The nature of interlayering in clays from a podzol (Spodosol) from the Tatra Mountains, Poland
Résumé
Interlayered clays are common constituents of several soil orders. The presence of interlayering is indicated by modified thermal stability of soil vermiculites and smectites. In most studies the clays have been reported as Al-hydroxy-interlayered minerals. Despite the abundance of organic compounds in many soils, the potential existence of soil organo-clay intercalations has rarely been considered. In the present study three clay subfractions separated from the eluvial (E) horizon of one podzol from the Tatra Mts., Poland, were studied using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and elemental CHNS analysis, in the natural state and after being subjected to organic matter removal, free iron oxides removal, saturation with different cations, and heating at 330 °C and 550 °C. All fractions contain a "~14 Å clay". In the natural state the "~14 Å clay" shows high thermal resistance, manifested by only a partial shift to 10 Å after heating at 330 °C. This behavior strongly suggests the presence of interlayering. Saturation with K+ shifted the ~ 14 Å reflection to ~ 13-11 Å, which suggests displacement of a charged species from the interlayer. Clay sample treatment with H2O2 and NaOCl reduced the stability of the interlayered phase because 330 ° C heat treatment shifted the ~ 14 Å phase to ~ 10 Å, which suggests that the interlayered phase might be organic. Furthermore, the 13-18% organic carbon content of the clays and near disappearance of infrared peaks at 2855 cm− 1, 2926 cm− 1, 1738 cm− 1, ~ 1600 cm− 1, and ~ 1400 cm− 1 after H2O2 or NaOCl treatment suggests that the clay interlayer phase is mostly organic. Both Al-hydroxy and organic interlayers can be evaluated using a combination of X-ray diffraction, elemental analysis, and infrared spectroscopy and should be considered as possible interlayer phases during the study of interlayered clays.