Mineralogical and geochemical study of apatite and dolomite from the Bayan Obo giant Fe-REE-Nb deposit in Inner Mongolia: New evidences for genesis

The Bayan Obo Fe-REE-Nb deposit is the world's largest resource of REE and its origin still remains controversial. To decipher the genesis of this unique deposit, we conducted a detailed mineralogical observations using scanning electron microscope (SEM), cathodoluminescence (CL) and in-situ micro-analyses on chemical compositions of the dolomite and apatite by EPMA and LA-ICPMS techniques. A wide range in SrO contents in dolomite mineral grains from coarse-grained dolomite marble has been observed. The SrO contents in the margin of the dolomite mineral reach up to 1.04 wt%, while the SrO contents in the core are as low as 0.16 wt%. In contrast, the SrO contents of the dolomite minerals of fine-grained dolomite marble are basically invariable, mainly concentrating on the range of 0.1 wt%-0.2 wt%. The MnO and FeO concentrations of dolomite mineral grains from the coarse-grained dolomite marble (MnO, 0.24 wt%-0.45 wt%; FeO, 2.27 wt%-3.42 wt%) are significantly lower than those of dolomite from fine-grained dolomite marble (MnO, 0.84 wt%-3.32 wt%; FeO, 3.59 wt%-12.16 wt%). The big differences in major elements between two types of the H8 dolomite marble imply different forming processes. Three types of apatite show big differences in cathodoluminescent signatures, major and trace elements. Type I fluorapatite has few REE mineral inclusions and Type II fluorapatite hosts abundant tiny REE mineral (monazite) inclusions. Type III fluorapatite from strongly deformed coarse-grained dolomite marble forms abnormally large monocrystals with elongated orientation. Both Type I and Type II fluorapatite from fine-grained dolomite marble samples display the heterogeneous component regions under BSE, with obvious depletion in Na and REE in BSE-dark areas observed in the X-ray compositional maps. Unaltered (BSE-bright) regions in Type I and Type II fluorapatite have high REE (17470-77090 ppm), Y (714-8162 ppm), Na (2023-10258 ppm), Sr (2126-6422 ppm) concentrations, obviously different from Type III fluorapatite (REE, 2452-7496 ppm; Y, 157-285 ppm; Na, 501-1464 ppm; Sr, 6878-9949 ppm). The REE, Na, Th and Pb depletion in BSE-dark regions in Type I and Type II apatite correspond to two styles of REE re mobilization during fluid-induced dissolution-reprecipitation processes. Late-stage REE, Na, Ba, CO32-, SO42- rich mesothermal hydrothermal fluid evolved from carbonatite was responsible for REE leaching in Type I fluorapatite. The Sr-rich, Na-poor, REE-poor Type III fluorapatite and associated elevated SrO contents in the margin of dolomite imply that the deposit underwent subsequent fluid infiltration by Sr-rich, REE-poor, Na-poor metamorphic fluid, causing the REE leaching in Type II fluorapatite and the consequent formation of monazite inclusions. As a common REE-bearing mineral in Bayan Obo deposit, apatite displays a diversity of textures and occurrences, fingerprints multi-stage metasomatic fluids and provides new insights into the mechanism of REE enrichment and remobilization

Analysis of Influencing Factors on the Gas Separation Performance of Carbon Molecular Sieve Membrane Using Machine Learning Technique

Gas separation performance of the carbon molecular sieve (CMS) membrane is influenced by multiple factors including the microstructural characteristics of carbon and gas properties. In this work, the support vector regression (SVR) method as a machine learning technique was applied to the correlation between the gas separation performance, the multiple membrane structure, and gas characteristic factors of the self-manufactured CMS membrane. A simple quantitative index based on the Robeson’s upper bound line, which indicated the gas permeability and selectivity simultaneously, was proposed to measure the gas separation performance of CMS membrane. Based on the calculation results, the inferred key factors affecting the gas permeability of CMS membrane were the fractional free volume (FFV) of the precursor, the average interlayer spacing of graphite-like carbon sheet, and the final carbonization temperature. Moreover, the most influential factors for the gas separation performance were supposed to be the two structural factors of precursor influencing the porosity of CMS membrane, the carbon residue and the FFV, and the ratio of the gas kinetic diameters. The results would be helpful to the structural optimization and the separation performance improvement of CMS membrane

All-perfluoropolymer, nonlinear stability-assisted monolithic surface combines topology-specific superwettability with ultradurability

Developing versatile and robust surfaces that mimic the skins of living beings to regulate air/liquid/solid matter is critical for many bioinspired applications. Despite notable achievements, such as in the case of developing robust superhydrophobic surfaces, it remains elusive to realize simultaneously topology-specific superwettability and multipronged durability owing to their inherent tradeoff and the lack of a scalable fabrication method. Here, we present a largely unexplored strategy of preparing an all-perfluoropolymer (Teflon), nonlinear stability-assisted monolithic surface for efficient regulating matters. The key to achieving topology-specific superwettability and multilevel durability is the geometric-material mechanics design coupling superwettability stability and mechanical strength. The versatility of the surface is evidenced by its manufacturing feasibility, multiple-use modes (coating, membrane, and adhesive tape), long-term air trapping in 9-m-deep water, low-fouling droplet transportation, and self-cleaning of nanodirt. We also demonstrate its multilevel durability, including strong substrate adhesion, mechanical robustness, and chemical stability, all of which are needed for real-world applications