Aggregation and deposition of energetic nanoparticles in aqueous environments

New kinds of solid fuels and propellants comprised of nanomaterials are making their way into civilian and military applications yet the impact of their release on the environment remains largely unknown. Two such materials are boron and silicon nanoparticles (NPs). In this work, the effects of solution chemistry on the aggregation kinetics of these NPs were investigated, whereas sand column experiments were used to examine their transport behavior under saturated conditions. The role of two kinds of natural organic matter (NOM), i.e. Suwannee River humic acid (SRHA) and sodium alginate, on the aggregation and transport behavior of these NPs was also investigated.;Aggregation tests indicated the presence of reaction-controlled and diffusion-controlled regimes and yielded different critical coagulation concentrations (CCC) for various cations. Aggregation and deposition experimental data corresponded with the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) model and the clean-bed filtration model, respectively. Theoretical calculations indicated that both the primary and secondary energy minima play important roles in the deposition of NPs in the column experiments.;The presence of various ions and NOMs made the transport behavior of the NPs more complicated. The addition of NOM caused the boron NPs to stabilize in various electrolytes except in the presence of alginate and high Ca 2+ concentration, where the aggregation of boron NPs was enhanced. The stabilization of boron NPs in the presence of NOM is attributed to the increased electrostatic repulsion; while the induced destabilization is attributed to the affiliation of adsorbed alginate with Ca2+ as observed in the transmission electron microscope images.;The aggregation study of silicon NPs was qualitatively consistent with the traditional DLVO model. Enhanced aggregation was observed in the presence of SRHA and Ca2+, which was attributed to bridging generated by the SRHA-Ca2+-NPs aggregates. The deposition and re-entrainment of silicon NPs in the column experiments corresponded well with the theoretical DLVO energy interaction. It appears that steric effects contributed to the enhanced transport of silicon NPs in the presence of SRHA. Hence, the determination of the type of electrolytes and NOM are equally important as the nature of NPs for the prediction of their fate and transport.