Guangzhou Key Laboratory of Environmental Catalysis and Pollution Control, School of Environmental Science and Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou 510006, China.
School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China.
Sci Total Environ. 2020 Jun 20;722:137779. doi: 10.1016/j.scitotenv.2020.137779. Epub 2020 Mar 14.
The increasing excavation and utilization of rare earth elements (REEs) have resulted in an elevated release of these elements into the environment. Therefore, investigating the transport behavior of REEs is critical for a comprehensive understanding of their geochemical cycles and to propose potential pollution control strategies. This study investigated the transport, co-transport, and competitive retention of three REEs: La (a light REE), Gd (a middle REE), and Yb (a heavy REE), as well as the co-transport of REEs and kaolinite (a representative clay mineral) in porous media. Both observed and simulated breakthrough curves and retention profiles demonstrated that all ionic REEs exhibited considerable breakthrough and slight retention with almost uniform shapes in quartz sand (QS) owing to the weak affinity of ionic REEs to QS. The breakthrough of REEs in all experiments followed the order of La > Gd > Yb, indicating that REE breakthrough increased with decreasing atomic number. The same elements exhibited their highest breakthrough during the co-transport of the three REEs, followed by co-transport of two REEs, and finally single transport. Furthermore, mathematical modeling indicated that the retention of REEs in QS was a predominantly kinetic process, whereby competitive blocking was the dominant mechanism for the enhanced breakthrough of REEs during co-transport, as compared to single transport. The co-transport of REEs and kaolinite demonstrated that kaolinite has a slight influence on the transport of REEs in QS under adsorption kinetics. However, REEs inhibited the transport and strongly enhanced the retention of kaolinite in QS due to a decreasing electrostatic repulsion between kaolinite and QS in the presence of REEs, even if the adsorption of REEs onto kaolinite was weak under adsorption kinetics. Therefore, this study increases our understanding of the transport mechanisms of REEs in the environment.
稀土元素（REEs）的开采和利用日益增加，导致这些元素大量释放到环境中。因此，研究 REEs 的迁移行为对于全面了解其地球化学循环以及提出潜在的污染控制策略至关重要。本研究考察了三种 REEs（La、Gd 和 Yb）在多孔介质中的迁移、共迁移和竞争保留行为，以及 REEs 和高岭石（一种代表性的粘土矿物）的共迁移行为。观察到和模拟的穿透曲线和保留曲线都表明，由于离子型 REEs 与石英砂（QS）的亲和力较弱，所有离子型 REEs 在 QS 中都表现出相当大的穿透和轻微的保留，且形状几乎均匀。所有实验中 REEs 的穿透顺序均为 La>Gd>Yb，表明 REEs 的穿透随着原子序数的降低而增加。同一元素在三种 REEs 的共迁移中表现出最高的穿透，其次是两种 REEs 的共迁移，最后是单一迁移。此外，数学模型表明，REEs 在 QS 中的保留主要是动力学过程，与单一迁移相比，共迁移中 REEs 的增强穿透主要是由于竞争阻塞的作用。REEs 和高岭石的共迁移表明，在吸附动力学条件下，高岭石对 QS 中 REEs 的迁移仅有轻微影响。然而，由于 REEs 降低了高岭石和 QS 之间的静电排斥，即使在吸附动力学条件下 REEs 对高岭石的吸附较弱，REEs 仍会抑制高岭石在 QS 中的迁移并强烈增强其保留。因此，本研究增加了我们对环境中 REEs 迁移机制的理解。
