Kouli_etal_2008_Groundwater modelling_BOOK.pdf - Pantelis ...

In: Groundwater: Modelling, Management… ISBN: 978-1-60456-832-5
Editors: L.F. Konig and J.L. Weiss, pp. 133-147 © 2008 Nova Science Publishers, Inc.
Chapter 4
MODELLING OF WATER-SOLID INTERACTIONS:
A DISCUSSION OF DIFFERENT APPROACHES
Marek Šváb 1 and Lenka Wimmerová 2
1 Institute of Chemical Technology in Prague, Technická 5, Prague 6, 166 28, Czech Rep.
2 Dekonta, a.s., Dřetovice 109, Stehelčeves, 273 42, Czech Rep.
Abstract
This contribution contains an explanation and discussion of two different approaches to
the modelling of water-solid interactions. The term ‘water-solid interaction’ means all
interactions that are important in the frame of remediation methods, groundwater treatment
and pollution migration, including adsorption, leaching of contaminants, minerals
weathering, etc.
The discussed approaches involve an exact modelling of interactions based on chemical
reactions as well as what is known as the ‘semi-empirical’ approach, which is applicable for
very complex systems. On one hand, the exact approach is very promising for a detailed
understanding of particular processes and can be specified by a possible transfer of results
among various systems. On the other hand, the semi-empirical approach can also be a simple
alternative for modelling very complex systems.
The calculation of the equilibrium solubility of zinc and copper in water under various
conditions (with and without ammonia as a complexation agent), including detailed speciation
of both metals complexes, is an example of the exact modelling. The influence of ammonia
nitrogen on the solubility of both metals is obvious: a local solubility maximum occurs at the
pH of 9.4. The results have been confirmed by equilibrium batch experiments with zinc and
copper hydroxides that have proven the local solubility maximum at the pH of 9.4.
The exact modelling is further demonstrated by the adsorption of an organic contaminant
from water on three adsorbents in a mixture demonstrating the distribution of the contaminant
between various adsorbents. Although these isotherms are not exact descriptions of particular
sorption reactions, the method of calculation demonstrates the principles of use of the exact
geochemical modelling for calculations of competitive sorption on different adsorbents.
As an example of the semi-empirical approach, a mathematical model aimed at predicting
the course of a continuous soil flushing process by use of the input data obtained from simple
batch laboratory experiments is described. An objective of the example is to apply this new
model to soil polluted by zinc and copper (11 949 mg/Kg -1 and 1 895 mg/Kg -1 , respectively)
by flushing this soil with an ammonia nitrogen solution with the pH of 9.4. The model
predicts correctly the period of time needed for the removal of weakly-bound metal fractions,