应力作用下岩石的化学动力学溶解机制研究

通过结合化学热力学及动力学、过渡态理论和岩石力学等方面的知识,建立了应力作用下岩石的溶解动力学模型,分析了应力作用对岩石固相物质活度及矿物溶解动力学速率的影响,探讨了应力作用下水岩相互作用机制。研究结果表明：岩石所承受应力与周围流体压力之间存在的应力差所产生的化学势差是应力作用下溶解反应的驱动力;应力的施加显著提高了岩石中固相物质的活度,由此加快了矿物溶解反应的动力学速率;应力作用下的岩石细观溶解机制可根据固液界面应力分配及优先溶解部位上的差别分别用水膜扩散模型或岛渠模型进行描述;应力作用下水岩相互作用存在着应力、化学与渗流的3场耦合问题：应力推动化学反应的发生,化学作用使得岩石表面的细观形貌发生改变,局部的应力分布及大小也随着形貌的变化而改变,进而影响化学反应发生的位置及进程,同时也改变渗流通道的演化规律     

Kinetics and mechanism of polythionate oxidation to sulfate at low pH by O2 and Fe

Polythionates (S_xO₆²⁻) are important in redox transformations involving many sulfur compounds. Here we investigate the oxidation kinetics and mechanisms of trithionate and tetrathionate oxidation between pH 0.4 and pH 2 in the presence of Fe³⁺ and/or oxygen. In these solutions, Fe³⁺ plus oxygen oxidizes tetrathionate and trithionate at least an order of magnitude faster than oxygen alone. Kinetic measurements, coupled with density functional calculations, suggest that the rate-limiting step for tetrathionate oxidation involves Fe³⁺ attachment, followed by electron density shifts that result in formation of a sulfite radical and S₃O₃⁰ derivatives. The overall reaction orders for trithionate and tetrathionate are fractional due to rearrangement reactions and side reactions between reactants and intermediate products. The pseudo-first order rate coefficients for tetrathionate range from 10⁻¹¹ s⁻¹ at 25°C to 10⁻⁸ s⁻¹ at 70°C, compared to 2 × 10⁻⁷ s⁻¹ at 35 °C for trithionate. The apparent activation energy (E_A) for tetrathionate oxidation at pH 1.5 is 104.5 ± 4.13 kJ/mol. A rate law at pH 1.5 and 70°C between 0.5 and 5 millimolar [Fe³⁺] is of the form:

     

Chemical kinetics, speleothem growth and climate

The morphology and stratigraphy of speleothems are controlled by parameters that depend on climate. These are the water supply rates feeding the speleothem, e.g. a stalagmite, the growth rates dependent on the chemical kinetics of calcite precipitation and the supersaturation of the solution from which calcite is precipitated. To elucidate the basic principles of speleothem growth, a physical-chemical model of calcite precipitation is used to estimate growth rates under various geologically relevant conditions. Furthermore, we present a model that allows the computation of the growth history of stalagmites, i.e. their morphology and stratigraphy under varying climatic conditions. This enables us to see how climatic signals are inscribed into stalagmites. Owing to the counter-balancing effects of some parameters, it is not possible to read climatic conditions backwards from the morphology and stratigraphy of a speleothem in a simple way, but a basic understanding of the growth of speleothems can be a helpful supporting tool in the interpretation of palaeoclimatic records.     

水钠锰矿氧化硫化物的过程与动力学研究

水钠锰矿是表生环境中常见的氧化锰矿物之一,影响土壤溶液中硫化物的迁移、转化和归趋。本文考察了酸性水钠锰矿氧化硫化钠溶液的反应过程,采用分光光度法、离子色谱法分析S2-及其氧化产物的浓度和变化趋势,用XRD、SEM表征酸性水钠锰矿粉末反应前后的晶体结构和微观形貌,探讨了温度、pH值、矿物用量对S2-氧化速率的影响。结果表明,S2-的氧化产物主要为单质S,其氧化速率符合准一级动力学规律,且氧化速率随着温度升高、pH值降低和矿物用量增加而增大;酸性水钠锰矿首先被还原生成Mn(OH)2,Mn(OH)2在空气中与O2作用转化成Mn3O4,Mn3O4可进一步转化生成MnOOH。     

天然锰钾矿氧化降解水体中苯酚机理研究

根据锰的溶出、氧气不参与反应、酸度是影响苯酚降解的主要因素等实验结果，推测天然锰钾矿与苯酚的作用机制。研究表明：反应8h，总有机碳去除率达88．7％；锰钾矿在硝酸存在时产生的氧自由基与苯酚发生氧化还原反应，使苯酚降解。根据检出的对苯醌、联苯二酚、2-羟基-苯并呋喃等中间物质推测出苯酚降解的反应途径。     

Outer-sphere electron transfer kinetics of metal ion oxidation by molecular oxygen

Density functional theory molecular orbital calculations and Marcus theory have been combined to assess the rates and physicochemical factors controlling the outer-sphere oxidation of divalent V, Cr, Mn, Fe, and Co aquo and hydroxo ions by O₂ in homogeneous aqueous solution. Key quantities in the elementary oxidation step include the inner-sphere component of the reorganization energy, the thermodynamic driving force, and electrostatic work terms describing the interactions occurring, in this case, between the net charges on the product species. Collectively, these factors and their interplay have a large influence on the rate of the oxidation cross-reaction.An inner-sphere pathway for the self-exchange reactions and oxidation by O₂ of Mn²⁺ and Cr²⁺ ions has been supported indirectly in this study by comparing predicted outer-sphere rates with the results of previous experiments. Likewise, an outer-sphere pathway is suggested for the similar sets of reactions involving the V, Fe, and Co ions. An assessment of the self-exchange reaction for the oxygen/superoxide couple has led to predicted rates in excellent agreement with direct measurements. Predicted rates of oxidation for the hexaquo Fe ion are also in agreement with experiment, while the predicted rates for the outer-sphere oxidation of its hydrolysis products are ∼2 to 3 (monohydroxo) and ∼4 (dihydroxo) orders of magnitude slower than the observed rates. This suggests an inner-sphere pathway is appropriate to explain the relatively fast rates observed for the hydrolyzed Fe species.     

Oxygen and sulfur isotope systematics of sulfate produced by bacterial and abiotic oxidation of pyrite

To better understand reaction pathways of pyrite oxidation and biogeochemical controls on δ¹⁸O and δ³⁴S values of the generated sulfate in acid mine drainage (AMD) and other natural environments, we conducted a series of pyrite oxidation experiments in the laboratory. Our biological and abiotic experiments were conducted under aerobic conditions by using O₂ as an oxidizing agent and under anaerobic conditions by using dissolved Fe(III)_aq as an oxidant with varying δ¹⁸O_H2O values in the presence and absence of Acidithiobacillus ferrooxidans. In addition, aerobic biological experiments were designed as short- and long-term experiments where the final pH was controlled at ∼2.7 and 2.2, respectively. Due to the slower kinetics of abiotic sulfide oxidation, the aerobic abiotic experiments were only conducted as long term with a final pH of ∼2.7. The δ³⁴S_SO4 values from both the biological and abiotic anaerobic experiments indicated a small but significant sulfur isotope fractionation (∼−0.7‰) in contrast to no significant fractionation observed from any of the aerobic experiments. Relative percentages of the incorporation of water-derived oxygen and dissolved oxygen (O₂) to sulfate were estimated, in addition to the oxygen isotope fractionation between sulfate and water, and dissolved oxygen. As expected, during the biological and abiotic anaerobic experiments all of the sulfate oxygen was derived from water. The percentage incorporation of water-derived oxygen into sulfate during the oxidation experiments by O₂ varied with longer incubation and lower pH, but not due to the presence or absence of bacteria. These percentages were estimated as 85%, 92% and 87% from the short-term biological, long-term biological and abiotic control experiments, respectively. An oxygen isotope fractionation effect between sulfate and water (ε¹⁸O_SO4-H2O) of ∼3.5‰ was determined for the anaerobic (biological and abiotic) experiments. This measured value was then used to estimate the oxygen isotope fractionation effects between sulfate and dissolved oxygen in the aerobic experiments which were −10.0‰, −10.8‰, and −9.8‰ for the short-term biological, long-term biological and abiotic control experiments, respectively. Based on the similarity between δ¹⁸O_SO4 values in the biological and abiotic experiments, it is suggested that δ¹⁸O_SO4 values cannot be used to distinguish biological and abiotic mechanisms of pyrite oxidation. The results presented here suggest that Fe(III)_aq is the primary oxidant for pyrite at pH < 3, even in the presence of dissolved oxygen, and that the main oxygen source of sulfate is water-oxygen under both aerobic and anaerobic conditions.     

The kinetics of iodide oxidation by the manganese oxide mineral birnessite

The kinetics of iodide (I⁻) and molecular iodine (I₂) oxidation by the manganese oxide mineral birnessite (δ-MnO₂) was investigated over the pH range 4.5-6.25. I⁻ oxidation to iodate proceeded as a two-step reaction through an I₂ intermediate. The rate of the reaction varied with both pH and birnessite concentration, with faster oxidation occurring at lower pH and higher birnessite concentration. The disappearance of I⁻ from solution was first order with respect to I⁻ concentration, pH, and birnessite concentration, such that −d[I⁻]/dt = k[I⁻][H⁺][MnO₂], where k, the third order rate constant, is equal to 1.08 ± 0.06 × 10⁷ M⁻² h⁻¹. The data are consistent with the formation of an inner sphere I⁻ surface complex as the first step of the reaction, and the adsorption of I⁻ exhibited significant pH dependence. Both I₂, and to a lesser extent, sorbed to birnessite. The results indicate that iodine transport in mildly acidic groundwater systems may not be conservative. Because of the higher adsorption of the oxidized I species I₂ and , as well as the biophilic nature of I₂, redox transformations of iodine must be taken into account when predicting I transport in aquifers and watersheds.     

The anaerobic degradation of organic matter in Danish coastal sediments: iron reduction, manganese reduction, and sulfate reduction

We used a combination of porewater and solid phase analysis, as well as a series of sediment incubations, to quantify organic carbon oxidation by dissimilatory Fe reduction, Mn reduction, and sulfate reduction, in sediments from the Skagerrak (located off the northeast coast of Jutland, Denmark). In the deep portion of the basin, surface Mn enrichments reached 3.5 wt%, and Mn reduction was the only important anaerobic carbon oxidation process in the upper 10 cm of the sediment. In the less Mn-rich sediments from intermediate depths in the basin, Fe reduction ranged from somewhat less, to far more important than sulfate reduction. Most of the Mn reduction in these sediments may have been coupled to the oxidation of acid volatile sulfides (AVS), rather than to dissimilatory reduction. High rates of metal oxide reduction at all sites were driven by active recycling of both Fe and Mn, encouraged by bioturbation. Recycling was so rapid that the residence time of Fe and Mn oxides, with respect to reduction, ranged from 70-250 days. These results require that, on average, an atom of Fe or Mn is oxidized and reduced between 100-300 times before ultimate burial into the sediment. We observed that dissolved Mn2+ was completely removed onto fully oxidized Mn oxides until the oxidation level of the oxides was reduced to about 3.8, presumably reflecting the saturation by Mn2+ of highly reactive surface adsorption sites. Fully oxidized Mn oxides in sediments, then, may act as a cap preventing Mn2+ escape. We speculate that in shallow sediments of the Skagerrak, surface Mn oxides are present in a somewhat reduced oxidation level (< 3.8) allowing Mn2+ to escape, and perhaps providing the Mn2+ which enriches sediments of the deep basin.     

天然锰钾矿氧化降解水体中苯酚实验研究

在酸性条件下进行了锰钾矿氧化降解水体中苯酚的实验研究，结果表明：室内自然光照和氧气环境不影响苯酚降解；反应溶液酸度越大，反应进行得越快；样品用量越多、粒径越小，越有利于降解反应；反应温度升高与振荡速度增大也有利于降解反应的进行；共存电解质氯化钠、氯化钙不影响降解反应，而磷酸钠与醋酸钠则不利于降解反应。当介质pH值为2、1，160～200目锰钾矿用量为10g／L，反应温度为25℃，振荡速度为200r／min，反应8h，对50mL浓度为100mg／L苯酚的降解率基本上达到100％，达到了工业排放标准。从反应产物初步推断，苯酚降解的实质是锰钾矿氧化降解作用，为处理苯酚废水增加了一种有效的方法，并拓宽了天然锰钾矿的开发应用前景。     

甲烷被黑云母氧化形成二氧化碳的实验研究与意义

CH4和CO2是岩浆热液系统中的重要挥发组分，两者之间的转换机制是一个重要的科学问题，在碳循环和流体作用等诸多方面都具有重要意义。例如在成矿过程中，CH4和CO2的加入会改变成矿流体性质，CO2还能缓冲流体pH，对成矿元素的迁移和沉淀富集有重要影响。前人通过研究瑞士阿尔卑斯山中部石炭纪、二叠纪、三叠纪地层裂隙石英中的流体包裹体发现，在较高温度条件下，黑云母的绿泥石化能将CH4氧化生成CO2，然而缺少相关的实验地球化学证据。因此，本项研究选择黑云母作为氧化剂开展了CH4的氧化实验研究。通过对黑云母- 甲烷- 水体系、黑云母- 碳化铝- 水体系以及甲烷- 水体系的实验研究发现，证实了黑云母能够将CH4氧化为CO2，起始反应温度约150℃，远低于地质研究结果。对于黑云母- 甲烷- 水体系和甲烷- 水体系实验，采用熔融毛细硅管作为反应腔，而对于黑云母- 碳化铝- 水体系实验，则采用粗石英管作为反应腔。对反应后黑云母残片的能谱分析表明，变价元素Fe含量大量降低，表明黑云母中三价Fe作为氧化剂参与了反应。这一结果为地质系统中黑云母等铁锰暗色矿物在中低温条件下氧化CH4形成CO2提供了实验和理论支撑。而CH4向CO2的转变过程，将改变热液流体的性质，有利于富CO2成矿流体的形成，对金属矿床形成具有重要意义。     

Substrate inhibition kinetics of phenol degradation by Pseudomonas fluorescence from steady state and wash-out data

The present study investigated the phenol utilization kinetics of a pure culture of an indigenous Pseudomonas fluorescence under steady state and non-steady state (washout) conditions. Steady states of a continuous culture with an inhibitory substrate was used to estimate kinetic parameters under substrate limitation (chemo stat operation) Pure cultures of an indigenous Pseudomonas fluorescence were grown in continuous culture on phenol as the sole source of carbon and energy at dilution rates of 0.010 - 0.20/h. Using different dilution rates, several steady states were investigated and the specific phenol consumption rates were calculated. In addition, phenol degradation was investigated by increasing the dilution rate above the critical dilution rate (washout cultivation). The results showed that the specific phenol consumption rate increased with increased dilution rate at steady state and phenol degradation by Pseudomonas fluorescence can be described by simple substrate inhibition kinetics under substrate limitation but cannot be described by simple substrate inhibition kinetics under washout cultivation. Fitting of the steady state data from continuous cultivation to various inhibition models resulted in the best fit for Haldane, Yano and Koga (2), Aiba and Teissier kinetic inhibition models. The r_smax value of 0.229 mg/mg/h obtained from the inhibition model equations was comparable to the experimentally calculated r_smax value of 0.246 mg/mg/h obtained under washout cultivation. Therefore, the biokinetic constants evaluated using these models showed good tolerance and growth of the indigenous organism.     

氧协同菱铁矿降解微囊藻毒素机理研究

已知在无氧条件下天然矿物菱铁矿能成功水解微囊藻毒素-LR(MC-LR),然而实际应用过程中难以避免水中溶解氧(O₂)的存在,因此有必要深入研究不同溶氧量(DOC)条件下菱铁矿对MC-LR降解的影响。本文通过在无氧和有氧条件下菱铁矿对MC-LR的降解实验,发现在有氧条件下(溶氧量1.62～21.87 mg/L), MC-LR的降解速率均比无氧条件(k₀=0.030 16 mg·L^-1·h^-1)高且其降解速率随O₂含量增加而依次增加,当O₂加入量为1.0 mL(溶氧量21.87 mg/L)时,菱铁矿对MC-LR降解速率最大(0.083 34 mg·L^-1·h^-1),为无氧条件下的2.76倍。通过外加腐殖酸(humic acid, HA)和自由基进行捕获实验,发现FeCO₃能直接活化O₂产生超氧自由基(·O~-₂),以实现对MC-LR的氧化,但外加HA抑...     

The effect of As, Co, and Ni impurities on pyrite oxidation kinetics: An electrochemical study of synthetic pyrite

Synthetic pyrite crystals doped with As, Co, or Ni, undoped pyrite, and natural arsenian pyrite from Leadville, Colorado were investigated with electrochemical techniques and solid-state measurements of semiconducting properties to determine the effect of impurity content on pyrite’s oxidation behavior. Potential step experiments, cyclic voltammetry, and AC voltammetry were performed in a standard three-electrode electrochemical cell setup. A pH 1.78 sulfuric acid solution containing 1 mM ferric iron, open to atmospheric oxygen, was chosen to approximate water affected by acid drainage. Van der Pauw/Hall effect measurements determined resistivity, carrier concentration and carrier mobility.The anodic dissolution of pyrite and the reduction of ferric iron half-reactions are taken as proxies for natural pyrite oxidation. Pyrite containing no impurities is least reactive. Pyrite with As is more reactive than pyrite with either Ni or Co despite lower dopant concentration. As, Co, and Ni impurities introduce bulk defect states at different energy levels within the band gap. Higher reactivity of impure pyrite suggests that introduced defect levels lead to higher density of occupied surface states at the solid-solution interface and increased metallic behavior. The current density generated from potential step experiments increased with increasing As concentration. The higher reactivity of As-doped pyrite may be related to p-type conductivity and corrosion by holes. The results of this study suggest that considering the impurity content of pyrite in mining waste may lead to more accurate risk assessment of acid producing potential.     

Formation of ferriolivine and magnesioferrite from Mg — Fe-olivine: Reactions and kinetics of oxidation

Olivine samples (Fa 11) have been oxidized in air (f _O2 = 0.2 atm) at temperatures ranging from 350–700 °C and examined by Mössbauer spectroscopy, transmission electron microscopy, X-ray powder diffraction and thermomagnetic analysis. Oxidation of olivine was found to result in ferriolivine, magnesioferrite (major oxide phase) and magnetite (minor oxide phase) formation. Ferriolivine forms planar (001) precipitates, 0.6 nm in thickness, in the olivine host; the composition is likely to be Mg_0.5 v _0.5(Fe³⁺)_1.0SiO₄. Magnesioferrite MgFe₂O₄ exsolves as fine-grained precipitates (5–6 nm in size) filling interstices between the ferriolivine planar precipitates. Oxidation kinetic data at 700 °C show two stages of oxidation corresponding to formation of ferriolivine in the first stage and magnesioferrite in the second stage. The linear rate law with a rate constant k _Fol = 1.23 · 10^-3 s^-1 was found for the first stage whereas a parabolic rate-law with a constant of k _oxi = 3.28 · 10^-3 s^-1 was determined for the second stage of oxidation. It was found that ferriolivine is not an intermediate metastable phase in the oxidation process, terminated by magnesioferrite formation. The ferriolivine and magnesioferrite are considered to have formed by independent reactions which do not necessarily proceed simultaneously.     

Pyrite oxidation: a state-of-the-art assessment of the reaction mechanism

The oxidation of pyrite to release ferrous iron and sulfate ions to solution involves the transfer of seven electrons from each sulfur atom in the mineral to an aqueous oxidant. Because only one or, at most, two electrons can be transferred at a time, the overall oxidation process is quite complex. Furthermore, pyrite is a semiconductor, so the electrons are transferred from sulfur atoms at an anodic site, where oxygen atoms from water molecules attach to the sulfur atoms to form sulfoxy species, through the crystal to cathodic Fe(II) sites, where they are acquired by the oxidant species. The reaction at the cathodic sites is the rate-determining step for the overall process. This paper maps out the most important steps in this overall process.     

The mechanism and kinetics of DTPA-promoted dissolution of barite

The dissolution rate of natural barite, BaSO₄, was measured in solutions of DTPA (diethylene triamine penta-acetic acid) to investigate the mechanism of ligand-promoted dissolution using a strong chelating agent. Experiments were carried out over a range of DTPA concentrations 0.5–0.0001 M solutions, at room temperature (22 °C), as well as a range of temperatures, 22–80 °C at 1 atm. The dissolution rate is inversely related to the DTPA concentration in solution. A more dilute DTPA solution is shown to be more efficient as a solvent in terms of the approach to the equilibrium saturation value for the dissolution of Ba²⁺. An analysis of the temperature dependence of the dissolution rate at high pH by the determination of activation energies indicates that the reaction is probably controlled by the pre-exponential term in the rate constant. This indicates that reaction frequency mostly controls differences in reactivity and suggests an explanation for the results in terms of stearic hindrance due to adsorbed DTPA molecules at the barite surface. The effect of DTPA on the solvation of the Ba²⁺ ion may also influence the dissolution rate.     

Rates of microbial hydrogen oxidation and sulfate reduction in Opalinus Clay rock

Hydrogen gas (H₂) may be produced by the anoxic corrosion of steel components in underground structures, such as geological repositories for radioactive waste. In such environments, hydrogen was shown to serve as an electron donor for autotrophic bacteria. High gas overpressures are to be avoided in radioactive waste repositories and, thus, microbial consumption of H₂ is generally viewed as beneficial. However, to fully consider this biological process in models of repository evolution over time, it is crucial to determine the in situ rates of microbial hydrogen oxidation and sulfate reduction. These rates were estimated through two distinct in situ experiments, using several measurement and calculation methods. Volumetric consumption rates were calculated to be between 1.13 and 1.93 μmol cm⁻³ day⁻¹ for H₂, and 0.14 and 0.20 μmol cm⁻³ day⁻¹ for sulfate. Based on the stoichiometry of the reaction, there is an excess of H₂ consumed, suggesting that it serves as an electron donor to reduce electron acceptors other than sulfate, and/or that some H₂ is lost via diffusion. These rate estimates are critical to evaluate whether biological H₂ consumption can negate H₂ production in repositories, and to determine whether sulfate reduction can consume sulfate faster than it is replenished by diffusion, which could lead to methanogenic conditions.     

Anaerobic oxidation of methane and sulfate reduction along the Chilean continental margin

Anaerobic oxidation of methane (AOM) and sulfate reduction (SR) were investigated in sediments of the Chilean upwelling region at three stations between 800 and 3000 m water depth. Major goals of this study were to quantify and evaluate rates of AOM and SR in a coastal marine upwelling system with high organic input, to analyze the impact of AOM on the methane budget, and to determine the contribution of AOM to SR within the sulfate-methane transition zone (SMT). Furthermore, we investigated the formation of authigenic carbonates correlated with AOM. We determined the vertical distribution of AOM and SR activity, methane, sulfate, sulfide, pH, total chlorins, and a variety of other geochemical parameters. Depth-integrated rates of AOM within the SMT were between 7 and 1124 mmol m⁻² a⁻¹, effectively removing methane below the sediment-water interface. Single measurements revealed AOM peaks of 2 to 51 nmol cm⁻³ d⁻¹, with highest rates at the shallowest station (800 m). The methane turnover was higher than in other diffusive systems of similar ocean depth. This higher turnover was most likely due to elevated organic matter input in this upwelling region offering significant amounts of substrates for methanogenesis. SR within the SMT was mostly fuelled by methane. AOM led to the formation of isotopically light DIC (δ¹³C: −24.6‰ VPDB) and of distinct layers of authigenic carbonates (δ¹³C: −14.6‰ VPDB).