The present work, basically of the fraction clay characterization, mainly of the kaolinite and its exchange with some metallic cation (Na+, K+ e Fe3+), in Amazon soil. The samples of Latosoil Yellow were collected from a pedon located in the vivinity of the Presidente Figueiredo city. State of Amazon, Brazil. The particles were fractionated on the basis of particle size, and sand, silt in clay fractions were obtained. The samples of the clay fraction were treated with H2O2/HC1 to eliminate the organic matter and oxide of free iron and submitted the analyses using the following techniques: X-ray diffraction, infrared spectroscopy, ultraviolet-visible spectroscopy, atomic absorption spectroscopy, as well as, volumetric, gravimetric and flame photometric analyses. The obtained results showed that the clay fraction presents to the following constitution: gibsite, goethite, quartz, organic material and kaolinite. Being the kaolinite the final member of the series, with little distribuition of negative. For this study, it was possible to also propose that the fraction treated clay possesses capacity of retention of 2.21% of adsortion water, in the case of cations monovalence: 1.3 and 2.7 meq/100g of sample, for K+ and Na+, respectively. However, that fraction retains about 21.7 meq/100g of sample for the Fe3+. That value elevated for the retention of Fe3+ is probably attributed to the several species hydrolyzed of Fe3+ in that caused the reduction in the pH value for 2,2 and it can also facilitate, the substituition of Fe3+ for Al3+, by in the octahedral site.
kaolinite; X-ray; infrared