The transformation of clay minerals in the particle size fractions of two soils from different latitude in China

Abstract

The behavior of clay minerals in different size fractions of soil colloids are very particular, mostly in the nanoparticle (25–100 nm) fractions, where clay minerals are very reactive and have a significant role in the transport of nutrients. In this work, the characterizations of clay minerals in the particle fractions (<2000, 450–2000, 100–450, and 25–100 nm) of an Oxisol and an Alfisol were studied by conventional and synchrotron X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FTIR), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and thermogravimetric analysis (TG) to better understand the transformations of clay minerals and their crystalline structure within the size particle fractions. Kaolinite dominated in all the particle size fractions and the moderate amount of HIV and illite present in the larger size particles (<2000, 450–2000 and 100–450 nm) reduced gradually in nanoparticles of the Oxisol. Kaolinite dominated in the bulk samples (<2000 nm), vermiculite prevailed in the 450–2000 nm fraction; illite, kaolinite and vermiculite were equally common in the 100–450 nm fractions, and illite dominated in the nanoparticles of the Alfisol. The reduction of kaolinite and the transformation of illite into vermiculite in the Alfisol occurred along the particle size fractions. The increase of the FWHM values, the deformation of the hydroxyl group of kaolinite and illite as well as the highest total of weight loss in their crystals occurred in the nanoparticles of the Alfisol rather than the Oxisol. It revealed that the reduction in crystal ordering in the crystals of clay minerals was greater in the nanoparticle fraction of the Alfisol compared to the Oxisol. The influence of climate, vegetation, parent material has been evidenced in the transformation of clay minerals in this study.