Geochemical Nonequilibrium Effects

The purpose of the next example is to illustrate the influence of the reaction parameter (see Eq. (lb)) on the transport of the solute. The decay terms are neglected here. The value of a can be applied in order to control the conditions for which the reactions are in equilibrium or not. While for large values of ce= 10 Ms the processes take place at equilibrium conditions (the curves C/CO and S/SO overlap each other (Fig. 6.4)), for a= 10 Ms (the smallest value of a) a typical nonequilibrium case is considered. The sorbed concentration is much lower than the solute concentration (Fig. 6.4). This indicates, the geochemical system is far from equilibrium. 

Further values for the example are listed in the following Table 6.3. 

Transfonnation processes are very important for the treatment of many organic contaminants with permeable reactive barriers. The components and their products undergo sorption reactions. This sorption reactions may be either in equilibrium or nonequilibrium. Desintegration of tetrachloroethene or trichloroethylene are two of many examples, that can be treated with this permeable reactive barriers. Khandelwal and Rabideau (1999) developed analytical and semi-analytical solutions for this problem. They consider the sorption reaction with a nonequdibrium model. We verified the numerical RF-RTM model with their analytical solution. 

This example shows the migration and degradation of TCE (trichloroethylene) and its reaction products cl2DCE (c-l,2-dichloroethene) and VC (vinyl chloride) in a zero-valent iron PRB (permeable reactive barrier) (Kandelwal and Rabideau, 1999)  

The simulations were performed for a 1 m thick wall. The apparent velocity and 

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New Geochemical Simulator Rockflow-RTM Development and Benchmarking 6.5.2 Geochemical Nonequilibrium Effects... 

Johnson TM, Bullen TD (2004) Mass-dependent fractionation of selenium and chromim isotopes in low-temperature environments. Rev Mineral Geochem 55 289-317 Kim S-T, O Neil JR (1997) Equilibrium and nonequilibrium oxygen isotope effects in synthetic carbonates. Geochim Cosmochim Acta 61 3461-3475... 

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