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Carbonate rock strengthening techniques are widely used in cultural heritage preservations. Recently, there has been a growing interest in their application in the oil and gas sector to improve the hardness and stability of fracture surfaces compared to the predominant host mineral. In this study, two rock lithologies were treated (chalk and limestone) at ambient temperature using 0.9 M NaF and 0.1 M ZnSO4 solutions with the aim of improving the hardness of the rock surfaces by transforming their mineralogy. The carbonate rocks were characterized before and after treatment using various techniques to establish changes in their mineralogical compositions (using x-ray diffraction (XRD), scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM–EDS), and X-ray photoelectron spectroscopy (XPS) techniques) and petrophysical/mechanical properties (using Brinell test, impulse hammer, scratch test, steady-state gas injection). The reaction rates were monitored using inductively coupled plasma optical emission spectrometry and ion chromatography (ICP-OES) over a period of 2–5 days at 4–6 h intervals. It was found that the NaF treatment yielded a 4% and 6% improvement in indentation resistance of limestone and chalk, respectively. The ZnSO4 treatment produced the most notable improvement in rock hardness (presented by Young’s modulus), with a 21% improvement for chalk and a 17% improvement for limestone, respectively. The novel findings in this study suggest that NaF and ZnSO4 are potential carbonate rock strengthening agents that can be utilized in various industrial applications, such as, for example, solving conductivity reduction problems arising in hydraulic fractures due to rock softening.

Unusual hydrothermal native As-sulfide ± native Ag ± arsenide ± antimonide ± sulfosalt ore shoots and their co-genetic sulfide-fluorite-barite-quartz host veins, which are common in the region and in whole Central Europe, were investigated at three localities in the Schwarzwald, SW Germany, to understand the physico-chemical processes governing the change from a normal (= common) hydrothermal to an exceptional ore shoot regime. Based on fluid inclusions, the formation of the gangue minerals is the result of binary mixing between a NaCl-rich brine and a CaCl2-rich brine (both ~ 20 wt% NaCl aq.). This mixing correlation, major and minor fluid composition, formation temperature (~ 150 °C), and δ34S signature are identical (within error) in ore shoots and host veins. Thermodynamic modeling indicates that ore shoot formation must have resulted from a change in redox conditions by a local influx of a volumetrically minor reducing agent, probably hydrocarbons. The elemental content and the mineralogy of each ore shoot locality (Ag-As-rich: Münstertal; Ag–Ni-As-rich: Urberg; Ag–Ni-As-Sb-rich: Wieden) reflect the metal content of the binary mixed fluid, while mineral textures, successions, and assemblages are thermodynamically and, regarding sulfur, kinetically controlled. The formation of vein and ore shoot sulfides requires an addition of sulfide, most probably from the sulfide-bearing host rocks, because thermodynamic and kinetic reasons suggest that the two major vein-forming and metal-bearing fluids are not the source of the sulfur. The final ore shoot textures are influenced by later hydrothermal remobilization processes of As and Ag. This results in a number of sulfosalts, mostly proustite-pyrargyrite. Interestingly, the greater thermodynamic stability of Sb-endmember sulfosalts enables them to form even in As-dominated fluid systems., Eberhard Karls Universität Tübingen (1020)

The thermal stability of CeO2 nanomaterials can directly impact both the uniformity of the supported catalysts and the catalytic behavior of CeO2 itself. However, knowledge about the thermal stability of CeO2 is still deficient. Here, we conduct in-situ transmission electron microscopy experiments and theoretical calculations to elucidate the thermal stability of CeO2 nanomaterials under different environments. A sinter ( 700 °C) are observed within CeO2 nanoflowers under O2. The sinter firstly occurs among the nanoflowers’ monomers and then the sintered nanoparticles structurally decompose to tiny nanoparticles from the strain interface. Under a vacuum environment, the CeO2 nanoflowers firstly undergo a transition from cubic fluorite CeO2 to hexagonal Ce2O3, accompanied by the oxygen release. The Ce2O3 nanoparticles further atomically sublimate from the edges to the center under high temperatures. Theoretical calculation results reveal a considerably lower energy barrier for the structural decomposition under O2 and for the sublimation under vacuum. This work provides a perspective on the structural design and performance optimization of CeO2-based catalysts.

Fluorite is widely employed as a fluxing agent in metallurgical processes, inevitably leading to severe pollution. In this study, to promote the development of sustainable metallurgy, B2O3 is used as a fluxing agent of CaO–SiO2–MgO–Al2O3–TiO2–Cr2O3 slag, acting as a replacement for CaF2. The effect of B2O3 on the melting temperature and viscosity of CaO–SiO2–MgO–Al2O3–TiO2–Cr2O3 slag was investigated using a melting-point and melting-rate measurement instrument and a melting physical property comprehensive measurement instrument. Scanning electron microscopy was used to observe the microstructure of the precipitated phase, and X-ray diffraction was used to identify its phase composition. The results indicated that both the melting temperature and viscosity decreased with increasing B2O3 content. Moreover, B2O3 had a significant influence on the morphology of the precipitated phase, particularly for the shape and size of the precipitated particles. Accordingly, with the increase in the B2O3 content, the composition of the precipitated phase and the corresponding diffraction peak intensities changed. The results of this study provide a theoretical and technical basis for the comprehensive utilization of Cr-containing high-titanium melting slag.

We reported a rapid synthesis of Sm3+/Zr4+ co-doped Gd2Ti2O7 pyrochlore simulated nuclear wastes solidification by self-propagation plus quick pressing technique. With increment excess contents of Sm2O3 and ZrO2 from 0 to 10wt%, the phase composition of the products is a mixed phase of pyrochlore structure and defective fluorite structure by X-ray diffraction (XRD) analysis and Raman spectrum. In addition, the SEM results demonstrate the fracture surface and microstructure of Gd2Ti2O7-based pyrochlore. The densified pyrochlore waste form exhibits high bulk density of 5.56 g·cm−3 and vickers hardness of 11.20±0.2 GPa. The leaching tests show that the elemental leaching rates of Gd, Sm, and Cu after 42 days are 1.92×10−4, 1.51×10−4, and 3.90×10−3 g·m−2·d−1, respectively.

In this study, the use of eggshells was suggested as an adsorbent for fluoride removal, and their mechanism of fluoride removal was investigated. The eggshells underwent thermal treatment to improve their adsorption capacity; 800 °C was found to be the optimal temperature for treatment. Eggshells thermally treated at 800 °C (ES-800) were mainly composed of Ca (82.4%) and C (15.9%), and the peaks of ES-800 obtained from X-ray diffraction (XRD) corresponded to calcite, portlandite, and lime. Fluorine adsorption by ES-800 reached 70% of the equilibrium adsorption amount within 15 min and gradually increased until 24 h. The maximum adsorption capacity of ES-800 at pH 7 and 25 °C was 258.28 mg/g, which is 18 times larger than that of activated alumina; this is classified as the best available technology by the United States Environmental Protection Agency. Both enthalpy and entropy increased in the process of fluoride adsorption onto ES-800. Fluoride adsorption of ES-800 decreased from 59.16 to 11.85 mg/g with an increase in pH from 3 to 11. Fluoride adsorption decreased in the presence of anions, whose impact follows the order: HPO43- > HCO3- >> SO42- > Cl-. XRD, and X-ray photoelectron spectroscopy analysis revealed that fluoride removal was achieved by the formation of calcium fluorite (CaF2). Thus, it can be concluded that eggshells can function as highly efficient adsorbents for fluoride removal, replacing bone char and activated alumina; further, their adsorption capacity can be improved by thermal treatment.

Isothermal reduction experiments at 1400 °C, which used carbon-bearing pellets mainly made from Bayan Obo complex iron ore and pulverized coal, could effectively separate rare earth (RE) slag and iron. Different instruments were used to study the precipitation of RE slag and the growth behavior of the RE phase in RE slag during the process of cooling from 1400 °C. The experimental results show the presence of three main phases in the RE slag—the RE phase (Ca, Ce, La)5(SiO4)6F, cuspidine (Ca4Si2O7F2), and fluorite (CaF2), which precipitated at 1352 °C, 1218 °C, and 1045 °C, respectively. The RE phase grew along a specific growth track and finally manifested with a hollow hexagon morphology. The edge nucleation layer-by-layer growth model was applied to explain the formation of the hollow crystal structure. Further, the growth kinetics of the RE phase formation from molten slag were also described.

The source and evolution of ore-forming fluids is important to understand the genesis of Carlin-type gold deposit. Constraints on the source and evolution of ore fluid components by the conventional geochemical methods have long been a challenge due to the very fine-grained nature and complex textures of hydrothermal minerals in these deposits. In this study, we present the crush-leach analyzed solute data of fluid inclusion extracts within quartz, calcite, realgar, and fluorite from the Shuiyindong, Nibao, and Yata gold deposits in the Youjiang Basin, providing new insights into the source and evolution of ore-forming fluids. The results show that the high molar Cl/Br ratios up to 2 508 in fluid inclusion extracts are indicative of a contribution of magmatic hydrothermal fluids. Fluids mixing between basinal and magmatic-hydrothermal fluids are evident on the plots of Cl/Br versus Na/K ratios, showing that ore-stage milky quartz near the magmatic-hydrothermal fluids reflects magma origin of the ore-forming fluids, whereas late ore-stage drusy quartz and realgar near the defined basinal fluids suggest the later input of basinal fluids in late-ore stage. Although the predominately host rocks in Shuiyindong, Nibao and Yata gold deposit are bioclastic limestone, sedimentary tuff, and calcareous siltstone, respectively, the solute data of fluid inclusion extracts records they underwent the similar fluid-rocks reactions between the Na-rich magmatic hydrothermal fluids and the Ca- and Mg-rich host rocks. This study highlights the solute data of fluid inclusion extracts obtained by crush-leach analyses have the potential to fingerprint the source and evolution of ore-forming fluids of the Carlin-type gold deposit.

Huangshaping is a world-class skarn deposit hosting abundant W–Sn polymetallic mineralization in the Nanling Range, South China. Although the geochemistry of skarn-hosted mineral deposits has been extensively studied, the role of the prograde-to-retrograde stage transition in the enrichment and precipitation of metallic elements in high-temperature systems has received little study to date. Here, we analyzed garnet, scheelite, and cassiterite in high-temperature granite porphyry-related W–Sn polymetallic system of the Huangshaping deposit to investigate these processes. Three generations of garnet (Grt I, Grt II, and Grt III), two generations of scheelite (Sch I and Sch II), and two types of cassiterite (Cst I and Cst II) were distinguished with regard to their mineral associations, microscopic characteristics, and geochemical features. The results show that grossular–andradite garnet formed from Al-rich andradite (Grt I, Al2O3: 8.18 wt%) in the early prograde stage and pure Fe-andradite (Grt III, Al2O3: 0.15 wt%) in the late prograde stage. Mo-rich scheelite (Sch Ia, MoO3: 19.41 wt%) formed in the prograde stage and coexisted with Grt III, sharing the same REE patterns. A shift from HREE enrichment in Grt I to HREE depletion in Grt III reflects progressive uptake of REEs by secondary mineral phases. Grt III has the highest average contents of W (905 ppm), Mo (19 ppm), and Sn (5610 ppm), suggesting an enrichment of metallic elements at the end of the prograde stage. In contrast, Mo-poor scheelite (Sch II, MoO3: 0.63 wt%) co-crystallized with molybdenite and fluorite in the retrograde stage and shares similar REE patterns with the granite porphyry. Skarn mineralization at Huangshaping was a two-step process controlled by metamorphic stage. The prograde stage was characterized by high temperatures and fO2 and a Cl-rich fluid, and it resulted in enrichment of ore-forming elements with minor scheelite precipitation. The retrograde stage was characterized by lower temperatures and fO2 and a F-rich fluid, and it resulted in major precipitation of ore minerals (scheelite, molybdenite, and cassiterite). Dissolution–reprecipitation reactions played an important role in extraction of metallic elements from decomposing anhydrous skarn minerals and formation of ore minerals. A decrease in the high-field-strength element (HFSE) content of cassiterite from proximal skarn (Cst I) to distal skarn (Cst II) indicates declining temperature accompanied by precipitation of fluorite. This study examines the transition from the prograde stage to the retrograde stage in the Huangshaping deposit, and it provides insights into the genesis of other skarn W–Sn polymetallic deposits in the Nanling magmatic–tectonic–metallogenic belt.

Present study has been carried out to identify the processes controlling groundwater quality of Moradabad city, Uttar Pradesh. A total 188 groundwater samples were collected and analyzed for major ions in pre- and post-monsoon seasons of years 2012 and 2013. Analysis results showed higher concentration of Na, K, Cl, SO4 and NO3. LL diagram showed dominance of alkalis and Cl + SO4, in three sampling seasons except in post-monsoon 2012, when Na + K–Cl + SO4 facies is recorded in 50% samples. There is dearth of HCO3 complexes in the pre-monsoon season of 2012, and then, their appearance in the post-monsoon season with alkali bicarbonates being 50%. This trend is reversed in 2013. Groundwater composition showed potential impact of varying rainfall pattern suggesting that chemistry of groundwater is intimately related to meteorological parameters. To predict minerals and their reactivity in groundwater, saturation index (SI) was calculated for pre- and post-monsoon of 2012. Groundwater is highly under-saturated with respect to halite, sulphates of Ca and fluorite and super-saturated with respect to chalcedony, quartz and talc, and these minerals may possibly be precipitated out. Relationship of SiO2 with Cl and TDS gives unequivocal evidence of anthropogenic factors having significant effect in determining the chemical characteristics of groundwater. Groundwater chemistry of the area is sum total of factors, such as, meteorological, hydrological and lithological and a set of processes related to various domains of anthropogenic activities, where variation in intensity and distribution of rainfall seems to be one of the driving factors responsible for overall temporal variations in groundwater chemistry.

Bayan Obo ore contains mainly bastnaesite, monazite and associated iron, fluorite, calcite, dolomite, barite, and trace amount of columbite. Due to its complex mineral compositions and similar mineral properties, it is difficult to separate and obtain rare earth and fluorite concentrates with high purity by conventional magnetic separation and flotation. In this paper, a stepwise magnetic separation process comprised of wet permanent magnetic separation (PMS), wet electromagnetic separation (EMS), and superconducting magnetic separation (SCMS) was proposed to pre-concentrate iron, rare earth, and fluorite minerals from Bayan Obo ore. The results showed that iron, rare earth, and fluorite preconcentrates with high purity and low impurity content could be achieved, which might be helpful to shorten the technological process and improve the separation efficiency for the subsequent flotation of iron, rare earth, and fluorite minerals.

The effects of melt composition, temperature and pressure on the solubility of fluorite (CaF2), i.e., fluorine concentration in silicate melts in equilibrium with fluorite, are summarized in this paper. The authors present a statistic study based on experimental data in literature and propose a predictive model to estimate F concentration in melt at the saturation of fluorite (C F in melt Fl-sat ). The modeling indicates that the compositional effect of melt cations on the variation in C F in melt Fl-sat can be expressed quantitatively as one parameter FSI (fluorite saturation index): FSI=(3AlNM+Fe2++6Mg+Ca+1.5Na-K)/(Si+Ti+AlNF+Fe3+), in which all cations are in mole, and AlNF and AlNM are Al as network-forming and network-modifying cations, respectively. The dependence of C F in melt Fl-sat on FSI is regressed as: C F in melt Fl-sat =1.130−2.014·exp (1 000/T)+2.747·exp (P/T)+0.111·C melt H2O +17.641·FSI, in which T is temperature in Kelvin, P is pressure in MPa, C melt H2O is melt H2O content in wt.%, and C F in melt Fl-sat is in wt.% (normalized to anhydrous basis). The reference dataset used to establish the expression for conditions within 540–1 010 °C, 50–500 MPa, 0–7 wt.% melt H2O content, 0.4 to 1.7 for A/CNK, 0.3 wt.%–7.0 wt.% for C F in melt Fl-sat . The discrepancy of C F in melt Fl-sat between calculated and measured values is less than ±0.62 wt.% with a confidence interval of 95%. The expression of FSI and its effect on C F in melt Fl-sat indicate that fluorine incorporation in silicate melts is largely controlled by bonding with network-modifying cations, favorably with Mg, AlNM, Na, Ca and Fe2+ in a decreasing order. The proposed model for predicting C F in melt Fl-sat is also supported by our new experiments saturated with magmatic fluorite performed at 100–200 MPa and 800–900 °C. The modeling of magma fractional crystallization emphasizes that the saturation of fluorite is dependent on both the compositions of primary magmas and their initial F contents.

A series of Y2O3 fully stabilized HfO2 ceramics (Hf1−xYxO2−0.5x, x = 0.20, 0.24, 0.28, 0.32, 0.36 and 0.40) were synthesized by solid-state reaction at 1500 °C. The phase composition, thermal conductivity and sintering behavior at 1400 °C of the ceramic bulks were studied. The Hf1−xYxO2−0.5x ceramics were comprised of pure cubic phase with disordered fluorite structure. No phase transformation occurred in the ceramics with Y3+ doping concentration ranging from 0.24 to 0.36. Both Hf0.64Y0.36O1.82 and Hf0.6Y0.4O1.8 samples revealed the lowest grain growth rate when sintered at 1400 °C, indicating good resistance to sintering. However, the Vicker’s hardness and Young’s modulus after annealed for 96 h at 1400 °C for the Hf0.64Y0.36O1.82 sample were 8.97 and 200 GPa, respectively, much lower than those of the Hf0.6Y0.4O1.8 (14.51 and 237 GPa, respectively). The thermal conductivity of Hf1−xYxO2−0.5x first decreased and then increased slowly as the Y3+ content increased, and the associated mechanism was discussed.

The Sanjiu uranium ore field, located in the central of Zhuguangshan granitic batholith, is a newly discovered granite-related uranium ore field in South China. The main sulfide in the ore field is pyrite, which is closely related to uranium mineralization. The textures, major and trace elements, S–He–Ar isotopes compositions of pyrites in ores of different grade were observed and/or analyzed by optical microscope, scanning electron microscope, electron microprobe, laser ablation inductively coupled plasma mass spectrometry, and noble gas mass spectrometer (Helix-SFT). It is observed that these U-related pyrites are generally euhedral–subhedral with dissolution textures, anhedral variety with colloform texture, veinlet and fine particles, and the color of the associated minerals is mostly dark hue, such as purple–black fluorite, dark-red hematite, and dark-green chlorite, etc. The analytical results show that the average compositions of major elements in pyrite are FeS1.944. Pyrites are characterized by S-deficiency, low content of Co and Th, and Co/Ni > 1, which indicate that these ores are of low-temperature hydrothermal origin. We found that the higher the grade of ore, the more deficient in S, the more obvious negative δ34S, and the higher REE content (close to U-rich granitic pluton) of pyrite. The S–He–Ar isotopic compositions of various varieties of pyrites indicate that the ore-forming fluids mainly come from crust-derived fluids and mixed with mantle-derived fluids.

Located in the northeastern Hunan Province of South China, the Taolin Pb-Zn deposit is one of many metallic deposits structurally controlled by extensional faults in the central segment of the Jiangnan Orogen. The deposit occurs in a tectonic breccia zone between the Mufushan pluton and the Neoproterozoic Lengjiaxi Group. Field and microscopic observations reveal that the hydrothermal ore-forming processes at Taolin can be divided into five stages, from early to late: (1) coarse-grained quartz, (2) quartz + fluorite + chlorite + claybank sphalerite (Sp1) + galena + chalcopyrite, (3) quartz + barite + pale-yellow sphalerite (Sp2) + galena + chalcopyrite, (4) quartz ± chalcopyrite, and (5) fine-grained quartz, in which the stages 2 and 3 are regarded as the main Pb-Zn-forming events. LA-ICP-MS analyses show that Sp1 has higher contents of Fe, Mn, Co, In, and Sn, but lower contents of Ge and Sb, relative to the Sp2. Trace element concentrations of the sphalerite suggest a medium-low temperature hydrothermal event dominated in the Taolin deposit and that the ore fluids gradually decreased in the estimated average temperature and became relatively oxidized from stages 2 to 3. The δ18O values of ore fluids calculated from in situ analysis on the stages 2 and 3 quartz suggest the ore fluids are from a mixture of magmatic and meteoric waters. The δ34S values of sulfides/sulfates from stages 2 and 3 mineralization indicate a dominating magmatic affinity for sulfur. Further, lead isotope compositions for the stages 2 and 3 sulfides are similar to those of the Mufushan pluton, indicating that the ore metals may have been derived from the latter. We thus propose that the Taolin deposit precipitated from a medium-low temperature magmatic-hydrothermal system most likely related to the Mufushan pluton.

Groundwater quality samples from 33 wells were collected in the lower Ketar watershed (Ethiopia) to study its suitability for domestic and irrigation purposes. Samples were evaluated for major ions and physicochemical properties. In 58% of the samples analyzed, Ca2+ is the dominant cation and Na+ dominates the remaining 42% of the samples. Among the anions found during analyzation, HCO3− is the solo dominant ion in all the wells sampled. The order of the concentration of the major ions was Ca2+ > Na+ > Mg2+ > K+ for the cations and HCO3− > SO42− > Cl > NO3− for the anions. AquaChem analysis shows that Ca–HCO3 and Na–HCO3 are the major water types in the area. The analyses indicated that the dissolution of fluorite or fluorapatite is the possible source of the high fluoride concentration in the area. And, the interactions between water and rock and cation exchanges mainly determine the water quality. The suitability of the groundwater for use in irrigation was evaluated based on the salinity (EC), SAR, %Na, RSC, PI, KR, and the USSL Salinity diagram. The groundwater from most of the wells can be used for irrigation without any significant restriction except for a few of the wells downstream. Its suitability for domestic use was evaluated by comparing with the WHO standard limits. The parameters limiting the use of this groundwater for drinking purposes are F− (94%), HCO3− (45%), and Ca2+ (33%). All the remaining major cations and anions complied with the WHO standard limits for drinking.

Petrographic and mineralogical observations are corroborated with the hydrochemistry data to identify the exact lithological source of fluoride contamination in the central part of India. Groundwater samples (n = 57) representing both shallow and deep aquifers and lithological formations ranging from Archean to Late Cretaceous from central part of India were studied, where fluoride contamination in drinking water is causing a serious environmental health hazard. About 90% samples show high fluoride content than the maximum permissible limit of 1.5 mg/L. Fluoride concentrations in different rock formations such as granite gneisses, limestones, sandstones, and basalts were studied which shows maximum fluoride values of up to 4.9 mg/L. Several parameters (including Saturation Index and Gibbs’s plots) were evaluated to understand the factors which controlled the groundwater quality in the area. All signifies water–rock interaction as a major factor influencing composition of groundwater in both the seasons as well as support geogenic enrichment of fluoride. Low-temperature hydrothermal mineralization of fluorite in the limestone aquifers is responsible for the dissolution of fluorine in groundwaters with highest concentration. Moderate concentrations of fluoride up to 2.7 mg/L are observed in the basement granite gneisses. Our mineralogical studies recognized abundant fluor-apatite in granite gneiss aquifers, with high F−content ranging from 2.5 to 4.2 wt%, as a major contributor of fluoride in groundwaters. Rock-water interactions amplified in alkaline environments played an important role in the dissolution of fluorine in both the aquifers. Identification of main geogenic source of fluoride will be helpful for proper management of drinking water sources in the highly affected areas.

In this study, we aimed to investigate the structural, morphology and electrical properties of praseodymium and samarium co-doped ceria electrolytes, synthesized using the sol–gel method, for use as an electrolyte in low-temperature solid oxide fuel cell (LT-SOFC) applications. The X-ray diffraction result shows that all of the samples crystallized into a single-phase cubic fluorite form. The average relative densities of samples sintered at 1400°C is 97.9% of theoretical densities, indicating that they can be used as an electrolyte in LT-SOFC applications. A fascinating and maximum value of ionic conductivity $$1.94 \times 10^{ - 2}$$ S cm–1 and least activation energy (Ea = 0.55 eV) were found for the composition Ce0.8Sm0.1Pr0.1O1.9 at a temperature of 500°C. The ionic conductivity and activation energies of compositions Ce0.85Sm0.1Pr0.05O1.925 and Ce0.9Sm0.05Pr0.05O1.95 found at 500°C were ( $$1.41 \times 10^{ - 2}$$ S cm–1, Ea = 0.59 eV) and ( $$5.95 \times 10^{ - 3}$$ S cm–1, Ea = 0.64 eV), respectively. Moreover, all the Praseodymium and samarium co-doped ceria (PrSDC) samples conduct at lower temperature of 300°C. All these results confirmed that praseodymium and samarium co-doped ceria can be useful as a solid electrolyte in LT-SOFC applications.

Litho-geochemical characteristics of low and high fluoride (F−) groundwater along with hydrological processes were investigated to delineate its genesis and enrichment mechanism in a watershed sedimentary basin. In this study, groundwater F− concentration ranged from 0 to 20 mg/L with a mean and standard deviation of 2.8 and ± 3.7 mg/L, respectively. Out of N = 87, 63% of samples exceeded the World Health Organization (WHO) limit of 1.5 mg/L. The order of cationic and anionic dominance in groundwater samples with mean was found in decreasing order as Na+ > Mg2+ > Ca2+ > K+ and HCO3− > SO42− > Cl− > PO43− > NO3− measured in milligrams per liter. Groundwater chemistry changed from Ca-HCO3 to Na-HCO3 type and low to high fluoride as we moved from mountain foot towards the synclinal basin. Low fluoride groundwater reflected weathering, recharge, and reverse ion exchange processes with Ca–HCO3– and Ca–Mg–Cl–type water while high fluoride groundwater revealed base ion exchange, mixing, and desorption as dominant hydrological processes with Na-HCO3 and Na-Cl types of water. Gibb’s diagram showed rock weathering and mineral dissolution as the major geochemical processes controlling water chemistry with an insignificant role of evaporation in the semi-arid area. Fluoride was undersaturated with mineral fluorite, indicating fluoride in groundwater is released by secondary minerals. However, due to complex geological features, groundwater fluoride enrichment was affected by a broad-scale process across a wide area such as depth, residence time, and most important geomorphological units hosting the aquifer.

The article represents results of the study aimed on sensitivity of balsam poplar (Populus balsamifera L.) leaves to hydrogen fluoride airborne emissions in the vicinity of aluminum smelter. Widespread occurrence of poplar in urban land was one of the purposes to choose this plant as a research object. Reaction of poplar leaves on influence of hydrogen fluoride (HF) was investigated by ionometric technique, scanning electron microscopy-related method (SEM–EDS), X-ray diffraction analysis (XRD), and the thermodynamic modelling. The fluoride content in poplar leaves decreases with distance from the emission source. Leaves have signs of deterioration, e.g., chemical burns and necrosis, inside 2-km zone of the plant. In stomatal cells of poplar leaves, neogenic mineral fluorite (CaF2) was discovered. In sieve-tube elements of leaf phloem, a large quantity of secondary calcite (CaCO3) crystals was found. Ca2+ ions in enchylema react with F− that has released as part of airborne emissions from aluminum smelter. Result of their interaction is fluorite formation in stomatal cells of poplar leaves. Such fluorite is a mineral indicator of fluoride pollution in ground-level ambient air. Thermodynamic conditions of interaction of Ca2+ and F–, HCO3– and Ca2+ were estimated. The model of maintenance of phytochemical calcium barrier in the poplar leaves stomata in HF contamination was proposed and described.

The Jebel Lassel (JL) and Bou Izem (BIZ) Pb–Zn–F mineralizations are widely found in the Djamila nappe which is the dominant structural unit in the Kherrata area (northern Algeria). They are hosted respectively in Upper Cretaceous limestone and marly limestone and in dolomite from a Triassic complex at the contact of the thrust sheets. They occur in tension veins of different fillings and directions which can be divided into several types: (i) galena-calcite veins, (ii) sphalerite-calcite veins, and (iii) fluorite-calcite veins. The mineralizations consist mainly of galena or sphalerite, fluorite, and pyrite. Supergene oxidation minerals include cerusite, smithsonite, and iron oxides. Calcite, dolomite, and to a lesser extent quartz are the main gangue minerals. Fluid inclusions (FI) from Bou Izem fluorite samples occur in three phases at room temperature (L + V + halite) and homogenize by the dissolution of the halite crystal after the vapor bubble has disappeared. They are characterized by high salinities (28–39% wt% NaCl equiv.) and high homogenization temperatures (Th) (222–299 °C). Single-phase fluid inclusions are very abundant in quartz crystals from the Bou Izem borehole samples. These inclusions contain a CO2 and CH4 mixture and are nearly pure methane with less than 10% CO2. At the Jebel Lassel anticline, FIs in fluorite and sphalerite exhibit low ice-melting temperatures (– 11 and – 37 °C) and homogenization temperatures in the liquid phase of 103–174 °C. Primary FIs in calcite studied in late crystals associated with sulfides and fluorite have Th of 141–196 °C, with the final ice-melting temperatures (Tm(ice)), ranging from − 37 to − 8 °C, corresponding to salinity values ranging between 14 and more than 23.2 wt% NaCl equiv. δ13CV-PDB values of the calcite gangue, which vary between − 1 and + 2‰, indicate an inorganic carbon origin and are consistent with a marine origin of the host rocks and heritage. Most δ18OV-SMOW values of calcites are between + 16 and + 25‰ and indicate that the oxygen isotopic compositions of the fluids varied between + 5 and + 16 ‰. These values are typical of deep brines in sedimentary basins. δ34SV-CDT values vary from 9.5 to 9.8 (galena) and from 12.7 to 14.5‰ (sphalerite), and the high temperature of the fluid exclude all possibilities of bacterial sulfate reduction and indicate that the source of the sulfur is the thermochemical reduction of sulfate from Triassic evaporites (δ34S = + 15‰). The fluorite samples from JL and BIZ reveal that all patterns fit into two different types without (Eu) and (Ce) anomalies. Combined, geological, mineralogical, isotopic, and geochemical data of vein mineralization at Jebel Lassel and Bou Izem confirm the epigenetic character of the mineralization and enable us to classify them as Mississippi Valley-type deposits.

The A-type younger granite pluton and associated fluorite of Gabal El-Erediya, Eastern Desert, Egypt, have been investigated geologically and geochemically. Granites are genetically high-K-calc-alkaline syenogranites that show a high LREE/HREE ratio with noticeable negative Eu anomaly. Additionally, the visible tetrad pattern and negative Eu anomaly of the investigated granites point to fractional crystallization and fluid-melt interactions during the last stage of magmatic differentiation. They were probably generated within an extensional environment and were crystallized at temperature ~ 740 °C and pressure ~ 1.9 kbars. Two types of U-rich fluorite mineralizations were recorded including colorless and violet types. The hydrothermal fluids forming fluorites were related to late-stage differentiation of the felsic magma with a crystallization temperature ranging from 118 to 336 °C.

Hydrogeochemical methods were integrated to delineate the geochemical factors controlling fluoride (F-) contamination in groundwater at four sites in the districts of Lahore (Samada) and Kasur (Sari Chimba, Kot Maiga, and Chah Fatehwala) in Panjab province of Pakistan. Hydrochemical data and stoichiometric ratios indicate Na-Cl and Na-HCO3 as the dominant water types with silicate weathering influencing overall hydrogeochemistry of the study area. The groundwater F- concentrations ranged between 0.54 mg/L and 17.5 mg/L, with more than 70% samples having F- concentrations above the World Health Organization (WHO) provisional drinking water guideline (1.5 mg/L). Saturation indices determined that 100% samples were saturated with respect to calcite and 96% samples were undersaturated with respect to fluorite, indicating the influence of calcite precipitation on fluoride enrichment. A positive correlation was observed between fluoride with pH, Na+, and HCO3-, confirming that high fluoride concentrations were the result of weathering of silicate minerals and the exchange of OH- on clay surface under the alkaline pH conditions. The isotopic values of δ18O and δ2H in groundwater ranged from 9.14 to - 5.51‰ and 56.57 to - 39.5‰, respectively. The stable isotope data indicated the meteoric origin of groundwater with some evaporative effect, which is partly influencing groundwater quality such as high pH and salinity, as a result facilitating anion exchange (OH- for F-) on clays surface. The research indicates that the groundwater quality of the study area is not recommendable for drinking due to its high total dissolved solids (TDS) and elevated fluoride concentrations.

The defects in the ceria usually work as the active reaction sites in their industrial applications. In this article, we studied the formation and atomic process of the defects of ceria nanowires under heating by using in situ aberration-corrected transmission electron microscopy (Cs-TEM) method. With the temperature elevating, ceria nanowires are reduced and defects begin to appear and grow up. When temperature reaches 1,023 K, the defect morphology exhibits the rhombus or hexagon patterns, which are surrounded by {111} and {200} planes with lower surface energy, and the heated ceria still maintain the same cubic fluorite structure as their parent. It is also indicated that the formation of defects originates from the release of lattice oxygen and the volatilization of surface Ce ions. This work provides an important insight into designing ceria-based catalysts and ionic conductors.

Ceria-based electrolyte powders consisting of Fe2O3 and Sm2O3 double-doped ceria (Ce0.8Sm0.2−xFexO2−δ) were synthesized by a sol–gel method. The structure and electrochemical characters of the electrolyte materials have been studied. The phase formation of precursor powders was studied by the X-ray diffraction analysis (XRD). Microstructural and sinterability measurements were carried out on the sintered electrolyte discs. Electrochemical impedance spectroscopy (EIS) was used for estimate the electrochemical properties. The results displayed that crystalline cubic fluorite structured is formed after calcined at 700 °C. The electrochemical analysis results showed that the electrical properties of Ce0.8Sm0.2O1.9 (SDC) electrolytes substituted with certain Fe2O3 were superior and a total conductivity of 0.0263 S cm−1 could be obtained in the x = 0.1 sample. Therefore, it was concluded that co-doped with Fe2O3 and Sm2O3 could enhance the electrical conductivities of CeO2-based solid electrolyte, indicating that it is a potential electrolyte for SOFCs.

The newly discovered Baogudi gold district is located in the southwestern Guizhou Province, China, where there are numerous Carlin-type gold deposits. To better understand the geological and geochemical characteristics of the Baogudi gold district, we carried out petrographic observations, elemental analyses, and fluid inclusion and isotopic composition studies. We also compared the results with those of typical Carlin-type gold deposits in southwestern Guizhou. Three mineralization stages, namely, the sedimentation diagenesis, hydrothermal (main-ore and late-ore substages), and supergene stages, were identified based on field and petrographic observations. The main-ore and late-ore stages correspond to Au and Sb mineralization, respectively, which are similar to typical Carlin-type mineralization. The mass transfer associated with alteration and mineralization shows that a significant amount of Au, As, Sb, Hg, Tl, Mo, and S were added to mineralized rocks during the main-ore stage. Remarkably, arsenic, Sb, and S were added to the mineralized rocks during the late-ore stage. Element migration indicates that the sulfidation process was responsible for ore formation. Four types of fluid inclusions were identified in ore-related quartz and fluorite. The main-ore stage fluids are characterized by an H2O–NaCl–CO2–CH4 ± N2 system, with medium to low temperatures (180–260 °C) and low salinity (0–9.08% NaCl equivalent). The late-ore stage fluids featured H2O–NaCl ± CO2 ± CH4, with low temperature (120–200 °C) and low salinity (0–7.48% NaCl equivalent). The temperature, salinity, and CO2 and CH4 concentrations of ore-forming fluids decreased from the main-ore stage to the late-ore stage. The calculated δ13C, δD, and δ18O values of the ore-forming fluids range from − 14.3 to − 7.0‰, −76 to −55.7‰, and 4.5–15.0‰, respectively. Late-ore-stage stibnite had δ34S values ranging from − 0.6 to 1.9‰. These stable isotopic compositions indicate that the ore-forming fluids originated mainly from deep magmatic hydrothermal fluids, with minor contributions from strata. Collectively, the Baogudi metallogenic district has geological and geochemical characteristics that are typical of Carlin-type gold deposits in southwest Guizhou. It is likely that the Baogudi gold district, together with other Carlin-type gold deposits in southwestern Guizhou, was formed in response to a single widespread metallogenic event.

The defect fluorite titanium-doped yttrium niobate samples Y3Nb1−xTixO7−δ have been synthesized and investigated by the means of high-temperature X-ray diffraction, dilatometry, and thermogravimetry. Thermal expansion coefficients (TECs) as well as chemical expansion coefficients for material with 5, 10, and 15 mol% of titanium were determined. All investigated samples exhibit chemical contraction caused by Ti doping. The values of TECs obtained by two different methods show similar results, which suggests the isotropy of the polycrystalline ceramic. Thermogravimetric studies have shown that all of the compositions exhibit a mass increase upon being exposed to a humid air atmosphere. The total proton concentration calculated on the basis of these results was in the range of 0.1 mol%. Moreover, titanium content influences chemical expansion coefficient, water uptake, and protonic defects concentration, whereas it does not significantly affect the values of TECs.

We present 77 new granite whole-rock analyses from the Qattar and Gharib areas, Eastern Desert, Egypt. Both areas include a “normal” granite and either a hypersolvus (Gharib) or an almost plagioclase-free granite (Qattar) enriched in fluorite. According to earlier results, F influences element distribution in granitic melts forming complexes with specific elements as Nb, Ta, Ga, Hf, Th, Zn, Sn, whereas F excludes Ba and Sr. We use principal component analyses to split the granite into chemical groups allowing an unbiased study of the inter-group element distribution. This adds the heavy REEs and Y to the earlier lists of elements with an affinity for F. The light REEs show a decreasing affinity with decreasing atomic mass; fluorine separates Sm from Nd, whereas Zr follows La. Opposite to some, but in accordance with other earlier results, the ratio Nb/Ta is higher in the fluorite-enriched than in the other granite. Weak tetrad effects are present. Zircon in the hypersolvus granite is high in common lead. We suggest F to be instrumental for separating Pb2+ from Pb4+. Two hypotheses may explain the occurrence of the two contrasting granites: they have either different sources, or they are co-magmatic, but the magma was split into two discrete types. We apply the second hypothesis as our working hypothesis. The liquidus has a gentler slope with pressure than the diapir requiring crystallisation to be most important in the lower part of the magma chamber. Our hypothesis suggests that globules of magma, enriched in volatile components, form during crystallisation due to slow diffusion rates in the crystallizing magma. Elements accompanying F are distributed into this magma batch, which has a lowered density and viscosity than the rest of the magma due to its increased contents of volatile components. A mushroom-formed diapir rises, forming the hypersolvus (or almost plagioclase-free) granite. Due to an edge effect, it is concentrated close to the wall of the magma chamber. The size and form of the outcropping granite depend on the intersection of the diapir with the erosion surface. Fluorine only makes it possible to follow the process. The model may be generalised to explain the diversification of non-F enriched granite, since the buoyancy of a magma batch several thousand m3 in size has a much larger impact on the system than the small negative buoyancy of crystals or small crystal aggregates. A-type granite classified merely from its trace element content may form from separated F-enriched magma batches. This may be the reason for their high frequency in the Eastern Desert.

Commercial mold powders use a limited number of main mineral constituents, but may differ significantly in chemical composition. The main mineral raw materials of specimens investigated here are quartz, fluorite and free carbon, as well as wollastonite and carbonates. The investigations revealed the use of secondary raw materials like blast furnace slag, fly ash, glass scrap and phosphorous slag as further components. Since the formation of cuspidine was one major point of interest, the influence of the silica source on its formation was identified. A replacement of wollastonite by blast furnace slag reduced the temperature of the first precipitation of cuspidine by about 100 °C; the dissociation of sodium carbonate was lowered by ~ 40 °C. The lowest temperature of the first Na2CO3 dissociation could be achieved by using fluorine in combination with blast furnace slag. Cuspidine formation from the melt is further decreased if sodium and fluorine are both present. The use of glass scrap and phosphorous slag strongly reduced the temperature of first melt formation and enhanced cuspidine formation.

Recent exploration revealed a number of rare earth element (REE) deposits that are distributed along the Qinling Orogenic Belt, Central China. These deposits have an estimated total reserve of about 2 Mt. REE2O3, thus making this belt a world-class REE metallogenic province. Understanding the metallogenesis of the belt requires direct dating of REE minerals. In this study, LA-ICP-MS U-Th-Pb dating on bastnasite and monazite from the Huangshuian, Taipingzhen, and Miaoya deposits in different units of the belt was used to precisely determine the timing of the REE mineralization. The Huangshuian deposit in the north is a carbonatite-related Mo-(REE) deposit in which the REE minerals are closely associated with molybdenite. After correction for common Pb and excessed 206Pb decayed from 230Th, a weighted average 206Pb/238U age of 207 ± 4 Ma (n = 17; MSWD = 1.9) is obtained for bastnasite grains from this deposit. Such an age is slightly younger than that of the final collision (peak at 230–220 Ma) of the Qinling Orogenic Belt, thus indicating that the Mo-REE mineralization is likely related to a post-collisional extension setting. The Taipingzhen REE deposit in the middle contains sheet-like ore bodies composed of veins where bastnasite, the dominant REE mineral, is closely associated with quartz, fluorite, and barite. In situ bastnasite U-Th-Pb dating shows that the REE mineralization in this deposit has formed at 421 ± 7 Ma (n = 17; MSWD = 1.5), synchronous with extension-related magmatism in the region. The Miaoya deposit in the south is the largest one in the belt, and it is essentially a REE-mineralized syenite-carbonatite complex. In this deposit, the monazite grains are closely associated with major minerals of the syenites or carbonatites (e.g., K-feldspar or calcite), but commonly exhibit complex internal textures. Different domains of monazite yield two groups of U-Pb ages at 414 ± 11 Ma (n = 5; MSWD = 0.91) and 231 ± 2 Ma (n = 21; MSWD = 3.1), whereas the bastnasite has an age of 206 ± 4 Ma (n = 14; MSWD = 1.5). The early age of 414 Ma is obtained from homogenous monazite grains and in good agreement with zircon U-Pb ages of the Miaoya syenite-carbonatite complex, and thus is considered to represent the timing of the major REE mineralization in the deposit. The younger ages of 231–206 Ma are obtained from monazite grains with complex internal textures and bastnasite in late veinlets, thus recording secondary, consecutive REE remobilization events likely related to the compression process during formation of the Qinling Orogenic Belt. Our new U-Th-Pb ages, in combination with previously geochronological data, demonstrate that there are two episodes of REE mineralization at 440–410 Ma and 220–200 Ma in the Qinling Orogenic Belt.

Several samples of (U1−xNdx)3O8 with different Nd content were prepared by different process. After high temperature oxidation, the final oxidized products were found to be a mixture of small particles Nd-rich (U1−yNdy)O2+v phases and large particles Nd-poor (U1−zNdz)3O8−w phases by XRD and SEM analysis. This study indicated that (U1−xNdx)3O8 powder formed a solid solution firstly at 1100 °C or high. The recrystallization of this solid solution happened and the RE-rich fluorite phase formed concurrently when the temperature began to decrease. The present work will provide more information to understand the oxidation behavior of rare-earth doped U3O8 phase at high temperature.

In order to explore the radiation effects of Gd2Zr2O7 bearing multi-nuclides, the compounds with simulated typical waste after trialkyl phosphine oxides (TRPO) process were taken for this research. The pyrochlore-type compound (containing Zr4+, Mo6+, Ru4+, and Pd2+) were irradiated using 0.5 MeV He2+ ions at room temperature, with fluences ranging from 1 × 1015 ions/cm2 up to 1 × 1017 ions/cm2. The results discovered that the compound transformed from pyrochlore to fluorite phase after irradiation. Besides, a slight structural disordering and lattice swelling were observed. Furthermore, the microtopography of the irradiated ceramics was kept, and no aggregation of elements appeared on the He2+ ion irradiated surface.

Fault systems are zones of crustal weakness and are used as pathways for ascending hydrothermal fluids. One impressive example is the more than 150 km long Bavarian Pfahl system at the SW boundary of the Bohemian Massif. Dextral ductile shearing of Moldanubian basement has shaped a several hundred meter wide zone of mylonites and ultramylonites. This setting was reactivated under brittle conditions and infiltrated by fluids resulting in a multi-phase quartz lode. Structural analysis using scanning electron microscopy cathodoluminescence (SEM–CL) images has been carried out in combination with trace element and oxygen isotope analysis on quartz along the system. Three successive quartz phases have been distinguished due to their structural details and trace element contents. Cryptocrystalline quartz fabric in the first quartz phase results from crystallization from a silica gel, whereas in phases II and III, quartz precipitation is characterized by repeated fragmentation and sealing, visible due to strongly varying CL intensities. The δ18O of Bavarian Pfahl quartz decreases from 13.8‰ in the NW to 8.5‰ in the SE, whereas quartz from the close-by-situated Wolsendorf fluorite deposit shows δ18O between 15.9 and 18.5‰ (vs. SMOW). Flat shale-normalized rare earth element patterns point towards an upper crustal origin of the hydrothermal fluids. The southeastern part of the Bavarian Pfahl is interpreted to represent a deeper crustal level with higher mineralization temperatures (about 350 °C) compared to the rest of the Pfahl (

International audience; Natural radiation-induced red fluorescence of fluorite consists of two broad bands at 750 and 635 nm with very short decay times of 20.3 and less than 5 ns, respectively. The first one is connected to an M center compensated by Na, while the second is connected to an M+ center, possibly formed as result of the M center’s destruction by UV irradiation. The optically active centers in naturally irradiated fluorite responsible for red luminescence and purple color are different from one another. The most probable reason for the purple color is colloidal calcium and not the MNa center.

Oxygen vacancies in complex oxides are indispensable for information and energy technologies. There are several means to create oxygen vacancies in bulk materials. However, the use of ionic interfaces to create oxygen vacancies has not been fully explored. Herein, we report an oxide nanobrush architecture designed to create high-density interfacial oxygen vacancies. An atomically well-defined (111) heterointerface between the fluorite CeO2 and the bixbyite Y2O3 is found to induce a charge modulation between Y3+ and Ce4+ ions enabled by the chemical valence mismatch between the two elements. Local structure and chemical analyses, along with theoretical calculations, suggest that more than 10% of oxygen atoms are spontaneously removed without deteriorating the lattice structure. Our fluorite–bixbyite nanobrush provides an excellent platform for the rational design of interfacial oxide architectures to precisely create, control, and transport oxygen vacancies critical for developing ionotronic and memristive devices for advanced energy and neuromorphic computing technologies., Oxygen vacancies can impart interesting properties in complex oxides, but specific architectures designed to create high-density oxygen vacancies are largely unknown. Here the authors report a fluorite-bixbyite nanobrush platform to tune interfacial oxygen and show that an atomically well-defined heterointerface can induce charge modulation.

Natural fluorite, anhydrite and apatite under deep UV excitation exhibits several narrow emission bands in the spectral range of 225–300 nm with the strongest peaks at 230–240 nm and 260–290 nm and with half-widths of 20–30 nm. They are characterized by narrow excitation band peaking at 220 nm and very short decay times of 20–50 ns. Those spectral-kinetic parameters enable their interpretation as 4f5d–4f transitions in Pr3+ luminescence center. Such kind of luminescence has been studied extensively over the past several decades in synthetic phosphors, including those which are analogous to natural compounds, but it is the first time 5d–4f luminescence transitions of Pr3+ is being proved in minerals.

The Freiberg mining district in the Erzgebirge hosts three principal types of polymetallic veins. These are (1) the quartz-bearing polymetallic sulfide type, (2) the carbonate-bearing polymetallic sulfide type, and (3) the barite-fluorite-sulfide type. We investigated the genesis of each vein-type using Rb-Sr sphalerite geochronology, Sm-Nd fluorite geochronology, and Pb, Sr, and Nd isotope systematics of ore and gangue minerals. Field relationships and the Rb-Sr and Pb isotope systematics of sulfides from quartz-bearing polymetallic sulfide veins and carbonate-bearing polymetallic sulfide veins confirm their close genetic affiliation and yield a combined Rb-Sr errorchron age of 276 ± 16 Ma. The high mean squared weighted deviation (MSWD) value of 42 on the regression is considered to reflect initial isotopic heterogeneity, which is probably related to fluid-rock interaction during the hydrothermal mineralization process. Although some sphalerites from barite-fluorite-sulfide veins have strongly disturbed Rb-Sr isotope systematics, six sphalerites and one co-genetic fahlore yield a robust isochron age of 121.3 ± 4.2 Ma with an MSWD of 2.9. This age is supported by a fluorite Sm-Nd isochron age of 101 ± 18 Ma (MSWD = 1.3). The new ages and radiogenic isotope data place robust constraints on the long-held hypothesis that veins in the Freiberg district formed during two hydrothermal events. The Lower Permian age of first stage quartz-bearing polymetallic sulfide veins and carbonate-bearing polymetallic sulfide veins coincides with post-Variscan crustal reorganization and Rotliegend volcanism. The Mid-Cretaceous age of second stage barite-fluorite-sulfide veins coincides with opening of the North Atlantic Ocean during the break-up of Pangea.

The high-grade Th-U-Y zone is one of the numerous mineralized zones found in the El Garra El Hamra hydrothermally altered syenites in southwestern Egypt. It is characterized by the thorium minerals thorite and thorogummite, which are closely associated with xenotime-(Y). This zone of mineralization is localized in the eastern part of the El Garra El Hamra hydrothermally altered syenites. This zone does not relate to the first phase of syenites that appeared on the surface but is linked to the other, hidden phase of the syenitic body. Additionally, the fluids responsible for the mineralization of this zone belong to the late-stage hydrothermal event as well as the fault action due to the fact that it had continued reactivations for a long period of time. The studied mineralized zone also contains ceriopyrochlore-(Ce),(Ce,Ca,)2 (Nb,Ta)2O6 (OH), fluorite (CaF2) and barite (BaSO4), which are found in considerable amounts, whereas apatite (Ca5(PO4)3F) and chromite (FeCr2O4) are rarely found together with Fe-oxi-hydroxides (hematite and goethite) with a minor amount of jarosite (KFe33+(OH)6(SO4)2). Finally, the main constituent mineral in the zone is the pseudomorph perthite in addition to quartz, which is found as deformed crystals. A technological sample was collected from this zone and was found to assay 4.62 weight percent thorium (Th), 0.37 weight percent uranium (U) and 3.12 weight percent rare earth elements (REEs). From the chemical and mineralogical composition of the studied technological sample, the leachabilities of Th, U and REEs were investigated using sulfuric acid (H2SO4) agitation leaching and pug leaching methods. The latter was found to be preferred under the conditions of 0.54 ton H2SO4 per ton of altered syenite at 110 °C for two hours.

Carbonate gangue in historically important post-Variscan polymetallic Pb-Zn-Cu-Ag vein systems in the Upper Harz Mountains has elevated rare earth element contents (ΣREE+Y, 1500 ± 340 ppm; n = 16) in bulk samples. This enrichment is due to the occurrence of abundant micrometer-sized synchysite inclusions in calcite, identified via Raman spectroscopy. Calcite bulk analyses have roof-shaped PAAS-normalized REE patterns with a Eu peak but without Ce or Y anomalies and with a steeply dipping HREE pattern. Microbeam analysis (electron microprobe and LA-ICPMS) identifies these patterns as dominated by synchysite-(Ce–Nd) with strong Eu enrichment in the weight percent range and LREE/HREE fractionation (La/Lu ~ 100, PAAS-normalized). The synchysite component in calcite gangue is detected in polymetallic veins all over the Harz Mountains, which seems to be a diagnostic feature of the region and suggests a large-scale Mesozoic fluid system. However, the Upper (western) Harz systems with no fluorite have more elevated REE content, compared with the Lower (eastern) Harz fluorite-rich systems with less REE content. Carbonate gangue in the Upper Harz systems has homogeneous 87Sr/86Sri around 0.714 and eNdi of ~ − 9, while carbonate gangue in the Lower Harz systems has 87Sr/86Sri around 0.716 and eNdi of − 2 to − 5. Fluorite in the Lower Harz Mountains has strong positive Y anomalies and variable Eu anomalies at generally low REE abundances and no REE-mineral inclusions. Both Sr and Nd isotope compositions in the fluorite are very variable and indicate an open system (87Sr/86Sri, 0.710–0.718; eNdi, − 3 to − 17). The synchysite MREE enrichment in calcite gangue in the Upper Harz Mountains compares favorably with carbonatite-related LREE-dominated bastnasite from China and elsewhere and allows an interesting perspective as a by-product of Pb–Zn mining.

Rare-earth deposits associated with intrusive carbonatite complexes are the world’s most important source of these elements (REE). One of the largest deposits of this type is Maoniuping in the Mianning-Dechang metallogenic belt of eastern Tibet (Sichuan, China). In the currently mined central part of the deposit (Dagudao section), REE mineralization is hosted by a structurally and mineralogically complex Late Oligocene (26.4 ± 1.2 Ma, 40Ar/39Ar age of fluorphlogopite associated with bastnasite) hydrothermal vein system developed in a coeval syenite intrusion. Low-grade stockworks of multiple veinlets and breccias in the lower part of the orebody grade upwards into progressively thicker veins (up to 12 m in width) that are typically zoned and comprise ferromagnesian micas (biotite to fluorphlogopite), sodium clinopyroxenes (aegirine to aegirine-augite), sodium amphiboles (magnesio-arfvedsonite to fluororichterite), K-feldspar, fluorite, barite, calcite, and bastnasite. The latter four minerals are most common in the uppermost 80 m of the Dagudao section and represent the climax of hydrothermal activity. Systematic variations in the fluid inclusion data indicate a continuous hydrothermal evolution from about 230–400 °C (fluid inclusions in feldspar, clinopyroxene, and amphibole) to 140–240 °C (fluid inclusions in bastnasite, fluorite, calcite). Hydrothermal REE transport was probably controlled by F−, (SO4)2−, Cl−, and (CO3)2− as complexing ligands. We propose that at Dagudao, silicate magmas produced orthomagmatic fluids that explored and expanded a fissure system generated by strike-slip faulting. Initially, the fluids had appreciable capacity to transport REE and, consequently, no major mineralization developed. The earliest minerals to precipitate were alkali- and Fe-rich silicates containing low levels of F, which caused progressive enrichment of the fluid in Ca, Mg, F, Cl, REE, (SO4)2−, and (CO3)2−, leading to the crystallization of aegirine-augite, fluororichterite, fluorphlogopite, fluorite, barite, calcite, and bastnasite gradually. Barite, fluorite, calcite, and bastnasite are the most common minerals in typical ores, and bastnasite generally postdates these gangue minerals. Thus, it is very probable that fluid cooling and formation of large amount of fluorite, barite, and calcite triggered bastnasite precipitation in the waning stage of hydrothermal activity.

Bi0.85−xCa0.15ZrxO1.5−δ (0.12 ≤ x ≤ 0.24) oxygen ion conductors were synthesized by solid-state reaction method. Small quantities of CaZrO3 and Ca0.15Zr0.85O0.85 second phases were observed on the grain boundaries of the Bi0.85−xCa0.15ZrxO1.5−δ matrix with cubic fluorite structure. The lattice parameter a of Bi0.85−xCa0.15ZrxO1.5−δ lay within the range of 5.512 A to 5.525 A. The conductivity of all the Bi0.85−xCa0.15ZrxO1.5−δ samples increased with temperature. The Bi0.70Ca0.15Zr0.15O1.5−δ sample exhibited the highest conductivity of 0.05 S/cm at 750°C. The typical impedance spectra of the Bi0.85−xCa0.15ZrxO1.5−δ samples showed that the main resistance resulted from charge-transfer polarization at low temperatures, while the grain-boundary resistance dominated when the temperature was increased to above 600°C because of the CaZrO3 and Ca0.15Zr0.85O1.85 second phases appearing at grain boundaries.

Casting powders are commonly used in continuous casting of steels. The chemical composition of these powders is based on various oxides, carbonaceous materials and fluoride compounds. The purpose of fluorite (CaF2) addition is to control viscosity, fluidity temperature and cuspidine crystallization during casting. Unfortunately, fluoride compounds are lost in the vapour phase during the casting operations, due to the high vapour pressure of these compounds. In view of the environmental problems associated with the evaporation of fluoride from the casting powders, a kinetic study on the fluoride evaporation was carried out. Three commercial casting powders with different fluoride contents (between 2.6 and 10.6 mass%) were selected in this study. Powders characterization includes the melting behaviour determined by hot stage microscopy, the physical properties such as viscosity estimated by Fact Sage 7.1 and surface tension calculated on the base of contact angle measurements. The crystallization tendency of the samples was determined by microscopy observations on samples quenched from 1300 °C. The emission study includes thermal analysis (DTA–TG) tests. The different phases present in the system were predicted through thermodynamic simulation. The gaseous species predicted were: NaF, KF, (NaF)2, NaAlF4, KAlF4 and SiF4. It was possible to establish that the fluoride gases emissions occur when the samples present liquid phases. The type of fluoride gas is determined by the chemical composition of the casting powders, while the percentage of emissions depends on both the viscosity and surface tension of liquids.

UO2 pellets doped with 1, 5 and 10 mol% Th before and after oxidation were analyzed by using Raman spectroscopy to investigate the Th doping effect on the structural changes during oxidation of UO2. While the Raman spectra of all sample pellets showed a close-to-perfect fluorite structure before oxidation, those of oxidized (U1−yTh y )O2+x (0.03 ≤ x ≤ 0.06) pellets showed distinct defect structures after oxidation at 1150 °C with CO/CO2 = 0.001. The increasing relative ratio of first-order longitudinal optical modes of (U1−yTh y )O2+x with increasing doping levels should represent the defect structure due to the Th doping effect.

A series of (Gd,A)2(Zr,B)2O7 samples bearing various amounts of complex TRPO waste (0, 25 and 40 wt%) were irradiated with 0.5 MeV He2+ ions at fluences ranging from 1 × 1014 to 1 × 1017 ions/cm2. All the irradiated samples transformed from pyrochlore to disordered fluorite structure with micro-swelling. The irradiation tolerance of the (Gd,A)2(Zr,B)2O7 solid solutions weakened with increased TRPO waste content. However, no obvious amorphization was observed even in ceramics bearing the highest amount of TRPO waste. Raman spectroscopy revealed that the vibration frequencies of the atomic bonds changed, and the bands became broader due to irradiation induced disorder.

The co-reduction roasting and grinding magnetic separation‒of seaside titanomagnetite and blast furnace dust was investigated with and without fluorite addition at a reduction roasting temperature of 1250°C for 60 min, a grinding fineness of −43 μm accounting for 69.02wt% of the total, and a low-intensity magnetic field strength of 151 kA/m. The mineral composition, microstructure, and state of the roasted products were analyzed, and the concentrations of CO and CO2 were analyzed in the co-reduction roasting. Better results were achieved with a small fluorite dosage (≤4wt%) in the process of co-reduction. In addition, F− was found to reduce the melting point and viscosity of the slag phase because of the high content of aluminate and silicate minerals in the blast furnace dust. The low moisture content of the blast furnace dust and calcic minerals inhibited the hydrolysis of CaF2 and the loss of F−. Compared with the blast furnace dust from Chengdeng, the blast furnace dusts from Jiugang and Jinxin inhibited the diffusion of F− when used as reducing agents, leading to weaker effects of fluorite.

For application in nuclear waste management, it is essential to study the self-irradiation effect in long-term deep geological disposal repository. In this study, accelerated irradiation experiment was conducted on Nd2Zr2O7 pyrochlore matrix by using 0.5 MeV He2+ ions with fluences ranging from 1 × 1014 to 1 × 1017 ions/cm2. A series of results figure out that Nd2Zr2O7 matrix transforms from pyrochlore into fluorite after radiation experiment and some weak structural disordering is led with intensified irradiation. Moreover, the surface micrography shows slight changes after irradiation.

In this work, we have studied the structural behavior of Fluortie-type (F-type) Ce-based oxides of compositions $$\hbox {Ln}_{2}\hbox {Ce}_{2}\hbox {O}_{7}$$ ( $$\hbox {Ln} = \hbox {Pr}$$ , Nd and Eu). F-type oxides can be considered as multi-functional materials due to the deficiency of anions. $$\hbox {Pr}_{2}\hbox {Ce}_{2}\hbox {O}_{7}$$ (PCO), $$\hbox {Nd}_{2}\hbox {Ce}_{2}\hbox {O}_{7}$$ (NCO) and $$\hbox {Eu}_{2}\hbox {Ce}_{2}\hbox {O}_{7}$$ (ECO) were prepared by ethylene glycol-assisted sol–gel method. The structural investigation of these oxides was carried out by Powder XRD and Rietveld refinement. All the materials were found to crystallize in the cubic lattice with space group $$Fm{\overline{3}}m$$ . Raman spectra of these materials are reliable with their XRD data. The morphology and bandgap energy of all the samples were obtained from SEM and KM plot, respectively. The visible light photocatalytic performance of these oxides was examined against the degradation of methylene blue under ambient conditions. The photoluminescence property of the rare earth ions was also studied, and the color coordinates were calculated using CIE 1931 chromaticity. Synopsis Fluorite ( $$\hbox {AO}_{2}$$ , (a)) geometry can be explained as a face centered cubic arrangement of the cations with the anions filling all the tetrahedral spaces with $$Fm{\overline{3}} m$$ space group. Fluorite with one-eighth of anion deficiency leads to P-type oxides with space group $$Fd{\overline{3}}m$$ (b) and C-type oxides with space group Ia3 (c).

The large-scale uniform CeO2 hollow nanospheres with diameter of about 600 nm and rough surface have been successfully synthesized via a simple template-free hydrothermal technology. The obtained samples were examined by XRD, SEM, TEM, XPS, Raman scattering and UV–Vis spectra. The results show that the samples have a cubic fluorite structure of CeO2 with no crystalline impurity phase and many Ce3+ ions and oxygen vacancies exist in the surface of CeO2 sample. A red-shifting of the band gap is observed for the CeO2 hollow nanospheres contrasting with the bulk one, which is mainly attributed to the influences of the Ce3+ ions and oxygen vacancies.

The similar floatabilities of calcium minerals and the huge difference between scheelite and wolframite have resulted in difficulties during their separation by flotation in Shizhuyuan Mine. In this study, novel collectors, lead complexes of benzohydroxamic acid (Pb–BHA), were introduced to modify the surface properties of scheelite and wolframite, thereby effectively and selectively improving floatability. The Pb–BHA complexes are found to be selective for the separation of scheelite and calcium minerals with little use of depressants and enable the synchronous flotation of scheelite and wolframite. Hence, a novel flotation process was developed for the recovery of tungsten minerals. The process is simplified greatly, and the recovery is improved by almost 10%. Removing or decreasing the amount of water glass contributes to the improvement of tungsten and fluorite recovery and the circulation of water and reagents, which benefits the environment.