Modeling the influence of aggregation on nanoparticle transport and retention in porous media
Abstract
A number of experimental studies relating to nanoparticle transport have observed the influence of particle-particle interactions (i.e., aggregation) on particle-soil grain interactions (i.e., deposition) in porous media. To date, however, nanoparticle transport models have neglected such particle-particle interactions. Here, a one-dimensional Lagrangian particle transport simulator is presented which couples particle transport and retention in porous media with particle-particle interactions. A random-walk particle-tracking approach is employed to simulate the transport of nanoparticles, with Smoluchowski's second-order expression for perikinetic aggregation incorporated to represent particle-particle interactions. Aggregates are treated as fractal objects to relate cluster mass to size, and a correlation developed by Tufenkji and Elimelech (2004) for single collector contact efficiency is implemented to describe time-dependent transport behavior of growing aggregates. A maximum collector capacity-based extension of colloid filtration theory was coupled with the particle straining of Bradford et al. (2003) to describe the retention of particles in the porous medium. The developed simulator is implemented in a sensitivity study to identify the most important physicochemical factors that influence aggregation and deposition of silver nanoparticles under steady flow conditions in uniform sands. Under reaction-limited conditions (i.e. an aggregation attachment efficiency of less than 1), for aggregation of particles with a primary diameter of 12nm, particle mobility (i.e. the percent elution of particles) increased with aggregation in a ca. 15 cm sand column due to a reduction in the magnitude of Brownian forces. For a substantially longer travel distance (i.e. field scale problems) or at a slower flow velocity (i.e. typical groundwater velocities), however, aggregates may become large enough for the interception, sedimentation, and/or straining processes to dominate Brownian process thereby hindering the particle transport. The results of the sensitivity study suggest that flow velocity, primary particle diameter, fractal dimension, and aggregation attachment efficiency are the primary factors influencing the fate of nanoparticles as they interact with the surrounding soil grains and with one another.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.H13E1387T
- Keywords:
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- 1805 HYDROLOGY / Computational hydrology;
- 1832 HYDROLOGY / Groundwater transport;
- 1847 HYDROLOGY / Modeling