The impact of nanoparticle aggregation on their size exclusion during transport in porous media: One- and three-dimensional modelling investigations

Abstract

Greater particle mobility in subsurface environments due to larger size, known as size exclusion, has been responsible for colloid-facilitated transport of groundwater contaminants. Although size exclusion is not expected for primary engineered nanoparticles (NP), they can grow in size due to aggregation, thereby undergoing size exclusion. To investigate this hypothesis, an accurate population balance modelling approach and other colloid transport theories, have been incorporated into a three-dimensional transport model, MT3D-USGS. Results show that incorporating aggregation into the transport model improves the predictivity of current theoretical and empirical approaches to NP deposition in porous media. Considering an artificial size-variable acceleration factor in the model, NP breakthrough curves display an earlier arrival when aggregation is included than without. Disregarding the acceleration factor, aggregation enhances NP mobility at regions close to the injection point at a field scale and causes their retention at greater distances through alteration of their diffusivities, secondary interaction-energy minima, and settling behaviour. This results in a change of residual concentration profiles from exponential for non-aggregating dispersions to non-monotonic for aggregating dispersions. Overall, aggregation, hitherto believed to hinder the migration of NP in subsurface porous media, may under certain physicochemical conditions enhance their mobilities and deliver them to further distances.

Modeling the Transport of Aggregating Nanoparticles in Porous Media

“…(2015) obtained the same result by developing a Lagrangian model that accounted for aggregation and incorporated the population balance Equation . Contrarily, Babakhani (2019) reported that for a specific size range of nanoparticles when aggregation was accounted for, the breakthrough concentration decreased (as also shown in Figure 5c). The differences in the results presented by the various authors are caused by the attachment behavior, because an increase in nanoparticle aggregate size may lead to either increased or decreased attachment (see Figure 2).…”

“…Other models use simplifying or empirical reaction rates (Babakhani et al., 2019), and general attachment equations (Wang et al., 2018) to account for transport and aggregation of particles. The mathematical model developed by Babakhani (2019) takes into account transport and aggregation of nanoparticles and evaluates their size exclusion. It was shown that accounting for particle aggregation improved substantially the predictive ability of the model.…”

“…It was shown that accounting for particle aggregation improved substantially the predictive ability of the model. However, the Babakhani (2019) mathematical model does not contain explicit transport and aggregation terms and does not account for thorough particle attachment onto the solid matrix (e.g., with a two site reversible/irreversible kinetic model).…”

Comparison of the colloidal stability, mobility, and performance of nanoscale zerovalent iron and sulfidated derivatives

“…Relatively lower spikes in Fe concentration were observed in the nZVI and S-nZVI columns around 24-30 PV s. However, S-nZVI had the highest elution in the last 10 PV. The earlier breakthrough of FeSSi likely resulted from size exclusion effects due to its larger size (200 nm) compared to the other two NPs (nZVI = 60 nm, and S-nZVI = 100 nm) (Babakhani, 2019). Size exclusion refers to the exclusion of particles from pores and stagnant domains that have smaller diameter or are less accessible, which allows larger particles to have higher mobility/breakthrough (Sirivithayapakorn and Keller, 2003).…”

Nanomaterials and Annelid Immunity: A Comparative Survey to Reveal the Common Stress and Defense Responses of Two Sentinel Species to Nanomaterials in the Environment

“…Surprisingly, an unexpected decrease in the effect, in terms of interference with the correct development of larvae, was observed at the highest exposure concentration of MWCNTs (9.00 mg/L). This apparent reduction in the toxic effect at high concentrations is probably due to the formation of large MWCNT aggregates that, through precipitating on the seabed by gravitational sedimentation [ 95 , 96 ], interact less with the larvae.…”