Aggregation, attachment, and transport of nanoscale titanium dioxide (nTiO₂) in subsurface environments: effects of complex water chemistry and medium

Rastghalam, Zahra Sadat (2019) Aggregation, attachment, and transport of nanoscale titanium dioxide (nTiO₂) in subsurface environments: effects of complex water chemistry and medium. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The transport of contaminants in subsurface environments is influenced by water chemistry and properties of the transport media. Due to the development and application of nanotechnology, engineered nanoparticles, such as nanoscale titanium dioxide (nTiO₂), are being released into the aquatic environment, which may pose serious hazards to the ecosystem. Extensive research has been performed to understand engineered nanoparticle’s fate and transport in groundwater. Many of the studies focus on the influence of simple water chemistry (e.g., pH, ionic strength, dissolved ions) and well-defined porous media (e.g., quartz sand or glass beads). The results obtained from some other studies emphasize the need to consider the effect of heterogeneous media, along with complex water chemistry, when evaluating engineered nanoparticle contamination risks. The objective of this thesis is to elucidate the effect of complex water chemistry and geochemically heterogeneous media on nTiO₂ transport and deposition, and the related mechanisms (e.g., ripening, precipitation, deposition, aggregation, blocking, straining) were explained. Batch experiments illustrated that nTiO₂ aggregation and attachment were strongly influenced by pH and Ca²⁺, both of which modified nTiO₂ surface charges. The effect of phosphate on nTiO₂ and illite attachment to sand was influenced by pH and cation valency. Moreover, illite attachment to sand was much lower than that of nTiO2 under all the conditions tested in this study. Results from column experiments showed that under complex physicochemical conditions, nTiO₂ transport is not only controlled by the interactions between nTiO₂ and common groundwater/aquifer components (e.g., suspended illite clay, phosphate, Fe oxyhydroxide coating) but also the interactions between these components. Finally, column experiments illustrated the importance of soil and sediment mineralogical and organic components, including Fe oxyhydroxides, clay (e.g., illite), and solid organic matter (e.g., peat moss) on nTiO₂ transport. Results from this thesis research contributed to the knowledge of the individual and synergistic effects of complex water chemistry and geochemically heterogeneous media on the fate and transport of engineered nanoparticles in natural environments.

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