Table of Contents
ISRN Soil Science
Volume 2012 (2012), Article ID 783876, 11 pages
http://dx.doi.org/10.5402/2012/783876
Review Article

Rare Earth Elements: Their Importance in Understanding Soil Genesis

Department of Agriculture, Southeast Missouri State University, 1 University Plaza, Cape Girardeau, MO 63701, USA

Received 5 January 2012; Accepted 23 February 2012

Academic Editors: G. Benckiser, L. Mercury, and W. Peijnenburg

Copyright © 2012 Michael T. Aide and Christine Aide. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The rare earth elements (REEs) are commonly defined as lanthanum (La) and the 14 elements comprising the Lanthanide series. The REE’s typically exhibit trivalent oxidation states; however, Europium may also occur as Eu2+ and Cerium may occur as Ce4+. The REE’s ionic radii decrease on progression from La to Lu, which results in a slight but predictable change in their chemical affinity. Typically, the light REE (La to Sm) reside in trace minerals such as apatite, epidote and allanite, whereas the heavy REE (Gd to Lu) are associated with minerals such as zircon. Investigations typically show that the REE are depleted in near-surface horizons and accumulate in deeper horizons or the regolith as clay-oxyhydroxide adsorbates or REE-phosphate precipitates. Numerous studies show the heavy REE accumulating in the deeper soil regions to a greater extent than the light REE, whereas other studies show the light REE’s preferentially accumulating at greater soil depths. The degree of interhorizon transport has great potential to become an index of weather intensity. The various REE soil migration pathways have been isolated, including lessivage, soil organic matter complexation, leaching in percolating water, adsorption by inorganic colloids, and precipitated by phosphate-bearing minerals.