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The X-Ray investigation of anthropogenic salinization influence on the clay mineralogy of Seriogovo soils

Yulia S. Simakova 

Institute of Geology of RAS (IG), Pervomaiskaya st., Syktyvkar 167982, Russian Federation

Abstract
The objects of our investigation are the podzolic soils from the Seriogovo salt plug territory where salt mineral waters deposites are situated. Seriogovo salt plug is confined to Mezen syneclise of Russian platform. Samples were obtained from 7 soil cross sections near the Seryogovo salt deposite: R-4, R-6, R-7, PR-1 – uncontaminated (background) and R-5, R-8, R-9 – saline cross sections at the depth 0-103 cm.

The mineralogical composition of the clay fraction (<2 µm) of samples was determined by x-ray diffractometry. The clay samples were subjected to several standard treatments before XRD-analysis. Diffraction patterns were obtained of clay samples: a) air-dried, b) glycerol-saturated, c) treated by 1N HCl at 100oC and d) heated for 1h at 550oC. The d(060)-values were used to distinguish dioctahedral (0.1510 nm) and trioctahedral (0.1538 nm) minerals.

X-ray analysis indicates that almost all clay samples of background sections contain smectite, illite, chlorite, kaolinite with dominated smectite. In clay samples of saline soils chlorite, vermiculite, interstratified chlorite/vermiculite, kaolinite, illite and galite are contained. Chlorite became the predominant 1.4-nm-mineral. Smectite is the most abundant mineral in the clay fraction of uncontaminated soils. The smectite is not well ordered, evident by incomplete collapse to 1.0 nm when heated to 550oC. Small amount of disordered chlorite contains in this samples. In the lower parts of saline cross sections smectite is almost absent, the most abundant minerals are pedogenic dioctahedral chlorite and interstratified minerals. The XRD patterns for the clay fraction of the uncontaminated section has an intense peak of 0.1540 nm and a smaller peak of 0.1507 nm suggesting that in this samples trioctahedral minerals are dominated, but also samples contains some dioctahedral minerals. The samples of the saline section also has both trioctahedral and dioctahedral minerals but the intensity of the peak for the dioctahedral mineral, however, is proportionally larger than in the uncontaminated clay.
The investigations display the difference between the clay minerals of saline and background soil samples of Seriogovo deposits because of their transformation under the environmental changes. The expandable layer silicates typical for the soils transformed to the unexpandable dioctahedral soil chlorite. Transformation reactions involves the introduction of non-exchangable hydroxyl-Al polymers into the interlamellar space of pre-existing smectite or vermiculite. We can propose that interlayer octahedral layers are more stable than exchangeable cations of clay minerals’ crystal structure in the saline environment.The results presented suggest that chlorite was formed diagenetically by prolonged periodic percolation of salt brines through pervious layer silicates.
 

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Presentation: Poster at 11th European Powder Diffraction Conference, Poster session, by Yulia S. Simakova
See On-line Journal of 11th European Powder Diffraction Conference

Submitted: 2008-03-24 07:53
Revised:   2009-06-07 00:48