Failure of mine pillars, especially in deep underground mines, significantly threatens the safety of miners and equipment. Previous studies on mine pillar stability design have used classical constitutive models that ignore the intermediate principal stress component when determining the factor of safety. In this study, we develop and implement a three-dimensional modified Hoek–Brown (HB) constitutive model that incorporates the intermediate principal stress component into the numerical simulation tool FLAC^3D. Furthermore, we propose and apply a strength-reduction technique to determine a more accurate factor of safety for mine pillars. This novel approach provides a more comprehensive and realistic method for geomechanical analysis and pillar design, enhancing our understanding of pillar stability. Through numerical analysis, we illustrate the impact of the intermediate principal stress component on mine pillar plasticity. The factor of safety is calculated via the strength reduction method, revealing a substantial improvement from 1.7 with the classical HB model to 2.0 with the 3D HB model. Including the intermediate principal stress component reduces the evolution of plasticity in the mine pillar. For instance, the volume of plastic zones diminishes, and the factor of safety increases as the width-to-height ratio increases. Exemplary simulations show that ignoring the effect of the intermediate principal stress component, including underestimating safety levels, designing suboptimal pillar design, and misinterpreting in situ observations and measurements, can lead to severe consequences.

The harmful effects of heavy metals on the environment have attracted considerable attention. Adsorption is an effective method for removing heavy metals from water and soil. Clay minerals are abundant in the environment and have the advantages of a wide range of sources, low cost, and renewability. Clay minerals can be used as adsorbents to achieve the effective removal of heavy metals. In this review, clay minerals are systematically classified based on crystal interlayer structure, molecular structure, and corresponding physical and chemical properties. Then, the adsorption effects of clay minerals as adsorbents on common heavy metals in the environment are summarized, and the adsorption performance of modified clay minerals on heavy metals is improved. Finally, the experimental studies using clay minerals as adsorbents for soil groundwater remediation are summarized. In addition, clay minerals are not only used in the field of heavy metal adsorption and removal but also act as ideal catalysts and catalyst carrier materials. This review provides some references for the further applications of clay minerals in the field of environmental remediation and actual industry.

This study aims to investigate the impact of various water-to-binder (w/b) ratios by mass (0.3–2.0) on the performance of limestone calcined clay cement (LC³) pastes. The flowability, setting time, density, unconfined compressive strength, hydration, and microstructure of LC³ pastes under different w/b ratios were thoroughly investigated. The results show that increasing the w/b ratio extends the flowability and setting time while significantly reducing the unconfined compressive strength of LC³ pastes. LC³ pastes with w/b ratios above 0.6 exhibited a final flow diameter surpassing 167 mm, indicating good flowability. The 28-d unconfined compressive strength decreased from 82.3 to 1.3 MPa as the w/b ratio increased from 0.3 to 2.0. This study confirmed that the relationship between unconfined compressive strength and the w/b ratio of LC³ follows Abram’s law. Furthermore, a modified gel/space ratio was proposed to reflect the concentration of solid products, effectively explaining the influence of the w/b ratio on strength, with an R² of 0.96.

Lepidolite is an essential lithium resource with diverse applications in lithium-ion batteries, ceramics, glass, and other industrial sectors. Efficient flotation of lepidolite is crucial for the extraction and recycling of lithium resources, holding significant economic and environmental importance. This review provides a comprehensive overview of the research progress on the processes, reagents, and mechanistic understanding of lepidolite flotation, grounded in the fundamental properties of lepidolite and its major gangue minerals. The article critically analyzes the current lepidolite flotation technologies and highlights the research focus on overcoming the challenge of significant fine-grained lepidolite losses during the flotation process. Through synthesis and discussion, the review also presents an outlook on the future development of lepidolite flotation technology. This comprehensive review serves as a valuable reference for advancing lepidolite flotation techniques, providing insights that enhance the efficient recovery and utilization of lithium resources, as well as the development of the new energy industry.

Cemented tailings backfill (CTB) comprises tailings, binders, and water and is filled into goaves to regulate the ground pressure and ensure production safety. Thus, shortening the curing time of CTB has been a popular research topic in backfill mining as it maximizes the extraction of the neighboring stopes while lowering mining-related costs. In this study, a self-made horn microwave experimental device was developed to rapidly enhance CTB’s strength property. Subsequently, the microwave-curing effects on the upper surface temperature, strength, deformation coefficient, and hydration reaction of CTB were explored through uniaxial compressive strength, X-ray diffraction, and thermogravimetric/differential thermogravimetric experiments. Experimental marks revealed that the strength property of early-aged (up to 7 d) CTB composites could be rapidly enhanced by microwave curing, except for the 7-d-cured fills with microwave curing times of 5–7 min. Moreover, the hydration reactions of CTB after 3- and 7-d curing were substantially accelerated by microwave curing. Thus, this study offers a novel method of satisfactorily increasing early-aged CTB strength and exploring its hydration mechanisms effectively.

Given the current reserves, numerous South African Witwatersrand gold and Bushveld platinum mines have a shorter remaining lifespan than the period they have been in full production. This situation presents a paradox: while mines aim for sustainable development, the inherently unsustainable nature of mining poses challenges. A fundamental question emerges: how can mines approaching the end of their economic lives enhance sustainability? One approach is to extend their production lifespan. This approach is especially important in the context of South Africa with its already unacceptably high unemployment rate. Mature mines in established mining jurisdictions face sustainability issues. Thus, this study argues that innovative skills development, research, and partnerships can help sustain mining operations, although commodity prices fluctuate and mines near the end of their economic viability. The study presents novel ideas to assist mature mines in extending their life and reducing the vulnerability of affected mine workers.

Carbon dioxide capture, utilization, and storage (CCUS) has become a focal point of research for scientists worldwide to address the global warming issue. Among these studies, utilizing mine tailings as CO₂ mineralization materials has emerged as a new research approach in recent years. This study reviews the research progress of using mine tailings for CO₂ mineralization and sequestration. The reaction mechanisms of CO₂ mineralization using tailings have been introduced first. Notably, ultramafic tailings containing divalent cations, such as Ca²⁺, Mg²⁺, and Fe²⁺, can react with CO₂ to produce carbonate precipitates. Furthermore, factors including the size of mineral particles, reaction temperature, and pressure will influence the mineralization reaction rate. The activation methods of tailings to accelerate mineral carbonation have been summarized. The activation of tailings for mineralization generally includes acid leaching, ammonium salt pH swing, and physical grinding. Newly developed methods, such as a combination of acid digestion and electrolysis of olivine, have also been introduced. Thereafter, the processes and technologies for CO₂ sequestration through tailings mineralization have been analyzed. The in-situ and ex-situ mineral carbonation processes have been introduced. The last part explores the technical approaches of synergistic mineralization and storage of CO₂ by cemented tailings backfill in underground mined-out areas, which is considered to be one of the key technological pathways for CCUS in the future. However, critical technical challenges must still be addressed for this process, including low-cost multiphase CO₂ storage in backfill plants, synergistic transportation of backfill slurries and CO₂, and in-situ injection processes of CO₂ in mined-out stopes to produce suitable carbon curing environments. The research content of this article can provide valuable insights for studies on the mineralization and storage of CO₂ using tailings.

A novel quaternary ammonium salt collector, LH-01, was employed for the reverse cationic flotation of a magnesium-depleted concentrate (P₂O₅ grade of 19.72wt%, SiO₂ content of 44.26wt%). We achieved an outstanding phosphate concentrate with a P₂O₅ grade of 35.16wt%, a SiO₂ content of 6.06wt%, and a P₂O₅ recovery of 75.88%. This process was accomplished through two sequential reverse cationic flotation processes designed for quartz removal. Importantly, the quartz removal by LH-01 reached 94.17%, far superior to that by dodecyltrimethylammonium chloride, achieving highly selective separation of quartz and apatite. To understand the adsorption mechanism and kinetics of the collector LH-01 on quartz and apatite surfaces, various techniques, such as quartz crystal microbalance with dissipation, atomic force microscopy, and X-ray photoelectron spectroscopy, were employed. Results revealed that the adsorption layer of LH-01 on the apatite surface was thin and rigid, with a significantly lower hydrophobic effect than that of the viscoelastic multiple adsorption layer formed by LH-01 on the quartz surface. This disparity was identified as the primary factor contributing to the selective flotation separation of apatite and quartz. Moreover, the adsorption of LH-01 on the quartz surface was the result of multiple forces, including electrostatic adsorption, multiple-hydrogen-bond adsorption, and intermolecular hydrophobic association.

The green transition’s push for electrification has substantially increased the demand for copper, making it a critical raw material. This extravagant demand has made it profitable to extract copper from low-grade sulfide ores, which contain less than 0.3wt% copper. However, processing such low-grade ores requires extensive amounts of chemicals, raising environmental concerns. Thus, several investigations have been conducted on non-traditional lixiviants for copper extraction. Surprisingly, few studies have comprehensively reviewed this area to provide a comprehensive understanding and highlight gaps. This review analyzes investigations that have worked on the leaching process of copper into solutions using environmentally friendly reagents, particularly organic acids and amino acids, and compare them to conventional inorganic acids and examines recent advancements in ecofriendly leaching agents, specifically their application in copper leaching. The primary objective is to highlight the significance of these green reagents in mobilizing copper from solid to solution phases. It was highlighted that factors, such as mineralogy, mechanical activation, impurities, particle size, temperature, and initial concentration of the leaching agent, influence the leaching efficiency of organic and amino acids from primary and secondary copper resources. These variables interact in more complex ways than those encountered with conventional leaching methods. Research in this area has shown promising results, both in terms of extraction efficiency and reduced environmental impact, making it an exciting and essential area for further exploration and development. This shift towards using nonconventional lixiviants represents a significant step forward in the quest for more sustainable and environmentally responsible mining practices and recycling processes.

Flyrock is a significant environmental and safety concern in mining and construction. It arises from various geological and blast design factors, posing risks to workers, machinery, and nearby structures. This study examined how these factors affect the rate and distance of flyrock projections caused by blasts. To address this issue, advanced machine learning (ML) models were used to predict flyrock distances in the Akoko Edo dolomite quarries. The models examined included bidirectional recurrent neural networks (BRNNs), support vector regression (SVR) with different kernels (SVR-S, SVR-RBF, SVR-L, SVR-P), long short-term memory (LSTM) networks, and random forest (RF) algorithms. A case study was conducted using 258 blasting data samples to develop these models. Key factors influencing flyrock were identified: blast hole burden distance, maximum instantaneous charge, and rock brittleness index. Using these factors, a flyrock possibility assessment chart was created to enhance the safety of small-scale mining operations. The model’s prediction accuracy was evaluated using correlation coefficients and four performance metrics. The LSTM model stood out, achieving the highest coefficient of correlation (R² = 0.99) for both training and testing datasets. This indicates that the LSTM model accurately predicts blast-induced flyrock distance. The study also revealed that the Gaussian-RBF kernel SVR has high prediction accuracy when compared to other SVR variants (SVR-S, SVR-L, and SVR-P). In conclusion, the study compared various ML models for flyrock reduction and found that the LSTM model was the most effective in estimating blast-induced flyrock distances.