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首页> 外文期刊>Environmental Science & Technology >Water Structure and Aqueous Uranyl(Ⅵ) Adsorption Equilibria onto External Surfaces of Beidellite, Montmorillonite, and Pyrophyllite: Results from Molecular Simulations
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Water Structure and Aqueous Uranyl(Ⅵ) Adsorption Equilibria onto External Surfaces of Beidellite, Montmorillonite, and Pyrophyllite: Results from Molecular Simulations

机译：贝得石，蒙脱石和叶蜡石外表面的水结构和铀酰（Ⅵ）水溶液的吸附平衡：分子模拟的结果

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摘要

Molecular dynamics simulations were performed to provide a systematic study of aqueous uranyl adsorption onto the external surface of 2:1 dioctahedral clays. Our understanding of this key process is critical in predicting the fate of radioactive contaminants in natural groundwaters. These simulations provide atomistic detail to help explain experimental trends in uranyl adsorption onto natural media containing smectite clays. Aqueous uranyl concentrations ranged from 0.027 to 0.162 M. Sodium ions and carbonate ions (0.027-0.243 M) were also present in the aqueous regions to more faithfully model a stream of uranyl-containing groundwater contacting a mineral system comprised of Na-smectite. No adsorption occurred near the pyrophyllite surface, and there was little difference in uranyl adsorption onto the beidellite and montmorillonite, despite the difference in location of clay layer charge between the two. At low uranyl concentration, the pentaaquouranyl complex dominates in solution and readily adsorbs to the clay basal plane. At higher uranyl (and carbonate) concentrations, the mono(carbonato) complex forms in solution, and uranyl adsorption decreases. Sodium adsorption onto beidellite occurred both as inner- and outer-sphere surface complexes, again with little effect on uranyl adsorption. Uranyl surface complexes consisted primarily of the pentaaquo cation (85%) and to a lesser extent the mono-(carbonato) species (15%). Speciation diagrams of the aqueous region indicate that the mono(carbonato)uranyl complex is abundant at high ionic strength. Oligomeric uranyl complexes are observed at high ionic strength, particularly near the pyrophyllite and montmorillonite surfaces. Atomic density profiles of water oxygen and hydrogen atoms are nearly identical near the beidellite and montmorillonite surfaces. Water structure therefore appears to be governed by the presence of adsorbed ions and not by the location of layer charge associated with the substrate. The water oxygen density near the pyrophyllite surface is similar to the other cases, but the hydrogen density profile indicates reduced hydrogen bonding between adsorbed water molecules and the surface.
机译：进行了分子动力学模拟，以系统研究铀基水溶液在2：1八面体粘土外表面的吸附情况。我们对这一关键过程的理解对于预测天然地下水中放射性污染物的命运至关重要。这些模拟提供了原子学上的细节，以帮助解释铀酰吸附到含有绿土的天然介质上的实验趋势。铀酰水溶液的浓度范围为0.027至0.162M。在含水区域中还存在钠离子和碳酸盐离子（0.027-0.243 M），以更真实地模拟与包含Na-蒙脱石的矿物系统接触的含铀酰的地下水流。在叶蜡石表面附近没有吸附发生，尽管在两者之间粘土层电荷的位置不同，但在铀基吸附到贝得石和蒙脱石上几乎没有差异。在低的铀酰浓度下，五萘醌基络合物在溶液中占主导地位，并容易吸附到粘土基面上。在较高的铀酰（和碳酸根）浓度下，单（碳酸根）络合物在溶液中形成，并且铀酰吸附降低。钠在贝得石上的吸附以内球和外球表面复合物的形式发生，对铀酰的吸附也几乎没有影响。铀酰表面复合物主要由五元阳离子组成（85％），在较小程度上由单（碳酸根）物种组成（15％）。水性区域的形态图表明，单（碳酸根）呋喃基络合物在高离子强度下含量很高。在高离子强度下，特别是在叶蜡石和蒙脱石表面附近观察到低聚的铀酰复合物。水氧和氢原子的原子密度分布在贝得石和蒙脱石表面附近几乎相同。因此，水结构似乎受吸附离子的存在支配，而不是受与基质相关的层电荷的位置支配。叶蜡石表面附近的水氧密度与其他情况相似，但是氢密度分布表明吸附的水分子与表面之间的氢键减少。

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  • 来源
    《Environmental Science & Technology》 |2006年第12期|p.3865-3871|共7页
  • 作者

    JEFFERY A. GREATHOUSE; RANDALL T. CYGAN;

  • 作者单位

    Geochemistry Department, Sandia National Laboratories, Albuquerque, New Mexico 87185-0754;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 环境化学;
  • 关键词

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