Evaluation, compilation and comparison of state of the art PHREEQC thermodynamic database files to generate a new one

Geothermal brines are a complex topic for geochemists and present many challenges to scientists who wish to understand them and their processes, e.g. for mineral extraction, geothermal power or heat generation. One of these challenges is uncontrolled mineral precipitation, which can be induced by changes in pressure, temperature, or pH. Geochemical modeling is used to predict the scaling potential when one of these parameters is affected. Any modeling software consists of a set of equations and a thermodynamic database file (TDF) containing thermodynamic data for all aqueous, solid or gaseous species that can be modeled. These thermodynamic data are derived from experiments and are usually extrapolated to higher temperatures, pressures, salinities, or pH values. Because different experiments have been performed for a mineral, the basis of the extrapolation may vary or different types of experiments have been performed to determine the thermodynamic data. This results today in different extrapolated data sets that are used in these TDFs for modeling. The same model using different TDFs can lead to divergent and inconsistent results.
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For new users, it is quite challenging to understand when a particular TDF can be used and what its limitations are. Therefore, the authors have created a new database with improved thermodynamic data for 15 new minerals by evaluating peer-reviewed experimental data and comparing it with the most used PHREEQC TDFs to determine the most accurate data sets. The idea is to improve the accuracy of modeling low-pressure, high-temperature systems, such as surface geothermal plants, with respect to scaling. In addition, the previously mentioned inconsistent modeling results also occur for degassing models. It is planned to evaluate and verify the TDFs in this regard as well with tailored experimental data generation to address this challenge.