Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China.
Chemosphere. 2010 Sep;81(3):415-21. doi: 10.1016/j.chemosphere.2010.06.069.
The use of ethylenediaminetetraacetic acid (EDTA) for soil remediation is under concern due to its non-biodegradability and toxicity; thus, its biodegradable structural isomer, [S,S]-ethylenediamine disuccinate ([S,S]-EDDS), has been proposed as an emerging substitute. In this study, batch experiments were performed to quantify the Pb extraction from goethite by EDTA and EDDS, respectively, and attenuated total reflectance-Fourier transform infrared (ATR/FT-IR) spectroscopy was used to investigate the corresponding mechanisms at the solid-liquid interface at different pH and reaction times. The Pb extraction was pH-dependent for both chelating agents; mildly alkaline condition was favorable for EDDS, while mildly acidic condition for EDTA. The discrepancy between two structural isomers might be caused by their pH-dependent zwitterionic structures. The ATR/FT-IR results revealed that under acidic conditions, hydrogen-bonded carboxyl groups were present in both zwitterionic EDDS and EDTA. However, ring structure of zwitterionic EDDS formed with stable intramolecular hydrogen bond might limit the availability for EDDS to extract Pb from goethite. On the other hand, each protonated amine of zwitterionic EDTA could form hydrogen bonds with two neighbouring carboxyl groups, intensifying the negative charge of carboxyl groups and enhancing the Pb extraction efficiency. However, there was a higher amount of re-adsorption of PbEDTA than PbEDDS, because zwitterionic EDTA resulted in a greater Pb extraction and facilitated iron dissolution which significantly altered the goethite morphology, particle size, and surface area. These results suggested that, despite being structural isomers, EDDS and EDTA resulted in varying extents of Pb extraction and re-adsorption due to their different zwitterionic properties.
乙二胺四乙酸（EDTA）由于其不可生物降解性和毒性而引起土壤修复的关注；因此，其可生物降解的结构异构体[S，S]-乙二胺二琥珀酸（[S，S]-EDDS）已被提议作为一种新兴替代品。在这项研究中，进行了批处理实验，以分别量化 EDTA 和 EDDS 从针铁矿中提取 Pb 的情况，并使用衰减全反射傅里叶变换红外（ATR/FT-IR）光谱在不同 pH 和反应时间下研究固液界面上的相应机制。两种螯合剂的 Pb 提取均与 pH 有关；EDDS 对碱性条件有利，而 EDTA 对酸性条件有利。两种结构异构体之间的差异可能是由于其 pH 依赖性的两性离子结构。ATR/FT-IR 结果表明，在酸性条件下，两性离子 EDDS 和 EDTA 中均存在氢键合的羧基。然而，两性离子 EDDS 的环结构形成了稳定的分子内氢键，可能限制了 EDDS 从针铁矿中提取 Pb 的能力。另一方面，两性离子 EDTA 的每个质子化胺都可以与两个相邻的羧基形成氢键，从而增强了羧基的负电荷并提高了 Pb 提取效率。然而，PbEDTA 的再吸附量高于 PbEDDS，因为两性离子 EDTA 导致 Pb 提取量更大，促进了铁的溶解，从而极大地改变了针铁矿的形态，粒径和表面积。这些结果表明，尽管是结构异构体，但由于它们的两性离子特性不同，EDDS 和 EDTA 导致 Pb 的提取和再吸附程度不同。
