Kofod, Verena Haury, Nandimandalam Janardhana Raju and Margot Isenbeck-Schroter

Max Kofod, Verena Haury, Nandimandalam Janardhana Raju and Margot Isenbeck-Schroter 

Geochemical Processes Conceptual Models for Reactive Transport in Soil and Groundwater. Research Report. Deutsche Forschungsgemednschaft (DFG). 

Copyright 2002 WILEY-VCH Verlag GmbH Co. KGaA, Wemheim. ISBN 978-3-527-27764 3 

PHREEQC is a computer programme for hydrogeochemical calculations such as speci-ation of water constituents, mineral-water saturation indices, batch reactions, ID-transport (Parkhurst and Appelo, 1999). The recent version of the programme (PHREEQC2 Ver. 2.3) is able to model sorption processes using the surface complexa-tion concept (Dzombak and Morel, 1990). At present PHREEQC2 is distributed with a set of surface complexation constants that are derived from amorphous, freshly precipitated iron hydroxide. The data for the surface complexation reactions in the database of PHREEQC2 are taken from Dzombak and Morel (1990). 

The iron hydroxide material that was used in the column experiments differs significantly from amorphous hydroxides. The most obvious difference between the iron hydroxide used and the freshly precipitated amorphous substance is the considerably lower specific area. One important question concerning the modelling of these column experiments is whether the surface complexation constants derived for amorphous, freshly precipitated iron hydroxides by Dzombak and Morel are also suitable for other iron hydroxide materials. If this is the case, then it would be sufficient to adjust the available surface sites to achieve an adequate model of the oxoanion transport through aquifers containing iron hydroxides. 

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