electronic universal testing machine and FLIR A615 infrared thermal imager were used to carry out uniaxial loading and temperature detection, respectively. The unconfined compressive strength (UCS), X-ray diffraction (XRD), average infrared radiation temperature (AIRT), variance of original infrared image temperature (VOIIT), and variance of successive minus infrared image temperature (VSMIT) of the samples were compared and analyzed. The results indicated that when curing reaches 14 d, the strength approaches its peak, with minimal changes in strength over a delayed period; furthermore, as the ratio of F to G continues to increase, the mineralization effect gradually strengthens, reaching its optimum level at a ratio of 5:3. However, when the ratio exceeds 5:3, signs of deteriorating mineralization effect start to appear. During the loading process, the AIRT of the mineralized samples showed a continuous increase, but the VOIIT and VSMIT of the mineralized sample both exhibited significant fluctuations or rapid increases during damage rupture. Moreover, the rise in the AIRT value was found to be linked to the increase in the ratio of F to G. This indicates that F has a higher thermal–mechanical conversion efficiency compared to G, so the temperature change will be greater during the loading process. The drastic changes in the VOIIT and VSMIT indicate that they can be used as sensitive response indicators for sample rupture, and can predict and warn of damage rupture in mineralized samples. Research work can provide practical guidance and reference for underground backfilling of CO₂ mineralization industrial waste.