Effect of Particle-Scale Heterogeneity on Uranium(VI) Transport in Unsaturated Porous Media
Uranium (VI) sorption and transport was evaluated in mixtures of silt loam and coarse sand sediments using traditional static batch sorption, saturated column, and unsaturated centrifugation experiments to evaluate the association of mobile and immobile water domains with particles of different size and surface reactivity. Exclusion of conservative tracers and a decrease in uranium sorption compared to what was predicted by the Kd-mass-avg value observed in sediment mixtures where the mass fraction of silt loam was 10%. This is consistent with behavior that was previously reported for coarse and fine sand separates. No exclusion of the conservative tracer, as predicted for the moderate water content range, was measured during unsaturated transport in sediment mixtures that contained 30% or more silt loam by mass. However, sorption was greater than predicted based on the Kd-mass-avg value, which suggests the fine-textured silt was in contact with the mobile water domain. This is the first evidence linking sorption to transport in a particular water domain. Results of this investigation demonstrate the interaction between the geochemical and hydrodynamic processes has a profound effect on transport in unsaturated sediments. In particular, analyses of the data from the experiments on sediment mixtures illustrate how the hydrodynamic conditions have a significant impact on the breakthrough of sorptive solutes. Definition of the fraction of mobile water was especially important for defining the front of the BTC, which is integral to predicting the arrival time of solutes at a particular depth/location in the sediment.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 924051
- Report Number(s):
- PNNL-SA-54849; 820201000; TRN: US0801972
- Journal Information:
- Vadose Zone Journal, 7(1):67-78, Vol. 7, Issue 1
- Country of Publication:
- United States
- Language:
- English
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