A theoretical model to predict the influence of physicochemical conditions on colloid transport, attachment, detachment, and blocking in porous media

Authors: Bradford, Scott; LIN, DANTONG - Lanzhou University

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2024
Publication Date: 12/12/2024
Citation: Bradford, S.A., Lin, D. 2024. A theoretical model to predict the influence of physicochemical conditions on colloid transport, attachment, detachment, and blocking in porous media. Journal of Hydrology. 650. Article 132483. https://doi.org/10.1016/j.jhydrol.2024.132483.
DOI: https://doi.org/10.1016/j.jhydrol.2024.132483

Interpretive Summary: Mathematical models are needed to predict the fate of colloids (such as clays, dissolved organic matter, microbes, and nanoparticles) in soils and sediments for many industrial and environmental applications. However, colloid transport is sensitive to many factors that are poorly quantified in existing models. An improved modeling approach was developed to predict the fate of colloids in soils by accounting for underlying removal processes, including attachment, detachment, and blocking. Model results show expected removal trends for different colloid and grain sizes, water velocities, solution and solid phase chemistries, and various amounts and types of heterogeneities on grain surfaces. This information will be of use to scientists, engineers, consultants, and public health officials that are concerned with risk assessment from colloids (e.g., pathogens and nanoparticles) and associated contaminants. It will also aid in the design of processes that are influenced by colloids such as water treatment, managed aquifer recharge, petroleum recovery, and cleaning of surfaces.

Technical Abstract: Knowledge of the transport of colloids (including clays, dissolved organic matter, microorganisms, and nanoparticles) and colloid-associated contaminants in porous media is needed for many industrial and environmental applications. However, mathematical models of colloid transport are limited by difficulty in predicting the sensitivity of parameters to a wide range of physicochemical conditions. This paper presents an approach to predict the influence of physicochemical conditions on colloid transport, attachment, detachment, and blocking. Collector surfaces can have selected amounts, sizes, and/or distributions of nanoscale charge heterogeneity (CH), nanoscale roughness (NR), and microscopic roughness (MR). The model employs filtration theory to predict colloid mass transfer to and from collector surfaces. Upscaled values of attachment and detachment efficiencies, the maximum retention capacity, and the probability for colloids to enter from the secondary to the primary minimum are determined by conducting torque and energy balance calculations over the heterogeneous surface of the porous medium. This analysis considered distributions of applied hydrodynamic torques, interaction energy profiles, resisting adhesive torques, and a Maxwellian kinetic energy distribution for diffusing colloids. Simulated breakthrough curves, low concentration tailing, blocking, and deposition profiles show expected trends with CH, NR, MR, zeta potential, solution ionic strength, collector size, colloid size, Darcy velocity, and colloid input concentration. New insights are gained about the important role of hydrodynamics on colloid attachment and detachment. Parameters also show that colloids in a secondary minimum may transition to a primary minimum. This has important implications for one-site and two-site kinetic models of colloid attachment and detachment.