Geochimica et Cosmochimica Acta最新文献

{"title":"Modeling Solubility Induced Elemental Fractionation of Noble Gases in Oils","authors":"Hai Hoang ,&nbsp;Khac Hieu Ho ,&nbsp;Anne Battani ,&nbsp;James Alexander Scott ,&nbsp;Julien Collell ,&nbsp;Magali Pujol ,&nbsp;Guillaume Galliero","doi":"10.1016/j.gca.2024.09.004","DOIUrl":"10.1016/j.gca.2024.09.004","url":null,"abstract":"<div><div>This study explores the estimation of solubility-induced elemental fractionation of noble gases in hydrocarbon-based oils through existing empirical and theoretical models, complemented by a novel molecular simulation-based approach. Quantifying such fractionation is essential for a deeper understanding of fluid processes and migration in subsurface geological resources, an area currently lacking in experimental data. To address this, the research introduces a predictive model that employs the Peng-Robinson equation of state and a fugacity-coefficient-based method to assess noble gas elemental fractionation in hydrocarbons, including normal alkanes, cycloalkanes, and aromatics. However, this model struggles with precise quantitative predictions, prompting the introduction of adjusted cross-interaction parameters to enhance its performance. Furthermore, molecular simulations, in conjunction with the refined equation of state, are shown to offer a novel method for calculating noble gas fractionation coefficients across different hydrocarbon solvents. A key finding is the identification of a universal master curve, demonstrating that noble gas solubility fractionation at low pressure in simple hydrocarbon solvents can be quantitatively determined by temperature and density alone, without the need for detailed compositional information. Consequently, a new correlation is proposed for deriving elemental fractionation coefficients based solely on oil temperature and density, offering significant improvements over existing empirical methods for a wide range of temperatures. Although limitations are noted when applying this approach to oils rich in complex heavy components like resins and asphaltenes, it allows to address inconsistencies observed in traditionally used experimental correlations at high temperatures.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"388 ","pages":"Pages 127-142"},"PeriodicalIF":4.5,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142321786","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Acceptance for the 2024 V.M. Goldschmidt Award to Donald E. Canfield","authors":"Donald E. Canfield","doi":"10.1016/j.gca.2024.10.030","DOIUrl":"10.1016/j.gca.2024.10.030","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"388 ","pages":"Pages 309-314"},"PeriodicalIF":4.5,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673648","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The roles of celestine and barite in modulating strontium and barium water column concentrations in the northeast Pacific Ocean","authors":"Zvi Steiner ,&nbsp;Alexandra V. Turchyn ,&nbsp;Patrizia Ziveri ,&nbsp;Alan M. Shiller ,&nbsp;Phoebe J. Lam ,&nbsp;Adina Paytan ,&nbsp;Eric P. Achterberg","doi":"10.1016/j.gca.2024.10.003","DOIUrl":"10.1016/j.gca.2024.10.003","url":null,"abstract":"<div><div>The water column distributions of the alkaline earth metals strontium (Sr) and barium (Ba) were studied along a transect from Hawaii to Alaska. Despite similarity in the chemical properties of Sr and Ba, we find that changes in their concentrations along the transect are governed by different chemical and biological processes, meaning that these elements can be treated as independent variables in modern and ancient environments. Alaskan margin sediments are a particularly important source of dissolved Ba to the North Pacific, likely through a combination of saline submarine groundwater discharge and reductive dissolution of manganese (Mn) oxides. Abyssal North Pacific sediments are also a source of Ba to the bottom waters but a sink for Sr. We find that over 90 % of the water column variability in Sr concentrations is driven by precipitation and dissolution of the celestine (SrSO₄) skeletons of Acantharia. However, the high Ba content of Acantharia celestine accounts for only 5–8 % of the global ocean variability in Ba concentrations in the water column. Similarly, the effects of barite (BaSO₄) precipitation and/or dissolution on the marine Sr cycle is negligible, accounting for &lt;1 % of the water column concentration structure for Sr and ∼3 % of the sedimentary Sr burial. The Sr-Ba-PO₄ concentration distributions in the North Pacific are inconsistent with significant export of barite to the deep ocean and sediment. This suggests most of the barite formed at intermediate depths dissolves at similar horizons to its formation. The Ba content of phytoplankton organic matter is too low to constitute a major source for particulate Ba in the mesopelagic North Pacific, which suggests Ba is concentrated in marine aggregates by heterotrophic micro-organisms.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"388 ","pages":"Pages 182-194"},"PeriodicalIF":4.5,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673569","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Quantifying mass-dependent isotope fractionation and nuclear field shift effects for the light rare Earth elements in hydrous systems","authors":"Mark Nestmeyer ,&nbsp;Alex J. McCoy-West","doi":"10.1016/j.gca.2024.10.007","DOIUrl":"10.1016/j.gca.2024.10.007","url":null,"abstract":"<div><div>The improving sensitivity of mass-spectrometers has opened the potential of using stable isotope signatures of the rare Earth elements (REE) as geochemical tracers. However, thus far only limited studies have utilised REE stable isotopes, despite resolvable variations having been observed in a range of systems. An interesting but poorly explored area remains variations in aqueous environments across a range of temperatures including seawater, marine sediments, ion adsorption deposits or hydrothermal systems. Furthermore, the magnitudes and competing effects of mass-dependent isotope fractionation and mass-independent nuclear field shift effects, which can be significant factor for heavy elements especially at high temperatures, remain poorly understood.</div><div>To contribute to a holistic understanding of REE isotope signatures, we calculated reduced partition function ratios (as <em>10³lnβ</em>) for mass-dependent and nuclear field shift effects for aqueous La, Ce, and Nd complexes from first principles. Theoretical calculations were compared with experimental data, and this demonstrates that calculations involving a combination of two explicit hydration shells and additional implicit solvation effects are required to accurately describe the coordination and molecular vibrations of aqueous complexes. This data was then combined with speciation modelling of seawater and hydrothermal fluids to assess isotope fractionation in hydrous systems. The predicted magnitude of isotope fractionation is significant in low (T = 25 °C) temperature systems (Δ^139/138La_Max-Min = 0.20 ‰, Δ^142/140Ce_Max-Min = 0.33 ‰, Δ^146/144Nd_Max-Min = 0.34 ‰) and remains above currently achievable analytical uncertainties even at high (T = 500 °C) temperatures (±0.015 ‰ for <em>δ</em>^146/144Nd; ±0.040 ‰ for <em>δ</em>^142/140Ce). Unless oxidation occurs, which is only relevant for Ce in terrestrial environments, nuclear field shift effects are negligible even at temperatures up to 500 °C. The large difference in nuclear charge radius between ¹⁴⁰Ce and ¹⁴²Ce strongly enriches the lighter Ce isotope in the higher oxidation state (<em>10³lnβ</em>_{Ce(IV)-Ce(III)} = −0.45 at 25 °C) which almost completely cancels out the opposing mass-dependent effect (<em>10³lnβ</em>_{Ce(IV)-Ce(III)} = +0.46 at 25 °C). This means that variations in <em>δ</em>^142/140Ce isotope signatures cannot easily be related to oxidation in ancient or recent environments.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"388 ","pages":"Pages 236-252"},"PeriodicalIF":4.5,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673656","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Carbon Cycling in Marine Particles Based on Inorganic and Organic Stable Isotopes","authors":"Sijia Dong ,&nbsp;Frank J. Pavia ,&nbsp;Adam V. Subhas ,&nbsp;William R. Gray ,&nbsp;Jess F. Adkins ,&nbsp;William M. Berelson","doi":"10.1016/j.gca.2024.10.005","DOIUrl":"10.1016/j.gca.2024.10.005","url":null,"abstract":"<div><div>The marine carbon cycle has a central role in biogeochemical cycling and a close interaction with the climate system. Here, we use the stable carbon isotope (<span><math><mrow><mi>δ</mi></mrow></math></span> ¹³C) of particulate inorganic carbon (PIC) and particulate organic carbon (POC) in marine particles to diagnose carbonate dissolution and organic matter respiration processes in the ocean water column. We show PIC dissolution both in the euphotic zone, potentially driven by POC remineralization, and a preferential dissolution of coccoliths compared to foraminifera below the saturation horizon in the water column. Within the oxygen deficient zone (ODZ), POC remineralization and consequent respiration-driven PIC dissolution are both significantly diminished. We also demonstrate that POC remineralization preferentially removes a ¹³C-enriched component compared to isotopically-light bulk POC in both the large size fraction (LSF, &gt; 51<span><math><mrow><mi>μ</mi></mrow></math></span> m) and small size fraction (SSF, 0.5 – 51<span><math><mrow><mi>μ</mi></mrow></math></span> m) of the pump particles, but exhibits a greater impact on the large particles because of its smaller inventory. Simultaneously, addition of a ¹³C-enriched heterotrophic or chemoautotrophic component to the SSF further increases the isotopic offset between SSF and LSF POC. Overall, this study uses <span><math><mrow><mi>δ</mi></mrow></math></span> ¹³C to provide novel evidence for different biogeochemical processes in marine particles, and demonstrates carbonate dissolution in the ocean water column, both driven by bulk seawater chemistry and organic matter respiration within particles. The absence of O₂ in the ODZ likely protects carbonate from dissolving by severely limiting organic matter respiration, thus reducing shallow PIC dissolution within the ODZs.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"388 ","pages":"Pages 208-220"},"PeriodicalIF":4.5,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673700","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Acceptance for the 2024 C. C. Patterson Award to Satoshi Utsunomiya","authors":"Satoshi Utsunomiya","doi":"10.1016/j.gca.2024.10.034","DOIUrl":"10.1016/j.gca.2024.10.034","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"388 ","pages":"Page 318"},"PeriodicalIF":4.5,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673615","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Equilibrium condensation of a solar composition gas, revisited: The anorthite effect","authors":"Glenn J. MacPherson ,&nbsp;Michail I. Petaev","doi":"10.1016/j.gca.2024.12.032","DOIUrl":"10.1016/j.gca.2024.12.032","url":null,"abstract":"<div><div>New full equilibrium condensation calculations for a hot gas of solar composition show that anorthite condenses prior to forsterite at nebular pressures of 10⁻⁶, 10⁻⁵, 10⁻⁴, and 10⁻³ bars. Because of this difference relative to most previous condensation calculations, the predicted bulk composition trend for total condensed solids now more closely matches the trend defined by natural refractory inclusion bulk compositions. Especially this is true for Type B, Type C, and fine-grained spinel-rich inclusions. Some mismatch exists between our (and others’) calculations with respect to the MgO and SiO₂ compositions of natural inclusions. This is likely due to the kinetically-controlled condensation of spinel prior to melilite. We also explored the effects of pyroxene solid solution models and small degrees of fractional condensation, and found no significant effects on the condensation sequence. Although fractional condensation certainly occurred in the pre-solar nebula, our calculations require the degree of such fractionation to have been less than ∼1 %. Finally, although mass-dependent isotopic fractionation in Type B inclusions indicates some evaporative loss of magnesium and silicon during the molten stage of Type B inclusions, our results remove the <em>necessity</em> that such evaporation occurred in order to explain the bulk compositions of Type Bs. Nevertheless, our results are not incompatible with such evaporative loss.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"391 ","pages":"Pages 248-261"},"PeriodicalIF":4.5,"publicationDate":"2024-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143020257","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Methane Index and TEX86 values in cold seep sediments: Implications for paleo-environmental reconstructions","authors":"Sze Ling Ho ,&nbsp;Yu-Shih Lin ,&nbsp;Pei-Ling Wang ,&nbsp;Tzu-Ting Chen ,&nbsp;Pei-Ting Lee ,&nbsp;Hui-Hsin Wang ,&nbsp;Tzu-Jung Cheng ,&nbsp;Yun-Ju Wang ,&nbsp;Chih-Chieh Su ,&nbsp;Min-Te Chen","doi":"10.1016/j.gca.2024.12.033","DOIUrl":"10.1016/j.gca.2024.12.033","url":null,"abstract":"<div><div>The isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) derived from archaea are widely used in the reconstruction of past climate and environment through proxies such as the Methane Index (MI) and TEX₈₆. A pre-requisite for the application of TEX₈₆, which serves as a proxy for upper ocean temperature, is that the sedimentary GDGTs primarily originate from planktonic Marine Group I Thaumarchaeota. The MI is commonly used as a quality control measure for TEX₈₆ reconstruction to identify samples affected by methanotrophic GDGTs. Recently, the MI has also been used for the reconstruction of past methane cycling. However, the spatial variability of GDGT-based proxies and the relationship between MI and TEX₈₆ remain unclear. In this study, we generated a comprehensive suite of data, including gas, porewater, bulk sediment geochemistry, archaeal cell abundance, GDGTs and their derived proxies. We collected sediment cores from four study sites offshore Southwest Taiwan characterized by the absence or presence of anaerobic oxidation of methane (AOM) and differences in the depth of the sulfate-methane transition zone (SMTZ). The distance between the coring sites varied from ∼20 cm to ∼2 km. The geochemical and DNA data indicated the presence of SMTZs at depths ranging from 4 cm to 290 cm in sediments. AOM-related GDGTs were predominantly composed of GDGT-2, followed by GDGT-1, GDGT-0 and GDGT-3. Although MI values in the SMTZ could reach as high as 0.7, they did not strictly vary based on the SMTZ depth nor the methane consumption rate. This, coupled with the discrepancies in the downcore profiles of gas and porewater geochemistry compared to archaeal DNA and GDGTs, suggest that the duration of SMTZ presence could be a key factor influencing sedimentary MI values. We observed strong relationships between TEX₈₆ and MI at AOM sites; however, the direction of these relationships varied across different locations. Despite this, TEX₈₆-derived temperatures showed good agreement between sites (&lt;1.5 °C between sites located ∼2 km apart), and with climatology data. Consequently, our findings suggest that even in samples with high MI values above the threshold of 0.3, the bias on TEX₈₆-derived temperatures may not be as significant as generally assumed.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"391 ","pages":"Pages 262-276"},"PeriodicalIF":4.5,"publicationDate":"2024-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142985990","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Antimony(V) reaction with particulate natural organic matter: Sorption behavior, binding mechanism, and environmental implications","authors":"Christian Mikutta ,&nbsp;Iso Christl ,&nbsp;Kerstin Hockmann ,&nbsp;Max Niegisch ,&nbsp;Laura S. Schnee","doi":"10.1016/j.gca.2024.12.030","DOIUrl":"10.1016/j.gca.2024.12.030","url":null,"abstract":"<div><div>Antimony (Sb) is a metalloid extensively used in industrial products with a high potential for accumulation in organic-rich soils. Under oxic conditions, dissolved Sb occurs in its pentavalent oxidation state, Sb(V), but little is known about sorptive interactions between Sb(V) and natural organic matter (OM). Therefore, we conducted batch experiments with Sb(V) and particulate OM (POM) of peat as a model sorbent for particulate soil OM. We varied reaction time (1–21 d), concentrations of Sb(V) (1–218 µM) and POM (1–5 g L⁻¹), pH (1.5–10.5), as well as type (NaCl and CaCl₂) and concentration of the background electrolyte (no salt, 0.01 and 0.1 M). Additionally, we explored the molecular mechanism of Sb(V) binding to POM at pH ≤ 4 using X-ray absorption spectroscopy. Based on this information, we modelled Sb(V) sorption data with the Stockholm Humic Model (SHM). Sorption of Sb(V) to POM did not cause Sb reduction and decreased from 109 mmol kg⁻¹ at pH 3 to 72.4 mmol kg⁻¹ at pH 5 (1 g L⁻¹ POM, 0.01 M NaCl). Although sorption maxima were found at pH 1.8–2.8, up to ∼ 10 % of total Sb(V) was still removed from solution at pH 6. An increase in POM concentration, ionic strength, and the presence of Ca²⁺ promoted Sb(V) sorption. The high Sb(V) sorption capacity of POM was associated with a low binding affinity. Sorption kinetics of Sb(V) were slow and generally showed bi-phasic patterns. Apparent half-life times of the fast and slow sorption process at pH 4 and 5 were on average 12.7 and 117 h, respectively. The slowly sorbing Sb(V) was ascribed to diffusion of Sb(V) into net-negatively charged POM particles. X-ray absorption spectroscopy analyses showed 6.3 ± 0.4 O atoms at 1.98 ± 0.01 Å (mean ± SD), followed by 2.1 ± 0.4 C atoms at 2.82 ± 0.05 Å, implying pentavalent Sb in octahedral coordination and bidentate complexation by polycarboxylic, hydroxy-carboxylic, and/or polyol ligands in 5- or 6-membered ring structures. The SHM accurately described Sb(V) sorption edges and sorption isotherm data collected at pH 3–5. SHM calculations implied that Sb(V) sorption to POM may be quantitatively relevant even at pH &gt; 7 and impairs the precipitation of Ca-antimonates at acidic pH. We also predicted competition effects showing that Al, Pb, and MoO₄²⁻ can cause substantial desorption of Sb(V) when present in excess over Sb(V). Model predictions also indicated that Sb(V) complexation by POM in organic soils becomes negligible in presence of &gt; 1 wt% metal oxides. Overall, our results show that although POM has an enormous potential for Sb(V) sequestration over a broad pH range, competing ions and mineral sorbents may strongly decrease Sb(V) binding by POM. This implies that Sb(V) binding to POM is only relevant in oxic metal-poor soil environments such as ombrotrophic peats, organic surface layers, and OM-rich microenvironments of mineral soils.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"391 ","pages":"Pages 218-236"},"PeriodicalIF":4.5,"publicationDate":"2024-12-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143020020","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Gamma-irradiation-induced reduction of aqueous Se(VI) by natural pyrite","authors":"Jingye She ,&nbsp;Danwen Qin ,&nbsp;Andreas C. Scheinost ,&nbsp;Mingliang Kang ,&nbsp;Wujian Jin ,&nbsp;Hanqin Weng ,&nbsp;Hanyu Wu ,&nbsp;Jianrong Zeng","doi":"10.1016/j.gca.2024.12.031","DOIUrl":"10.1016/j.gca.2024.12.031","url":null,"abstract":"<div><div>Although the reduction of Se(VI) to Se⁰ and FeSe₂ by pyrite is thermodynamically favorable, well-crystallized natural pyrite remains chemically inert to aqueous Se(VI) under conventional conditions. In this study, the interaction of aqueous Se(VI) with natural arsenic-rich and arsenic-free pyrites was studied under gamma-irradiation at pH ∼4.0 to ∼9.0, mimicking the conditions near a nuclear waste repository. The results showed that gamma-irradiation significantly boosts the reductive precipitation of Se(VI) by arsenic-rich pyrite at pH ∼4.0 to ∼9.0. For arsenic-free pyrite, this enhancement was observed within a narrower pH range of ∼5.0 to ∼6.0, and a distinct red precipitate, indicative of Se⁰, formed during the reaction at pH ∼6.0 under an absorbed dose of 100 kGy at a dose rate of 100 Gy/min. The reduction process involving arsenic-rich pyrite is more sensitive to the absorbed dose rate, with a decrease in Se(VI) removal efficiency at higher dose rates. Conversely, both the absorbed dose and the dose rate have significant effects on the reactions involving the arsenic-free pyrite. Transmission electron microscopy and X-ray absorption spectroscopy analyses verified the occurrence of Se⁰ nanoparticles on pyrite surfaces via the intermediate product of Se(IV). It is suggested that the ·OH radical generated by water radiolysis can be scavenged by pyrite and/or its non-oxidative dissolved solutes such as Fe²⁺ and H₃AsO₃/AsO₃³⁻ impurities, allowing the concurrent e_aq⁻ and ·H, primarily e_aq⁻, to reduce Se(VI), thereby altering the reaction pathway between pyrite and aqueous Se(VI) under gamma-irradiation. This work offers important insights into the geochemical behavior of ⁷⁹Se in the near-field of a nuclear waste repository.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"391 ","pages":"Pages 237-247"},"PeriodicalIF":4.5,"publicationDate":"2024-12-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142936030","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}