Investigation of the Solution Complexation Behavior of the Rare Earth Elements with Naturally Occurring Organic Ligands in Natural Terrestrial Waters

0001086 Johannesson了解稀土元素和其他重金属在环境中的化学行为对于预测它们对环境的影响以及它们在环境中的归宿和迁移至关重要。 影响天然沃茨中这些和其它重金属的最重要因素之一是溶液络合作用。 例如，溶液络合作用可以控制重金属在环境中的流动性、有效溶解度、反应性和毒性。 不幸的是，金属形态与天然存在的有机配体，其直接连接到这些过程和总金属浓度，只有知之甚少的大多数痕量金属，包括稀土元素。 尽管确实存在允许预测稀土元素与无机配体络合的地球化学模型（即，天然沃茨中的CO 32-、P43-、SO 42-、OH-、Cl-，它们与天然沃茨中天然存在的有机配体的原位配位行为尚未得到专门研究。 尽管许多简单有机酸与稀土络合物的稳定常数与最强的稀土无机物（即，碳酸盐）络合物。 因此，有机络合作用也可能控制天然沃茨中稀土元素的形态，正如许多过渡金属阳离子的情况一样。 因此，考虑到对天然沃茨中稀土元素与有机配体的[原位]络合知之甚少，我们研究的主要目标是：（1）修改和开发一种特定的电化学技术，以（a）测量天然沃茨中与天然存在的有机配体络合的溶解稀土元素的分数，和（B）测量强度（即，（2）应用改进的电化学方法测量沃茨中稀土元素的有机络合作用，所述水体跨越天然沃茨的pH范围并且含有各种浓度的无机络合配体和溶解的有机碳浓度;以及（3）建立稀土溶液络合的定性模型，解决无机配体和天然有机配体之间的竞争，并建立在早期平衡的基础上热力学模型 这些目标将采用实验室和现场相结合的方法来实现。 我们将修改竞争性配体平衡/吸附阴极溶出伏安法（CLE/ACSV）技术目前用于过渡金属，以量化的溶解稀土元素的量，发生在天然沃茨作为溶液络合物与天然存在的有机配体。 将收集天然水样品以比较和对比浓度，其中有机配体必须与无机碳酸盐络合物、具有中等浓度或无机络合配体和低DOC的中性pH沃茨以及具有高DOC的酸性沃茨竞争。 我们的研究结果与天然有机配体的稀土络合将结合目前使用的平衡（无机配体形态）模型。

0001086JohannessonUnderstanding the chemical behavior of the rare earth elements (REE) and other heavy metals in the environment is critical to predicting their impact on, as well as their fate and transport within, the environment. One of the most important factor affecting these and other heavy metals in natural waters is solution complexation. Solution complexation, for example, may exert controls on the mobility, effective solubility, reactivity, and toxicity of heavy metals in the environment. Unfortunately, metal speciation with naturally occurring organic ligands, and its direct connection to those processes and total metal concentrations, is only poorly known for most trace metals, including the REEs. Although geochemical models do exist that allow predictions to be made of REEs complexation with inorganic ligands (i.e., CO32-, P 4 3-, SO42-, OH-, CI- in natural waters, their in situ complexation behavior with naturally occurring organic ligands in natural waters has not been specifically studied. This disparity in our understanding of REE complexation exists despite the fact that stability constants for REE complexes with many simple organic acids are of the same magnitude, or greater, than stability constants for the strongest REE-inorganic (i.e., carbonate) complexes. Therefore, it is possible that organic complexation also controls the speciation of the REEs in natural waters, as has been shown to be the case for many transition metal cations. Consequently, considering what little is known about the [in situ] complexation of REEs with organic ligands in natural waters, the chief objectives of our study are: (1) modify and develop a specific electrochemical technique to (a) measure the fraction of dissolved REEs complexed with naturally occurring organic ligands in natural waters, and (b) measure the strength (i.e., conditional stability constants) of these naturally occurring REE-organic ligand complexes; (2) apply the modified electrochemical method to measure organic complexation of REEs in waters that span the pH range of natural waters and contain various concentrations of inorganic complexing ligands and dissolved organic carbon concentrations; and (3) develop a qualitative model of REE solution complexation that addresses competition between inorganic ligands and naturally occurring organic ligands and that builds upon an earlier equilibrium thermodynamic model. These objectives will be addressed using a combined laboratory and field approach. We will modify the competitive ligand equilibration/adsorptive cathodic stripping voltammetry (CLE/ACSV) technique currently used for transition metals to quantify the amount of dissolved REEs that occur in natural waters as solution complexes with naturally occurring organic ligands. Natural water samples will be collected to compare and contrast concentrations, where organic ligands must compete with inorganic carbonate complexes, neutral pH waters with moderate concentrations or inorganic complexing ligands and low DOC, and acidic waters with high DOC. Our results concerning REE complexation with natural organic ligands will be combined with an equilibrium (inorganic ligand speciation) model currently in use.