Key Laboratory of Marine Environment Science and Ecology, Ministry of Education and College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China.
Key Laboratory of Marine Environment Science and Ecology, Ministry of Education and College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China; Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering, Ocean University of China, Qingdao 266100, China.
Sci Total Environ. 2020 Apr 10;712:135502. doi: 10.1016/j.scitotenv.2019.135502. Epub 2019 Dec 4.
Dissolved organic nitrogen (DON) with a mixture of various organic nitrogen (N) is recognized as an emerging groundwater contaminant. Investigating the behavior and mechanism of DON sorption onto clay minerals, which are key components of vadose zone media, is crucial to evaluating its leaching potential. Considering the interactions among multiple DON compounds (DONs) may influence their sorption behaviors, the sorption of three typical DONs (amino acid, protein and urea) to clay minerals in single-, binary- and ternary-solute systems were explored, respectively. In addition, a combination of multiple methods, including physiochemical characterization, Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD) and pH variation analysis, were used to provide insight into the governing mechanisms. Results indicated that the sorption kinetics and isotherms of single systems were well-fitted by pseudo-second-order and Freundlich isotherm models, respectively. The mechanisms involved in the sorption of DONs onto clay minerals varied with the sorption time. The dominant interactions included van der Waals forces, ligand exchange, and hydrogen bonding (H-bonding) in the initial phase of the sorption process, whereas electrostatic interactions were predominant in the later stage as H was released into the solution. In binary-solute systems, either cooperative or competitive sorption was observed depending on the co-solute combination. For instance, the sorption behaviors of amino acids and urea were simultaneously enhanced in the binary system because of the formation of highly charged complexes as new active sites. Proteins sorption, however, was inhibited by the coexistence of urea as a result of active site depletion and protein denaturation. In ternary-solute systems, the sorption of DONs was balanced by cooperative and competitive sorption processes. These findings elucidated the sorption behaviors of DONs onto clay minerals in multi-solute systems and contributed to the evaluation of the mobility of DONs in the vadose zone and their leachability into groundwater.
溶解有机氮 (DON) 是一种混合了各种有机氮 (N) 的物质，被认为是一种新兴的地下水污染物。研究 DON 与粘土矿物的吸附行为和机制对于评估其淋滤潜力至关重要，因为粘土矿物是包气带介质的关键组成部分。考虑到多种 DON 化合物 (DONs) 之间的相互作用可能会影响它们的吸附行为，分别在单、双和三元溶质体系中研究了三种典型 DON（氨基酸、蛋白质和尿素）在粘土矿物上的吸附行为。此外，还结合了多种方法，包括物理化学特性表征、傅里叶变换红外光谱 (FTIR)、X 射线衍射 (XRD) 和 pH 值变化分析，以深入了解控制机制。结果表明，单体系的吸附动力学和等温线分别很好地符合准二级和 Freundlich 等温模型。DONs 在粘土矿物上的吸附机制随吸附时间而变化。在吸附过程的初始阶段，主要的相互作用包括范德华力、配体交换和氢键 (H-bonding)，而在后期随着 H 释放到溶液中，静电相互作用占主导地位。在双元体系中，根据共溶质的组合，观察到协同或竞争吸附。例如，由于形成了带高电荷的配合物作为新的活性位点，氨基酸和尿素在二元体系中的吸附行为同时得到增强。然而，由于活性位点耗尽和蛋白质变性，蛋白质的吸附受到共存的尿素的抑制。在三元体系中，DONs 的吸附受到协同和竞争吸附过程的平衡。这些发现阐明了 DONs 在多溶质体系中在粘土矿物上的吸附行为，有助于评估 DONs 在包气带中的迁移性及其淋滤到地下水中的可能性。
