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Title: Coupled effects of hydrodynamic and solution chemistry conditions on long-term nanoparticle transport and deposition in saturated porous media

Author
item SASIDHARAN, SALINI - Commonwealth Scientific And Industrial Research Organisation (CSIRO)
item TORKZABAN, SAEED - Commonwealth Scientific And Industrial Research Organisation (CSIRO)
item Bradford, Scott
item DILLON, PETER - Commonwealth Scientific And Industrial Research Organisation (CSIRO)
item COOK, PETER - Commonwealth Scientific And Industrial Research Organisation (CSIRO)

Submitted to: Colloids and Surfaces A: Physicochemical and Engineering Aspects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2014
Publication Date: 6/5/2014
Citation: Sasidharan, S., Torkzaban, S., Bradford, S.A., Dillon, P.J., Cook, P.G. 2014. Coupled effects of hydrodynamic and solution chemistry conditions on long-term nanoparticle transport and deposition in saturated porous media. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 457:169-179.

Interpretive Summary: An understanding of nanoparticle (NP) transport and retention in soils and aquifers is needed for a wide range of environment applications, including risk assessment for pathogenic viruses. The objective of this study was to investigate the long-term retention behavior of NPs under different solution chemistry and water velocity conditions. Results indicate that multiple rates of NP retention occurred in soil due to spatial differences in retention sites and strengths, and controlling mass transfer processes. Furthermore, only a small fraction of the solid surface contributed to NP retention, and this fraction changed with the solution chemistry and water velocity conditions. A mathematical model was utilized to describe these observations. This information will be of interest to scientists and engineers concerned with predicting the fate of NPs in soils and groundwater.

Technical Abstract: This study aims to systematically explore the coupled effects of hydrodynamic and solution chemistry conditions on the long-term transport and deposition kinetics of nanoparticles (NPs) in saturated porous media. Column transport experiments were carried out at various solution ionic strengths (IS), ion types, and flow velocities utilizing negatively charged carboxyl-modified latex NPs of two different sizes (50 and 100 nm). These experiments were designed to obtain the long-term breakthrough curves (BTCs) in order to unambiguously determine the full deposition kinetics and the fraction of the solid surface area (Sf) that was available for NP deposition. The BTCs exhibited a bimodal shape with increasing solution IS; e.g., BTCs were initially delayed, next they rapidly increased, and then they slowly approached the influent particle concentration. NP deposition was much more pronounced in the presence of Ca2+ than Na+ at any given solution IS. Deposition dynamics of NPs was successfully simulated using a two-site kinetic model that accounted for irreversible deposition and blocking (e.g., a decreasing deposition rate as the site filled) on each site. Results showed that Sf values were controlled by the coupled effects of flow velocity, solution chemistry, and particle size. Data analyses further demonstrated that only a small fraction of solid surface area contributed in NP deposition even at the highest IS (60 mM) and lowest flow velocity (1 m/day) tested. Consistent with previous studies, our results imply that NP deposition occurred because of physicochemical interactions between the negatively charged COOH groups on the NPs and nanoscale physical and/or chemical heterogeneities on the sand surfaces that produced localized nanoscale favorable sites. Furthermore, our results suggest that the NP interactions with the collector surfaces tended to strengthen with increasing contact time.