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Two‐region flow and rate‐limited sorption of uranium (VI) during transport in an unsaturated silt loam
Author(s) -
Gamerdinger A. P.,
Kaplan D. I.,
Wellman D. M.,
Serne R. J.
Publication year - 2001
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2001wr000244
Subject(s) - sorption , saturation (graph theory) , loam , mass transfer , flow velocity , partition coefficient , centrifuge , soil science , volumetric flow rate , water flow , moisture , chemistry , tracer , analytical chemistry (journal) , mineralogy , materials science , thermodynamics , flow (mathematics) , geology , environmental chemistry , chromatography , adsorption , soil water , mechanics , mathematics , physics , organic chemistry , combinatorics , nuclear physics
Uranium (VI) sorption during unsaturated transport was evaluated using a centrifuge method; conventional saturated columns and batch incubation procedures were used to isolate flow effects on sorption processes. Uranium (VI) sorption was dependent on flow velocity, and modeling indicated that 60% of sorption was rate‐limited. Breakthrough curves were described and independently predicted with a two‐site model; the mass transfer coefficient for sorption was assumed to be linearly related to velocity. While two‐region flow contributed to disparity in apparent K d values (linear distribution coefficient) at different water contents, the effect was explained by increased velocity in the mobile flow domain and not a decrease in availability of sorption sites. Hydrodynamic parameters for two‐region transport, determined for a nonsorptive tracer at faster velocity (16 cm h −1 ), were fixed and described U(VI) transport at slower velocity (2 cm h −1 ). The rate‐limited parameter for mass transfer between mobile and immobile water domains was linearly related to the average pore water velocity. Effective retardation factors varied with moisture saturation and the apparent K d value and ranged from 7 for faster velocity experiments in a saturated column to 44 at slow velocity and 40% moisture saturation.