World Congress of Soil Science Logo 18th World Congress of Soil Science
July 9-15, 2006 - Philadelphia, Pennsylvania, USA
International Union of Soil Sciences

Tuesday, 11 July 2006

This presentation is part of 44: 2.4A Poorly Ordered Nanoparticulate materials (PONM) in Soils - Theater

Composition and Sustainability of Smectites' Nanoparticles in Boreal Acid Soils.

Sofia N. Lessovaia1, Eduard A. Goilo1, and Joern Kasbohm2. (1) St-Petersburg State University, Dep. of Soil Science, 199178 V.O. 16 line, d.29, St-Petersburg, Russia, (2) Greifswald University, Inst .of Geological Sciences, Greifswald, Germany

Smectite minerals are characterized by the most disordered structure and by smallest sizes of particles among phyllosilicates, so they could be considered as soil nanoparticles. Specificities of smectites composition and structure as isomorphic substitution and extremely low level of structure order. It is well known that smectites are first minerals among phyllosilicates which are dissolved and removed from upper horizons of acid soils in the boreal zone. In spite of this fact, smectites are more or less regular distributed in the acid, weakly differentiated soils on parent materials in which smectites dominate among clay minerals. These soils are stretched on the east of European Russia. The aim of this research was to find out characteristic of crystal-chemical features of soil smectites studying by the X-ray diffractions and Transmission Electronic Microscope method (TEM) with micro-probe analyzer. Chemical composition of smectites were established on the base of TEM-data (Kasbohm and et. al., 2000) with using Köster model (1977). The iron parameters in the clay-size fractions of the soils were studied by Moessbauer spectroscopy. The objects are smectites of Chromic Luvisols fine fractions that are enriched by smectites because of sola development on Permian red colored clays. The crystal-chemical parameters of studied smectites as a result of TEM data with micro-probe analyzer are represented by montmorillonite (smectite with charge location in the octahedral sheet) and beidellite (smectite with charge location in the tetrahedral sheet). Their specificity is high iron content in the structure, especially in a number of particles of beidellite that are classified as Fe-beidellite. According to X-ray data, the layer charge of smectites increases in the upper horizons in comparison with the bottom ones. We believe that there is mechanism of layer charge increase. This mechanism takes place in case of iron enrichment of clay minerals. The parameters of iron in the smectite group minerals based on the Moessbauer spectroscopy data were done previously (Johnston and Cardile, 1987; Luca, 1991 and et. all). These results were based on the Tsiporsky and Drits model (1984). According to this model, the inner doublet in the moessbauer specters belongs to the trans –OH sites, the outer one to the cis-OH sites. In the smectites with charge location in the octahedral sheet (montmorillonite) trans –OH sites are previously occupied, except of in the smectites with charge location in the tetrahedral sheet (beidellite and nontronite) these positions are vacancy and cis-OH sites are occupied. Our own data showed that the redistribution of iron in the octahedral (trans- and cis-sites) and tetrahedral sheets in the studied sola takes place. In the bottom horizon, almost all iron Fe3+ (85%) is in the trans octahedral position (quadrupole splitting (Qs) 0.60 – 0.63mm/s; isomer shift (Is) 0.50 – 0.66mm/s). In the middle part of soil, iron is partially in tetrahedral sheets (15%) (Qs 0.46 mm/s; Is 0.36 mm/s). In the top horizon the percentage of iron in tetrahedral sheets increases (27%); this shift takes place concurrently with the growth of iron portion in the cis octahedral position (25%) (Qs 1.40mm/s; IS 0.80 mm/s). The iron redistribution leads to the charge rearrangement and location in the tetrahedral sheets. Thus, the increase of iron percentage in the tetrahedral sheets takes place simultaneously with the layer charge increase that leads to the raise of the sustainability of soil smectites.

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