Kinetic Desorption and Sorption of U(VI) during Reactive Transport in a Contaminated Hanford Sediment
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- 作者：Nikolla P. Qafoku ; John M.Zachara ; Chongxuan Liu ; Paul L.Gassman ; Odeta S. Qafoku ; and Steven C. Smith
- 刊名：Environmental Science & Technology
- 出版年：2005
- 出版时间：May 1, 2005
- 年：2005
- 卷：39
- 期：9
- 页码：3157 - 3165
- 全文大小：371K
- 年卷期：v.39,no.9(May 1, 2005)
- ISSN：1520-5851
文摘
Column experiments were conducted to investigate U(VI)desorption and sorption kinetics in a sand-textured, U(VI)-contaminated (22.7 
mol kg-1) capillary fringe sedimentfrom the U.S. Department of Energy (DOE) Hanford site.Saturated column experiments were performed under mildlyalkaline conditions representative of the Hanford sitewhere uranyl-carbonate and calcium-uranyl-carbonatecomplexes dominate aqueous speciation. A U(VI)-freesolution was used to study contaminant U(VI) desorptionin columns where different flow rates were applied. Sorbed,contaminant U(VI) was partially labile (11.8%), andextended leaching times and water volumes were requiredfor complete desorption of the labile fraction. Uranium(VI) sorption was studied after the desorption of labile,contaminant U(VI) using different U(VI) concentrations in theleaching solution. Strong kinetic effects were observedfor both U(VI) sorption and desorption, with half-life rangingfrom 8.5 to 48.5 h for sorption and from 39.3 to 150 h fordesorption. Although U(VI) is semi-mobile in mildly alkaline,subsurface environments, we observed substantial U(VI)adsorption, significant retardation during transport,and atypical breakthrough curves with extended tailing. Adistributed rate model was applied to describe theeffluent data and to allow comparisons between thedesorption rate of contaminant U(VI) with the rate of short-term U(VI) sorption. Desorption was the slower process.We speculate that the kinetic behavior results from transportor chemical phenomena within the phyllosilicate-dominated fine fraction present in the sediment. Ourresults suggest that U(VI) release and transport in thevadose zone and aquifer system from which the sedimentwas obtained are kinetically controlled.
mol kg-1) capillary fringe sedimentfrom the U.S. Department of Energy (DOE) Hanford site.Saturated column experiments were performed under mildlyalkaline conditions representative of the Hanford sitewhere uranyl-carbonate and calcium-uranyl-carbonatecomplexes dominate aqueous speciation. A U(VI)-freesolution was used to study contaminant U(VI) desorptionin columns where different flow rates were applied. Sorbed,contaminant U(VI) was partially labile (11.8%), andextended leaching times and water volumes were requiredfor complete desorption of the labile fraction. Uranium(VI) sorption was studied after the desorption of labile,contaminant U(VI) using different U(VI) concentrations in theleaching solution. Strong kinetic effects were observedfor both U(VI) sorption and desorption, with half-life rangingfrom 8.5 to 48.5 h for sorption and from 39.3 to 150 h fordesorption. Although U(VI) is semi-mobile in mildly alkaline,subsurface environments, we observed substantial U(VI)adsorption, significant retardation during transport,and atypical breakthrough curves with extended tailing. Adistributed rate model was applied to describe theeffluent data and to allow comparisons between thedesorption rate of contaminant U(VI) with the rate of short-term U(VI) sorption. Desorption was the slower process.We speculate that the kinetic behavior results from transportor chemical phenomena within the phyllosilicate-dominated fine fraction present in the sediment. Ourresults suggest that U(VI) release and transport in thevadose zone and aquifer system from which the sedimentwas obtained are kinetically controlled.