RELATIONSHIP BETWEEN MAGNETIZATION AND TRACE ELEMENTS CONTENT OF BRAZILIAN SOILS FROM DIFFERENT PARENT MATERIALS.

Abstract

Magnetic minerals are important in some Brazilian soils and they are a possible source of trace elements, especially in the highly weathered soils. The purpose of this investigation was thus to determine the trace element content in the magnetically separated sand, silt, and clay fractions from soils of different lithological origins in order to test the hypothesis that higher levels of magnetization are directly proportional to the contents of these elements. To accomplish this objective, the samples were dissolved by concentrated HCl/HF/HClO 4 acid attack, and the contents of Cd, Cr, Cu, Ni, Pb, Zn, Zr, and V were analyzed by atomic emission spectroscopy with inductively coupled plasma (ICP-AES). The contents of trace elements in the total, magnetic and nonmagnetic sand, silt, and clay fractions were within the normal range presented by whole soils with the exception of Cd, which was higher. Magnetization (σ s ) of the total, magnetic and nonmagnetic soil fractions was evaluated with a special analytical balance. The σ s values were higher for sand and lower for silt and clay fractions. The magnetically concentrated fractions gave results with variation in the same fashion but reaching higher values. The relationship between trace elements in soil fractions and magnetization, studied by correlation analysis, gave higher and more significant correlation coefficients when a soil derived from itabirite was excluded from the analysis. Because itabirite and mafic rocks have high magnetization, the correlation result demonstrates that there is a strongly significant association between magnetization and trace element contents for the soils derived from mafic rocks. Analysis of variance showed that there were significant differences between trace element contents of the magnetic compared with the nonmagnetic fractions of the soils derived from mafic rocks, especially in their sand and silt fractions. Tukey's test for comparison of means showed that mafic rocks have a higher content of trace elements compared with the other parent materials. The results obtained confirm the geochemical affinity of trace elements and the components of the magnetic fraction of the soils derived from the mafic rocks, mainly for sand and silt fractions, where higher contents of the investigated trace elements were observed.