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 from 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.