Guangzhou Institute of Geochemistry
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Microbial-mediated bastnaesite dissolution as a viable source of clay-adsorbed rare earth elements in the regolith-hosted deposits
No full textUnderstanding the weathering processes of minerals containing rare earth elements (REE) is crucial for unraveling the genesis of regolith-hosted REE deposits. However, the weathering mechanisms of bastnaesite, a primary REE carrier in parent rocks, remain uncertain. Discrepancies between field observations and thermodynamic calculations regarding its weatherability during mineral-groundwater interactions have raised questions about the factors controlling the natural weathering of bastnaesite. Here, we propose that microbial activities significantly contribute to the dissolution of bastnaesite. To test this hypothesis, we conducted bio-weathering experiments using natural bastnaesite and a wild strain, Bacillus thuringiensis (Bt) isolated from regolith-hosted REE deposits. The results indicate that, consistent with thermodynamic predictions, bastnaesite exhibited resistance to dissolution under simulated groundwater pH conditions (similar to 6). However, the presence of Bt significantly enhanced bastnaesite dissolution. Bt exuded various types of organic acids, acidifying the solution during bio-weathering. Comparative biotic and abiotic experiments demonstrated that Bt could induce bastnaesite dissolution through acidolysis and ligand complexation. These effects were further strengthened by direct cell attachment to the mineral surfaces. Existing field studies suggest the rapid dissolution of bastnaesite during the very early rock weathering period, adding uncertainty about the contribution of bastnaesite to the enrichment of clay-adsorbed REE. Our results indicate that the dissolution of bastnaesite is largely pH-dependent, with bio-dissolution rates (R-Ce = 10(-13) - 10(-12) molm(-2)s(-1)) close to or slightly lower than the lab-determined dissolution rates of feldspars and micas at weakly acidic to neutral pH levels. Since the weathering of these aluminosilicate minerals provides the dominant source of clay minerals, we infer that some REE released from bastnaesite can be retained by clay minerals in the weathering profile. These findings may provide new insights into the natural weathering of bastnaesite and advance our understanding of the REE biogeochemical cycling during the formation of regolith-hosted REE deposits
Decoupling Temperature and Light Effects on Terpene Emissions From Subtropical Eucalyptus: Insights From Controlled Field Experiments
No full textEmissions of biogenic volatile organic compounds (BVOCs) from plants are significantly influenced by both temperature and light, yet the individual contribution of these factors, particularly for emissions of monoterpenes (MTs) and sesquiterpenes (SQTs) from tropical and subtropical plant species, remain poorly quantified due to their covariant effects. In this study, we conducted in situ and controlled field experiments on subtropical Eucalyptus trees using a portable LI-6800 photosynthesis system to isolate and quantify the temperature and light responses of major MTs. Additionally, we qualitatively assessed the light dependence of minor MTs and SQTs through dynamic chamber measurements. Our results revealed distinct light dependence across different compounds: beta-ocimenes were fully light-dependent but exhibited unexpected suppression under high light conditions, whereas alpha-pinene and 1,8-cineole were light-independent. Temperature response experiments indicated that the temperature sensitivity (beta) for light-dependent beta-ocimenes (0.095 K-1) and light-independent alpha-pinene (0.071 K-1) and 1,8-cineole (0.102 K-1) were similar to the model value (0.1 K-1), but significantly lower than previously reported values from uncontrolled tropical measurements (0.2 K-1), suggesting an influence of light on observed temperature sensitivity. Chamber-based results revealed that acyclic MTs and alpha-phellandrene were fully light-dependent, similar to beta-ocimenes, while cyclic MTs and the SQT alpha-longipinene were light-independent and followed an exponential temperature function. Other SQTs exhibited partial light-dependence and would need a hybrid modeling approach. These results provide valuable insights into the emission mechanisms of various terpene types, with important implications for enhancing predictive models of BVOC emissions
Generation characteristics of polybrominated and polychlorinated dibenzo-<i>p</i>-dioxins/furans (PBDD/Fs and PCDD/Fs) under varying incineration conditions of municipal solid waste
No full textMunicipal solid waste incinerators (MSWIs) are deemed important sources of polychlorinated and polybrominated dibenzo-p-dioxin/furans (PCDD/Fs and PBDD/Fs). However, compared to PCDD/Fs, the emission characteristics of MSWI-derived PBDD/Fs have been rarely studied. Here we selected a long-term operating MSWI, investigated the generation of PBDD/Fs under varying incineration conditions within the normal range, and compared them to those of PCDD/Fs. Generally, PBDD/Fs exhibited mass-based emission factors (mass-EFs) one order of magnitude higher than those of PCDD/Fs and were predominantly released via slag, as were PCDD/ Fs, though at lower percentages. Both PBDD/Fs and PCDD/Fs showed significant changes in emissions with the variations in waste load, O2 content, and waste composition, particularly PBDD/Fs. Comparatively, furnacederived PBDD/Fs demonstrated heightened sensitivity to waste load and composition, whereas PCDD/Fs were primarily influenced by O2 levels, followed by waste composition; PCDD/Fs consistently exhibited increasing mass-EFs under unconventional conditions and PCDD/Fs in filtered fly ash were highly sensitive to all the three variables, while filtered PBDD/Fs remained insensitive to these conditions. Data comparison between raw flue gas and filtered fly ash indicated secondary generation of PBDD/Fs and PCDD/Fs during gas purification, as well as the insufficient dioxin-trapping efficiency of bag filters, particularly for PBDD/Fs. Therefore, MSWI-derived PBDD/Fs and dioxins in slag and other MSWI-derived wastes warrant significant attention
A water probe for direct pH measurement of individual particles via micro-Raman spectroscopy
No full textThe acidity of atmospheric aerosols influences fundamental physicochemical processes that affect climate and human health. We recently developed a novel and facile water-probebased method for directly measuring of the pH for micrometer-size droplets, providing a promising technique to better understand aerosol acidity in the atmosphere. The complex chemical composition of fine particles in the ambient air, however, poses certain challenges to using a water-probe for pH measurement, including interference from interactions between compositions and the influence of similar compositions on water structure. To explore the universality of our method, it was employed to measure the pH of ammonium, nitrate, carbonate, sulfate, and chloride particles. The pH of particles covering a broad range (0-14) were accurately determined, thereby demonstrating that our method can be generally applied, even to alkaline particles. Furthermore, a standard spectral library was developed by integrating the standard spectra of common hydrated ions extracted through the waterprobe. The library can be employed to identify particle composition and overcome the spectral overlap problem resulting from similar effects. Using the spectral library, all ions were identified and their concentrations were determined, in tum allowing successful pH measurement of multicomponent (ammonium-sulfate-nitrate-chloride) particles. Insights into the synergistic effect of Cl-, NO3 -, and NH4 + depletion obtained with our approach revealed the interplay between pH and volatile partitioning. Given the ubiquity of component partitioning and pH variation in particles, the water probe may provide a new perspective on the underlying mechanisms of aerosol aging and aerosol-cloud interaction. (c) 2024 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V
Acidity of Atmospheric Waters Induces Enhanced H<sub>2</sub>O<sub>2</sub> Production through Photosensitized Chemistry of Phenolic Substances
No full textHydrogen peroxide (H2O2) is known to convert SO2 to sulfuric acid and acts as a dominant reservoir of highly reactive hydroxyl radical (OH) in atmospheric waters (cloud, fog, rain, and aerosol liquid water). Here, we conclusively demonstrate that photosensitized oxidation of phenolic substances (catechol, o-cresol, and guaiacol) by the excited triplet state of nonphenolic compound (3,4-dimethoxybenzaldehyde, DMB) represents an unrecognized significant source of H2O2. Intriguingly, the highest H2O2 formation rate, (3.43 +/- 0.14) x 10-9 M s-1, and H2O2 yield (Phi H2O2 ), (7.68 +/- 0.08) x 10-1, were observed by photosensitized chemistry of catechol at low pH values (2.50) typical of cloud and aerosol water. The quantum chemical calculations revealed that the fraction of the protonated triplet state of DMB increases with a pH decrease, resulting in a faster formation of H2O2. A detailed mechanism was proposed describing the formation of H2O2 from the photosensitized reaction
Polycyclic Andean-type orogenic evolution of the Dunhuang block in NW China: A result of Paleozoic reconfiguration of oceanic subduction systems
No full textDespite numerous studies of metamorphic and magmatic rocks from the Dunhuang block, its protracted Cambrian to Permian geodynamic evolution as well as its role in the final amalgamation of the Tarim-North- China Craton Collage during the Pangea assembly, remain controversial. In order to understand the evolution of the Dunhuang block in the frame of Paleozoic plate tectonics, we review and synthetize recently published P-T data along with geochronological and geochemical data for its northern, central and southern mountain ranges, which we placed in the context of structural observations. Zircon and monazite U-Pb ages combined with P-T constraints determined for Ordovician to Devonian metamorphic rocks reveal that M1 and M2 metamorphic events define a clockwise P-T evolution and distinctly hot metamorphic gradients. Ordovician to Devonian protracted garnet growth evidenced by low (Yb/Gd)N ratios in metamorphic zircon and monazite, together with low Th/U ratios, negative epsilon Hf(t) and Eu anomalies in magmatic and metamorphic zircon, mark a period of continuous metamorphism accompanied by crustal reworking during thickening of a previously thermally softened crust. Zircon and monazite U-Pb ages suggest that the early Paleozoic D1-M1 and D2-M2 events started ca. 10 m.y. earlier and lasted longer in the northern and central ranges compared to the southern range consisting of significantly older crustal basement components. In all three mountain ranges, the formation of an E-W trending steep cleavage related to D3-M3 event was concomitant with emplacement of numerous late Devonian to Carboniferous diorites and I-type granitoids. The negative epsilon Hf(t) of magmatic zircon and high (Yb/Gd)N ratios in metamorphic zircon and monazite show that a magma-assisted N-S-directed shortening event responsible for further crustal reworking started in the late Devonian and lasted over 60 m.y. The latest Permian M4 metamorphic event, restricted mainly to the southern range, defines anticlockwise P-T paths associated with the emplacement of high-K calc-alkaline granitoids. This event is characterized by the increasing from negative to positive zircon epsilon Hf(t) values, suggesting input of juvenile crustal and mantle-derived material. High metamorphic gradients and the petrogenesis of magmatic arc-related rocks intruding a Precambrian basement suggest that the Dunhuang block developed as a supra-subduction continental hot orogenic system formed above subducting oceanic plates similar to the northern and southern margins of the American Cordillera. Our data show that its evolution was related to two kinematically independent early to middle and late Paleozoic orogenic cycles. In the context of plate tectonic reconstructions, the revised chronology of events points to the kinematic interplay between the continental blocks moving within the Proto-Tethys oceanic domain in association with the south- dipping Panthalassa, Paleo-Asian, and north-dipping Paleo-Tethys oceanic subduction systems
Uphill diffusion of lithium along phosphorus gradients in olivine from mafic layered intrusions
No full textLithium (Li) concentration and Li isotopes of olivine have been widely adopted to decipher the mantle-crust interaction and short-lived magmatic processes in the shallow magma chambers. However, the diffusion behavior of Li in olivine has not yet been fully understood, which may bias the interpretation of Li concentration and Li isotopes observed in natural olivine. In this study, high-resolution elemental mapping (Li, P, Fe, Mn, Ca, Al, and Ni) combined with in situ Li concentration and Li isotope analyses were conducted for olivine grains from two ca. 260 Ma mafic layered intrusions in SW China, to decode the origin of coupled Li-P zoning and multimode diffusion of Li in natural olivine. The 2-D elemental maps and compositional profiles reveal complex, coupled Li-P zoning patterns. The Li-P-rich zones contain 3.5 to 6.1 ppm Li and 187 to 776 ppm P, higher than those of Li-P-poor olivine domains that contain 0.7 to 2.8 ppm Li and 29 to 166 ppm P. Particularly, the Li-P-rich zones in each grain commonly have lower delta 7Li* than that of the Li-P-poor domains, with the maximum fractionation of Li isotopes in a single grain being up to 15 parts per thousand. Numerical modeling shows that rapid olivine growth can result in variable degrees of Li and P enrichment in concentration and an increase of delta 7Li* in the Li-P-rich zone of olivine, which is inconsistent with our observations. Instead, the inverse variations of Li concentration and Li isotopic profiles can be well simulated in an uphill diffusion mode of Li along pre-existing sharp P gradients, accompanying by simultaneous coupled and non-coupled diffusion of Li within a single olivine. The large variation of delta 7Li* is thus interpreted as kinetic fractionation, which may be caused by dehydration of olivine due to exsolution of a fluid phase from the interstitial liquid of a crystal mush. Three distinct Li-P variation trends of olivine are summarized in this study and can be used to distinguish the process of crystal growth from postcrystallization diffusion. Our results should have important bearings on the understanding of complex crystallization and solidification processes of crustal magma chambers
Hydrothermal origin of platinum-group minerals during serpentinization of the podiform chromitites from the Kizildag ophiolite in southern Turkiye
No full textPlatinum-group minerals (PGMs) in podiform chromitites usually occur in the interior and/or edge of chromite. However, the origin of PGMs in podiform chromitites has long been a matter of debate. Here we examined sub-micro to nanoscale textural features, morphologies, and compositions of PGMs from the disseminated, banded, massive and nodular chromitites in the Kizildag ophiolite in southern Turkiye, and found both primary and secondary PGMs. The aim of this study is to reveal the transformation processes from primary to secondary PGMs, thereby taking a thorough examination of the origin of these PGMs. Primary PGMs include laurite and Os-Ir alloy, which are prevalent in all samples. They are typically enclosed within or located at the edge of chromite, and formed either prior to or contemporaneously with the crystallization of chromite at temperature of 1100-1200 degrees C and logfS(2) values of -2 to -1. In contrast, PGE-bearing pentlandite are commonly present at the edge of chromite, corresponding to an increase of fS(2) with the progressive crystallization of chromite. These primary PGMs and PGE-bearing pentlandite in the intergranular space of chromite are susceptible to alter and transform into secondary PGMs and base metal mineral assemblages, which include Os-Ru nanophases (Os-Ru nanoparticle and OsRu3 nanoalloy) + awaruite (FeNi3) + trevorite (Fe2NiO4) in nodular chromitite, Os-rich laurite + Os-Ir(Ru) alloy/oxide + pentlandite + millerite (NiS) in banded and massive chromitite, and Ru(Ir) oxide + heazlewoodite (Ni3S2) in disseminated chromitite. The development of these diverse assemblages can be attributed to the degrees of serpentinization of chromitites. The nodular chromitite underwent weak serpentinization and had low water/rock ratios (<similar to 1), fS(2) and fO(2), leading to the conversion of IPGE (Os, Ir and Ru)bearing pentlandite into Os-Ru nanoparticle- and OsRu3 nanoalloy-bearing awaruite. The massive and disseminated chromitites had high water/rock ratios and high fS(2) and fO(2) relative to those of the nodular chromitite during serpentinization, and consequently the corresponding pentlandite was transformed into heazlewoodite and/or millerite associated with S loss. Meanwhile, Ir, Os and possibly Ru were released from laurite to form Os-Ir(Ru) alloy/oxide at the edge of laurite. Our observation highlights that primary PGMs and pentlandite in the chromitites of the Kizildag ophiolite have been modified under different physical-chemical conditions during serpentinization, resulting in the formation of complex secondary PGMs and base metal mineral assemblages
Controlling factors and geological applications of the drimane-skeleton compound content and composition of crude oils in complex petroleum systems: New insights from the Western Pearl River Mouth Basin, South China Sea
No full textCrude oils generally contain drimane-skeleton compounds, but the uncertainty of the main factors controlling drimane distributions limits their effective geological applications, especially in complex petroleum systems. In this study, the drimane-skeleton compound composition and the relative content of each drimane-skeleton compound to C 30 hopane (CDSC) were systematically studied for crude oils in different structural regions of the Western Pearl River Mouth (WPRM) Basin, South China Sea. The results show that the C DSC of crude oil is mainly controlled by its organic sources. Higher C DSC values in crude oil indicates a greater contribution from terrigenous organic matter to their source rocks. For crude oils from source rocks with similar biotic inputs, the C DSC values are controlled mainly by the depositional environment. Higher C DSC values in crude oil correspond to higher concentrations of clay minerals and lower salinities. In addition, the drimane-skeleton compound composition of crude oil is largely controlled by its maturity. The ratios of drimane to homodrimane (Dr/HDr), total rearranged drimane to total drimane and homodrimane (TRDr/TDr), and 8-rearranged drimane to 9-rearranged drimane (8RDr/9RDr) synchronously increase with increasing maturity. These ratios can effectively characterize the maturity of various types of crude oils. The maturity range characterized by the drimane maturity parameters is greater than that characterized by conventional maturity parameters. Correlation diagrams based on drimane parameters and other organic geochemical parameters can be used to classify crude oils and reveal their sources and origins, which has great application potential in complex petroliferous basins, especially in deep and ultra-deep petroleum systems with abundant light oil/condensate
Molecular simulation on Cs, Rb retention in Na/K-montmorillonite interlayer coupling clay swelling/collapse
No full textA key issue about radioactive waste disposal and nuclear accident contamination control is the retention of radionuclides in clay minerals. The cation (Cs+, Rb+, Na+, K+) selectivity in montmorillonite (Mt) interlayers have not been quantitatively studied. This work employs classical molecular dynamics (CMD) to systematically investigate the interlayer structure, swelling properties, diffusion dynamics, and cation exchange processes. The selectivity of alkali ions within the interlayer space coupled with clay swelling/collapse under different water activity (a(w)) and cation activity, has been quantified. Both Cs-, Rb-Mt demonstrate a monolayer hydrate configuration as the most stable state. The mobility of intercalated species, as indicated by self-diffusion coefficients, exhibits a stepwise trend with increasing water content. The cationic selectivity within the interlayer follows the order Cs+ > Rb+ > K+ > Na (+) at a(w) = 1.0. The logarithm values of the selectivity coefficients for Cs/Rb relative to Na/K are as follows: logK(c)(Cs/K) = 0.73, logK(c)(Cs/Na) = 1.62, logK(c)(Rb/K) = 0.62, and logK(c)(Rb/Na) = 1.57 at a(w) = 1.0. A model correlating selectivity coefficients with water activity has been proposed. It is noted that Cs+ and Rb+ ions tend to accumulate within the interlayer as water activity decreases, and interlayer Rb+ competes with Cs+ for exchange positions at low water activity. These results can be used to quantify cationic partitioning during the remediation of radiocesium contamination in soil and weathering processes of sediments