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首页> 外文期刊>Marine Chemistry >Retention behavior of dissolved uranium during ultrafiltration: Implications for colloidal U in surface waters
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Retention behavior of dissolved uranium during ultrafiltration: Implications for colloidal U in surface waters

机译：超滤过程中溶解铀的保留行为：对地表水中胶态铀的影响

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摘要

While uranium (U) in natural waters is very soluble and highly mobile as U(VI), a colloidal, ultrafilterable, form of U was, at times, reported to be important. Laboratory experiments were thus carried out to examine the behavior of dissolved U during ultrafiltration (1 kDa, Amicon S1OY1) of both natural (containing colloids) and spiked artificial river waters (containing no colloids). In addition, the distribution of dissolved and colloidal U was determined for samples collected across a salinity gradient in Galveston Bay (Texas, USA) using ICP-MS. Results of laboratory experiments showed that the constant permeation model can be used to predict the ultrafiltration behavior of U in both natural and synthetic river waters. Most importantly, we found that low molecular weight (< 1 kDa) U can indeed be retained by a 1 kDa membrane by as much as 30-60%. This behavior is similar to that previously reported for SO_4, a major anion in sea water, and suggests an artifactual retention of dissolved U through preferential rejection by negatively charged membranes. Concentrations of total dissolved U increased from 2.9±0.9 nmol kg~(-1) in the Trinity River freshwater endmember to 8-9 nmol kg~(-1) in higher salinity estuarine waters of Galveston Bay. The annual export flux of dissolved U from the Trinity River was estimated to be 6.3 × 10~4 moles, corresponding to a weathering rate of 0.75 moles-U/km~2/yr in the Trinity River basin. Colloidal U, derived using the ultrafiltration permeation model, accounted for ～15% of the total dissolved U in river waters but was negligible in the higher salinity coastal waters. Therefore, apparent colloidal U concentrations calculated from the concentration difference between initial and permeate solutions, or measured directly from the retentate solution under low concentration factors (ratio of initial volume to final volume of retentate), can be significantly overestimated compared with truly colloidal U concentrations derived from the ultrafiltration permeation model. The association of dissolved U with nanoparticles and macromolecular organic matter in higher salinity seawater seems minimal and most dissolved U in seawater should be in the form of anionic U with a molecular weight < 1 kDa.
机译：尽管天然水中的铀（U）与U（VI）一样易溶且具有很高的移动性，但据报道有时会以胶体，超滤形式的U形式发挥重要作用。因此，进行了实验室实验，以检查天然（含有胶体）和加标人工河水（不含胶体）的超滤（1 kDa，Amicon S1OY1）中溶解的铀的行为。此外，使用ICP-MS测定了在加尔维斯顿湾（美国得克萨斯州）的盐度梯度范围内采集的样品中溶解和胶态U的分布。实验室实验结果表明，恒定渗透模型可用于预测天然和合成河水中铀的超滤行为。最重要的是，我们发现低分子量（<1 kDa）U确实可以被1 kDa膜保留多达30-60％。此行为类似于先前报道的海水中主要阴离子SO_4的行为，并表明通过带负电荷的膜的优先排斥作用，溶解的U可以人为保留。总溶解铀的浓度从三一河淡水终端成员中的2.9±0.9 nmol kg〜（-1）增加到加尔维斯顿湾高盐度河口水中的8-9 nmol kg〜（-1）。三位一体河的溶解性铀的年出口通量估计为6.3×10〜4摩尔，相当于三位一体河流域的风化率为0.75摩尔-U / km〜2 / yr。使用超滤渗透模型得到的胶态铀约占河水中溶解铀总量的约15％，但在盐度较高的沿海水域可忽略不计。因此，与真正的胶态U浓度相比，根据初始溶液和渗透液之间的浓度差计算得出的表观胶态U浓度，或在低浓度因子（初始体积与最终滞留物的比值）下直接从截留液中测量得出的明显胶态U浓度。来自超滤渗透模型。在较高盐度的海水中溶解的U与纳米颗粒和高分子有机物的结合似乎很少，海水中大多数溶解的U应以分子量小于1 kDa的阴离子U的形式存在。

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