Search Results (148)

Calcium carbide slag is a highly alkaline solid waste generated during acetylene production, but its long-term accumulation causes land occupation and persistent environmental risks such as soil alkalinization and water pollution. To support circular economy and carbon emission reduction goals, in this study, we develop an integrated physical decontamination–mineralization process combining calcination, magnetic separation, sedimentation, and CO₂ mineralization. After calcination, magnetic separation, and 8 h of gravity sedimentation, the removal efficiency of Si reaches about 67% (residual Si content reduces to 0.43%), while those of Fe and Al are 75.4% and 74.2%, respectively. The purified calcium-rich slurry is then used for CO₂ mineralization. Under a solid-to-liquid ratio of 10% and a CO₂ flow rate of 0.4 L/min, CO₂ is fixed as carbonate solids, yielding calcite-type CaCO₃ with 97.88% ± 0.35% purity. This process is centered on physical separation and uses no acids, alkalis, or ammonium salts, avoiding secondary pollution while achieving waste valorization and permanent CO₂ sequestration. In this study, we provide a scalable, low-impact pathway for alkaline solid waste valorization and carbon emission reduction, contributing to sustainable consumption and production (SDG 12) and climate action (SDG 13). Full article

Analytical studies of archeological materials often face challenges, such as the merging of heterogeneous, multidimensional datasets from complementary analytical techniques, and incorporating site- and user-defined parameters. In this study, a data fusion methodology is applied that combines micro-X-ray fluorescence (micro-XRF) spectrometry and handheld Raman spectroscopy to investigate degradation layers and identify pollution sources on two monuments in an urban background: the Temple of Hephaestus and the Byzantine Church of Ag. Theodoroi, in Athens, Greece. A total of 12 samples were collected for laboratory measurements and 32 in situ measurements were conducted. Statistical and unsupervised machine learning tools, namely correlation analysis, Principal Component Analysis and k-means clustering, were applied to the merged datasets. Additionally, selected elements’ ratios were calculated to infer their sources. The black crusts were identified as heterogeneous mixtures of calcium sulfate dihydrate, calcite, and particulate pollutants, with their composition reflecting their preservation state. Vehicular emission indicators were dominant in both sites, while secondary domestic heating pollutant indicators were more prevalent at Ag. Theodoroi. Orientation had a minor role compared to pollutant sources in differentiating degradation patterns. The integrated comparison of the different outputs highlighted the interpretive potential of the approach, particularly in improving the readability of the multivariate structure and supporting the development of targeted conservation strategies for monuments in polluted urban contexts. Full article

The volcanic island of Fuerteventura (Canary Islands, Spain) offers the opportunity to investigate aqueous alteration in Mars-like environments. As on Mars, landscapes on Fuerteventura are typified by mafic volcanic landforms, minimal precipitation, strong winds, and minimal or absent vegetation. In this study, we perform reflectance spectral and geochemical analysis of near-surface basaltic materials from Fuerteventura’s Gairía caldera, as well as samples from a nearby arroyo. Tephra, outcrop rock, and soil-like material exhibit variations in color, spectral properties, mineralogy, and major oxides. Visible/near-infrared (VNIR) spectra of orange/light-brown materials have higher reflectance values and much stronger features attributed to phyllosilicates (including H₂O and Al-OH bands near 1.41–1.45, 1.91–1.92, 2.21, and 2.76 µm characteristic of montmorillonite in caldera and arroyo samples, plus shoulder features near 1.38 and 2.17 µm and a band at 2.70 µm indicative of kaolinite/halloysite in arroyo samples) compared to black/brown materials. Additionally, several of the highly altered samples contain spectral bands due to calcite at 2.33, 2.53, 3.36, 3.47, and 3.97 µm. Major oxide data reveal similar distinctions between lighter orange/tan (altered) versus darker (unaltered) samples. Lighter and orange-colored samples show elevated Al₂O₃ and depleted Fe₂O_3T, MgO, CaO, and Na₂O, as well as higher chemical index of alteration (CIA) values, overall characteristic of water-soluble cation release (and secondary clay formation) during incipient-to-intermediate chemical weathering of basalt. Gairía weathering trends inform phyllosilicate formation in arid volcanic settings broadly. Of particular interest is the chemical alteration of basalt to montmorillonite and kaolinite/halloysite taking place in warm but water-limited desert conditions, suggesting the potential for clay formation in analogous (warm but relatively dry) paleoenvironments on early Mars. Full article

In the semi-arid Batna Belezma region of northeastern Algeria, groundwater is a vital resource for agriculture and drinking water. However, the climate leads to intense evaporation, which affects its quality. This study aims to identify the key hydrogeochemical processes that control groundwater composition in the Merouana Basin and to evaluate the predictive performance of machine learning (ML) models. A total of 30 groundwater samples were analyzed using multivariate statistical techniques, including Principal Component Analysis (PCA), and were modeled using PHREEQC to assess mineral saturation states. Additionally, ML-based regression models, including K-Nearest Neighbors (KNN), Support Vector Machine (SVM), Random Forest (RF), and Extreme Gradient Boosting (XGB),were employed to predict groundwater chemistry. The results indicate that the dominant ion distribution follows the following trend: Ca²⁺ > Mg²⁺ > Na⁺ and HCO₃⁻ > SO₄²⁻ > Cl⁻. Alkaline earth metals (Ca²⁺ and Mg²⁺) constitute the major fraction of total dissolved cations, reflecting carbonate equilibrium and dolomite dissolution processes. In contrast, Na⁺ represents a smaller proportion of the cationic load; however, its hydro-agronomic significance is substantial due to its influence on sodium adsorption ratio (SAR) and soil permeability. The PHREEQC modeling showed that calcite and dolomite precipitation promote evaporite dissolution, while most samples remain undersaturated with respect to gypsum. The PCA results reveal high positive loadings of Mg²⁺, Cl⁻, SO₄²⁻, HCO₃⁻, and EC, suggesting that ion exchange and seawater mixing are the primary controlling processes, with carbonate weathering playing a secondary role. To enhance predictive assessment, several supervised machine learning models were tested. Among them, the Random Forest model achieved the highest predictive performance (R² = 0.96) with low RMSE and MAE values, confirming its robustness and reliability. The results indicate that silicate weathering and mineral dissolution are the primary mechanisms governing groundwater chemistry. The integration of multivariate statistics and machine learning provides a comprehensive understanding of groundwater evolution and offers a reliable predictive framework for sustainable water resource management in semi-arid environments. Geochemical model performance showed a high global accuracy (GPI = 0.91), confirming a strong agreement between observed and simulated chemical data. However, the HH value (0.81) indicates some discrepancies, particularly for specific ions or extreme conditions. Full article

Moderate thermal exposure can significantly influence the mechanical behavior of volcanic rocks by inducing microcrack development and altering crack network characteristics. However, quantifying such damage processes remains challenging when relying solely on conventional mechanical parameters. In this study, the evolution of crack network complexity in andesite and andesitic–basaltic rocks subjected to moderate thermal exposure (200 °C) is investigated using fractal analysis integrated with mechanical and mineralogical observations. Six core specimens were tested under uniaxial compression, including three natural specimens and three specimens thermally treated at 200 °C prior to loading. After failure, crack surfaces were digitized and fractal dimensions (D) were calculated using the box-counting method. Petrographic observations and X-ray powder diffraction (XRPD) analyses were conducted to characterize the mineralogical composition and microstructural features controlling crack development. The results indicate that thermal exposure primarily reduces rock stiffness rather than peak strength. While the uniaxial compressive strength (UCS) of two specimens remains nearly unchanged after heating, the elastic modulus (E) decreases in all thermally treated specimens. Mineralogical observations reveal a heterogeneous volcanic fabric dominated by plagioclase and pyroxene within a fine-grained groundmass, with secondary calcite phases occurring in veins and pocket fillings. Fractal analysis shows generally lower D values in thermally treated specimens, suggesting crack redistribution and coalescence rather than increased network complexity, consistent with the observed reduction in stiffness and a tendency toward more ductile deformation behavior. Full article

Abandoned mining areas provide valuable opportunities to investigate ore-forming processes, supergene mineral transformations, and the geochemical behaviour of metals. In this sense, the old Preguiça mine (Beja, Portugal), exploited for Fe–Zn–Pb, was studied providing new mineralogical and geochemical data aimed at improving the understanding of the secondary mineral assemblages of this deposit. A total of 70 samples collected from three accessible underground levels (first, second and third) and mine waste, complemented by 16 samples from a deeper level (fourth) previously collected, were analysed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and a portable X-ray fluorescence (pXRF) equipment. Mineralogical phases are dominated by a wide range of secondary oxides, carbonates, arsenates, vanadates, silicates, phosphates and sulphates, but remnants of primary sulphides were also found. The following minerals can be emphasised: goethite, hematite, calcite, dolomite, descloizite, willemite, mimetite, cerussite, smithsonite and fraipontite. The presence of massicot in the Preguiça mine, is described for the first time. Bulk geochemical analyses show high concentrations of Fe, Ca, Zn and Pb, consistent with the observed mineralogy. The presence of vanadium- and arsenic-bearing minerals highlights the occurrence of critical raw materials, supporting the importance of reassessing other abandoned mining areas in the context of sustainable resource management and strategic raw-material planning. Full article

The organization of safe industrial waste management is an integral part of the global sustainable development strategy. This study provides a preliminary assessment of the processing and recycling potential of strongly alkaline (pH 11–12) sediments accumulated in an abandoned sludge pond (Berezniki, Perm Krai, Russia), based on the initial characterization of their material composition. Sediment samples from the sludge pond were collected, layer-by-layer, over the entire depths of four sediment cores. The collected samples have the following characteristics: sediment particles are composed of up to 80% fine particles < 0.05 mm, with up to 20% fine particles < 0.002 mm. XRD data showed that the sediment consisted of calcite (67.7 wt.%), halite (11.5 wt.%), and other hydrogenic and terrigenous minerals. XRF data also found that the primary constituents in the sediment are CaO (up to 40%), Cl (up to 13%), and LOI (up to 35%). The results of the material composition study indicate a high degree of similarity between the accumulated sediments and solid waste from soda ash production, known as ammonia–soda residue (ASR). Based on experience with calcium-containing waste, this study recommends options for the secondary use of sludge, identifying two main possibilities: environmental protection and construction. We have developed an algorithm for the recycling and reuse of sludge that identifies risks, limitations, and recommended next steps. However, significant knowledge gaps regarding the environmental, toxicological, and the physical–mechanical properties of sludge prevent us from recommending a specific disposal option. The results of this review will serve as guidelines to help develop a roadmap for the disposal process. They will also inform decision-makers about sustainability issues related to industrial waste disposal. Full article

During the extraction of shale oil from the Longmaxi Formation in the Sichuan Basin, it is found that the core samples contain natural fractures cemented by various minerals. However, the core extraction process is complex and expensive. In order to further investigate how cracks propagate and initiate in samples containing cementing layers under compression conditions, this study developed an experimental method involving plug cutting and mineral cementation reconstruction for the preparation of representative semi-artificial core samples. Through comprehensive analysis using computed tomography (CT), stereomicroscopy, and mechanical testing, we have demonstrated a high degree of consistency between artificial cemented cracks and natural cemented cracks. Through triaxial compression and Brazilian splitting experiments on artificially cemented samples, we found that low and high confining pressures significantly affect crack morphology. By using Abaqus finite element simulation to add crack propagation modes during the compression process of cement layers, we showed that different mineral cements (quartz, clay, and calcite) have secondary effects on crack morphology on the basis of confining pressure. Full article

As the largest known ancient jade mining site, the Mazongshan Site is crucial for understanding the “West–to–East Jade Transportation” system in ancient China. However, its vast nephrite materials remain poorly characterized mineralogically and geochemically. This study employs a multi-technique approach, including polarized light microscopy, SEM-EDS, XRD, CRS, EPMA, and ICP-MS to analyze Mazongshan nephrite. The results identify tremolite as the principal mineral, with accessory minerals including diopside, apatite, serpentine, calcite, dolomite, graphite, hornblende, epidote, forsterite, and albite, as well as limonite occurring as a secondary mineral formed by oxidation. Its rare earth element patterns show significant negative Eu anomalies, low total REE concentrations, and low levels of Cr, Ni, and Co. These results confirm a metamorphic origin for the deposit. Most significantly, the high compositional affinity it exhibits with Hetian nephrite from Xinjiang, together with evidence of ancient mining, has led us to reconsider the prevalence of nephrite materials used during the Warring States to Han periods. Full article

Conventional synchronous grouting materials often exhibit low early strength, delayed setting, and insufficient utilization of excavated soil, hindering the green and efficient advancement of metro shield tunneling technology. To overcome these challenges, this study developed a high-performance grouting material by utilizing shield muck—primarily composed of quartz (71.47%) and calcite (15.3%)—as the main raw material, with sodium trimethylsilanolate (TMS-Na) introduced as a performance enhancer. Through orthogonal experiments and range analysis, the influences of cement content, slag content, and TMS-Na dosage on the workability and mechanical properties of synchronous grouting materials were systematically evaluated. Microstructural evolution was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric (TG) analysis, and mercury intrusion porosimetry (MIP) to elucidate the mechanism by which TMS-Na modifies the grout microstructure. The results demonstrate that incorporating 8% slag and 0.2% TMS-Na increases the utilization rate of shield muck to 60.8%. Compared with conventional grouts, the novel material exhibits approximately 97.4% and 93.3% enhancements in 3-day and 28-day compressive strength, respectively, alongside an impermeability grade reaching P10. The addition of slag improves the apparent density and early strength of the grout, although its contribution diminishes at later ages. TMS-Na effectively activates the hydration reactivity of slag, accelerates early hydration, reduces the setting time, and participates in a secondary hydration reaction with argillaceous siltstone present in the excavated soil, promoting the formation of additional calcium silicate hydrate (C-S-H). This process densifies the hardened grout matrix, refines the pore structure, and significantly enhances both mechanical performance and impermeability. Field application in a trial tunnel section confirms that the proposed grouting material achieves complete cavity filling, eliminates water leakage, controls ground deformation effectively, and offers favorable economic viability, demonstrating strong potential for large-scale engineering application. Full article

Addressing the challenges of poorly developed fractures and low individual well water yields within the Tianjin Ordovician–Wumishan carbonate thermal reservoir, alongside the rapid reaction rates and short effective distances observed during conventional acid fracturing operations, this study employed an XRD core analysis to confirm reservoir calcite contents exceeding 90%. Based on this finding, an acid formulation incorporating a 2% SPR-12 retarder was developed. High-temperature high-pressure reactor experiments demonstrated that this system successfully reduced the acid–rock reaction rate from 0.122 g·min⁻¹·cm⁻² to 0.037 g·min⁻¹·cm⁻² and increased the retardation efficiency from 34.07% to 68%. This significantly extended the acid penetration distance and enhanced the fracture network connectivity within the reservoir. The field trial conditions informed the parameter optimization via E-StimPlan^® 3D simulations, ultimately determining that a fracture extension of 400 m could be achieved with a 20 MPa breakdown pressure. Conductivity experiments validated that a flow rate of 1.3 m³/min generated pillar-supported wormhole structures, yielding a final conductivity of 46.8 μm²·cm. The pumping pressure plummeted from 20 MPa to 1 MPa, confirming effective fracture network communication. Gas lift backflow for 20 h mitigated secondary precipitation risks. After implementation, the water production rate of this well increased from 12.33 m³/h to 95 m³/h, with a dynamic water level of 158.85 m. The water temperature rose from 62 °C to 88 °C and remained stable. Compared to current acidizing and fracturing methods applied in geothermal wells, the new acid fluid system and process have increased the geothermal production capacity by 275.8%, while reducing acid consumption by 50%, providing critical technological support for the efficient development of carbonate thermal reservoirs. Full article

Coal combustion residues are often useful components for the cement industry. This study represents a material characterization and screening analysis by focusing on the mineralogical, physicochemical, and petrographic compositions of fly and bottom ash samples from four Greek power plants in order to evaluate their suitability and potential in industrial applications, especially as fillers in cement manufacturing. Proximate analysis revealed LOI values exceeding ASTM C618-22 limits. The sum of SiO₂, CaO, and Al₂O₃ classifies the studied samples as Class C except one. Iron and magnesium oxides are among the major components, while S, Ni, and Sr are also contained in significant amounts. Calcite, quartz, and plagioclases dominate, corresponding to their geochemical profile, while secondary mineral phases (i.e., neo-formed minerals during coal combustion) such as natrolite and gehlenite, were also identified. Relatively high amounts of carbonized organic matter and unburnt organic particles point to the incomplete combustion process, revealing the risk of slagging into the combustion chamber; this is confirmed through the high slagging and fouling indices. The amount of the magnetic fraction is low; magnetic spherules with complex surface structures and a wide range of spherule sizes were observed. While the pozzolanic character of the samples is strong, high values of LOI, S content, and carbonized organic material make them suitable for the cement industry after further treatment only. Full article

The ceramics industry has long embraced the principles of the circular economy, with a strong focus on the reuse and recovery of raw materials essential to the production cycle. This approach reduces costs by reintroducing secondary raw materials—such as production scraps and recycled materials—into the manufacturing process after appropriate recovery treatments. This study aims to contribute to the transition of the ceramic industry toward a circular economy by incorporating industrial by-products into monoporosa ceramic bodies, thereby transforming waste materials into valuable resources. Monoporosa is a porous, single-fired ceramic wall tile characterized by a high carbonate content and low bulk density. However, the role of secondary raw materials in monoporosa formulations, as well as their influence on processing behavior (e.g., during sintering) and on key technological properties, is not yet fully understood. This work investigates a standard monoporosa formulation based on conventional raw materials (sand, calcite, feldspars, and clays) and compares it with new formulations in which industrial waste materials from local and national sources—originating from other industrial processes—are used as partial or total substitutes for some of the traditional raw materials, particularly sand and calcite. The industrial by-products examined include biomass bottom ash, foundry sand, and marble cutting and processing sludge. All materials were characterized using chemical–mineralogical, thermal, and morphological analyses and were incorporated into the ceramic bodies at different substitution levels (10%, 50%, and 100%) to replace natural raw materials. Their behavior within the mixtures was evaluated to determine ceramic suitability and acceptable replacement ratios. Furthermore, the effects of these additions on water absorption, thermal expansion coefficient, and microstructural characteristics were assessed. Based on the positive results obtained, this study demonstrates the feasibility of using, in particular, two secondary raw materials—foundry sand and marble sludge—in monoporosa body formulations, allowing for the complete replacement of the original raw materials and thereby contributing to the development of more sustainable ceramic compositions. Full article

This paper presents a comprehensive characterization of bottom ash generated during biomass combustion in fluidized boilers, with a focus on its potential use in a circular economy. Two biomass bottom ash samples (BBA 1 and BBA 2) from commercial combined heat and power plants were tested. The scope of this study included the determination of chemical composition, phase composition, and leachability testing of selected impurities. The results showed that the bottom ashes tested are calcium silicate materials with varying proportions of calcium phases (anhydrite, portlandite, and calcite) and silica phases (quartz), depending on the type of biomass and combustion technology. Thermal analysis confirmed the presence of characteristic dehydration, decarbonation, and polymorphic transformations of quartz, with a low organic content. Leachability tests showed low mobility of most trace elements and heavy metals, with increased solubility of sulfates, chlorides, and alkali ions, typical for fluidized ash. The concentrations of As, Cd, Cr, Cu, Pb, Zn, and Hg in the eluates were low or below the limit of quantification, indicating the favorable chemical stability of the tested waste. The results obtained suggest that bottom ashes from biomass combustion in fluidized boilers may be a promising secondary raw material for engineering applications, especially in binding materials and bonded layers, and potentially also in selected agricultural applications, provided that the contents of sulfates, chlorides, and pH are controlled. Full article

The Weishan rare earth element (REE) deposit, located in western Shandong, North China Block, is a typical carbonatite REE deposit and constitutes the third largest light REE resource in China. Its mineralization is closely related to the multi-stage evolution of a carbonatite magma–hydrothermal system. However, the mechanisms governing REE enrichment, migration, and precipitation remain insufficiently constrained from a mineralogical perspective, which hampers the understanding of the ore-forming processes and the establishment of predictive exploration models. Apatite is a pervasively developed REE phase in the Weishan deposit which occurs in multiple generations, and thus represents an ideal recorder of the magmatic–hydrothermal evolution. In this study, different generations of apatite hosted in carbonatite orebodies from the Weishan deposit were investigated using cathodoluminescence (CL), electron probe microanalysis (EPMA), and in situ LA-ICP-MS trace element analysis. Three types of apatite were identified. In paragenetic sequence, Ap-1 occurs as polycrystalline aggregates coexisting with calcite, is enriched in Na, Sr, and LREEs, and shows high (La/Yb)_N ratios, suggesting crystallization from an evolved carbonatite magma. Ap-2 and Ap-3 display typical replacement textures: both contain abundant dissolution pits and dissolution channels within the grains, which are filled by secondary minerals such as monazite and ancylite, and thus exhibit characteristic features of fluid-mediated dissolution–reprecipitation during the hydrothermal stage. Ap-2 is commonly associated with barite and strontianite, whereas Ap-3 is associated with pyrite and monazite and is characterized by relatively sharp grain boundaries with adjacent minerals. From Ap-1 to Ap-3, total REE contents decrease systematically, whereas Na, Sr, and P contents increase. All three apatite types lack Eu anomalies but display positive Ce anomalies. Discrimination diagrams involving LREE-Sr/Y and log(Ce)-log(Eu/Y) indicate that apatite in the Weishan REE deposit formed during the magmatic to hydrothermal evolution of a carbonatite, and that the dissolution of early magmatic apatite, followed by element remobilization and mineral reprecipitation, effectively records the progressive evolution of the ore-forming fluid. Full article