Environment and Resources College, Shanxi University, No.92 Wucheng Rd, Taiyuan, 030006, China.
Environ Sci Pollut Res Int. 2018 Nov;25(33):33521-33537. doi: 10.1007/s11356-018-3296-0. Epub 2018 Sep 28.
This study reports the adsorption of five rare earth elements (REEs) (belonging to light (Nd, Eu, Gd), medium (Tb), and heavy (Y) REE group) on montmorillonite-supported zero-valent iron nanoparticles (nZVI-M). Various parameters about REEs adsorption were investigated: the pH value, the adsorption kinetic, the maximum adsorption capacity, and the adsorption isotherm. The temperature (293-313 K) had a limited effect on the final adsorption equilibrium capacity and the analysis of thermodynamic studies suggests it was spontaneous (negative values of ∆G) and exothermic (negative values of ∆H). The system randomness decreased after adsorption (negative values of ∆S). In addition, the values of thermodynamic parameters and the activation energy were strongly dependent on the temperature range because different kinds of REEs participated in the reaction in the form of hydrated ions and followed a randomly and complexly dissociative adsorption mechanism. According to the intraparticle diffusion model analysis, the adsorption of REEs on nZVI-M was dominated by chemisorption and the nano size of nZVI-M reduced the diffusion thickness and the resistance to intraparticle diffusion. Based on the characterization of adsorbent by XPS, the adsorption mechanisms of REEs on nZVI-M were ion exchange and surface complexation.
本研究报告了五种稀土元素（REEs）（属于轻（Nd、Eu、Gd）、中（Tb）和重（Y）REE 族）在蒙脱石负载零价铁纳米颗粒（nZVI-M）上的吸附。研究了 REEs 吸附的各种参数：pH 值、吸附动力学、最大吸附容量和吸附等温线。温度（293-313 K）对最终吸附平衡容量的影响有限，热力学研究表明吸附是自发的（∆G 为负值）和放热的（∆H 为负值）。吸附后体系的无序度降低（∆S 为负值）。此外，热力学参数和活化能的值强烈依赖于温度范围，因为不同类型的 REEs 以水合离子的形式参与反应，并遵循随机和复杂的解离吸附机制。根据内扩散模型分析，REEs 在 nZVI-M 上的吸附主要是化学吸附，nZVI-M 的纳米尺寸降低了内扩散的扩散厚度和阻力。基于 XPS 对吸附剂的表征，REEs 在 nZVI-M 上的吸附机制为离子交换和表面络合。
