Distribution and fractionation of the rare earth elements in Brazilian soils

Abstract

The distribution and fractionation of Sc, Y and 14 rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) were investigated in 144 samples (topsoil and subsoil) from 88 sites distributed across Brazil. Although, a wide range of natural variability in REE content was observed, overall the REE median contents were relatively low compared with those reported in soils form other parts of the world. The REE contents in Brazilian soils showed significant correlation mainly with Fe, Mn and Ti oxides, as well as organic matter. REE distribution in soils basically depend on the parent material, while fractionation of individual REEs depend on soil characteristics that are partly influenced by pedogenic process. Soils developed from alkaline igneous rocks showed the highest average content of REEs followed by sedimentary rocks, unconsolidated clay sediments, metamorphic rocks, basic igneous rocks, unconsolidated sand and silt sediments, and acid igneous rocks. REE normalized patterns varied significantly within each geological formation, except for soils derived from alkaline igneous rocks. The greatest variations were observed in the light REEs. Graphic inspection using exploratory data analysis tools such as Q-Q normal plots and boxplots was effective to recognize patterns and identify different data groups, determine threshold values and thus define the range of the background REE variability. The data set generated in this study may be used as a preliminary reference for regulatory actions in the Brazilian environmental legislation.

Rare Earth Element Concentrations in Brazilian Benchmark Soils

“…The REE concentrations in the soil is mainly governed by parent materials (Liu, 1988;Hu et al, 2006), but weathering conditions, organic matter, and clay concentrations are also important to determine these levels (Tyler, 2004). The abundance of REEs found here is very similar to that reported for soils of Brazil (Paye et al, 2016) and other countries (Wei et al, 1991;Yoshida et al, 1998;Tyler and Olsson, 2002;Sadeghi et al, 2013) and follows the Oddo-Harkins rule, which holds that elements with an even atomic number (such as Ce) are more common than elements with an odd atomic number (such as La). ) were also found in higher concentrations than trace elements (Ni and Co) measured in the same soils (Biondi et al, 2011).…”

“…Taking into account the growing global economic importance of REEs, the use of these elements in several Earth science fields (Laveuf and Cornu, 2009;Li et al, 2013;Chen et al, 2014;Abbott et al, 2015;Pagano et al, 2015), and the scarcity of data available for Brazil (Pérez et al, 1997;Paye et al, 2016) and other tropical regions, this study was carried out to determine the REE concentrations in soils of a Brazilian benchmark collection that represents all the soil orders found in the country. Additionally, we demonstrate that a geochemical association exists between Fe and REEs in these soils.…”

Geochemistry and Spatial Variability of Rare Earth Elements in Soils under Different Geological and Climate Patterns of the Brazilian Northeast

“…Standardization was the first step in determining whether depletion or enrichment occurred relative to reference material. It also facilitated comparison of the REE content results with soils from other locations; normalization with the upper continental crust is common (Paye et al, 2016;Censi et al, 2017;Silva et al, 2017). …”

Lanthanides in Soils of the Cherepovets Steel Mill

“…Soil-forming processes have no significant influence (compared to the share of residual fraction and many other HMs in the studied soils) on redistribution of lanthanides among soil components [30][31][32]. The highest effect of pedogenesis on the fractional composition of lanthanides has been determined in the fraction bound to organic matter (Figure 7).…”