Guangzhou Institute of Geochemistry
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Martian Smectites Formation Regulated by Environmental CO<sub>2</sub> and Si
No full textDespite the anticipated abundant carbonates due to historical atmospheric CO2 levels, Mars presents a geological puzzle with MgFe-smectites dominating the Noachian and early Hesperian terrains, contrasted by sparse carbonate deposits. To address this point, we explored the impact of CO2 on MgFe-smectite formation, emphasizing the role of variable Si concentrations within the simulated Martian environment. Hydrothermal experiments, conducted under a constant CO2 concentration (C0.5) and varying Si concentrations (Si0.5 to Si4), reveal a transformation from pyroaurite to MgFe-smectite via lizardite as an intermediary phase. This transformation underscores the crucial role of Si in this mineral sequence. Notably, experiments demonstrate that the interlayer CO32- in pyroaurite is released into aqueous environments during the mineral conversion, potentially impacting the Martian CO2 budget. These findings could explain isolated carbonate outcrops and the possibility of hydrotalcite-group minerals on Mars today. Further Mars exploration should consider identifying hydrotalcite-group minerals for their implications on the planet's climate and habitability
Industrial-scale sustainable rare earth mining enabled by electrokinetics
No full textOwing to their irreplaceable role in several essential technologies, rare earth elements (REEs) are critical raw materials for the global economy. However, the supply of REEs raises serious sustainability concerns due to the large environmental footprint of conventional mining processes. We previously proposed an electrokinetic mining (EKM) technique that could enable green and selective extraction of REEs from ores. Here we further develop this technique to industrial scale by addressing challenges related to electrode reliability and flow leakage and evaluate its mining efficiency, environmental footprint and economic performance. Moreover, a voltage gradient barrier strategy based on electroosmosis is developed to facilitate electrokinetic REEs mining. As a result, we successfully achieved a high REE recovery efficiency of 95% on a 5,000-ton REEs ore. A rigorous environmental risk assessment revealed a 95% reduction of ammonia emissions, indicating a notably reduced environmental footprint. A comparative technoeconomic analysis between the conventional and the EKM techniques demonstrates the economic viability of the EKM technique. This work validates a new sustainable path for REEs mining, paving the way to a greener resources supply
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
Mercury evidence for volcanism driving environmental changes during the protracted Late Ordovician mass extinction and early Silurian recovery
No full textVolcanism has been proposed as the trigger for the environmental perturbations and associated mass extinction during the Ordovician-Silurian (O-S) transition. However, the timing, duration, and intensity of volcanic eruptions during this critical period and their relationships to environmental perturbations and biotic changes remain unresolved. In this study, we use mercury (Hg) concentrations and isotopes from marine sediments in South China to reconstruct the evolution of volcanism from the Late Ordovician to early Silurian. Our results show that strong Hg enrichment coupled with generally near-zero to slightly positive Delta 199Hg values occurred before, during, and after the classically defined Late Ordovician Mass Extinction (LOME), suggesting a significant influx of volcanogenic Hg. The Hg enrichment intervals coincided with global warming, oceanic anoxia, and negative excursions in carbon and sulfur isotopes, suggesting that volcanism drove the environmental perturbations during the O-S transition. The coincidence of Hg enrichment with extinction horizons supports the hypothesis that volcanism may have contributed to LOME. Our study also suggests that volcanism persisted for approximately 3 million years after mass extinction and may have delayed the recovery of marine ecosystems during early Silurian
Seasonal and spatial variability of dissolved organic nitrogen concentration and composition in Daya Bay, China
No full textDissolved organic nitrogen (DON) has recently been recognized as an important nitrogen source for marine phytoplankton. However, the composition, sources, and biogeochemical cycling of DON in coastal ecosystems remain poorly understood. This study investigates the spatial distribution and seasonal variability of DON in Daya Bay, a subtropical semi-enclosed bay in the northern South China Sea. We measured DON concentrations, the DIN:DIP ratio, and the spectral characteristics of dissolved organic matter (DOM), including a(350), SUVA(254), and fluorescence components. Our findings reveal clear seasonal differences in the controlling factors for DON distribution: in summer, land-based sources and biological activities dominate, whereas in winter, oceanic circulation and its associated water mass mixing play a predominant role. The combined spectral indexes suggest that the transformation of DON is significantly more active in summer than in winter. Additionally, most stations exhibited low DIN:DIP ratios (2 mu g/L) during the summer months, while DIP concentrations in Daya Bay remained generally low (<1 mu mol L-1). This suggests that phytoplankton may assimilate DON, potentially leading to algal blooms and changes in population structure. Overall, these findings highlight the potential role of DON in the coastal nitrogen budget and phytoplankton dynamics, emphasizing the need for further investigation
A systematic review of the source, formation mechanism, and environmental effects of HONO in the indoor air
No full textThe vast majority of human life is spent in indoor environments, and indoor air quality is closely related to human health and well-being. Nitrous acid (HONO), as the main pollutant in indoor environment, has become an emerging indoor contaminant which is widely concerned at home and abroad. HONO is prone to produce hydroxyl free radicals (center dot OH) upon exposure to ultraviolet radiation, which leads to a series of photochemical reactions and ultimately indoor pollution, causing adverse effects on human health. HONO is ubiquitous in indoor environment, and its production process is dynamic and complex. In this work, the primary sources and mechanisms of indoor HONO were reviewed, including the homogeneous reactions, heterogeneous reactions, photolysis of surface nitrates, and other major reaction processes as well as detailed mechanisms leading to the formation of HONO were analyzed. The research progress related to NO2 heterogeneous light-induced reaction on indoor surfaces were summarized. Furthermore, the environmental implications of HONO on indoor air quality and health risk were emphasized, and some important research directions such as indoor multiphase chemical processes, emerging contaminants transformation, modeling and health risk assessment under complex environment were discussed. Indoor HONO serves as a bridge connecting indoor chemistry with the assessment of indoor air quality. Consequently, the comprehensive understanding of the primary sources and formation mechanisms of HONO will help to further improve the current major air quality models, ultimately optimizing the research of indoor chemistry and its impact on human health
A systematic review of the source, formation mechanism, and environmental effects of HONO in the indoor air
No full textThe vast majority of human life is spent in indoor environments, and indoor air quality is closely related to human health and well-being. Nitrous acid (HONO), as the main pollutant in indoor environment, has become an emerging indoor contaminant which is widely concerned at home and abroad. HONO is prone to produce hydroxyl free radicals (center dot OH) upon exposure to ultraviolet radiation, which leads to a series of photochemical reactions and ultimately indoor pollution, causing adverse effects on human health. HONO is ubiquitous in indoor environment, and its production process is dynamic and complex. In this work, the primary sources and mechanisms of indoor HONO were reviewed, including the homogeneous reactions, heterogeneous reactions, photolysis of surface nitrates, and other major reaction processes as well as detailed mechanisms leading to the formation of HONO were analyzed. The research progress related to NO2 heterogeneous light-induced reaction on indoor surfaces were summarized. Furthermore, the environmental implications of HONO on indoor air quality and health risk were emphasized, and some important research directions such as indoor multiphase chemical processes, emerging contaminants transformation, modeling and health risk assessment under complex environment were discussed. Indoor HONO serves as a bridge connecting indoor chemistry with the assessment of indoor air quality. Consequently, the comprehensive understanding of the primary sources and formation mechanisms of HONO will help to further improve the current major air quality models, ultimately optimizing the research of indoor chemistry and its impact on human health
Eocene tearing and fragmentation of Indian lithosphere beneath the Woka rift, southern Tibet
No full textWhen and how the syncontractional N-S- trending rifts formed in the Himalayan Tibetan Plateau are crucial, yet unsolved issues that could help establish the interplay between geodynamic evolution and uplift of the plateau. Recent geophysical observations indicate that although Indian lithosphere tearing is the most likely trigger for rift formation, the timing of this tearing remains uncertain. To address this issue, we studied the Woka rift, which represents a typical N-S- trending rift in southern Tibet. Our results show that granitoids from the hanging wall and footwall of the Woka rift have significantly different magma crystallization temperatures (770-860 degrees C versus 650-750 degrees C) and crustal thickness (-40 km versus- 60 km) during the Eocene. These differences were most likely linked to tearing of the Indian lithosphere. The integration of crustal thickness trends and bedrock emplacement depth from the Eocene to the Oligocene suggest that the hanging wall exhumed at a faster rate than the footwall. From this information, it is clear that the Woka rift did not undergo E-W extension during this period. Integrating data from geophysics, thermochronology, mantle-derived, N-S-trending dikes, and adakitic rocks, we propose that Indian lithospheric tearing and fragmentation during the Eocene caused weakening of the Tibetan middle-lower crust rather than directly triggering surface extension of the Woka rift. This study has significant implications for the deep lithospheric processes and surface responses in the Himalayan-Tibetan Plateau
Eocene tearing and fragmentation of Indian lithosphere beneath the Woka rift, southern Tibet
No full textWhen and how the syncontractional N-S- trending rifts formed in the Himalayan Tibetan Plateau are crucial, yet unsolved issues that could help establish the interplay between geodynamic evolution and uplift of the plateau. Recent geophysical observations indicate that although Indian lithosphere tearing is the most likely trigger for rift formation, the timing of this tearing remains uncertain. To address this issue, we studied the Woka rift, which represents a typical N-S- trending rift in southern Tibet. Our results show that granitoids from the hanging wall and footwall of the Woka rift have significantly different magma crystallization temperatures (770-860 degrees C versus 650-750 degrees C) and crustal thickness (-40 km versus- 60 km) during the Eocene. These differences were most likely linked to tearing of the Indian lithosphere. The integration of crustal thickness trends and bedrock emplacement depth from the Eocene to the Oligocene suggest that the hanging wall exhumed at a faster rate than the footwall. From this information, it is clear that the Woka rift did not undergo E-W extension during this period. Integrating data from geophysics, thermochronology, mantle-derived, N-S-trending dikes, and adakitic rocks, we propose that Indian lithospheric tearing and fragmentation during the Eocene caused weakening of the Tibetan middle-lower crust rather than directly triggering surface extension of the Woka rift. This study has significant implications for the deep lithospheric processes and surface responses in the Himalayan-Tibetan Plateau
<i>Using δD of methyl aromatics and oils to trace the reservoir charging characteristics of complex petroleum systems in Tarim Basin, northwestern China</i>
No full textAromatization occurs steadily during the petroleum evolution stage of light oil/condensate (LOC) formation, for which the composition and delta D of aromatics are of considerable geochemical significance. This paper presents a study on the composition and delta D of monomethyl aromatic compounds (toluene, methylnaphthalene, methylphenanthrene, and methyldibenzothiophene) and related hydrocarbon compounds in LOCs from the Tazhong uplift area of the Tarim Basin in China. Thermal maturity, the source rock of the LOCs, and the effect of gas washing on the oils are discussed. The calculated reflectance of the oils using methyldibenzothiophene and dimethylnaphthalene parameters is approximately 1.15%-1.5%. The thermal maturity of the oils in the Tazhong I fault-slope zone is slightly higher than that of the oils in the Tazhong 10 structural belt due to the more intense gas washing of the oils in the former. The varying degrees of gas washing also caused enrichment of low-carbon-number aromatic hydrocarbons and their H-2 isotopes in the oils of the Tazhong I fault-slope zone relative to those of the Tazhong 10 structural belt. In addition to the contributions from lower Cambrian and Middle-Upper Ordovician source rocks, these crude oils may have received contributions from upper Cambrian Furongian source rocks deposited within locally shielded environments. Crude oils such as TZ62(Silurian) and ZG432(Ordovician) contain heavy delta C-13 but light delta D isotopic compositions and may represent end member oils derived from Furongian source rocks