Sorption of DONs onto clay minerals in single-solute and multi-solute systems: Implications for DONs mobility in the vadose zone and leachability into groundwater

Leyun Wang; Jia Xin; Hui Nai; Tianyuan Zheng; Feifei Tian; Xilai Zheng

doi:10.1016/j.scitotenv.2019.135502

Sorption of DONs onto clay minerals in single-solute and multi-solute systems: Implications for DONs mobility in the vadose zone and leachability into groundwater

Sci Total Environ. 2020 Apr 10:712:135502. doi: 10.1016/j.scitotenv.2019.135502. Epub 2019 Dec 4.

Authors

Leyun Wang¹, Jia Xin², Hui Nai¹, Tianyuan Zheng³, Feifei Tian¹, Xilai Zheng⁴

Affiliations

¹ 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.
² 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. Electronic address: xinj15@ouc.edu.cn.
³ College of Engineering, Ocean University of China, Qingdao 266100, China.
⁴ 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. Electronic address: zhxilai@ouc.edu.cn.

PMID: 32050391
DOI: 10.1016/j.scitotenv.2019.135502

Abstract

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.

Keywords: Clay mineral; Dissolved organic nitrogen; Leaching; Multi-solute system; Sorption behavior; Vadose zone.