Regulatory role of mobile fine particles in anomalous solute transport in porous media.

The co-transport of solute and fine particles (FPs) in aquifers increases the difficulty of accurate prediction of solute transport. However, there is a lack of mechanisms explaining the change in solute transport caused by FP retention. Therefore, we coupled computational fluid dynamics and discrete element method (CFD-DEM) alongside advection and dispersion equation (ADE) to investigate the co-transport processes. It was found that FPs play a regulatory role in the anomalous solute transport during co-transport: the change in FP deposition morphology makes the degree of anomalous solute transport decrease first then increase during co-transport (contrary to the variation trend of fitting parameter β in continuous-time random walk). The local pore clogging caused by FPs increases the percentage of solute storage zones (SSZs), thus induce significant anomalous solute transport, with a minimum β value reaching 1.43. However, due to deposition of FPs in the initial SSZs or formation of wider flow paths inside the agglomerations, the anomalous solute transport behavior will be alleviated. This study highlights the interaction between FP retention and anomalous solute transport in porous media such as soil and aquifer, providing novel insights into the accurate prediction of solute transport.