Geochemical Transactions最新文献

{"title":"Biomineralisation by earthworms – an investigation into the stability and distribution of amorphous calcium carbonate","authors":"Mark E Hodson,&nbsp;Liane G Benning,&nbsp;Bea Demarchi,&nbsp;Kirsty E H Penkman,&nbsp;Juan D Rodriguez-Blanco,&nbsp;Paul F Schofield,&nbsp;Emma A A Versteegh","doi":"10.1186/s12932-015-0019-z","DOIUrl":"https://doi.org/10.1186/s12932-015-0019-z","url":null,"abstract":"<p>Many biominerals form from amorphous calcium carbonate (ACC), but this phase is highly unstable when synthesised in its pure form inorganically. Several species of earthworm secrete calcium carbonate granules which contain highly stable ACC. We analysed the milky fluid from which granules form and solid granules for amino acid (by liquid chromatography) and functional group (by Fourier transform infrared (FTIR) spectroscopy) compositions. Granule elemental composition was determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and electron microprobe analysis (EMPA). Mass of ACC present in solid granules was quantified using FTIR and compared to granule elemental and amino acid compositions. Bulk analysis of granules was of powdered bulk material. Spatially resolved analysis was of thin sections of granules using synchrotron-based μ-FTIR and EMPA electron microprobe analysis.</p><p>The milky fluid from which granules form is amino acid-rich (≤ 136 ± 3 nmol mg^?1 (n = 3; ± std dev) per individual amino acid); the CaCO₃ phase present is ACC. Even four years after production, granules contain ACC. No correlation exists between mass of ACC present and granule elemental composition. Granule amino acid concentrations correlate well with ACC content (r ≥ 0.7, p ≤ 0.05) consistent with a role for amino acids (or the proteins they make up) in ACC stabilisation. Intra-granule variation in ACC (RSD = 16%) and amino acid concentration (RSD = 22–35%) was high for granules produced by the same earthworm. Maps of ACC distribution produced using synchrotron-based μ-FTIR mapping of granule thin sections and the relative intensity of the ν₂: ν₄ peak ratio, cluster analysis and component regression using ACC and calcite standards showed similar spatial distributions of likely ACC-rich and calcite-rich areas. We could not identify organic peaks in the μ-FTIR spectra and thus could not determine whether ACC-rich domains also had relatively high amino acid concentrations. No correlation exists between ACC distribution and elemental concentrations determined by EMPA.</p><p>ACC present in earthworm CaCO₃ granules is highly stable. Our results suggest a role for amino acids (or proteins) in this stability. We see no evidence for stabilisation of ACC by incorporation of inorganic components.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"16 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2015-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-015-0019-z","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"5516344","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Zn isotope fractionation in a pristine larch forest on permafrost-dominated soils in Central Siberia","authors":"Jerome Viers,&nbsp;Anatoly S Prokushkin,&nbsp;Oleg S Pokrovsky,&nbsp;Alexander V Kirdyanov,&nbsp;Cyril Zouiten,&nbsp;Jerome Chmeleff,&nbsp;Merlin Meheut,&nbsp;Francois Chabaux,&nbsp;Priscia Oliva,&nbsp;Bernard Dupré","doi":"10.1186/s12932-015-0018-0","DOIUrl":"https://doi.org/10.1186/s12932-015-0018-0","url":null,"abstract":"<p>Stable Zn isotopes fractionation was studied in main biogeochemical compartments of a pristine larch forest of Central Siberia developed over continuous permafrost basalt rocks. Two north- and south-oriented watershed slopes having distinctly different vegetation biomass and active layer depth were used as natural proxy for predicting possible future climate changes occurring in this region. In addition, peat bog zone exhibiting totally different vegetation, hydrology and soil temperature regime has been studied.</p><p>The isotopic composition of soil profile from Central Siberia is rather constant with a δ⁶⁶Zn value around 0.2‰ close to the value of various basalts. Zn isotopic composition in mosses (<i>Sphagnum fuscum and Pleurozium schreberi</i>) exhibits differences between surface layers presenting values from 0.14 to 0.2‰ and bottom layers presenting significantly higher values (0.5 – 0.7‰) than the underlain mineral surface. The humification of both dead moss and larch needles leads to retain the fraction where Zn bound most strongly thus releasing the lighter isotopes in solution and preserving the heavy isotopes in the humification products, in general accord with previous experimental and modeling works [GCA 75:7632–7643, 2011].</p><p>The larch <i>(Larix gmelinii</i>) from North and South-facing slopes is enriched in heavy isotopes compared to soil reservoir while larch from Sphagnum peatbog is enriched in light isotopes. This difference may result from stronger complexation of Zn by organic ligands and humification products in the peat bog compared to mineral surfaces in North- and South-facing slope.</p><p>During the course of the growing period, Zn followed the behavior of macronutrients with a decrease of concentration from June to September. During this period, an enrichment of larch needles by heavier Zn isotopes is observed in the various habitats. We suggest that the increase of the depth of rooting zone, and the decrease of DOC and Zn concentration in soil solution from the root uptake zone with progressively thawing soil could provoke heavy isotopes to become more available for the larch roots at the end of the vegetative season compared to the beginning of the season, because the decrease of DOC will facilitate the uptake of heavy isotope as it will be less retained in strong organic complexes.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"16 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2015-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-015-0018-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4633588","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Geochemical evidence for the link between sulfate reduction, sulfide oxidation and phosphate accumulation in a Late Cretaceous upwelling system","authors":"Heiko Alsenz,&nbsp;Peter Illner,&nbsp;Sarit Ashckenazi-Polivoda,&nbsp;Aaron Meilijson,&nbsp;Sigal Abramovich,&nbsp;Shimon Feinstein,&nbsp;Ahuva Almogi-Labin,&nbsp;Zsolt Berner,&nbsp;Wilhelm Püttmann","doi":"10.1186/s12932-015-0017-1","DOIUrl":"https://doi.org/10.1186/s12932-015-0017-1","url":null,"abstract":"<p>On Late Cretaceous Tethyan upwelling sediments from the Mishash/Ghareb Formation (Negev, Israel), bulk geochemical and biomarker analyses were performed to explain the high proportion of phosphates in the lower part and of organic matter (OM) preserved in upper parts of the studied section. The profile is composed of three facies types; the underlying Phosphate Member (PM), the Oil Shale Member (OSM) and the overlying Marl Member (MM).</p><p>Total organic carbon (TOC) contents are highly variable over the whole profile reaching from 0.6% in the MM, to 24.5% in the OSM. Total iron (TFe) varies from 0.1% in the PM to 3.3% in the OSM. Total sulfur (TS) ranges between 0.1% in the MM and 3.4% in the OSM, resulting in a high C/S ratio of 6.5 in the OSM section. A mean proportion of 11.5% total phosphorus (TP) in the PM changed abruptly with the facies to a mean value of only 0.9% in the OSM and the MM.</p><p>The TOC/TOC_OR ratios argue for a high bacterial sulfate reduction activity and in addition, results from fatty acid analyses indicate that the activity of sulfide-oxidizing activity of bacteria was high during deposition of the PM, while decreasing during the deposition of the OSM.</p><p>The upwelling conditions effected a high primary productivity and consequently the presence of abundant OM. This, in combination with high sulfate availability in the sediments of the PM resulted in a higher sulfide production due to the activity of sulfate-reducing bacteria. Iron availability was a limiting factor during the deposition of the whole section, affecting the incorporation of S into OM. This resulted in the preservation of a substantial part of OM against microbial degradation due to naturally-occurring sulfurization processes expressed by the high C/S ratio of 6.5 in the OSM.</p><p>Further, the abundant sulfide in the pore water supported the growth of sulfide-oxidizing bacteria promoting the deposition of P, which amounted to as much as 15% in the PM. These conditions changed drastically from the PM to the OSM, resulting in a significant reduction of the apatite precipitation and a high concentration of reactive S species reacting with the OM.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"16 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2015-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-015-0017-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4404895","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Chronoamperometric study of elemental sulphur (S) nanoparticles (NPs) in NaCl water solution: new methodology for S NPs sizing and detection","authors":"Elvira Bura-Nakić,&nbsp;Marija Marguš,&nbsp;Darija Jurašin,&nbsp;Ivana Milanović,&nbsp;Irena Ciglenečki-Jušić","doi":"10.1186/s12932-015-0016-2","DOIUrl":"https://doi.org/10.1186/s12932-015-0016-2","url":null,"abstract":"<p>Elemental sulfur (S) persists in natural aquatic environment in a variety of forms with different size distributions from dissolved to particulate. Determination of S speciation mainly consists of the application of chromatographic and electrochemical techniques while its size determination is limited only to the application of microscopic and light scattering techniques. S biological and geochemical importance together with recent increases of S industrial applications requires the development of different analytical tools for S sizing and quantification. In recent years the use of electrochemical measurements as a direct, fast, and inexpensive technique for the different nanoparticles (NPs) characterization (Ag, Au, Pt) is increasing. In this work, electrochemical i.e. chronoamperometric measurements at the Hg electrode are performed for determination of the size distribution of the S NPs.</p><p>S NPs were synthesized in aqueous medium by sodium polysulphide acidic hydrolysis. Chronoamperometric measurements reveal the polydisperse nature of the formed suspension of S NPs. The electrochemical results were compared with dynamic light scattering measurements parallel run in the same S NPs suspensions. The two methods show fairly good agreement, both suggesting a log-normal size distribution of the S NPs sizes characterized by similar parameters.</p><p>The preliminary results highlight the amperometric measurements as a promising tool for the size determination of the S NPs in the water environment.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"16 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2015-02-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-015-0016-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4488336","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Real-time drilling mud gas monitoring for qualitative evaluation of hydrocarbon gas composition during deep sea drilling in the Nankai Trough Kumano Basin","authors":"Sebastian B Hammerschmidt,&nbsp;Thomas Wiersberg,&nbsp;Verena B Heuer,&nbsp;Jenny Wendt,&nbsp;Jörg Erzinger,&nbsp;Achim Kopf","doi":"10.1186/s12932-014-0015-8","DOIUrl":"https://doi.org/10.1186/s12932-014-0015-8","url":null,"abstract":"<p>Integrated Ocean Drilling Program Expedition 338 was the second scientific expedition with <i>D/V Chikyu</i> during which riser drilling was conducted as part of the Nankai Trough Seismogenic Zone Experiment. Riser drilling enabled sampling and real-time monitoring of drilling mud gas with an onboard scientific drilling mud gas monitoring system (“SciGas”). A second, independent system was provided by Geoservices, a commercial mud logging service. Both systems allowed the determination of (non-) hydrocarbon gas, while the SciGas system also monitored the methane carbon isotope ratio (δ¹³C_CH4). The hydrocarbon gas composition was predominated by methane (&gt; 1%), while ethane and propane were up to two orders of magnitude lower. δ¹³C_CH4 values suggested an onset of thermogenic gas not earlier than 1600 meter below seafloor. This study aims on evaluating the onboard data and subsequent geological interpretations by conducting shorebased analyses of drilling mud gas samples.</p><p>During shipboard monitoring of drilling mud gas the SciGas and Geoservices systems recorded up to 8.64% and 16.4% methane, respectively. Ethane and propane concentrations reached up to 0.03 and 0.013%, respectively, in the SciGas system, but 0.09% and 0.23% in the Geoservices data. Shorebased analyses of discrete samples by gas chromatography showed a gas composition with ~0.01 to 1.04% methane, 2 – 18 ppmv ethane, and 2 – 4 ppmv propane. Quadruple mass spectrometry yielded similar results for methane (0.04 to 4.98%). With δD values between -171‰ and -164‰, the stable hydrogen isotopic composition of methane showed little downhole variability.</p><p>Although the two independent mud gas monitoring systems and shorebased analysis of discrete gas sample yielded different absolute concentrations they all agree well with respect to downhole variations of hydrocarbon gases. The data point to predominantly biogenic methane sources but suggest some contribution from thermogenic sources at depth, probably due to mixing. In situ thermogenic gas production at depths shallower 2000 mbsf is unlikely based on in situ temperature estimations between 81°C and 85°C and a cumulative time-temperature index of 0.23. In conclusion, the onboard SciGas data acquisition helps to provide a preliminary, qualitative evaluation of the gas composition, the in situ temperature and the possibility of gas migration.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"15 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2014-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-014-0015-8","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4637395","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"A method for preparation and cleaning of uniformly sized arsenopyrite particles","authors":"Hariprasad Parthasarathy,&nbsp;John P Baltrus,&nbsp;David A Dzombak,&nbsp;Athanasios K Karamalidis","doi":"10.1186/s12932-014-0014-9","DOIUrl":"https://doi.org/10.1186/s12932-014-0014-9","url":null,"abstract":"<p>The oxidative dissolution of sulfide minerals, such as arsenopyrite (FeAsS), is of critical importance in many geochemical systems. A comprehensive understanding of their dissolution rates entails careful preparation of the mineral surface. Measurements of dissolution rates of arsenic from arsenopyrite are dependent on the size and degree of oxidation of its particles, among other factors. In this work, a method was developed for preparation and cleaning of arsenopyrite particles with size range of 15-250 μm. Four different cleaning methods were evaluated for effectiveness based on the removal of oxidized species of iron (Fe), arsenic (As) and sulfur (S) from the surface. The percentage oxidation of the surface was determined using X-ray photoelectron spectroscopy (XPS), and surface stoichiometry was measured using scanning electron microscopy - energy dispersive X-ray spectroscopy (SEM-EDS).</p><p>Results indicate that sonicating the arsenopyrite particles and then cleaning them with 12N HCl followed by 50% ethanol, and drying in nitrogen was the most effective method. This method was successful in greatly reducing the oxide species of Fe while completely removing oxides of As and S from the arsenopyrite surface.</p><p>Although sonication and acid cleaning have been widely used for mineral preparation, the method described in this study can significantly reduce grain size heterogeneity as well as surface oxidation, which enables greater control in surface and dissolution experiments.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"15 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2014-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-014-0014-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4476112","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Activity of zero-valent sulfur in sulfidic natural waters","authors":"George R Helz","doi":"10.1186/s12932-014-0013-x","DOIUrl":"https://doi.org/10.1186/s12932-014-0013-x","url":null,"abstract":"<p>Ionic and molecular carriers of dissolved (filter-passing) zero-valent sulfur (S⁰) in anaerobic natural waters include polysulfides, S_n^2?, molecular S₈(aq), organic macromolecules and certain higher valent thioanions. Because S⁰ is rapidly transferred among these various carriers, its biogeochemical roles in such processes as dehalogenation of organic compounds, chelation of trace metals, and anaerobic microbial metabolism are not determined solely by one ionic or molecular species. Here, S⁰ is treated collectively as a virtual thermodynamic component, and computational as well as graphical methods for quantifying its activity (a_S0) in natural waters are presented. From a_S0, concentrations of the ionic and molecular carriers of S⁰ can be calculated easily.</p><p>Concentration ratios of any two polysulfide ions define a_S0 (Method I). Unfortunately these concentrations are often too low in nature for accurate quantification with current methods. Measurements of total divalent sulfur (ΣS^-II), zero-valent sulfur (ΣS⁰) and pH provide a more widely applicable approach (Method II). Systematic errors in ΣS⁰ measurements are the main limit to accuracy of this method at the present time. Alternative methods based on greigite solubility and potentiometry are discussed. A critical comparison of Methods I and II reveals inconsistencies at low ΣS⁰/ΣS^-II that imply errors in the thermodynamic data for HS₂^? and S₂^?. For samples having low ΣS⁰/ΣS^-II, an interim remedy is recommended: letting pK_a2?=?6.3 for all HS_n^? ions.</p><p>Newly assembled data for a_S0 in a selection of anaerobic natural waters indicate that S⁰ is always metastable in the surveyed samples with respect to disproportionation to sulfide and sulfate. In all the surveyed environments, sulfur-rich minerals, such as greigite, covellite and orpiment, are stable in preference to their sulfur-poor cohorts, mackinawite, chalcocite and realgar. The a_S0 values in the dataset span conditions favoring Hg-polysulfide complexes vs. Hg-sulfide complexes, implying that a_S0 could affect Hg-methylation rates in nature. No support is found for the common assumption that a_S0?=?1 in reducing natural waters. This paper calls attention to an urgent need for improved measurement methods, especially for total zero-valent sulfur, as well as new determinations of ionization constants for all HS_n^? species.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"15 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2014-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-014-0013-x","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4741632","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Sulfur and oxygen isotope insights into sulfur cycling in shallow-sea hydrothermal vents, Milos, Greece","authors":"William P Gilhooly,&nbsp;David A Fike,&nbsp;Gregory K Druschel,&nbsp;Fotios-Christos A Kafantaris,&nbsp;Roy E Price,&nbsp;Jan P Amend","doi":"10.1186/s12932-014-0012-y","DOIUrl":"https://doi.org/10.1186/s12932-014-0012-y","url":null,"abstract":"<p>Shallow-sea (5?m depth) hydrothermal venting off Milos Island provides an ideal opportunity to target transitions between igneous abiogenic sulfide inputs and biogenic sulfide production during microbial sulfate reduction. Seafloor vent features include large (&gt;1?m²) white patches containing hydrothermal minerals (elemental sulfur and orange/yellow patches of arsenic-sulfides) and cells of sulfur oxidizing and reducing microorganisms. Sulfide-sensitive film deployed in the vent and non-vent sediments captured strong geochemical spatial patterns that varied from advective to diffusive sulfide transport from the subsurface. Despite clear visual evidence for the close association of vent organisms and hydrothermalism, the sulfur and oxygen isotope composition of pore fluids did not permit delineation of a biotic signal separate from an abiotic signal. Hydrogen sulfide (H₂S) in the free gas had uniform δ³⁴S values (2.5?±?0.28‰, n?=?4) that were nearly identical to pore water H₂S (2.7?±?0.36‰, n?=?21). In pore water sulfate, there were no paired increases in δ³⁴S_SO4 and δ¹⁸O_SO4 as expected of microbial sulfate reduction. Instead, pore water δ³⁴S_SO4 values decreased (from approximately 21‰ to 17‰) as temperature increased (up to 97.4°C) across each hydrothermal feature. We interpret the inverse relationship between temperature and δ³⁴S_SO4 as a mixing process between oxic seawater and ³⁴S-depleted hydrothermal inputs that are oxidized during seawater entrainment. An isotope mass balance model suggests secondary sulfate from sulfide oxidation provides at least 15% of the bulk sulfate pool. Coincident with this trend in δ³⁴S_SO4, the oxygen isotope composition of sulfate tended to be ¹⁸O-enriched in low pH (&lt;5), high temperature (&gt;75°C) pore waters. The shift toward high δ¹⁸O_SO4 is consistent with equilibrium isotope exchange under acidic and high temperature conditions. The source of H₂S contained in hydrothermal fluids could not be determined with the present dataset; however, the end-member δ³⁴S value of H₂S discharged to the seafloor is consistent with equilibrium isotope exchange with subsurface anhydrite veins at a temperature of ~300°C. Any biological sulfur cycling within these hydrothermal systems is masked by abiotic chemical reactions driven by mixing between low-sulfate, H₂S-rich hydrothermal fluids and oxic, sulfate-rich seawater.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"15 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2014-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-014-0012-y","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4481810","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"An improved pyrite pretreatment protocol for kinetic and isotopic studies","authors":"Natella Mirzoyan,&nbsp;Alexey Kamyshny,&nbsp;Itay Halevy","doi":"10.1186/s12932-014-0010-0","DOIUrl":"https://doi.org/10.1186/s12932-014-0010-0","url":null,"abstract":"<p>Pyrite is one of the most abundant and widespread of the sulfide minerals with a central role in biogeochemical cycles of iron and sulfur. Due to its diverse roles in the natural and anthropogenic sulfur cycle, pyrite has been extensively studied in various experimental investigations of the kinetics of its dissolution and oxidation, the isotopic fractionations associated with these reactions, the microbiological processes involved, and the effects of pyrite on human health. Elemental sulfur (S⁰) is a common product of incomplete pyrite oxidation. Preexisting S⁰ impurities as unaccounted reaction products are a source of experimental uncertainty, as are adhered fine grains of pyrite and its oxidation products. Removal of these impurities is, therefore, desirable.</p><p>A robust standardized pretreatment protocol for removal of fine particles and oxidation impurities from pyrite is lacking. Here we describe a protocol for S⁰ and fine particle removal from the surface of pyrite by rinsing in acid followed by repeated ultrasonication with warm acetone.</p><p>Our data demonstrate the presence of large fractions of S⁰ on untreated pyrite particle surfaces, of which only up to 60% was removed by a commonly used pretreatment method described by Moses <i>et al</i>. (GCA 51:1561-1571, 1987). In comparison, after pretreatment by the protocol proposed here, approximately 98% S⁰ removal efficiency was achieved. Additionally, the new procedure was more efficient at removal of fine particles of adhered pyrite and its oxidation products and did not appear to affect the particle size distribution, the specific surface area, or the properties of grain surfaces.</p><p>The suggested pyrite pretreatment protocol is more efficient in removal of impurities from pyrite grains, and provides multiple advantages for both kinetic and isotopic investigations of pyrite transformations under various environmental conditions.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"15 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2014-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-014-0010-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4481814","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Elemental sulfur coarsening kinetics","authors":"Angel A Garcia,&nbsp;Gregory K Druschel","doi":"10.1186/s12932-014-0011-z","DOIUrl":"https://doi.org/10.1186/s12932-014-0011-z","url":null,"abstract":"<p>Elemental sulfur exists is a variety of forms in natural systems, from dissolved forms (noted as S_8(diss) or in water as S_8(aq)) to bulk elemental sulfur (most stable as α-S₈). Elemental sulfur can form via several biotic and abiotic processes, many beginning with small sulfur oxide or polysulfidic sulfur molecules that coarsen into S₈ rings that then coalesce into larger forms:</p><p>Formation of elemental sulfur can be possible via two primary techniques to create an emulsion of liquid sulfur in water called sulfur sols that approximate some mechanisms of possible elemental sulfur formation in natural systems. These techniques produce hydrophobic (S_8(Weimarn)) and hydrophilic (S_{8(polysulfide)}) sols that exist as nanoparticle and colloidal suspensions. These sols begin as small sulfur oxide or polysulfidic sulfur molecules, or dissolved S_8(aq) forms, but quickly become nanoparticulate and coarsen into micron sized particles via a combination of classical nucleation, aggregation processes, and/or Ostwald ripening.</p><p>We conducted a series of experiments to study the rate of elemental sulfur particle coarsening using dynamic light scattering (DLS) analysis under different physical and chemical conditions. Rates of nucleation and initial coarsening occur over seconds to minutes at rates too fast to measure by DLS, with subsequent coarsening of S_8(nano) and S_8(sol) being strongly temperature dependent, with rates up to 20 times faster at 75°C compared to 20°C. The addition of surfactants (utilizing ionic and nonionic surfactants as model compounds) results in a significant reduction of coarsening rates, in addition to known effects of these molecules on elemental sulfur solubility. DLS and cryo-SEM results suggest coarsening is largely a product of ripening processes rather than particle aggregation, especially at higher temperatures. Fitting of the coarsening rate data to established models for Ostwald ripening additionally support this as a primary mechanism of coarsening.</p><p>Elemental sulfur sols coarsen rapidly at elevated temperatures and experience significant effects on both solubility and particle coarsening kinetics due to interaction with surfactants. Growth of elemental sulfur nanoparticles and sols is largely governed by Ostwald ripening processes.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"15 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2014-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-014-0011-z","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4236366","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}