Equilibrium Models in Hydro- and Geochemistry
In the last decades, a large variety of models and computer programs has been developed for applications in hydro- and geochemistry. From a thermodynamic point of view they solve the following task:
||temperature T, pressure P, and total concentrations of elements
||concentrations ci (or molar amounts ni) of chemical species in aqueous and other phases in equilibrium state
In all calculations partial/local equilibrium is assumed, therefore they are also termed “thermodynamic equilibrium models” (in contrast to kinetic models).
Despite the huge diversity we encounter in hydro/geochemistry models and software today, all these approaches fall into two major categories:
LMA. The LMA approach is common, and available in many computer programs, such as PhreeqC, Minteq, Wateq4f, EQ3/6, Chess/JChess, The Geochemist’s Workbench and others. The program aqion, that relies on the numerical solver of PhreeqC, belongs to the LMA category as well.
GEM. The GEM approach, represented by codes such as Solgasmix, ChemSage, FactSage, Selektor or GEMS-PSI, is less common, but is becoming increasingly popular.
The mathematical treatment of the equilibrium speciation problem yields nonlinear equation systems that can only be solved iteratively (such as root finding with Newton-Raphson method and other techniques). Thus, the application of numerical computer programs is a natural consequence.
Remarks & References
[last modified: 2015-11-24]