Geochemical reactions

In order to finish computer modelling in an acceptable time (some few hours) we modelled a redox reaction, which is characteristic for this anoxic aquifer, and also is understood well enough in order to be considered as sum-reaction. It is the redox reaction between DOC in groundwater and iron(III)oxide or iron(III)hydroxide in the solid phase of the aquifer. If we assume DOC simplified as CH2O, and the iron(III)oxides and/or iron(III)hydroxides as Fe(OH)3, we will get the following reaction  

This reaction is assumed to be characteristic for this particular anoxic aquifer and is known to have a rather small reaction rate (Schiiring et al., 2000). In each cell and each time step the concentration of DOC in the groundwater will be decreased by a kinetic with a chosen order, at the same time eliminating a stoichiometric equivalent ammmt of Fe(III) from the iron(III)oxide stocks of the aquifer. If one or the other reaction partner is no longer available, the reaction will come to an end. The state of concentration of each cell can be accessed in the groundwater and in the aquifer at any time. 

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In both instances, samples of the fluids in the zone are collected at intervals to characterize the nature of geochemical reactions and to track changes over time. 

Mito S., Xue Z., et al. Case study of geochemical reactions at the Nagaoka C02 injection site, Japan. 2008 International Journal of Greenhouse Gas Control 2 309-318. 

X109 Solar system Earth Cycling of planets (stationary states) Geochemical reactions... 

Beginning in the late 1980s, a number of groups have worked to develop reactive transport models of geochemical reaction in systems open to groundwater flow. As models of this class have become more sophisticated, reliable, and accessible, they have assumed increased importance in the geosciences (e.g., Steefel et al., 2005). The models are a natural marriage (Rubin, 1983 Bahr and Rubin, 1987) of the local equilibrium and kinetic models already discussed with the mass transport... 

This choice of basis follows naturally from the steps normally taken to study a geochemical reaction by hand. An aqueous geochemist balances a reaction between two species or minerals in terms of water, the minerals that would be formed or consumed during the reaction, any gases such as O2 or CO2 that remain at known fugacity as the reaction proceeds, and, as necessary, the predominant aqueous species in solution. We will show later that formalizing our basis choice in this way provides for a simple mathematical description of equilibrium in multicomponent systems and yields equations that can be evaluated rapidly. 

As discussed already in Chapter 7, redox reactions constitute a second class of geochemical reactions that in many cases proceed too slowly in the natural environment to attain equilibrium. The kinetics of redox reactions, both homogeneous and those catalyzed on a mineral surface are considered in detail in the next chapter, Chapter 17, and the role microbial life plays in catalyzing redox reactions is discussed in Chapter 18. 

Delany, J. M. and T. J. Wolery, 1984, Fixed-fugacity option for the eq<5 geochemical reaction path code. Lawrence Livermore National Laboratory Report UCRL-53598. 

Plummer, L. N., D.L. Parkhurst, G. W. Fleming and S. A. Dunkle, 1988, PHRQPITZ, a computer program incorporating Pitzer s equations for calculation of geochemical reactions in brines. US Geological Survey Water-Resources Investigations Report 88—4153. 

Thompson, J. B., Jr., 1970, Geochemical reaction and open systems. Geochimica et Cosmochimica Acta 34,529-551. 

In the decade since I published the first edition of this book,1 the field of geochemical reaction modeling has expanded sharply in its breadth of application, especially in the environmental sciences. The descriptions of microbial activity, surface chemistry, and redox chemistry within reaction models have become more robust and rigorous. Increasingly, modelers are called upon to analyze not just geochemical but biogeochemical reaction processes. 

Geochemical Reaction Modeling, Oxford University Press, 1996. 

Parkhurst, D., Kipp, K., Engesgaard, P., Charlton, S. 2004. PHAST - A program for simulating ground-water flow, solute transport, and multicomponent geochemical reactions. U.S. Geological Survey Techniques and Methods 6-A8. 

Measurements made in the Type I pile and the Type III pile show no depletion in oxygen or increase in carbon dioxide concentrations, indicating gas transport mechanisms are fast relative to the rate of the oxygen consumption and carbon dioxide production due to geochemical reactions. In the Covered pile, significant depletions in oxygen and increases in carbon dioxide concentration have been observed at some locations, suggesting gas transport rates are limited by the till... 

Charlton, S.R. Parkhurst, D.L 2002. PHREEQCI-A computer program for speciation,reaction-path, advective transport, and inverse geochemical reactions. U.S. Geological Surveys Water-Resources Investigations, 95-4227. 

Bethke, C.M. (1996). Geochemical Reaction Modeling Concepts and Applications. Oxford University Press, Oxford. 

A specialty of geology concerned with earth processes, earth resources, and engineering properties of earth materials and relevant to (1) the protection of human health and natural ecosystems from adverse biochemical and/or geochemical reactions to naturally occurring chemicals or to chemical compounds released into the environment by human activities and (2) the protection of life, safety, and well-being of humans from natural processes, such as floods, hurricanes, earthquakes and landslides, through land-use planning. 

A USGS model for computing the chemical evolution of the aqueous phase as the result of specified geochemical reactions. Based on an ion-pairing aqueous model,... 

Catagenesis Geochemical reactions that occur in the sediments following burial on time scales greater than 1000 years and at temperatures of 50 to 150°C. 

In the previous sections of this book, we focused on the nature of contaminants and the geochemical reactions that can occur in the subsurface environment. Chemical compounds introduced into infiltrating water or in contact with soil or rock surfaces are subject to chemically and biologically induced transformations. Other compounds are retained by the soil constituents as sorbed or bound residues. Thus, in terms of geochemical interactions and reactions among dissolved chemical species, interphase transfer occurs in the form of dissolution, precipitation, volatilization, and various forms of physicochemical retention on the solid surfaces. 

Activation energies of some important geochemical reactions are listed in table 8.27. 

Table 8.27 Activation energies of geochemical reactions (kJ/mole) (after Lasaga, 1981a, 1984)...

Delany J. M., Puigdomenech L, and Wolery T. J. (1986). Precipitation Kinetics Option for the EQ6 Geochemical Reaction Path Code Lawrence Livermore National Laboratory, Livermore, Cal., UCRL-53642. 

Another geochemical reaction that has been investigated extensively as a geospeedometer by high-temperature geochemists is the hydrous species reaction in rhyolitic melt. As the H2O component dissolves in silicate melt, it partially reacts with oxygen in the melt to form OH groups (Reaction 1-10) ... 

This review article summarizes the factors that influence the storage of C02 in deep aquifers. A case study of expected mineral-brine-C02 reactions in the Rose Run Sandstone, a deep aquifer and oil- and gas-containing formation in the Appalachian Basin area of eastern Ohio, USA, is presented. Geochemical reactions between C02, brine, and formation minerals are emphasized in the example because these reactions determine the ultimate fate of C02. 

Mineral trapping is the fixing of C02 in carbonate minerals as a result of geochemical reactions among aquifer brines, formation minerals, and aqueous species of C02. The density of C02 in... 

Stromberg, B. Banwart, S. A. 1994. Kinetic modelling of geochemical reactions at the Aitik mining waste rock site in northern Sweden. Applied Geochemistry, 9, 583-595. 

Plummer, L. N. Prestemon, E. C. Parkhurst, D. L. 1991. An Interactive Code (NETPATH) for Modeling Net Geochemical Reactions Along a Flow Path. U.S. Geological Survey, Water Resources Investigations Report 91-4078. 

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