Chemical equilibrium models

Chemical equilibrium between seawater and marine sediments wiU be considered below following SiUen (1961, 1967a, b), Kramer (1965), Stumm and Morgan (1970), and Sayles and Margelsdorf (1977). Constituent minerals of sediments involve silicates, carbonates, phosphates and sulfates as follows. 

Na-montmorillonite, H-montmorillonite, K-illite, H-illite, phillipsite ((K, Na, Ca)2.4(Al,Si)i6032l2H20), strontianite (SrC03), celestite (SrS04), chlorite, kaolin-ite, OH-apatite, FC02-apatite, calcite, aragonite, gypsum, and Mg-illite. 

Chemical composition of seawater in equilibrium with above minerals can be calculated using equilibrium constants listed in Table 4.2, mass balance equations and electroneutrality relation. The calculated results by Kramer (1965) are mostly 

4Si02(quartz) -1- 2Al2Si207-2H20(kaolinite) -1- 2Ca -t 7H2O  

Si02(quartz) -1- Al2Si02-2H20(kaolinite) + 7H2O -1 5Mg +  

The equilibrium model is easy to generate, as discussed in Section 9.1.6. The reaction is changed from kinetic to equilibrium and the equilibrium constant is calculated from Gibbs free energies. 

DESIGN OF MTBE AND ETBE REACTIVE DISTILLATION COLUMNS 

the same idea was applied to the ETBE simulation. However, the results were quite unexpected. The conversion dropped to less than 50%, and the concentrations of both reactants in the entire reaction zone were quite high. We are at a loss to explain these results. 

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Meylan S, Odzak N, Behra R, Sigg L (2004) Speciation of copper and zinc in natural freshwater comparison of voltammetric measurements, diffusive gradients in thin Aims (DGT) and chemical equilibrium models. An Chim Acta 510 91... 

Several workers have intended to estimate the chemical compositions of Kuroko ore fluids based on the chemical equilibrium model (Sato, 1973 Kajiwara, 1973 Ichikuni, 1975 Shikazono, 1976 Ohmoto et al., 1983) and computer simulation of the changes in mineralogy and chemical composition of hydrothermal solution during seawater-rock interaction. Although the calculated results (Tables 1.5 and 1.6) are different, they all show that the Kuroko ore fluids have the chemical features (1 )-(4) mentioned above. 

D. R. Parker, R. L. Chaney, and W. A. Norvell. Chemical equilibrium models applications to plant nutrition research. Chemiccd Equilbrium and Reaction Models (R. H. Loeppert, ed.), Madison, WI, Soil Science Society of America Special Publication, 42 163 (1995). 

Chan, M. Yen, T.F. A Chemical Equilibrium Model for Interfadal Activity of Crude Oil in Aqueous Alkaline Solution The Effects of pH, Alkali and Salt, Canadian J. Chem. Eng. 1982, 60, 305. 

Fowle and Fein (1999) measured the sorption of Cd, Cu, and Pb by B. subtilis and B. licheniformis using the batch technique with single or mixed metals and one or both bacterial species. The sorption parameters estimated from the model were in excellent agreement with those measured experimentally, indicating that chemical equilibrium modeling of aqueous metal sorption by bacterial surfaces could accurately predict the distribution of metals in complex multicomponent systems. Fein and Delea (1999) also tested the applicability of a chemical equilibrium approach to describing aqueous and surface complexation reactions in a Cd-EDTA-Z . subtilis system. The experimental values were consistent with those derived from chemical modeling. 

Fein JB, Daughney CJ, Yee N, Davis TA (1997) A chemical equilibrium model for metal adsorption onto bacterial surfaces. Geochim Cosmochim Acta 61 3319-3328... 

Fowle DA, Fein JB (1999) Competitive adsorption of metal cations onto two gram positive bacteria testing the chemical equilibrium model. Geochim Cosmochim Acta 63 3059-3067... 

Greenberg, J. P. and N. Mpller, 1989, The prediction of mineral solubilities in natural waters, a chemical equilibrium model for the Na-K-Ca-Cl-S04-H20 system to high concentration from 0 to 250 °C. Geochimica Cosmochimica Acta 53,2503-2518. 

Tipping E., 1994, WHAM - a chemical equilibrium model and computer code for waters, sediments and soils incorporating a discrete site/electrostatic model of ion-binding by humic substances. Computers and Geosciences 20,973-1023. 

A chemical equilibrium modeling system that can be used to perform calculations on low temperature (0-50°C), low to moderate ionic strength (<0.5 M) aqueous systems. 

Large concentrations of Fe + develop in the soil solution in the weeks following flooding, often several mM or tens of mM (Figure 4.5). Calculations with chemical equilibrium models show that the ion activity products of pure ferrous hydroxides, carbonates and other minerals are often exceeded 100-fold (Neue and Bloom, 1989). Evidently precipitation of these minerals is inhibited, probably as a result of adsorption of foreign solutes, such as dissolved organic matter and phosphate ions, onto nucleation sites (Section 3.7). However, once a sufficient supersaturation has been reached there is a rapid precipitation of amorphous solid phases, which may later re-order to more crystalline forms. Only a small part of the Fe(II) formed in reduction remains in solution the bulk is sorbed in exchangeable forms or, eventually, precipitated. 

Medium-chain alcohols such as 2-butoxyethanol (BE) exist as microaggregates in water which in many respects resemble micellar systems. Mixed micelles can be formed between such alcohols and surfactants. The thermodynamics of the system BE-sodlum decanoate (Na-Dec)-water was studied through direct measurements of volumes (flow denslmetry), enthalpies and heat capacities (flow microcalorimetry). Data are reported as transfer functions. The observed trends are analyzed with a recently published chemical equilibrium model (J. Solution Chem. 13,1,1984). By adjusting the distribution constant and the thermodynamic property of the solute In the mixed micelle. It Is possible to fit nearly quantitatively the transfer of BE from water to aqueous NaDec. The model Is not as successful for the transfert of NaDec from water to aqueous BE at low BE concentrations Indicating self-association of NaDec Induced by BE. The model can be used to evaluate the thermodynamic properties of both components of the mixed micelle. 

The functions of transfer can be simulated with the chemical equilibrium model of Roux et al. ( )... 

Figure 3 Volumes of transfer of sodium decanoate from water to 2-butoxyethanol solutions at 25 C. Simulations (curves A and 6) with a chemical equilibrium model ...

The chemical equilibrium model of Roux et al (6) is a powerful tool for the study of the thermodynamics of mixed micellar solutions. It can estimate the distribution constant of the surfactant 3 between water and micelles of the surfactant 2 and the thermodynamic properties of the surfactant 3 in the mixed micelles. For this it is necessary to obtain reliable data over a large concentration range of solute 2. 

Chudnenko, K. V., Karpov, I. K., Kulik, D. A., Berner, U. R., Hummel, W. Artimenko, M. V. 2004. GEM Uncertainty Space Approach for Sensitivity Analysis of Solid-Aqueous Chemical Equilibrium Models A Pilot Study. PSI Technical Report TM-44-04-01, Paul Scherrer Institut, Villigen, Switzerland. 

Two different approaches have been taken by researchers to determine the secondary mineralogy of CCBs (1) direct observation, which is accomplished via analysis of weathered ash materials, and (2) prediction, based on chemical equilibrium solubility calculations for ash pore-waters and/or experimental ash leachate or extractant solutions. Because the secondary phases are typically present in very low abundance, their characterization by direct analysis is difficult. On the other hand, predictions based on chemical equilibrium modelling or laboratory leaching experiments may not be reliable indicators of element leachability or accurately indicate the secondary phases that will form under field conditions (Eighmy et al. 1994 Janssen-Jurkovicova et al. 1994). 

In addition, several other models have been used with method I to calculate binary or ternary phase diagrams (183, 188-201). Among these models are the quasi chemical equilibrium model (188,190), truncated Mar-gules expansions (183,191, 192), Gaussian formalism (193), orthogonal series... 

Dudal, Y., and Gerard, F. (2004). Accounting for natural organic matter in aqueous chemical equilibrium models A review of the theories and applications. Earth-Sci. Rev. 66, 199-216. 

Figure 7 further shows that, as gaseous C02 moves up the absorber, phase equilibrium is achieved at the vapor-liquid interface. C02 then diffuses through the liquid film while reacting with the amines before it reaches the bulk liquid. Each reaction is constrained by chemical equilibrium but does not necessarily reach chemical equilibrium, depending primarily on the residence time (or liquid film thickness and liquid holdup for the bulk liquid) and temperature. Certainly kinetic rate expressions and the kinetic parameters need to be established for the kinetics-controlled reactions. While concentration-based kinetic rate expressions are often reported in the literature, activity-based kinetic rate expressions should be used in order to guarantee model consistency with the chemical equilibrium model for the aqueous phase solution chemistry. 

Combination of wet chemical extraction with instrumental speciation techniques or chemical equilibrium modelling... 

Table 11.2 Results of chemical equilibrium modelling of the contribution of ferrous iron phases to the proportion of iron (in %) extracted from an anoxic freshwater sediment from the Elbe River near Hamburg (Germany) by the first two acetate buffer steps of a modified Tessier sequential extraction scheme...

The chemical equilibrium model, FREZCHEM, requires calculation of solute activity coefficients (7) and the osmotic coefficient ((f)) in concentrated solutions (Chap. 3). In this work, the Pitzer approach is used to calculate these quantities. 

The FREZCHEM model is a chemical equilibrium model. For a reaction such as gypsum dissolution... 

Despite these application limitations, it nevertheless is true that chemical equilibrium models can generally provide reasonable approximations of many, but not all, real-world chemical processes. The better we understand the biogeochemistry of natural systems, the better we can adapt our geochemical models for specific systems. One need only peruse standard geochemical textbooks (e.g., Nordstrom and Munoz 1994 Drever 1997 Millero 2001) to sense the importance of such models in geochemical applications. 

In aquatic ecosystems, complexation to organic and inorganic ligands and competition between toxic metals and Ca or Mg ions for biological adsorption sites reduce the actual amount of metal available for uptake by organisms. Chemical equilibrium models applicable to natural systems include RANDOM (Murray and Linder 1983 ... 

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