title: Numerical simulation of reactive processes in an experiment with partially saturated bentonite.
abstract: Bentonites are preferred materials for use as engineered barriers for high-level nuclear waste repositories. Simulation of geochemical processes in bentonite is therefore important for long-term safety assessment of those repositories. In this work, the porewater chemistry of a bentonite sample subject to simultaneous heating and hydration, as studied by Cuevas et al. [Cuevas, J., Villar, M., Fernández, A., Gómez, P., Martín, P., 1997. Porewaters extracted from compacted bentonite subjected to simultaneous heating and hydration. Applied Geochemistry 12, 473-481.], was assessed with a non-isothermal reactive transport model by coupling the geochemical software PHREEQC2 with the object-oriented FEM simulator GeoSys/RockFlow. Reactive transport modelling includes heat transport, two-phase flow, multicomponent transport and geochemical reactions in the liquid phase, i.e. ion exchange, mineral dissolution/precipitation and equilibrium reactions. Simulations show that the easily soluble minerals in bentonite determine the porewater chemistry. Temperature affects both two-phase flow and geochemical reactions. Porosity change due to dissolution/precipitation is low during the experiment. However, changes of the effective porosity caused by bentonite swelling can be very large. The simulated results agree well with the experimental data.
authors.affiliation: Center for Applied Geoscience, Chair of GeoSystemsResearch, University of Tübingen, Sigwartstr. 10. D-72076 Tübingen, Germany. mingliang.xie@uni-tuebingen.de
authors.forename: Mingliang
authors.initials: M
authors.lastname: Xie
authors.forename: Sebastian
authors.initials: S
authors.lastname: Bauer
authors.forename: Olaf
authors.initials: O
authors.lastname: Kolditz
authors.forename: Thomas
authors.initials: T
authors.lastname: Nowak
authors.forename: Hua
authors.initials: H
authors.lastname: Shao
mesh_terms: D001546:Bentonite / Q000737:chemistry*; D002021:Buffers; D011232:Chemical Precipitation; D003198:Computer Simulation; D006358:Hot Temperature; D007474:Ion Exchange; D008962:Models, Theoretical; D010539:Permeability; D016062:Porosity; D011850:Radioactive Waste; D012995:Solubility; D018505:Waste Management / Q000379:methods; D014872:Water Movements
chemical_list: D002021:Buffers; D011850:Radioactive Waste; D001546:Bentonite