地球化学模式程序的原理,分类与功能

地球化学模式是用化学反应式和数学公式来描述地球化学作用的一种概念化的模式，在这种概念化的模式基础上利用数学方法和计算机语言编制的软件便是地球化学模式程序。按照原理和复杂程度可把地球化学模式程序分为３大类，即质量平衡程序、物质转化程序和溶质迁移程序。地球化学模式程序的主要功能包括计算元素在水溶液中的存在形式，预测各类地球化学反应进行的方向，物质的溶解与沉淀，溶液的Ｅｈ、ｐＨ值，计算地球化学作用的反应速度和反应途径等。     

Modeling reactive transport in non-ideal aqueous–solid solution system

The numerical simulation of reactive mass transport processes in complex geochemical environments is an important tool for the performance assessment of future waste repositories. A new combination of the multi-component mass transport code GeoSys/RockFlow and the Gibbs Energy Minimization (GEM) equilibrium solver GEM-Selektor is used to calculate the accurate equilibrium of multiple non-ideal solid solutions which are important for the immobilization of radionuclides such as Ra. The coupled code is verified by a widely used benchmark of dissolution–precipitation in a calcite–dolomite system. A more complex application shown in this paper is the transport of Ra in the near-field of a nuclear waste repository. Depending on the initial inventories of Sr, Ba and sulfate, non-ideal sulfate and carbonate solid solutions can fix mobile Ra cations. Due to the complex geochemical interactions, the reactive transport simulations can describe the migration of Ra in a much more realistic way than using the traditional linear K_D approach only.     

HYTEC results of the MoMas reactive transport benchmark

A specific benchmark has been developed by the French research group MoMas in order to improve numerical solution methods applied by reactive transport models, i.e., codes that couple hydrodynamic flow and mass transport in porous media with geochemical reactions. The HYTEC model has been applied to this benchmark exercise, and this paper summarizes some of the principal results. HYTEC is a general-purpose code, applied by industrials and research groups to a wide variety of domains, including soil pollution, nuclear waste storage, cement degradation, water purification systems, storage of CO₂, and valorization of stabilized wastes. The code has been applied to the benchmark test-cases without any specific modification. Apart from the benchmark imposed output, additional information is provided to highlight the behavior of HYTEC specifically and the simulation results in particular.     

Sensitivity and uncertainty analysis of mixing and mass balance calculations with standard and PCA-based geochemical codes

One of the most important observations that can be obtained from the study of an aquifer system dominated by mixing is the contribution of each end-member water to the chemical composition of every water parcel in the aquifer. Once the first-order effect of mixing has been taken into account via the mixing proportions, water–rock interaction can be used to explain the remaining variability. There are many sources of uncertainty that can prevent the accurate calculation of the mixing proportions of a mixing-dominated system, but the type and intensity of the chemical reactions that have taken place as a consequence of mixing is one of the most critical. Here the uncertainty in the computed mixing proportions of samples from a “synthetic” aquifer system derived from the actuation of different chemical reactions are assessed (always remembering that the chemical reactions are a second-order effect). These uncertainties are explored using two different geochemical codes in order to infer the limits of both methodological approaches: PHREEQC, as an example of a standard geochemical code; and M3, as an example of a Principal Component-based geochemical code. Several synthetic water samples are created with the direct approach of PHREEQC, both by pure mixing and including different types of chemical reactions. Together with the chemical information of the end-member waters, these samples are then fed into PHREEQC (inverse modelling) and M3 and the mixing proportions and mineral mass transfers are computed. PHREEQC calculations give a reasonable estimate of the real mixing proportions and the chemistry of the groundwaters. However, similar mixing proportions and mass transfers can be obtained using different sets of reactions, indicating a source of uncertainty that should be overcome with additional chemical information. For M3, where synthetic samples have been included in a real data set of groundwater samples from the Scandinavian Shield, mixing proportions are only mildly affected either by the number of compositional variables or the number of samples used for the Principal Component Analysis (PCA). However, the robustness of the output is quite sensitive to whether only conservative compositional variables are used or both conservative and non-conservative compositional variables. Mass balance calculations in M3 are much more sensitive to non-conservative compositional variables and the recommendation here is not to use non-conservative variables with PCA-based codes if any information about reactions is to be obtained.     

GEMSFIT: a generic fitting tool for geochemical activity models

GEMSFIT, a parallelized open-source tool for fitting thermodynamic activity models has been developed. It is the first open-source implementation of a generic geochemical-thermodynamic fitting tool coupled to a chemical equilibrium solver which uses the direct Gibbs energy minimization (GEM) approach. This enables speciation-based fitting of complex solution systems such as solid solutions and mixed solvents. The extendable framework of GEMSFIT provides a generic interface for fitting geochemical activity models at varying system compositions, temperatures and pressures. GEMSFIT provides the most common tools for statistical analysis which allow thorough evaluation of the fitted parameters. The program can receive input of measured data from a PostgreSQL database server or exported spreadsheets. The fitting tool allows for bound, linear, and nonlinear (in)equality-constrained minimization of weighted squared residuals of highly nonlinear systems over a wide temperature and pressure interval only limited by user-supplied thermodynamic data. Results from parameter regression as well as from statistical analysis can be visualized and directly printed to various graphical formats. Efficient use of the code is facilitated by a graphical user interface which assists in setting up GEMSFIT input files. The usage and resulting output of GEMSFIT is demonstrated by results from parameter regression of the extended universal quasichemical aqueous activity model for geothermal brines.     

Dual-thermodynamic estimation of stoichiometry and stability of solid solution end members in aqueous–solid solution systems

The dual-thermodynamic (DualTh) approach is shown to provide a useful alternative to other methods in: (i) forward modelling of equilibrium speciation, activities, and element partitioning in a heterogeneous system involving several variable-composition phases, such as the aqueous–solid solution system; (ii) estimation of interaction parameters of a non-ideal mixing model from known bulk compositions of coexisting aqueous and solid-solution phases; and (iii) retrieval of unknown stoichiometries and apparent standard chemical potentials of trace solid-solution end-members. Inverse-modelling tasks (ii) and (iii) can be performed when the solid solution of interest is shown experimentally to co-exist with the aqueous phase either in the equilibrium or at the minimum stoichiometric saturation state.DualTh calculations exploit the ability of Gibbs energy minimisation (GEM) algorithms to find simultaneously two numerical solutions of the isobaric–isothermal chemical equilibrium speciation problem: (1) primal solution x — a vector of amounts of components (species) in phases; and (2) dual solution u — a vector of chemical potentials of stoichiometry units (usually chemical elements and charge). Conversely, the chemical potential of a phase component can be found in two complementary ways: (i) primal via its standard-state potential, concentration and activity coefficient (the latter two are functions of the x vector); and (ii) dual through its formula stoichiometry multiplied by the u vector. The DualTh methods compare primal and dual values of the chemical potential in simple and straightforward equations that can be easily computed in a spreadsheet, or implemented in GEM geochemical modelling codes.     

基于Julia加速的射频大地电磁法正演模拟与位移电流作用研究

射频大地电磁法(Radio-magnetotelluric, RMT)是浅地表电磁勘探的重要手段之一。由于勘探频段为10～300 kHz,其电磁场传播受地下介质介电常数的影响较大。传统准静态条件下的电磁响应严重制约RMT正演模拟精度,并进一步影响反演成像分辨率。针对这一问题,提出了一种基于Julia并行加速的全电流RMT电磁响应数值模拟方法,利用Julia的分布式计算将各频点的计算发送到不同进程进行求解,从而达到加速计算的目的,同时在计算中考虑位移电流的影响,提升正演的模拟精度。通过计算几种典型高阻/高介电模型的RMT响应,分析并总结了位移电流对射频段电磁场视电阻率及相位响应的影响规律。数值模拟结果表明：当浅部存在高阻覆盖层时,基于准静态假设条件计算的RMT视电阻率和相位响应偏高,且频率越高、覆盖层电阻率越大,响应偏差越大;对于煤炭采空区模型,RMT法能有效反映异常体位置,但忽略位移电流会在采空区及其附近引起较大计算误差;起伏地形的算例表明地形会覆盖地下异常体的RMT数值响应,尤其是地形拐角处;2种不同规模的并行算例对比证明了并行算法的高效性,且随着求解问题规模增大,并行算法效率也随之...     

A simulation chain for early prediction of rainfall-induced landslides

A new simulation chain for early prediction of rainfall-induced landslides in unsaturated soils is presented. It includes a special computational weather code for forecasting the evolution of the synoptic weather and its changes due to interaction with the Earth’s surface (rainfall pattern), and a hydro-mechanical code to analyse rainfall effects on slope stability by computing degree of saturation and pore pressure changes due to rainwater infiltration. The linkage between these two numerical codes is ensured by an interface with the aim of bringing the data provided by the first code, which operates at basin or slope scale. The simulation chain can work in computational times that may be considered suitable for civil protection operations.     

Wechselwirkungsreaktionen Untertagedeponie-relevanter chemisch-toxischer Abfälle mit hochsalinaren Lösungen

The complex reactions between high saline solutions and toxic chemical wastes were investigated by means of laboratory experiments and geochemical modelling. The specific boundary conditions of an underground repository in salt formations were taken into account. In order to determine the chemical equilibrium compositions of the resulting solutions a new leaching procedure was developed and successfully employed with several toxic wastes. The results for a fly ash waste stemming from a glass smelting furnace are given in detail. Zinc and cadmium are the two most prominent heavy metals, that accumulate significantly in the leachates. In order to gain an insight into the complex dissolution and precipitation processes in such multi-component systems, geochemical modelling was performed using the program code EQ3/6 and the Pitzer formalism for calculating the activity coefficients. The thermodynamic database used was extended and Pitzer coefficients for Zn and Cd in high saline solutions were derived from literature data and added to the database. The results of the geochemical modelling of the investigated reactions were in good agreement with the experimental data. On this basis the maximum concentrations that can be leached from the investigated fly ash into a Mg-rich saline solution, that is typical for a salt repository in Northern Germany, are predicted to be 0,181 mol/kg H₂O zinc and 0,00317 mol/kg H₂O cadmium, respectively.     

Geochemical study of pottery sherds from an archaeological site near Mošnje (Slovenia)

This study is a geochemical analytical approach to the characterization of pottery samples from an archaeological site near Mo?nje (Slovenia). Inductively coupled plasma–mass spectrometry and statistical analyses were used to determine detailed geochemical properties of the pottery sherds and to identify potentially individual groups among the samples studied. The geochemical results indicated the existence of four major groups of the pottery sherds: the first and second groups are assembled from eight samples, all generally characterized by their high CaO and TOT/C content; the third group comprised the samples with the highest SiO₂ concentrations; and the fourth group is represented by the samples K3, K5 and K13. The principal component analysis and cluster analysis validated the existing groups and revealed a high degree of chemical similarity between these groups. The geochemical and statistical data confirmed the archaeologists’ hypothesis and interpretation of a similar origin/alteration of source material/probable local ceramic production for the majority of the pottery sherds; the imported origin of samples K3 and K13 was recognized, while sample K5 had been intentionally imported as a sample for comparative purposes.     

计算流体地球化学研究的进展

成矿作用的化学机理可以通过实验和计算机模拟进行研究。随着计算机运算能力的不断增强 ,在地球化学中正在形成一门新兴学科———计算地球化学。其中热质输运模拟、化学质量迁移数值模拟和流体输运化学反应耦合动力学研究取得了显著进展。建立在Darcy定律和守恒方程基础上的多孔介质热质输运模拟通过流函数图、等温线图及速率矢量图等 ,从古水文学和流体地球化学方面高度动态研究成矿作用。根据化学和热力学原理进行的化学质量迁移数值模拟则通过矿物和流体中化学物种的热力学数据 ,预测多组分体系中发生的流体岩石相互作用 ,定量揭示经历了复杂化学反应进程的成矿作用的化学行为。将上述两方面结合的流体输运化学反应耦合动力学 ,可以从时间和空间上模拟真实成矿流体系统复杂的动力学行为 ,是计算流体地球化学的发展方向。     

Methodology for bounding calculations of nuclear criticality of fissile material accumulations external to a waste container at Yucca Mountain, Nevada

The possibility of nuclear criticality, however remote, in the vicinity of the proposed repository at Yucca Mountain, Nevada generates justified concerns and may impact the performance of the repository. A heuristic approach is presented here for determining the amount, spatial distribution and other characteristics of fissile material accumulation in the rock beneath a waste package that could contribute to such an event. This study is concerned primarily with waste packages containing special spent fuel from the Department of Energy and high-level nuclear waste glass. Mixing with less alkaline waters and the subsequent drop in pH is the mechanism that is most efficient for precipitating fissile material from the waste package internal leachate, in contrast to natural deposits in which redox changes are the main precipitation driver. External accumulation size is determined by (1) computing the chemical composition of the leachate leaving a package as its internal materials degrade (with the batch geochemical code EQ3/6), (2) determining precipitation of fissile material into mineral phases (using the 1D geochemical code PHREEQC) as the effluent mixes with percolation water, and (3) heuristically scaling results to a 3D volume and computing the criticality coefficient (using the code MCNP). Loci for accumulation are the multiple lithophysal cavities and the fracture system. A bounding conservative approach is used by necessity in Step 3. Nuclear criticality is sensitive to small variations in the distribution of fissile material and parameters of natural systems vary by orders of magnitude. Because the most likely combinations of parameters are not conducive to nuclear criticality, this study focuses on extreme values of parameter probabilistic distributions, such as limited flow into the package associated with a large percolation rate, combinations of material degradation rates favoring actinide release, and very high host-rock porosity values. By considering these combinations, most favorable to criticality but unlikely, it was concluded that external nuclear criticality is not a concern at the proposed repository.     

MT3D-通用的三维地下水污染物运移数值模型

定量研究污染物在地下水中的运移过程通常采用数值模拟方法。MT3D是一套基于有限差分方法的污染物运移模拟软件，近年来在国外水文地质和水环境模拟等领域的研究中已经得到较为广泛的认可。MT3D比较全面地考虑了污染物在地下水中的对流、弥散和化学反应等过程，可以灵活处理各种复杂的源汇项和边界条件，能够准确模拟承压、无压和越流含水层中的污染物运移过程。MT3D具有模块化的程序结构、灵活的求解方法以及全面的模拟功能，非常适合实际问题的研究，值得在国内推广使用。     

A sequential partly iterative approach for multicomponent reactive transport with CORE2D

CORE^2D V4 is a finite element code for modeling partly or fully saturated water flow, heat transport, and multicomponent reactive solute transport under both local chemical equilibrium and kinetic conditions. It can handle coupled microbial processes and geochemical reactions such as acid–base, aqueous complexation, redox, mineral dissolution/precipitation, gas dissolution/exsolution, ion exchange, sorption via linear and nonlinear isotherms, and sorption via surface complexation. Hydraulic parameters may change due to mineral precipitation/dissolution reactions. Coupled transport and chemical equations are solved by using sequential iterative approaches. A sequential partly iterative approach (SPIA) is presented which improves the accuracy of the traditional sequential non-iterative approach (SNIA) and is more efficient than the general sequential iterative approach (SIA). While SNIA leads to a substantial saving of computing time, it introduces numerical errors which are especially large for cation exchange reactions. SPIA improves the efficiency of SIA because the iteration between transport and chemical equations is only performed in nodes with a large mass transfer between solid and liquid phases. The efficiency and accuracy of SPIA are compared to those of SIA and SNIA using synthetic examples and a case study of reactive transport through the Llobregat Delta aquitard in Spain. SPIA is found to be as accurate as SIA while requiring significantly less CPU time. In addition, SPIA is much more accurate than SNIA with only a minor increase in computing time. A further enhancement of the efficiency of SPIA is achieved by improving the efficiency of the Newton–Raphson method used for solving chemical equations. Such an improvement is obtained by working with increments of log concentrations and ignoring the terms of the Jacobian matrix containing derivatives of activity coefficients. A proof is given for the symmetry and non-singularity of the Jacobian matrix. Numerical analyses performed with synthetic examples confirm that these modifications improve the efficiency and convergence of the iterative algorithm. Changbing Yang is now at The University of Texas at Austin, USA.     

支护结构作用的箱基沉降计算新方法

现行规范在计算箱基沉降时,没有考虑支护结构的作用,使得理论计算与实际沉降之间存在误差。通过物理模拟、理论分析和数值模拟,研究箱基与支护结构结合、分离下,不同墙体材料、不同墙体厚度、不同插入深度比等工况下侧摩阻力对箱型基础沉降的影响,试验结果显示,摩擦力在箱基沉降中的作用很明显,它与墙体与土体之间的摩擦系数、墙体与土体的接触面积密切相关。在此,提出了一种计算箱基沉降的新方法,该法将箱基沉降分为3部分：箱型基础底上段回弹再压缩变形带来的地基变形、箱型基础底上段压缩变形、箱型基础的下段土体变形。以青岛中银大厦为实例,应用FLAC3D对基础沉降进行了数值分析。数值分析中按文中方法以及按前人方法的计算结果与实测数据进行了对比,结果表明文中的方法具有更好的可行性,对修订规范具有借鉴意义。     

Modeling Geochemically Caused Permanent Stratification in Lake Waldsee (Germany)

A geochemical model was incorporated into a stratification model for lakes to create the model package: DYCD-CORE, a numerical code that couples the thermal and hydrodynamic capabilities of DYRESM and the geochemical capabilities of the reactive transport model CORE^2D V4. Based on the chemical composition of solutes calculated in each node for each time step, density was computed using specific partial molal volumes of all considered solutes and fed back into the stratification module of the program package. The density calculated each time step leads to a strong coupling of hydrodynamics and hydrogeochemistry and reflects the complex interaction as it is present in all lakes. To demonstrate the functionality of the numerical approach, an example of an iron-meromictic lake was chosen, where the reactivity of the dissolved iron kept the water body perennially stratified. To critically validate the model results, temperatures were continously measured at high vertical and temporal resolution in a field investigation of Waldsee (near Döbern, Germany). Multiparameterprobe profiles and water samples confirmed the continous chemical stratification and served as initial and boundary conditions for the simulation period. The model package DYCD-CORE could reproduce the permanent stratification as it were in the lake. A demonstration run using the standard UNESCO equation for density, and hence assuming non-reactive solutes, failed entirely. Hence, stratification models using salinity for density are not suited for simulating density created by lake-internal geochemical transformation of solutes. However, density can be based directly on the simultaneous numerical simulation of lake geochemistry. Predictive modeling of changing lake circulation in a variable climate or considering change of use will require a proper inclusion of the geochemistry as demonstrated in this paper.     

Determination of Thirteen Rare-Earth Elements by High-Performance Liquid Chromatography in Thirty and of K, Rb, Cs, Sr and Ba by Isotope Dilution Mass Spectrometry in Eighteen International Geochemical Reference Samples

This study reports the results of thirteen rare-earth elements in thirty geochemical reference samples. Three alkali (K, Rb, Cs) and two alkaline earth (Sr, Ba) elements were also determined in eighteen reference samples. The analytical procedure involved is based on spiked samples and later measurement of the rare-earth elements by high-performance liquid chromatography and the alkalies and alkaline earths by thermo-quartz mass spectrometric isotope dilution (THQ-MSID). Whenever possible, the results are compared with literature values.     

现代微区测试技术在确定宝玉石产地来源中的应用及其研究进展

宝玉石产地来源的研究是近几年地质学、宝石学和考古学界的热门话题之一。一方面,不同产地来源的宝玉石可能具有不同的品质特征及经济价值,其研究有助于珠宝首饰价值的判断,为各国海关执法提供技术支持;另一方面,古代宝玉石产地的确定对了解古代宝玉石的开采与古代科技的发展水平及不同区域的文化交流均具有重要意义。在总结前人研究成果的基础上,结合现代微区测试技术的最新研究成果,从微量元素、包裹体以及同位素分析等方面探讨总结了微区测试技术在确定宝玉石产地来源研究中的应用。当前的研究结果显示,不同的技术方法对确定宝玉石的产地来源均有一定的意义,但宝玉石产地来源的最终确定往往需要依赖更大范围和更深入地对宝石矿床的地球化学进行多技术手段的交叉分析。显然,确定各种不同类型宝玉石产地来源的标型特征及建立相关重要宝石产地的地球化学数据库,是最终解决宝玉石产地来源鉴定问题的关键。     

A database of dissolution and precipitation rates for clay-rocks minerals

Many geoscientific fields use reactive transport codes to set up and interpret experiments as well as to understand natural processes. Reactive transport codes are also useful to give insights in the long term evolution of systems such as radioactive waste repositories or CO₂ storage sites, for which experiments cannot reach the targeted time scale nor the dimension of those systems. The consideration of kinetic reaction rates is often required to reproduce correctly the geochemical and transport processes of interest. However, kinetic data are scattered in the literature, making data and selection a tedious task. Kinetic parameters on a single system are also highly variable depending on data choice, interpretation and chosen kinetic modelling approaches, thus making inter-comparison of modelling studies difficult. The present work aims at proposing a compilation of kinetic parameters to overcome part of above cited problems. The proposed selection was done (i) to ensure consistency of data selection criteria and data treatment and (ii) to ease the use of common kinetic parameters that are independent of the chosen geochemical modelling code. For those two reasons, the kinetic formalism of the transition state theory (TST) was chosen. The selection of minerals is currently limited to those present in clay rich rocks and cements, reflecting the effort made at predicting the evolution of radioactive waste underground storage systems. Still, the proposed compilation should also be useful for other applications such as CO₂ sequestration.     

水溶液体系的化学平衡模型

概括了化学平衡计算的历史及特点；对在地球化学研究中常用的水溶液体系化学平衡模型作了简要的介绍；讨论了水溶液体系化学平衡模型研究的现状及今后的发展动向。