PHREEQE

BLP MPTER AT123D PHREEQE CEQUALtCM PLUMES MULIIMED... 

A number of models of both types have been described in the literature. Of the models, DYNAMIX would appear to have the greatest potential for use in simulating chemical transport in the deep-well environment because it incorporates the reaction-progress code PHREEQE, which can handle deep-well temperatures. PHREEQE, however, does not incorporate pressure equilibria. 

A coefficient of 0.2 is used sometimes instead of 0.3. The only variable specific to the species in question is the charge Zj, which of course is known. For this reason, the Davies equation is especially easy to apply within geochemical models designed for work at 25 °C, such as WATEQ (Ball et al., 1979) and its successors, and PHREEQE (Parkhurst et al., 1980). 

Parkhurst, D. L., D. C. Thorstenson and L. N. Plummer, 1980, Phreeqe - a computer program for geochemical calculations. US Geological Survey Water-Resources Investigations Report 80-96. 

PHREEQE http //water.usgs.gov/software/phreeqe.htmi... 

PHREEQE can calculate pH, redox potential, concentration of elements, molalities and activities of aqueous species, and mineral or gas mass transfer as a function of reaction progress. The program is capable of simulating reactions due to mixing, titrating, net irreversible reaction, temperature changes, and mineral- or gas- phase equilibration. 

Falck, W.E. (1991) Multisite binding equilibria and speciation codes incorporation of the electrostatic interaction approach into PHREEQE. Comput. Geosci., 17, 1219-1234. 

Parkhurst, D.L., Thorstenson, D.C. and Plummer, N.L. (1980) PHREEQE -A Computer Program for Geochemical Calculations. US Geological Survey Water Research Investigation Report 80-96. 

Parkhurst DL, Thorstenson D, Plummer L. 1990. PHREEQE a computer program for geochemical calculations. No. USGS/WRI-80-96. Reston (VA) US Geological Survey, 195 p. http //water.usgs.gov/software/phreeqe.html (accessed December 28, 2007). 

The most frequently used models are MINTEQA2 (Allison et al. 1991),WATEQ4F (Ball Nordstrom 1991), PHREEQC (PHREEQE) (Parkhurst Appelo 1999, Parkhurst 1995 Parkhurst et al. 1980) and EQ 3/6 (Wolery 1992a and 1992b). 

The program PHREEQC dates back to 1980 (Parkhurst et al. 1980), at that time written in FORTRAN and named PHREEQE. The option of the program comprised ... 

In 1988, a version of PHREEQE was written including PITZER equations for ionic strengths greater 1 mol/L thus applicable for brines or highly concentrated electrolytic solutions (PHRQPITZ, Plummer et al. 1988). PHREEQM (Appelo Postma 1994) included all options of PHREEQE and additionally a one-... 

Parkhurst DL, Plummer LN, Thorstenson DC (1980) PHREEQE - A computer program for geochemical calculations.-Rev.U S Geol.Survey Water Resources Inv. Rept. 80 - 96... 

D.L. Parkhurst, Users Guide to PHREEQ C A Computer Programme for Speciation, Reaction-path, Advective Transport, and Inverse Geochemical Calculations, US Geological Survey Water Resources Inv. Report, 1995, 95. 

A computer code is obviously not a model. A computer code that incorporates a geochemical model is one of several possible tools for interpreting water-rock interactions in low-temperature geochemistry. The computer codes in common use and examples of their application will be the main focus of this chapter. It is unfortunate that one commonly finds, in the literature, reference to the MINTEQ model or the PHREEQE model or the EQ3/6 model when these are not models but computer codes. Some of the models used by these codes are the same so that a different code name does not necessarily mean a different model is being used. 

In another example, five test cases were computed by PHREEQE and EQ3/6 and the same thermodynamic database was run for each program (INTERA, 1983) to test for any code differences. The five examples were speciation of seawater with major ions, speciation of seawater with complete analysis, dissolution of microchne in dilute HCl, reduction of hematite and calcite by titration with methane, and dedolomitization with gypsum dissolution and increasing temperature. The results were nearly identical for each test case. Test cases need to become standard practice when using geochemical codes so that the results will have better credibility. A comparison of code computations with experimental data on activity coefficients and mineral solubilities over a range of conditions also will improve credibility (Nordstrom, 1994). 

INTERA (1983) Geochemical models suitable for performance assessment of nuclear waste storage comparison of PHREEQE and EQ3/EQ6. INTERA Environmental Consultants, Inc., ONWI-473, 114pp. 

Parkhurst D. L., Plummer L. N., and Thorstenson D. C. (1980) PHREEQE—A Computer Program for Geochemical Calculations. US Geol. Surv. Water-Resour. Invest. Report 80-96, 195pp. 

Plummer L. N. and Parkhurst D. L. (1990) Application of the Pitzer equations to the PHREEQE geochemical model. In Chemical Modelling of Aqueous Systems II, Symp. Ser. 416 (eds. D. C. Melchior and R. L. Bassett). American Chemical Society, Washington, DC, pp. 128-137. 

Uranium solubility is increased even more in the nitrate microcosms, and one possible explanation is the conversion of acetate to CO2, coupled with nitrate reduction, which would give higher dissolved carbonate concentrations in the nitrate microcosms. However, PHREEQE modelling showed that the higher CO concentration would not greatly affect uranium speciation in solution and is therefore unlikely to account for the enhanced solubility. Alternatively, as nitrate is reduced to ammonium (NH/), which promotes cation exchange, this could lead to displacement of U02 from surface complexes, which are the predominant uranyl species on mineral surfaces. " ... 

Method 1 In the first method, the initial content (Aq) for DIC was calculated using the measured hydrochemical data (see Table V) by the geochemical code PHREEQE (31,32) and assuming the closed system conditions represented by the following equation ... 

Selecting the least components (also called master species) is one of the fundamental and essential input decisions made in geochemical computer codes such as PHREEQE (Parkhurst et al. 1990), WATEQF (Ball and Nordstrom 1991), and M1NTEQA2 (Allison et al. 1991), for example. 

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