Geochimica et Cosmochimica Acta最新文献

{"title":"A spectroscopic study of the stability of uranyl-carbonate complexes at 25–150 °C and re-visiting the data available for uranyl-chloride, uranyl-sulfate, and uranyl-hydroxide species","authors":"A. Migdisov ,&nbsp;E. Bastrakov ,&nbsp;C. Alcorn ,&nbsp;M. Reece ,&nbsp;H. Boukhalfa ,&nbsp;F.A. Capporuscio ,&nbsp;C. Jove-Colon","doi":"10.1016/j.gca.2024.04.023","DOIUrl":"10.1016/j.gca.2024.04.023","url":null,"abstract":"<div><div><span>The stabilities of uranyl-carbonate and uranyl-hydroxide aqueous complexes were experimentally determined at temperatures ranging from 25 to 125 °C using in situ UV–vis and Raman spectroscopic techniques. Combined with earlier determinations of the stability of chloride, sulfate, and hydroxide complexes at temperatures up to 250 °C, these data permit to create a consolidated dataset suitable for modeling of U(VI) mobilization in natural systems. The parameters of the Modified Ryzhenko-Bryzgalin and the Helgeson-Kirkham-Flowers (HKF) Equations of State (EoS) were derived based on this dataset and used for thermodynamic modeling different scenarios of U(VI) mobilization. These models suggest that at conditions relevant to natural systems, carbonate-mediated transport of U(VI) is likely suppressed by the high stability of solid UO</span>₂(OH)₂ and Na₂U₂O₇. In contrast, sulfate-mediated mobilization mechanisms are highly efficient at acidic and near-neutral pH conditions and can lead to effective hydrothermal mobilization of U(VI).</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"406 ","pages":"Pages 326-339"},"PeriodicalIF":5.0,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140768103","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":"Gold(I)-bisulfite complexation in hydrothermal nanodroplets: A molecular dynamics study","authors":"Wallace C.H. Hui,&nbsp;Kono H. Lemke","doi":"10.1016/j.gca.2025.01.015","DOIUrl":"10.1016/j.gca.2025.01.015","url":null,"abstract":"<div><div><span>Water nanodroplets present a unique environment for gold hydrothermal transport, with fluid properties in aqueous nanodroplets distinct from bulk liquid and vapor phases. By performing classical and </span><em>ab initio</em><span> molecular dynamics simulations, we have probed the stability of water nanodroplets (H</span>₂O)<em>_n</em> (<em>n</em><span> = 100, 1000) at 25 °C and 100 °C. The solvation and complexation of gold(I)-bisulfite AuHSO</span>₃<span> in nanodroplet environments were also examined, with a particular focus on surface and interior solvation<span>. Classical TIP4P/2005 molecular dynamics simulations reveal extreme densities in the interior of (H</span></span>₂O)₁₀₀ and (H₂O)₁₀₀₀ nanodroplets compared to droplet surface regions. At 25 °C, the interior region of (H₂O)₁₀₀ exhibits fluctuating densities at 1.016–1.079 g/cm³, with two maxima at 1.079 g/cm³ and 1.074 g/cm³, corresponding to pressures of ∼ 2.23 kbar and 2.07 kbar, respectively; Reduced densities are predicted for the larger (H₂O)₁₀₀₀ systems, these being 1.013 g/cm³ (25 °C, 370 bar) and 0.968 g/cm³ (100 °C, 220 bar). The outer regions, on the other hand, featured densities intermediate between saturated liquid and vapor conditions, as part of a transition from liquid to vapor-like densities at the edge of the droplet. Born-Oppenheimer molecular dynamics simulations at 100 °C show that the gold(I)-bisulfite complex H₂O-AuHSO₃<span> maintains a near linear solvation structure (θ</span>_O-Au-S = 172°-174°) in bulk aqueous fluids and at surface and interior sites of (H₂O)₁₀₀ nanodroplets. Distance constrained simulations reveal that, upon extension of the gold(I)-bisulfite Au-S contact (equilibrium <em>r</em>_Au-S = 2.3 Å), HSO₃⁻<span> is displaced by a water molecule, forming a two-water solvation shell around Au</span>⁺<span>. Thermodynamic integration gives gold(I)-bisulfite dissociation energies (ΔG) of 17.65 ± 0.37 kcal/mol (bulk), 20.22 ± 0.38 kcal/mol (nanodroplet surface), and 18.31 ± 0.31 kcal/mol (nanodroplet interior). Our </span><em>ab initio</em> molecular dynamics results demonstrate that water nanodroplets are stable at hydrothermal conditions and would play an important role in the speciation and transport of gold in volcanic and hydrothermal vapors.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"406 ","pages":"Pages 317-325"},"PeriodicalIF":5.0,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143462870","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 solubility of La hydroxide and stability of La3+ and La hydroxyl complexes at acidic to mildly acidic pH from 25 to 250 °C","authors":"Kevin Padilla,&nbsp;Alexander P. Gysi","doi":"10.1016/j.gca.2024.12.006","DOIUrl":"10.1016/j.gca.2024.12.006","url":null,"abstract":"<div><div><span>The mobility of rare earth elements<span> (REE) in natural hydrothermal systems can be assessed using geochemical modeling, which requires reliable thermodynamic data of relevant aqueous species. In this study, we evaluate the controls of pH and temperature on La speciation and the role of hydroxyl complexes in REE transport at hydrothermal conditions. Batch-type hydrothermal solubility experiments were conducted using synthetic La hydroxide powders equilibrated in perchloric acid-based aqueous solutions at temperatures between 150 and 250 °C and starting pH of 2 to 5. The La hydroxide solubility is retrograde with temperature and displays a strong pH dependence with a decrease in La concentrations from acidic to mildly acidic pH spanning between 3 and 5 orders of magnitude (e.g. log La molality of −2.5 to −7.2 at 250 °C). Thermodynamic optimizations using GEMSFITS allow to retrieve the standard partial molal Gibbs energies for the La</span></span>³⁺ aqua ion and the formation constants for the La hydroxyl species (i.e., LaOH²⁺, La(OH)₂⁺, La(OH)₃⁰<span>) between 25 and 250 °C. A comparison between the experimentally derived thermodynamic properties with the calculated values from the Helgeson-Kirkham-Flowers equation of state parameters indicates an increased divergence with temperature. Discrepancies in standard partial molal Gibbs energies range between ∼ 1 − 12 kJ/mol and result in a predicted La hydroxide solubility differing by up to 3 orders of magnitude at 250 °C. Speciation calculations indicate a higher stability of La</span>³⁺ and LaOH²⁺<span> over the other La hydroxyl species in the studied pH range of 3.4 to 6. The optimized thermodynamic properties for La aqueous species have important implications for modeling the solubility of REE minerals such as monazite and the mobility of REE in hydrothermal systems.</span></div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"406 ","pages":"Pages 175-188"},"PeriodicalIF":5.0,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142841533","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":"Stability and structure of aqueous Sb (III) chloride complexes from 25 °C to 250 °C at 25 MPa at high chloride ion concentrations","authors":"Avinaash A. Persaud,&nbsp;Swaroop Sasidharanpillai,&nbsp;Jenny S. Cox,&nbsp;Peter R. Tremaine","doi":"10.1016/j.gca.2024.12.013","DOIUrl":"10.1016/j.gca.2024.12.013","url":null,"abstract":"<div><div><span><span>Despite their importance in modelling the formation of antimony-containing hydrothermal ore deposits, only a few values for the thermodynamic properties of the antimony(III) chloride and sulfide complexes have been reported above ambient conditions. The existing </span>thermochemical<span><span> data, which extend to ∼250 °C, and the structures of the equilibrium antimony chloride and hydroxy chloride complexes, are largely based on solubility data and </span>EXAFS<span> studies. In the present study, polarized Raman spectroscopy<span> with pressure-controlled, high-pressure fused-silica capillary cells was used to identify the complexes of antimony present in highly-concentrated aqueous lithium chloride solutions (&gt;2 mol·kg</span></span></span></span>⁻¹<span><span>) from 25 to 250 °C at 25 MPa. Vibrational band assignments were made by comparison with computational studies using Gaussian 16 (B3LYP, IEFPCM </span>solvation model), which showed that SbCl</span>₆³⁻ (octahedral), SbCl₄⁻ (see-saw) and SbCl₃⁰ (trigonal pyramidal) are the predominant aqueous antimony species up to 250 °C. Quantitative speciation data from the solvent-subtracted, reduced isotropic spectra were used to determine the stepwise formation constants, <em>K</em>₃,₄ and <em>K</em>₄,₆<span>, together with the Lindsay-Meissner-Tester activity coefficient model. Attempts to fit </span><em>K</em>₄,₆ to the ionic-strength suggested that the predominant species of SbCl₆³⁻<span> under these conditions is an ion pair, LiSbCl</span>₆²⁻, whose formation constant is expressed as <em>K</em>₄,_6Li. The experimental equilibrium concentrations and the fitted values of <em>K</em>₃,₄ and <em>K</em>₄,_6Li show that the equilibria shift with increasing temperature, such that SbCl₄⁻<span> becomes the dominant species in concentrated solutions at 250 °C. This study includes new evidence based on Raman band<span> assignments to resolve the controversy of whether the dominant species at high alkalinities and lower temperatures is SbCl</span></span>₆³⁻ or SbCl₅²⁻.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"406 ","pages":"Pages 148-163"},"PeriodicalIF":5.0,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145326685","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":"Potential for formation of methylated thioarsenates in geothermal environments","authors":"Ketao Yan ,&nbsp;Qinghai Guo ,&nbsp;Luxia Wang ,&nbsp;Yi Liu ,&nbsp;Britta Planer-Friedrich","doi":"10.1016/j.gca.2024.10.012","DOIUrl":"10.1016/j.gca.2024.10.012","url":null,"abstract":"<div><div><span>Geothermal waters typically have elevated arsenic (As) concentrations. Various As species have been identified, including methylated thioarsenates, which present a high environmental and health risk due to high mobility and toxicity. Upon discharge from hot springs, temperature and geogenic sulfide excess decrease, while redox potential increases. The combined effects of those parameters on activities of sulfate-reducing bacteria and </span>methanogens<span><span> and thereby on extent of As methylation<span> versus thiolation is currently unknown. Here, we incubated sediments from alkaline hot springs and outflow channels at the Tengchong geothermal region in southwestern China, where inorganic and methylated thioarsenates had been detected, at temperatures between 20 to 90 °C with different initial aqueous As and sulfur species. Results from field samples and incubation experiments showed methylated thioarsenates, but no methylated oxyarsenates, implying quantitative thiolation even at low sulfide concentrations. </span></span>Enrichment cultures<span> derived from one sediment with quantitative formation of dimethyl-dithioarsenate (DMDTA) at 55 °C, showed a dominance of inorganic trithioarsenate at 35 °C and monomethylated thioarsenates at 55 °C when incubated with two other sediments. The rate-limiting step was microbially mediated As methylation<span> from arsenite<span>, which was not observed at 20 °C or &gt;= 75 °C, in contrast to thiolation of already methylated arsenates. Addition of free sulfide and thiosulfate to incubation experiments promoted formation of inorganic or monomethylated high-thiolated arsenates, while sulfate promoted full methylation and formation of DMDTA, probably due to continuous low supply of microbially produced sulfide. Since DMDTA is more mobile and toxic than inorganic and monomethylated thioarsenates, understanding constraints to its formation is especially important for future risk assessment.</span></span></span></span></div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"406 ","pages":"Pages 119-133"},"PeriodicalIF":5.0,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673654","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":"Hydrothermal solution calorimetry in acidic aqueous solutions and revisiting the standard partial molal thermodynamic properties of Nd3+ from 25 to 300 °C","authors":"Yerko Figueroa Penarrieta,&nbsp;Alexander P. Gysi","doi":"10.1016/j.gca.2024.07.014","DOIUrl":"10.1016/j.gca.2024.07.014","url":null,"abstract":"<div><div><span>The mobility of rare earth elements (REE) can be predicted in aqueous fluids using geochemical modeling but the accuracy of these models strongly depends on the availability of robust thermodynamic properties for the REE aqueous species. The REE</span>³⁺ aqua ions are important in the derivation of the formation constants of all the major REE complexes including the chloride, sulfate, and fluoride species which predominate in many hydrothermal-magmatic systems. However, the thermodynamic properties of the REE³⁺<span> aqua ions are still commonly derived from the Helgeson-Kirkham-Flowers (HKF) equation of state<span> parameters tabulated several decades ago. The standard state thermodynamic properties at reference conditions (25 °C and 1 bar) and their extrapolations to high temperature need to be verified, if not revised, based on hydrothermal experiments. In this study, the enthalpy of solution was measured for synthetic Nd hydroxide from 25 to 150 °C to retrieve the standard partial molal thermodynamic properties of Nd</span></span>³⁺<span><span> as a function of temperature. The experiments were conducted in aqueous perchloric acid based solutions with starting pH of 2 and varying </span>ionic strength (0.01–0.09 mol/kg NaClO</span>₄<span>). The standard partial molal enthalpy of formation (Δ</span>_f<em>H</em>°) of Nd³⁺<span><span> derived from the experimental study displays differences of up to 10 kJ/mol compared to the enthalpy values derived from the HKF equation of state in the studied temperature range. These inaccuracies are resolved by adjusting the standard partial molal </span>Gibbs energy of formation (Δ</span>_f<em>G</em>°) of Nd³⁺ at 25 °C and 1 bar from −672.0 to −679.7 kJ/mol. The heat capacity function (<em>C_p</em>°) derived between 25 and 150 °C can be described by: <em>C_p</em>° = <em>a</em>₀ + <em>a</em>₁⋅<em>T</em> + <em>a</em>₂⋅<em>T</em>⁻², with <em>a</em>₀ = 1256, <em>a</em>₁ = −2.68, <em>a</em>₂ = −55.56⋅10⁶ and <em>T</em> in Kelvin. A set of recommended thermodynamic properties is provided for the Nd³⁺<span> aqua ions and corrections are provided for the chloride and fluoride species to remain internally consistent with the experimentally derived properties. These results allow predicting accurately the solubility of monazite between 25 and 300 °C. Before these corrections, the properties for the Nd</span>³⁺<span> aqua ions derived from the HKF parameters resulted in up to ∼1.5 orders of magnitude lower monazite solubility than determined experimentally. Therefore, a revision of the REE</span>⁺³ aqua ions properties is necessary to accurately predict the mobility of REE in hydrothermal acidic solutions.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"406 ","pages":"Pages 227-242"},"PeriodicalIF":5.0,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145326687","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":"Tantalum in hydrothermal fluids","authors":"Bin Hu ,&nbsp;Barbara Etschmann ,&nbsp;Denis Testemale ,&nbsp;Weihua Liu ,&nbsp;Qiushi Guan ,&nbsp;Harald Müller ,&nbsp;Joël Brugger","doi":"10.1016/j.gca.2024.10.019","DOIUrl":"10.1016/j.gca.2024.10.019","url":null,"abstract":"<div><div>Understanding the behaviour of tantalum (Ta) in hydrothermal systems is pivotal for understanding its geochemical enrichment processes and economic extraction via hydrometallurgy. Yet, its behaviour in hydrothermal systems remains poorly characterised. This study investigates the coordination chemistry, speciation, and solubility of pentavalent Ta(V) in fluoride (F) − and chloride (Cl) −rich hydrothermal solutions up to 413 °C and 800 bar, utilising <em>in-situ</em> High Energy Resolution Fluorescence Detected X-ray Absorption Spectroscopy (HERFD-XAS). The results reveal the stability of high order fluoridotantalate complexes in fluoride-rich fluids solutions up to the highest investigated temperature, highlighting fluoride’s paramount role in enhancing Ta solubility through the formation of stable fluoridotantalate complexes in aqueous solutions. A transition from nonafluoridotantalate tetraanion (TaF₉⁴⁻) to heptafluoridotantalate dianion (TaF₇²⁻) complexes was observed as a function of temperature in solutions containing ≥1 <em>m</em> fluoride. Conversely, our findings indicate a negligible role for chloride in Ta complexation even in high Cl (∼6 <em>m</em>) aqueous solutions, suggesting that Ta chloride complexes do not contribute significantly to Ta transport in hydrothermal systems. Existing solubility data were reinterpreted based on an updated speciation model that integrates the <em>in-situ</em> XAS results. This confirms that Ta(OH)₅(aq) predominates in solutions containing &lt;0.02 <em>m</em> fluoride; oxyfluoridotantalate anions such as [TaF₃(OH)₃⁻] dominate in solutions containing intermediate fluoride concentrations (0.02–1 <em>m</em>), and the fluoridotantalate anions [TaF₉⁴⁻ to TaF₇²⁻] occur in more concentrated fluoride solutions (&gt;1 <em>m</em>) at hydrothermal conditions (∼100–400 °C). Derived thermodynamic data for these species enable better understanding and geochemical modelling of Ta transport in hydrothermal fluids, highlighting the potential of F-rich fluids to transport significant amounts of Ta.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"406 ","pages":"Pages 243-261"},"PeriodicalIF":5.0,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673598","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 role of sulfur in palladium transport and fractionation from platinum by hydrothermal fluids","authors":"C. Laskar ,&nbsp;E.F. Bazarkina ,&nbsp;G.S. Pokrovski","doi":"10.1016/j.gca.2024.12.019","DOIUrl":"10.1016/j.gca.2024.12.019","url":null,"abstract":"<div><div>The solubility of palladium sulfide (PdS_(s)) has been measured in H₂S/HS^– aqueous solutions across wide ranges of sulfur concentrations (0.5–1.2 molal) and pH (5–8) at temperatures from 50 to 300 °C and pressures from 90 to 600 bar, using a hydrothermal flexible-cell reactor allowing controlled fluid injection and sampling. Combined with thermodynamic modeling and analysis of available literature data, our results demonstrate that palladium tetrahydrosulfide, Pd^II(HS)₄^2–, is the dominant complex in sulfide-rich moderate-temperature hydrothermal fluids. The equilibrium constants of PdS_(s) dissolution reaction, PdS_(s) + 3 H₂S⁰_(aq) = Pd(HS)₄^2– + 2H⁺ (K_s4,Pd), generated in this study can be described by the function log₁₀K_s4,Pd = (196.4 ± 60.0) – (11384 ± 3567)/<em>T</em>(K) – (71.24 ± 19.52) × log₁₀<em>T</em>(K), valid over the temperature range 25–300 °C and from saturated vapor pressure to 600 bar. Our results, combined with recent analogous PtS_(s) solubility data, enabled the derivation of a self-consistent set of thermodynamic properties of Pd(HS)₄^2– and Pt(HS)₄^2– in the framework of the HKF model. Solubility predictions of PdS_(s) using these properties yield maximum solubility values of 1 ppb Pd, as the tetrahydrosulfide complex, in H₂S-bearing hydrothermal fluids (&gt;0.01 m S) at moderate temperatures (50–350 °C) and near-neutral pH (6–7), whereas chloride complexes are predominant at acidic pH (&lt;4). The Pd/Pt atomic ratio in typical H₂S-bearing hydrothermal fluids at 300 °C in equilibrium with PdS_(s) and PtS_(s) varies from &gt; 10⁴ at pH &lt; 2 to 10^–2 at pH &gt; 3, corresponding to the change from chloride- to sulfide-dominated speciation for both metals. However, the absolute solubilities of both chloride and sulfide complexes are too small over the whole pH range to significantly contribute to Pd vs. Pt fractionations observed in hydrothermal environments. Among different factors that may lead to such fractionations, the role of polysulfide sulfur species, including trisulfur radical ions, should be considered in future studies.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"406 ","pages":"Pages 134-147"},"PeriodicalIF":5.0,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142936031","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":"Carbonation processes in Oman peridotite: temperature-dependent reactions and Mg isotope composition of reacting fluids","authors":"Giuseppe D. Saldi ,&nbsp;Thierry Decrausaz ,&nbsp;Vasileios Mavromatis ,&nbsp;Pascale Bénézeth","doi":"10.1016/j.gca.2025.01.029","DOIUrl":"10.1016/j.gca.2025.01.029","url":null,"abstract":"<div><div>The study of natural analogues of CO₂ mineral sequestration combined with the experimental quantification of carbonation reactions constitutes a fundamental approach to understand the spatial and structural distribution of carbonated bodies and the time scales by which large amounts of CO₂<span> can be stored in solid form into geologic formations. To better quantify the carbonation rates of ultramafic rocks and study the evolution of dissolved Mg isotope composition during their interaction with CO</span>₂<span><span>-rich fluids, a series of batch carbonation experiments using a partially serpentinized harzburgite from the Semail </span>ophiolite (Oman) was conducted at 90–180 °C and at constant CO</span>₂ partial pressures (∼ 15–20 bar). The yield of the carbonation reaction increased from ∼ 0 at 90 °C to a maximum of 31 mol % at 150 °C, decreasing to 12 mol % at 180 °C over a period of one month. Magnesites containing 3–9 wt% of Fe and silica polymorphs (SiO_2(am) and chalcedony) were the main reaction products, with a fraction of secondary Mg-silicates that increased with increasing temperature, significantly reducing the carbonation extent at 180 °C. The aqueous fluid became progressively enriched in heavy isotopes with the progress of the carbonation reaction. The apparent Mg isotope fractionations between the rock and bulk fluid (Δ²⁶Mg = δ²⁶Mg_solid − δ²⁶Mg_fluid) varied from −1.6 ‰ at 120 °C to −0.9 ‰ at 180 °C, consistent with the preferential uptake of ²⁴<span>Mg by carbonate minerals and the decrease of isotope fractionation with increasing temperature. The average magnesite isotope compositions (−1.6 ‰ ≤ δ</span>²⁶Mg ≤ -0.3 ‰) derived from mass-balance calculations were found to be within the range of δ²⁶Mg values reported for Oman listvenites, suggesting that the carbonation processes in this geological unit took place within the temperature range considered in this study (∼120–180 °C).</div><div>Comparison of experimental results with observations of a well-studied natural analogue provides new indications on the optimum conditions for the development of CO₂<span> sequestration methods in peridotites, or </span><em>ex situ</em><span> carbonation techniques using ultramafic minerals. The observed evolution of the Mg isotopic composition of the fluid also suggests that the use of Mg-isotopes could be an effective tool to monitor the spatial and temporal progress of carbonation reactions during field-scale CO</span>₂ storage operations in ultramafic rocks.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"406 ","pages":"Pages 101-118"},"PeriodicalIF":5.0,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143125392","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 antimonite-thioantimonates-antimonate pathway: Insights from sulfidic hot springs and microbial culture experiments for a novel mechanism of abiotic antimonite oxidation","authors":"Qinghai Guo ,&nbsp;Junbiao Qian ,&nbsp;Yu Li ,&nbsp;Luxia Wang ,&nbsp;Yue Meng ,&nbsp;Britta Planer-Friedrich","doi":"10.1016/j.gca.2025.01.007","DOIUrl":"10.1016/j.gca.2025.01.007","url":null,"abstract":"<div><div><span><span>Antimony speciation in natural waters is of great environmental significance, and mechanisms involved in antimonite<span><span> oxidation have been a research hotspot during the past years. In the present study, a new antimonite oxidation mechanism, which could be responsible for occurrence of appreciable antimonate in sulfidic </span>hot springs, was proposed. Within the investigated hydrothermal areas in the Yunnan-Sichuan-Tibet </span></span>Geothermal Province, much more antimonate formed in the neutral to alkaline sulfidic hot springs with low E</span>_H values than in the acidic hot springs low in sulfide and with high E_H<span> values, and antimonite-oxidizing microorganisms<span> were rare in both neutral to alkaline and acidic hot springs. Antimonite oxidation experiments designed according to the key hydrochemical and microbial parameters of these hot springs indicated that the antimonite oxidation rates were the highest under abiotic, anoxic and dark, and sulfidic conditions and at pH 10, and there was a significant positive relationship between the proportions of antimonate and thioantimonates in the experimental solutions. Moreover, antimonite was oxidized only to a quite low degree even under microbial culture<span> conditions with microorganisms-bearing hot spring sediments being used. These results implied that the antimonite oxidation in the sulfidic hot springs could occur via thiolation of antimonite followed by further transformation of thioantimonates into antimonate. This antimonite-thioantimonates-antimonate pathway may be prevalent in some other sulfidic environments, like paddy soils, mining areas, or euxinic basins.</span></span></span></div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"406 ","pages":"Pages 164-174"},"PeriodicalIF":5.0,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143020256","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}