| Abstract
| - Uranium contamination of soils and sediments oftenoriginates from acidic or alkaline waste sources, withdiffusion being a major transport mechanism. Measurementsof U(VI) diffusion from initially pH 2 and pH 11 solutionsinto a slightly alkaline Altamont soil and a neutral Oak Ridgesoil were obtained through monitoring uptake fromboundary reservoirs and from U concentration profileswithin soil columns. The soils provided pH buffering, resultingin diffusion at nearly constant pH. Micro X-ray absorptionnear edge structure spectra confirmed that U remainedin U(VI) forms in all soils. Time trends of U(VI) depletion fromreservoirs and U(VI) concentration profiles within soilcolumns yielded Kd values consistent with those determinedin batch tests at similar concentrations (≈1 mM) andmuch lower than values for sorption at much lowerconcentrations (nM to μM). These results show that U(VI)transport at high concentrations can be relatively fast at non-neutral pH, with negligible surface diffusion, because of weaksorption.
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