Department of Environmental Science and Engineering, State Key Laboratory of Multiphase Flow in Power Engineering, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an 710049, China.
Department of Environmental Science and Engineering, State Key Laboratory of Multiphase Flow in Power Engineering, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an 710049, China.
Sci Total Environ. 2021 Jun 1;771:144800. doi: 10.1016/j.scitotenv.2020.144800. Epub 2021 Jan 27.
Cation exchange is one of the dominant mechanisms in the adsorption of cationic ammonium nitrogen (NH) from water. In this study, we focus on the role of counter cations in cation exchange process of NH to enhance the adsorption capacity. Five amorphous titanates namely lithium titanate (LiT), sodium titanate (NaT), potassium titanate (KT), strontium titanate (SrT) and barium titanate (BaT) with different counter cation were facilely synthesized. The adsorption performance for NH by these samples is in the order of LiT> NaT > KT> > SrT > BaT. The maximum adsorption capacity of LiT calculated by Langmuir is as high as 50.31 mg·g. According to the experimental results and theoretical analysis, the electrostatic interaction between counter ions (cations in framework or eternal solution) and charged framework (fixed ions) is the main influence factor during cation exchange process in general. The cation valence and the hydrated ionic radius of the counter ions can inversely affect the ion exchange equilibrium and the affinity of counter ions to titanates. Therefore, a definition of a brief parameter, affinity coefficient K (relating to ion valence and distance between opposite charged ions), is introduced and used to explain the difference in adsorption performance of five titanates for NH. The conclusion about cation exchange and ions affinity may provide possible strategies for enhancement of cationic contaminant adsorption from water or wastewater.
离子交换是水中阳离子铵氮 (NH) 吸附的主要机制之一。在本研究中，我们专注于抗衡离子在 NH 离子交换过程中的作用，以提高吸附容量。我们简便地合成了五种无定形钛酸盐，即氧化锂钛（LiT）、氧化钠钛（NaT）、氧化钾钛（KT）、氧化锶钛（SrT）和氧化钡钛（BaT），它们具有不同的抗衡离子。这些样品对 NH 的吸附性能顺序为 LiT> NaT > KT > SrT > BaT。LiT 通过 Langmuir 计算得出的最大吸附容量高达 50.31mg·g。根据实验结果和理论分析，一般来说，在离子交换过程中，抗衡离子（骨架或外部溶液中的阳离子）与带电骨架（固定离子）之间的静电相互作用是主要影响因素。抗衡离子的阳离子价态和水合离子半径会反相影响离子交换平衡和抗衡离子对钛酸盐的亲和力。因此，引入并使用了一个简单参数的定义，即亲和力系数 K（与离子价态和相反电荷离子之间的距离有关），来解释五种钛酸盐对 NH 的吸附性能差异。关于离子交换和离子亲和力的结论可能为增强水中或废水中阳离子污染物的吸附提供可能的策略。
