HR: 0800h
AN: H51G-0857    [Abstracts]
TI: Transport of engineered zeolite and natural nanoparticles in porous media
AU: * Keller, A A
EM: keller@bren.ucsb.edu
AF: University of California, 3420 Bren Hall UCSB, Santa Barbara, CA 93106, United States
AU: Wang, P
EM: pwang@bren.ucsb.edu
AF: University of California, 3420 Bren Hall UCSB, Santa Barbara, CA 93106, United States
AB: There are many natural nanoparticles (NPs) that are ubiquitous in the environment such as soil and sediment colloids. In addition, many new engineered NPs, such as tailored zeolites, are being developed for applications in which they may be released into the environment. The fate and transport of the NPs is very much related with contaminant fate and transport. This study focused on transport of engineered zeolite nanoparticles (NPs) and natural soil and sediment colloidal NPs within porous media under saturated conditions. Clean medium-sized sand grains were used as the porous media and NPs were injected into the column as a pulse. KCl or CaCl2 with varying concentrations was used as background electrolyte. The results showed that, interestingly, the zeta- potential of the natural colloids and Zeolite-Ca decreased (more negative) with increasing KCl concentration while increased (less negative) with increasing CaCl2 concentration. This unexpected results was attributed to the fact that the natural colloids and Zeolite-Ca are saturated with divalent cations (Ca2+ and/or Mg2+) originally and the replacement of these divalent cations with K+ on the colloid surfaces caused the zeta-potential to drop with increasing KCl concentrations. The zeta-potential measurement of Zeolite-K increased with either KCl or CaCl2 concentration. Consistently early breakthrough was observed for NP compared with conservative tracers (KCL or CaCl2) and the effect was more pronounced with higher water flowrate. Zeolite-K showed significantly higher degree of transport (defined as percent of NPs transported out of the column) than Zeolite-Ca under the otherwise same conditions. With KCl as the background electrolyte, the significantly higher NP transport was observed than with CaCl2. Overall, as the ionic strength of the flowing fluid increased, the transport of the NPs decreased, largely due to the compressed double layer under the higher ionic strength. Besides, as the flow rate of the flowing fluid increased, the transport of the NPs increased due to less interaction time between the NPs and the porous media. Analysis of NP transport data showed that Zeolite-Ca fell into the same category as natural colloids while Zeolite-K deviated significantly from the others, suggesting the cations on the cation exchange capacity (CEC) sites play a large role in NP transport. Our results also revealed that the CEC/(surface area) can be a good indicator for predicting relative transport of the NP within the same group. An empirical model was developed to predict NP transport under the experimental conditions. The model parameters include flow rate, ionic strength of the solution, charge density (CEC/surface area). In sum, for the hydrophilic colloids, the chemistry (such as cation species) on the colloids surfaces and flowing fluid is important for predicting their transport in the environment.
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1834 Human impacts
SC: Hydrology [H]
MN: 2007 Fall Meeting