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

Wilfried Pfingsten1, Jens Mibus2 & Roland Kuechler2

1 Waste Management Laboratory, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

wilfried.pfingsten@psi.ch

2 Forschungszentrum Rossendorf, D-01314 Dresden, Germany

Abstract Experimentally determined kinetic data for gypsum dissolution by pure water have been used to investigate different model concepts for mineral dissolution integrated into four different coupled codes. All concepts include a kinetic approach, but with different parameter dependency details. In the case of gypsum dissolution, only those concepts which included an explicit dependency on the actual gypsum mineral surface area gave good agreement with the measurements. Concepts which did not include such a dependency could not reproduce the measurements. More complex dissolution rate equations were necessary to describe the experiments. Nevertheless, the accessible mineral surface area, which decreased during the dissolution, was not directly measurable in the experiment and is a model parameter, albeit one which reproduced measured Ca2+ concentration in solution. Solution chemistry measurements required that the kinetic dissolution model included a temporally evolving accessible mineral surface area in order to correctly describe the gypsum dissolution experiment.

Keywords code comparison; column experiment; coupled codes; gypsum dissolution; mineral surface area; reaction rates