Influence of clay colloids, humic acid and water chemistry on the stability, aggregation and deposition of nanoscale titanium dioxide (nTiO₂)

Abstract

Fate and transport of engineered nanoscale titanium dioxide (nTiO₂) have received much attention during the past decade. The stability, concurrent aggregation and deposition of nTiO₂ in water with complicated components, however, have not been fully examined. The objective of this thesis was to determine the individual and synergistic effect of pH, cation valence, humic acid, Fe/Al oxyhydroxide coatings and clay colloids on nTiO₂ stability, aggregation and deposition, and elucidate the related mechanisms. We conducted systematic laboratory experiments to determine nTiO2 stability, aggregation and deposition onto a quartz sand in NaCl and MgCl₂ solutions, both in the absence and presence of humic acid and clay colloids. Results showed that nTiO₂ formed hetero-aggregates and the heteroaggregates may either deposit or remain suspended depending on their interactions with quartz sand and Fe/Al oxyhydroxide coatings. Humic acid was found to make nTiO₂ stable to prevent nTiO₂ aggregation and deposition under most conditions.