Uranium contamination of soils and sediments often originates from acidic or alkaline waste sources,with diffusion being a majortransport mechanism.Measurements of U(VI)diffusion from initially pH 2 and pH 11 solutions into a slightly alkaline Altamont soil and a neutral Oak Ridge soil were obtained through monitoring uptake from boundary reservoirs and from U concentration profiles within soil columns.The soils provided pH buffering,resulting in diffusion at nearly constant pH.Micro X-ray absorption near edge structure spectra confirmed that U remained in U(VI)forms in all soils.Time trends of U(VI)depletion from reservoirs and U(VI)concentration profiles within soil columns yielded k_d values consistent with those determined in batch tests at similar concentrations(=1 mM)and much lower than values for sorption at much lower concentrations(nM to muM).These results show that U(VI)transport at high concentrations can be relatively fast at non-neutral pH,with negligible surface diffusion,because of weak sorption.
展开▼
Lawrence Berkeley National Laboratory,Berkeley,California 94720,University of California,Berkeley,California 94720,and University of Chicago,Chicago,Illinois 60637;
