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1.
Higher fullerenes(C84,C90,C92,C94 and C96) were successfully isolated from the Soxhlet extract of the synthetical "Graphote Smokes" soot(GS sample) by using a big Cosmosil Buckysep(Phenomenex) column(250 mm × 10 mm) with a large injection.The fractions isolated have been determined by high performance liquid chro-matography(HPLC) and laser desorption mass spectrometry(LDMS).It is found that there are different fullerenes molecules in different fractions with retention time.The result indicates that fullerenes do exist in GS samples.Also,it excludes the suspicion to some extent that fullerene molecules might be generated by the laser desorption process in the LDMS.In addition,it also provides the experimental basis for the study of natural higher fullerenes and might be helpful to figure out the question if higher fullerenes do exist in the natural samples.  相似文献   

2.
Fullerenes have been detected in carbonaceous chondrite meteorites and in breccia samples from meteorite impact craters, but questions have been raised about contradictory results from similar samples and the sensitivities and accuracies of different analytical methods. We analyzed samples from three impact craters and detected C60 in samples from several locations; we also observed differences in the detection capabilities of various analytical techniques used in the search for fullerenes. The presence of C60 in rocks from the Onaping Formation of the Sudbury impact crater was confirmed. Low levels of C60 were also detected for the first time in samples from the Gardnos (Norway) and Ries (Germany) impact structures.We detected C60 in these samples using surface-enhanced laser desorption/ ionization (SELDI), but the related technique of microprobe laser-desorption, laser-ionization mass spectrometry (μL2MS) did not observe C60 above detection limits. We attribute the absence of μL2MS signal to aggregate formation caused by phthalic acid esters, which appear to easily contaminate samples either during storage or demineralization in plastic containers. The μL2MS technique is incapable of detecting aggregated C60, but aggregation does not suppress detection in SELDI. Phthalate-induced aggregation did, however, enhance SELDI detection of C60 in some cases, and we suggest that this enhancement may help explain previously reported differences in C60 detection from natural samples between laser desorption mass spectrometry (LDMS, a technique analogous to SELDI that has detected fullerenes in meteorite and impact breccia samples) and high-pressure liquid chromatography (HPLC). This work highlights the effects of phthalates and other indigenous compounds or contaminants on certain mass spectrometric techniques and lends support to the idea that several complementary analytical methods should be employed to investigate complex natural samples.  相似文献   

3.
We report here for the first time the presence of the natural, toluene-soluble C60 and the toluene-insoluble high-pressure and temperature phase of fullerene C60 in the carbonaceous matter extracted from the iridium-rich layers of the intertrappean sediments of Anjar, India. The toluene-insoluble form of fullerene is formed at high-temperature and pressure (HPT) and is distinguished from normal fullerene by UV-visible and Fourier-transform infrared (FT-IR) spectroscopic techniques. The C60 fullerene has been identified by high-resolution electron-impact ionization mass spectrometric analysis, as well as by Fourier-transform infrared (FT-IR), UV-visible, and 13C-nuclear magnetic resonance (NMR) spectroscopy. In iridium-poor horizons of this section, fullerenes are absent, but complex hydrocarbons are sometimes present. The FT-IR spectroscopic studies on the insoluble fullerenes show strong absorption peaks at about 740 and 509 cm−1 and a number of weak peaks at 1380, 1300, 1205, 1120, 1000, 608, 554, and 441 cm−1, which are characteristic of a high-pressure and temperature C60 fullerene. The UV-visible spectra of the toluene-soluble fullerene, as well as the insoluble fullerene, show strong absorption bands at 270 and 348 nm, which are characteristic of pristine fullerene C60. The toluene-insoluble carbon-rich residue shows additional absorption bands at 710, 640, and 395 nm. These UV-visible bands independently confirm the presence of the high-pressure-temperature (HPT) phase of fullerene C60. Conditions of high-pressure and temperature required for formation of the HPT fullerene phase can be created by an energetic impact event. Therefore, the presence of HPT fullerene in the KT boundary layer at Anjar is linked to the impact event at the KT transition.  相似文献   

4.
Andesitic pillow lavas containing biogenic, solid bitumen (SB) are a constituent of a Neoproterozoic volcanosedimentary sequence (Teplá-Barrandian unit, Bohemian Massif) in the Mítov area of the Czech Republic. A black shale formation that is crosscut by these andesitic basalts is 565 Ma old. Carbon disulfide extracts of two powdered samples of SB contain 0.2 and 0.3 ppm of C60, respectively, as determined by high-pressure liquid chromatography. The peak assignment based on retention time is fully supported by high-resolution electron ionization mass spectrometry (EI-MS). No C70 was detected, nor was C60 found in two other SB samples from this locality. Other investigated carbonaceous samples from Bohemia (coals and anthracites of Upper Paleozoic age and anthraxolite, graphitoids, and graphite of Upper Proterozoic age) did not contain fullerenes at concentrations above the detection limit of 0.01 ppm. The absence of C60 in these samples was confirmed by EI-MS. The proposed mechanism of fullerene formation involves a primary algal phase, generation of a hydrocarbonaceous mixture in the course of thermal evolution of the sedimentary series, and their high-temperature transformation related to the extrusion of basalt. An important feature for fullerene conservation was the enclosure of fullerenes in SB with a structure similar to glasslike carbon, where the fullerene was protected against oxidation.  相似文献   

5.
Solid-state 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopic experiments have been performed on isolated meteoritic Insoluble Organic Matter (IOM) spanning four different carbonaceous chondrite meteorite groups; a CR2 (EET92042), a CI1 (Orgueil), a CM2 (Murchison), and the unique C2 meteorite, Tagish Lake. These solid state NMR experiments reveal considerable variation in bulk organic composition across the different meteorite group’s IOM. The fraction of aromatic carbon increases as CR2 < CI1 < CM2 < Tagish Lake. The increases in aromatic carbon are offset by reductions in aliphatic (sp3) carbon moieties, e.g., “CHx,” and “CHx(O,N).” Oxidized sp2 bonded carbon, e.g., carboxyls and ketones grouped as “CO,” are largely conservative across these meteorite groups. Single pulse (SP) 13C magic angle spinning (MAS) NMR experiments reveal the presence of nanodiamonds with an apparent concentration ranking in the IOM of CR2 < CI1 < CM2 < Tagish Lake. A pair of independent NMR experiments reveals that, on average, the aromatic moieties in the IOM of all four meteoritic IOM fractions are highly substituted. Fast spinning SP 1H MAS NMR spectral data combined with other NMR experimental data reveal that the average hydrogen content of sp3 bonded carbon functional groups is low, requiring a high degree of aliphatic chain branching in each IOM fraction. The variation in chemistry across the meteorite groups is consistent with alteration by low temperature chemical oxidation. It is concluded that such chemistry principally affected the aliphatic moieties whereas the aromatic moieties and nanodiamonds may have been largely unaffected.  相似文献   

6.
We have conducted the first systematic analyses of molecular distribution and δD values of individual compounds in pyrolysates of insoluble organic matter (IOM) from different carbonaceous chondrite groups, using flash pyrolysis coupled to gas chromatography-mass spectrometry and compound-specific D/H analysis. IOM samples from six meteorites of different classifications, Elephant Moraine (EET) 92042 (CR2), Orgueil (CI1), Allan Hills (ALH) 83100 (CM1/2), Murchison (CM2), ALH 85013 (CM2), and Tagish Lake (C2) were isolated and studied. Except for the pyrolysate of Tagish Lake IOM, pyrolysates of all five meteorite IOM samples were dominated by an extensive series of aromatic (C1 to C7 alkyl-substituted benzenes, C0 to C2 alkyl-substituted naphthalenes), with aliphatic (straight chain and branched C10 to C15 alkanes) hydrocarbons and several S- and O- containing compounds (C1 to C2 alkylthiophenes, benzothiophene, benzaldehyde) being also present. The strong similarity in the pyrolysates of different carbonaceous chondrites suggests certain common characteristics in the formation mechanisms of IOM from different meteorites. The Tagish Lake IOM sample is unique in that its pyrolysate lacks most of the alkyl-substituted aromatic hydrocarbons detected in other meteorite IOM samples, suggesting distinctively different formation processes. Both bulk δD values of meteorite IOMs and weighted-average δD values of individual compounds in pyrolysates show a decreasing trend: CR2 > CI1 > CM2 > C2 (Tagish Lake), with the EET 92042 (CR2) IOM having the highest δD values (∼2000‰ higher than other samples). We attribute the high D contents in the IOM to primitive interstellar organic sources.  相似文献   

7.
Using a simple ionic model with polarizable oxygen ions and dissociating water molecules, we have calculated the energetics governing the distribution of Fe(II)/Fe(III) ions at the reduced (2 × 1) surface of α-Fe2O3 (hematite) (0 1 2) under dry and hydrated conditions. The results show that systems with Fe(II) ions located in the near-surface region have lower potential energy for both dry and hydrated surfaces. The distribution is governed by coupling of the ferrous iron centers to positive charge associated with missing oxygen atoms on the dry reduced (2 × 1) (0 2 1) surface. As the surface is hydroxylated, the missing oxygen rows are filled and protons from dissociated water molecules become the positive charge centers, which couple more weakly to the ferrous iron centers. At the same time, the first-layer iron centers change from fourfold or fivefold coordination to sixfold coordination lowering the potential energy of ferric iron in the first layer and favoring migration of ferrous iron from the immediate surface sites. This effect can also be understood as reflecting stronger solvation of Fe(III) by the adsorbed water molecules and by hydrolysis reactions favoring Fe(III) ions at the immediate surface. The balance between these two driving forces, which changes as a function of hydration, provides a compelling explanation for the anomalous coverage dependence of water desorption in ultra-high vacuum experiments.  相似文献   

8.
Here we report the elemental and isotopic compositions of the insoluble organic material (IOM) isolated from several previously unanalyzed meteorites, as well as the reanalyses of H isotopic compositions of some previously measured samples (Alexander et al., 2007). The IOM in ordinary chondrites (OCs) has very large D enrichments that increase with increasing metamorphism and decreasing H/C, the most extreme δD value measured being almost 12,000‰. We propose that such large isotopic fractionations could be produced in the OC parent bodies through the loss of isotopically very light H2 generated when Fe was oxidized by water at low temperatures (<200 °C). We suggest that similar isotopic fractionations were not generated in the IOM of CV and CO chondrites with similar metamorphic grades and IOM H/C ratios because proportionately less water was consumed during metamorphism, and the remaining water buffered the H isotopic composition of the IOM even a H was being lost from it.Hydrogen would also have been generated during the alteration of CI, CM and CR carbonaceous chondrites. The IOM in these meteorites exhibit a considerable range in isotopic compositions, but all are enriched in D, as well as 15N, relative to terrestrial values. We explore whether these enrichments could also have been produced by the loss of H2, but conclude that the most isotopically anomalous IOM compositions in meteorites from these groups are probably closest to their primordial values. The less isotopically anomalous IOM has probably been modified by parent body processes. The response of IOM to these processes was complex and varied, presumably reflecting differences in conditions within and between parent bodies.The D enrichments associated with H2 generation, along with exchange between D-rich IOM and water in the parent bodies, means that it is unlikely that any chondrites retain the primordial H isotopic composition of the water ice that they accreted. The H isotopic compositions of the most water-rich chondrites, the CMs and CIs, are probably the least modified and their compositions (δD ? −25‰) suggest that their water did not form at large radial distances from the Sun where ice is predicted to be very D-rich. Yet models to explain the O isotopic composition of inner Solar System bodies require that large amounts of ice were transported from the outer to the inner Solar System.  相似文献   

9.
Hydration of organic coatings in soils is expected to affect the sorption of oxyanions onto hydrous Fe and Al oxides. We hypothesized that the hydration of polygalacturonate (PGA) coatings on alumina (Al2O3) increases their permeability for phosphate. Pure and PGA-coated alumina were equilibrated in deionized water for 2 and 170 h at pH 5 and 20 °C before studying (i) their porosity with N2 gas adsorption and 1H NMR relaxometry, (ii) structural changes of PGA-coatings with differential scanning calorimetry (DSC), and (iii) the kinetics of phosphate sorption and PGA desorption in batch experiments. Scanning electron micrographs revealed that PGA molecules formed three-dimensional networks with pores ranging in size from <10 to several hundred nanometers. Our NMR results showed that the water content of intraparticle alumina pores decreased upon PGA sorption, indicating a displacement of pore water by PGA. The amount of water in interparticle alumina pores increased strongly after PGA addition, however, and was attributed to water in pores of PGA and/or in pores at the PGA-alumina interface. The flexibility of PGA molecules and the fraction of a PGA gel phase increased within one week of hydration, implying restructuring of PGA. Hydration of PGA coatings increased the amount of phosphate defined as instantaneously sorbed by 84%, showing that restructuring of PGA enhanced the accessibility of phosphate to external alumina surfaces. Despite the fact that the efficacy of phosphate to displace PGA was higher after 170 h than after 2 h, a higher phosphate surface loading was required after 170 h to set off PGA desorption. Our findings imply that the number of PGA chain segments directly attached to the alumina surface decreased with time. We conclude that hydration/dehydration of polymeric surface coatings affects the sorption kinetics of oxyanions, and may thus control the sorption and transport of solutes in soils.  相似文献   

10.
The insoluble organic matter (IOM) of the Orgueil meteorite contains deuterium-rich radicals detectable by Electron Paramagnetic Resonance (EPR) techniques (Gourier et al., 2008). However the structure of these deuterium carriers remains poorly constrained. In this work, their electronic structure is deduced from the measurement of the spin states S by transient nutation in pulsed-EPR. It is shown that these deuterium-rich radicals are dominated by biradicaloids (species with S = 0 ground state and thermally accessible S = 1 state) and biradicals (species with S = 1 ground state) representing ∼61% and ∼31% of the radicals in the IOM of Orgueil, respectively, while single radicals (S = 1/2) contribute only to ∼8%. This is definitely different from mature terrestrial IOMs, which are known to contain almost exclusively S = 1/2 radicals. A structural model is proposed, whereby the occurrence of dominant biradicaloids and biradicals is the direct consequence of the structure of the IOM, made of a network of small aromatic moieties linked by branched and short aliphatic units. This implies that the formation of stable biradicaloids and biradicals by C-H breaking and their deuterium enrichment are produced after the formation of the IOM in the primitive solar system. These results reinforce the idea that the formation of the IOM and the deuterium-rich hotspots are the product of ion chemistry in the solar disk.  相似文献   

11.
We conducted hydrothermal flow-through experiments at 430 °C and 31 MPa to investigate the mechanism of silica precipitation on granite under crustal conditions. Two experiments were performed using different input solutions: a single-component Si solution, and a multi-component solution with minor Al, Na, and K. The degree of supersaturation with respect to quartz, Ω = CSi/CSi,Qtz,eq, where CSi and CSi,Qtz,eq indicate Si concentration in solutions and the solubility of quartz within water, respectively, decreased from 3-3.5 to <1.1 along the flow path. A variety of silica minerals formed during the experiments (opal-A, opal-C, chalcedony, and quartz), and their occurrences and modal abundances changed in response to Ω and the presence of additives in the solution.For near-equilibrium solutions (Ω < ∼1.2), silica precipitation occurred in a simple way in both experiments, being restricted to overgrowths on pre-existing quartz surfaces in the granite. At higher saturation levels (Ω > ∼1.2), silica minerals were deposited on other surfaces in addition to quartz. In the single-component experiment, the dominant silica minerals changed in the order of opal-A → opal-C → quartz with decreasing Si concentration along the flow path. In contrast, in the multi-component experiment, quartz and minor chalcedony formed throughout the entire reaction vessel. This finding indicates that impurities (Na, K, and Al) in the solutions inhibited the precipitation of opal and enhanced the direct nucleation of quartz. The systematic appearance of metastable silica minerals were examined by nucleation processes and macroscopic precipitation kinetics. Our experimental results indicate that different precipitation mechanisms yield contrasting textures, which in turn suggests that vein textures can be used as indicators of solution chemistry within the fracture.  相似文献   

12.
天然富勒烯的地质产状与成因   总被引：2，自引：2，他引：0  
天然富勒烯研究是富勒烯科学和地质科学相交叉的一个新兴研究领域,迄今为止已在桑加岩、闪电熔岩、陨石撞击坑中的含碳质角砾岩、古近系/白垩系地层界线(E/K)的含碳粘土岩、三叠系/二叠系(T/P)界线岩石(粘土岩、硅质岩)、恐龙蛋壳、煤、重质油、固体沥青以及半天然的烟灰、木炭、书墨等物质中检测到富勒烯的存在,但含量很低。多数天然富勒烯的地质分布、成因机制与陨石撞击、野火、闪电等有关,但部分天然富勒烯的成因尚不清楚。天然富勒烯研究扩展了人们对自然界碳结构及其演化的认识,在地质事件、事件地层如陨石撞击事件、E/K界线、T/P界线等的研究中充分显示了其独特的方法和应用价值。  相似文献   

13.
Organic ligands affect the sorption and mobility of radionuclides in soils. Batch desorption experiments on goethite particles reveal the extent of uranyl desorption and hence bioavailability with different organic acids. The desorptive strength increases in the following order: background electrolyte < Na-alginate < desferrioxamine B (DFO-B) < oxalate. The sequence is consistent with decreasing molecular size and mass from alginate via DFO-B to oxalate. The concomitant Fe release in the desorption experiments indicates that desorption from goethite and not dissolution of goethite governs the mobility of adsorbed U(VI). A compilation of DFO-B surface excesses on goethite from our experiments together with literature values indicate that DFO-B adsorbs at a constant ∼3% to the goethite surface. It is surprising that such a small fraction suffices to account for the considerable uranyl desorption and thus remobilization of a radionuclide into solution. Oxalate displays higher surface concentrations but still lower than the determined uranyl surface excess. It follows that based on the high U(VI) stability constants, both organic ligands induce the desorption of uranyl species by increasing the chemical affinity of the aqueous phase. In the case of alginate, desorption of uranyl is weak and adsorbed alginate hampers any considerable detachment of U(VI) in the presence of the more potent ligands, DFO-B and oxalate. This inhibition is based on biosorption and in this respect polysaccharides in soils may retard and even halt the advance of actinides through the soil column. This hypothesis calls for further studies into the interaction of siderophores and polysaccharides with soil adsorbents and their role in the mobilization of contaminant metals.  相似文献   

14.
Two types of laboratory experiments were used to quantify magnesium isotopic fractionations associated with chemical and thermal (Soret) diffusion in silicate liquids. Chemical diffusion couples juxtaposing a molten natural basalt (SUNY MORB) and a molten natural rhyolite (Lake County Obsidian) were run in a piston cylinder apparatus and used to determine the isotopic fractionation of magnesium as it diffused from molten basalt to molten rhyolite. The thermal diffusion experiments were also run in a piston cylinder apparatus but with a sample made entirely of molten SUNY MORB displaced from the hotspot of the assembly furnace so that the sample would have a temperature difference of about 100-200 °C from one end to the other. The chemical diffusion experiments showed fractionations of 26Mg/24Mg by as much as 7‰, which resulted in an estimate for the mass dependence of the self-diffusion coefficients of the magnesium isotopes corresponding to D26Mg/D24Mg=(24/26)β with β = 0.05. The thermal diffusion experiments showed that a temperature difference of about 100 °C resulted in the MgO, CaO, and FeO components of the basalt becoming slightly enriched by about 1 wt% in the colder end while SiO2 was enriched by several wt% in the hotter end. The temperature gradient also fractionated the magnesium isotopes. A temperature difference of about 150 °C produced an 8‰ enrichment of 26Mg/24Mg at the colder end relative to the hotter end. The magnesium isotopic fractionation as a function of temperature in molten basalt corresponds to 3.6 × 10−2‰/°C/amu.  相似文献   

15.
Various iron-bearing primary phases and rocks have been weathered experimentally to simulate possible present and past weathering processes occurring on Mars. We used magnetite, monoclinic and hexagonal pyrrhotites, and metallic iron as it is suggested that meteoritic input to the martian surface may account for an important source of reduced iron. The phases were weathered in two different atmospheres: one composed of CO2 + H2O, to model the present and primary martian atmosphere, and a CO2 + H2O + H2O2 atmosphere to simulate the effect of strong oxidizing agents. Experiments were conducted at room temperature and a pressure of 0.75 atm. Magnetite is the only stable phase in the experiments and is thus likely to be released on the surface of Mars from primary rocks during weathering processes. Siderite, elemental sulfur, ferrous sulfates and ferric (oxy)hydroxides (goethite and lepidocrocite) are the main products in a water-bearing atmosphere, depending on the substrate. In the peroxide atmosphere, weathering products are dominated by ferric sulfates and goethite. A kinetic model was then developed for iron weathering in a water atmosphere, using the shrinking core model (SCM). This model includes competition between chemical reaction and diffusion of reactants through porous layers of secondary products. The results indicate that for short time scales, the mechanism is dominated by a chemical reaction with second order kinetics (k = 7.75 × 10−5 g−1/h), whereas for longer time scales, the mechanism is diffusion-controlled (DeA = 2.71 × 10−10 m2/h). The results indicate that a primary CO2- and H2O-rich atmosphere should favour sulfur, ferrous phases such as siderite or Fe2+-sulfates, associated with ferric (oxy)hydroxides (goethite and lepidocrocite). Further evolution to more oxidizing conditions may have forced these precursors to evolve into ferric sulfates and goethite/hematite.  相似文献   

16.
It is essential to have suitable tools able to trace the fate of manure organic matter in the environment to assess whether manure disposal on the soils of catchments could affect the organic quality of rivers. Sterol compounds – mainly expressed as C29 + 28/C27 and 5β/C27 ratios – have been shown to be specific molecular tracers of pig, dairy and poultry manures in soils. The objective of this study was to measure C29 + 28/C27 and 5β/C27 ratios in five Brittany rivers (Elorn, Yar, Léguer, Min Ran and Couesnon) draining agricultural catchments receiving massive annual inputs of pig, poultry and dairy manures and compare these ratios with ratios published for enriched soils and manure samples. The particulate organic fractions from the studied rivers yielded steroid signatures typical of animal manures. More specifically, a stanol compound diagnostic of pig slurry – the 5β-stanol known as coprostanol – was found to be very widespread, with particularly high concentrations in one of the rivers (Elorn). The C29 + 28/C27 and 5β/C27 ratios of the particulate fractions of the rivers were compared with ratios measured directly in pig, dairy and poultry manure samples, as well as with the breeding activities on river catchments. These comparisons show that the steroid profiles of the five investigated rivers correlate closely with the types of manure (i.e. pig, poultry or dairy) spread on soils in their catchments. For instance, the C29 + 28/C27 and 5β/C27 ratios in the Elorn river are similar to the values typical of pig slurry (e.g. 5β/C27 > 4); compared with other catchments, the soils in this area receive by far the largest amount of pig slurry. By contrast, the Yar river drains a catchment receiving only poultry and dairy manures, and its soils exhibit C29 + 28/C27 and 5β/C27 ratios similar to those of dairy and poultry manures (e.g. 5β/C27 ∼ 1). Thus, this study indicates that the organic quality of rivers is modified in catchments where there is intense manure spreading on soils. It also provides evidence that rivers draining areas receiving different manure types may exhibit differences in the long-term evolution of their OM content. Indeed, two of the investigated river catchments receive dominantly dairy and poultry manure, and exhibit clear long-term upward trends in OM. On the other hand, one catchment receiving high proportions of pig slurry clearly shows a long-term downward trend in OM contents. A survey of the literature shows that the relative amount of OM and N received by soils in agricultural catchments could be the key parameter in determining the direction of the long-term OM trend of the river, rather than the absolute amount and/or type of manure that is applied to the soil. In any case, the present study suggests that sterol/stanol compounds may be of diagnostic value in determining whether a stream or a river is undergoing contamination by manure-derived organic matter.  相似文献   

17.
Arsenic is a prevalent contaminant at US Superfund sites where remediation by pump and treat systems is often complicated by slow desorption of As from Fe and Al (hydr)oxides in aquifer solids. Chemical amendments that either compete with As for sorption sites or dissolve Fe and Al (hydr)oxides can increase As mobility and improve pump and treat remediation efficiency. The goal of this work was to determine optimal amendments for improving pump and treat at As contaminated sites such as the Vineland Chemical Co. Superfund site in southern New Jersey. Extraction and column experiments were performed using As contaminated aquifer solids (81 ± 1 mg/kg), site groundwater, and either phosphate (NaH2PO4·H2O) or oxalic acid (C2H2O4·2H2O). In extraction experiments, phosphate mobilized between 11% and 94% of As from the aquifer solids depending on phosphate concentration and extraction time (1 mM–1 M; 1–24 h) and oxalic acid mobilized between 38% and 102% depending on oxalic acid concentration and extraction time (1–400 mM; 1–24 h). In column experiments, phosphate additions induced more As mobilization in the first few pore volumes but oxalic acid was more effective at mobilizing As overall and at lower amendment concentrations. At the end of the laboratory column experiments, 48% of As had been mobilized from the aquifer sediments with 100 mM phosphate and 88% had been mobilized with 10 mM oxalic acid compared with 5% with ambient groundwater alone. Furthermore, simple extrapolations based on pore volumes suggest that chemical treatments could lower the time necessary for clean up at the Vineland site from 600 a with ambient groundwater alone to potentially as little as 4 a with 10 mM oxalic acid.  相似文献   

18.
The late Holocene environmental history of the Lesotho highlands, southern Africa, is poorly understood with few detailed studies to date. At Likoaeng, Senqu Valley, Lesotho, a 3 m stratified sedimentary sequence from an open-air archaeological site records vegetation development for the period 3400-1070 cal. BP. Phytolith analyses and bulk sediment organic matter δ13C indicate that C4 grassland dominated the lower part of the sequence until approximately 2960 cal. BP when there was a switch to C3 Pooid grassland (2960-2160 cal. BP). Also noted was a change from hunting mainly bovids to a dominance of fishing at the site. The change in grassland type and archaeological subsistence strategies corresponds with an episode of neoglacial cooling and the expansion of Alpine sourgrasses into lower altitudes. From 2160 to 1600 cal. BP grassland became a mix of C3 and C4 types and by 1600-1070 cal. BP there was a return to C4 dominated grassland. During this latter phase there was a reversal from fishing to hunting again (and eventually some keeping of domestic livestock) at the site. These data outline the vegetation response to latitudinal shifts of frontal systems, and relatively strong atmospheric circulation variability, perhaps underpinned by variations of polar water into the Benguela Current during the late Holocene.  相似文献   

19.
Paired analyses of Os isotope composition and concentration of bulk sediment and leachable Os in a metalliferous pelagic clay sequence from the North Pacific, ODP Site 886C, are used to reconstruct the marine Os isotope record and the particulate meteoritic Os flux between 65.5 and 78 Ma. Measured 187Os/188Os of bulk sediments ranges from approximately 0.64 to 0.32 and those of leach analyses are very similar to bulk analyses. Hydrogenous Os dominates the sedimentary Os inventory throughout most of the studied interval. As a result the measured 187Os/188Os of leachable Os approximates that of contemporaneous seawater. The ODP 886C record shows rising 187Os/188Os in the deepest portion of the core, with a local maximum of 0.66 close to 74 Ma. The 67-72 Ma portion of the record is characterized by nearly constant 187Os/188Os ratios close to 0.6. The structure of the marine Os isotope record from ODP 886C differs markedly from the seawater 87Sr/86Sr curve, which rises monotonically throughout the time interval studied here. Calculated particulate meteoritic Os fluxes are between 0.5 and 2 pg cm−2 kyr−1 throughout most of the studied interval. Two discrete intervals of the core (one of which is within Cretaceous Tertiary, boundary KTB interval) are characterized by higher fluxes of meteoritic Os. Excluding these two intervals, the average background flux of particulate meteoritic Os is roughly half of that estimated from analyses of Cenozoic marine sediments. These are the first Os isotope data to provide evidence of resolvable temporal variations in the background flux of particulate meteoritic material to the Earth.  相似文献   

20.
The solubility of molybdenum (Mo) was determined at temperatures from 500 °C to 800 °C and 150 to 300 MPa in KCl-H2O and pure H2O solutions in cold-seal experiments. The solutions were trapped as synthetic fluid inclusions in quartz at experimental conditions, and analyzed by laser ablation inductively coupled plasma mass spectrometry (LA ICPMS).Mo solubilities of 1.6 wt% in the case of KCl-bearing aqueous solutions and up to 0.8 wt% in pure H2O were found. Mo solubility is temperature dependent, but not pressure dependent over the investigated range, and correlates positively with salinity (KCl concentration). Molar ratios of ∼1 for Mo/Cl and Mo/K are derived based on our data. In combination with results of synchrotron X-ray absorption spectroscopy of individual fluid inclusions, it is suggested that Mo-oxo-chloride complexes are present at high salinity (>20 wt% KCl) and ion pairs at moderate to low salinity (<11 wt% KCl) in KCl-H2O aqueous solutions. Similarly, in the pure H2O experiments molybdic acid is the dominant species in aqueous solution. The results of these hydrothermal Mo experiments fit with earlier studies conducted at lower temperatures and indicate that high Mo concentrations can be transported in aqueous solutions. Therefore, the Mo concentration in aqueous fluids seems not to be the limiting factor for ore formation, whereas precipitation processes and the availability of sulfur appear to be the main controlling factors in the formation of molybdenite (MoS2).  相似文献   

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