Reactive transport codes applied to gypsum dissolution in a laboratory column experiment with focus on sensitivity of model concepts and data uncertainty

Experimentally determined kinetic gypsum dissolution by pure water has been used as a data set to investigate different model concepts for mineral dissolution integrated into the four different couple codes. All concepts include a kinetic approach, but with different detail of parameter dependency. In the case of gypsum dissolution, only those concepts, which include an explicit dependency on the actual gypsum mineral surface area, gave good agreement with the measurements. Concepts which do not include such a dependency could not reproduce the measurements. More complex rate equations were necessary to describe the experiments. Nevertheless, the accessible mineral surface area, which decreases during the dissolution, was not directly measurable in the experiment and is so far a model parameter, albeit the one which reproduced measured Ca2+ in solution. Solution chemistry measurements forced the kinetic dissolution model to include a temporal evolving accessible mineral surface area to correctly describe the dissolution experiment.