A new type of cemented paste backfill (CPB) was prepared using sodium hydroxide (NaOH) as the activator, slag and silica fume (SF) as the binder, and tailings as the aggregate. The effects of proportion of replacement of 0%, 5%, 10%, 15%, and 20% silica fume on the properties of CPB were studied. The strength formation mechanism of CPB was explored through a combination of scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and Fourier transform infrared (FTIR) spectroscopy. The SEM images were analyzed by IMAGE J software, and the porosity of CPB with different silica fume contents was obtained. The results show that as the amount of silica fume increases, the unconfined compressive strength (UCS) increases first and then decreases. When the amount of silica fume was approximately 5%, CPB with a larger UCS can be obtained. When the silica fume content increased from 0% to 5%, because silica fume has good activity and small particles, more calcium silicate hydrate (C–S–H) gels and Mg-Al type layered double hydrotalcites (LDHs) were generated in CPB, which made it denser and improved its strength compared with the non-silica fume group. C–S–H gels were the main source of CPB strength. With a further increase in the amount of silica fume, thaumasite produced inside of CPB, reducing the content of C–S–H gels. Moreover, due to the expansion of thaumasite, it is easy to generate a large number of micro cracks in CPB, which weakens the strength of CPB.

Abandoned lead and zinc (Pb-Zn) mines around the world produce large amounts of acid mine drainage (AMD) containing Pb(II), which is toxic and accumulates in the environment and in living organisms. Bentonite-steel slag composite particles (BSC) are a new type of acid mine drainage (AMD) treatment material that can remove heavy metal ions and reduce acidity. To date, there have been no reports on the treatment of Pb(II)-containing AMD using BSC. Therefore, the effects of pH, reaction time, temperature, and Pb(II) concentration on the adsorption of Pb(II) onto BSC were studied. Moreover, the BSC before and after the reaction, as well as the precipitation after the reaction, were characterized by scanning electron microscopy and X-ray diffraction analyses. The effect of pH on the adsorption process is similar to that of the formation of soluble and insoluble hydrolysates of Pb(II) on pH. The adsorption mechanism includes ion exchange, complexation, precipitation, and synergistic adsorption–coagulation effect. Adsorption kinetics are best-fit with the pseudo-second order kinetics model ( $R^2$ > 0.98). Furthermore, the total adsorption rate is controlled by liquid film diffusion and in-particle diffusion, the liquid film diffusion rate being higher than the in-particle diffusion rate. The isothermal adsorption of Pb(II) onto BSC fit well with Langmuir and Brunauer Emmett Teller (BET) isotherms ( $R^2$ > 0.995), and both single layer adsorption and local multilayer adsorption were observed. Thermodynamic analysis revealed that the adsorption process is spontaneous and endothermic, and that the degree of freedom increases with time. In summary, this study provides a theoretical basis for the use of BSC in treating AMD containing Pb(II).

In order to quantitatively evaluate the degree of protection in protective layer mining and provide guidance for the design of a secondary outburst elimination scheme, a variable weight-projection gray target dynamic evaluation model for the effectiveness of protective layer mining is established. The improved order relation analysis method was used to determine the subjective weight of each index toward the decision-making goal based on numerical diversity characteristics, and the initial fixed-weight calculation for mixed multi-attribute metrics was processed through the degree of index action. The variable weight function was used to dynamically adjust the fixed weight through the penalty and incentive index methods. Four indexes (gas content, gas pressure, coal seam permeability coefficient, and expansion deformation) were selected, the outburst elimination and anti-reflection were taken as the guide, and the critical value of each index for eliminating burst and the critical value of pressure relief were taken as the positive and negative bullseyes. Based on the variable weight-projection gray target decision model, the distance between the two target centers of each scheme was calculated; at the same time, the variable weight vector changed dynamically with the evaluation scheme to achieve the dynamic quantitative evaluation of the degree of protection. Additionally, compared with the calculation results of fixed weights, it was found that the variable weight-projection bullseye distance can more accurately reflect the dynamic control effect of differences in numerical combinations of multi-attribute indexes in different decision schemes based on the degree of protection of protective layer mining. Taking a mine in PingMei as the engineering background, Ding protected the Wu area, and the degree of protection in the Wu group coal seam reached 116.29%, eliminating the outburst risk of the coal seam. The Wu protected the Ji group coal seam, with the degree of outburst risk in the Ji group being reduced by 14.27, and the Ding + Wu group protected the Ji group coal seam, with the degree of outburst risk of the Ji group being reduced by 20.71%, but not eliminated. The evaluation model quantifies the degree of protection of protective layer mining, and provides a theoretical basis for further assessing whether the working face should strengthen the enhancing permeability or whether it needs to be used in tandem with high-strength outburst elimination methods.

One of the primary causes of casualties as a result of underground coal mine disasters is the generation of high concentrations of carbon monoxide (CO). In this study, a copper (Cu)–manganese (Mn)–tin (Sn) composite oxide catalyst was prepared using the co-precipitation method, and the effects of CO concentration (1–7%), reaction temperature (25–300 °C), and water poisoning degree (0–100%) on CO catalytic oxidation performance were systematically investigated using a dynamic activity testing system. The results demonstrated that within the CO concentration range of 1–7%, the catalyst was able to reduce the CO concentration to below 0.55% in a maximum of 248 s and maintain this level in a relatively stable state. Meanwhile, both the catalytic activity and maximum instantaneous reaction rate exhibited a linear increase with the rise in the CO concentration. Elevated temperature significantly shortened the equilibrium time and reduced the equilibrium concentration, achieving 99.99% elimination efficiency at 300 °C; however, catalyst activity decreased with increasing temperature due to adsorption step limitations. Water poisoning severely affected catalyst performance, with activity, elimination efficiency, and long-term stability exhibiting exponential decay as the water poisoning degree increased, with the most significant performance decline occurring in the 0–60% range. Based on the dynamic gas concentration analysis, the CO oxidation process with this catalyst exhibited characteristics consistent with the Mars–van Krevelen mechanism. These findings provide an experimental basis for evaluating the applicability of Sn-containing catalysts in extreme underground coal mine environments.

To address the recurring issue of excessive carbon monoxide (CO) concentrations at the return corner of fully mechanized mining faces under goaf conditions, this study investigated the elimination of CO at ambient temperature and pressure using deep eutectic solvents (DESs). CO, a colorless, odorless, and highly toxic gas, is notoriously difficult to remove under conventional conditions. A series of DESs were prepared and screened, revealing that the ethanol-modified system [Emim]Cl-CuCl-1.0E exhibited optimal CO elimination performance under conditions of 298.15 K and atmospheric pressure. Further investigations measured the viscosity-temperature relationship and thermal stability of this system while systematically examining the effects of temperature, CO contact time, and storage duration on its elimination efficiency. Analysis by FTIR and Raman spectroscopy indicated that Cu(I) ions play a crucial role in the CO absorption process. The introduction of ethanol significantly enhanced the activity of the Cu(I) ions, thereby effectively improving the CO elimination capacity of the system. This study proposes a novel potential method for managing CO in goaf areas and provides an experimental foundation for the application of DESs in the field of gas purification.