RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics
RES³T is a digitized version of a thermodynamic sorption database as required for the parametrization of Surface Complexation Models (SCM). It is mineral-specific and can therefore also be used for additive models of more complex solid phases such as rocks or soils.
The web-based user interface allows selecting minerals, sorptives and model subtypes to assess the respective surface and sorption parameters, to convert parameter units and to normalize parameters to infinite dilution and to reference site densities. Data records comprise of mineral properties, specific surface area values, characteristics of surface binding sites and their protolysis, sorption ligand information, and surface complexation reactions with their associated SCM parameters.
The following SCM variants are implemented, representing different models for the Electric Double Layer (EDL): the Non-Electrostatic Model, the Diffuse Double Layer Model, the Constant Capacitance Model, the Triple Layer Model, the Basic Stern Model, and the 1-pK Model as extended to CD-MuSiC. For every SCM type (where applicable), also the concept of strong and weak binding sites is included. Surface species composed from up to two different ligands can be incorporated.
An extensive bibliography (in most cases including abstracts and digital object identifiers (DOI)) is also searchable. It provides links not only to the above listed data items, but also to background information concerning surface complexation model theories, related software for data processing and modeling, and sorption experiment techniques.
The database will help to substitute conventional distribution coefficients (Kd values) at present most often applied in geochemical modelling (e.g. reactive transport codes) by the mechanistic description of sorption phenomena with SCM. Such an approach, associated to terms such as "Smart Kd", "Bottom-up" or "Component additivity" is more robust with respect to extrapolation beyond laboratory conditions. Thus it can explain the sorption behaviour of contaminants as function of geochemical conditions; can back-up conventional distribution coefficients; evaluate trends of sorption with respect to changes in key chemical parameters and to assess related uncertainties and sensitivities. Consequently, it supports directly the selection of Kd values for modelling contaminant migration in engineered barriers and in the geosphere which eventually predicts contaminant transport in the environment in a more reliable way. Furthermore, it assists the identification of critical data gaps, the evaluation of existing parameter sets, consistency tests and the establishment of selected reference data sets.
As to the knowledge of the authors, so far there is no such digital thermodynamic database for surface complexation equilibria existent world-wide, despite the vast amount of available data. As the major contributors as well as the funding originates from the huge task of providing thermodynamic foundations for the safe storage of nuclear waste, the focus of RES³T is clearly set on radionuclides and fission products. It should also be mentioned that the data are provided free of any charge, for legal issues please refer to our disclaimer. And of course any critical feedback is very much welcomed.
A comprehensive application case of this "Bottom-up" approach has been developed within the ESTRAL and WEIMAR projects, see www.smartkd-concept.de for details.