Morphological characterization of soil clay fraction in nanometric scale

The atomic force microscopy (AFM) is a technique for direct three dimensional measurements of the mineral structure in nanometric scale. In the literature, there are studies which approach the characterization of surfaces in atomic scale through AFM, such as humic substances and minerals. However, the number of studies aiming to characterize the clay fraction minerals in soil using this technique is not representative. In this study, AFM was employed to characterize the clay fraction morphology and microtopography in the surface layer of a Rhodic Ferralsol in Brazil, and X-ray diffraction (XRD) together with the Rietveld Method (RM) to characterize and quantify the main minerals. Images analyzed presented particles from 3 to 25 nm. Through XRD and RM mineralogical analysis, the minerals found in higher amounts from the most to the least were, gibbsite, kaolinite, hematite, anatase, goethite, magnetite, calcite, vermiculite and rutile. AFM images made it possible to identify, by observing the height and shape, the particles that corresponded to kaolinite, goethite and gibbsite. This study shows the potential of the AFM technique to measure clay in nanometric scale and the possible identification of minerals present in the clay fraction with the use of XRD and RM.