Multi-component reactive transport in heterogeneous media and its decoupling solution

• A decoupling approach to solve the problems involving heterogeneous media is presented.
• A model for heterogeneous media was established and solved in COMSOL.
• The results obtained by the proposed method are compared to those from PHAST.
• Evolution and distribution of flow, concentration, and porosity were all modelled.

The multi-component reactive transport model is widely used in contaminant transport, water–rock interaction, and other earth science fields. Since its complexity lies in its solution, a decoupling approach is used to simplify the model to enhance computational efficiency. A decoupling approach is presented for heterogeneous media, and used to solve the model in this situation. The whole domain is divided into several sub-domains due to the different reactions which may occur and the corresponding component matrix was obtained. The boundary between sub-domains could be divided into two parts, inflow and outflow, which are defined as the Neumann condition and the Dirichlet one, and the concentration of the latter could be calculated by the component in the adjacent sub-domain. Then the models in each sub-domain can be connected and solved. Taking a heterogeneous porous media as an example in which permanganate is partially dissolved during the process, firstly the result obtained by this method without considering porosity variation is compared to that from PHAST: good agreement is achieved, then while considering the change of porosity caused by the dissolution of the permanganate, the flow field, species concentration and porosity of the whole domain and typical sections and points during the reaction are analysed. It is concluded that: the decoupling approach to heterogeneous media is appropriate, and the results from the model could reflect the variation of physical fields due to groundwater in heterogeneous media.