Search Results (151)

The aim of this study was to improve the efficiency of in situ uranium leaching by developing a specialized methodology for selecting rational parameters for the chemical treatment of production wells. This approach was designed to enhance the filtration properties of ores and extend the uninterrupted operation period of wells, considering the clay content of the productive horizon, the geological characteristics of the ore-bearing layer, and the composition of precipitation-forming materials. The mineralogical characteristics of ore and precipitate samples formed during the in situ leaching of uranium under various mining and geological conditions at a uranium deposit in the Syrdarya depression were identified using an X-ray diffraction analysis. It was established that ores of the Santonian stage are relatively homogeneous and consist mainly of quartz. During well operation, the precipitates formed are predominantly gypsum, which has little impact on the filtration properties of the ore. Ores of the Maastrichtian stage are less homogeneous and mainly composed of quartz and smectite, with minor amounts of potassium feldspar and kaolinite. The leaching of these ores results in the formation of gypsum with quartz impurities, which gradually reduces the filtration properties of the ore. Ores of the Campanian stage are heterogeneous, consisting mainly of quartz with varying proportions of clay minerals and gypsum. The leaching of these ores generates a variety of precipitates that significantly reduce the filtration properties of the productive horizon. Effective compositions and concentrations of decolmatant (clog removal) solutions were selected under laboratory conditions using a specially developed methodology and a TESCAN MIRA scanning electron microscope. Based on a scanning electron microscope analysis of the samples, the effectiveness of a decolmatizing solution based on hydrochloric and hydrofluoric acids (taking into account the concentration of the acids in the solution) was established for the destruction of precipitate formation during the in situ leaching of uranium. Geological blocks were ranked by their clay content to select rational parameters of decolmatant solutions for the efficient enhancement of ore filtration properties and the prevention of precipitation formation. Pilot-scale testing of the selected decolmatant parameters under various mining and geological conditions allowed the optimal chemical treatment parameters to be determined based on the clay content and the composition of precipitates in the productive horizon. An analysis of pilot well trials using the new approach showed an increase in the uninterrupted operational period of wells by 30%–40% under average mineral acid concentrations and by 25%–45% under maximum concentrations with surfactant additives in complex geological settings. As a result, an effective methodology for ranking geological blocks based on their ore clay content and precipitate composition was developed to determine the rational parameters of decolmatant solutions, enabling a maximized filtration performance and an extended well service life. This makes it possible to reduce the operating costs of extraction, control the geotechnological parameters of uranium well mining, and improve the efficiency of the in situ leaching of uranium under complex mining and geological conditions. Additionally, the approach increases the environmental and operational safety during uranium ore leaching intensification. Full article

The most important bauxite deposits in Türkiye are located in the Seydişehir (Konya) and Akseki (Antalya) regions, situated along the western Taurus Mountain, with a total reserve of approximately 44 million tons. Some of the bauxite deposits have been exploited for alumina since the 1970s. In this study, bauxite samples, collected from six different deposits were examined to determine their mineralogical and chemical composition, as well as their REE content, with the aim of identifying which bauxite types are enriched in REEs and assessing their economic potential. The samples included massive, oolitic, and brecciated bauxite types, which were analyzed using optical microscopy, X-ray diffraction (XRD), X-ray fluorescence (XRF) and inductive coupled plasma-mass spectrometry (ICP-MS), field emission scanning electron microscopy (FESEM-EDX), and electron probe micro-analysis (EPMA). Massive bauxites were found to be more homogeneous in both mineralogical and chemical composition, predominantly composed of diaspore, boehmite, and rare gibbsite. Hematite is the most abundant iron oxide mineral in all bauxites, while goethite, rutile, and anatase occur in smaller quantities. Quartz, feldspar, kaolinite, dolomite, and pyrite were specifically determined in brecciated bauxites. Average oxide contents were determined as 52.94% Al₂O₃, 18.21% Fe₂O₃, 7.04% TiO₂, and 2.69% SiO₂. Na₂O, K₂O, and MgO values are typically below 0.5%, while CaO averages 3.54%. The total REE content of the bauxites ranged from 161 to 4072 ppm, with an average of 723 ppm. Oolitic-massive bauxites exhibit the highest REE enrichment. Cerium (Ce) was the most abundant REE, ranging from 87 to 453 ppm (avg. 218 ppm), followed by lanthanum (La), which reached up to 2561 ppm in some of the massive bauxite samples. LREEs such as La, Ce, Pr, and Nd were notably enriched compared to HREEs. The lack of a positive correlation between REEs and major element oxides, as well as with their occurrences in distinct association with Al- and Fe-oxides-hydroxides based on FESEM-EDS and EPMA analyses, suggests that the REEs are present as discrete mineral phases. Furthermore, these findings indicate that the REEs are not incorporated into the crystal structures of other minerals through isomorphic substitution or adsorption. Full article

This work investigates, for the first time, the application of a modified natural magnetite material with 35% of lanthanum for phosphorus (P) recovery from synthetic and actual wastewater under both static (batch) and dynamic (continuous stirred tank reactor (CSTR)) conditions. The characterization results showed that the natural feedstock mainly comprises magnetite and kaolinite. Moreover, the lanthanum-modified magnetite (La-MM) exhibited more enhanced textural, structural, and surface chemistry properties than the natural feedstock. In particular, its surface area (82.7 m² g⁻¹) and total pore volume (0.160 cm³ g⁻¹) were higher by 86.6% and 255.5%, respectively. The La-MM efficiently recovered P in batch mode under diverse experimental settings with an adsorption capacity of 50.7 mg g⁻¹, which is significantly greater than that of various engineered materials. It also maintained high efficiency even when used for the treatment of actual wastewater, with an adsorption capacity of 47.3 mg g⁻¹. In CSTR mode, the amount of P recovered from synthetic solutions and real wastewater decreased to 33.8 and 10.2 mg g⁻¹, respectively, due to the limited contact time. The phosphorus recovery process involves mainly electrostatic attraction over a wide pH interval, complexation, and precipitation as lanthanum phosphates. This investigation indicates that lanthanum-modified natural feedstocks from magnetite deposits can be regarded as promising materials for P recovery from aqueous solutions. Full article

Zinc oxide (ZnO) photocatalysts are recognized for their ease of synthesis, cost-effectiveness, efficiency, scalability, and environmental compatibility, making them highly suitable for addressing wastewater contamination. In this study, various compositions of kaolinite were used for the hydrothermal deposition of ZnO, including 0.5%, 0.75%, 1%, and 1.25%. The main purpose of this study was to evaluate the effect of kaolinite toward the enhanced performance of ZnO through modification of particle size, morphology and surface functional groups. Several analytical techniques were employed to obtain structural and optical results, including scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and UV–visible spectroscopy, revealing significant changes in particle shape, particle size, surface functional groups, and optical band gap when kaolinite was added. The ZnO/kaolinite composite (sample 4) with 1.25% kaolinite content demonstrated outstanding photocatalytic performance for the degradation of methylene blue in natural sunlight. For sample 4, 15 mg of the dye in a 3.4 × 10⁻⁵ M dye solution exhibited a degradation efficiency of 99%. In contrast, when using 15 mg of catalyst dose and 1.5 × 10⁻⁵ M dye solution, the degradation efficiency was observed to be almost 100%, thus indicating that catalyst dose and dye concentration affect degradation efficiency. The reusability test revealed that sample 4 retained degradation efficiency of 98% after five cycles without showing any morphological changes. By decorating ZnO with kaolinite mineral clay, this study provides exciting findings and insights into the development of low-cost photocatalysts, which could be used to produce solar-powered hydrogen and treat wastewater. Full article

The Sanandaj–Sirjan Zone and Zagros Fold–Thrust Belt in Iran host numerous Mediterranean-type karst bauxite deposits; however, their formation mechanisms and critical raw material potential remain ambiguous. This study combines mineralogical and geochemical analyses to explore (1) the formation of authigenic minerals, (2) the role of microbial organic processes in Fe cycling, and (3) the assessment of their critical raw materials potential. Mineralogical analyses of the Late Cretaceous Daresard and Middle–Late Permian Yakshawa bauxites reveal distinct horizons reflecting their genetic conditions: Yakshawa exhibits a vertical weathering sequence (clay-rich base → ferruginous oolites → nodular massive bauxite → bleached cap), while Daresard shows karst-controlled profiles (breccia → oolitic-pisolitic ore → deferrified boehmite). Authigenic illite forms via isochemical reactions involving kaolinite and K-feldspar dissolution. Scanning electron microscopy evidence demonstrates illite replacing kaolinite with burial depth enhancing crystallinity. Diaspore forms through both gibbsite transformation and direct precipitation from aluminum-rich solutions under surface conditions in reducing microbial karst environments, typically associated with pyrite, anatase, and fluorocarbonates under neutral–weakly alkaline conditions. Redox-controlled Fe-Al fractionation governs bauxite horizon development: (1) microbial sulfate reduction facilitates Fe³⁺ → Fe²⁺ reduction under anoxic conditions, forming Fe-rich horizons, while (2) oxidative weathering (↑Eh, ↓moisture) promotes Al-hydroxide/clay enrichment in upper profiles, evidenced by progressive total organic carbon depletion (0.57 → 0.08%). This biotic–abiotic coupling ultimately generates stratified, high-grade bauxite. Finally, both the Yakshawa and Daresard karst bauxite ores are enriched in critical raw materials. It is worth noting that the overall enrichment appears to be mostly driven by the processes that led to the formation of the ores and not by the chemical features of the parent rocks. Divergent bauxitization pathways and early diagenetic processes—controlled by paleoclimatic fluctuations, redox shifts, and organic matter decay—govern critical raw material distributions, unlike typical Mediterranean-type deposits where parent rock composition dominates critical raw material partitioning. Full article

The Roman site at Makariopolsko village in Northeastern Bulgaria has been identified as a ceramic production center, featuring single- and double-chamber kilns, abundant ceramic material, and a nearby water source. Geological assessments also reveal local clay deposits. Previous archaeological studies have noted similar Roman production sites in the region, primarily focusing on the study of the kilns and the macroscopic description and classification of the ceramics. However, there has been a lack of research into the pottery’s composition and the sourcing of raw materials, which is essential for understanding the area’s cultural and economic context. This study aims to determine the raw material and firing temperature of the ceramic from the site at Makariopolsko village. Clay samples (both raw and fired at 1100 °C) and ceramic were subjected to chemical, statistical, phase X-ray structural, and thermal analyses. The findings indicate the use of calcareous illite–kaolinitic clay, sourced locally, with an added sandy component. The ceramics were fired at temperatures of 570–760 °C and 920–945 °C. These results, which support the site’s identification as a pottery production center, highlight advanced pottery skills and the dual functional capabilities of the kilns. Additionally, they pave the way for further research into regional production center relationships. Full article

The Carajás Mineral Province hosts one of the world’s most extensive sulfide-bearing copper belts. These deposits are typically covered by thick regolith, including gossans, laterites, colluviums, and soil, which can be used as important exploration indicators. In some cases, these covers can be mined alongside the parent hypogene ore. Therefore, accurate identification of copper-bearing minerals is essential for selecting the most appropriate metallurgical techniques. This study investigated the saprolite horizon overlying the Alvo 118 deposit, where the parent rocks are chloritites hosting copper-bearing hypogene sulfides, partially altered to an immature gossan. Saprolite formation was primarily controlled by the weathering of chlorite, mostly converted into kaolinite, with smectite and vermiculite serving as intermediates, forming a typical lower saprolite association. During weathering, iron released from chlorite and indirectly by vermiculite and smectite contributed to the formation of ferrihydrite, goethite, and hematite. Magnetite octahedrons, relics of the hypogene ore, pseudomorphic phases, are embedded in the clay mineral matrix. While FTIR analysis of kaolinite showed no evidence of copper retention, Mössbauer spectroscopy enabled the quantification of iron-bearing minerals, revealing a strong correlation between CuO contents and goethite and ferrihydrite. These results suggest that goethite and ferrihydrite may be the main copper carriers in the deposit, consistent with findings from similar deposits. Weak acid leaching is proposed as the most effective technique for copper extraction from this mineralization type. Full article

In the western Tarim Basin, Carboniferous granular dolostones deposited on a carbonate platform contain a small amount of terrigenous materials of sand-size fraction, agglomerated clay minerals, or similar phases. However, the role of terrigenous materials on dolomitization is still unclear. The aim of this study was to reveal the dolomitization mechanism. The granular dolomites have small crystal size, earthy yellow color, and fabric-retentive texture, with relatively good order. These features indicate dolomites precipitated during early diagenesis. The ratio of rare earth elements (RREs) abundance of the stable isotopes ⁸⁷Sr/⁸⁶Sr relative to Post-Archean Australian Shale (PAAS) normalized patterns was used to study the source of the dolomitizing fluids. The composition of REEs is characterized by heavy rare earth (HREE) enrichment (average Nd_SN/Yb_SN = 0.83). There is a positive (La/La*)_SN anomaly and slightly positive (Gd/Gd*)_SN and (Y/Y*)_SN anomaly; δ¹⁸O of seawater in fractionation equilibrium with granular dolostones was from −2.8‰ to 1.7‰ PDB, implying the dolomitizing fluid was contemporary, slightly evaporated seawater. The granular dolostones on the relatively thick shoals were subject to subaerial exposure before pervasive dolomitization, with evidence that the input of detrital kaolinite predated the formation of dolomites. Higher ⁸⁷Sr/⁸⁶Sr values and ∑REE in granular dolostones than the values in equivalent limestones indicate that dolomitization was related to terrigenous materials. Within the terrigenous materials, the negative-charged clay minerals may have catalyzed the dolomitization, resulting in dramatically decreased induction time for precipitation of proto-dolomites. A greater amount of terrigenous materials occurred on the shoals at the sea level fall, resulting from enhanced river entrenchment and downcutting. As a result, after subaerial exposure, the penesaline water flow through the limy allochems sediments lead to dolomitization, with the catalysis of illite on relatively thick shoals. Full article

A set of samples from the Monte Castelo kaolin deposits (Burela, NW Spain), corresponding to igneous acidic rocks affected by chemical weathering with variable intensity have been investigated in order to establish the mineralogical and chemical changes with weathering, and the micro- and nano-scale textures developed. For the study, XRD, FESEM, HRTEM and chemical analyses have been used. The more intense the weathering, the more the dissolution of aluminosilicates (albite, K feldspars and K micas) and the crystallization of kaolinite is favored. Kaolinite grows, forming booklets and generating a fine-grained matrix and, along the cleavages of muscovite, forming mica–kaolinite intergrowths. Bidimensional crystallographic continuity between mica and kaolinite has been observed and no intermediate phases have been identified as a consequence of the high W/R ratio. Kaolin mainly contains kaolinite with high crystallinity; however, when there are quartz impurities, they interfere with the ‘optimal’ reflections for the calculation of the Hinckley index. In this case, the use of the AGFI index almost eliminates the effect that the relative intensities of the quartz and feldspar impurities may have on those of kaolinite. With weathering, there is a progressive decrease in the contents of most chemical elements, except Al, TiO₂, HREEs, Ta, Hf, Th, U, V, Cr, S, Zr, Mo and Sn. Full article

Clays deposited in marine evaporite sequences are strongly altered, and the most important factor determining their transformation is brine concentration. An X-ray diffraction study of clay minerals associated with the Lower and Middle Miocene evaporite formations of the Ukrainian Carpathian Foredeep indicated that the clay mineral assemblages in the gypsum facies are composed of smectite and illite, and, in some samples, mixed-layer chlorite–smectite and illite–smectite, as well as chlorite. In the halite facies, illite, chlorite, and mixed-layer illite–smectite occur in rock salt of Eggenburgian age (Vorotyshcha Suite); in addition to those minerals, smectite, corrensite, and mixed-layer chlorite–smectite occur in the Badenian rock salt (Tyras Suite); and in the potash facies, illite and chlorite were recorded. Such clay mineral assemblages resulted from the aggradational transformation of unstable and labile minerals and phases (kaolinite, smectite, and mixed-layer phases) that finally pass into illite and chlorite, minerals that are stable in an evaporite environment. In addition to brine concentration control, another important factor in the transformations of clay minerals was the sorption of organic components on the mineral structure, which slows the transformation processes. The assemblage of clay minerals in the weathering zone of the evaporite deposits, besides inherited illite and chlorite, also contains mixed-layer illite–smectite and kaolinite. The appearance of those clay minerals in hypergene deposits is the consequence of two processes: degradational transformation (illite–smectite) and neoformation (kaolinite) in conditions of decreased ionic concentrations during desalination. Full article

This study focuses on the Hailijing sandstone-hosted uranium deposit in the Songliao Basin. Through a combination of petrographic analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), and geochemical analysis, the epigenetic alteration of the deposit was systematically investigated, and the alteration zonation was delineated. On this basis, the metallogenic mechanisms were further explored. The results indicate that six major types of alteration can be identified in the ore-bearing strata of the Hailijing uranium deposit: hematitization, limonitization, carbonatization, pyritization, clay mineralization (including kaolinite, illite, and illite-smectite mixed-layer), and baritization. The mineral assemblages at different stages of alteration vary: during the sedimentary diagenetic stage, the assemblage consists of “hematite + clay minerals + II-type pyrite (framboidal pyrite) + III-type pyrite (euhedral granular pyrite)”; during the uranium mineralization stage, it transitions to “ankerite + barite + I-type pyrite (colloidal pyrite) + minor kaolinite”; and in the post-ore stage, alteration is characterized by calcite cementation in red sandstones. Based on petrological, mineralogical, and geochemical characteristics, as well as the spatial distribution of the host gray sandstones, it is inferred that during uranium mineralization stage, the ore-bearing strata underwent reduction by uranium-rich reducing fluids sourced from the Lower Cretaceous Jiufotang Formation. The primary red sandstones of the Lower Yaojia Formation, formed under arid to semi-arid conditions, experienced varying degrees of reduction, resulting in a color transition from light red, brownish red, and yellowish brown to grayish-yellow and gray. Accordingly, four alteration zones are distinguished in the Hailijing uranium deposit: the primary red zone, weakly reduced pink zone, moderately reduced grayish-yellow zone, and strongly reduced gray zone. Furthermore, as the uranium-rich reducing fluids migrated from a high-temperature, high-pressure deep system to the low-temperature, low-pressure ore-bearing sandstone strata near the surface, uranium was unloaded, precipitated, and enriched, ultimately forming multi-layered and tabular-shaped uranium orebodies within the gray sandstone. This study elucidates the epigenetic alteration processes and metallogenic mechanisms of the Hailijing uranium deposit, providing a critical theoretical basis for further uranium exploration in the southern Songliao Basin. Full article

Transport and vehicle traffic are closely connected with particulate matter (PM) pollution, inducing various fractions into the atmosphere, some of them forming significant deposits on the surface of the car. They are washed away during carwash-inducing slurries collecting the PM deposits, which are characteristic of a large area. Crystalline PM matter was investigated by XRD coupled with polarized optical microscopy (POM). Organic matters were investigated by Fourier-Transform Infrared spectrometry (FTIR) and gas chromatography, GC-MS. Their microstructure and elemental composition were investigated by SEM-EDX. The crystalline features contain mainly quartz, calcite, and clay (muscovite and kaolinite) particles having traces of goethite and lepidocrocite. Slurry particle size distribution was established by sieving on the following meshes: 63 µm, 125 µm, 250 µm, 500 µm, 1000 µm, 2000 µm, and 4000 µm. Coarse fractions of 250–4000 μm are dominated by quartz and calcite particles. The quartz and calcite amount decreases with particle size, while the muscovite and kaolinite amount increases in the finest fractions of 0–125 μm. Organic matter was evidenced, firstly, by FTIR spectroscopy, revealing mostly CH₂; C=O, and NH₄ bonds that are more intense for the fine particulate fractions. The organic deposits form mainly amorphous crusts associated with micro- and nano-plastic particles related to the phthalates and traces of the washing detergents. Atomic Force Microscopy revealed their size range between 60 and 90 nm and evidenced nanoparticles within samples. The nanofractions adhere to the bigger particles in humid environments, assuring their immobilization to reduce their hazardous potential. Carwash slurry blending with fertile soil ensures proper grass seed germination and growth at mixtures of up to 60% slurry, allowing its sustainable reconversion as soil for landfill and dump rehabilitation, preventing the PM emission hazard. Blended compositions containing more than 60% slurry have noxious effects on the grass seeds, inhibiting their germination. Full article

North China Craton (NCC) formed the world’s largest karstic bauxite belt in the Late Carboniferous, with significant variations in metallogenic sources and conditions, which affect the overall understanding of karstic bauxite genesis. The Xiangcaowa bauxite deposit in the southern NCC is a large deposit of uncertain provenance and genesis. This study employed geological, mineralogical, and chronology analysis to investigate the sources and genesis of Xiangcaowa bauxite, further contributing to a full understanding of the origin of bauxite throughout the NCC. Xiangcaowa ore-bearing rock series is composed of bauxite and claystone layers. The composition of bauxite ore encompasses diaspore, kaolinite, anatase, pyrite, zircon, and rutile. Widely developed mineral assemblages, such as diaspore–anatase–pyrite, indicate that bauxite is mainly formed in reducing and alkaline karstic depressions. Detrital zircons, aged ~450, ~520, ~950, and ~1100 Ma, predominantly originate from igneous rocks in the North Qinling Orogenic Belt (NQOB), and the ~1650 and ~2400 Ma zircon age populations are primarily from the southern margin of the NCC. Detrital rutiles, which are concentrated in 800–510 Ma, are primarily from the metamorphic rocks of the South Qinling Orogenic Belt (SQOB); rutiles aged ~1500–910 Ma are primarily from metamorphic rocks in the NQOB. These results confirm that the principal sources of the bauxite are the igneous and metamorphic rocks within the NQOB, along with the metamorphic rocks of the SQOB, while the basement rocks of the NCC contribute only minorly to its formation. A large karstic bauxite deposit was formed by the transport of large amounts of weathered material into extensive karstic depressions where reducing and alkaline conditions favoured diaspore deposition. Full article

In this study, we investigated and evaluated the mineralization pattern of ion-adsorption rare earth deposits in granite weathering crusts using remote sensing technology for the southeastern region of Guangxi, and we proposed a strategy for sustainable mining and utilization. Through detailed analysis of the stratification characteristics, mineralogical features, and rare earth element (REE) distribution patterns of the weathering crust, it is found that the rare earth minerals are mainly enriched in the completely weathered layers, with light rare earth elements (La, Ce, Pr, Nd) dominating. This study reveals the transformation mechanism of rocks and minerals during the weathering process, especially the important role of kaolinite, feldspar, and smectite in the enrichment of rare earth elements. Combined with remote sensing image analysis, the intrinsic connection between linear tectonics and mineralization is explored, and potential directions for sustainable exploration are proposed. This study deepens the understanding of the mineralization mechanism of rare earth deposits in the region and provides scientific basis and technical support for the sustainable exploration and development of rare earth resources, and it has important economic and environmental significance. Full article

The Lhasa River, as one of the major rivers on the Tibetan Plateau, is of great value for the study of climate and environmental changes on the Tibetan Plateau. In this paper, the grain size and the mineralogical and geochemical characteristics of the sediments from the Lhasa River were investigated. The results show the following: (1) The average grain size of the Lhasa River sediments is coarse (65.5% sand, 23.6% silt), and the sorting is overall poor; the skewness is mostly positive, and the kurtosis is wide, which reflects the obvious characteristics of river sand deposition. (2) The mineral composition of the Lhasa River sediments is dominated by quartz (38.4%), feldspar, and plagioclase feldspar, followed by clay minerals, and the content of carbonate minerals is relatively low; the content of clay minerals in the illite content is as high as 83.3%, while the chlorite content is slightly higher than kaolinite, and smectite content is very low. The chemical index of illite is less than 0.4, indicating that illite is mainly iron-rich magnesium illite. (3) The value of the chemical weathering index (CIA) of the sediments is low, implying that the sediments are in a weak–moderate chemical weathering state and dominated by physical weathering. Comprehensive analyses further revealed that the weathering process of the sediments in the Lhasa River was influenced by both climate and lithology, i.e., sediment composition is influenced not only by chemical weathering in a dry, cold climate but also by physical weathering of granites exposed over large areas. The results of this study can provide scientific references for further in-depth research on the environmental and climatic effects of the Tibetan Plateau. Full article