Search Results (95)

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

In this study, high-energy milled (HEM) samples of natural phosphorites from Estonian deposits were investigated. The activation was performed via planetary mill with Cr-Ni grinders with a diameter of 20 mm. This method is an ecological alternative, since it eliminates the disadvantages of conventional acid methods, namely the release of gaseous and solid technogenic products. The aim of the study is to determine the changes in the structure to follow the solid-state transitions and the isomorphic substitutions in the anionic sub-lattice in the structure of the main mineral apatite in the samples from Estonia, under the influence of HEM activation. It is also interesting to investigate the influence of HEM on structural-phase transformations on the structure of impurity minerals-free calcite/dolomite, pyrite, quartz, as well as to assess their influence on the thermal behavior of the main mineral apatite. The effect of HEM is monitored by using a complex of analytical methods, such as chemical analysis, powder X-ray diffraction (PXRD), wavelength-dispersive X-ray fluorescence (WD-XRF) analysis, and Fourier-transformed infrared (FTIR) analysis. The obtained results prove the correlation in the behavior of the studied samples with regard to their quartz content and bonded or non-bonded carbonate ions. After HEM activation of the raw samples, the following is established: (i) anionic isomorphism with formation of A and A-B type carbonate-apatites and hydroxyl-fluorapatite; (ii) solid-phase synthesis of calcium orthophosphate-CaHPO₄ (monetite) and dicalcium diphosphate-β-Ca₂P₂O₇; (iii) enhanced chemical reactivity by approximately three times by increasing the solubility via HEM activation. The dry milling method used is a suitable approach for solving technological projects to improve the composition and structure of soils, increasing soil fertility by introducing soluble forms of calcium phosphates. It provides a variety of application purposes depending on the composition, impurities, and processing as a soil improver, natural mineral fertilizer, or activator. Full article

This study investigated the distribution and source of heavy metals and dispersed elements in the high-salinity brine of Qarhan Salt Lake. The brine with an average total dissolved solid content of 332.22 g/L, dominated by Cl⁻ (216.41 g/L) and Mg²⁺ (44.76 g/L), indicated strong evaporation and dolomite dissolution. As (6.57 ± 3.59 μg/L) and Hg (0.48 ± 0.14 μg/L) showed uniform distribution while Li (69.66 mg/L), B₂O₃ (317.80 mg/L), and Zn (5.69 mg/L) were highly enriched, highlighting the resource potential and geochemical complexity. Correlation analysis revealed that water–rock interaction played a key role in element differentiation, with Sr and Ca²⁺/Cl⁻ showing strong positive correlations (r = 0.693/0.768), reflecting isomorphic substitution and dissolution. Meanwhile, Na⁺ and Mg²⁺/Ca²⁺ showed negative correlations (r = −0.732/−0.889), suggesting cation exchange and gypsum precipitation. The self-organizing map yielded four clusters of elements and positive matrix factorization model identified four sources; the elements in the Salt Lake brine mainly came from the river water supply, weathering and leaching of minerals, and dissolution of salt-bearing layers and were locally influenced by human activities. The research provided valuable insights for future sustainable development and the environmental protection of the region. Full article

Investigations of the synthesis of multicomponent coatings and their subsequent application to metal substrates to increase the wear resistance of materials is relevant for industry. Nickel compounds obtained from oxidized magnesia-iron nickel ores with a desorption rate of more than 94% were used to create Ni-MoO₃-WO₃ electroplating. Such composite samples formed from an aqueous alcohol solution reduced the content of sodium and ammonium chlorides. The annealing and dehydration of samples at a temperature of 725 °C in an air atmosphere made it possible to achieve the highest level of crystallinity. In this case, an isomorphic substitution of W atoms by Mo occurs, which is confirmed by electron paramagnetic resonance (EPR) spectroscopy studies. The invariance of the shape of the EPR spectrum with a sequential increase in microwave radiation power revealed the stability of the bonds between the particles. The surface morphology of Ni-MoO₃-WO₃ films deposited on an Al substrate is smooth and has low roughness. In this case, an increased degree of wear resistance has been achieved. Thus, a recipe for the formation of an electroplating with stable bonds between the components and increased wear resistance was obtained. Full article

Apatites are very important compounds of mineralogical and biological meaning. Apatites originated from the calcium hydroxy compound 3Ca₃(PO₄)₂·Ca(OH)₂ and potentially might form three series of isomorphic salts, derived from cationic substitutions in the positions of Ca(I) and Ca(II) ions in the core compound; anionic substitutions of phosphates; and substitutions of anions and very simple chemical entities instead of the hydroxyl group in channel locations. The energies coupled with the ion exchanges inside those three locations were studied using our original method resulting from the transformation of Braggs’ law. The energy changes resulting from the ion exchanges were studied in connection with either the ionic radii for the cations or ionic volumes for the anions. The same series were observed when the variabilities of energy were confronted with the variabilities in the sinus of diffraction angle Θ showing changes in momentum transfer. In particular, the relationships between the energy changes and the coupled changes in the universal crystallographic parameter d showed the surprising uniformity of all ion exchanges in the apatites. The incremental change in the Braggs’ d-parameter always demands the same change in the energy, with good approximation, independently of the location of the ion exchange. So, the isomorphism of the apatites is not triple but a uniform one at the energy level. Such an approach enables the estimation of the volume of the ion-□ (□-vacancies) agglomerates. The introduction of ions with greater volumes exerts the phenomenon of swelling of apatite cells, which can be quantitatively estimated. The dependence of diffraction spectra on the temperature allows for the determination of minimal values of crystallographic cell volumes and d parameters at the temperature of 0 K. In sum, the study of energies connected with the change of Bragg dimension d is a new and valuable method of insight into the behaviour of apatite crystals. Full article

In recent years, domestic research on the ion substitution behavior and chromaticity of the mineral composition of “Ya’an Green” remains insufficient, while there is almost no relevant research on “Ya’an Green” abroad. In this study, X-ray powder diffraction (XRD), electron probe microanalysis (EPMA), infrared spectroscopy (IR), ultraviolet–visible spectroscopy (UV-Vis), and colorimetry were employed. The results indicate that the green and yellow matrices of “Ya’an Green” are primarily composed of muscovite, with rutile also present in the yellow matrix. In contrast, the white–green samples are mainly composed of quartz, with muscovite as a secondary mineral. Additionally, it was observed that the (004) crystal plane of muscovite exhibits a peak shift to lower 2θ angles, attributed to the substitution of Al³⁺ by ions with larger radii, such as Ba²⁺, Cr³⁺, and Fe²⁺, leading to an increase in unit cell parameters and a consequent shift in the peak to lower wavenumbers. The main elements of “Ya’an Green” are Al, Si, and K, with minor elements including Na, Fe, and Cr. Furthermore, Mg²⁺, Ca²⁺, Ti⁴⁺, Cr³⁺, and Fe²⁺ in the samples can substitute for Al³⁺ through isomorphic substitution. The infrared spectrum of muscovite in the ‘Ya’an Green’ sample shows three typical absorption peaks, 422 cm⁻¹ and 513 cm⁻¹ caused by Si-O bending vibration, 697 cm⁻¹ and 837 cm⁻¹ caused by Si-O-Al vibration, 948 cm⁻¹ caused by O-H bending vibration, and 3647 cm⁻¹ caused by O-H stretching vibration. The peak at 837 cm⁻¹ exhibits varying degrees of shift due to the substitution of Al³⁺ by ions with larger radii. The ultraviolet–visible spectra display two broad absorption bands at 422 nm and 615 nm, which are caused by Cr³⁺ transition, indicating that Cr is the chromogenic element responsible for the green color. A correlation was observed between the Cr³⁺ content and the hue angle h in “Ya’an Green” samples: the higher the Cr³⁺ content, the closer the hue angle is to 136^°, resulting in a darker green color, while lower Cr³⁺ content leads to a deviation from the dark green hue. This study establishes for the first time the correlation between the mineral composition of ‘Ya’an Green’ and its chromatic parameters and explores the linear relationship between its color and the number of color-causing elements and elemental substitution, which provide data support and theoretical models for the study of the color of seal stones. Full article

Carbonaceous shale has garnered significant interest as a viable alternative source of rare earth elements (REEs) besides conventional REE-bearing ores. This study characterized rare earth element + Yttrium+ Scandium (REYs) enrichment in the 11 core samples of carbonaceous shale (7) and coal (4) collected from Arnot Mine. Major elements of the studied carbonaceous shale (CS) and coal showed high amounts of SiO₂, Al₂O₃, and Fe₂O₃, indicating a high content of aluminosilicate and iron-rich minerals. The plots Na₂O + K₂O against SiO₂ suggested alkali granite, granite, and granodiorite provenance sources for the studied shale and coal. The samples showed enrichment in low and heavy rare elements crystallized from a low potassium tholeiitic and medium calc-alkaline magma based on the plots of La_N/Yb_N and K₂O vs. SiO₂. The mineralogical and maceral analysis revealed the dominant presence of kaolinite (15%–45%), and it was suggested as the cation exchange site resulting from the isomorphous substitution of Al³⁺ for Si⁴⁺. Additionally, siderite was suggested as one of the REY hosts due to the Fe³⁺ site forming a complex with the REE³⁺ ions. Furthermore, the samples were classified as lignite to sub-bituminous coal category with dominant minerals including kaolinite, quartz, and siderite. The outlook coefficient (Coutl) of REY in CS revealed a promising area for economically viable, having two enrichment types, including low (La, Ce, Pr, Nd, and Sm) and heavy (Ho, Er, Tm, Yb, and Lu). The Eu_N/Eu_N* and Ce_N/Ce_N* ratio for the current studied samples exhibited a weak negative to no anomaly, and most of the studied samples were characterized by distinctive positive Gd anomalies derived from sediment source regions weathered from alkali granite, granite, and granodiorite provenance formed from a low potassium tholeiitic and medium calc-alkaline magma. Full article

During the development of the disposal concept in a crystalline massif of the Russian Federation, a question arose regarding the selection of the most suitable types of bentonite for a buffer layer. Data on the composition, structure, surface, and adsorption properties of four promising deposits have been obtained. The correlations between genesis and specific surface area (SSA) revealed in this study indicate that bentonites of volcanogenic-sedimentary origin have lower SSA in comparison with those of sedimentary and hydrothermal origin. The main contribution to the charge of the 2:1 layer is made by isomorphic substitutions in the tetrahedral sheet, which directly affects the sorption properties of bentonites. The influence of smectite structure on adsorption properties have been described. In particular, the dependencies between the layer charge and cation exchange capacity (CEC) have been analyzed. At the same time, the research indicates that, unlike the CEC, the specific surface area of a deposit is determined by its geological history. Special attention is being paid to refining methodological approaches for deriving crystal chemical formulae of smectites, which will be needed in the future for modelling changes in bentonite over a long-term perspective. Full article

Discovered within the North Himalayan Metallogenic Belt (NHMB), the Zhaxikang Pb–Zn–Ag–Sb deposit stands as the sole super-large scale ore deposit in the region. This deposit holds significant quantities of Pb and Zn (2.066 million tons at 6.38% average grade), Ag (2661 tons at an average of 101.64 g/t), and Sb (0.235 million tons at 1.14% average grade), making it one of China’s foremost Sb–polymetallic deposits. Stibnite represents the main carrier of Sb in this deposit and has been of great attention since its initial discovery. However, the trace element composition of stibnite in the Zhaxikang deposit has not yet been determined. This study carried out an analysis of the distribution patterns and substitution processes of trace elements within stibnite gathered from the Zhaxikang deposit, aiming to provide crucial information on ore-forming processes. Utilizing high-precision laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), we discovered that the studied stibnite is notably enriched in arsenic (~100 ppm) and lead (~10 ppm). Furthermore, the notably consistent time-resolved profiles suggest that elements such as Fe, Cu, As, In, Sn, Hg, and Pb predominantly exist as solid solutions within stibnite. Consequently, it is probable that the enrichment of Cu, Pb, and Sn in stibnite is due to isomorphic substitution reactions, including 3Pb²⁺↔2Sb³⁺, Cu⁺ + Pb²⁺↔Sb³⁺, and In³⁺ + Sn³⁺↔2Sb³⁺. Apart from that, Mn, Pb, and Hg with the spiky signals indicate their existence within stibnite as micro-inclusions. Overall, we found that the trace element substitutions in stibnite from the Zhaxikang Pb–Zn–Ag–Sb deposit are complicated. Incorporations of trace elements such as Pb, Cu, and In into stibnite are largely influenced by a variety of factors. The simple lattice structure and constant trace elements in studied stibnite indicate a low-temperature hydrothermal system and a relatively stable process for stibnite formation. Full article

To characterize the trace-element characteristics of chrysoberyl, we studied twenty-six chrysoberyl samples from various localities by using laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS), photoluminescence (PL), and ultraviolet–visible–near-infrared (UV–Vis–NIR) spectroscopy. Chemical analysis has confirmed the existence of trace elements, including Fe, Ti, Ga, Sn, B, Cr, and V. The phenomenon of ionic isomorphic substitution frequently occurs at lattice sites within chrysoberyl. Notably, the isomorphic substitution of Al³⁺ in octahedral sites is significant, with the primary substituting elements being Fe, Ti, Cr, V, Ga, and Sn. The PL spectra of chrysoberyl samples exhibit sharp peaks at 678 and 680 nm, which are attributed to Cr³⁺, even in samples in which the Cr concentration is below the detection limit of LA-ICP-MS. This demonstrates the high-sensitivity feature of PL spectroscopy. The UV–Vis–NIR spectra of chrysoberyl samples consistently exhibit a band at 440 nm, and strong double narrow bands near 367 nm and 375 nm are observed. These spectral features are associated with Fe³⁺ chromophores—specifically, Fe³⁺-Fe³⁺ pairs or clusters and Fe³⁺ ions, respectively. By combining LA–ICP–MS analysis and PL mapping on a sample exhibiting color zoning, it has been found that the darker sections contain a higher concentration of Cr compared to the lighter sections, while the concentrations of other elements remain largely consistent. In other words, subtle variations in Cr concentration may be the underlying cause of color zoning in chrysoberyl. Full article

Zheshengite (IMA2022-011), Pb₄ZnZn₂(AsO₄)₂(PO₄)₂(OH)₂, is a new mineral from Sanguozhuang Village in the eastern Dongchuan Copper Ore Field, Yunnan Province, China. The new mineral is named after Zhesheng Ma (1937–). Zheshengite occurs as prismatic single crystals with chisel-like terminations on hemimorphite, with crystal sizes ranging from 0.02 to 0.05 mm. It is a brittle mineral with irregular fractures, a Mohs hardness of 2½ to 3, perfect cleavage on {011}, and a calculated density of 6.26 g/cm³. The empirical formula of zheshengite, based on 18 O atoms per formula unit, is (Pb_4.12Ca_0.01)_∑4.13(Zn_0.83Cu_0.23Fe_0.04)_∑1.10Zn_2.00[(As_0.90P_0.10)_∑1.00O₄]₂[(P_0.94Si_0.01)_∑0.95O₄]₂(OH)₂. Zheshengite exhibits a triclinic structure (space group P−1, no. 2), with unit-cell parameters: a = 4.7746(4) Å, b = 8.4920 (7) Å, c = 10.4056 (8) Å, α = 97.087 (7)°, β = 101.060 (7)°, γ = 92.996 (7)°, V = 409.66 (6) ų, and Z = 1. As a member of the dongchuanite group, zheshengite features a dongchuanite-type structure. This study reveals the impact of As–P isomorphic substitution on unit-cell parameters in the dongchuanite group, identifying correlations between As content and changes in parameters a and V, which may serve as diagnostic indicators for dongchuanite group minerals. In addition, the structure studies of zheshengite may have implications for environmental protection. Full article

New data on the crystal structure, chemical composition, and nature of extra-framework components of the orthorhombic sodalite-group mineral vladimirivanovite were obtained using chemical and single-crystal X-ray diffraction data as well as infrared and Raman spectroscopy. The crystal structure of vladimirivanovite is based on the sodalite-type aluminosilicate framework with ordered Al and Si atoms. Sodalite-like cages are mainly occupied by Na⁺ and Ca²⁺ cations and (SO₄)²⁻ anions. It was shown that vladimirivanovite is characterized by significant variations in the content of extra-framework polysulfide groups (S₃^•−, S₄), as well as other neutral molecules (H₂O and CO₂), the presence of which in the structure is the main cause of structural modulations and the orientation disordering of sulfate anions. Three samples with different S₃^•−:S₄ ratios were studied. All of them are orthorhombic (space group Pnaa) with the unit-cell parameters a ≈ 9.1, b ≈ 12.9, and c ≈ 38.6 Å; Z = 6. The general crystal-chemical formula of vladimirivanovite is (Na⁺_6.0–6.4Ca²⁺_1.5–1.7)(Al₆Si₆O₂₄)(SO₄²⁻,S₃^•−,S₄)_1.7–1.9(CO₂)_0–0.1·nH₂O (n = 1–3), where the S₄ molecule occurs in different conformation states. Full article

Chromium-substituted aluminophosphate (CrAPO-5) with the AFI crystal structure was prepared for the first time by using microwave conditions at the stage of gel formation and crystallization. This approach allowed the reduction of the time required for the synthesis of CrAPO-5 from 60–70 h to 6 h. CrAPO-5 metal aluminophosphate prepared by microwave-assisted synthesis is studied by UV-visible and IR spectroscopy and X-ray photoelectron spectroscopy. The material is characterized by the presence of Cr³⁺ and Cr²⁺ ions in the framework with predominating Cr³⁺ ions introduced via isomorphous substitution, as well as some minor amounts of extra-framework Cr³⁺ species, which are present presumably in the state of α-Cr₂O₃. The latter species can be partially reduced to Cr²⁺ species in the presence of CO or H₂. XPS study of CrAPO-5 revealed the presence of Cr³⁺ ions in the framework. A TPR experiment showed that the reduction of chromium starts at about 450–500 °C. Full article

Powdered layered double hydroxide (CaFe-LDH) was synthesized via hydrothermal co-precipitation, demonstrating successful preparation upon characterization. Subsequently, experiments were conducted to assess its efficacy in immobilizing divalent cadmium (Cd(II)). The findings substantiated the effectiveness of CaFe-LDH in immobilizing Cd(II) within soil. Various influencing factors, including LDH dosage, pH, and soil heavy metal concentration, were systematically investigated, revealing CaFe-LDH’s superiority in Cd(II) immobilization. Notably, the leaching concentration of Cd(II) was notably reduced from 142.30 mg/L to 32.99 mg/L, with a maximum adsorption capacity of 31.10 mg/L, underscoring the significant role of CaFe-LDH in Cd(II) removal. Furthermore, the stability of CaFe-LDH was confirmed via toxicity characteristic leaching procedure (TCLP) experiments and plant potting tests. In-depth analysis of the immobilization mechanism through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM) elucidated isomorphous substitution and surface adsorption as the primary mechanisms responsible for Cd(II) immobilization in contaminated soils. Additionally, isomorphic substitution and adsorption onto oxygen-containing functional groups were observed. This comprehensive study underscores the promising potential of CaFe-LDH in immobilizing Cd(II) in contaminated soil. With its commendable immobilization properties and recyclability, CaFe-LDH emerges as a promising solution for remediating heavy-metal-contaminated soils. Full article

The Jinchanghe Pb-Zn polymetallic deposit is a representative distal skarn deposit in the Baoshan block. Due to limited research on the sources of ore-forming metals and trace elemental geochemistry of sulfides, the sources and mineralization environments of the Jinchanghe skarn Pb-Zn polymetallic deposit are still controversial. In this study, copper and sulfur isotopes and trace elements of sulfides from the Jinchanghe Pb-Zn polymetallic deposit were analyzed to reveal the sources of ore-forming materials and the ore-forming environments. The trace elemental analysis results show abundant Co, Ni, Mn and Se elements, and less As, Tl and Sb elements dominantly enter pyrite by isomorphic substitution, except for some Zn and Cu that occur as sulfide inclusions in Py1. Abundant Fe and Mn elements could substitute Zn to enter the sphalerite crystal lattice by the isomorphic substitution mechanism of (Fe²⁺ + Mn²⁺) ↔ 2Zn²⁺, and less Ag and Sb elements could enter the sphalerite by the isomorphic substitution mechanism of (Ag⁺ + Sb³⁺) ↔ 2Zn²⁺. The Cu-S isotopic and trace elemental compositions jointly suggest that the Jinchanghe distal skarn Pb-Zn polymetallic deposit formed from magmatic hydrothermal fluids with a sedimentary host-rock contribution, under mesothermal conditions (260 °C on sphalerite). Full article