Geochemical behaviour of palladium in soils and Pd/PdO model substances in the presence of the organic complexing agents L-methionine and citric acid.
Geochemical behaviour of palladium in soils and Pd/PdO model substances in the presence of the organic complexing agents L-methionine and citric acid.
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DOI：
10.1039/c5em00521c
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发表时间：
2016-01
期刊：
影响因子：
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通讯作者：
F. Zereini;C. Wiseman;My Vang;P. Albers;W. Schneider;R. Schindl;K. Leopold
中科院分区：
文献类型：
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作者：
F. Zereini;C. Wiseman;My Vang;P. Albers;W. Schneider;R. Schindl;K. Leopold
铂族金属（PGE）排放物的风险评估，特别是铂（Pt），钯（Pd）和铑（Rh）的排放物的风险评估，主要是基于有关车辆排气转化器中使用的金属形式的数据，已知实际上是生物惰性和固定的。然而，为了充分评估铂族元素的潜在影响，需要关于这些金属在排放后环境条件下的化学行为的数据。假设对环境中的金属具有高亲和力的络合剂有助于增加PGE的生物可及性。研究了有机络合剂L-蛋氨酸和柠檬酸对土壤和模型物质（Pd黑和PdO）中Pd的地球化学行为的调节作用。采用土壤和模型物质进行了批实验，考察了络合剂浓度、pH值和萃取时间对Pd溶解度及其化学转化的影响。颗粒表面化学进行了检查，使用X射线光电子能谱（XPS）在各种条件下，包括低和高O2水平的溶液处理的样品。观察到Pd在有机络合剂的存在下比Pt和Rh更可溶。土壤中的钯更容易与有机络合剂相比，模型物质的增溶。例如，在提取7天后，L-甲硫氨酸（0.1 M）处理的土壤和钯黑样品的平均可溶性钯分数分别为12.4 ± 5.9%和0.554 ± 0.024%。表面化学分析（XPS）证实了金属Pd表面的氧化时，用有机络合剂处理。用于实验目的的有机络合剂的类型被观察到是影响溶解度的最重要的因素，其次是溶液pH值和萃取时间。结果表明，金属钯可以转化为更生物可及的物种在存在的有机络合剂，这是普遍存在于环境中。
Risk assessments of platinum group metal (PGE) emissions, notably those of platinum (Pt), palladium (Pd) and rhodium (Rh), have been mostly based on data regarding the metallic forms used in vehicular exhaust converters, known to be virtually biologically inert and immobile. To adequately assess the potential impacts of PGE, however, data on the chemical behaviour of these metals under ambient conditions post-emission is needed. Complexing agents with a high affinity for metals in the environment are hypothesized to contribute to an increased bioaccessibility of PGE. The purpose of this study is to examine the modulating effects of the organic complexing agents, L-methionine and citric acid, on the geochemical behavior of Pd in soils and model substances (Pd black and PdO). Batch experimental tests were conducted with soils and model substances to examine the impacts of the concentration of complexing agents, pH and length of extraction period on Pd solubility and its chemical transformation. Particle surface chemistry was examined using X-ray photoelectron spectroscopy (XPS) on samples treated with solutions under various conditions, including low and high O2 levels. Pd was observed to be more soluble in the presence of organic complexing agents, compared to Pt and Rh. Pd in soils was more readily solubilized with organic complexing agents compared to the model substances. After 7 days of extraction, L-methionine (0.1 M) treated soil and Pd black samples, for instance, had mean soluble Pd fractions of 12.4 ± 5.9% and 0.554 ± 0.024%, respectively. Surface chemistry analyses (XPS) confirmed the oxidation of metallic Pd surfaces when treated with organic complexing agents. The type of organic complexing agent used for experimental purposes was observed to be the most important factor influencing solubility, followed by solution pH and time of extraction. The results demonstrate that metallic Pd can be transformed into more bioaccessible species in the presence of organic complexing agents which are ubiquitous in the environment.