Kohler Matthias, Curtis Gary P, Meece David E, Davis James A
Environmental Science and Engineering Division, Colorado School of Mines, Golden, Colorado 80401, USA.
Environ Sci Technol. 2004 Jan 1;38(1):240-7. doi: 10.1021/es0341236.
Assessing the quantity of U(VI) that participates in sorption/desorption processes in a contaminated aquifer is an important task when investigating U migration behavior. U-contaminated aquifer sediments were obtained from 16 different locations at a former U mill tailings site at Naturita, CO (U.S.A.) and were extracted with an artificial groundwater, a high pH sodium bicarbonate solution, hydroxylamine hydrochloride solution, and concentrated nitric acid. With an isotopic exchange method, both a KD value for the specific experimental conditions as well as the total exchangeable mass of U(VI) was determined. Except for one sample, KD values determined by isotopic exchange with U-contaminated sediments that were in equilibrium with atmospheric CO2 agreed within a factor of 2 with KD values predicted from a nonelectrostatic surface complexation model (NEM) developed from U(VI) adsorption experiments with uncontaminated sediments. The labile fraction of U(VI) and U extracted by the bicarbonate solution were highly correlated (r2 = 0.997), with a slope of 0.96 +/- 0.01. The proximity of the slope to one suggests that both methods likely access the same reservoir of U(VI) associated with the sediments. The results indicate that the bicarbonate extraction method is useful for estimating the mass of labile U(VI) in sediments that do not contain U(IV). In-situ KD values calculated from the measured labile U(VI) and the dissolved U(VI) in the Naturita alluvial aquifer agreed within a factor of 3 with in-situ KD values predicted with the NEM and groundwater chemistry at each well.
在研究铀的迁移行为时，评估受污染含水层中参与吸附/解吸过程的U(VI)的量是一项重要任务。从美国科罗拉多州纳图里塔市一个以前的铀矿尾矿场的16个不同地点获取了受铀污染的含水层沉积物，并用人工地下水、高pH值的碳酸氢钠溶液、盐酸羟胺溶液和浓硝酸进行萃取。采用同位素交换法，测定了特定实验条件下的KD值以及U(VI)的总可交换质量。除了一个样品外，通过与与大气CO2处于平衡状态的受铀污染沉积物进行同位素交换测定的KD值，与根据用未受污染沉积物进行的U(VI)吸附实验开发的非静电表面络合模型（NEM）预测的KD值在2倍因子范围内一致。碳酸氢盐溶液萃取的U(VI)和U的不稳定部分高度相关（r2 = 0.997），斜率为0.96 +/- 0.01。斜率接近1表明这两种方法可能获取的是与沉积物相关的同一U(VI)储库。结果表明，碳酸氢盐萃取法可用于估算不含U(IV)的沉积物中不稳定U(VI)的质量。根据纳图里塔冲积含水层中测得的不稳定U(VI)和溶解的U(VI)计算出的原位KD值，与用NEM和各井地下水化学预测的原位KD值在3倍因子范围内一致。
