University of Michigan, Ann Arbor, Michigan 48109, USA.
Environ Sci Technol. 2009 Dec 15;43(24):9368-73. doi: 10.1021/es902164n.
A study of U(VI) adsorption by aquifer sediment samples from a former uranium mill tailings site at Rifle, Colorado, was conducted under oxic conditions as a function of pH, U(VI), Ca, and dissolved carbonate concentration. Batch adsorption experiments were performed using <2 mm size sediment fractions, a sand-sized fraction, and artificial groundwater solutions prepared to simulate the field groundwater composition. To encompass the geochemical conditions of the alluvial aquifer at the site, the experimental conditions ranged from 6.8 x 10(-8) to 10(-5) M in U(VI), 7.2 to 8.0 in pH, 3.0 x 10(-3) to 6.0 x 10(-3) M in [Ca(2+)], and 0.05 to 2.6% in partial pressure of carbon dioxide. Surface area normalized U(VI) adsorption K(d) values for the sand and <2 mm sediment fraction were similar, suggesting a similar reactive surface coating on both fractions. A two-site two-reaction, nonelectrostatic generalized composite surface complexation model was developed and successfully simulated the U(VI) adsorption data. The model successfully predicted U(VI) adsorption observed from a multilevel sampling well installed at the site. A comparison of the model with the one developed previously for a uranium mill tailings site at Naturita, Colorado, indicated that possible calcite nonequilibrium of dissolved calcium concentration should be evaluated. The modeling results also illustrate the importance of the range of data used in deriving the best fit model parameters.
对科罗拉多州里弗尔（Rifle）一处前铀矿尾矿场含水层沉积物样本进行的铀（VI）吸附研究，在有氧条件下进行，考察了 pH 值、U（VI）、Ca 和溶解碳酸根浓度等因素对 U（VI）吸附的影响。采用<2mm 粒径的沉积物、沙粒径以及人工地下水溶液进行批式吸附实验，这些人工地下水溶液的配制模拟了现场地下水中的成分。为了涵盖该场址冲积含水层的地球化学条件，实验条件下 U（VI）（总）浓度为 6.8 x 10(-8) 到 10(-5) M，pH 值为 7.2 到 8.0，[Ca(2+)]为 3.0 x 10(-3) 到 6.0 x 10(-3) M，二氧化碳分压为 0.05 到 2.6%。沙粒和<2mm 粒径沉积物的比表面积归一化 U（VI）吸附 K(d) 值相似，这表明这两种粒径的沉积物具有相似的反应性表面涂层。建立了一个两位置两反应、非静电广义复合表面络合模型，并成功模拟了 U（VI）吸附数据。该模型成功预测了在该场址安装的多井采样井中观察到的 U（VI）吸附。将该模型与之前为科罗拉多州纳图拉（Naturita）的一处铀矿尾矿场开发的模型进行比较表明，应评估溶解钙浓度的方解石非平衡问题。建模结果还说明了在得出最佳拟合模型参数时所使用的数据范围的重要性。
