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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.
This article was published in the following journal.
Name: The Science of the total environment
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A group of elements that include SCANDIUM; YTTRIUM; and the LANTHANOID SERIES ELEMENTS. Historically, the rare earth metals got their name from the fact that they were never found in their pure elemental form, but as an oxide. In addition they were very difficult to purify. They are not truly rare and comprise about 25% of the metals in the earth's crust.
Discrete segments of DNA which can excise and reintegrate to another site in the genome. Most are inactive, i.e., have not been found to exist outside the integrated state. DNA transposable elements include bacterial IS (insertion sequence) elements, Tn elements, the maize controlling elements Ac and Ds, Drosophila P, gypsy, and pogo elements, the human Tigger elements and the Tc and mariner elements which are found throughout the animal kingdom.
An element of the rare earth family of metals. It has the atomic symbol Y, atomic number 39, and atomic weight 88.91. In conjunction with other rare earths, yttrium is used as a phosphor in television receivers and is a component of the yttrium-aluminum garnet (YAG) lasers.
Copies of transposable elements interspersed throughout the genome, some of which are still active and often referred to as "jumping genes". There are two classes of interspersed repetitive elements. Class I elements (or RETROELEMENTS - such as retrotransposons, retroviruses, LONG INTERSPERSED NUCLEOTIDE ELEMENTS and SHORT INTERSPERSED NUCLEOTIDE ELEMENTS) transpose via reverse transcription of an RNA intermediate. Class II elements (or DNA TRANSPOSABLE ELEMENTS - such as transposons, Tn elements, insertion sequence elements and mobile gene cassettes of bacterial integrons) transpose directly from one site in the DNA to another.
Elements with partially filled d orbitals. They constitute groups 3-12 of the periodic table of elements.