Applied Geochemistry最新文献

Kinetic modeling of microbial reactions is a common tool for addressing the central environmental questions of our time, from contaminant remediation to the global carbon cycle. This review presents an overview of trait-based frameworks for modeling the kinetics of microbial reactions, with an emphasis on environmental application. I first highlight two key model assumptions: the simplification of microbial communities as ensembles of microbial functional groups and the description of microbial metabolism at a coarse-grained level with three metabolic reactions – catabolic reaction, biomass synthesis, and maintenance. Next, I aim to establish a connection between microbial rate laws and the mechanisms of metabolic reactions. For metabolic reactions limited by single substrates, the widely used rate law is the Monod equation. However, in cases where substrates are solids or nonaqueous phase liquids (NAPLs), the Contois equation and the Best equation may offer better alternatives. In microbial metabolisms limited by multiple nutrients simultaneously, two competing rate laws exist: the multiplicative rate law and Liebig's law of the minimum. Then I present two strategies for extending the modeling framework developed for laboratory cultures to natural environments. One strategy follows the multiplicative rate law and incorporates dimensionless functions to account for pH, temperature, salinity, cell density, and other environmental conditions. The other strategy focuses on the physiology of natural microbes, explicitly considering dormancy, biomass decay, and physiological acclimation. After that, I highlight recent improvements enabled by the application of molecular biology tools, ranging from functional gene-based models to metabolic models. Finally, I discuss the inherent limitations of trait-based modeling frameworks and their implications for model development and evaluation, including the gap between functional groups represented in silico and microbial communities found in natural environments, as well as the requirement of internal consistency in microbial parameter sets.

Understanding the stability of the bentonite buffer when exposed to cement leachates at temperatures exceeding 100°C is crucial for optimizing the design of deep geological repositories (DGRs) for high-level radioactive wastes (HLRWs) and minimizing the required site area. Experiments were conducted under hydrothermal conditions at 150°C for 30–150 days using deionized (DI) water (pH 6) and K-rich solutions (1 mol/L KCl, pH 6 and 1 mol/L KOH, pH 13) on Ca-bentonite. The 1 mol K concentration is comparable to 15 times the cation exchange capacity (CEC) of raw bentonite. Using various analytical techniques, the mineralogical, physicochemical, swelling, and Cs adsorption characteristics of raw and reacted bentonite samples were determined. Almost no changes in the properties of bentonite reacted with DI water were found for a given reaction time. For bentonite reacted with a 1 mol/L KCl solution, the cation exchange of Ca by K was a primary alteration process, resulting in a slight decrease in swelling capacity. However, almost no mineralogical changes were observed and consequently, there was minimal change in the Cs adsorption capacity. In contrast, for the bentonite reacted with a 1 mol/L KOH solution, the dominant alteration process was the transformation of minerals in bentonite into zeolite minerals, which resulted in significant changes in physicochemical properties, in particular, a decrease in the swelling capacity. On the other hand, the Cs adsorption capacity increased up to 2 times compared with the raw bentonite.

Radon is classified as a Class 1 carcinogen, being the leading cause of lung cancer in non-smokers. Understanding the prominent sources of radon helps to mitigate against the adverse effects of radon exposure. Considering soil-gas radon is the main contributor to indoor radon, it is possible that soil geochemistry can be used as a proxy for the soil radon emanation potential or geogenic radon classes for a particular location. This paper investigates the relationship between soil geochemistry and geogenic radon. A large area of 17,983 km² from the West, Midlands and East of Ireland was selected to represent a range of geology types and radon categories. A rigorous assessment is presented to investigate the relationship of geogenic radon and topsoil geochemistry; using univariate processes (i.e. r², Pearson r and heatmaps) and multivariate techniques (i.e. principle component analysis (PCA) and machine learning (ML) algorithms including Gaussian process regression, logistic regression and random forest). Here, PCA and ML techniques were used to test the utility of soil geochemistry to predict geogenic radon classes. Gaussian Process Regression yielded the highest accuracy (74%) and f1-score (0.74) of all models. The feature importance (i.e. highest ranking elements for predicting geogenic radon class) from the ML models outputs elements including [Y, Tl, Mn, Cr, Co, Be, Sc and Rb]. The PCA biplot demonstrates that these elements cluster in conjunction with higher geogenic radon categories. Multivariate data analysis reveals that certain elements important for predicting higher geogenic radon classes, also covary together within topsoil samples; here these are termed “radon-prone elements”. Spatial covariance of radon-prone elements permits soil geochemistry to be used as a tool for understanding the distribution of geogenic radon. The methodology presented in this paper provides a comprehensive geo-statistical approach to investigate the relation between topsoil geochemistry and geogenic radon. This approach could be applied as a diagnostic tool to assist radon mitigation measures, hence adding value to legacy soil geochemistry datasets.

Groundwater iodine has direct importance for human dietary iodine intake in areas where drinking water is of groundwater origin. Iodine affected aquifer system in Datong Basin of North China was studied with a focus on strontium isotopes and major ion chemistry, in order to estimate the controlling hydrological and geochemical processes. The data revealed a rather complicated mixing pattern of various groundwater source end-members that were subject to different water-rock interactions, such as silicate weathering, evaporite and carbonate dissolution. Groundwater from the recharge area of east margin was characteristic by ⁸⁷Sr/⁸⁶Sr ratios higher than 0.71643, which implied the silicate weathering process. Groundwater from the discharge area and west margin might be originated from evaporite and carbonate dissolution processes with low ⁸⁷Sr/⁸⁶Sr ratios. Mixing models of three end-members based on Sr isotope and contents reflected that the type of water-rock interactions shifted from silicate weathering towards evaporite dissolution along the groundwater flow path from east margin to basin center. Abundant iodine and natural organic matters (NOMs) were discovered in groundwater located at the discharge area with Sr isotopic values between 0.710 and 0.717, implying evaporite dissolution governing iodine and NOMs enrichment in groundwater. Silicate weathering process had negligible influence on iodine and NOMs enrichment in groundwater. While carbonate dissolution made negative contribution for iodine releasing to aqueous phases. The PHREEQC inverse modeling results illustrated that dissolution of halite, calcite, gypsum and kaolinite and cation exchange significantly changed chemical composition of groundwater along the groundwater paths from the two basin margins to central area.

Increased exposure to arsenic (As) has been reported in many arid and semi-arid areas, where drinking water and agricultural irrigation strongly rely on groundwater. High-As groundwater occurred widely in the Northern Henan Plain, which belongs to the lower Yellow River alluvial plain area, posing a new threat to the health of local residents. Based on 77 groundwater samples collected from different hydrogeological units, the sources and optical characteristics of dissolved organic matter (DOM) components in groundwater were analyzed using a three-dimensional fluorescence spectroscopy excitation-emission matrix (3D-EEM) and parallel factor analysis (PARAFAC), to reveal the influence of organic matter on As mobilization and enrichment in Quaternary alluvial aquifers. The results showed that high-As groundwater was concentrated in the areas of the piedmont alluvial depressions and the Yellow River crevasse splay, which was closely related to the richness of organic matter in the buried sediments of the Yellow River paleochannels. Vertically, the variability of groundwater As was governed by the redox conditions and anthropogenic activities, leading to elevated As levels in deep aquifers. High-As groundwater was characterized by high content of humic-like components (C2+C3), strong humification, and weak authigenic sources, which can be attributed to the effects of frequent diversion of the Yellow River and the introduction of more terrestrial humic-like components by intensive agricultural activities (e.g., irrigation). The significant correlations between Fe²⁺ and As and NH₄⁺ (r = 0.65, 0.48, p < 0.05) as well as the maximum fluorescence intensity of C2 and C3 with As (r = 0.59, 0.74, p < 0.05) reflected the dominant impact of DOM on As migration. The terrestrial-derived high molecular weight organic matter C2 facilitated As mobilization through complexation reactions, while the labile humic-like component C3 triggered the reductive dissolution of iron oxides/hydroxides through microbial metabolic processes, which together contributed to the enrichment of As in groundwater from the Northern Henan Plain.

The Djibouti area is located in the Afar depression which corresponds to the core of a major hot spot at the junction of three rifts: The Red Sea oceanic rift, the Gulf of Aden oceanic rift and the East African continental rift. In the extension of the Gulf of Aden, the opening of the Gulf of Tadjourah in the last 30 million years was followed by the establishment of parallel NW-SE oriented depressions (Gobaad, Hanle, Gaggade, Assal-Ghoubbet). This region is characterised by high heat flow, complex volcanic and tectonic activity, and a dense network of faults favorable to the development of hydrothermal activities. A field survey was conducted to study the gas composition and origin in thermal springs and fumaroles along a transect running from the Lake Abbhé to Djibouti. Hydrogen traces were detected at fumaroles and hot springs associated with hydrothermal systems at the edges of the Gobaad, Hanlé, Gaggade, Assal-Ghoubbet and Arta area. The processes governing to the origin of H₂ and its consumption at different levels of the magmatic-hydrothermal systems are discussed. H₂ is interpreted as related to several processes including, chemical equilibrium in magmatic gases, alteration of Fe^II-rich rocks, and oxidation of volcanic H₂S. Methane associated with the hydrogen has mostly an abiotic origin and could result from the reaction of hydrogen with carbon oxides. Also, helium emanations have been observed notably on the sides of the Lake Abbhé in boiling hot springs. Gas samples have shown R/RA isotopic ratios of helium up to 10, which is are characteristic values for helium of mantle origin characterized an ³He enrichment with respect to air values.

The goal of this study is to determine the interaction coefficients between alkali metal ions M⁺ (M = Li, Na, K, Rb, Cs, NH₄), the sulfate ion $S{O}_4^{2-}$, and ion pairs $\text{MS}{O}_4^{-}$ for the use in the SIT model for activity coefficients, which is popular among solution chemists and adopted by OECD Nuclear Energy Agency (NEA) to develop a thermodynamic database relevant to the safety of radioactive waste repositories. As alkali metal sulfates are partially associated electrolytes, relations from the thermodynamics of associated solutions (“equilibrium model”) are employed for the correct treatment of tabulated activity and osmotic coefficients. As a part of this work, a compilation of stability constants of the ion pairs $\text{MS}{O}_4^{-}$ is made together with selection of the recommended values. In addition, solubility values in ternary $M_{2}S{O}_4-N_{2}S{O}_4-H_{2}O$ are used to expand the list of relevant interactions. In total, the numerical values of the SIT coefficients are determined for 38 ionic interactions among indicated species. All values refer to 298.15 K and 0.1 MPa.

This study has developed a novel variational autoencoder architecture by incorporating the spectrum separable module, termed SSM-VAE, so as to recognize the multi-mineral-species geochemical patterns over the Shangluo district, central China, and then facilitate a better understanding of the regional metallogenesis. The primary advantage of SSM-VAE is its ability to explore the interlayer correlations and then integrate them into the reconstructed features, which greatly improved the geological interpretability of the model products. In the training process, a hybrid loss function with a geologically-constrained term derived from the fractal analysis was designed to guide the model to focus on anomalies related to mineralization. Afterward, the factor analysis together with the EM-MML thresholding algorithm were integrated as a post-processing tool. Finally, the mineral-spot identification rate (δ) versus the size of the anomalous area (S) are used to validate the ore-bearing potential of different anomaly divisions. Comparing to other state-of-the-art models without regard to the interlayer correlations, SSM-VAE can produce well-zoned, mineral species-specific, and more metalliferous anomalous patches. To be specific, we separated out 10 zoned anomaly divisions, and on average, when S = 1% there are 8.5013 mineral spots falling within.

The Battle Mountain area is a major porphyry style Au (–Cu) district in northern Nevada, forming one end of the Battle Mountain-Eureka mineral trend. This trend, along with several others in the north-central Nevada region, hosts some of the world's most prolific gold mineralization, which is oftentimes associated with a suite of trace elements including arsenic, antimony, tungsten, and thallium and can be related to or overprinted by hydrothermal alteration. However, determining the extent of control hydrothermal fluids exert on some of the deposits in the region has been difficult to ascertain. One of the associated trace metals in the region, thallium (Tl), is a highly incompatible element and, as such, dominantly resides in the continental crust, where it can be easily remobilized during hydrothermal alteration. While previous work has demonstrated the effects of hydrothermal alteration on Tl distribution and fractionation, the controls responsible for the observed Tl fractionation during hydrothermal alteration are still poorly characterized but may provide insight into fluid behavior. Here, we present new Tl isotope composition and concentration data for a suite of 54 mineral separates obtained from 43 samples from the Battle Mountain area, which range from unaltered intrusive igneous rocks through varying types and degrees of hydrothermally altered rocks.

Measured Tl concentrations vary by more than an order of magnitude, from below detection limit (0.2 ppm in this study) to 2.0 ppm, while ε²⁰⁵Tl ranges between −5.0 and +2.2 (ε²⁰⁵Tl is the deviation of the ²⁰⁵Tl/²⁰³Tl isotope ratio of a sample from a standard in parts per 10⁴). Thallium concentrations correlate positively with whole-rock potassium (K), thus show strong increases during K alteration, and demonstrate significantly lower ε²⁰⁵Tl values within K-altered samples. Conversely, during later, overprinting Na–Ca alteration, both K and Tl are removed, resulting in a noted decrease in Tl concentrations coupled with a shift to significantly higher ε²⁰⁵Tl values. It appears that during hydrothermal alteration, ²⁰³Tl is more easily (re)mobilized and (re)distributed, which reflects: 1) a first-order hydrothermal alteration control that relates to the transport of Tl during the formation of a new, metasomatic mineral assemblage (particularly the breakdown and/or formation of K-bearing minerals) and 2) a second-order mineralogical control, relating to inter-mineral equilibrium, which also results in a small fractionation effect.

Antimony pollution caused by mining activities is a current environmental concern. This study investigates the processes involved in the Sb release and mobility in the abandoned Sb mine of Su Suergiu (SE Sardinia, Italy). Analyses of outcropping rocks, mine wastes and smelting slags by means of X-Ray Powder Diffraction, Scanning Electron Microscopy - Energy Dispersive Spectroscopy and Electron Microprobe – Wavelength Dispersive Spectroscopy provided mineralogical and compositional data which contributed to the discussion about the oxidation pathways of Sb phases. The main Sb sources are metallic Sb and Sb₂O₃ (valentinite/senarmontite), dumped in the smelting slag heaps as residues of metallurgical processes, and primary stibnite (Sb₂S₃) found in natural outcrops and mine wastes. These minerals, subjected to weathering processes, release Sb in solution where it is oxidized and remains as dissolved ${Sb\left(OH\right)}_6^{-}$. Carbonates and Na phases, like hydrate NaAl-silicate derived from metallurgical processes, influence the geochemical equilibria of the smelting slag heaps, where the precipitation of the rare mopungite, Na[Sb(OH)₆], has been observed. At Su Suergiu, mopungite originates from a dissolution-precipitation process as the last forming mineral of the oxidation pathways, limiting the Sb mobility by bonding the ${Sb\left(OH\right)}_6^{-}$ in solution. Among the detected Sb secondary phases (e.g., Sb-oxides, FeSb-oxides, etc.), mopungite is the prevalent Sb binder although it acts as a temporary sink because its stability is influenced by the hydrological regime, its solubility, and the water physicochemical parameters. Secondary Sb-bearing minerals can control the dispersion of Sb in contaminated area. At Su Suergiu the role of Fe-bearing compounds on Sb mobility is subordinate to that of mopungite due to the specific geochemical conditions related to the metallurgical activities. The relevance of this study arises from the known toxicity of Sb and from its worldwide diffuse mining, that results in the widespread occurrence of Na–Sb-rich residues produced by Sb smelting plants.