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.

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.

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.

This article explores the utilization potential of three distinct mine tailings (MT) viz.; red mud (RM), iron tailings (FeT), and zinc tailings (ZT) as geopolymer binders to stabilize the soil for road subgrade application. The strength and durability of soil treated with various MT -based geopolymers are examined through a succession of unconfined compressive strength (UCS), California bearing ratio (CBR) and alternate wetting -drying tests respectively. Furthermore, permeability tests are also conducted to examine the hydraulic response of soil amended with MT -based geopolymers. Finally, leaching study is performed to examine the geo-environmental implications of various geopolymer specimens. The experimental results reveal that the UCS of untreated soil is increased from 0.39 MPa to 5.24 MPa, 5.13 MPa and 3.78 MPa with the use of RM, FeT, and ZT-based geopolymers respectively. The study further shows a 26 -fold, 19 -fold, and 15.8 -fold increase in the soaked CBR values of soil when it is stabilized with RM, FeT, and ZT-based geopolymers respectively. In contrast to untreated soil, soil stabilized with MT -based geopolymers exhibit excellent weathering resistance to alternate wettingdrying cycles showcasing its exceptional durability under challenging environmental conditions. Irrespective of the MT content, curing environment, and the alkali activator concentrations, soil treated with MT -based geopolymers is found to satisfy both the strength (i.e. UCS = 0.75-1.5 MPa and CBR > 5%) as well as durability criteria (i.e. % loss in mass < 10%) specified by Indian Road Congress for subgrade soil. Moreover, the leaching study shows the concentrations of toxic elements (Zn, Cd, Fe, Pb, Ni etc.) to be within the permissible limits specified by USEPA thereby dispelling any environmental concerns associated with the use of MT -based geopolymers.