Search Results (48)

The spatial variability in rock mass mechanical parameters critically affects slope stability assessments. This study investigated the southern slope of the Bayan Obo open-pit mine. A representative elementary volume (REV) with a side length of 14 m was determined through discrete fracture network (DFN) simulations. Based on the rock quality designation (RQD) data from 40 boreholes, a three-dimensional spatial distribution model of the RQD was constructed using Ordinary Kriging interpolation. The RQD values were converted into geological strength index (GSI) values through an empirical correlation, and the generalized Hoek–Brown criterion was applied to develop a spatially heterogeneous equivalent mechanical parameter field. Numerical simulations were performed using FLAC3D, with the slope stability evaluated using the point safety factor (PSF) method. For comparison, three homogeneous benchmark models based on the 5th, 25th, and 50th percentiles produced profile-scale safety factors of 0.96–1.92 and failed to replicate the observed failure geometry. By contrast, the heterogeneous model yielded safety factors of approximately 1.03–1.08 and accurately reproduced the mapped sliding surface. These findings demonstrate that incorporating spatial heterogeneity significantly improves the accuracy of slope stability assessments, providing a robust theoretical basis for targeted monitoring and reinforcement design. Full article

The Bayan Obo deposit, located on the northern margin of the North China Plate (NCP), is the world’s largest comprehensive Fe-REE-Nb deposit. After its formation, this deposit was affected by multiple tectonic thermal events, but the ages of these geological events are controversial. To determine the evolutionary history of the Bayan Obo deposit, we conducted a detailed study of the macroscopic and microscopic deformation characteristics of the ore district and selected representative minerals, such as riebeckite and biotite, which are widely present in the banded rocks of the deposit, for an ⁴⁰Ar-³⁹Ar isotopic analysis. The results show that a large number of deformation structures have developed in the carbonatite and surrounding rocks, including mineral bands, boudins, tight folds, and rotated porphyroclasts, suggesting that the region has undergone intense compression and shearing and that the deformation temperature can reach ~550 °C. ⁴⁰Ar-³⁹Ar plateau ages of 414.9 ± 1.4 Ma and 264.5 ± 2.5 Ma were obtained for the riebeckite and biotite, respectively. Using these results in conjunction with regional geological data and considering the closure temperature of the mineral isotope system, it was inferred that these two ages corresponded to two distinct reworking events experienced by the deposit during the Early Paleozoic and Late Paleozoic following its initial formation. These events corresponded to the collision between the Bainaomiao Arc and the NCP and the magmatic activity induced by a continental–continental collision during the closure of the Paleo-Asian Ocean (PAO), respectively. Full article

To address the limitations of traditional early warning methods in open-pit slope displacement monitoring—particularly their neglect of spatiotemporal correlations and their difficulty in analyzing multi-scale non-stationary sequences—this study proposes an early warning framework that integrates spatiotemporal clustering with multi-scale decomposition. Taking the southern slope of the Bayan Obo Main Pit as a case study, high-risk deformation zones were identified using DBSCAN-based spatiotemporal clustering applied to slope radar monitoring data. The displacement time series were decomposed using Variational Mode Decomposition (VMD) into trend and periodic components, for which Gated Recurrent Unit (GRU) and Long Short-Term Memory (LSTM) models were respectively developed. The results indicate that (1) DBSCAN effectively detects clusters characterized by high average cumulative displacement and broad spatial distribution, while filtering out isolated outliers. (2) The trend component prediction achieved a coefficient of determination (R²) of 0.99755, while the periodic component prediction yielded a root mean square error (RMSE) of just 0.0978 mm. The reconstructed total displacement achieved an R² of 0.9973, verifying the proposed multi-scale decomposition and hybrid modeling framework’s high accuracy and robustness in slope deformation modeling and early warning. Full article

Bayan Obo rare earth concentrate (BOREC) is composed of bastnaesite, monazite and fluorite, which is recognized as a refractory mineral in the world. In order to solve the problems of waste gas treatment and comprehensive utilization efficiency of BOREC decomposed by the current concentrated sulfuric acid roasting method (500–700 °C), H₂SO₄-HCl mixed acid assisted by aluminum salt was used to leach out the bastnaesite, and the optimal conditions were determined as follows: c(H⁺) = 7 mol/L, c(1/2H₂SO₄):c(HCl) = 5:1, c(Al₂(SO₄)₃) = 0.25 mol/L, temperature 135 °C, liquid–solid ratio of 42:1, and reaction time 3 h. At this time, the leaching rates of concentrate and rare earth (La, Ce, Pr and Nd) were 74.08% and 71.95%, respectively, and the decomposition rate of bastnaesite was 96.83%. At the same time, the yield of calcium sulfate was 77.35% and the purity was 99.22%. Subsequently, sodium sulfate was added with m(Na₂SO₄):m(RE₂O₃) = 2.5:1, and the recovery rate of rare earth was 99.5%, and the purity of rare earth double salt product was 98.47% at a temperature of 90 °C. After most of the acid had been extracted with triethyloctanamine, sodium fluoride was added with a fluorine–aluminum ratio of 6:1, sodium carbonate was used to adjust pH = 3, and cryolite was obtained with a purity of 95.59% and an aluminum recovery rate of 99.6% at 90 °C. Since the separation of bastnaesite and monazite has been basically realized in the leaching stage, it is conducive to the docking of subsequent alkali decomposition and recovery of trisodium phosphate, realizing the comprehensive recovery of rare earth, fluorine, calcium, aluminum and phosphorus. Full article

The Bayan Obo is the largest carbonatite-type rare earth deposit in the world. It not only has a large amount of light rare earth element (LREE) resources but also hosts approximately 9 million tons of medium and heavy rare earth element (M+HREE) resources. However, the M+HREE resources have not received enough attention, which hinders their further utilization. In this study, we conduct a systematic investigation of the distribution and process mineralogy properties of M+HREE in different types of ores in the Bayan Obo deposit. The high-value area (>0.1%) of M+HREE elements is found concentrated in the central and deeper parts of the Main and East orebodies. The content of M+HREE varies among different types of ores, with the Aegirine type (1005 ppm) and Fluorite type (1204 ppm) showing a higher average M+HREE concentration. The minerals rich in M+HREE include bastnäsite, monazite, Ca-fluorocarbonate, Ba-fluorocarbonate, allanite, aeschynite, and fergusonite, each with concentrations exceeding 4000 ppm. Aeschynite and fergusonite, in particular, exhibit high M+HREE concentrations and are enriched in fluorite-type and aegirine-type ores. Analysis of the mixed raw ores from the production line at the concentrating plant reveals an M+HREE concentration of approximately 0.2% and a concentration of the seven target minerals at around 12%. However, the particle size distribution and monomer dissociation degree are limited to below 22.3 µm and 40%, respectively. Based on these integrated analyses, we propose that the fluorite-type and aegirine-type ores within the Main and East open-pits are potential M+HREE targets. Furthermore, the recycling and utilization of M+HREE resources in the Bayan Obo deposit require a well-structured process flow and the selection of advanced processing equipment in the future. Full article

Aiming at the high-value application of rare earth elements lanthanum (La), an Al-50% La alloy was selected and prepared in a vacuum medium-frequency induction furnace. The geometric characteristics of the Al-50% La alloy powders were compared and studied, with the powders prepared by two different methods: mechanical pulverization and gas atomization. The results showed that an Al-49.09% La master alloy was obtained, and the only intermediate phase containing La in the experimental alloy was Al₁₁La₃. From the perspectives of chemical and phase composition, La has a high yield. Additionally, an Al-La alloy with controllable rare earth intermediate phases can be obtained. The Al-La alloy powders prepared by the mechanical pulverization method are irregular in shape, but the particle size is relatively small, ranging from 0.25 to 66.9 μm. Submicron powders were obtained, with 4.38% of the powders having an equivalent particle size of less than 1 μm. Considering the characteristic of the selective laser melting (SLM) process forming micro-melt pools, a small amount of submicron Al-La alloy powders prepared by the mechanical pulverization method can be used as a trace additive for SLM preparation of CP-Ti. The powders prepared by gas atomization have good sphericity, with a particle size range of 1.65 to 76.0 μm. Among them, the powders with a size of 2–10 μm account for 75.52%, and this part of the powders can be used for the powder metallurgy preparation of composite materials. Full article

Nioboixiolite-(□) is a new mineral found in a carbonatite sill from the Bayan Obo mine, Baotou City, Inner Mongolia, China. It occurs as anhedral to subhedral grains (100 to 500 μm in diameter) that are disseminated in carbonatite rock composed of dolomite, calcite, magnetite, apatite, biotite, actionlike, zircon, and columbite-(Fe). Most of these grains are highly serrated, with numerous inclusions of columbite-(Fe). The mineral is gray to deep black in color; is opaque, with a semi-metallic luster; has a black streak; and is brittle, with an uneven conchoidal splintery. The Mohs hardness is 6–6½, and the calculated density is 6.05 g/cm³. The reflection color is gray with a blue tone, and there is no double reflection color. The measured reflectivity of nioboixiolite-(□) is about 10.6%~12.1%, close to that of ixiolite (11%–13%). Nioboixiolite-(□) is non-fluorescent under 254 nm (short-wave) and 366 nm (long-wave) ultraviolet light. The average chemical analysis results (wt.%) of twelve electron microprobe analyses are F 0.01, MnO 0.12, MgO 0.15, BaO 0.62, PbO 0.91, SrO 1.49, CaO 2.76, Al₂O₃ 0.01, TREE₂O₃ 1.58, Fe₂O₃ 3.57, ThO₂ 0.11, SiO₂ 1.69, TiO₂ 3.68, Ta₂O₅ 13.95, Nb₂O₅ 47.04, and UO₃ 21.56, with a total of 99.25. The simplified formula is [Nb⁵⁺, Ta⁵⁺,Ti⁴⁺, Fe³⁺,□,]O₂. X-ray diffraction data show that nioboixiolite-(□) is orthorhombic, belonging to the space group Pbcn (#60). The refined unit cell parameters are a = 4.7071(5) Å, b = 5.7097(7) Å, c = 5.1111(6) Å, V = 138.31(3), and β = 90(1) °Å³ with Z = 4. In the crystal structure of nioboixiolite-(□), all cations occupy a single M1 site. In these minerals, edge-sharing M₁O₆ octahedra form chains along the c direction. In this direction, the chains are connected with each other via common vertices of the octahedra. The strongest measured X-ray powder diffraction lines are [d in Å, (I/I0), (hkl)]: 3.662(20) (110), 2.975(100) (111), 2.501(20) (021), 1.770(20) (122), 1.458(20) (023). A type specimen was deposited in the Geological Museum of China with catalogue number M16118, No. 15, Yangrou Hutong, Xisi, Beijing 100031, People’s Republic of China. Full article

With the development of the steel industry, China’s demand for niobium is increasing. However, domestic niobium resources are not yet stably supplied and are heavily dependent on imports from abroad (nearly 100%). It is urgent to develop domestic niobium resources. The Bayan Obo deposit is the largest rare earth element deposit in the world and contains a huge amount of niobium resources. However, the niobium resource has not been exploited due to the fine-grained size and heterogeneous and scattered occurrences of Nb minerals. To promote the utilization of niobium resources in the Bayan Obo deposit, we focused on the mineralogical and geochemical characterization of six types of ores and mineral processing samples from the Bayan Obo deposit, using optical microscopes, EPMA, TIMA, and LA–ICP–MS. Our results show that: (1) the niobium mineral compositions are complex, with the main Nb minerals including aeschynite group minerals, columbite–(Fe), fluorcalciopyrochlore, Nb–bearing rutile, baotite, fergusonite–(Y), fersmite, and a small amount of samarskite–(Y). Aeschynite group minerals, columbite–(Fe), and fluorcalciopyrochlore are the main niobium-carrying minerals and should be the primary focus of industrial recycling and utilization. Based on mineralogical and geochemical investigation, the size of the aeschynite group minerals is large enough for mineral processing. Aeschynite group minerals are thus a significant potential recovery target for niobium, as well as for medium–heavy REE resources. The Nb–rich aegirine-type ores with aeschynite group mineral megacrysts are suggested to be the most significant niobium resource for mineral processing and prospecting. Combined with geological features, mining, and mineral processing, niobium beneficiation efforts of aeschynite group minerals are crucial for making breakthroughs in the utilization of niobium resources at the Bayan Obo. Full article

The surface properties of bastnaesite and parisite are similar to their associated gangue mineral, fluorite, which makes the flotation separation of these two rare earth minerals from fluorite one of the industry’s most significant challenges. This study systematically investigates the inhibitory effects and mechanisms of sodium silicate (SS) on bastnaesite, parisite, and fluorite in an octyl hydroxamic acid (OHA) collector system through flotation experiments, various modern analytical methods, and DFT simulations. The flotation test results indicate that the inhibition effects of SS on the three minerals are in the order: fluorite > parisite > bastnaesite. Detection and analysis results indicate that SS forms hydrophilic complexes with Ca atoms on the surfaces of fluorite and parisite, enhancing surface hydrophilicity and inhibiting OHA adsorption, but its impact on bastnaesite is relatively minor. DFT simulation results show that OHA forms covalent bonds with metal ions on mineral surfaces, favoring five-membered hydroxamic-(O-O)-Ce/Ca complexes, and reacts more strongly with Ce atoms than Ca atoms. SS primarily forms covalent bonds with metal atoms on mineral surfaces via the SiO(OH)₃⁻ component, and OHA and SS compete for adsorption on the mineral surfaces. OHA has a stronger affinity for bastnaesite, whereas SS shows the highest affinity for fluorite, followed by parisite, and the weakest affinity for bastnaesite. Full article

Industrial pure zirconium plays an essential role as a structural material in the nuclear energy sector. Understanding the deformation mechanisms is crucial for effectively managing the plasticity and texture evolution of industrial pure zirconium. In the present study, the texture and microstructure evolution of industrial pure zirconium during the cold-rolling process have been characterized by XRD, EBSD, and TEM. The influences of various twins on texture evolution have also been simulated by the reaction stress model. The effects of slip and twinning on the deformation behavior and texture evolution have been discussed based on crystallographic and experimental considerations. Cold rolling yields a typical bimodal texture, resulting in the preferential <$2\stackrel{\mathrm{-}}{1}\stackrel{\mathrm{-}}{1}0$>//RD orientation. The activation of the deformation mechanisms during cold rolling follows the sequential trend of slip, twinning, local slip. Experimental characterization and reaction stress simulation illustrate that T1 twins dominate in the early stage, whereas C2 twins develop at the later stage of the cold-rolling process. Twinning, especially the T1 twin, contributes to the formation of the {0001}<$10\stackrel{\mathrm{-}}{1}0$> orientation. Full article

Bayan Obo is a well-known polymetallic deposit containing significant quantities of rare earth elements, niobium, thorium, and iron. However, the epoch in which mineralization occurred and the mineralization process are still debated due to the complex nature of its mineralization and geological evolution. Inadequate geophysical exploration has further contributed to this lack of clarity surrounding critical issues, such as the deep link between the main orebody and the eastern orebody, the form and distribution of the extensive dolomite, and the geologic structures in the area. Therefore, we implemented the time-domain controlled-source electromagnetic method (CSEM) to acquire electrical structures at depths down to 2.5 km between the Main and Eastern mines. According to the inverted resistivity structure, in conjunction with existing geological and drilling data, we classified the main lithologies and faults based on their resistivity characteristics. Overall, the mineralized carbonatite reflects high to moderately high resistivity. The mineralized carbonatite dips overall from north to south, with a maximum extension depth not exceeding 1.5 km, and its range of occurrence is controlled by nearly east–west-striking faults distributed along the bounding line between the roof and floor rocks. The Main and Eastern mines are connected at depth, but the morphology and position of the ore bodies have significantly changed due to multiple phases of tectonic activity. The electrical structure does not reveal any obvious syncline structures, further refuting the traditional view that the Bayan syncline controls ore formation. Full article

The Bayan Obo ore deposit is a world-renowned polymetallic coexistence mine that integrates important elements, such as rare earths, iron, niobium, and titanium. The chemical properties of niobium and titanium are similar, and the two often coexist in the Bayan Obo deposit as isomorphs, making them difficult to separate. Therefore, the separation of niobium and titanium is crucial for the efficient utilization of niobium resources in the Bayan Obo ore deposit of China. To discuss the feasibility of separating niobium and titanium by selective electrolysis, cyclic voltammetry and square wave voltammetry were used to study the reduction mechanism of niobium oxide and titanium oxide in NaF–Na₃AlF₆ molten salt. The results revealed significant differences in the diffusion coefficients and reduction steps of Nb⁵⁺ and Ti⁴⁺ during reduction at a molybdenum cathode. At 950 °C, the diffusion coefficient of Nb⁵⁺ during reduction at a molybdenum cathode was 3.57 × 10^–6 cm²/s. Also, in the NaF–Na₃AlF₆ system, Nb⁵⁺ underwent a three-step reduction as follows: Nb(V)→Nb(IV)→Nb(I)→Nb. The diffusion coefficient of Ti⁴⁺ during reduction at the molybdenum cathode was 9.92 × 10^–7 cm²/s, and Ti⁴⁺ underwent a two-step reduction in the NaF–Na₃AlF₆ system: Ti(IV)→Ti(I)→Ti. When Nb₂O₅ and TiO₂ were both present in the NaF–Na₃AlF₆ system, the deposition potential of niobium metal (−0.64 V) differed from that of titanium metal (−0.77 V). These differences in diffusion coefficient, reduction step, and deposition potential enabled selective electrolytic separation of niobium and titanium. Full article

The atomic-level structure and electronic properties of monazite were investigated using a first-principles method based on density functional theory (DFT). First, the geometric structure of monazite was optimized, followed by calculations of its Mulliken population, electron density, and density of states, which were subsequently analyzed. The findings of this analysis suggest that monazite is highly susceptible to cleavage along the {100} plane during crushing and grinding. When SPA was utilized as the collector, the recovery rate of monazite was higher than that when LF-P8 was used. The zeta potential and adsorption energy results indicated that the zeta potential after SPA adsorption tended towards negativity, and the adsorption energy was smaller, indicating that SPA exhibited stronger adsorption performance. LF-P8 was stably adsorbed on the monazite (100) surface via mononuclear double coordination. SPA was stably adsorbed on the surface of monazite (100) via binuclear double coordination. The results of this study provide valuable insights into the adsorption of monazite by commonly used flotation collectors. These findings are of substantial importance for future endeavors in designing flotation collectors capable of achieving selective monazite flotation. Full article

A novel environmentally friendly one-step decomposition strategy for mixed rare earth concentrate of Bayan Obo in sulfuric acid solution was proposed in this work. In this process, more than 84% of bastnasite and monazite were decomposed in the leaching step at a temperature lower than the boiling point of sulfuric acid solution. So, the dilapidation of sulfuric acid in this current proposed process will be reduced to a large extent. The stability region of rare earth ion in the RE(La, Ce, Nd)-F-P-SO₄-H₂O system at 170 °C has been proven through Eh-pH diagrams. The factors influencing decomposition of rare earth concentrate in this process were also investigated and the optimal leaching conditions were determined to be a leaching temperature of 170 °C with an ore/acid ratio of 1:5 (g/mL), a sulfuric acid concentrate of 75% and a leaching time of 80 min. The mineralogical changes occurring during the H₂SO₄ leaching process were investigated by X-ray diffraction and SEM-EDS. The analysis results showed that bastnasite and most of monazite had been decomposed, leaving only a small amount of monazite in the leaching residue. Full article

Mg₈₀Ni_16−xAl_xY₄ (x = 2, 4, 8) alloys were prepared by induction levitation melting, and the effect of substitution of Al for Ni on the microstructure and hydrogen storage properties was studied in the present work. The results illustrated that the solidification path, phase constitution, and grain size were significantly altered by Al addition. Appropriate Al addition improved abundance and grain refinement of the Mg, Mg₂Ni, and Mg₁₅NiY ternary eutectic. But as Al further increased, Mg solidified independently rather than in the formation of the ternary eutectic. More Al favored the formation of Al₃Ni₂Y but suppressed Mg₂Ni and YMgNi₄. Although the hydrogen absorption activation and the kinetic property deteriorated, the thermodynamic stability of hydrides was enhanced by adding Al. Hydrogen absorption ability under low pressure was improved, and the Mg₈₀Ni₈Al₈Y₄ alloy could absorb nearly 3.5 wt% hydrogen under 1 bar hydrogen at 250 °C. Full article