第一讲PHREEQC软件简介 地下水污染与防治解析ppt课件.ppt

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1、PHREEQC软件简介,PHREEQC的发展过程,PHREEQC之前的版本是PHREEQE。PHREEQE是1980年美国地质调查局的Plummer 和Parkhurst等开发出来的，用于地球化学模拟达15年之久。PHREEQC于1995年正式推出，它是在PHREEQE的源程序基础上用C语言重写而成的，消除了PHREEQE的缺陷与局限性。PHREEQC发展至今已近10年，其版本不断更新，加入了很多新内容，已发展到版本2中的2.11子版本。由于其现有的模拟能力在同类软件中最强大，所以在国际上被广泛使用。,PHREEQC的功能,PHREEQC以离子联系的水化学模型为基础，可以推算：（1）生成物和饱

2、和系数；（2）涉及到可逆反应以及不可逆反应的批反应和一维（1D）运移计算；其中，涉及到的可逆反应包括水、矿物/无机溶液、气体、固体溶液、表面络合、离子交换平衡；不可逆反应包括指定成分摩尔转换、动态控制反应、溶液混合和温度变化；（3）逆向建模，可以发现一系列矿物和气体克分子在水中以不确定组成的转移。,PHREEQC 第二版的新特点,和第一版相比，PHREEQC 第二版的新特点如下：具有在一维运移计算中模拟弥散（或扩散）和滞流区的能力，使用用户确定的速率表达式模拟分子反应，模拟标准的多种成分或非标准的两种成分的固体溶液的沉淀和溶解，模拟定体积气相和定压力气相，考虑表面系数或交换位置随着无机物的溶解

3、和沉淀或者分子反应的变化而变化，自动采用多套收敛参数，打印用户指定量到原始输出文件和（或）适合输入到扩展表格的文件上，以一种与扩展表程序更兼容的形式确定溶解成分等。,二、PHREEQC的局限性,1. 水溶液模型PHREEQC用相关的离子和Debye-Hckel方程计算非理想溶液，这种类型的水溶液模型在较低的离子强度下比较合适，但在高离子强度下（海水范围或更高）则会失真。另外，数据库缺乏内部的连续性。因为随程序发布的两个数据库phreeqc.dat和wareq.dat中的lgKs 和反应焓来自于各种文献，未曾系统地确定溶液模型中单个lgK，也未曾确定当前数据库中水溶液模型是否与原始的实验数据相适

4、应。使用时，随程序提供的数据文件可首先考虑，但使用哪种水溶液组分和热力学数据则由用户自己确定。,2. 离子交换模型,离子交换模型假设交换组分的热力学活度等于它的当量分数，或者用当量分数乘以Debye-Hckel活度系数，以此定义交换组分的活度（Appelo, 1994），更加复杂的交换模型还不能实现。在许多野外研究中，离子交换模拟需要用研究区的介质进行离子交换试验，通过实验获得的数据来确定合适的模型。,3. 表面络合,PHREEQC加入了Dzombak 和Morel（1990）发明的双层模型。双层模型是显式地计算扩散层组成（Borkovec and Westall, 1983）和非静电层表面络

5、合（Davis and Kent, 1990）的模型。其它模型，如三层、四层模型在PHREEQC中当前仍无法处理，根据Langmuir或Freundlich的等温吸附理论的吸附模拟可以处理成非静电模型的一种特例。Davis and Kent（1990）评论表面络合模拟时指出使用物质的浓度作为被吸附组分的标准状态在理论上是有问题的。PHREEQC版本2使用的是表面组分的物质的分数作为其活度而不是物质的浓度。在标准状态下，这一变化对单齿状表面组分是没有影响的，但对多齿状表面则影响很大。表面络合位置数目、表面积、被吸附组分、合适的等的确定也是不确定的，实际模拟时需要用实际的野外介质进行实验研究，通过

6、获取的实验数据来确定合适的表面络合模型，并加入PHREEQC中进行模拟。,4. 固溶液,PHREEQC使用Guggenheim方法来确定非理想的二元固溶液（Glynn and Reardon, 1990），尚无法计算非理想的三元固溶液。可以通过假设为理想状态来模拟两种或更多种成分的固溶液，但是这种理想状态的假设过于简化，除相同元素的同位素假设处于理想状态之外，其他情况不行。,5. 溶质运移模拟,模拟一维对流弥散或滞留区中的扩散时，PHREEQC使用的是显式优先差分算法。当网格划分较粗时，此算法出现数值弥散。大量的数值弥散取决于反应模型本身，数值弥散在有些情况下，可能较严重，如线性离子交换、表面

7、络合滞留区的扩散，但当化学反应抵消弥散效应时，数值弥散较小。因此，推荐的做法是逐步模拟。首先用粗网格尽快获得结果并研究水化学反应过程，最后用细化网格评价数值弥散对反应组分和结果组分的影响。,6. 收敛问题,PHREEQC可以发现输入的数据是否存在错误，但不能发现所建立的化学模型的无理性错误。例如，可通过元素的添加或减少来使溶液达到电荷平衡。如果元素无电离组分，或者即使元素的浓度减少到零时仍存在电荷平衡，则数值方法不能收敛。其它的物理性错误有：（1）当想达到某固定浓度时而加入了碱（事实上应加入酸）；（2）当非碳酸碱度已经超过了数据输入中的总碱度时数值方法不能收敛。不过现在数值方法已经非常稳定了，

8、所有已知的收敛问题已解决。偶尔需要使用关键字KNOBS的缩放属性，这种情况只有在总溶解度小于110-15 mol/kg时才需使用。,7. 逆向模拟,与以前的逆向模拟相比，PHREEQC最大的进步是在确定你想模型的处理时引入了非确定性设置。然而，由于算法处理小数据的方法问题，这种算法显示出的结果中有矛盾的现象。通过修改容许度可使算法能弥补这一问题。此外，PHREEQC中不能处理矿物沉淀时同位素的Rayleigh分馏效应，这也是一个不足之处。,PHREEQCI,A Graphical User Interface to the Geochemical Model PHREEQC U.S. Geol

9、ogical Survey April 2002,Introduction,PHREEQCI Version 2 是地球化学计算机程序PHREEQC (Version 2)完全基于窗口的图形用户界面；PHREEQCI 可用于交互式地执行 PHREEQC （第二版）所有的模拟计算能力物种形成、批量反应、一维(1D)反应-传输、以及逆向模拟 。,Applications,Mine drainage 矿山排水Radioactive-waste isolation 放射性废弃物隔离Contaminant migration 污染物迁移Natural and engineered aquifer rem

10、ediation 天然或工程含水层修复Aquifer storage and recovery 含水层蓄水和恢复Water treatment 水处理Natural systems 天然系统Laboratory experiments 实验室试验,Features of the interface,Compatible with Windows 95 and 98,Windows NT 4.0, Windows ME, Windows2000, and Windows XP Automated installation using InstallShield Interactive acces

11、s to all of the capabilities of PHREEQCcreate and modify input data files, run simulations, and display results,Modeling capabilities,Aqueous, mineral, gas, surface, ion-exchange, and solid-solution equilibria Kinetic reactions 1D diffusion or advection and dispersion with dual-porosity medium A pow

12、erful inverse modeling capability allows identification of reactions that account for the chemical evolution in observed water compositions Extensive geochemical databases,Operation,PHREEQCI Version 2 is a computer program for simulating chemical reactions and transport processes in natural or conta

13、minated water. PHREEQCI provides all of the capabilities of the geochemical model PHREEQC (Parkhurst and Appelo, 1999), including： speciation, batch-reaction, 1D reactive-transport, and inverse modeling.,Operation（Continue）,Data for PHREEQC are entered through a series of keyword data blocks, each o

14、f which provides a specific type of information. For example, the SOLUTION keyword data block defines the chemical composition of a solution. PHREEQCI provides tabbed dialog boxes for each PHREEQC keyword.,Figure 1. Main screen of PHREEQCI, with the SOLUTION keyword dialog box open.,1. Speciation Mo

15、deling,ApplicationsSpeciation modeling is useful in situations where the possibility of mineral dissolution or precipitation needs to be known, as in water treatment, aquifer storage and recovery, artificial recharge, and well injection. DescriptionSpeciation modeling uses a chemical analysis of a w

16、ater to calculate the distribution of aqueous species by using an ion-association aqueous model. The most important results of speciation calculations are saturation indices for minerals, which indicate whether a mineral should dissolve or precipitate.,Keyword data blocks used inspeciation modeling

17、include:,SOLUTIONdefine the chemical composition of a solution. SOLUTION_SPREADdefine the chemical composition of multiple solutions in a spreadsheet format.,2. Batch-Reaction Modeling,ApplicationsBatch-reaction modeling can be applied to problems in laboratory, natural, or contaminated systems. The

18、 reaction capabilities of PHREEQC have been used frequently in the study of mine drainage, radioactive-waste disposal, degradation of organic matter, and microbially mediated reactions.,Batch-Reaction Modeling (Continue),DescriptionBatch reactions can be divided into equilibrium and nonequilibrium r

19、eactions. Equilibrium reactions include equilibration of a solution with an assemblage of minerals and specified-pressure gases, ion-exchange sites, surface-complexation sites, a finite gas phase, and (or) solid solutions. Nonequilibrium reactions include kinetic reactions, addition or removal of el

20、ements from solution, mixing, and changing temperature.,Keyword data blocks used in batch-reaction modeling include:,EQUILIBRIUM_PHASESan assemblage of minerals and gases that react to equilibrium (or until exhausted). EXCHANGEone or more sets of reaction sites for exchangeable ions, an important re

21、action for major cations. SURFACEone or more sets of sites that react by surface complexation, a major reaction for phosphorus, arsenic, and other trace elements. GAS_PHASEa finite reservoir of gas that reacts with a solution.,Keyword data blocks used in batch-reaction modeling (Continue),SOLID_SOLU

22、TIONSsolids that precipitate as mixtures of minerals, an important reaction for radio nuclides and other trace metals. KINETICSany nonequilibrium reaction, for which a rate expression can be formulated. RATESBASIC language statements define rate expressions for kinetic reactions. REACTIONaddition an

23、d removal of specified elements from solution.,Keyword data blocks used in batch-reaction modeling (Continue),MIXmixing together specified fractions of solutions. REACTION_TEMPERATUREchanging the temperature of the reaction system. USEuse the composition of previously defined or saved (SAVE keyword)

24、 SOLUTION, EQUILIBRIUM_PHASES, EXCHANGE, SURFACE, GAS_PHASE, SOLID_SOLUTION, or a previously defined KINETICS, REACTION, MIX, or REACTION_TEMPERATURE data block. SAVEsave the composition following the batch reaction of the SOLUTION, EQUILIBRIUM_PHASES, EXCHANGE, SURFACE, GAS_PHASE, or SOLID_SOLUTION

25、 for use in subsequent reactions.,3. Transport Modeling,ApplicationsThe reactive transport capabilities can be used to study ：contaminant migration of nutrients, metals, radio nuclides, and organic compounds; natural and engineered aquifer remediation; diffusion in sediment pore water; the chemical

26、evolution of natural systems; and laboratory column experiments.,Transport Modeling (Continue),DescriptionReactive-transport modeling simulates advection, dispersion, and chemical reactions as water moves through a 1D column. The column is divided into a number of cells, and reactant compositions an

27、d nonequilibrium reactions can be defined for each cell. All of the reactants and reactions described for batch reactions can be applied to the cells for transport modeling. The TRANSPORT keyword data block is used to simulate advection and dispersion, or pure diffusion, in the column. The TRANSPORT

28、 data block also can be used to simulate a dual-porosity medium, where water flows through the column but simultaneously allows for diffusion into stagnant side pores. The ADVECTION keyword data block is used to simulate purely advective transport.,Keyword data blocks for transport calculations:,TRA

29、NSPORT1D advection, dispersion, and reaction modeling. ADVECTION1D advection and reaction modeling.,4. Inverse Modeling,ApplicationsInverse modeling can be used to deduce geochemical reactions and mixing in local and regional aquifer systems, and in aquifer storage and recovery studies. DescriptionI

30、nverse modeling calculates geochemical reactions that account for the change in chemical composition of water along a flow path. For inverse modeling, at least two chemical analyses of water are needed at different points along the flow path, as well as a set of minerals and gases that are potential

31、ly reactive. Mole transfers of phases are calculated that account for the change in water composition along the flow path. The numerical method accounts for uncertainties in analytical data.,Keyword data block for inverse modeling:,INVERSE_MODELINGdeduce mixing, mineral, and gas reactions that accou

32、nt for the chemical evolution of waters.,How to Obtain PHREEQCI and PHREEQC?,Versions of PHREEQCI and PHREEQC may be obtained at no cost from the USGS at World Wide Web address: http:/water.usgs.gov/software Many other hydrologic computer models are also available from this site.,References,Parkhurst, D.L. and Appelo, C.A.J., 1999, Users guide to PHREEQC (Version2) A computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations: U.S. Geological Survey Water-Resources Investigations Report 99-4259, 310 p.,