Search Results (171)

The Damiao titanomagnetite deposit on the northern margin of the North China Craton is a typical Fe-Ti-P polymetallic ore with significant deep resource potential. However, the mineralogical factors controlling its beneficiation remain poorly quantified. This study integrates multi-element analysis, chemical phase analysis, XRD, EPMA, and MLA to systematically characterize the ore’s chemistry, mineralogy, element deportment, grain size, dissemination, and liberation. Results show that Fe (25.81% TFe), Ti (6.50% TiO₂), and P (0.95% P₂O₅) are the main valuables. Fe is mainly in magnetite (59.53%), Ti in ilmenite (48.90%) and rutile (33.89%), and P almost entirely in fluorapatite. Magnetite, ilmenite, apatite, and pyrite are coarse-grained and achieve >80% free + rich intergrowths at 60% passing −0.074 mm, while rutile is fine and poorly liberated, representing the key titanium bottleneck. Silicate-bound iron (28.07% of Fe) causes irreversible loss; Ca-gangue (>20%) and chlorite slimes interfere with flotation. A staged flowsheet—primary grinding, magnetic separation, regrinding of rough concentrate, desulfurization, and sequential flotation—is proposed. This work provides a mineralogical basis for process optimization and offers references for similar deposits. Full article

The magmatic Ni-Co-Cu mineralization in the Iken deposit in the central part of the Kun-Manie complex, Amur Oblast, Russia, hosted by an olivine-bearing websterite, is of a low-sulfide type. The fine-grained disseminations of base metal sulfides (BMS), dominantly pyrrhotite, pentlandite (a major source of Ni of industrial importance), and chalcopyrite, are followed by a scarce Pd-Pt-Ag mineralization. Elevated contents of Al in orthopyroxene (mean 2.78 wt.% Al₂O₃) along with Al–Na enrichment in clinopyroxene (diopside; mean 5.10 wt.% Al₂O₃) are associated with highly aluminous compositions of low-chromium members of the spinel–hercynite series. High levels of TiO₂ in kaersutite and titanian phlogopite also reflect a pronounced degree of fractionation of the ore-forming melt. Minor portions of sulfide melt are distributed evenly as a result of immiscibility at advanced stages of orthopyroxene crystallization, after the formation of olivine. Differentiated grains of droplet-like BMS largely settled in situ close to grain boundaries of orthopyroxene or occupied interstitial spaces of pyroxenes and olivine in association with spinel–hercynite and fluorapatite. A combination of late saturation in S with relatively quick cooling rates of the hypabyssal body prevented the effective settlement and accumulation of sulfide droplets in the ore zone. The well-developed lamellae of troilite (Fe₅₀S₅₀) exsolved from the host pyrrhotite Fe₄₈S₅₂ during subsolidus cooling, as a consequence of a low-temperature reaction triggered by a sudden drop in fO₂. An influx of mantle-derived fluid bearing CO₂, CO, and CH₄ with the rising magma could be the primary cause of the fO₂ reduction. Also, graphite-bearing metasedimentary rocks could have been assimilated. Tiny grains of minerals of noble metals (moncheite and merenskyite with essential amounts of melonite component, sperrylite, hessite, alloy Au_63.2Ag_36.8, and argentopentlandite) deposited late in a fluid-enriched medium under submagmatic conditions. Full article

Dental caries remains the most prevalent chronic disease worldwide, yet early enamel lesions are reversible if managed with appropriate remineralizing agents. This narrative review synthesizes current evidence on remineralizing agents, their mechanisms of action, and clinical applications, with a focus on dental materials used in preventive and minimally invasive dentistry. Traditional fluoride-based approaches enhance remineralization through fluorapatite formation; however, their effectiveness is limited when calcium and phosphate bioavailability is insufficient. Biomimetic agents, including casein phosphopeptide–amorphous calcium phosphate (CPP-ACP), bioactive glasses, tricalcium phosphate, and nano-hydroxyapatite, provide these bioavailable ions and demonstrate superior performance under challenging clinical conditions. Emerging therapies such as probiotics, photodynamic therapy, and laser-assisted mineralization show promise but require further clinical validation. Based on the primary mechanism of action, an original classification of remineralizing agents is proposed, grouping them into fluoride-based agents, calcium-phosphate systems, nanotechnology-based systems, biofilm modifiers, biomimetic and emerging systems, and adjunctive antimicrobial therapies. The review concludes that bioavailable calcium represents a critical limiting factor in remineralization under certain conditions, and that combination protocols incorporating multiple remineralizing agents, tailored to individual patient risk profiles, achieve superior outcomes compared to single-agent approaches. Clinicians are encouraged to adopt minimally invasive, patient-tailored remineralization strategies that arrest lesions before cavitation, preserving natural tooth structure and reducing the lifelong restorative burden. Full article

Most existing dental restorative materials exhibit limited bioactivity, insufficient acid resistance, and poor mechanical compatibility with natural tooth structures. This study involved an in vitro approach in which a biomimetic fluoride-modified functionally gradient dental restorative material was prepared from sol–gel-derived mesoporous silica through mineralization induced via SBF solution. They synthesized bioactive restorative materials by introducing silica into a simulated body fluid (SBF) for biomimetic mineralization and generating hydroxyapatite on the silica surface. XRD, FTIR, SEM, and EDS analyses confirmed the presence of hydroxyapatite and fluorapatite-like phases. The results showed statistically significant improvements (p < 0.05) in the mechanical properties. The surface hardness of the developed restorative system ranged from 214 HV for the prepared silica to 392 HV for the fluoride-modified specimens. Biomimetic mineralization and fluoride modification increased the shear bond strength to dentin substrates from 9.2 MPa to 21.4 MPa and the wear from 12.8 mg to 3.6 mg, respectively. Acid resistance evaluation also showed that the specimens with fluoride modification had the highest value of hardness retention (92.1%) after acid resistance due to the formation of chemically stable and dense apatite-rich layers on the surface. The functionally graded structure demonstrated a partial biomimetic resemblance to certain hierarchical and functional characteristics of natural dental tissues under in vitro conditions. In vitro studies on bioactivity, mechanical properties, and resistance to acidic environments of the synthesized restorative showed promising results for future dental restoration applications. Full article

This study investigates Cambrian and Sinian carbonate outcrops in the Tarim Basin using 19 stratigraphically diverse rock samples. Through integrated X-ray diffraction mineralogical analysis, triaxial compression testing, and Brazilian splitting experiments, we systematically characterized rock mechanical properties and their correlations with microscopic mineral constituents. Key findings demonstrate remarkably distinct mechanical properties across formations: vuggy dolomites from the Xiaqiulitage formation exhibit the lowest compressive strength (minimum 200.0 MPa) and tensile strength (3.85 MPa), while the Yuertusi formation’s Y5 layer dolomites achieve exceptional tensile strength (21.69 MPa). Mineral composition fundamentally controls rock strength: dolomite or quartz concentrations exceeding 90% significantly enhance strength, whereas calcareous minerals (calcite, fluorapatite) degrade mechanical integrity. Most specimens display pronounced brittle failure characteristics; uniquely, basal dolostones of the Awatage formation exhibit distinctive plastic deformation. This research elucidates the synergistic effects of tectonic history, mineral assemblages, and microtextural attributes on rock mechanical behavior, providing critical theoretical underpinnings for deep carbonate reservoir development in overpressured basins. Full article

Understanding the differences between synthetic and natural hydroxyapatite under conditions that mimic the oral environment, particularly the demineralization and remineralization processes of dental enamel, is essential for assessing their suitability as enamel models in biomineralization studies. The present study aims to systematically compare the structural, chemical, and morphological properties of well-crystallized synthetic carbonated hydroxyapatite (CHA) and natural non-biogenic hydroxyapatite (HA) before and after exposure to solutions with demineralizing and remineralizing activity. Two highly informative surface characterization techniques—X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM)—were employed to examine the resulting surface changes. In addition, powder X-ray diffraction and infrared analyses were used to characterize the initial samples. Demineralization was induced using a lactic acid-based solution, while remineralization was performed through a two-step treatment involving polycarboxybetaine followed by artificial saliva. The results show that natural HA contains an additional fluorapatite phase and a wider range of trace elements (Na, F, Si), leading to a more complex structure. During demineralization, synthetic CHA exhibits more pronounced surface changes and faster dissolution, whereas natural HA demonstrates greater chemical stability. The remineralization process leads to the formation of new surface layers on both materials. Synthetic CHA develops a fine-grained, homogeneous layer enriched in carbonate and hydrated species, while natural HA shows localized crystal growth within structural defects. The results demonstrate that natural HA exhibits greater chemical stability during demineralization and a more enamel-like response during remineralization, whereas synthetic CHA undergoes more pronounced surface restructuring and forms a highly hydrated, carbonate-rich surface layer. Full article

Objectives: This study characterised the bioactive properties (i.e., ion release, pH rise, and apatite formation) of a newly developed Voco Profluorid + BioMin F varnish. Three additional varnishes were investigated for comparison: Clinpro™ White Varnish (3M™, St. Paul, MN, USA), MI Varnish (GC, Tokyo, Japan), and Profluorid varnish (VOCO GmbH, Cuxhaven, Germany). The Clinpro™ White and MI varnishes were chosen for comparison due to their similar composition of active ingredients. Profluorid served as a standard fluoride-only varnish reference. Methods: Dental varnish ingredients were characterised using ATR-FTIR, XRD, and ¹⁹F and ³¹P MAS-NMR. Coated coverslips were immersed in Tris buffer and artificial saliva (pH 4.0 and 7.0) for 2–24 h. Ion release was analysed using ICP-OES and a fluoride ion-selective electrode whilst monitoring pH changes. Post-immersion, coverslips were analysed by XRD and MAS-NMR to assess possible apatite formation. Results: XRD and ¹⁹F MAS-NMR detected NaF in all four varnishes. BioMin F varnish showed a ³¹P peak matching BioMin F glass, with an additional brushite peak, indicating partial reaction of the bioactive glass (BAG) with rosin resin water. All varnishes released fluoride and calcium, but only BioMin F and MI varnishes released phosphate, which is essential for the formation of calcium fluorapatite. Post-immersion analysis confirmed fluorapatite formation in BioMin F and, to a lesser extent, the Profluorid varnish. No apatite formation was observed in the other two varnishes. MI varnish exhibited calcium fluoride formation before and after immersion, as evidenced by XRD and ¹⁹F MAS-NMR analysis. Conclusions: The novel BioMin F varnish potentially promotes remineralisation by providing a sustained and slow release of therapeutic ions that are essential for the formation of fluorapatite. Full article

Pelletizing is an effective way of converting abundant phosphate ore fines into usable feedstocks for yellow-phosphorus production. In this work, the oxidation-roasting behavior of siliceous–calcareous phosphate ore pellets and siliceous phosphate ore pellets was evaluated in a laboratory tube furnace. The consolidation mechanisms were revealed using optical microscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The results indicate that siliceous phosphate ore pellets exhibit superior oxidation-roasting performance relative to siliceous–calcareous phosphate ore pellets. After roasting, oxidized siliceous–calcareous phosphate ore pellets show a loose and porous framework with large pores, thin walls, and occasional surface cracking. The consolidation of siliceous–calcareous phosphate ore pellets is mainly governed by the recrystallization bonding of silicon–magnesium-bearing fluorapatite. In contrast, oxidized siliceous phosphate ore pellets display a denser microstructure and stronger intergranular bonding. The dominant bonding forms are the recrystallization bonding of silicon-bearing fluorapatite and solid-state bonding between silicon-bearing fluorapatite particles and quartz particles. Furthermore, carbonate gangue minerals are detrimental to strength development because CO₂ release during roasting promotes the development of interconnected porosity and defects, thereby reducing the compressive strength of oxidized phosphate ore pellets. Full article

In this study, the characteristics of sulfide minerals during the acidic double reverse flotation of phosphate ore and the adsorption mechanisms of sodium oleate (NaOL) and dodecyl trimethyl ammonium bromide (DTAB) were investigated. Micro-flotation test results indicated that NaOL effectively collected galena, sphalerite, and pyrite at a concentration of 1 × 10⁻³ mol/L and pH 4–5.5, whereas DTAB exhibited selectivity for galena at 1 × 10⁻⁴ mol/L. Mixed mineral flotation revealed that NaOL induced a non-selective bulk flotation of sulfides with dolomite, resulting in a high froth yield of 93.23%, while the DTAB system showed superior selectivity with a froth yield of 54.91%. Surface analyses (Zeta potential, FTIR, and XPS) confirmed that NaOL chemisorbs onto sulfide surfaces via metal-oleate complexes, whereas DTAB adsorption is dominated by electrostatic attraction. Bench-scale tests validated the “double-rejection” flowsheet, significantly upgrading the P₂O₅ grade from 23.38% to 31.47% by sequentially partitioning Pb, Zn and Fe into the froth tailings. Size-by-assay analysis indicated that the sulfide separation was primarily controlled by the extent of mineral liberation. These findings provide a robust theoretical framework and practical guidance for the simultaneous management of sulfide minerals during phosphate beneficiation. Full article

Phosphatic deposits from the Lower Cambrian Pedroche Formation (Sierra de Córdoba, Spain) provide key insights into early diagenetic mineralization processes during the Cambrian radiation. This study applies an integrated multi-analytical approach combining Raman spectroscopy, SEM–EDS, LA-ICP-MS, and ToF-SIMS to investigate mineralogical, elemental, and molecular signatures of phosphatized bioclastic carbonates and associated siliciclastic facies from the Los Lagares-1 borehole. Results reveal a systematic phosphatization gradient from carbonate-dominated skeletal rims to phosphate-rich interiors composed of carbonate fluorapatite with variable carbonate and hydroxyl substitution. Trace-element systematics and REE patterns indicate seawater-influenced phosphogenesis under suboxic porewater conditions, coupled to iron reduction and early diagenetic clay mineral formation. In contrast, the siliciclastic siltstone facies preserves poorly crystalline phosphate phases associated with detrital aluminosilicates and chlorite, reflecting distinct porewater chemistry and crystallization kinetics. ToF-SIMS mapping demonstrates spatial coupling between fluorine and phosphate within fossil structures, confirming fluorapatite formation and localized organic matter entombment. These results highlight the strong control of host lithology on phosphate crystallization pathways and trace-element redistribution, and provide new constraints on microbially mediated phosphogenesis in restricted Early Cambrian reef–lagoon systems along the northern Gondwanan margin. Full article

Fluorapatite is a typical phosphate rock resource. Fluorapatite tends to generate fine mud agglomeration, which induces dehydration challenges owing to its inherently fine particle size and negative surface charge. In this paper, phosphate tailings slurries from a phosphate mine in Hubei Province, China, were selected as the research object, and flocculation–dehydration experiments were conducted using anionic, cationic, and nonionic polyacrylamide (PAM) flocculants. The results show that the maximum settling velocity is 51 mm/s and the moisture content of filter cake is 41.54%, which were obtained when the unit consumption of cationic flocculant with molecular weight 12 million was 1000 g/t. The mechanism of sedimentation and dehydration was studied by infrared spectroscopy and a particle size analyzer. The results showed that polyacrylamide was effectively adsorbed on the mineral surface, and the size of flocs increased significantly. Finally, the mechanism of sedimentation and dehydration was proposed. It has important guiding significance for the efficient solid–liquid separation and water circulation of fluorapatite mineral processing wastewater. Full article

The timing of uranium mineralization in the Xiangshan ore field has long been controversial. Although various geochronometers have been applied by previous researchers, including pyrite Rb-Sr, mica Ar-Ar, and fluorite Sm-Nd, the results remain inconsistent and inconclusive. In recent years, the discovery of abundant Pb-Zn veins in the deeper parts of the Xiangshan ore field has further complicated the interpretation of its metallogenic history. In this study, abundant vein-type hydrothermal apatites closely associated with U-Pb-Zn polymetallic mineralization were identified in both uranium and Pb-Zn ore veins. Combined major-element Electron Probe Microprobe Analysis (EPMA), Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) U-Pb dating, and trace-element analysis were conducted on these apatite grains. The results suggest a mineralization age of 130.9 ± 1.1 Ma for the Shannan uranium deposit, which is consistent with the previously reported apatite U-Pb age of 131.3 ± 7.2 Ma from the Zoujiashan uranium deposit and coincides with the main pulse of volcanic-intrusive activity in the Xiangshan ore field (133–137 Ma). The deep Niutoushan Pb-Zn deposit suggests a younger mineralization age of 124.5 ± 1.3 Ma, which is consistent with a thermal event age of 125.6 Ma determined by zircon fission-track dating and the zircon LA-ICP-MS U-Pb age of late-stage granite porphyry (125.4 ± 1.0 Ma). These ages may constrain the timing of U-Pb-Zn polymetallic mineralization in the Xiangshan ore field. Both magmatic and hydrothermal apatites are classified as fluorapatite and exhibit similar chondrite-normalized rare earth element (REE) patterns. Compared with magmatic apatites, hydrothermal apatites are characterized by elevated Th, U, Ca, and Sr contents, depletion in light rare earth elements (LREEs), Mn, and Na, and distinctly lower Th/U ratios. On major-element variation diagrams, magmatic and hydrothermal apatites define coherent trends but display clear compositional differences related to their formation stages. Apatites from uranium ore veins show strongly negative Eu anomalies and weakly positive Ce anomalies, similar to magmatic apatites. In contrast, apatites from Pb-Zn ore veins display positive Eu anomalies and weakly negative Ce anomalies, with lower Mn and Ga contents and higher SO₃ contents relative to both magmatic apatites and hydrothermal apatites from uranium ore veins. These features indicate that the ore-forming fluids during Pb-Zn mineralization were characterized by significantly higher oxygen fugacity than those during uranium mineralization and magmatism. Combined with published Sr isotopic data for the Xiangshan ore field, we propose that both uranium and Pb-Zn mineralization were genetically linked to the prolonged magmatic evolution of the deep volcanic-intrusive complex. The subsequent incursion of meteoric water modified the physicochemical conditions of the ore-forming system, particularly during the formation of the Pb-Zn mineralization. Full article

The efficient recovery of rare earth elements from associated rare-earth-bearing phosphate ores is of paramount importance for expanding the supply of rare earth resources. In contrast to conventional studies that focus on extracting rare earths either from phosphate concentrates or from phosphogypsum generated during the sulfuric acid wet-process, this study takes as its subject the rare-earth-enriched residue—an intermediate product obtained after the selective leaching of phosphorus via the hydrochloric acid route—from a rare-earth-bearing phosphate ore in Zhijin, Guizhou Province. The occurrence states, leaching behavior, and kinetic mechanisms of rare earth elements within this residue were systematically elucidated. Analyses using scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM–EDS) and aberration-corrected scanning transmission electron microscopy (STEM) reveal that rare earth elements are hosted in residual fluorapatite and newly formed CaF₂ through isomorphic substitution. The substitution of REE³⁺ for Ca²⁺ induces lattice contraction in CaF₂, with the interplanar spacing decreasing from 0.27 nm to 0.26 nm. Through single-factor experiments and response surface methodology (RSM) optimization, the optimal leaching conditions were determined to be a temperature of 80 °C, a leaching time of 120 min, a hydrochloric acid dosage of 160% of the theoretical requirement, a solid–liquid ratio of 1:6, and a agitation speed of 500 r·min⁻¹. Under these conditions, the leaching efficiency of rare earth elements reached as high as 92.69%. Kinetic analysis indicates that the leaching process follows the shrinking-core model, with the rate controlled by diffusion through the solid product layer. The apparent activation energy was calculated to be 37.2 kJ·mol⁻¹, characteristic of a diffusion-controlled process. Furthermore, response surface analysis of variance confirms that leaching temperature and time are the most significant factors influencing rare earth leaching. This study elucidates, from multiple perspectives, the leaching mechanism of rare earth elements from enriched residues within a hydrochloric acid system, thereby providing important theoretical support for the efficient recovery and process optimization of rare earth resources from associated phosphate ores. Full article

Pegmatites with miarolitic cavities have not previously been reported from the Larsemann Hills, East Antarctica, and their age and origin remain poorly constrained. We report the first geochemical and geochronological data for fluorapatite from a newly discovered pegmatite with miarolitic cavities in the Larsemann Hills. Large Fe-rich fluorapatite crystals (up to 5 cm) contain abundant oriented monazite-(Ce) inclusions and display elevated REE (1397–7966 ppm), relatively high Y (945–4192 ppm), and low Sr (52.2–83.5 ppm). Their trace-element signatures plot within the fields of partial melts, high-grade metamorphic rocks, and evolved fluid-rich magmatic systems. U–Pb dating of fluorapatite yields concordant ages of 519 ± 4 Ma (ID-TIMS) and 521 ± 31 Ma (LA-ICP-MS), indicating crystallization during the D₄ stage of the Pan-African orogeny. The isotopic equilibrium between apatite and monazite inclusions suggests synchronous formation and late-stage fluid overprinting. Combined geological, geochemical, and isotopic evidence shows that the pegmatite formed in situ as a product of anatexis of the Broknes paragneisses and evolved within a volatile-rich magmatic–hydrothermal system. These results provide the first direct age constraints on pegmatites with miarolitic cavities in Antarctica and shed new light on the final stages of East Gondwana assembly. Full article

Rare earth elements (REEs), as significant associated resources in sedimentary phosphate deposits, are commonly processed via the conventional hydrochloric acid wet-process phosphoric acid route (IMI process). In this method, phosphate and rare earth elements are typically leached simultaneously, which subsequently complicates their separation. In this study, a dolomitic rare earth-bearing phosphate concentrate from the Zhijin region of Guizhou Province was selected as the research subject. A stepwise phosphorus-prioritized leaching process was proposed, whereby precise regulation of hydrochloric acid dosage and reaction temperature enabled the preferential leaching of phosphorus (91.27%) and the directed enrichment of rare earth elements in the leaching residue (enrichment ratio of 4.7), thereby achieving efficient phosphorus–rare earth separation at the source. Subsequent process mineralogical analyses of the phosphate concentrate and the leaching residue revealed that rare earth elements occur in fluorapatite predominantly through isomorphic substitution. Following preferential phosphorus leaching, the residual Ca combines with F to form CaF₂, while rare earth elements become concentrated within the leaching residue. Finally, kinetic investigations and response surface analyses demonstrated that the preferential phosphorus leaching process is governed by diffusion through the solid product layer. Among the influencing factors, hydrochloric acid dosage (A), leaching temperature (C), and the interactions between leaching time and the solid–liquid ratio (B, D) were identified as the most significant parameters affecting phosphorus leaching efficiency. This study elucidates, from a mechanistic perspective, the governing principles of phosphorus dissolution and rare earth enrichment within the hydrochloric acid preferential leaching system, thereby providing important theoretical support and technical guidance for simultaneously achieving efficient phosphorus extraction and targeted rare earth enrichment within the hydrochloric acid wet-process phosphoric acid production route. Full article