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Pre-existing concealed goafs underneath open-pit slopes (PCO-goafs) pose a serious threat to the stability of open-pit slopes (OP-slopes), which is a common problem worldwide. In this paper, the variable weight-target approaching method, equilibrium beam theory, Pratt's arch theory, and numerical simulation are used to analyze the management solutions and stability of five PCO-goaf groups in the Nannihu molybdenum mine located in Luoyang City, Henan Province, China. The five PCO-goaf groups, numbered 1#, 2#, 3#, 4#, and 5#, are divided into four hazard classes, ranging from extremely poor to good stability. The stability of 1#, 2#, and 4# is poor and must be managed by filling, and the design strength of backfill is 1.2 MPa; caving is used to treat 3# and 5#, and the safe thickness of the overlying roof is calculated to be 10.5–41 m. After treatment, the safety coefficient of the slope is greater than 1.2, indicating that the slope is stable. This study provides insight and guidance for the safe operation of open-pit mines threatened by the existence of PCO-goafs. [ABSTRACT FROM AUTHOR]

Phosphogypsum (PG), a hard-to-dissipate by-product of the phosphorus fertilizer production industry, places strain on the biogeochemical cycles and ecosystem functions of storage sites. This pervasive problem is already widespread worldwide and requires careful stewardship. In this study, we review the presence of potentially toxic elements (PTEs) in PG and describe their associations with soil properties, anthropogenic activities, and surrounding organisms. Then, we review different ex-/in-situ solutions for promoting the sustainable management of PG, with an emphasis on in-situ cemented paste backfill, which offers a cost-effective and highly scalable opportunity to advance the value-added recovery of PG. However, concerns related to the PTEs' retention capacity and long-term effectiveness limit the implementation of this strategy. Furthermore, given that the large-scale demand for ordinary Portland cement from this conventional option has resulted in significant CO2 emissions, the technology has recently undergone additional scrutiny to meet the climate mitigation ambition of the Paris Agreement and China's Carbon Neutrality Economy. Therefore, we discuss the ways by which we can integrate innovative strategies, including supplementary cementitious materials, alternative binder solutions, CO2 mineralization, CO2 curing, and optimization of the supply chain for the profitability and sustainability of PG remediation. However, to maximize the co-benefits in environmental, social, and economic, future research must bridge the gap between the feasibility of expanding these advanced pathways and the multidisciplinary needs. [ABSTRACT FROM AUTHOR]

Ground vibrations induced by underground mining blasting has a significant impact on the stability and safety of surface buildings near mines. Due to the thick rock layers overlying underground mines, there is presently limited accuracy in regard to predicting ground vibrations induced by underground mine blasting. Therefore, this study aims to improve the accuracy of predicting ground vibrations induced by underground blasting by comprehensively measuring the peak particle velocity (PPV) in all three directions and independently considering on the impact of vertical distance. Random forest regression (RFR), bagging regression (BR), and gradient boosting regression (GBR) were used to regress the X-axis PPV (X-PPV), Y-axis PPV (Y-PPV), and Z-axis PPV (Z-PPV) based on blasting records measured at an iron mine. In addition, a genetic algorithm, gray wolf optimizer (GWO), and a particle swarm optimization were used to optimize the parameters of the RFR, BR, and GBR. The comparison results show that GWO-GBR is the optimal model for the prediction of the X-PPV (R2 = 0.8072), Y-PPV (R2 = 0.9147), and Z-PPV (R2 = 0.9265), respectively. Thus, the GWO-GBR model proposed in this study is considered a highly reliable model for predicting ground vibrations induced by underground mine blasting to ensure the safety of the mines' surroundings. [ABSTRACT FROM AUTHOR]

The treatment of large amounts of copper slag is an unavoidable issue resulting from the high demand for copper during the global transition to a sustainable development path. Metal-rich copper slag might serve as a potential source of metals through secondary recovery. In this study, two copper slags (CS1 and CS2) with different metallurgical properties were characterized, focusing on secondary metal recovery. The X-ray diffraction (XRD) results show that fayalite (Fe2SiO4) and magnetite (Fe3O4) were the main crystalline phases in both CS1 and CS2. In addition, CS2 exhibited a more stable amorphous silicate network than CS1, which was attributed to the differences in the content of Si-O-3NBO linkages. The sequential extraction of Zn, Cu, Fe, and Pb from the slags was also explored, with the Cu content in CS1 being substantially lower than that in CS2. All metals were distributed in the F5 residue fraction. Cu was the most mobile metal as a result of the large proportion of soluble fractions (F1–F3), followed by Zn and Fe. This study explored the chemical speciation of Zn, Cu, Fe, and Pb from copper slags, which has practical implications for secondary metal recovery from such materials. [ABSTRACT FROM AUTHOR]

The empty-space subsequent filling mining method is the main mining scheme for underground metal mines to achieve large-scale mechanized mining. The stage height, one of the main parameters of this method, affects the various production process aspects of the mine and influences the stability of the goaf. In order to determine the stage height scientifically and rationally in the empty-space subsequent filling mining method, a formula for the stabilized critical safe height of a high goaf in an underground metal mine was derived based on Pu's arch equilibrium theory, Bieniawski's pillar strength limit theory, and the Kastner equation and combined with the results of an orthogonal analysis to rank the importance of the main factors in the formula. A copper mine in Jiangxi Province was used as a case study, with the reliability of the formula verified by numerical simulation and industrial testing. The factors in the formula influencing the critical stabilized safe height of the goaf were, in descending order, the compressive strength of the rock body, the width of the two-step mining pillar, the width of the one-step mining room, the mining height, and the depth of mining. Based on the calculation results, the recommended stage heights are 30 m (−378 m middle section) and 25 m (−478 m middle section) in the area of poor rock body stability and 50 m in the area of better rock body stability. The simulation results show that the goaf is significantly affected by the compressive stress under the condition of a certain rock body stability and that the compressive stress increases with increasing goaf height. The minimum recommended values of the sidewall safety coefficients in areas of poor and better rock stability are 1.04 and 1.06, respectively. The volume deviation coefficients of the three industrial test mines were all controlled within 3%, indicating that no obvious collapse and destabilization phenomenon occurred in the goaf. This paper provides some theoretical and applied guidance for the stage height design of similar underground metal mines using the empty-space subsequent filling mining method. [ABSTRACT FROM AUTHOR]