Reactive Transport in Heterogeneous Media

摘要

We analyze the dynamics of reactive transport in heterogeneous media, emphasizing the nature of the chemical reactions and the role of small-scale fluctuations induced by the structure of the porous medium, which is the main component of geological formations. Our goal is the interpretation of the results of laboratory-scale experiments, for which detailed characterization of the system is possible. Modelling approaches have been based on continuum and particle tracking (PT) schemes, which differ in how the fluctuations are incorporated. We choose PT methods wherein space-time transitions are drawn from appropriate probability distributions that have been tested to account for anomalous (non-Fickian) transport. While PT methods have been employed for many years to describe conservative transport, their application to laboratory-scale reactive transport problems in the context of both Fickian and non-Fickian regimes is relatively recent. We concentrate on experimental observations of different types of reactions in heterogeneous media: (1) the dynamics of a bimolecular reactive transport (A+ B → C) in passive (non-reactive) media, and (2) a multi-step chemical reaction, as exemplified in the process of dedolomitization involving both dissolution and precipitation. The fluctuations in a number of the key variables controlling the processes prove to have a dominant role; elucidation of this role forms the basis of the present study. An implication of these findings is that subtle changes in patterns of water flow, as a result of climate change or changes in land use, may have significant effects on water quality.