Coupled Reactive Transport Modeling of Redox Processes in a Nitrate-Polluted Sandy Aquifer

The reactive transport modeling of a complicated suite of reactions apparent in the aquifer during the application of N-containing fertilizers is reported. The unconfined sandy aquifer can be subdivided into an oxic zone which contains groundwater with oxygen and nitrate and an anoxic zone characterized by elevated iron and sulfate concentrations in groundwater. Oxygen and nitrate are being reduced by pyrite and organic matter that commonly apparent in the aquifer. The oxidation of pyrite is modeled using the local equilibrium approach, whereas decomposition of organic matter, with the adoption of kinetic approach. The system is buffered by dissolution of aluminum and iron oxides. The modeling process is a two-step procedure. First, the processes are modeled in the one-dimensional (1D) column using PHREEQC code. Subsequently, the calibrated and verified data were copied and used in two-dimensional (2D) PHAST model. Prior to the performance of reactive transport modeling operations with PHAST, a reliable flow model was executed. Finally, predictions are made for the distribution of water chemistry for the year 2008. Model predicts that sulfate derived from the ongoing pyrite oxidation is reduced by the dissolved organic carbon at the higher depth and forms pyrite by the reaction with iron. The results of this study highlight the importance of understanding the interplay between the transport and chemical reactions that occur during the input of nitrate to the aquifer. Reactive transport modeling incorporating the use of a newly developed code PHAST have proved to be a powerful tool for analyzing and quantifying such interactions.     

Reactive Transport Process of Earthquake-induced Hydro-chemical Changes in Guanding Thermal Spring, Western Sichuan, China

Earthquake-related hydrochemical changes in thermal springs have been widely observed; however, quantitative modeling of the reactive transport process is absent. In the present study, we apply reactive transport simulation to capture the hydrochemical responses in a thermal spring following the Wenchuan Ms 8.0 and Lushan Ms 7.0 earthquakes. We first constrain deep reservoir geothermal fluid compositions and temperature by multicomponent geothermometry, and then a reactive geochemical transport model is constructed to reproduce the hydrochemical evolution process. The results show that the recharge from the shallow aquifer increases gradually until it reaches a peak because of the permeability enhancement caused by the Lushan earthquake, which may be the mechanism to explain the earthquake-related hydrochemical responses. In contrast to the postseismic effect of the Wenchuan earthquake, the chemical evolution can be considered as hydrochemical anomalies related to the Lushan earthquake. This study proves that the efficient simulation of reactive transport processes is useful for investigating earthquake-related signals in hydrochemical time series.     

不同排水条件下砂-黄土界面的剪切力学特性

为了研究异质土在不同排水条件下的力学机理,进行了一系列环剪试验,对单一黄土、单一砂、砂-黄土组成的异质土在剪切力学特性上的差异及其产生机理进行了比较分析。结果表明：在不同排水条件下,砂-黄土组成的异质土在相互接触剪切的过程中,剪切应力变化形态和抗剪强度与单一黄土、单一砂之间存在显著差异,即砂-黄土组成的异质土在其剪切过程中呈现出了黏性土的剪切力学特征;在相同剪切速率条件下,砂-黄土组成的异质土在不同排水条件下的抗剪强度比单一黄土和单一砂的抗剪强度至少降低了71%和51%。不同排水条件下砂-黄土的剪切力学性质出现了差异,其主要原因与剪切面处砂与黄土之间的相互作用以及剪切面处土体内孔隙水状态有关。     

不同排水条件下饱和砂土快速大剪切力学特性

为探索滑坡灾害中土在复杂条件下的剪切力学特性,本文利用大型环剪试验机,通过进行各种排水条件下的连续大位移剪切试验,对不同法向应力、剪切速率和孔隙水压力等复杂条件下饱和砂土的力学特性及其变化机理进行了研究。结果表明：1）在连续快速剪切条件下,砂土剪切力学特性在干燥、不排水和排水等条件下呈现不同的变化形式。其中在不排水条件下,饱和砂出现一定的应变软化现象。2）在相同正应力和剪切速率的环剪试验中,饱和砂在不同排水条件下（上排水、下排水、上下排水）的抗剪强度出现显著差异。3）在排水环剪试验条件下,砂土剪切应力与强度的差异性变化不仅与土体内细土颗粒运移和结构变化有关,并且受到剪切过程中不同排水条件下孔隙水压力变化的影响和控制。4）排水环剪条件下,饱和砂孔隙水压力的消散变化不仅与不同排水方式下土体内所形成的排水通道顺畅程度有关,并且受到不同剪切速率和法向应力的影响作用。     

Fracture Permeability Alteration due to Chemical and Mechanical Processes: A Coupled High-Resolution Model

Reactive fluid-flow experiments in fractures subjected to normal stress suggest the potential for either increased or decreased permeability resulting from fracture-surface dissolution. We present a computational model that couples mechanical deformation and chemical alteration of fractures subjected to constant normal stress and reactive fluid flow. The model explicitly represents micro-scale roughness of the fracture surfaces and calculates elastic deformation of the rough surfaces using a semi-analytical approach that ensures the surfaces remain in static equilibrium. A depth-averaged reactive transport model calculates chemical alteration of the surfaces, which leads to alteration of the contacting fracture surfaces. The mechanical deformation and chemical alteration calculations are explicitly coupled, which is justified by the disparate timescales required for equilibration of mechanical stresses and reactive transport processes. An idealized analytical representation of dissolution from a single contacting asperity shows that under reaction-limited conditions, contacting asperities can dissolve faster than the open regions of the fracture. Computational simulations in fractures with hundreds of contacting asperities show that the transition from transport-limited conditions (low flow rates) to reaction-rate-limited conditions (high flow rates) causes a shift from monotonically increasing permeability to a more complicated process in which permeability initially decreases and then increases as contacting asperities begin to dissolve. These results are qualitatively consistent with a number of experimental observations reported in the literature and suggest the potential importance of the relative magnitude of mass transport and reaction kinetics on the evolution of fracture permeability in fractures subjected to combined normal stress and reactive fluid flow.     

Numerical Modelling of Dissolving and Driving Exploitation of Potash Salt in the Qarhan Playa ? A Coupled Model of Reactive Solute Transport and Chemical Equilibrium in a Multi-component Underground Brine System

Firstly, the macroscopic chemical equilibrium state of a series of chemical reactions between intercrystal brine and its media salt layer （salt deposit） in Qarhan Salt Lake was studied by using the Pitzer theory. The concept of macroscopic solubility product and its relation with accumulated ore dissolving ratio were presented, which are used in the numerical model of dissolving and driving exploitation of potassium salt in Qarhan Salt Lake. And secondly, with a model forming idea of transport model for reacting solutes in the multi-component fresh groundwater system in porous media being a reference, a two-dimensional transport model coupled with a series of chemical reactions in a multi-component brine porous system （salt deposits） was developed by using the Pitzer theory. Meanwhile, the model was applied to model potassium/magnesium transport in Qarhan Salt Lake in order to study the transfer law of solid and liquid phases in the dissolving and driving process and to design the optimal injection/abstraction strategy for dissolving and capturing maximum Potassium/ Magnesium in the mining of salt deposits in Qarhan Salt Lake.     

Coupled Model of Two-phase Debris Flow, Sediment Transport and Morphological Evolution

The volume fraction of the solid and liquid phase of debris flows,which evolves simultaneously across terrains,largely determines the dynamic property of debris flows. The entrainment process significantly influences the amplitude of the volume fraction. In this paper,we present a depth-averaged two-phase debris-flow model describing the simultaneous evolution of the phase velocity and depth,the solid and fluid volume fractions and the bed morphological evolution. The model employs the Mohr–Coulomb plasticity for the solid stress,and the fluid stress is modeled as a Newtonian viscous stress. The interfacial momentum transfer includes viscous drag and buoyancy. A new extended entrainment rate formula that satisfies the boundary momentum jump condition(Iverson and Ouyang,2015) is presented. In this formula,the basal traction stress is a function of the solid volume fraction and can take advantage of both the Coulomb and velocity-dependent friction models. A finite volume method using Roe's Riemann approximation is suggested to solve the equations. Three computational cases are conducted and compared with experiments or previous results. The results show that the current computational model and framework are robust and suitable for capturing the characteristics of debris flows.     

Forward Coupled Modeling and Assessment of Gravity Anomalies Caused by Pumping Tests in Unconfined Aquifers Under Unsteady-State Conditions

Analysis of drawdown data from pumping tests is the most common method for identification of aquifer properties and estimation of hydraulic parameters in hydrogeology. Limited hard hydraulic data from wells, expensive and intrusive, can be supplemented with geophysical spatially distributed information. Gravity, sensible to mass variations, can provide information about hydraulic parameters and storage coefficients of aquifers. A satisfactory use of gravity requires the computation of temporal evolution of gravity anomalies related with the dynamic hydraulic process. For simplified and ideal problems, the calculation can be accomplished with analytical solutions. However, the limitations of analytical solutions in capturing some relevant characteristics, like heterogeneities, that require the use of numerical models, are well known. This article shows how the time-dependent gravity anomaly caused by a pumping test can be calculated in a unique code, in a coupled manner and in a single run. The methodology avoids the use and transference of data between various codes and can be utilized in a coupled hydrogeophysical inversion procedure. Additionally, it is flexible enough to include a wide range of characteristics that can be encountered in any pumping test, and is an adequate framework for field survey planning via analysis and study of time-dependent gravity curves.     

Dissolution of Quartz, Albite, and Orthoclase in H2O-Saturated Haplogranitic Melt at 800{degrees}C and 200 MPa: Diffusive Transport Properties of Granitic Melts at Crustal Anatectic Conditions

We have conducted experiments on dissolution of quartz, albite,orthoclase, and corundum into H₂O-saturated haplogranite meltat 800°C and 200 MPa over a duration of 120–1488 hwith the aim of ascertaining the diffusive transport propertiesof granitic melts at crustal anatectic temperatures. Cylindersof anhydrous starting glass and a single mineral phase (quartzor feldspar) were juxtaposed along flat and polished surfacesinside gold or platinum capsules with 10 wt % added H₂O. Concentrationprofiles in glass (quenched melt) perpendicular to the mineral–glassinterfaces and comparison with relevant phase diagrams suggestthat melts at the interface are saturated in the dissolvingphases after 384 h, and with longer durations the concentrationprofiles are controlled only by diffusion of components in themelt. The evolution of the concentration profiles with timeindicates that uncoupled diffusion in the melt takes place alongthe following four linearly independent directions in oxidecomposition space: SiO₂, Na₂O, and K₂O axes (Si-, Na-, and K-eigenvectors,respectively), and a direction between the Al₂O₃, Na₂O, andK₂O axes (Al-eigenvector), such that the Al/Na molar ratio isequal to that of the bulk melt and the Al/(Na + K) molar ratiois equal to the equilibrium ASI (= mol. Al₂O₃/[Na₂O + K₂O])of the melt. Experiments in which a glass cylinder was sandwichedbetween two mineral cylinders—quartz and albite, quartzand K-feldspar, or albite and corundum—tested the validityof the inferred directions of uncoupled diffusion and exploredlong-range chemical communication in the melt via chemical potentialgradients. The application of available solutions to the diffusionequations for the experimental quartz and feldspar dissolutiondata provides diffusivities along the directions of the Si-eigenvectorand Al-eigenvector of (2·0–2·8) x 10^–15m²/s and (0·6–2·4) x 10^–14 m²/s, respectively.Minimum diffusivities of alkalis [(3–9) x 10^–11m²/s] are orders of magnitude greater than the tetrahedral componentsof the melt. The information provided here determines the rateat which crustal anatexis can occur when sufficient heat issupplied and diffusion is the only mass transport (mixing) processin the melt. The calculated diffusivities imply that a quartzo-feldspathicsource rock with initial grain size of 2–3 mm undergoinghydrostatic, H₂O-saturated melting at 800°C (infinite heatsupply) could produce 20–30 vol. % of homogeneous meltin less than 1–10 years. Slower diffusion in H₂O-undersaturatedmelts will increase this time frame. KEY WORDS: chemical diffusion; haplogranite; mineral dissolution experiments; crustal anatexis     

新型常压热解离化学电离装置的研制及应用

为了克服常压热解离化学电离装置(TDCI)热源控制不稳定、背景干扰较大、实验重现性相对较差等问题。文章在前期研究的基础上,分别对仪器各组成部件进行优化和改进,研制出能够根据待测物的热稳定性、极性、挥发性、熔点等性质,能够对仪器的温度、加热时间、加速电压等仪器参数连续、精确可调的新型常压热解电离源实验装置,并进行了优化和表征。与原研制的TDCI实验装置相比,新型TDCI电离装置的高压调节和温度控制的连续性和精确度以及热源的稳定性得到了极大的提高。高压调节的最小刻度从原来的1 V减小到0.1 V,温度控制系统的调控精确由原来的±5℃减小到±1℃。采用新型TDCI-MS技术,在常压和无需样品预处理的条件下,实现了实际样品可乐中痕量兴奋剂可卡因和牛奶中弱极性物质三聚氰胺的快速检测,单个样品检测时间都小于30 s,检出限低,可卡因和三聚氰胺的最低检出限分别为1.12×10^-12 g/mL和2.62×10^-11 g/mL,重现性好,相对标准偏差(RSD)为4.61%~9.80%,优于原TDCI电离装置的检测结果,完全满足实际样品的检测需要。由于其具有独立稳定的加热装置,与表面解吸常压电离源相比,本仪器装置更适于难挥发性化合物的快速分析。     

Reactive Transport Modeling of Subaqueous Sediment Caps and Implications for the Long-Term Fate of Arsenic, Mercury, and Methylmercury

A 1-D biogeochemical reactive transport model with a full set of equilibrium and kinetic biogeochemical reactions was developed to simulate the fate and transport of arsenic and mercury in subaqueous sediment caps. Model simulations (50?years) were performed for freshwater and estuarine scenarios with an anaerobic porewater and either a diffusion-only or a diffusion plus 0.1-m/year upward advective flux through the cap. A biological habitat layer in the top 0.15?m of the cap was simulated with the addition of organic carbon. For arsenic, the generation of sulfate-reducing conditions limits the formation of iron oxide phases available for adsorption. As a result, subaqueous sediment caps may be relatively ineffective for mitigating contaminant arsenic migration when influent concentrations are high and sorption capacity is insufficient. For mercury, sulfate reduction promotes the precipitation of metacinnabar (HgS) below the habitat layer, and associated fluxes across the sediment–water interface are low. As such, cap thickness is a key design parameter that can be adjusted to control the depth below the sediment–water interface at which mercury sulfide precipitates. The highest dissolved methylmercury concentrations occur in the habitat layer in estuarine environments under conditions of advecting porewater, but the highest sediment concentrations are predicted to occur in freshwater environments due to sorption on sediment organic matter. Site-specific reactive transport simulations are a powerful tool for identifying the major controls on sediment- and porewater-contaminant arsenic and mercury concentrations that result from coupling between physical conditions and biologically mediated chemical reactions.     

贵州省开阳县马岔河温泉水化学特征及成因

结合马岔河区域内多年的水质分析、监测资料,系统阐述了马岔河温泉水文地球化学特征,利用同位素手段,分析了马岔河温泉的水源、补给区高程;利用Na-K-Mg三角图解法判断水岩平衡状态,判断结果为马岔河温泉属于未成熟水,只能利用SiO2温标计算温泉的热浩温度。通过分析,认为其水源为大气降水,热源为深循环加热,热储温度72．33℃,热储深度为2690m。马岔河温泉的地质成因为：在正常区域地热场环境中,大气降水沿高渗透率的岩石渗入地下,深部地下水沿断层破碎带向马岔河运移,循环加热,深部地下水在马岔河断束上涌汇集,并与近源低温地下水混合,在地势低洼处出露形成温泉。     

鄂尔多斯盆地深部咸水层二氧化碳地质储存热-水动力-力学(THM)耦合过程数值模拟

注入CO₂到深部咸水层(CO₂地质储存)被认为是一种直接有效地减少CO₂向大气排放的途径。CO₂地质储存涉及到热、水动力和力学耦合过程,该耦合过程是预测CO₂在储层中的迁移转化、评价储层储存能力和分析潜在风险的关键。基于Terzaghi固结理论,在热-水动力(TH)耦合软件TOUGH2框架中加入了力学模块,形成了新的热-水动力-力学(THM)模拟器。结合鄂尔多斯盆地CO₂捕获和储存(CCS)示范工程场地的地质、水文地质条件,采用新的THM模拟器数值分析了CO₂注入后地层中的温度、压力、CO₂饱和度、位移和有效应力的时空变化特征。结果显示:在井口保持8 MPa和35℃情况下,能够实现10万 t/a的CO₂注入量;压力上升的范围远远大于CO₂运移和温度降低的范围,注入20 a后,其最大距离分别达到接近边界10 km、620 m和100 m;位移和应力变化主要与压力变化相关,注入引起最大抬升为0.14 m,在注入井附近位置储层中有效应力变化水平方向要大于垂直方向,而在远井位置相反;注入引起井附近有效应力明显减小,从而导致了孔隙度和渗透率的增大,增强了CO₂注入能力。     

Chemical and Thermal Evolution of Archaean Sialic Crust, Southern West Greenland

The Archaean rocks of West Greenland are predominantly bandedquartzofeldspathic gneisses enclosing thin migmatized sheetsof older metabasic and metasedimentary lithologies. Isotopicdating (Moorbath & Pankhurst, 1976) indicates that muchof the Archaean crust presently exposed in southern West Greenlandwas generated from predominantly upper mantle sources 3000-2800m.y. ago. Parts of this crust crystallized under prograde granulitefacies conditions 2950-2750 m.y. ago. The granulite gneisseswere severely depleted in some of the lithophile and heat producingelements, Si, Na, Sr, Rb, U and Th, during the granulite metamorphism.These elements appear to have been transferred to higher crustallevels by the migration of a dispersed vapour phase. The pressureand temperature recorded by amphibolite and granulite faciesassemblages have been estimated using thermometers and barometerscalibrated against the results of phase equilibrium experiments.These estimates (800 °C, 10.5 kb and 630 °C, 7.3 kbfor granulite and amphibolite facies respectively) indicatethat the Archaean continental crust in southern West Greenlandwas at least 30–40 km thick 2800 m.y. ago. Water vapourpressures in the granulites were extremely low, 0.3 to 0.1 P_total.The thermal evolution of the Archaean crust during the period3000-2700 m.y. was controlled by the emplacement of large volumesof acid-intermediate melts into a relatively thin metabasiccrust. The thermal perturbations generated by this convectivetransfer of heat from the upper mantle to the crust relaxedduring the period immediately following crustal accretion. Progradegranulite facies assemblages could have developed under stronglydehydrating conditions and progressively falling temperatures,or during a phase of rising temperature in the lower crust.     

Dynamic Brazilian Tests of Granite Under Coupled Static and Dynamic Loads

Rocks in underground projects at great depth, which are under high static stresses, may be subjected to dynamic disturbance at the same time. In our previous work (Li et al. Int J Rock Mech Min Sci 45(5):739–748, 2008), the dynamic compressive behaviour of pre-stressed rocks was investigated using coupled-load equipment. The current work is devoted to the investigation of the dynamic tensile behaviour of granite rocks under coupled loads using the Brazilian disc (BD) method with the aid of a high-speed camera. Through wave analyses, stress measurements and crack photography, the fundamental problems of BD tests, such as stress equilibrium and crack initiation, were investigated by the consideration of different loading stresses with abruptly or slowly rising stress waves. The specially shaped striker method was used for the coupled-load test; this generates a slowly rising stress wave, which allows gradual stress accumulation in the specimen, whilst maintaining the load at both ends of the specimen in an equilibrium state. The test results showed that the tensile strength of the granite under coupled loads decreases with increases in the static pre-stresses, which might lead to modifications of the blasting design or support design in deep underground projects. Furthermore, the failure patterns of specimens under coupled loads have been investigated.     

Monte Carlo Simulations of Radiative and Neutrino Transport under Astrophysical Conditions

Monte Carlo simulations are utilized to model radiative and neutrino transfer in astrophysics. An algorithm that can be used to study radiative transport in astrophysical plasma based on simulations of photon trajectories in a medium is described. Formation of the hard X-ray spectrum of the Galactic microquasar SS 433 is considered in detail as an example. Specific requirements for applying such simulations to neutrino transport in a densemedium and algorithmic differences compared to its application to photon transport are discussed.     

Fate and Transport of Hydrophobic Organic Chemicals in the Lower Passaic River: Insights from 2,3,7,8-Tetrachlorodibenzo-p-Dioxin

The fate and transport of hydrophobic organic chemicals (HOCs) is particularly complex in estuaries because of bidirectional longitudinal currents, density stratification, the tendency to trap sediments, and significant dilution in the downstream bay or ocean. Investigations of HOCs in estuaries are further complicated because HOCs typically enter from multiple sources. The distribution of contaminants in estuarine sediment beds reflect a time integration of a complex balance of time- and space-variable fate and transport processes and loading history. A unique opportunity to study HOC fate and transport exists in the Lower Passaic River (LPR), where a pesticide manufacturer was the dominant source of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) to the estuary and the distribution of this “tracer of opportunity” provides insights about fate and transport processes in estuarine systems. This paper presents observed sediment 2,3,7,8-TCDD patterns within the LPR and the adjacent Newark Bay, and interprets them in terms of fate and transport processes that likely distributed the contaminant from its dominant source, drawing upon other physical datasets as needed. Major observations include that estuarine transport processes have distributed 2,3,7,8-TCDD approximately 18 km upstream of the source and downstream across Newark Bay, and that, generally, HOC trapping processes within the LPR have been highly effective, particularly near the 2,3,7,8-TCDD source and in downstream areas. The present LPR surface sediment 2,3,7,8-TCDD distribution indicates spatially variable recovery, which appears broadly driven by historical net sedimentation patterns, though the dominant processes may be shifting as the system continues to evolve.