Speciation models triple layer model

Triple layer model TLM is very popular and it is build into many commercial speciation programs. It combines the 2-pK model, i.e. reactions (5.32) and (5.33) with binding of inert electrolyte ... 

CCM) (Stumm et al., 1970, 1976, 1980 Schindler et al., 1976), the triple-layer model (TLM) (Davis and Leckie, 1978, 1980 Davis et al., 1978 Hayes and Leckie, 1987 Hayes et al., 1988), and the 1 pK basic Stem model (Bolt and van Riemsdijk, 1982 Van Riemsdijk et al., 1986, 1987). The application of many of the commonly used computer models in the determination of the speciation in solution phase has been dealt with exhaustively by Lumsdon and Evans (1995). 

HYDRAQL A version of MINEQL, a chemical speciation code, which has been expanded to simulate adsorption with the triple layer model. 

When represents a metal cation not in the background electrolyte, the intrinsic constants are determined by fitting the triple layer model to adsorption edge data. This fitting entails a surface speciation calculation with previously measured values of the intrinsic constants in Eq. 5.61, the capacitance parameters Ci and C2, and the parameter Af. The computation includes Eqs. 5.58, 5.59, and 5.69, as well as surface charge and mole balance equations imposed as constraints. " ... 

Comprehensive recent surveys of the triple layer model are to be found in J. A. Davis and J. O. Leckie, Speciation of adsorbed ions at the oxide/water interface, in Chemical Modeling in Aqueous Systems (E. A. Jenne, ed. American Chemical Society, Washington, D.C., 1979) and in R, O, James and... 

Recent developments in spectroscopic techniques offer the opportunity to increase our understanding of oxyanion surface speciation and binding. This understanding is essential to properly use mechanistic sorption models, such as the constant capacitance model and the triple layer model. A recent criticisms of these models is that selection of the surface species and reaction from the sorption data alone results in an empirical model which could be replaced with the traditional Langmuir model (7). However determination of the surface species and reactions will constrain the parameterization and allow for mechanistic evaluation of the sorption models. Knowledge of the actual species and reaction should also enable more generalized prediction of sorption behavior outside the range of the actual experiment, which is not possible at present. 

The sphalerite-ferrous surface binding constants in NaCl solutions were determined. Applications of the hybrid triple-layer model in predicting electrokinetics, surface charge density, metal ion adsorption, and surface solution speciation were described and illustrated with examples. 

A more mechanistic and robust depiction of reversible metal adsorption is provided by SCMs that account explicitly for competitive speciation reactions using an equilibrium thermodynamic framework. Examples of SCMs in current use include the constant capacitance model (CCM), the diffuse double-layer model (DDLM), and the triple-layer model (TLM) (Stumm Morgan, 1996 Koretsky, 2000). Each of these models envisages... 

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