Estimating Intrinsic Formation Constants of Mineral Surface Species Using a Genetic Algorithm |
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| Authors: | Adrián Villegas-Jiménez Alfonso Mucci |
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| Institution: | 1.Earth and Planetary Sciences,McGill University,Montréal,Canada |
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| Abstract: | The application of a powerful evolutionary optimization technique for the estimation of intrinsic formation constants describing
geologically relevant adsorption reactions at mineral surfaces is introduced. We illustrate the optimization power of a simple
Genetic Algorithm (GA) for forward (aqueous chemical speciation calculations) and inverse (calibration of Surface Complexation
Models, SCMs) modeling problems of varying degrees of complexity, including problems where conventional deterministic derivative-based
root-finding techniques such as Newton–Raphson, implemented in popular programs such as FITEQL, fail to converge or yield
poor data fits upon convergence.
Subject to sound a priori physical–chemical constraints, adequate solution encoding schemes, and simple GA operators, the
GA conducts an exhaustive probabilistic search in a broad solution space and finds a suitable solution regardless of the input
values and without requiring sophisticated GA implementations (e.g., advanced GA operators, parallel genetic programming).
The drawback of the GA approach is the large number of iterations that must be performed to obtain a satisfactory solution.
Nevertheless, for computationally demanding problems, the efficiency of the optimization can be greatly improved by combining
heuristic GA optimization with the Newton–Raphson approach to exploit the power of deterministic techniques after the evolutionary-driven
set of potential solutions has reached a suitable level of numerical viability. Despite the computational requirements of
the GA, its robustness, flexibility, and simplicity make it a very powerful, alternative tool for the calibration of SCMs,
a critical step in the generation of a reliable thermodynamic database describing adsorption equilibria. The latter is fundamental
to the forward modeling of the adsorption behavior of minerals and geologically based adsorbents in hydro-geological settings
(e.g., aquifers, pore waters, water basins) and/or in engineered reactors (e.g., mining, hazardous waste disposal industries). |
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