Search Results (326)

Acid mine drainage (AMD) generation in sulfide waste rock deposits involves complex hydrogeochemical processes that require controlled experimental approaches to improve our understanding of them. In this study, a laboratory-scale waste rock dam reactor was operated for 31 weeks using representative materials from the Iberian Pyrite Belt. Continuous monitoring of physicochemical parameters and weekly chemical analyses generated a big dataset that was evaluated using graphical and statistical approaches. The reactor successfully reproduced the principal hydrogeochemical processes characteristic of AMD environments, including sulfide oxidation, contaminant transport and attenuation. Graphical and statistical analyses consistently validated the proposed conceptual hydrogeochemical model. Sulfate concentrations were identified as the main control on electrical conductivity, while alternating wet and dry periods governed pH fluctuations through precipitation–dissolution and redissolution processes. The progressive decrease in dissolved metals and sulfate along the reactor reflected precipitation processes comparable to those observed in natural AMD systems. The reactor reproduced, at a small scale, both the temporal evolution and the three hydrological phases described for natural waste rock dams, demonstrating its reliability as a reproducible experimental platform for hydrogeochemical modeling and the investigation of AMD generation under controlled conditions. An effective diagnosis of contamination processes in mine waters is essential for future remediation interventions. Full article

Determining the shear strength parameters of granular materials in high waste rock dump slopes is essential for reliable slope stability analysis. In this study, dump materials were sampled from six benches (elevations 2800–2950 m) of an open-pit mine dump slope, and in situ density tests, gradation analyses, and large-scale consolidated drained (CD) triaxial tests were performed. Two PFC2D slope models—one with uniform (spatially averaged) parameters and one with elevation-dependent (layered) parameters—were then established to quantify how spatial heterogeneity affects stability predictions. The results show pronounced vertical heterogeneity: density, porosity, gradation, and shear strength parameters vary systematically among benches, reflecting the combined effects of compaction history and particle segregation during dumping. All specimens exhibited strain hardening and continuous shear contraction, and specimens with a denser, better-graded structure showed higher strength and lower compressibility. The layered model yields a higher factor of safety and shallower, bench-scale slip surfaces, whereas the uniform model underestimates stability and misplaces the critical slip zones. These findings demonstrate that elevation-dependent parameter assignment better represents the heterogeneous failure mechanism of high dump slopes and should be preferred over uniform parameterization in stability analyses of similar waste rock dumps. Full article

To alleviate the shortage of high-quality natural aggregates and promote the sustainable utilization of mining waste rock, this study employed lead–zinc mine waste rock-derived aggregate to replace 50% of the coarse aggregate by mass in cement-stabilized crushed stone. A series of tests, including drying shrinkage, thermal shrinkage, freeze–thaw cycling, scouring, and sulfate attack, were conducted to investigate the cracking resistance and durability of the resulting mixtures. The effects of basalt fiber, low-alkali cement, and a sulfate-resistant agent were further evaluated. Although the waste rock aggregates exhibited relatively inferior particle morphology, they could be incorporated into cement-stabilized crushed stone through rational gradation design. Among the investigated fiber contents, the mixture containing 4‰ basalt fiber exhibited relatively favorable shrinkage, freeze–thaw, and scouring resistance. The sulfate-resistant agent reduced mass loss and strength degradation under the investigated sulfate wet–dry cycling conditions. In contrast, low-alkali cement showed limited effectiveness in improving shrinkage resistance and freeze–thaw durability. These results provide experimental evidence for the feasibility of using lead–zinc mine waste rock as a partial coarse aggregate replacement in road base materials under the investigated laboratory conditions. Full article

Waste rock wool (WRW) has attracted increasing attention as a supplementary cementitious material (SCM) because of its mineral composition and its potential for reducing industrial waste. Although thermal treatment is commonly applied during WRW recycling, the practical necessity of additional low-temperature thermal treatment after mechanical activation remains unclear. This study evaluated the feasibility of mechanically activated WRW as an SCM by comparing materials with and without subsequent thermal treatment at 250 °C. Cement paste containing 15 wt.% WRW was prepared, and the effects of thermal treatment were evaluated through X-ray fluorescence (XRF), scanning electron microscopy (SEM), compressive strength testing, and thermogravimetric analysis (TGA). The XRF and SEM results revealed only negligible differences in chemical composition and particle morphology between the thermally treated and non-thermally treated WRW. Although both WRW mixtures exhibited lower early-age compressive strengths than the Plain mixture, comparable or higher long-term strengths were achieved. The TGA results also showed only minor differences in calcium hydroxide content and degree of hydration between the two WRW mixtures. Overall, additional low-temperature thermal treatment provided limited practical benefits beyond mechanical activation alone. These findings demonstrate that mechanically activated WRW without subsequent thermal treatment is a feasible supplementary cementitious material, offering a simplified and more energy-efficient recycling strategy for cementitious applications. Full article

Ecological restoration of abandoned mountainous mines remains challenging because of complex geological conditions, severe substrate degradation, and long-term environmental impacts. Conventional restoration strategies primarily emphasize vegetation establishment and slope stabilization, while the potential contribution of carbon sequestration is often insufficiently considered. Enhanced Rock Weathering (ERW) has recently emerged as a promising negative-emission technology that accelerates the natural weathering of silicate minerals to remove atmospheric CO₂ while improving soil quality. This paper synthesizes current knowledge on ERW and proposes a conceptual framework for integrating this technology into the ecological restoration of abandoned mountainous mines. The framework comprises four complementary dimensions: (1) Physical Restoration, utilizing fragmented rock materials to improve slope stability and substrate structure; (2) Acid–Base Neutralization, exploiting alkaline silicate minerals to alleviate acid mine drainage (AMD) and regulate geochemical conditions; (3) Pedogenic Optimization, promoting soil formation, improving soil physicochemical properties, and facilitating CO₂ infiltration and mineral carbonation; and (4) Biological Synergy, enhancing plant–microbe–mineral interactions to accelerate weathering processes and support long-term ecosystem development. Drawing on existing evidence, we discuss how the use of on-site waste rock as reactive substrates may simultaneously reduce restoration-related carbon emissions, provide essential mineral nutrients (e.g., Ca, Mg, and K), and enhance carbon sequestration potential. Overall, this synthesis suggests that integrating ERW into abandoned mine restoration has the potential to simultaneously advance ecological rehabilitation and climate-change mitigation. The proposed framework provides a theoretical basis for future experimental validation, field-scale implementation, and the development of low-carbon strategies for sustainable mine restoration. Full article

This PRISMA-guided scoping review examines the use of waste materials in civil engineering as a sustainable approach to reducing environmental impacts, conserving natural resources, and supporting circular economy principles. The rapid growth of urbanization, industrialization, mining, and agricultural activities generates large amounts of waste materials, including fly ash, ground granulated blast-furnace slag, bauxite residue, mining tailings, waste rock, acid-mine drainage sludge, waste plastics, post-consumer vulcanized rubber, recycled construction materials, and agricultural ashes. The disposal of these materials often creates serious environmental and land-use problems, making their reuse increasingly important. In this context, civil engineering is one of the most promising sectors for large-scale waste valorization because of its high material demand and its ability to use different waste streams into practical applications such as concrete and cementitious systems, pavement and asphalt engineering, geotechnical works, and other infrastructure sectors. This review critically evaluates the global availability, material characteristics, engineering applications, environmental and economic benefits, recent advances, and key challenges related to major industrial, mining, agricultural, polymeric, and construction-derived wastes. Although significant progress has been made in this field, wider implementation is still limited by variations in material properties, technical and environmental challenges, economic constraints, and limited field validation of long-term performance. By bringing together current knowledge from different waste streams and civil engineering sectors, this review highlights important research gaps and future directions to support more sustainable, resilient, and resource-efficient infrastructure development. The effective use of waste materials in civil engineering can play an important role in reducing carbon emissions, improving resource efficiency, and supporting global sustainability. Full article

The disposal of waste rock wool insulation materials has become an increasing environmental concern, while their reuse in cementitious composites remains insufficiently explored, particularly under elevated-temperature conditions. Moreover, limited information is available regarding the influence of fiber pretreatment on the residual mechanical performance of cementitious mortars after fire exposure. Therefore, this study investigates the effect of untreated rock wool fibers (URWFs) and hydrothermally treated rock wool fibers (TRWFs) on the mechanical and thermal performance of cementitious mortar. The waste fibers were hydrothermally treated by immersing 40 g of fibers in 1 L of water, stirring for 10 min, followed by filtration and oven drying at 105 °C for 24 h. Mortar specimens incorporating eight fiber dosages (2.5%, 5.0%, 7.5%, 10.0%, 12.5%, 15.0%, 17.5%, and 20.0% by weight of cement) were tested for compressive strength after 28 days of curing and after exposure to elevated temperatures of 400, 500, and 600 °C for 2 h, followed by natural air cooling. The results demonstrated that hydrothermal treatment significantly enhanced the residual compressive strength of fiber-reinforced mortars compared with untreated fibers, with the greatest improvement observed after exposure to high temperatures. The optimum fiber content (2.5–5.0%) provided the highest retained strength ratio, improving residual compressive strength by 25.1% compared with the corresponding URWF, while exhibiting a retained strength ratio of 54.8%, slightly exceeding the control mixture 54.5%. TRWF mortars also exhibited lower water absorption of up to 18% reduction, and lower densities of up to 60% reduction compared to URWF mortars, indicating improved matrix densification, fiber–matrix bonding, and thermal stability. These findings demonstrate that hydrothermal treatment is an effective and sustainable approach for upgrading waste rock wool fibers into value-added reinforcement for lightweight, low-permeability cementitious mortars with improved fire resistance. The study is limited to compressive strength evaluation, and future work should investigate tensile and flexural behavior, ductility, energy absorption, crack propagation, and long-term durability. Full article

Phosphate rock is a finite resource whose extraction in sedimentary deposits generates substantial volumes of waste rock. This study develops a panel-scale 3D geological modeling workflow for operational material accounting in a multilayer sedimentary phosphate deposit. Phosphate layers were modeled using a hanging wall–footwall approach and evaluated against independent well data. Bone Phosphate of Lime (BPL) grades were estimated from borehole-layer composite assay values using nearest neighbor, inverse distance weighting, and ordinary kriging. Domain-wise external validation showed that ordinary kriging provided the most consistent agreement with withheld observations in most mineable layers. Each mineable layer was treated as an independent estimation domain, with one composite BPL value retained per drillhole and per mineable layer. The validated block models were regularized to the mine plan and aggregated into operational strips, enabling strip-scale material accounting and mineability filtering under operation-specific technical criteria. To limit disclosure of confidential operational quantities, panel-scale resource, recoverable resource, and residual ore results are presented in relative rather than absolute terms. The results show that most modeled phosphate-bearing material satisfies the applied criteria and is classified as recoverable, whereas residual phosphate-bearing material excluded by the operational criteria remains concentrated in a limited subset of layers. The terms ‘resource,’ ‘recoverable resource,’ and ‘residual ore’ are used throughout in an operational material-accounting sense only and are not intended in the sense of any international mineral reporting code. Strip-based stripping ratio maps further reveal spatial variability in waste-to-ore and waste-to-grade relationships. The resulting workflow provides a quantitative spatial basis for future scenario-based assessment of waste management and selective dumping alternatives in sedimentary phosphate mining. Full article

This work develops a sustainable, low-viscosity grout material by incorporating industrial byproducts (rice husk ash, RIA; and fly ash, FLA) to address key challenges in rock stabilization: clogging susceptibility, high cost, poor environmental performance, and unbalanced engineering properties. Through single-factor experiments and an entropy-weighted Taguchi–grey relational analysis, the optimal mix ratio was determined to be 10% RIA, 10% FLA, and 0.45% polycarboxylate superplasticizer (POS), and a liquid-to-solid ratio of 1.05. Improved workability: The viscosity of the slurry significantly decreases, allowing its injection into rock fissures as small as micrometers. The slurry setting time and strength meet the requirements for the emergency repair of engineering rock masses. Cost efficiency: Utilizing waste materials reduces production costs by 17.9% per ton. Environmental benefits: CO₂ emissions decrease by 36.3% (150.62 g/kg vs. 237 g/kg for conventional grout), whereas leaching tests confirm that heavy metal concentrations (As < 0.1 ppm, Pb < 0.5 ppm) comply with environmental standards. Microstructural analysis reveals that RIA enhances density through pore-filling effects and pozzolanic activity. This study provides a practical, eco-friendly solution for rapid rock stabilization, aligns with circular economy principles, and supports sustainable infrastructure development. Full article

Urban mining is gaining importance as demand for critical metals continues to rise. Waste light-emitting diode (LED) lamps are a valuable secondary source of gallium, rare earth elements, precious metals, and base metals, yet accurately quantifying these metals remains challenging. In this work, various LED waste streams from a lamp recycler were subjected to critical metal characterization. The strengths and weaknesses of established metal assay techniques were evaluated to advance the determination of gallium, rare earth elements (Ho, Lu, Tb, Y, Er, Nd, Ce), and precious metals (Au, Ag, Pt, Pd) in LED waste. Metal assays, including alkaline fusion, four-acid digestion, aqua regia, a fire assay, and energy-dispersive X-ray fluorescence, were compared, and precision was assessed using a newly created LED lamp reference material and OREAS465. A metal-analysis-driven approach was developed to quantify the reduction in mining through recycling LED lamps using the rock-to-metal ratio metric. The economic value of LED waste streams, together with their recyclability and grindability, was assessed. The results indicate that LED strips can contain up to 147,484 g/t Cu, 452 g/t Ga, 367 g/t Lu, 89 g/t Tb, and 95 g/t of precious metals. Recycling one tonne of waste LEDs can offset mining 75.5 tonnes of rock and primary ore. The estimated economic value of mixed LED waste was USD 3351 per tonne, increasing to USD 4089 per tonne after physical separation. The results demonstrate the importance of robust analytical methods for accurate metal accounting and provide a stronger foundation for assessing the recycling potential of LED waste. Full article

Traditionally, waste rock generated in underground mines is transported to the surface and stored in waste rock piles. This practice requires substantial energy consumption and incurs additional operational costs. In Canada, an alternative approach involves directly dumping waste rock into stopes being filled with paste backfill. This method eliminates the need to transport waste rock to the surface and avoid the crushing of large rock blocks into smaller particles, as well as the use of specialized equipment for mechanically mixing the two materials. Consequently, both energy consumption and greenhouse gas emissions are reduced. Furthermore, binder consumption decreases because a portion of the cemented paste backfill is replaced by uncemented waste rock. Despite these advantages, no practical tool is currently available to assist backfill engineers in determining the appropriate amount of waste rock to be dumped. As a result, excessive quantities of waste rock may be added to the paste backfill, leading to inadequate mixing between the two materials. When exposed during the excavation of an adjacent stope, the resulting fill mass may become unstable and fail, causing undesirable consequences. To address this issue, a series of laboratory experiments were conducted to evaluate the effect of several factors, including the solids content and thickness of the paste backfill, the dumping height, the maximum particle size of the waste rock, and the stope dimensions, on the maximum allowed mass of waste rock. Based on the experimental results, an empirical equation was developed to estimate the maximum allowed waste rock mass that can be dumped without causing non-mixing between waste rock and paste backfill. The predictive capability of the proposed equation was successfully validated using additional independent experimental data. Full article

Soil contamination by heavy metals (HMs) [or potential toxic elements (PTEs)] poses serious risks to ecosystems and human health. Metals persist in the environment and can reach groundwater and freshwater as part of the food-chain. In soils, anthropogenic inputs dominate over geogenic sources. Metal mobility is strongly controlled by factors such as pH, mineralogy, and erosion processes that transport metal-bearing clay fractions. Wind and water can transport soil, mainly clay particles that can usually bind contaminants such as HMs. Using waste material is a tool suggested from the circular economy, so waste becomes a valuable resource. This study evaluates the immobilization efficiency of several heavy metals (Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn) using phosphate amendments—synthetic hydroxyapatite, phosphatic rock from Florida and Morocco—applied to a brownfield site. Heavy metal immobilization followed a two-step mechanism: first rapid surface complexation and secondly partial dissolution of hydroxyapatite and ion exchange with Ca, leading to the precipitation of metal-substituted hydroxyapatite phases. Synthetic hydroxyapatite generally shows the best efficiency, whereas phosphatic rocks were less effective but still provided a measurable immobilization. From a circular economy perspective, however, phosphatic rocks remain attractive due to their lower cost, availability, and waste-valorization potential. Full article

Oil recovery from carbonate reservoirs is one of the critical challenges in the oil industry due to the strongly oil-wet nature, natural fractures, and the heterogeneity of carbonate rocks. Subsequently, waterflooding can only displace oil from large fractures, leaving the majority of oil trapped in the rock matrix. This work suggests that nanofluid flooding, as a predesigned flooding method, is an alternative to conventional waterflooding. Various concentrations of silica nanofluid at different nanoparticle concentrations were formulated and systematically investigated for their characteristics, stability at reservoir conditions, and their influence on wettability and oil recovery. Silica nanoparticles were sustainably synthesized from waste materials to ensure the feasibility and environmental friendliness of the process. Results indicated that the synthesized silica has an amorphous crystalline nature characterized by nano-sized particles. Additionally, treating silica nanoparticles with a silane group significantly enhances the stability of nanofluids in a high-salinity environment. Most interestingly, by comparing the amount of oil recovered, the results revealed that implementing nanofluid flooding as a secondary oil recovery, rather than waterflooding, can produce around 12% more oil, in addition to eliminating a whole waterflooding step. This is the first study to alter the traditional flooding scenario and directly conduct nanofluid flooding as secondary oil recovery, without being preceded by waterflooding, using sustainably synthesized nanoparticles. Considering the water crisis in the Middle East, this approach can save substantial amounts of water, which improves the sustainable development of communities. Full article

This study investigates the effect of waste cement dust (CD) and rock wool (RW) inorganic fiber on the tribological performance of brake friction composite materials. Five formulations were fabricated by varying CD from 65 to 45 wt.% and RW from 5 to 25 wt.% and evaluated for tribological properties on a Chase friction testing machine in accordance with IS 2742 test procedures. The results show that composites containing higher CD and lower RW exhibited higher coefficients of friction, lower friction variability, and improved fade resistance. In contrast, composites containing higher RW and lower CD showed improved recovery characteristics and substantially enhanced wear resistance. The performance coefficient of friction decreased from about 0.521 to 0.442 as the formulation shifted from CD-rich to RW-rich compositions, while the variability coefficient increased from about 0.364 to 0.516. The highest wear was recorded for the composite containing 65 wt.% CD and 5 wt.% RW inorganic fiber, whereas the lowest friction fluctuations were obtained for the composite containing 55 wt.% CD and 15 wt.% RW inorganic fiber. Finally, a simple ranking process-based decision-making technique was employed to evaluate the overall performance of all the composites, suggesting 55 wt.% CD as the optimal content. These findings confirm the potential of waste CD as a viable functional constituent in brake friction composites when combined with RW inorganic fiber in an optimized manner. Full article

Using solid wastes to fabricate sustainable backfill materials for mining engineering is crucial for environmental sustainability worldwide. In this study, the use of coal gangue aggregates as a sustainable alternative to natural aggregates in geopolymer gel backfill materials was explored, which contributes to green mining development. Through uniaxial compression tests, the effects of fine gangue content, mass concentration, and the binder content of geopolymer backfill materials on the compressive behavior of coal gangue geopolymer gel backfill–rock combinations (CGBRC) were systematically evaluated. Digital Image Correlation (DIC) and acoustic emission (AE) techniques were employed to reveal the strain field evolution and damage progression of CGBRC. Results show that as the content of fine coal gangue increases, the compressive strength first increases and then decreases. Compared with the compressive strength at a 20% content, the compressive strength at a 40% content increased by 33.2%, while the elastic modulus increased by 11.2%. Meanwhile, with the increase in mass concentration and binder content, the compressive strength and elastic modulus of coal gangue geopolymer filling materials show an increasing trend, reaching peak values at 86% mass concentration and 32% binder content, respectively. The strain concentration zones mainly form near the backfill interface, with propagation paths governed by backfill strength. Damage evolution undergoes three stages including rapid accumulation during compaction, gradual development in the elastic-plastic stage, and abrupt acceleration at failure. The interfacial debonding behavior is primarily influenced by the strength difference between the backfill and surrounding rock. Specimen failure is dominated by brittle shear fracture, categorized into three modes based on crack paths relative to the backfill, which include penetrating backfill failure, axisymmetric interface failure, and centrally symmetric interface failure. These findings offer theoretical and technical support for coal gangue resource utilization and green mining practices, advancing sustainable solid waste management. Full article