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A Film Depositional Model of Permeability for Mineral Reactions in Unsaturated Media

A film depositional modeling approach is developed for modeling changes in permeability due to mineral precipitation and dissolution reactions in unsaturated porous media. Such a model is needed for describing glass dissolution and secondary mineral precipitation in a low‐level waste facility. The model is based on the assumption that the mineral precipitate is deposited on the pore walls as a continuous film, which may cause a reduction in permeability. Previous work in saturated media has used continuous pore‐size distributions to represent the pore space. In this study, the film depositional model is developed for a discrete pore‐size distribution, which is determined using the unsaturated hydraulic properties of the porous medium. This facilitates the process of dynamically updating the unsaturated hydraulic parameters used to describe fluid flow through the media. Single mineral test simulations have been conducted to test both the Mualem and Childs and Collis‐George permeability models. Results from simulation of the simultaneous dissolution of low‐level glassified waste and secondary mineral precipitation show that the film depositional models yield physically reasonable predictions of permeability changes due to solid–aqueous phase reactions.