Search Results (842)

To reveal the varieties and color genesis of emerald-green tourmaline crystals from Tanzania, a systematic study was conducted using conventional gemological tests, X-ray diffraction, Fourier-transform infrared spectroscopy, polarized ultraviolet–visible spectroscopy (UV–vis), X-ray photoelectron spectroscopy (XPS), low-temperature photoluminescence (PL) spectroscopy, and electron probe microanalysis (EPMA). The results indicate that the tourmaline is dravite. Its UV–vis absorption spectrum shows strong broad absorption bands at approximately 436 and 600 nm, with a pronounced transmission at 520 nm, which directly accounts for its emerald green color. Obvious polarized absorption was observed along and perpendicular to the c-axis. XPS and PL results confirm that chromium is present in the samples in the form of Cr³⁺. EPMA compositional analysis indicated a low Cr₂O₃ content of 0.804 wt.%; combined with crystal structural properties and spectral responses, these results suggest that Cr³⁺ preferentially occupies the Y site in the crystal structure and that d–d electronic transitions represent the underlying mechanism of its color formation. This study comprehensively illustrated the mineralogical and spectral properties of Cr-bearing dravite, providing fundamental data for further research on its genesis and gemological application. Full article

Phosphorus (P) accumulation in intensively agricultural soils represents a growing environmental concern due to its potential mobilization and contribution to eutrophication. This study investigated the mechanisms controlling P availability and redistribution in agricultural soils from the Elota–Piaxtla Irrigation District (northwestern Mexico) during cropping and non-cropping periods. Soil P fractions were determined using the Hedley sequential extraction method and related to soil physicochemical properties through a correlation analysis. During the cropping period, P in Fe/Al hydroxides dominated (45–67% of total P), indicating strong adsorption and fixation in fine-textured soils. In contrast, the non-cropping period showed a significant increase in organic P in humic substances (up to 55%), suggesting enhanced biological transformation and residue recycling. Labile P fractions decreased from 60% to 44% of total P between sampling periods, while moderately labile fractions increased, indicating seasonal redistribution of P pools. Statistical analysis revealed that P dynamics were primarily governed by mineralogical characteristics and organic matter transformations rather than by individual soil properties. The accumulation of moderately labile and organic P fractions during fallow periods highlights a latent environmental risk, particularly in irrigated systems prone to runoff and erosion. These findings emphasize the need for fraction-based nutrient management strategies that integrate both agronomic efficiency and environmental protection in intensive agricultural soil. Full article

The eruption of the Tajogaite volcano (Cumbre Vieja) on La Palma Island (Spain) generated a significant amount of volcanic ash (VA). This study evaluates the valorisation of VA, considered a “natural waste,” as a partial substitute for Portland cement or in combination with lime. By using this waste, this study aims to promote its valorisation and contribute to the circular economy on the island and in nearby areas. After the ash undergoes a drying and grinding process, various tests are conducted to assess its physical, mineralogical, and chemical properties. These tests include particle size distribution, powder X-ray diffraction, and field emission electron microscopy, among others. Methods such as the Frattini test, the R³ method, thermogravimetric analysis and calorimetry are used to measure pozzolanic reactivity. The values obtained using the Frattini and R³ methods indicate that VA has low-moderate reactivity. The mechanical properties of mortar specimens based on Portland cement blends and hydrated lime are analysed, where a portion of these binders is replaced with VA. It has been observed that the compressive strengths of the specimens with 15%, 25%, and 35% of cement replaced by VA in cement blends show favourable results after 90 and 365 days of curing. Mortars with a 25% replacement reach compressive strengths exceeding 40 MPa versus 57 MPa of the control after 28 days of curing, which is adequate for many applications in civil engineering. The study highlights the importance of exploring eco-friendly materials and believes that the addition of VA can be a valuable and effective enhancement for mortars. This research marks a significant endeavour in exploring the volcanic ash produced by the Tajogaite Volcano eruption, particularly in relation to its mechanical behaviour in lime-pozzolan mortars. Full article

Tight gas is a critical unconventional energy resource, yet the geological characteristics and accumulation processes of tight gas in China’s Songliao Basin remain poorly documented. This study aims to investigate the tight gas system in the Songliao Basin as a representative continental basin, with key objectives including evaluating source rock and reservoir properties via mineralogical and geochemical analyses, characterizing lithologies and pore types, determining the gas charging mechanism in tight media, and identifying the main controlling factors for accumulation. Geochemical results indicate that the Shahezi Formation contains medium to good mudstones and excellent coals. Reservoirs consist of tight sandstones and conglomerates deposited in fan delta and braided river delta systems, with pore spaces dominated by dissolution pores and microfractures, resulting in ultra-low porosity and permeability. Conventional buoyancy-driven migration is ineffective; instead, gas charging is driven by hydrocarbon generation expansion force, creating overpressure that expels pore water and forces gas into reservoirs through fault-sand conduits. Accumulation is controlled by continuous gas supply from thick, highly mature source rocks, dissolution-enhanced and fracture-dominated reservoir space, and sufficient source–reservoir pressure difference. This study elucidates tight gas characteristics and accumulation mechanisms in continental basins, providing data applicable to both continental and marine settings. Full article

Natural lateral particle segregation commonly occurs during the hydraulic deposition of slurry and thickened tailings in surface tailings storage facilities (TSFs), producing spatial heterogeneity in physical, hydrogeotechnical, and mineralogical properties, as well as in the water table. In sulfide-rich tailings, such heterogeneity complicates the design of reclamation cover systems, which are themselves affected by it. This study investigates the impact of physical and rheological properties of hard-rock mine tailings slurries on their segregation under hydrodynamic conditions. It proposes a multiparametric equation for the segregation index (SI) based on Buckingham’s π theorem. For this purpose, six flume experiments were conducted using tailings with initial solid mass concentrations of 63%, 66%, and 69% at slopes of 0.5% and 1%. Results revealed strong exponential correlations (R² > 0.95) between SI and tailings’ physical properties (solid concentration, bulk density) as well as rheological parameters (Herschel–Bulkley yield stress and flow index, Cross infinite dynamic viscosity). The SI equation was developed using MATLAB R2025b nonlinear least-squares optimization with a trust-region reflective algorithm. Using an SI threshold of 0.05 to define non-segregating behavior, the proposed model can predict segregation tendencies as a function of tailings properties and slope conditions. Further laboratory and field investigations are needed to validate and generalize the criterion. Full article

An effective process flow-sheet for valuable component recovery from fine fractions has been developed based on Satpayev deposit ilmenite ore mineralogical and technological property analysis. Ore mineral composition was studied using X-ray diffraction and electron probe microanalysis. Experimental studies were conducted using a Falcon L40 centrifugal concentrator and a WHIMS 3X4L high-gradient magnetic separator. High efficiency of fine fraction centrifugal beneficiation was established: titanium relative recovery efficiency from fine fractions exceeded 86% for −0.03 + 0.02 mm fraction and exceeded 57% for the −0.02 + 0.01 mm fraction. Larger particle size classes bigger than 0.03 and 0.04 mm titanium recovery exceeded 94%. Concentrate cleaning using high-gradient magnetic separation resulted in a product with a TiO₂ grade of 47% and titanium recovery of up to 90% from the operation. The process flow-sheet designed resulted in ilmenite concentrate production with a TiO₂ grade of 53.40% and a recovery rate of 92.30%, as well as zircon-bearing and quartz products suitable for further processing. Full article

The stability of tailings dams is governed predominantly by the physical properties and geotechnical behavior of their primary construction material—tailings. Consequently, a systematic understanding of these characteristics is of great significance for the rational design and long-term stable operation of tailings dams. This review focuses on the physical properties and geotechnical behavior observed in different types of tailings. In terms of physical properties, the particle size distribution exhibits a pronounced hydraulic classification characteristic within the impoundment, consisting predominantly of silt-sized particles and displaying an overall trend toward finer gradation. The mineralogical and chemical composition is dominated by quartz, hematite, and silicates. However, significant spatial variability exists both between different tailings types and across distinct zones within the same tailings pond. Regarding geotechnical behavior, the permeability of tailings is governed by a fines content threshold: below this threshold, permeability decreases with increasing fines content, while beyond it, the permeability stabilizes. When studying consolidation and compression behavior using slurry specimens, the compression curves exhibit nonlinear characteristics, primarily described by the modified Gibson theory. The shear behavior of tailings is significantly influenced by confining pressure, drainage conditions, anisotropy and stress paths. The presence of transitional behavior leads to the critical state line determined based on a single sampling method erroneously assessing the dilation/cosntraction characteristics of in situ tailings, thereby affecting the assessment of liquefaction risk. Future research should focus on the seepage, consolidation and shear properties of clayey fine-grained tailings and unsaturated tailings, and aim to elucidate the key controlling factors of transitional behavior to enhance the reliability of tailings dam stability assessments. Full article

This systematic research was conducted as the first comprehensive scientific analysis of ancient lime plaster samples from Anuradhapura, a World Heritage Site in Sri Lanka. Five ancient heritage sites from 1st to 10th Century AD, covering two stupa domes: Abhayagiri (AP01) and Jethavana (AP02), Monk residence building near Ruwanweliseya Stupa (AP03), Deeghapashan Rock Shelter Building of Abhayagiri Monastery Complex (AP04), and Vessagiriya Rock Shelter wall lime Plaster (AP05) were examined by employing Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray fluorescence (XRF), thermogravimetric analysis (TGA), optical microscopy (OM), scanning electron microscopy (SEM) and gas chromatography-mass spectrometry (GC-MS). The current work investigated the composition, mineralogical and microstructural properties, binding media, and organic additives. Our findings indicate that calcareous lime from seashells and river sand are the main raw materials, with ratios of 1:2.7, 1:2.0, 1:2.4, 1:4.4, and 1:3.7 for the AP01, AP02, AP03, AP04, and AP05 samples, respectively. Data also suggest that plant-based materials, mainly wood apple wax, along with nanoscale fibrous materials, were used as the main additives to enhance the properties of lime plasters. This study provides insights into the raw materials, their mixing ratios, and the techniques employed in the lime plastering of ancient Anuradhapura City, and serves as a scientific reference for the conservation and restoration of ancient buildings resilient to climate change. Full article

This study examines the complex interplay between dynamic response and mineralogical microstructures across various geological formations, particularly differentiating between mineralized and metamorphic rocks. Utilizing a comprehensive vibration-based approach, in conjunction with petrographic analysis and ultrasonic wave propagation, the study clarifies the significant impact of microstructural features, such as disseminated sulfides and foliated planes, on the complex’s global dynamic behavior. This study investigates six representative rock samples from mineralized and metamorphic geological zones using integrated petrographic analysis, ultrasonic wave velocity testing, density and physical property measurements, and free-vibration dynamic analysis. The results show that the composition and mechanical properties differ significantly. Mineralized rocks contain a high proportion of sulfide minerals, reaching approximately 75% in some samples, and exhibit significantly higher densities, with the APZ sample reaching 3950 kg/m³. In contrast, metamorphic rocks have an average density of 2700 kg/m³. This difference in composition leads to different dynamic responses. Mineralized zones have dynamic elastic moduli that are much higher than those of metamorphic rocks, with Young’s Modulus reaching up to 134.17 GPa and shear moduli ranging from 49.78 GPa to 56.14 GPa, which is about 50% higher than metamorphic rocks (28.9 GPa to 30.5 GPa). However, macro-mechanical deflection tests show that highly foliated metamorphic rocks (like PFT) exhibit the largest deflection of 0.52 mm, while demineralized rocks (like CP) exhibit the smallest deflection of 0.26 mm. Dynamic vibration analysis shows that microstructural “flaws” significantly affect energy dissipation. For example, the Transitional Phase Zone (TPZ) in mineralized rocks has the highest damping ratio (1.67%) and the lowest natural frequency (270 Hz) in its suite. This is different from the more rigid Advanced Pyritization Zone (APZ), which has a damping ratio of 1.1% and a frequency of 395 Hz. These new correlations provide a more accurate basis for the non-destructive assessment of structural stability in mineralized settings, highlighting that local micro-stiffness does not necessarily indicate macroscopic dynamic rigidity. Full article

Oily sludge is one of the most challenging solid wastes generated during petroleum production and wastewater treatment, posing long-term environmental risks and demanding effective resource-recovery strategies. This study systematically investigated the physicochemical characteristics, compositional differences, and oil–solid interaction mechanisms of oily sludge (OS) from three representative Chinese oilfields, Panjin, Daqing and Xinjiang, through integrated analyses of elemental composition, oil composition, X-ray diffractometer (XRD), Fourier-transform infrared (FT-IR), Gas chromatograph (GC), and Confocal laser scanning microscope (CLSM). The results revealed pronounced regional variations in oxidation degree, hydrocarbon composition, and mineralogy that critically influenced oil occurrence and removal behavior. The Panjin OS sample (PJ-OS) exhibited a high oxidation degree, enriched resins and asphaltenes, and compact film-like oil–solid structures, resulting in the lowest oil mobility and recovery potential. The Daqing OS (DQ-OS) was dominated by light saturates and showed the weakest oil–solid bonding, while the Xinjiang OS (XJ-OS) displayed moderate oxidation and intermediate properties. A novel room-temperature high-speed stirring cleaning method was applied to evaluate oil removal performance under ambient conditions. The residual oil contents after treatment were 4.43% (PJ-OS), 1.65% (DQ-OS), and 1.22% (XJ-OS), corresponding to removal efficiencies of 80.86%, 86.74%, and 90.33%, respectively. The cleaning efficiency was strongly governed by the sludge composition and oxidation state: higher O/C ratios and enrichment of polar heavy fractions enhanced oil–solid adhesion and hindered oil detachment, whereas higher saturate contents and lower oxidation degrees facilitated rapid oil separation. Overall, the findings demonstrate that the treatability of oily sludge is controlled by its intrinsic physicochemical properties. The proposed high-speed stirring technique provides a promising, energy-efficient, and environmentally sustainable approach for oily sludge remediation and resource recovery, offering valuable insights for optimizing treatment parameters and scaling up green petroleum waste management technologies. Full article

The cement industry plays a critical role in infrastructure development, but is a major contributor to CO₂ emissions, driving the search for low-carbon binders that can also valorize industrial wastes. This review examines the engineering performance of red mud (RM)-based binder systems, highlighting the relationships between mixture design, processing, fresh-state behavior, mechanical properties, durability, and microstructural evolution. Special attention is given to how RM’s particle characteristics and mineralogical/chemical composition influence reactivity during geopolymerization, thereby affecting strength development and pore structure. Across the literature, moderate RM incorporation (commonly ≤15–20%) generally preserves workable fresh properties and adequate compressive strength, whereas higher RM contents (≥30%) often increase total porosity and pore connectivity, resulting in reductions in strength and durability. To mitigate these drawbacks, effective strategies such as thermal activation of RM and synergistic blending with supplementary cementitious materials like ground granulated blast-furnace slag and phosphogypsum are consistently reported to enhance reaction extent, densify the gel matrix, refine pore structure, and improve long-term durability. Overall, RM-based cementitious binders demonstrate considerable potential for both structural and non-structural applications; however, further research is needed on long-term performance under realistic exposure conditions, scale-up and quality control to address RM variability, and performance-based mix design guidelines to support reliable field implementation. Full article

Acidic mine water generated during underground CO₂ sequestration and sulfide oxidation can alter the pore-fracture structure of coal, and threaten the stability of abandoned mine spaces. However, the mechanism through which acidic environments influence the deterioration of coal remains insufficiently understood. In this study, uniaxial compression experiments were conducted on coal samples treated with solutions with different pH values, and acoustic emission (AE) monitoring technology was used to characterize fracture activity and damage evolution during loading. A quantitative model linking acidity to the mechanical behavior of coal was established by integrating fractal theory with damage mechanics. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were further employed to reveal the microstructural and mineralogical mechanisms of coal deterioration. The results show that acidic environments significantly degrade the mechanical properties of coal samples. With decreasing pH, peak stress and elastic modulus of the selected representative sample progressively decrease, and the failure mode becomes increasingly fragmented and dispersed. At pH = 1, the degradation of peak stress and elastic modulus reaches 73.01% and 49.38%, respectively. Increasing acidity also enhances AE activity during loading and increases the correlation dimension, indicating greater crack complexity and instability. On this basis, the proposed quantitative model accurately describes the transformation process of coal samples from microscopic damage to macroscopic mechanical degradation induced by acidity. SEM and XRD results further show that stronger acidity promotes pore enlargement, crack interconnection, mineral dissolution, secondary mineral formation, and weakening of cementation, revealing the physical essence of the multi-scale damage and degradation of coal samples. The findings can provide a theoretical basis for assessing coal stability in acidic environments and ensuring the safe storage of CO₂ in abandoned mines. Full article

This study is a systematical investigation of the fundamental geological conditions for shale gas in the Wufeng–Longmaxi formations in western Hubei, China, using drilling core data, with Well Xiandi-2 serving as the key well for core observation and experimental testing, integrated with outcrop profiles and regional provincial-level shale gas block data. The analysis encompasses petrology, organic geochemistry, mineral composition, physical properties, pore types, and gas content. Through a comprehensive comparison with established shale gas production fields in the Sichuan Basin, the shale gas resource potential of the study area is evaluated, and favorable zones for shale gas exploration are delineated. The results indicate that the study area contains a continuous organic-rich shale interval with a 18.84 m net thickness, 2.3% average total organic carbon, 65–89% brittle mineral content, 2.36% average porosity, and thermal maturity within the gas window. Systematic comparison with the Jiaoshiba and Changning fields confirms comparable geological attributes, including organic matter abundance, reservoir porosity, and brittle mineralogy. Given this comparability, areas with burial depths shallower than 1500 m on the northwestern margin of the Xuefeng Uplift are interpreted to retain moderate shale gas resource potential. Three favorable zones are delineated as priority targets: the synclines on both sides of the Longtan normal fault and the Lianghekou Syncline. These findings provide practical exploration value: the identified favorable zones offer immediate drilling targets, the analytical workflow is transferable to other structurally complex blocks on the basin margin, and the potential of shallow-buried sequences expands exploration beyond the core Sichuan Basin into previously overlooked transitional zones. Full article

This study investigates Cambrian and Sinian carbonate outcrops in the Tarim Basin using 19 stratigraphically diverse rock samples. Through integrated X-ray diffraction mineralogical analysis, triaxial compression testing, and Brazilian splitting experiments, we systematically characterized rock mechanical properties and their correlations with microscopic mineral constituents. Key findings demonstrate remarkably distinct mechanical properties across formations: vuggy dolomites from the Xiaqiulitage formation exhibit the lowest compressive strength (minimum 200.0 MPa) and tensile strength (3.85 MPa), while the Yuertusi formation’s Y5 layer dolomites achieve exceptional tensile strength (21.69 MPa). Mineral composition fundamentally controls rock strength: dolomite or quartz concentrations exceeding 90% significantly enhance strength, whereas calcareous minerals (calcite, fluorapatite) degrade mechanical integrity. Most specimens display pronounced brittle failure characteristics; uniquely, basal dolostones of the Awatage formation exhibit distinctive plastic deformation. This research elucidates the synergistic effects of tectonic history, mineral assemblages, and microtextural attributes on rock mechanical behavior, providing critical theoretical underpinnings for deep carbonate reservoir development in overpressured basins. Full article

In alignment with global carbon neutrality goals, this study investigates the regulatory role of magnesium oxide (MgO) content on the macro–micro properties of carbonation-cured collapsible loess from the Hohhot region. While MgO carbonation is established for soil stabilization, the quantitative influence of MgO dosage on the specific phase evolution pathways and mechanical enhancement within the unique macro-porous fabric of aeolian loess remains poorly understood. Addressing this, we systematically examined loess specimens amended with varying MgO contents (10% to 30%) over carbonation periods up to 24 h. Unconfined compressive strength (UCS) tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to correlate mechanical performance with mineralogical and microstructural evolution. Results indicate that MgO content acts as a primary regulator of the carbonation process. Higher MgO dosages substantially increased CO₂ uptake, resulting in a significant relative mass gain—up to more than a two-fold difference between the highest and lowest content samples—and culminated in a compressive strength of 10.48 MPa for the 30% MgO specimen. Microstructural analysis revealed a distinct temporal evolution interpreted to be governed by MgO-mediated supersaturation levels. Initially, Mg(OH)₂ agglomerates provided early strength, which was subsequently enhanced by the formation of a three-dimensional framework of nesquehonite, followed by the development of an interlocking skeletal network of hydromagnesite crystals. These carbonate phases enhanced loess strength via a combination of pore infilling, particle cementation, and the construction of a reinforcing micro-skeleton. This work elucidates the link between MgO content and the microstructural evolution of carbonated loess, providing new insights for the synergistic integration of soil stabilization and carbon sequestration in loess regions. The findings offer a valuable reference for engineering applications in collapsible soil environments under the context of sustainable development. Full article