Chemical and Mineralogical Properties of Kaolinite‐Rich Brazilian Soils

作者：Vander Freitas Melo, Balwant Singh, Carlos Ernesto Gonçalves Reynaud Schaefer, Roberto Ferreira Novais, Maurício Paulo Ferreira Fontes · 发表于：Soil Science Society of America Journal · 年份：2001 · DOI：10.2136/sssaj2001.6541324x · 被引用次数：170 · 研究领域：Clay minerals and soil interactions、Iron oxide chemistry and applications、Soil and Unsaturated Flow

Highly weathered kaolinitic soils in Brazil often have adequate levels of K and Mg to support plant growth. The source of K and Mg in these soils and their relationship with the dominant mineral, kaolinite, is addressed in this article. Crystallographic, chemical, and morphological properties of kaolinite, from selected highly weathered Brazilian soils, were investigated by x‐ray diffraction (XRD), analytical electron microscopy (AEM), chemical, and thermal methods. Kaolinite properties showed significant variations such as d(001) spacing ranging between 0.713 to 0.728 nm, width at half height (WHH) between 0.30 to 0.97 °2θ, and dehydroxylation temperature between 489 to 518°C. Kaolinite in the clay fraction has relatively poor crystal order with a mean crystallinity index value(CI) of 12.7. The dominant forms of the clay‐fraction kaolinite were elongated and rounded, with relatively lower proportions of hexagonal particles. The silt‐fraction kaolinite showed a tendency to form subspherical large aggregates with high stability. The average Fe 2 O 3 level in the kaolinite of the clay fraction (19.1 g kg −1 ) was higher than that obtained for the silt fraction (6.6 g kg −1 ). The smaller kaolinite particles of the clay fraction showed a lower degree of crystal order, higher K and Mg levels, and lower dehydroxylation temperatures. From the strong relationship between the asymmetry index (AI) of the (001) diffraction line and the level of K in kaolinite from the younger soils, we...