Search Results (50)

The Kızılcaören alkaline silicate–carbonatite complex, located in the Sivrihisar (Eskişehir, NW Anatolia) region, includes phonolite, trachyte, carbonatite, pyroclastics, and REE mineralization (bastnäsite as a critical REE mineral). The emplacement and origin of this complex are poorly constrained, as previous studies mostly concentrated on the petrology of the alkaline rocks, carbonatite, and REE-mineralization, and little attention has been paid to the texture, composition, and origin of the pyroclastic rocks. The pyroclastic rocks in the region contain both rounded and angular-shaped cognate and wall-rock xenoliths derived from syenitic/trachytic hypabyssal rocks and carbonatites, as well as juvenile components such as carbonatite droplets and pelletal lapilli. The syenitic/trachytic hypabyssal rock fragments contain sanidine with high BaO (up to 3.3 wt.%) contents, amphibole (magnesio-fluoro-arfvedsonite), and apatite. Some clasts seem to have reacted with carbonatitic material, including high-SrO (up to 0.6 wt.%) calcite, dolomite, baryte, benstonite, fluorapatite. The carbonatite rock fragments are composed of calcite, baryte, fluorite, and bastnäsite. The carbonatite droplets have a spinifex-like texture and contain rhombohedral Mg-Fe-Ca carbonate admixtures, baryte, potassic-richterite, and parisite embedded in larger crystals of high-SrO (up to 0.7 wt.%) calcite. The spherical–elliptical pelletal lapilli (2–3 mm) contain a lithic center mantled by flow-aligned prismatic sanidine (with BaO up to 3.5 wt.%) microphenocrysts settled in a high-SrO (up to 0.7 wt.%) cryptocrystalline CaCO₃ matrix. All these components are embedded in an ultra-fine-grained matrix. The EPMA results from the matrix reveal that, chemically, it consists largely of BaO-rich sanidine, with minor carbonate, baryte and Fe-Ti oxide. The presence of pelletal lapilli, which is one of the most common and characteristic features of diatreme fillings in alkaline silicate–carbonatite complexes, reveals that the pyroclastic rocks in the region represent a tuffisite formed by intrusive fragmentation and fluidization processes in the presence of excess volatile components consisting mainly of CO₂ and F. Full article

The Xiaobaihegou fluorite deposit is located in the southwest of the Altyn-Tagh Orogen, NW China. However, the provenance, thermodynamic properties, and enrichment mechanisms of the ore-forming fluids in this deposit remain unclear. Fluorite mineralization primarily occurs in the vicinity of the contact zone between the granite and the wall rocks. The zircon U-Pb age of the alkali-feldspar granite in the Xiaobaihegou fluorite deposit is 482.3 ± 4.1 Ma. The ore-hosting lithologies are mainly calcareous rock series of the Altyn Group. The ore bodies are controlled by NE-trending faults and consist primarily of veined, brecciated, massive, and banded ores. The ore mineral assemblage is primarily composed of calcite and fluorite. The rare earth element (REE) patterns of fluorite and calcite in the Xiaobaihegou deposit exhibit right-dipping LREE enrichment with distinct negative Eu anomalies, which closely resemble those of the alkali-feldspar granite. This similarity suggests that the REE distribution patterns of fluorite and calcite were likely inherited from the pluton. The ore-forming process can be divided into an early stage and a late stage. The massive ores formed in the early stage contain mainly gas-rich two-phase fluid inclusions and CO₂-bearing three-phase inclusions, with homogenization temperatures ranging from 235 °C to 426 °C and salinities from 28.59% to 42.40% NaCl equivalent. In the late stage, brecciated and stockwork ores were formed. They host liquid-rich two-phase and gas-rich two-phase fluid inclusions, with homogenization temperatures ranging from 129 °C to 350 °C and salinities from 0.88% to 21.61% NaCl equivalent. The results of hydrogen and oxygen isotope studies indicate that the ore-forming fluids were derived from a mixture of magmatic–hydrothermal and meteoric water. Fluorite precipitation in the early stage was mainly due to the mixing of magmatic–hydrothermal solution and meteoric water, as well as a water–rock reaction. In the late stage, fluid mixing further occurred, resulting in a decrease in temperature and the formation of brecciated and stockwork ores. The ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios of fluorite from the deposit range from 0.71033 to 0.71272 and 0.511946 to 0.512073, respectively, indicating that the ore-forming material originates from the crust. Based on the ore-forming characteristics, it is proposed that Ca may be primarily leached from the strata formation, while F may predominantly originate from magmatic–hydrothermal solutions. The formation of fluorite deposits is closely related to the transition of the Central Altyn-Tagh Block and Qaidam Block from a compressional orogenic environment to an extensional tectonic environment. Full article

Y₅F₃[AsO₃]₄ crystallizes needle-shaped in the tetragonal space group P4/ncc with the lattice parameters a = 1143.80(8) pm, c = 1078.41(7) pm and c/a = 0.9428 for Z = 4. The yttrium-fluoride substructure linked via secondary contacts forms a three-dimensional network $\begin{array}{c}3\\ \infty \end{array}${[Y₅F₃]¹²⁺} and the remaining part consists of ψ¹-tetrahedral [AsO₃]³⁻ units, which leave lone-pair channels along [001]. In contrast, platelet-shaped Y₅Cl₃[AsO₃]₄ crystals adopt the monoclinic space group C2/c with the lattice parameters a = 1860.56(9) pm, b = 536.27(3) pm, c = 1639.04(8) pm and β = 105.739(3)° for Z = 4. Condensation of [(Y1,2)O₈]¹³⁻ polyhedra via four common edges each leads to fluorite-like $\begin{array}{c}2\\ \infty \end{array}$ {[(Y1,2)O $\begin{array}{c}e\\ 8/2\end{array}$ ]⁵⁻} layers spreading out parallel to the (100) plane. Their three-dimensional linkage occurs via the (Y3)³⁺ cations with their Cl⁻ ligands on the one hand and the As³⁺ cations with their lone-pairs of electrons on the other, which also form within [AsO₃]³⁻ anions lone-pair channels along [010]. Both colorless compounds can be obtained by solid-state reactions from corresponding mixtures of the binaries (Y₂O₃, As₂O₃ and YX₃ with X = F and Cl) at elevated temperatures of 825 °C, most advantageously under halide-flux assistance (CsBr for Y₅F₃[AsO₃]₄ and ZnCl₂ for Y₅Cl₃[AsO₃]₄). By replacing a few percent of YX₃ with EuX₃ or TbX₃, Eu³⁺- or Tb³⁺-doped samples are accessible, which show red or green luminescence upon excitation with ultraviolet radiation. Full article

Fluoride-enriched geothermal groundwater poses chronic health risks (e.g., dental and skeletal fluorosis) through prolonged exposure; nevertheless, hydrochemical-driven factors and the genetic mechanism of fluoride enrichment in such systems remain inadequately identified. This study employed hydrochemical characterization, isotopic tracing, and health risk models to elucidate the genetic mechanism of fluoride-enriched geothermal groundwater. The key findings reveal the following. (1) Geothermal groundwater (Cl-Na type; TDS 90–345 mg/L; pH 6.25–7.42) contrasts with alkaline river water (pH 7.48–8.05; SO₄-Na/HCO₃-Na) and saline seawater (TDS 23.9–28.2 g/L). Stable isotopes (δD, δ¹⁸O) confirm atmospheric precipitation recharge with an elevation of 69–635 m. (2) The Self-Organizing Map algorithm categorized 30 geothermal samples into three groups: Cluster I—low temperature and pH, high TDS; Cluster II—high temperature, low F⁻ concentration; and Cluster III—low TDS, and high pH and F⁻ concentration. (3) Fluoride enrichment in Cluster III originated from the evaporite/fluorite dissolution under alkaline conditions and cation exchange interactions, while the inhibition of CaF₂ dissolution by reverse cation exchange limited the accumulation of F⁻ in Cluster II and Cluster III samples. (4) Health risks disproportionately affect children (80% high risk) and women, necessitating pre-use defluorination. Full article

The Hammam–Zriba F–Ba (Zn–Pb) stratabound deposit is located within the Zaghouan Fluorite Province (ZFP), which is the most important mineral sub-province in NE Tunisia, with several CaF₂ deposits occurring mainly along the Zaghouan Fault and corresponding to an F-rich MVT mineral system developed along the unconformity surface between the uppermost Jurassic limestones and the late Cretaceous layers. Petrographic analysis, microthermometry, and Raman spectroscopy applied to fluid inclusions in fluorite revealed various types of inclusions containing brines, oil, CO₂, and CH₄ along with solid phases such as evenkite, graphite, kerogen and bitumen. Microthermometric data indicate homogenization temperatures ranging from 85 °C to 145 ± 5 °C and salinities of 13–22 wt.% NaCl equivalent. This study supports a model of heterogeneous trapping, where saline basinal brines, oil, and gases were simultaneously trapped within fluorite, which indicates fluid immiscibility. The Raman analysis identified previously undetected organic compounds, including the first documented occurrence of evenkite, a mineral hydrocarbon, co-genetically trapped with graphite. The identification of evenkite and graphite in fluid inclusions offers new insights into the composition of hydrocarbon-bearing fluids within the MVT deposits in Tunisia, contributing to an understanding of the mineralogical characteristics of these deposits. The identified hydrocarbons correspond to three oil families. Family I (aliphatic compounds) is attributed to the lower-Eocene Bou-Dabbous Formation, family II (aromatic compounds) is attributed to the Albian Fahdene Formation and the Cenomanian–Turonian Bahloul Formation, and family III is considered as a mixture of aliphatic and aromatic compounds generated by the three sources. The presence of graphite in fluid inclusions could suggest the involvement of a thermal effect from deep-seated sources through the reservoir to the site of fluorite precipitation. These findings suggest that the fluorite mineral system might have been linked with the interaction of multi-reservoir fluids, potentially linked to the neighboring petroleum system in northeastern Tunisia during the Miocene. This study aims to investigate the composition of fluid inclusions in fluorite from the Hammam–Zriba F–Ba (Zn–Pb) deposit, with a particular focus on the plausible sources of hydrocarbons and their implications for the genetic relationship between the mineralizing system and petroleum reservoirs. Full article

The Zaghouan Fluorite Province (ZFP) encloses F-Ba(Pb-Zn) ores hosted within Jurassic carbonate series, in northeastern Tunisia. Critical breakthroughs on the Jebel Stah fluorite deposits, an MVT-style F-mineralization, have been made within the Lower Jurassic limestones along the Zaghouan Fault, which is a major target for mineralization. This study presents the first REE-Y analyses conducted by LA-ICP-MS on fluorites in Tunisia, and specifically on the fluorites of Jebel Stah deposit. This analytical technique provides highly accurate insights into the geochemical regime of mineralizing fluids and the related scavenging sources. Distinct geochemical characteristics between two fluorite generations (G1 and G2) were revealed. Fluorites (Fl2) from the early generation (G1) showed low ΣREE + Y (36.3 and 39.73 ppm, respectively). When normalized to chondrites, early fluorite G1 displayed a bell-shaped REE + Y pattern with a depletion in LREE relative to HREE and a slight MREE hump. Late fluorite (Fl3) generation (G2) displayed higher ΣREE + Y concentrations (77.43 ppm), but an almost similar REE pattern. Ce/Ce* ratios demonstrated strong negative Ce anomalies in all fluorites, while Eu/Eu* ratios indicated weak negative Eu anomalies. The positive Y anomaly observed in the REE + Y patterns of fluorites G1 and G2 suggests Y-Ho fractionation in the fluid system. Moreover, significant degrees of differentiation between terbium (Tb) and lanthanum (La) have been observed in all fluorite samples. The plot of fluorites from both fluorite generations on the Tb/La–Tb/Ca diagram gives evidence of the sedimentary hydrothermal origin of the ore-forming fluids in the Jebel Stah F-deposit. Sr isotopes show that the mineralizing fluids are radiogenic and deeply sourced basinal brines, whereas the small variation in ⁸⁷Sr/⁸⁶Sr ratios suggests a similar source for Sr in fluorites G1 and G2. These results allow us to conclude that the economic fluorite (G1) ore of Jebel Stah was deposited due to the interaction of the deeply sourced hydrothermal fluid with the carbonated host rocks (dolomitization, an increase in pH, and Ca activity), whereas the late fluorite (G2) is an accessory and could have resulted from the mixing of the hydrothermal fluid with shallow meteoric waters. Full article

In the Wadi Nugrus area, south Eastern Desert of Egypt, A-type granite is highly deformed in a prominent NW-SE trending shear zone, likely related to the Najd shear system. Deformation of this post-collisional leucogranite allows the propagation of hydrothermal alterations due to fluid circulation inside the so-called “Nugrus Shear Zone (NSZ)”. This results in the remarkable destabilization of the magmatic dissemination of rare-metal and U-Th minerals in the granite. Relict magmatic minerals that survived destabilization are represented by (1) ferrocolumbite with 14–63–16.39 wt% FeO^t, (2) fresh igneous zircon, and (3) thorite. The destabilized ore minerals (hydrothermal) dominate over the fresh magmatic relict minerals. The former comprises the following: (1) altered columbite in the form of three distinct phases of niobates (fergusonite–petscheckite–uranopyrochlore), (2) altered thorite (Ce-bearing and P-F-rich), (3) betafite, (4) altered uranothorite, and (5) sulfides (mainly pyrite). It is evident that the destabilization of magmatic thorite can be distinguished into three stages of hydrothermal alteration, namely low-Zr Ce-bearing thorite (stage I), moderate-Zr Ce-bearing thorite (stage II), and high-Zr U-Nb-Y-bearing thorite (stage III). The two varieties of Ce-bearing thorite are sodic with 1.33–2.28 wt% and 1.51–1.80 wt% Na₂O, respectively, whereas the U-Nb-Y-bearing thorite is Na₂O-poor (0.06–0.07 wt%). Similarly, thorite in stages I and II are Ca-, P-, F-, and S-rich. Considerable P₂O₅ content (up to ~17 wt%) is reported in stage II Ce-bearing thorite, whereas stage III thorite is Si-rich (14.56–18.79 wt% SiO₂). Upon hydrothermal destabilization, the three niobate minerals replacing the dissemination of magmatic ferrocolumbite become enriched in UO₂ (up to 15.24 wt%, 7.86 wt%, and 10.88 wt%, respectively), and similarly, ThO₂ (up to 7.13 wt%, 5.71 wt%, and 9.52 wt%, respectively). Hydrothermal destabilization results in the complete dissolution of magmatic fluorite and phosphate minerals at pH = 2–7. This furnishes a source of Ca, P, Ce, Y, F, and Cl in the hydrothermal solution to destabilize/collapse the structure of magmatic ore minerals, particularly ferrocolumbite and thorite. Free elements in the hydrothermal solution are responsible for the crystallization of P- and F-rich Ce-bearing thorite minerals in three stages, as well as abnormal Y₂O₃ enrichment in three resulting niobates that contain up to 6.03 wt%, 2.93 wt%, and 2.65 wt%, respectively. The fresh undeformed Nugrus leucogranite is sulfide-poor. In contrast, sulfides are enriched in the deformed leucogranite inside the NSZ. Also, the intimate relationship of sulfides with destabilized rare-element minerals indicates the destabilization of these minerals during the hydrothermal stage under reduced conditions. Finally, the proposed paragenetic sequence suggests that most ore minerals are magmatic or hydrothermal primarily. In contrast, supergene minerals such as goethite, Fe-oxyhydroxide, altered betafite, and altered uranothorite are the least abundant. Full article

The rare earth calcium thermal reduction slag (RCS) generated during the production of heavy rare earth metal contains large amounts of rare earth and fluoride compounds. In this study, rare earth elements (REEs) and fluorine in the RCS were recovered by the CaO roasting–hydrochloric acid leaching method. Firstly, the thermodynamic feasibility of converting rare earth fluoride to rare earth oxides through CaO roasting was demonstrated. The influence of roasting conditions and leaching conditions on the leaching rate of the REEs was investigated. Optimal results, a 95.48% leaching rate of the REEs, were obtained under the following conditions: a CaO dosage of 15%, a roasting temperature of 1000 °C, and a roasting duration of 90 min. XRD, SEM, and EDS results revealed that during the calcination process, the REEs present in fluorite (CaF₂) in isomorphic form were transformed into acid-soluble rare earth oxides; furthermore, the rare earth metallic in the RCS remained unchanged even after roasting. In the leaching process, rare earth metals and rare earth oxides are efficiently extracted, while CaF₂ rarely dissolves. The leaching slag contained 97.31% CaF₂ with a F recovery of 96.92%. The kinetics of the rare earth leaching process was analyzed, and the results show that the three-dimensional diffusion control at the phase interface of the kinetic model best fits the process. The calculated apparent activation energy for the leaching rate of REEs is 20.869 kJ/mol. Therefore, efficient comprehensive recovery of rare earth and fluorite from RCS can be achieved by using the CaO roasting–hydrochloric acid leaching method. Full article

Upconversion nanoparticles (UCNPs) are well-reported for bioimaging. However, their applications are limited by low luminescence intensity. To enhance the intensity, often the UCNPs are coated with macromolecules or excited with high laser power, which is detrimental to their long-term biological applications. Herein, we report a novel approach to prepare co-doped CaF₂:Yb³⁺ (20%), Er³⁺ with varying concentrations of Er (2%, 2.5%, 3%, and 5%) at ambient temperature with minimal surfactant and high-pressure homogenization. Strong luminescence and effective red emission of the UCNPs were seen even at low power and without functionalization. X-ray diffraction (XRD) of UCNPs revealed the formation of highly crystalline, single-phase cubic fluorite-type nanostructures, and transmission electron microscopy (TEM) showed co-doped UCNPs are of $~$12 nm. The successful doping of Yb and Er was evident from TEM–energy dispersive X-ray analysis (TEM-EDAX) and X-ray photoelectron spectroscopy (XPS) studies. Photoluminescence studies of UCNPs revealed the effect of phonon coupling between host lattice (CaF₂), sensitizer (Yb³⁺), and activator (Er³⁺). They exhibited tunable upconversion luminescence (UCL) under irradiation of near-infrared (NIR) light (980 nm) at low laser powers (0.28–0.7 W). The UCL properties increased until 3% doping of Er³⁺ ions, after which quenching of UCL was observed with higher Er³⁺ ion concentration, probably due to non-radiative energy transfer and cross-relaxation between Yb³⁺-Er³⁺ and Er³⁺-Er³⁺ ions. The decay studies aligned with the above observation and showed the dependence of UCL on Er³⁺ concentration. Further, the UCNPs exhibited strong red emission under irradiation of 980 nm light and retained their red luminescence upon internalization into cancer cell lines, as evident from confocal microscopic imaging. The present study demonstrated an effective approach to designing UCNPs with tunable luminescence properties and their capability for cellular imaging under low laser power. Full article

Due to its acidic nature and high fluoride concentration, hydrated lime (Ca(OH)₂) is commonly used for neutralization and fluoride control in semiconductor wastewater treatment. This study investigated the efficacy of treating high fluoride-containing wastewater using hydrated lime derived from oyster shells as an alternative to limestone. Overall, the characteristics of removing pollutants in acidic wastewater using shell-based hydrated lime showed similar patterns to hydrated lime from limestone. The treatment efficiency was 50% or less under theoretical Ca/F molar ratio (=0.5) conditions for the formation of fluorite (CaF₂), while the fluorine removal rate reached 99% under somewhat higher Ca/F conditions due to the influence of ionic components in the wastewater. Interestingly, chloride content did not increase even in the initial reaction stages, in contrast to our concerns about oyster shells generally containing salt to a certain extent due to their growth in seawater; instead, the chloride concentration decreased over time, similar to nitrate (NO₃⁻). In controlling fluoride in wastewater, surpassing the theoretical Ca/F molar ratio, particularly considering the presence of other anionic species such as SO₄^²− and PO₄³⁻, the optimal Ca/F ratio for fluoride removal was found to be 1.59. This value is approximately 16% lower than the calculated value (Ca/F = 1.85) when accounting for other anions. X-ray diffraction results confirmed the presence of CaSO₄, Ca₃(PO₄)₂, and CaF₂ in the precipitate recovered after the reaction, indicating the effective removal of ionic contaminants. This observation suggests that oyster shell-derived hydrated lime could serve as a viable calcium resource for treating acidic wastewater and represents a potential alternative to traditional limestone-based methods. Full article

Er³⁺-doped fluorite crystals, including CaF₂ and SrF₂, are considered as attractive laser gain materials in the mid-infrared (MIR) region with merits of high laser efficiency as well as low doping concentration. In this work, a series of Er, La:CaF₂ crystals were grown and the modulation effect of co-doping La³⁺ ions on the spectral properties and mid-infrared laser performance was investigated. It was found that introducing La³⁺ ions can effectively manipulate the coordination environment of Er³⁺ ions embedded in CaF₂ crystal, thus modulating the shape and intensity of absorption and emission bands. On the other hand, La³⁺ ions can partially substitute Er³⁺ sites in the clusters to form mixed clusters, which affects the energy transfer processes between Er³⁺ ions as well as ~3 μm laser performance, which is dominated by energy transfer up-conversion (ETU) processes between Er³⁺ ions. By co-doping La³⁺ ions into Er:CaF₂ crystal at an appropriate concentration, the spectral parameter modulation can be achieved while maintaining a high MIR laser efficiency. Full article

The rural population in the Dry Zone of Sri Lanka is largely affected by Chronic Kidney Disease of Unknown etiology (CKDu). According to the multidisciplinary research carried out so far, quality of groundwater is considered one of the possible causative factors for CKDu. Therefore, assessment of the quality of groundwater being used for drinking and its evolution mechanism is the key to identifying the linkage between CKDu and drinking water. This study aimed to perform a detailed investigation on groundwater sources using isotopic, chemical, and hydrogeological methods in the CKDu-endemic (site A) and the control area (sedimentary formation—site B) in the Malwathu Oya basin and the control areas in the Malala Oya basin (site C) selected for a systematic comparison. Our investigation shows that elevated levels of TDS, magnesium, and fluoride in the shallow groundwater affected by climatic, geochemical, and hydrogeological processes may contribute to the CKDu in the Dry Zone of Sri Lanka. All the groundwater samples analysed have exceeded the hardness threshold. Prominent Mg hardness proportion together with excess F⁻ in the CKDu endemic area may produce nephrotoxic MgF₂ complexes that may trigger renal damage. In contrast, NaF complexes in the CKDu control area leads to reduction of F⁻ toxicity in the human body. Elevated F⁻ and Mg²⁺ are found in site A, low F⁻ and high Mg²⁺ in site B, and either combinations of low F⁻ and low Mg²⁺, high F⁻ and low Mg²⁺, or low F⁻ with high Mg²⁺ in site C. TDS, hardness, Mg²⁺, Na⁺, and F⁻ are formed with different mechanisms in the three selected areas. The primary process that regulates the evolution of groundwater types and contents in sites A and C is the weathering of silicates. Similarly, in site A, carbonate dissolution and reverse ion exchange are quite strong. Cation exchange and evaporite dissolution are more pronounced in site C. Shallow groundwaters are evapo-concentrated, hence their quality deteriorates more significantly than the deep groundwater in the CKDu endemic area. Dilution decreases the ion content in site A while evaporite dissolution increases it in site C after the rainy season. Evaporation and seawater mixing affect the quality of groundwater in site B. It is also found that a statistically significant difference exists in the F⁻/Na⁺, F⁻/Mg²⁺, and F⁻/Ca²⁺ between the endemic and control areas. Intensive rock weathering combined with desorption has added excess F⁻ to the groundwater in site A, while cation exchange and fluorite dissolution are contributing factors in site C. Full article

This study addresses the in situ mobility of fluoride and aluminum in two different ashfall deposits accumulated during the 2021 eruption of the Tajogaite volcano (La Palma, Canary Islands, Spain), which were exposed to contrasting conditions of ambient humidity and precipitation. We selected one site to the east of the volcanic emission center, located near the top of Cumbre Vieja Ridge and exposed to continuous humidity and rain, and another site to the west of the volcano situated in a lowland and characterized by much drier conditions. The mobility of fluoride and aluminum is markedly different at both sites, with the first sequence suggesting a downwards migration of Al and F, and the second sequence showing no sign of mobility. The migration of aluminum and fluorine results from the dissolution of different fluoride salts (mostly AlF₃ and CaF₂, as suggested by scanning electron microscopy) followed by vertical transport as ionic complexes (AlF₃, AlF₂⁺, AlF₄⁻) during the percolation of rainwater through the ashfall deposits. Geochemical calculations suggest that the mobility of fluorine at neutral to alkaline conditions (pH 7.0–9.0) is likely limited by the solubility of fluorite (CaF₂), whereas at slightly acidic conditions (pH < 6.5), the aqueous concentration of aluminum seems to be controlled by the solubility of gibbsite (Al(OH)₃). This study demonstrates that aluminum and fluoride can be transported from volcanic ash to the underlying soil or groundwater, which is an environmental concern that should be followed in the future. Full article

In response to the development of low-carbon smelting technology, reducing the use of fluor-containing materials in desulfurizers is an important research topic. The development of new-generation KR (Kambara Reactor) desulfurizers is shifting towards a higher Al₂O₃ content rather than CaF₂, yet there is currently an absence of thorough and comprehensive mechanisms for desulfurization. Consequently, this research provides an extensive comparison using a specially constructed small-scale KR desulfurization hot model test, alongside FactSage simulation and SEM analysis (of desulfurization process). The findings indicate that at 1400 °C, for the desulfurization of molten iron, the capacity for desulfurization initially increases and then diminishes as the Al₂O₃ content in the KR desulfurizer rises. With Al₂O₃ content in the desulfurizer below 22 wt.%, the phase composition predominantly consists of C₃A, employing a solid_(slag)–liquid_(metal) diffusion method for desulfurization. The optimal desulfurization capacity (Ls: 64.1) is observed when the Al₂O₃ content is 15 wt.%, attributed to the simultaneous presence of CaO particle precipitation and C₃A. However, as the Al₂O₃ content reaches 20 wt.%, all the oversaturated CaO integrates into C₃A, leading to a reduction in Ls from 64.1 to 10.7, thereby diminishing the desulfurization capacity by approximately sixfold. When Al₂O₃ exceeds 22 wt.%, the phase composition transitions from the C₃A to C₁₂A₇ phase, and the desulfurization approach shifts from solid_(slag)–liquid_(metal) to liquid_(slag)–liquid_(metal) diffusion, with Ls decreasing to 23.4. This reduction is due to C₁₂A₇’s lower sulfur capacity compared to C₃A and the absence of saturated CaO particle precipitation. Therefore, for Al₂O₃ to effectively replace fluorite in KR desulfurizers, a higher presence of C₃A phases and CaO particle precipitation are essential. The desulfurizer must contain over 65 wt.% CaO and maintain A_l2O₃ levels at 10~16.2 wt.%. Full article

The Yongfeng composite granitic pluton, located in the southern section of the Nanling area, is composed of the Yongfeng and Longshi biotite monzonitic granites. In order to reveal the genesis of this composite granitic pluton and its relationship with mineralization, this study conducted zircon U-Pb dating, whole-rock major and trace element analysis, and biotite electron probe analysis. The results show that the Yongfeng composite granitic pluton is rich in silicon and alkali, weakly peraluminous, and poor in calcium and iron. It shows the enrichment of light rare earth elements and a significant fractionation of light and heavy rare earth elements. It also shows the enrichment of large ion lithophile elements and depletion of Ba, K, P, Eu, and Ti relative to the primitive mantle. The contents of TFe₂O₃, MgO, CaO, TiO₂, and P₂O₅ are low and decrease with increasing SiO₂ content. The Yongfeng composite granitic pluton does not contain alkaline dark minerals. Its average zircon saturation temperature is 776 °C, average TFe₂O₃/MgO is 4.81, and average Zr + Nb + Ce + Y is 280.6 ppm, which correspond to a highly fractionated I-type granite. The Yongfeng and Longshi granites were respectively formed at 152.0 ± 1.0 Ma–151.3 ± 1.1 Ma and 148.9 ± 1.2 Ma. They were formed in the extensional tectonic setting during the post-orogenic stage, under the control of the breakup or retreat of the backplate after the subduction of the Pacific Plate into the Nanling hinterland. The magmatic system of the Yongfeng composite granitic pluton is characterized by high fractionation, high content of F, high temperature, and low oxygen fugacity, which is conducive to mineralization of Sn, Mo, and fluorite. Full article