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Quantifying uranium complexation by groundwater dissolved organic carbon using asymmetrical flow field-flow fractionation

机译:使用非对称流场-流分馏定量分析地下水溶解的有机碳引起的铀络合

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The long-term mobility of actinides in groundwaters is important for siting nuclear waste facilities and managing waste-rock piles at uranium mines. Dissolved organic carbon (DOC) may influence the mobility of uranium, but few field-based studies have been undertaken to examine this in typical groundwaters. In addition, few techniques are available to isolate DOC and directly quantify the metals complexed to it. Determination of U-organic matter association constants from analysis of field-collected samples compliments laboratory measurements, and these constants are needed for accurate transport calculations. The partitioning of U to DOC in a clay-rich aquitard was investigated in 10 groundwater samples collected between 2 and 30 m depths at one test site. A positive correlation was observed between the DOC (4-132 mg/L) and U concentrations (20-603 μg/L). The association of U and DOC was examined directly using on-line coupling of Asymmetrical Flow Field-Flow Fractionation (AsFlFFF) with UV absorbance (UVA) and inductively coupled plasma-mass spectrometer (ICP-MS) detectors. This method has the advantages of utilizing very small sample volumes (20-50 μL) as well as giving molecular weight information on U-organic matter complexes. AsFlFFF-UVA results showed that 47- . 98% of the DOC (4-136 mg C/L) was recovered in the AsFlFFF analysis, of which 25-64% occurred in the resolvable peak. This peak corresponded to a weight-average molecular weight of about 900-1400 Daltons (Da). In all cases, AsFlFFF-ICP-MS suggested that ≤ 2% of the U, likely present as U(VI), was complexed with the DOC. This result was in good agreement with the U speciation modeling performed on the sample taken from the 2.3 m depth, which predicted approximately 3% DOC-complexed U. This good agreement suggests that the AsFlFFF-ICP-MS method may be very useful for determining U-organic matter association in small volume samples. Because the pH (7.0-8.1) and carbonate concentrations of these waters are typical of many groundwaters, these data suggested that facilitated transport of U by DOC may be limited in its importance in many groundwater systems.
机译:act系元素在地下水中的长期迁移对于在铀矿中安置核废料设施和管理废石堆至关重要。溶解的有机碳(DOC)可能会影响铀的迁移率,但是很少进行基于野外的研究来研究典型地下水中的铀。此外,很少有技术可用于分离DOC并直接定量与其络合的金属。通过对现场采集的样品进行分析来确定U-有机物缔合常数,这是对实验室测量的补充,而这些常数对于精确的运输计算而言是必需的。在一个测试点收集了2至30 m深度的10个地下水样品中,研究了U在富含粘土的阿奎德中的DOC分配。 DOC(4-132 mg / L)和U浓度(20-603μg/ L)之间观察到正相关。使用不对称流场流分馏(AsFlFFF)与紫外线吸收剂(UVA)和电感耦合等离子体质谱仪(ICP-MS)的在线耦合,可以直接检测U和DOC的关联。该方法的优点是利用非常小的样品量(20-50μL),并提供有关U有机物复合物的分子量信息。 AsF1FFFF-UVA结果显示为47-。在AsFlFFF分析中,回收了98%的DOC(4-136 mg C / L),其中25-64%出现在可分离峰中。该峰对应于约900-1400道尔顿(Da)的重均分子量。在所有情况下,AsFlFFF-ICP-MS均表明,≤2%的U(可能以U(VI)形式存在)与DOC混合。该结果与对2.3 m深度的样品进行的U形态建模非常吻合,该样品预测DOC复合U约为3%。这种良好的一致性表明,AsFlFFF-ICP-MS方法可能对确定样品非常有用。小体积样品中的U-有机物关联。由于这些水的pH(7.0-8.1)和碳酸盐浓度是许多地下水的典型特征,因此这些数据表明DOC促进U的运输在许多地下水系统中的重要性可能受到限制。

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