Carbonate and sulfate psephites

Major types of coarse-detrital carbonate and sulfate rocks (psephites) are considered. Two large (allochthonous and autochthonous) genetic groups are defined. Characteristics of some representatives are given for each group. It is shown that psephites of the carbonate and sulfate composition differ from similar rocks of the quartz and quartz-silicate composition in terms of formation mechanisms and depositional environments.     

正十六烷与硫酸镁热氧化还原反应模拟实验研究

利用高压釜反应装置,在一定温度和压力下,对正十六烷与硫酸镁热化学还原反应含水体系进行了模拟,通过气相色谱仪、微库仑仪、毛细管气相色谱,脉冲火焰光度检测器、红外光谱仪及X射线衍射仪对气、油、固三相产物分别进行了分析,并进行了动力学研究.结果表明,该体系在温度为450～550℃时可以发生反应,主要生成氧化镁、硫、焦炭、硫化...     

The dependence of bacterial sulfate reduction on sulfate concentration in marine sediments

The effect of dissolved sulfate concentration on the rate of bacterial sulfate reduction in marine sediment from Long Island Sound was examined using a radio-sulfur technique. The experimental results show that the rate is independent of the dissolved sulfate concentration until low levels are reached (<3 mM), and that, when interpreted using a Monod-type rate law, a saturation constant, K_s, of 1.62 ± 0.16 M results. This weak dependence implies that the dissolved sulfate exerts only a limited influence on the rate of sulfate reduction in marine sediments. Given such a weak dependence, dissolved sulfate profiles in marine sediments must resemble profiles generated by models with sulfate independent kinetics. Initially, this would suggest that currently used sulfate-independent diagenetic models are appropriate in modelling sulfate profiles. However, comparison of these models with those containing weak sulfate-dependent kinetic terms shows that there exists considerable disagreement between these models when the parameter grouping $\text{(D}{}_{\mathrm{s}}\text{k)}\text{1}\text{2}\text{/w}$ is larger than ~0.2 and smaller than ~3.0. (Here D_s is the SO^;₄ diffusion coefficient, k the organic matter decay constant and w the sediment burial velocity.) When the currently used models are corrected by employing physically meaningful boundary conditions, this divergence disappears. The modelling results, therefore, confirm the conclusion that any sulfate dependence inherent to the reduction kinetics does not appreciably affect sulfate pore water profiles, and that previous diagenetic studies using strong sulfate dependent models are erroneous.     

甲烷和固态硫酸钙的热化学还原反应模拟实验初步研究

碳酸盐岩地层中常伴有硫酸盐岩的沉积，在一定的温度和压力条件下，干酪根热降解生成的气态烃与硫酸盐岩接触后发生热化学还原反应(简称为TSR反应)，使气态烃消失，这可能是造成生气死亡线的主要原因之一。本文对CH4-CaSO4热化学还原反应的热力学问题进行了探讨，发现该反应能够自发进行，而且升高温度对反应有利。利用高温高压模拟装置对CH4-CaSO4反应体系进行了初步的模拟实验研究，通过微库仑、气相色谱和傅里叶变换红外光谱(FT-IR)等分析手段对实验结果进行了进一步验证。结果表明，甲烷和固态硫酸钙能够发生热化学还原反应，生成硫化氢、碳酸钙和水。最后，将CH4-CaSO4反应体系同国内外的研究工作进行了对比，认为本实验研究能够更好地补充和完善TSR反应体系，解释地质条件下工业气藏的死亡线问题。     

A model for oxygen and sulfur isotope fractionation in sulfate during bacterial sulfate reduction processes

We present a model of bacterial sulfate reduction that includes equations describing the fractionation relationship between the sulfur and the oxygen isotope composition of residual sulfate (δ³⁴S_{SO4_residual}, δ¹⁸O_{SO4_residual}) and the amount of residual sulfate. The model is based exclusively on oxygen isotope exchange between cell-internal sulfur compounds and ambient water as the dominating mechanism controlling oxygen isotope fractionation processes. We show that our model explains δ³⁴S_{SO4_residual} vs. δ¹⁸O_{SO4_residual} patterns observed from natural environments and from laboratory experiments, whereas other models, favoring kinetic isotope fractionation processes as dominant process, fail to explain many (but not all) observed δ³⁴S_{SO4_residual} vs. δ¹⁸O_{SO4_residual} patterns. Moreover, we show that a “typical” δ³⁴S_{SO4_residual} vs. δ¹⁸O_{SO4_residual} slope does not exist. We postulate that measurements of δ³⁴S_{SO4_residual} and δ¹⁸O_{SO4_residual} can be used as a tool to determine cell-specific sulfate reduction rates, oxygen isotope exchange rates, and equilibrium oxygen isotope exchange factors. Data from culture experiments are used to determine the range of sulfur isotope fractionation factors in which a simplified set of equations can be used. Numerical examples demonstrate the application of the equations. We postulate that, during denitrification, the oxygen isotope effects in residual nitrate are also the result of oxygen isotope exchange with ambient water. Consequently, the equations for the relationship between δ³⁴S_{SO4_residual}, δ¹⁸O_{SO4_residual}, and the amount of residual sulfate could be modified and used to calculate the fractionation-relationship between δ¹⁵N_{NO3_residual}, δ¹⁸O_{NO3_residual}, and the amount of residual nitrate during denitrification.     

聚铁改性絮凝剂的合成与水处理试验

研究了一种通过用聚铁改性来制备聚硅酸硫酸铁的方法,考察了改性剂中的SiO2质量分数、铁硅比、活化时间、pH值等参数对PFSS(聚硅酸硫酸铁)性能的影响,并进行了水处理实验。结果表明,PFSS制备适宜参数条件为SiO2质量分数为2.0%、铁硅比10∶1、活化时间4.0h,此时其对原水中的浊度和高锰酸盐指数去除率可分别达到98.4%～72.4%,处理后的原水达到饮用水的水质要求。     

A molecular orbital study of bonding in sulfate molecules: Implications for sulfate crystal structures

Molecular orbital calculations have been completed on sulfate monomers and a dimer in a determination of minimum-energy geometries and electron density distributions. SO bond lengths calculated for the monomer and dimer correlate linearly with the fractional s-characters of the bonds, as observed for sulfate groups in crystals. With increasing coordination number of S, the bonded radii of S and O, as determined from electron density maps, increase at the same rate. This is at variance with the assumption that the radius of the oxide ion is nearly constant and that bond length variations arise primarily from changes in cation radii. The dimer shows a relatively large change in energy as its SOS angle is deformed from its minimum-energy value (125.6°) to 180°, in conformity with the small variation among observed angles. This is in contrast to the wide variation of bridging angles observed for silicate and phosphate dimers in crystals and molecules, and may imply that significant differences should be expected in the behavior of sulfates with respect to polymorphism and glass formation. The reaction energy of SO₃ + H₂O → H₂SO₄, calculated with second-order Møller-Plesset perturbation theory, agrees with the experimental value. Other properties of H₂SO₄ are also calculated and compared with experimental observations and previous calculations.     

A revised isotope fractionation model for dissimilatory sulfate reduction in sulfate reducing bacteria

Sulfur isotope fractionation during dissimilatory sulfate reduction has been conceptually described by the widely accepted Rees model as related to the stepwise reduction of sulfate to sulfide within the cells of bacteria. The magnitude of isotope fractionation is determined by the interplay between different reduction steps in a chain of reactions. Here we present a revision of Rees’ model for bacterial sulfate reduction that includes revised fractionation factors for the sulfite-sulfide step and incorporates new forward and reverse steps in the reduction of sulfite to sulfide, as well as exchange of sulfide between the cell and ambient water. With this model we show that in contrast to the Rees model, isotope fractionations well in excess of −46‰ are possible. Therefore, some of the large sulfur isotope fractionations observed in nature can be explained without the need of alternate pathways involving the oxidative sulfur cycle. We use this model to predict that large fractionations should occur under hypersulfidic conditions and where electron acceptor concentrations are limiting.     

Distribution and speciation of metals,phosphorus, sulfate and organic material in brackish estuary water affected by acid sulfate soils

Dissolved (<1 kDa) and colloidal (1 kDa-0.45 μm) size fractions of sulfate, organic carbon (OC), phosphate and 17 metals/metalloids were investigated in the acidic Vörå River and its estuary in Western Finland. In addition, geochemical modelling was used to predict the formation of free ions and complexes in these waters. The sampling was carried out during high-water flow in autumn and in spring when the abundantly occurring acid sulfate (AS) soils in the catchment area are extensively flushed. Based on the high concentrations of sulfate, acidity and several metals, it is clear that the Vörå River and its estuary is strongly affected by AS soils. The high dissolved form of metals limits also the existence of fish and other organisms in this estuary, and certainly also in other similar shallow brackish estuaries elsewhere in the Gulf of Bothnia. However, generally already <20% saline sea water reduces the concentration for OC and several elements (Al, Cu, Cr, Fe, Pb, PO₄ and U) by half and c. 20–30% saline sea water is needed to halve concentrations of Cd, Co, Mn, Ni and Zn. Consequently, these elements as well as organic matters were rapidly precipitated in the estuary, even after mixing with fairly small amounts of the alkaline brackish sea water. Aluminium, Cu, Fe and U most likely precipitate together with organic matter closest to the river mouth. Manganese is relatively persistent in solution and, thus, precipitates further down the estuary as Mn oxides, which concomitantly capture Ba, Cd, Co, Cu, Ni and Zn. In the inner estuary, the high contents of Al is as important than Fe in removing PO₄ and, thus, also reducing the risk of algae blooms in near coastal areas influenced by AS soils in the Gulf of Bothnia. Moreover, the dispersion of metals far out in the estuary is dependent on hydrological conditions, i.e. with high flows the plume of metal-rich water will spread further out in the estuary. Furthermore, the extensive drainage of the catchment and subsequent artificial enlargement of the river channel during recent decades has not only enabled oxidation of sulfidic sediments, but strongly increased flow peaks that reach further out in the estuary.     

Crystallisation of sodium sulfate: supersaturation and metastable phases

Crystallisation of sodium sulfate solutions by evaporation under controlled climatic conditions has revealed the existence of crystalline hydrated sodium sulfate salts not previously reported. The sodium sulfate phase crystallising and the concentration of the solution at the point of crystallisation depends on the climatic conditions (temperature and evaporation rate). During the rehydration of the anhydrous sodium sulfate phase, thenardite, another previously unreported phase was formed prior to the nucleation of the stable phase, mirabilite Na₂SO₄ · 10H₂O. The addition of organic inhibitors changes both the crystallisation and the rehydration behavior in this system.     

Characterization of sulfate ion in travertine

The mode of incorporation of sulfate ion in travertine was discussed on the basis of chemical compositions, i.r. and laser Raman spectra. These data strongly suggest that most of the sulfate ions in the calcitic travertine replace carbonate ions. This conclusion is in good harmony with the facts that calcite incorporates more sulfate ions than aragonite does and that the sulfate content of manganoan calcite decreases with increasing manganese content (Takano et al. 1977). Based on this conclusion, retarding effect of sulfate ion on the precipitation of calcite from solution was discussed.     

Goethite-enhanced anaerobic bio-decomposition of sulfate minerals

The effects of goethite on the anaerobic bio-decomposition of sulfate minerals were investigated by using the beef extract as a carbon source and the activated sludge as the source of mixed bacteria. Solution pH, sulfate concentration, total iron ion concentration and the solid products of four different batch tests were monitored and analyzed. Experimental results showed that the presence of iron oxide can improve the alkalinity of the reaction system which results in the increase of pH value. Moreover, the added goethite consumed a large amount of H₂S generated from the sulfate minerals by SRB, thereby significantly enhancing the decomposition of gypsum and anhydrite compared with the control batch tests. In addition, the SEM observation and the EDS spectra showed that there were some rod-shaped microorganisms and new generated minerals, such as iron sulfide, calcium carbonate crystals, and elemental sulfur. Both of the proliferation of new minerals (iron sulfide and calcium carbonate crystals) and the complete disappearance of sulfate minerals indicated that iron oxide can play the role in fixing the S element through the metabolism of SRB and hence improve the bio-decomposition of sulfate minerals.     

Enthalpy of formation of sulfate green rusts

As a contribution to the systematic study of iron oxide thermodynamics, this work reports enthalpies of formation of green rust, a double layered (Fe^II, Fe^III) hydroxide with the ideal stoichiometry , with sulfate as the anion in the interlayer. Samples were characterized by X-ray powder diffraction, thermogravimetric analysis, infrared spectroscopy, and Mössbauer spectroscopy. Full chemical analysis was performed. Contents of Fe^II, Fe^III, water, and sulfate were obtained. We report standard enthalpies of formation for green rust with different Fe^II/Fe^III ratios. Enthalpies of formation from single cation compounds, namely, Fe(OH)₂, Fe(OH)₃, FeSO₄ and H₂O show reasonable agreement with Gibbs free energies of formation from single cation compounds recalculated from the reported literature values. These values show that green rust has little stabilization over a mechanical mixture of these single cation compounds and there is no thermodynamic preference for any particular Fe^II/Fe^III ratio.     

Sulfur isotope measurement of sulfate and sulfide by high-resolution MC-ICP-MS

We have developed a technique for the accurate and precise determination of ³⁴S/³²S isotope ratios (δ³⁴S) in sulfur-bearing minerals using solution and laser ablation multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). We have examined and determined rigorous corrections for analytical difficulties such as instrumental mass bias, unresolved isobaric interferences, blanks, and laser ablation- and matrix-induced isotopic fractionation. Use of high resolution sector-field mass spectrometry removes major isobaric interferences from O₂⁺. Standard-sample bracketing is used to correct for the instrumental mass bias of unknown samples. Background on sulfur masses arising from memory effects and residual oxygen-tailing are typically minor (< 0.2‰, within analytical error), and are mathematically removed by on-peak zero subtraction and by bracketing of samples with standards determined at the same signal intensity (within 20%). Matrix effects are significant (up to 0.7‰) for matrix compositions relevant to many natural sulfur-bearing minerals. For solution analysis, sulfur isotope compositions are best determined using purified (matrix-clean) sulfur standards and sample solutions using the chemical purification protocol we present. For in situ analysis, where the complex matrix cannot be removed prior to analysis, appropriately matrix-matching standards and samples removes matrix artifacts and yields sulfur isotope ratios consistent with conventional techniques using matrix-clean analytes. Our method enables solid samples to be calibrated against aqueous standards; a consideration that is important when certified, isotopically-homogeneous and appropriately matrix-matched solid standards do not exist. Further, bulk and in situ analyses can be performed interchangeably in a single analytical session because the instrumental setup is identical for both. We validated the robustness of our analytical method through multiple isotope analyses of a range of reference materials and have compared these with isotope ratios determined using independent techniques. Long-term reproducibility of S isotope compositions is typically 0.20‰ and 0.45‰ (2σ) for solution and laser analysis, respectively. Our method affords the opportunity to make accurate and relatively precise S isotope measurement for a wide range of sulfur-bearing materials, and is particularly appropriate for geologic samples with complex matrix and for which high-resolution in situ analysis is critical.     

Geochemistry of an acidic chromium sulfate plume

The historical disposal of acidic chromium sulfate solutions into unlined lagoons between 1953 and 1970 at an industrial site resulted in formation of a dense aqueous phase liquid (DAPL) plume [specific gravity 1.11 g/cm³, pH 3, up to 4700 mg/L Cr(III), and up to 90,000 mg/L SO₄]. The DAPL sank through the shallow glacial till aquifer to an underlying impermeable gneissic bedrock from where it migrated downgradient along buried channels incised in the bedrock. Because of its high density, the plume chemistry is sharply stratified vertically. Chromium(III) predominates in the DAPL because excess Cr(VI) not reduced in the original process has been reduced by Fe(II) derived from silicates, while Cr(OH)₃(am) occurs as surface coatings on silicate minerals and as discrete particles mixed with Fe(OH)₃(am) and Al(OH)₃(am). The solubility of Cr(OH)₃(am) accurately describes Cr(III) concentrations in the plume and nearby groundwater, while Al and Fe in solution are also consistent with solubility-controlling oxyhydroxides. Because of these solubility controls, metal cations are attenuated relative to more mobile Cl and SO₄, resulting in a chromatographic separation of solutes downgradient from the plume origin. The good agreement between predicted and observed solution concentrations illustrates the utility of equilibrium modeling when interpreting metal transport characteristics and in determining the efficacy of natural attenuation in subsurface systems.     

硫酸根离子在弱透水层中的迁移行为

通过研究地下水中硫酸根离子通过弱透水层时迁移特征的变异规律及其环境效应作用,分析在不同黏性土壤厚度条件下硫酸根离子浓度的变化及其受pH、Eh、钙离子浓度变化的影响特征,以及在不同pH 值条件下硫酸根离子的浓度变化情况。利用土柱填装及淋滤法,得出地下水中硫酸根离子通过弱透水层时穿透能力很强的结论,并揭示了硫酸根离子浓度随渗透土壤厚度的增大而增大,随淋滤液pH 值增大而减小的规律。     

Crystallization of sodium sulfate salts in limestone

Crystallization pressure of salt crystals growing in confined pores is found to be the main cause for damage to stone and masonry. In this work, the crystallization of sodium sulfate salts in Cordova Cream and Indiana limestones is investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The DSC experiments indicate that sodium heptahydrate always precipitates prior to the decahydrate (mirabilite), at a temperature between 15 and 7°C in the selected stones. The threshold supersaturation for the nucleation of heptahydrate is less than 2. In constrast, mirabilite precipitates close to or below 0°C and its crystallization pattern is completely different: precipitation takes place abruptly when the threshold supersaturation is reached, which is greater than 7. Indeed, the DSC and the DMA experiments reveal the rare nature of the nucleation of mirabilite for the investigated stones. The crystallization pressure exerted by heptahydrate does not cause damage under the conditions of the cooling experiments. In contrast, mirabilite exerts a very high crystallization pressure on the pore wall causing damage of the stone; moreover, the transient stress can remain for a long period of time since the relaxation process is slow.     

Modeling solute transport and sulfate reduction in marsh sediments

The seasonal oscillation in sulfate and chloride concentration profiles in some salt marsh sediments is due to exchange of solutes with water on the surface of the marsh, and to the desiccation of the sediment in summer. Desiccation is manifested by disappearance of surface waters, fluctuations in the location of the water table, and by removal of water from the sediment above the water table. The loss of water from the pore space is commonly accompanied by entry of air into the soil, which oxidizes sulfide. The oxidation causes titratable alkalinity to decrease and results in CO₂ degassing.Diffusion models of salinity can account for the observed profiles but only as long as the marsh is maintained inundated. The complexities introduced to the solute transport equations by sediment desiccation invalidate steady-state modeling of solute transport and diagenesis. The concentration profiles of dissolved products of sulfate reduction, such as bicarbonate, require months to reestablish a steady state after being disrupted. If the profiles of dissolved products of sulfate reduction are disrupted seasonally, such as by a seasonal fluctuation in the water table, they may remain transient throughout the year.     

硫酸钠盐渍土击实特性与压实度评价试验研究

合理的压实度对减小硫酸盐渍土地基的盐胀和溶陷病害具有重要意义。为探讨硫酸盐渍土的击实特性、击实后的微结构特征以及合理的压实度评价方法,对不同试样制备条件下的硫酸盐渍土进行了击实试验和电镜扫描。结果表明,硫酸盐渍土的击实特性和击实后的微结构特征与土中硫酸钠的状态密切相关：硫酸钠溶液具有润滑性,其含量的增加能显著提高硫酸盐渍土的击实性能,击实后,试样的土团粒主要呈表面光滑的薄层状,土体为流纹状镶嵌结构;而十水硫酸钠具有支架作用,其含量的增加使硫酸盐渍土的击实性能大幅降低,击实后,试样的土团粒呈浑圆状、粒径很小,土体为网状架空结构。根据这一新认识,进一步分析了试样制备方法和闷料时间对硫酸盐渍土压实度的影响,并给出了相应的压实度评价建议。该研究成果可为硫酸盐渍土压实度的合理评价提供理论依据,对硫酸盐渍土地基的辗压施工工艺具有参考价值。