Numerical simulation of reactive processes in an experiment with partially saturated bentonite

• Published in: Journal of contaminant hydrology Vol. 83; no. 1; pp. 122 - 147
• Main Authors: Xie, Mingliang, Bauer, Sebastian, Kolditz, Olaf, Nowak, Thomas, Shao, Hua
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.02.2006; Elsevier Science
• Subjects: Bentonite; Bentonite - chemistry; Buffers; Chemical Precipitation; chemical reactions; Computer Simulation; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Geochemical reaction; geochemistry; hazardous waste; high-level radioactive waste repository; Hot Temperature; Hydrogeology; Hydrology. Hydrogeology; Ion Exchange; mathematical models; Models, Theoretical; Non-isothermal reactive transport; non-thermal reactive transport; Numerical modelling; Permeability; Pollution, environment geology; Porosity; Radioactive Waste; radionuclides; Solubility; Two-phase flow; waste disposal; Waste Management - methods; Water Movements; ASW, Greater Antilles, Puerto Rico, Mona I., Cueva; Greater Antilles, Puerto Rico; Bentonite; Non-isothermal reactive transport; Two-phase flow; Numerical modelling; Geochemical reaction; experimental studies; waste disposal; ion exchange; ground water; bentonite; pollution; radioactive waste; precipitation; safety; pore water; temperature; clastic rocks; models; liquid phase; porosity; dissolution; bicarbonate ion; swelling; transport; high-level waste; sedimentary rocks; sodium; two-phase models; hydration; numerical models; porous media
• DOI: 10.1016/j.jconhyd.2005.11.003
• ISSN: 0169-7722

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.