Hydrogel-encapsulated soil: a tool to measure contaminant attenuation in situ.
Hydrogel encapsulation presents a novel and powerful general method to observe many water-solid contaminant interactions in situ for a variety of aqueous media including groundwater, with a variety of nondestructive analytical methods, and with a variety of solids including contaminated soil. After intervals of groundwater immersion, polyacrylamide hydrogel-encapsulated solid specimens were retrieved, assayed nondestructively for uranium and other elements using X-ray fluorescence spectroscopy, and replaced in groundwater for continued reaction. Desorption dynamics of uranium from contaminated soils and other solids, when moved to uncontaminated groundwater, were fit to a general two-component kinetic retention model with slow-release and fast-release fractions for the total uranium. In a group of Oak Ridge soils with varying ambient uranium contamination (169-1360 mg/kg), the uranium fraction retained under long-term in situ kinetic behavior was strongly correlated (r(2) = 0.89) with residual uranium after laboratory sequential extraction of water-soluble and cation-exchangeable fractions of the soils. To illustrate how potential remedial techniques can be compared to natural attenuation, thermal stabilization of one soil increased the size of its long-term in situ retained fraction from 50% to 88% of the total uranium and increased the half-life of that long-term retained fraction from 990 to 40000 days.
Environmental Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6036, USA. spaldingbp@highland.net
Brian P
BP
Spalding
Scott C
SC
Brooks
David B
DB
Watson
D020100:Hydrogels; D012987:Soil; D012989:Soil Pollutants / Q000032:analysis*; D013050:Spectrometry, Fluorescence / Q000379:methods; D014501:Uranium / Q000032:analysis*; D014965:X-Rays
D020100:Hydrogels; D012987:Soil; D012989:Soil Pollutants; D014501:Uranium