Magnetic separation and evaluation of magnetization of Brazilian soils from different parent materials

Ten selected Brazilian soils representative of Oxisols, Ultisols, Alfisols and Inceptisols and derived from gneiss, basalt, sandstone, diabase and ita birite were sampled and examined to provide insight into the behavior of th eir magnetic minerals. The objective was to measure the magnetization of th e sand, silt and clay fractions and to submit the clay fraction to variable magnetic fields to obtain the magnetization curves and to study their magn etic behavior as related to their parent material Lithology. The separation procedure using a magnetic separator was done in two different ways: dry s eparation for the sand and wet separation for the silt and clay fractions. X-ray diffraction patterns of magnetic and nonmagnetic fractions were obtai ned and the segregation of ferrimagnetic minerals were shown. The magnetiza tion (sigma(s)) of the total and the magnetic and nonmagnetic soil fraction s was evaluated using a special analytical balance. The sigma(s) values obt ained varied from 0.03 to 17.72 J T-1 kg(-1) for sand; 0.05 to 8.91 J T-1 k g(-1) for silt and 0.05 to 2.54 J T-1 kg(-1) for the clay fractions. The re sults from the magnetically concentrated fractions varied in the same fashi on but reached higher values. Magnetization curves showed spontaneous magne tization (M-s) values of 0.6 to 3.35 J T-1 kg(-1), high field slopes (lambd a) ranging from 0.17 to 0.77 J T-2 kg(-1) and, clearly, the influence of th e parent material lithology on the nature of the soil magnetic behavior. Ma gnetic measurements suggested pathways for ferrimagnetic minerals transform ations in soil systems. (C) 2000 Elsevier Science B.V. All rights reserved.