reactiontransport

Reactive transport, also known as reaction-transport, is the study of how chemical species move and react within a flowing medium. It combines physical transport processes such as advection and dispersion with chemical reactions that may occur in the fluid phase or on mineral surfaces. The framework is used in environmental engineering, hydrogeology, geochemistry, and chemical engineering to predict the fate, distribution, and transformation of substances such as contaminants, nutrients, and tracers.

Mathematically, for each species i with concentration Ci, the balance is often written as ∂Ci/∂t + ∇·(u Ci) = ∇·(D ∇ Ci) + Ri(C,t). Here u is the advective velocity field, D is the dispersion-diffusion tensor, and Ri represents the net rate of production or loss due to chemical reactions, which may depend on multiple species and context (linear or nonlinear, homogeneous or surface-catalyzed).

In porous media, the flow field u commonly follows Darcy's law, linking velocity to pressure and permeability; porosity, sorption, and nonlinear kinetics can modify transport. Solutions rely on numerical methods such as finite difference, finite element, or finite volume schemes and often require coupling to hydrological models. Dimensionless groups like Peclet and Damköhler numbers help characterize transport-dominated versus reaction-dominated regimes and guide upscaling from pore-scale to continuum-scale descriptions.

Applications include predicting contaminant plumes and remediation effectiveness, nutrient cycling in soils, CO2 sequestration and mineral trapping, and performance assessment in catalytic reactors or energy storage materials.