Coal-based solid waste (CBSW; fly ash, weathered coal, coal gangue) from open-pit coal mining in extremely cold regions differentially releases salinity/alkalinity, heavy metals and acids, altering surrounding black-soil properties and reshaping its bacterial communities. We compared healthy farmland black soil (CK) with three dumping treatments—fly ash (FA), weathered coal (WC) and coal gangue (CG) (six replicates each; n = 24)—using full-length 16S rRNA sequencing (PacBio CCS), physicochemical, phospholipid fatty acid and enzyme-activity analyses. The wastes showed contrasting stress regimes: fly ash was slightly alkaline, saline and heavy-metal-enriched; weathered coal was strongly acidic and saline; and coal gangue was acidic–sulfidic. Dumping significantly altered soil pH, salinity and metal speciation, reducing organic matter by 36–61% and microbial biomass carbon by 45–74%. Alpha diversity responded in a type-specific manner: WC had the lowest Shannon index (4.72, −55.1%) and was dominated by Pseudomonadota (80.6%) with methylotrophy being enriched; FA retained the highest diversity (11.23); and CG was dominated by Actinobacteriota (45.1%). PERMANOVA and ANOSIM confirmed significant community separation. Nitrification was nearly lost under WC, while sulfate respiration was enriched under CG and sulfur respiration under FA, indicating type-specific restructuring of nitrogen and sulfur cycling. These results show that CBSW dumping drives restructuring and nitrogen–sulfur functional degradation of black-soil bacterial communities through type-specific environmental filtering, with weathered coal causing the most severe degradation, informing classified remediation.

Rainfall-induced seepage instability is a major concern for internal waste dump slopes in cold-region open-pit coal mines, where slope performance is influenced by groundwater conditions, moisture state, and seasonal temperature variations. This study investigates the internal waste dump slope of the Chaoyang open-pit coal mine and evaluates its seepage and stability responses under prescribed moisture and temperature states before and after rainfall, together with the effectiveness of drainage control. Soil specimens with moisture contents of 14%, 17.6% (natural), 23%, and 26% were tested at ambient temperature, −5 °C, and −15 °C by uniaxial compression and direct shear tests. The mechanical parameters measured under the prescribed moisture and temperature states were assigned to a GTS NX seepage–stability model. Twenty-four parametric cases, comprising four moisture contents, three temperature states, and pre- and post-rainfall conditions, were evaluated using the strength-reduction method, and an HDPE perforated drainage scheme was subsequently assessed. Under the ambient-temperature parameter state, increasing specimen moisture content from 14% to 26% reduced the pre-rainfall factor of safety from 1.41 to 1.18 and the post-rainfall value from 1.38 to 1.17. Parameter sets obtained from low-temperature-conditioned specimens produced higher calculated factors of safety; however, these cases represent prescribed mechanical states rather than the actual winter condition of the full-scale slope. Under the idealized drainage boundary, the pre- and post-rainfall factors of safety increased from 1.22 and 1.18 to 1.40 and 1.39, respectively. The results demonstrate the relative effects of laboratory-derived mechanical parameters, rainfall-induced seepage, and idealized drainage under the prescribed scenarios.

Abandoned open-pit coal mine slopes are compacted, infertile and water-limited, hindering vegetation restoration. This study evaluated the combined use of two waste materials—coal gangue (an alkaline, mineral-rich mining residue) and decomposed straw (a nutrient-rich agricultural residue)—as a composite substrate for restoring degraded slope soil. In a 60-day greenhouse pot experiment, slope soil from the Haizhou Open-Pit Coal Mine (Fuxin, China) was amended with coal gangue (5%, 10% or 15% by dry mass), decomposed straw (1%, 3% or 5%), or their nine full-factorial combinations (16 treatments in total, including an unamended control, each with three replicates), and sown with three herbaceous species (ryegrass, alfalfa and tall fescue). Soil physical and chemical properties and plant growth traits were measured. Relative to the unamended control, the composite substrates improved soil structure and fertility: soil water content and field water-holding capacity were highest under the 10% gangue + 5% straw treatment (25.6% and 25.89%, increases of 28.0% and 29.5%), bulk density was lowest, with the correspondingly highest total porosity, under the 15% gangue + 3% straw treatment (1.35 g/cm³, a 14.9% decrease). Organic matter (9.42 g/kg), total nitrogen (0.71 g/kg, +65.1%), available nitrogen (45.3 mg/kg, +33.0%) and available potassium (106.44 mg/kg, +26.2%) were highest under the 5% gangue + 5% straw treatment, which also gave the best growth of ryegrass and alfalfa (alfalfa aboveground and underground dry weight increased by 221% and 188%, respectively), whereas tall fescue grew best under the 5% gangue + 3% straw treatment. These results indicate that a 5% coal gangue + 5% decomposed straw composite substrate is a promising amendment for revegetating degraded open-pit slopes, although field validation is still required.

Spontaneous combustion in fire-affected coal seams can degrade coal quality, alter rock mechanical parameters and reduce mining profitability. Traditional pit limit optimization methods ignore coal fire-induced quality degradation, ignore the coupling effect of economic fluctuation and slope stability, and lack quantitative optimization for fire-affected open-pit mines. Here, we optimize loss-reducing mining boundaries for the southern fire-affected highwall in the first mining district of the Dananhu No. 2 Mine, Hami, Xinjiang. The aim is to move beyond binary decisions that either sterilize or fully extract fire-affected reserves. We instead integrate economic return, slope stability and coal-price uncertainty into a single boundary-optimization framework. First, we established a three-dimensional Cartesian coordinate system for the study area. We then modeled and fitted the coal-seam roof and floor using MATLAB-based multiple integration, reducing edge errors in solid surfaces. Laboratory analyses of borehole coal samples defined how calorific value varied with advance distance. These data were used to derive the coal-quality curve. Net mining profit was then formulated as the objective function, replacing the conventional stripping-ratio criterion. Profit was calculated across advance distances to identify the economically optimal boundary. Mechanical parameters of thermally altered rocks were obtained from laboratory deformation tests. Rhino and FLAC3D 6.0 were then used to evaluate three-dimensional slope stability at critical locations. Coal-price perturbation scenarios were finally introduced to test the sensitivity of net profit and optimal advance distance. Under the baseline coal price, the slope remained stable at an advance distance of 193 m. At this boundary, net profit reached a maximum of RMB 676.608 million. The southern surface boundary contracted by 47 m relative to the initial boundary, reducing unnecessary land disturbance. Sensitivity analysis showed that lower coal prices sharply reduced both the optimal advance distance and maximum net profit. When coal price decreased by 30%, the optimal advance distance contracted to approximately 116.9 m. Maximum net profit fell to approximately RMB 248.239 million. Higher coal prices expanded the optimal boundary outward. Once coal price reached approximately 128.7 yuan/t, or 18.5% above baseline, the optimum reached the upper constraint of 240 m. Net profit then increased substantially with further price growth. These results provide a quantitative basis for dynamic boundary optimization and disturbance-reducing extraction in fire-affected open-pit coal mines.