This study addresses the challenges of excessive fluidity and poor bonding performance in ultraretarded solidification mine tailings waste-based shotcrete. The research investigates the fundamental mechanical properties of this material by optimizing the proportions of mineral powder (A), soil-rock waste (B), and water content (C). Comprehensive analysis was conducted through mechanical property testing, scanning electron microscopy (SEM), and X-ray diffraction (XRD) to elucidate the hydration mechanisms. The results demonstrate that a mineral powder content of 20 % (A1B2C3 to A1B1C1) yields optimal performance, with compressive, splitting tensile, and flexural strengths reaching 138.5 %, 163 %, and 154 % of baseline values, respectively. Maximum compressive strengths of 16.12 MPa, 24.18 MPa, and 32.08 MPa were achieved under specific mix conditions (C1A1B1). Additionally, increasing the content of A and C was found to extend the setting time of the cementitious material. The optimal mix ratio, comprising 20 % A, 25 % B, and 4 % C, exhibited enhanced hydration degree and superior macroscopic performance. Field construction tests confirmed that the material's viscosity, fluidity, and rapid-setting properties meet practical engineering requirements.

Approximately 3.44 billion tons of copper mine tailings (MT) were produced globally in 2018 with an increase of 45% from 2010. Significant efforts are being made to manage these tailings through storage facilities, recycling, and reuse in different industries. Currently, a large portion of tailings are managed through the tailing storage facilities (TSF) where these tailings undergo hydro-thermal-mechanical stresses with seasonal cycles which are not comprehensively understood. This study presents an investigative study to evaluate the performance of control and cement-stabilized copper MT under the influence of seasonal cycles, freeze-thaw (F-T) and wet-dry (W-D) conditions, representing the seasonal variability in the cold and arid regions. The control and cement-stabilized MT samples were subjected to a maximum of 12 F-T and 12 W-D cycles and corresponding micro-and-macro behavior was investigated through scanning electron microscope (SEM), volumetric strain (epsilon v), wet density (r), moisture content loss, and unconfined compressive strength (UCS) tests. The results indicated the vulnerability of Copper MT to 67% and 75% strength loss reaching residual states with 12 F-T and 8 W-D cycles, respectively. Whereas the stabilized MT retained 39%-55% and 16%-34% strength with F-T and W-D cycles, demonstrating increased durability. This research highlights the impact of seasonal cycles and corresponding strength-deformation characteristics of control and stabilized Copper MT in cold and arid regions. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/

Numerical simulation of the stress-strain behavior of materials under various loading conditions requires an appropriate constitutive model, with the yield surface being one of its key components. Extensive studies have been conducted to identify the yield surface of soil materials (sand and clay) through laboratory methods. However, the identification of the yield surface of waste materials has received less attention to date. Waste materials are artificial soil-like substances produced during the crushing and concentration processes in mineral processing plants. In this paper, a laboratory program was carried out using an advanced triaxial stress-path and stress-control apparatus on reconstructed saturated samples from the Sungun mine, located in the northwest of Iran. These samples were reconstituted using the wet tamping method. Through analysis and interpretation of the results, the yield surfaces of these lightly over-consolidated materials, with both isotropic and anisotropic initial consolidation conditions, were determined. The dependency or non-dependency of the obtained yield surfaces was evaluated, and the effect of consolidation stress and the angle of the applied stress path on the variation trends of the secant shear modulus and secant bulk modulus-indicating structural anisotropy of the waste materials-were assessed. Finally, the structural anisotropy of the samples was examined using SEM images and statistical processing of particle orientation and a mathematical model for the obtained yield surfaces was proposed.

The waste generated during metal mining activities contains mixtures of heavy metals (HM) that are not biodegradable and can accumulate in the surrounding biota, increasing risk to human and environmental health. Plant species with the capacity to grow and develop on mine tailings can be used as a model system in phytoremediation studies. Dodonaea viscosa (L.) Jacq. is a shrub with wide geographical distribution and the ability to establish itself in mine tailings. The Sierra de Huautla Biosphere Reserve in Mexico contains a metallurgic district where mining activities have generated 780 million kg of waste with large concentrations of toxic heavy metals, mainly cadmium and lead. The present study evaluated the phytoremediation potential of D. viscosa in in situ conditions on soils contaminated with HMs (exposed) and reference sites (non-exposed) for one year. Also, the effects of cadmium (Cd) and lead (Pb) exposure in D. viscosa were analyzed via DNA damage (comet assay) morphological and physiological characters in exposed vs non-exposed individuals. The concentration of Cd and Pb was measured through atomic absorption spectrophotometry in the roots and leaves of plants. In total, 120 D. viscosa individuals were established, 60 growing in exposed and 60 in non-exposed soils. Exposed individuals of D. viscosa hyperaccumulated Cd and Pb in roots and leaves. At the end of the experiment, eight out of twelve characters under evaluation decreased significantly in HM-exposed plants in relation to individuals growing in non-exposed soils, except for stomatal index, stomatal coverage, and fresh leaf biomass. The micro-morphological and physiological traits of D. viscosa were not influenced by Cd and Pb bioaccumulation. In contrast, the bioaccumulation of Cd and Pb significantly influenced the macro-morphological characters and genetic damage; this last biomarker was 3.2 times higher in plants growing in exposed sites. The bioconcentration factor (BCF) of Cd and Pb in root and leaf tissue increased significantly over time. The mean BCF in root and leaf tissue was higher for Pb (877.58 and 798.77) than for Cd (50.86 and 23.02). After 12 months of exposure, D. viscosa individuals growing on mine tailing substrate showed that the total HM phytoextraction capacity was 7.56 kg center dot ha-1 for Pb and 0.307 kg center dot ha-1 for Cd. D. viscosa shows potential for phytoremediation of soils contaminated with Cd and Pb, given its capacity for establishing and developing naturally in contaminated soils with HM. Along with its bioaccumulation, biomass production, abundance, and high levels of bioconcentration factors, but without affecting plant development and not registering associated herbivores, it may incorporate HM into the trophic chain.

Gold mine tailings (GMTs) pose significant environmental challenges, and while alkali-activated materials (AAMs) have been widely used as sustainable alternatives to Portland cement for stabilizing geotechnical materials, further research is needed to optimize their composition and performance, particularly by incorporating traditional industrial waste residues to develop composite alkali-activated materials (CAAMs) with improved mechanical properties and reduced environmental impact. Different CAAMs admixtures (i.e., 0%, 3%, 5%, and 8%) and gold mine tailings were prepared, and the samples were solidified under saturated water and no air. In order to investigate the mechanical characteristics of CAAMs-stabilized GMTs, laboratory direct shear tests were carried out on samples after curing them for 3, 7, 14, and 28 days, respectively. The test results showed that with the extension of curing time, the brittleness of the samples increased, and the stress-displacement curves for all the cured specimens changed from plateau type to peak type. Both curing time and CAAMs content are conducive to improving the shear strength of CAAMs-stabilized GMTs samples, but the increase rate decreased as the vertical confining stress increased. Furthermore, the influence of CAAMs content on shear strength increment was larger than that of curing periods. The exponential growth model could well describe the change of shear strength with the curing periods under different vertical stresses. The paper can provide theoretical support for the application of CAAMs to enhance the stability of tailings dams.

Waste generation has been a source of environmental concern in case of inadequate management. However, the potential for resource recovery from waste has been highlighted, and circular economy strategies have been greatly promoted to achieve sustainability goals. Municipal solid waste incineration bottom ash (IBA) and mine tailings represent two relevant waste streams under study for geotechnical applications. The present work aims at investigating the physical, mechanical, chemical, and ecotoxicological characteristics of two mixtures of 90 % bottom ash and 10 % of two different mine tailings (one of iron and another of tungsten, tin, and copper) to evaluate their safe utilization. The results indicated that mixtures of IBA and mine tailings have good compressibility, permeability, and shear strength properties, comparable to granular soils. Additionally, adding 10 % mine tailings in the mixtures had minimal effect on the mechanical behaviour of IBA alone. No substantial concentration of potentially toxic metals or relevant ecotoxic effects were found in any of the analysed materials and their eluates. These results suggest that mixing IBA with mine tailings for geotechnical use, e.g., in embankments or road base/subbase may be a safe option. This represents a promising alternative for valorising both waste streams while promoting sustainable and circular solutions.

The increasing demand for mineral resources has generated mine tailings with heavy metals (HM) that negatively impact human and ecosystem health. Therefore, it is necessary to implement strategies that promote the immobilization or elimination of HM, like phytoremediation. However, the toxic effect of metals may affect plant establishment, growth, and fitness, reducing phytoremediation efficiency. Therefore, adding organic amendments to mine tailings, such as biochar, can favor the establishment of plants, reducing the bioavailability of HM and its subsequent incorporation into the food chain. Here, we evaluated HM bioaccumulation, biomass, morphological characters, chlorophyll content, and genotoxic damage in the herbaceous Crotalaria pumila to assess its potential for phytostabilization of HM in mine tailings. The study was carried out for 100 days on plants developed under greenhouse conditions under two treatments (tailing substrate and 75% tailing/25% coconut fiber biochar substrate); every 25 days, 12 plants were selected per treatment. C. pumila registered the following bioaccumulation patterns: Pb > Zn > Cu > Cd in root and in leaf tissues. Furthermore, the results showed that individuals that grew on mine tailing substrate bioaccumulated many times more metals (Zn: 2.1, Cu: 1.8, Cd: 5.0, Pb: 3.0) and showed higher genetic damage levels (1.5 times higher) compared to individuals grown on mine tailing substrate with biochar. In contrast, individuals grown on mine tailing substrate with biochar documented higher chlorophyll a and b content (1.1 times more, for both), as well as higher biomass (1.5 times more). Therefore, adding coconut fiber biochar to mine tailing has a positive effect on the establishment and development of C. pumila individuals with the potential to phytoextract and phytostabilize HM from polluted soils. Our results suggest that the binomial hyperaccumulator plant in combination with this particular biochar is an excellent system to phytostabilize soils contaminated with HM.

This paper presents a study on the stabilization of hazardous tin mine tailings (TMT) using a metakaolin-based geopolymer binder for their potential reuse as geomaterials in geotechnical works. The extensive laboratory testing evaluated the mechanical properties, such as unconfined compressive strength, and the durability properties, including mass loss during freezing-thawing and wetting-drying cycles. Environmental assessment included the analysis of leached heavy metal concentration using Toxicity Characteristic Leaching Procedure (TCLP). Additionally, Scanning Electron Microscopy (SEM) was conducted to investigate the microstructure of the stabilized TMT. Satisfactory results show that improvements in mechanical and durability properties depend on variations in metakaolin content, NaOH molarity, and compaction density. The novel porosity/binder index (eta/Biv) has proven to be effective in predicting the behavior of mixtures. Additionally, it demonstrated that freezing-thawing cycles have a more adverse impact on the durability of the examined mixtures. Laboratory results for mechanical strength, durability, and immobilization of hazardous heavy metals demonstrate the potential performance of TMTs for safe reuse in geotechnical works, specifically as a geomaterial for subbase and base layers of pavement exposure to severe environment and climate of the Andean highlands.

In this study, native ureolytic bacteria were isolated from copper tailings soils to perform microbial-induced carbonate precipitation (MICP) tests and evaluate their potential for biocement formation and their contribution to reduce the dispersion of particulate matter into the environment from tailings containing potentially toxic elements. It was possible to isolate a total of 46 bacteria; among them only three showed ureolytic activity: Priestia megaterium T130-1, Paenibacillus sp. T130-13 and Staphylococcus sp. T130-14. Biocement cores were made by mixing tailings with the isolated bacteria in presence of urea, resulting similar to those obtained with Sporosarcina pasteurii and Bacillus subtilis used as positive control. Indeed, XRD analysis conducted on biocement showed the presence of microcline (B. subtilis 17%; P. megaterium 11. 9%), clinochlore (S. pasteurii, 6.9%) and magnesiumhornblende (Paenibacillus sp. 17.8%; P. megaterium 14.6%); all these compounds were not initially present in the tailings soils. Moreover the presence of calcite (control 0.828%; Paenibacillus sp. 5.4%) and hematite (control 0.989%; B. subtilis 6.4%) was also significant unlike the untreated control. The development of biofilms containing abundant amount of Ca, C, and O on microscopic soil particles was evidenced by means of FE-SEM-EDX and XRD. Wind tunnel tests were carried out to investigate the resistance of biocement samples, accounted for a mass loss five holds lower than the control, i.e., the rate of wind erosion in the control corresponded to 82 g/m2h while for the biocement treated with Paenibacillus sp. it corresponded to only 16.371 g/m2h. Finally, in compression tests, the biocement samples prepared with P. megaterium (28.578 psi) and Paenibacillus sp. (28.404 psi) showed values similar to those obtained with S. pasteurii (27.102 psi), but significantly higher if compared to the control (15.427 psi), thus improving the compression resistance capacity of the samples by 85.2% and 84.1% with respect to the control. According to the results obtained, the biocement samples generated with the native strains showed improvements in the mechanical properties of the soil supporting them as potential candidates in applications for the stabilization of mining liabilities in open environments using bioaugmentation strategies with native strains isolated from the same mine tailing.

With continuous mine exploitation, regional ecosystems have been damaged, resulting in a decline in the carbon sink capacity of mining areas. There is a global shortage of effective soil ecological restoration techniques for mining areas, especially for vanadium (V) and titanium (Ti) magnetite tailings, and the impact of phytoremediation techniques on the soil carbon cycle remains unclear. Therefore, this study aimed to explore the effects of long-term Pongamia pinnata remediation on soil organic carbon transformation of V -Ti magnetite tailing to reveal the bacterial community driving mechanism. In this study, it was found that four soil active organic carbon components (ROC, POC, DOC, and MBC) and three carbon transformation related enzymes (S -CL, S -SC, and S-PPO) in vanadium titanium magnetite tailings significantly (P < 0.05) increased with P. pinnata remediation. The abundance of carbon transformation functional genes such as carbon degradation, carbon fixation, and methane oxidation were also significantly (P < 0.05) enriched. The network nodes, links, and modularity of the microbial community, carbon components, and carbon transformation genes were enhanced, indicating stronger connections among the soil microbes, carbon components, and carbon transformation functional genes. Structural equation model (SEM) analysis revealed that the bacterial communities indirectly affected the soil organic carbon fraction and enzyme activity to regulate the soil total organic carbon after P. pinnata remediation. The soil active organic carbon fraction and free light fraction carbon also directly regulated the soil carbon and nitrogen ratio by directly affecting the soil total organic carbon content. These results provide a theoretical reference for the use of phytoremediation to drive soil carbon transformation for carbon sequestration enhancement through the remediation of degraded ecosystems in mining areas.