The dissolution of synthetic Na-boltwoodite in sodium carbonate solutions
The dissolution of synthetic Na-boltwoodite in sodium carbonate solutions
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DOI：
10.1016/j.gca.2006.06.1553
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发表时间：
2006-10
影响因子：
5
通讯作者：
E. Ilton;Chongxuan Liu;W. Yantasee;Zhemin Wang;D. Moore;A. Felmy;J. Zachara
中科院分区：
文献类型：
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作者：
E. Ilton;Chongxuan Liu;W. Yantasee;Zhemin Wang;D. Moore;A. Felmy;J. Zachara
铀酰硅酸盐，例如铀闪石和钠水铀云母，似乎控制了铀在美国能源部Hanford地点的某些受污染沉积物中的溶解度[Liu，C.，扎卡拉，J. M.，卡福库岛，麦金利，J. P.，希尔德，S. M.，Wang， Z. 2004.美国汉福德场址地下沉积物中铀酰微沉淀物的溶解。地球化学。宇宙化学。法案68，4519-4537。]。因此，在从近中性到碱性pH值的宽范围碳酸氢盐浓度下测定了合成钠镁橄榄石Na（UO 2）（SiO 3OH）·1.5H2O的溶解度，这通常代表了汉福德遗址和钙质环境的孔隙水和地下水成分。实验是开放的。结果表明，Na-boltwodite的溶解度和溶解动力学均随碳酸氢盐浓度和pH值的增加而增加，在近中性pH（0 ~ 50 mM）和碱性pH（50 mM）范围内，Na-boltwodite的溶解度常数基本一致。平均logKspo=5.86±0.24或5.85±0.0.26;分别使用Pitzer离子相互作用模型或Davies方程。这些值接近于由[Nguyen，S.N.，席尔瓦，R. J.，威德，华盛顿小安德鲁斯，J.E.，1992.在303.15K温度下四种铀酰硅酸盐的标准吉布斯自由能：钠方钠石、铀闪石、钠硼铀石和钠铁矾。化学热力学杂志24，359-376。]在非常不同的条件下（pH 4.5，Ar气氛）。
Uranyl silicates such as uranophane and Na-boltwoodite appear to control the solubility of uranium in certain contaminated sediments at the US Department of Energy Hanford site [Liu, C., Zachara, J.M., Qafoku, O., McKinley, J.P., Heald, S.M., Wang, Z. 2004. Dissolution of uranyl microprecipitates in subsurface sediments at Hanford Site, USA. Geochim. Cosmochim. Acta68, 4519–4537.]. Consequently, the solubility of synthetic Na-boltwoodite, Na(UO2)(SiO3OH)·1.5H2O, was determined over a wide range of bicarbonate concentrations, from circumneutral to alkaline pH, that are representative of porewater and groundwater compositions at the Hanford site and calcareous environments generally. Experiments were open to air. Results show that Na-boltwoodite dissolution was nearly congruent and its solubility and dissolution kinetics increased with increasing bicarbonate concentration and pH. A consistent set of solubility constants were determined from circumneutral pH (0 added bicarbonate) to alkaline pH (50mM added bicarbonate). Average logKspo=5.86±0.24 or 5.85±0.0.26; using the Pitzer ion-interaction model or Davies equation, respectively. These values are close to the one determined by [Nguyen, S.N., Silva, R.J., Weed, H.C., Andrews, Jr., J.E., 1992. Standard Gibbs free energies of formation at the temperature 303.15K of four uranyl silicates: soddyite, uranophane, sodium boltwoodite, and sodium weeksite. J. Chem. Thermodynamics24, 359–376.] under very different conditions (pH 4.5, Ar atmosphere).