Search Results (983)

In this study, to solidify the silt in an expressway, a stabilizing agent composed of industrial wastes, such as ordinary Portland cement (OPC), calcium based alkaline activator (CAA), silicate solid waste material (SISWM) and sulfate solid waste material (SUSWM) was developed. Orthogonal experiments and comparative experiments were carried out to analyze the strength and water stability of the stabilized silt, and get the optimal proportion of each component in the stabilizing agent. A series of laboratory tests, including unconfined compressive strength (UCS), water stability (WS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analyses, were conducted on solidified silt samples treated with the stabilizing agent at optimal mixing ratios of OPC, CAA, SISWM, and SUSWM to elucidate the evolution of mineral composition and microstructure. Full article

The structural memory effect is normally considered one of the most important properties of LDHs. However, certain anions can have adverse effects on it. In this study, three types of CLDHs (Mg2Al1-CLDH, Mg2Al0.5Fe0.5-CLDH, Mg2Fe1-CLDH) were obtained and used to observe their regeneration behaviors in the presence of sulfate, silicate, and phosphate, respectively, at initial pH values of 10 and 13. The samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA-DTG), scanning electron microscope (SEM), and N2 adsorption–desorption isotherm (BET). The results suggested that silicate and phosphate have significant impacts on the regeneration of CLDHs, while sulfate does not. Specifically, phosphate and silicate reacted with MgO to generate magnesium silicate and magnesium phosphate dibasic, which were covered on the surface of particles and hindered the hydroxylation of metal oxides. However, a higher pH can suppress the formation of new substances and promote the regeneration of LDHs. Moreover, the CLDHs with high specific surface area had a stronger anti-interference performance regarding the effects of phosphate and silicate. Full article

Due to the complex mineral composition, low clay content, and strong heterogeneity of the mixed sedimentary shale in the Xinjiang Salt Lake Basin, the wettability characteristics of the reservoir and their influencing factors are not yet clear, which restricts the evaluation of oil-bearing properties and the identification of sweet spots. This paper analyzed mixed sedimentary shale samples from the Lucaogou Formation of the Jimsar Sag and the Fengcheng Formation of the Mahu Sag. Methods such as petrographic thin sections, X-ray diffraction, organic matter content analysis, and argon ion polishing scanning electron microscopy were used to examine the lithological and mineralogical characteristics, geochemical characteristics, and pore space characteristics of the mixed sedimentary shale reservoir. Alternating imbibition and nuclear magnetic resonance were employed to quantitatively characterize the wettability of the reservoir and to discuss the effects of compositional factors, lamina types, and pore structure on wettability. Research findings indicate that the total porosity, measured by the alternate imbibition method, reached 72% of the core porosity volume, confirming the effectiveness of alternate imbibition in filling open pores. The Lucaogou Formation exhibits moderate to strong oil-wet wettability, with oil-wet pores predominating and well-developed storage spaces; the Fengcheng Formation has a wide range of wettability, with a higher proportion of mixed-wet pores, strong heterogeneity, and weaker oil-wet properties compared to the Lucaogou Formation. TOC content has a two-segment relationship with wettability, where oil-wet properties increase with TOC content at low TOC levels, while at high TOC levels, the influence of minerals such as carbonates dominates; carbonate content shows an “L” type response to wettability, enhancing oil-wet properties at low levels (<20%), but reducing it due to the continuous weakening effect of minerals when excessive. Lamina types in the Fengcheng Formation significantly affect wettability differentiation, with carbonate-shale laminae dominating oil pores, siliceous laminae contributing to water pores, and carbonate–feldspathic laminae forming mixed pores; the Lucaogou Formation lacks significant laminae, and wettability is controlled by the synergistic effects of minerals, organic matter, and pore structure. Increased porosity strengthens oil-wet properties, with micropores promoting oil adsorption through their high specific surface area, while macropores dominate in terms of storage capacity. Wettability is the result of the synergistic effects of multiple factors, including TOC, minerals, lamina types, and pore structure. Based on the characteristic that oil-wet pores account for up to 74% in shale reservoirs (mixed-wet 12%, water-wet 14%), a wettability-targeted regulation strategy is implemented during actual shale development. Surfactants are used to modify oil-wet pores, while the natural state of water-wet and mixed-wet pores is maintained to avoid interference and preserve spontaneous imbibition advantages. The soaking period is thus compressed from 30 days to 3–5 days, thereby enhancing matrix displacement efficiency. Full article

The formation of acidic goaf water in abandoned coal mines poses significant environmental threats, especially in karst regions where the risk of groundwater contamination is heightened. This study investigates the geochemical processes responsible for the generation of acidic water through batch and column leaching experiments using coal mine surrounding rocks (CMSR) from Yangquan, China. The coal-bearing strata, primarily composed of sandstone, mudstone, shale, and limestone, contain high concentrations of pyrite (up to 12.26 wt%), which oxidizes to produce sulfuric acid, leading to a drastic reduction in pH (approximately 2.5) and the mobilization of toxic elements. The CMSR samples exhibit elevated levels of arsenic (11.0 mg/kg to 18.1 mg/kg), lead (69.5 mg/kg to 113.5 mg/kg), and cadmium (0.6 mg/kg to 2.6 mg/kg), all of which exceed natural crustal averages and present significant contamination risks. The fluorine content varies widely (106.1 mg/kg to 1885 mg/kg), with the highest concentrations found in sandstone. Sequential extraction analyses indicate that over 80% of fluorine is bound in residual phases, which limits its immediate release but poses long-term leaching hazards. The leaching experiments reveal a three-stage release mechanism: first, the initial oxidation of sulfides rapidly lowers the pH (to between 2.35 and 2.80), dissolving heavy metals and fluorides; second, slower weathering of aluminosilicates and adsorption by iron and aluminum hydroxides reduce the concentrations of dissolved elements; and third, concentrations stabilize as adsorption and slow silicate weathering regulate the long-term release of contaminants. The resulting acidic goaf water contains extremely high levels of metals (with aluminum at 191.4 mg/L and iron at 412.0 mg/L), which severely threaten groundwater, particularly in karst areas where rapid cross-layer contamination can occur. These findings provide crucial insights into the processes that drive the acidity of goaf water and the release of contaminants, which can aid in the development of effective mitigation strategies for abandoned mines. Targeted management is essential to safeguard water resources and ecological health in regions affected by mining activities. Full article

Understanding mineral–fluid interactions in shale under supercritical CO₂ (scCO₂) conditions is relevant for assessing long-term geochemical containment. This study characterizes mineralogical transformations and elemental redistribution in five Caney Shale samples serving as proxies for reservoir (R1, R2, R3) and caprock (D1, D2) facies, subjected to 30-day static exposure to pure scCO₂ at 60 °C and 17.23 MPa (2500 psi), with no brine or impurities introduced. SEM-EDS analyses were conducted before and after exposure, with mineral phases classified into silicates, carbonates, sulfides, and organic matter. Initial compositions were dominated by quartz (38–47 wt.%), illite (16–23 wt.%), carbonates (12–18 wt.%), and organic matter (8–11 wt.%). Post-exposure, carbonate loss ranged from 15 to 40% in reservoir samples and up to 20% in caprock samples. Illite and K-feldspar showed depletion of Fe²⁺, Mg²⁺, and K⁺ at grain edges and cleavages, while pyrite underwent oxidation with Fe redistribution. Organic matter exhibited scCO₂-induced surface alteration and apparent sorption effects, most pronounced in R2 and R3. Elemental mapping revealed Ca²⁺, Mg²⁺, Fe²⁺, and Si⁴⁺ mobilization near reactive interfaces, though no secondary mineral precipitates formed. Reservoir samples developed localized porosity, whereas caprock samples retained more structural clay integrity. The results advance understanding of mineral reactivity and elemental fluxes in shale-based CO₂ sequestration. Full article

In the context of efforts to reduce greenhouse gas emissions in the building sector, the reintegration of traditional earthen construction into modern architectural and renovation practices offers a sustainable alternative. To address the mechanical and water-resistance limitations of adobe bricks, the use of agricultural waste—such as rice husk—is increasingly being explored. This experimental study evaluates the effects of rice husk addition on the mechanical, hygrothermal, and acoustic properties of adobe bricks. Two soil types—one siliceous and one calcareous—were combined with 1, 2, and 3 wt% rice husk to produce bio-based earthen bricks. The influence of rice husk was found to depend strongly on the soils’ mineralogical and granulometric characteristics. The most significant improvements were in hygrothermal performance: at 3 wt%, thermal conductivity was reduced by up to 35% for calcareous soil and 20% for siliceous soil, indicating enhanced insulation. Specific heat capacity also increased with husk content, suggesting better thermal inertia. The moisture buffering capacity, already high in raw soils, is further improved due to increased surface porosity. Mechanically, rice husk incorporation had mixed effects: a modest increase in compressive strength was observed in siliceous soil at 1 wt%, while calcareous soil showed slight improvement at 3 wt%. Acoustic performance remained low across all samples, with minimal gains attributed to limited macro-porosity. These findings highlight the importance of soil composition in optimizing rice husk dosage and suggest promising potential for rice husk-stabilized adobe bricks, especially in thermally demanding environments. Full article

Glass curators often question how their treatments affect the long-term stability of historical glass. While damp cotton swabs are commonly used to remove surface salts and dust, the use of water remains controversial, particularly for heavily altered glass, due to concerns about worsening hydration. This study investigates the effect of water rinsing on an unstable soda-lime glass altered for six months (monoliths) and fifteen months (powders) at 35 °C and 85% relative humidity. Samples were then rinsed with Milli-Q water at 20 °C or 50 °C, and the monolithic glass was subsequently subjected to an additional 15 months of alteration under the same conditions. The glass surface was characterized by optical and scanning electron microscopy (SEM) as well as Raman spectroscopy to identify the nature of the salts. The evolution of the hydrated layer was assessed using transmission FTIR, Raman and solid-state NMR spectroscopies, ToF-SIMS, and thermogravimetric analysis (TGA). The results show that rinsing effectively removes surface salts—primarily sodium carbonate—and induces structural changes in the hydrated layer, promoting silicate network polymerization. Upon resuming alteration, rinsed monolithic samples exhibit no further degradation after the additional 15 months of alteration. These findings offer promising insights for conservation practices and may help curators refining their treatment strategies for altered glass. Full article

The quantitative pressure (P)–temperature (T) conditions of low-grade metamorphic rocks, such as pumpellyite–actinolite and greenschist facies, are largely unknown mainly owing to the difficulty in applying thermodynamic methods despite their importance in understanding the protolith and metamorphism within subducting oceanic crusts. In this study, Raman spectroscopy was applied to constrain the peak metamorphic conditions independent of thermodynamic methods for the lowest grade part (chlorite zone) of the Sanbagawa schists in the Shibukawa area, central Japan, where research on metamorphic conditions is limited. The metamorphic peak temperature of the pelitic schists estimated by Raman carbonaceous material geothermometry was 307 ± 27 °C to 395 ± 16 °C, which increased towards the northern fault (Median Tectonic Line). Raman geobarometry using the quartz-inclusions-in-spessartine system on a siliceous schist sample estimated a peak metamorphic pressure of 0.78–0.94 GPa at 360–390 °C. These results suggest that the rocks in the Shibukawa area were subducted to a depth equivalent to that of the garnet zone in central Shikoku and were then exhumed without experiencing further heating. The combination of Raman carbonaceous material geothermometry and Raman geobarometry (Raman geothermobarometry) can be effectively applied to estimate the metamorphic conditions of low-grade metamorphic rocks independent of thermodynamic methods. Full article

Recycled concrete fines (RCFs) have the potential to serve as a supplementary cementitious material (SCM) after carbonation. Traditionally, carbonation of RCFs results in calcium carbonate primarily in the form of calcite, which significantly limits the development of RCFs as an SCM. In this research, a wet grinding carbonation (WGC) technique was introduced to enhance the reactivity of RCFs. The research indicates that RCFs after WGC exhibit a finer particle size and a larger specific surface area. The carbonation products include calcite with smaller grains, metastable calcium carbonate, and nanoscale silica gel and Al-Si gel. When RCF-WGC is used as an SCM in ordinary Portland cement (OPC), it significantly promotes the hydration of the cement paste, as evidenced by the advancement and increased intensity of the exothermic peaks of aluminates and silicates. RCF-WGC can significantly enhance the compressive strength of hydrated samples, particularly at early ages. Specifically, at a curing age of 1 day, the compressive strength of WGC5, WGC10, and WGC20 samples increased by 9.9%, 22.5%, and 7.7%, respectively, compared to the Ref sample (0% RCF-WGC). At a curing age of 3 days, the compressive strength of the WGC5, WGC10, and WGC20 samples showed even more significant improvements, increasing by 20.8%, 21.9%, and 11.8%, respectively. The performance enhancement of the WGC samples is attributed to the chemical reactions involving nanoscale silica gel, Al-Si gel, and calcium carbonate in the RCFs. When RCF-WGC is used as an SCM to replace 5%, 10%, and 20% of cement, it can reduce carbon emissions by 27.5 kg/t, 55 kg/t, and 110 kg/t, respectively. Large-scale application of RCFs as a high-value SCM can significantly reduce the life-cycle carbon emissions of the cement industry, contributing to the achievement of carbon peaking in China’s cement sector. Full article

The southeastern Hainan Island boasts abundant hydrothermal resources, most of which are exposed as thermal springs. Analyzing the hydrochemical characteristics, hydrochemical evolutionary mechanisms, and material transition of these resources is significant for their exploitation and utilization. This study investigated the Nanping geothermal field in southeastern Hainan Island, using five groups of geothermal water samples collected in 2022, as well as seven groups of geothermal water samples, one group of shallow groundwater samples, and one group of surface water samples taken in 2023. Specifically, this study examined water–rock interactions in the geothermal field using the Gibbs model, ion ratios, chloro-alkaline indices (CAIs), and the sodium adsorption ratio (SAR). Moreover, the mineral transfer process in groundwater was analyzed using inverse hydrogeochemical simulation. The results indicate that in the study area the geothermal water temperatures range from 64 °C to 80 °C, pH values from 8.32 to 8.64, and TDS concentrations from 431 mg/L to 623 mg/L. The primary hydrochemical types of geothermal water in the study area include Cl-Na and Cl·HCO₃-Na, suggesting low-temperature, slightly alkaline geothermal water. The hydrochemical components of geothermal water in the study area are primarily affected by water–rock interactions. Besides the dissolution of silicate minerals and halite, cation exchange reactions contribute greatly to the formation of Na⁺ and K⁺ in geothermal water. Geothermal water receives recharge from the atmospheric precipitation of the Diaoluo Shan area in the northwest of the study area, with the recharge elevation ranging from 967 to 1115 m. The inverse hydrogeochemical simulation results reveal that during the water–rock interactions, silicate minerals, clay minerals, gypsum, and halite dissolve, while quartz and carbonate minerals precipitate. Additionally, these processes are accompanied by cation exchange reactions dominated by the replacement of Na⁺ in surrounding rocks by Ca²⁺ in geothermal water. This study can provide a geological basis for the exploitation, utilization, and management of the Nanping geothermal field. Full article

Because the loess widely used in the channel water conservancy projects in the Loess Plateau has a loose structure, low mechanical strength, and is prone to collapse when immersed in water, its comprehensive properties, such as structural strength and water resistance, must be greatly improved. Based on our previous work on the modification of Aga soil in Tibet, China, this study added hydrophobic n-dodecyltrimethoxysilane (WD10) to water glass solution (the main components are potassium silicate (K₂SiO₃) and silicic acid (H₂SiO₃) gel, referred to as PS) to obtain a composite coating PS-WD10, which was sprayed on the surface of loess blocks to achieve a full consolidation effect. We not only systematically investigated the morphology, chemical composition, and consolidation mechanism of the composite coating but also conducted in-depth and detailed research on its application performance such as friction resistance (structural strength), hydrophobicity, resistance to pure water and salt water immersion, and resistance to freeze–thaw cycles. The results showed that the PS-WD10 composite coating had better consolidation performance for loess blocks than the single coating of PS solution and WD10. For the loess block samples coated with the composite coatings, after 50 friction cycles, the weight loss rate was less than 15 wt%, and the water contact angle was above 120°. The main reason is that the good permeability of the PS solution and the excellent hydrophobicity of WD10 produce a good synergistic effect. The loess blocks coated with this composite coating are expected to replace traditional functional materials for water conservancy projects, such as cement and lime, in silt dam water conservancy projects, and also have better environmental protection and sustainability. Full article

Ceramic oxide coatings were fabricated on 7075 aluminum alloy via micro-arc oxidation (MAO) in a silicate-phosphate electrolyte under voltages of 250 V, 300 V, and 350 V for 600 s. The effect of the applied voltage on the surface morphology, microstructure, phase composition, microhardness, roughness, coating thickness, and corrosion resistance was systematically studied. The coating obtained at 300 V demonstrated a dense structure with relatively low surface roughness (2.3 μm) and a thickness of approximately 70 μm. This sample also exhibited the most balanced performance, combining relatively high microhardness (~422 HV) and the lowest corrosion current density (6.1 × 10⁻⁷ A/cm²) in a 3.5 wt.% NaCl solution. X-ray diffraction patterns revealed the presence of both γ- and α-Al₂O₃ phases in all coated samples, with a relative increase in α-phase intensity observed at an intermediate voltage. The results demonstrate that the applied voltage plays a critical role in determining the coating structure and performance, offering insights into the surface treatment of high-strength aluminum alloys for engineering applications. Full article

Carbonaceous–siliceous–argillaceous rock-type uranium deposits, a major uranium resource in China, pose significant environmental risks due to heavy metal contamination. Geochemical investigations in the former Zoige uranium mine revealed elevated As, Cd, Cr, Cu, Ni, U, and Zn concentrations in soils and sediments, particularly at river confluences and downstream regions, attributed to leachate migration from ore bodies and tailings ponds. Surface samples exhibited high Cd bioavailability. The integrated BCR and mineral analysis reveals that Acid-soluble and reducible fractions of Ni, Cu, Zn, As, and Pb are governed by carbonate dissolution and Fe-Mn oxide dynamics via silicate weathering, while residual and oxidizable fractions show weak mineral-phase dependencies. Positive Matrix Factorization identified natural lithogenic, anthropogenic–natural composite, mining-related sources. Pollution assessments using geo-accumulation index and contamination factor demonstrated severe contamination disparities: soils showed extreme Cd pollution, moderate U, As, Zn contamination, and no Cr, Pb pollution (overall moderate risk); sediments exhibited extreme Cd pollution, moderate Ni, Zn, U levels, and negligible Cr, Pb impacts (overall extreme risk). USEPA health risk models indicated notable non-carcinogenic (higher in adults) and carcinogenic risks (higher in children) for both age groups. Ecological risk assessments categorized As, Cr, Cu, Ni, Pb, and Zn as low risk, contrasting with Cd (extremely high risk) and sediment-bound U (high risk). These findings underscore mining legacy as a critical environmental stressor and highlight the necessity for multi-source pollution mitigation strategies. Full article

Mineralogical variability exerts a profound influence on the flotation performance of Platinum Group Metal (PGM) ores, particularly those from the Platreef deposit, where complex associations and textures influence recovery, grade, and kinetics. This study integrates the Mode of Occurrence (MOC) and mineral associations into a modified Kelsall flotation kinetics model, optimized using a Particle Swarm Optimization (PSO) algorithm, to improve prediction accuracy. Batch flotation tests were conducted on eight samples from two lithologies—Pegmatoidal Feldspathic Pyroxenite (P-FPX) and Feldspathic Pyroxenite (FPX)—with mineralogical characterization performed using MLA, QEMSCAN, and XRD. PGMs in liberated (L) and sulfide-associated (SL) forms accounted for up to 90.6% (FPX1), exhibiting high fast-floating fractions (θ_f = 0.77–0.84) and fast flotation rate constants (K_f = 1.45–1.78 min⁻¹). In contrast, PGMs locked in silicates (G class) showed suppressed kinetics (K_f < 0.09 min⁻¹, K_s anomalies up to 8.67 min⁻¹) and were associated with lower recovery (P-FPX3 = 83.25%) and increased model error (P-FPX4 = 57.3). FPX lithologies achieved the highest cumulative recovery (FPX4 = 90.35%) and the best concentrate grades (FPX3 = 116.5 g/t at 1 min), while P-FPX1 had the highest gold content (10.45%) and peak recovery (94.37%). Grade-recovery profiles showed steep declines after 7 min, particularly in slow-floating types (e.g., P-FPX2, FPX2), with fast-floating lithologies stabilizing above 85% recovery at 20 min. The model yielded R² values above 0.97 across all samples. This validates the predictive power of MOC-integrated flotation kinetics for complex PGM ores and supports its application in geometallurgical plant design. Model limitations in capturing complex locked ore textures (SAG, G classes) highlight the need for reclassification based on floatability indices and further integration of machine learning methods. Full article

As a critical mineral, magnesite plays a vital role in industries such as steelmaking, construction, and advanced technologies due to its high thermal stability and chemical resistance. However, the beneficiation of low-grade magnesite ores (~38.36% MgO) remains challenging due to the presence of iron, silica, and calcium-bearing impurities. This study proposes an integrated beneficiation strategy combining medium-intensity magnetic separation and flotation techniques to upgrade a low-grade magnesite ore. After grinding to 75 µm (d₈₀), the sample was subjected to two-stage magnetic separation at 5000 Gauss to remove Fe-bearing minerals, reducing Fe₂O₃ below 0.5%. The non-magnetic fraction was then treated through a two-stage reverse flotation process using dodecylamine (350 g/t) and diesel oil (60 g/t) at pH 7 to reject silicate gangue. This was followed by a four-stage direct flotation using sodium oleate (250 g/t), sodium silicate (350 g/t), and SHMP (100 g/t) at pH 10 to selectively recover magnesite while suppressing Ca-bearing minerals. The optimized flowsheet achieved a final concentrate with MgO > 46.5%, SiO₂ ≈ 1.05%, Fe₂O₃ ≈ 0.44%, and CaO ≈ 0.73%, meeting the specifications for refractory-grade magnesite. These results highlight the effectiveness of a combined magnetic–flotation route in upgrading complex, low-grade magnesite deposits for commercial use. Full article