Thermoddem: an example of alive thermochemical database
Résumé
The basic goal of the Thermoddem thermochemical database (http://thermoddem.brgm.fr/) is to gather standard thermodynamic data regarding chemical compounds encountered in most water-solid-gas systems, with a specific concern for environmental issues, cement phases and clay minerals. The construction of the database (since 2006) relies on a careful selection of published experimental data, constrained by a rigorous internal consistency. Data selection combines both solubility and calorimetric data in order to strengthen the coherence of the data set. A particular effort is paid to identifying the source of every data. Some examples will be presented for illustration. A major objective of thermochemical databases (TDB) is to be integrated into coupled reactive transport modelling codes. Therefore, it is of key importance to provide database formats adapted to the most widely used calculation codes and to make them freely available on the Internet. In addition, Thermoddem includes mineralogical and geological information to help the modeller to define and to select the geochemical reactive system in agreement with the problematic to handle. Geochemical and reactive transport modelling covers a wide range of temperature and pressure conditions, numerous reactive mechanisms (aqueous complexation, surface complexation and ionic exchanges, dissolution/precipitation or degassing reactions, kinetic processes, bacterial activity), and various contexts (dilute/saline waters, isobaric/anisobaric conditions). Models implemented in calculations codes for describing the different geochemical mechanisms evolve with time and new concepts are perpetually developed. Alive TDB have to adapt to these evolutions as for Thermoddem, which is this way developed. However one has to acknowledge that, despite the wide use of thermochemical databases, there is still a need for gathering a community that would actively contribute to help improving these tools. Furthermore a better scientific recognition could help supporting their development and maintenance.