INTEGRAÇÃO DE MÉTODOS DE CARACTERIZAÇÃO MINERALÓGICA DE SOLOS CAULINITÍCOS

Abstract

The soil is a complex and heterogeneous medium containing solid, liquid, gases and several organisms. Its solid phase is composed of minerals that present well defined and highly organized chemical composition. Tropical climate soils, classified as hardsetting, are kaolinitic and present low nutrient and organic matter amounts. Nowadays, there is no consensus about these soils hardsetting characteristics. The characterization of physical and chemical properties of these horizons and their granulometric fractions enables the physical, chemical and mineralogical investigation of five hardsetting soils in this study. Spectroscopic and microscopic techniques, thermal analysis and X-ray diffraction with the Rietveld Method were employed. The RM-XRD made possible to quantify and estimate crystallite average size and mineral micro-deformations. Part of these results was associated to Kaolinite, Halloysite, and Goethite isomorphic substitution. The quantitative XRF analyses revealed the content of chemical elements in the soils under study with higher accuracy. The thermal analysis techniques showed that Kaolinite of weathered soils is susceptible to dehydroxylation at lower temperatures. SEM micrographs revealed the particle typical shapes and these results were confirmed through the AFM that estimated the number of crystallites and the average number of kaolinite layers in the clay fraction. Most of the particles observed through microscopic techniques were ascribed to the Kaolinite, and their micromorphological characteristics could be compared to crystallite size and microdeformations obtained through the RM-XRD. Therefore, based on the results of spectroscopic, microscopic, thermal analyses and X-ray diffraction with Rietveld Method, it was possible to understand the several degrees of crystallinity of minerals which are part of the granulometric fractions of hardsetting horizons in kaolinitic soils.