EVOLUTION OF DIOCTAHEDRAL VERMICULITE IN SEA-WATER ENVIRONMENT- AN EXPERIMENTAL APPROACH

The aim of the study was to investigate the interaction of dioctahedral vermiculite (divermiculite) with sea-water. Because no divermiculite standard material was available, divermiculite-rich clay fraction from soil sample (1E) from the Tatra Mt. (Skiba 2013) was used. The sample reacted with sea water using three protocols: 1E+OW_C and 1E+GB_C were closed for a year in 1 dm³ of artificial oceanic water or in natural sea water of the Gdańsk Bay, respectively, whereas 1E+GB_O was immersed in 5 dm³ of the Gdańsk Bay water changed every 3 days for a half a year. After each experiment portions of samples were exchanged with Na⁺, Ca²⁺ or K⁺ cations, followed by dialysis. The obtained samples were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy with Energy Dispersive Spectroscopy system (SEM-EDS). The layer charge was measured with the OD method (Kuligiewicz et al. 2015).

Original sample 1E contained dioctahedral mica (illite)-vermiculite-smectite and illite-vermiculite mixed-layered minerals and traces of kaolinite and quartz, in accordance with Skiba (2013). XRD patterns of samples from closed systems showed a broad high-angle tails of 13.7 Å peaks. In addition 10.1 Å peaks intensities increased relative to other peaks intensity in all samples reacted with sea water. The layer charge of wettable interlayers decreased form 0.79 per formula unit (p.f.u.) in 1E sample down to 0.66 p.f.u. (sample 1E+GB_C). The K₂O content increased from 3.92% in 1E to 5.69% in sample 1E+GB_C.

Obtained results indicated contraction of divermiculite structure due to K fixation in reaction with sea water, irrespectively of the chemistry of sea water used. Limited availability of K in closed system did not allow to full collapse of all divermiculite interlayers into illite-like phase. The high-charge interlayers were likely to collapse first, which explains apparent layer charge decrease.

Acknowledgments:

This study was financed by National Science Centre, Poland [grant number: UMO-2016/23/N/ST10/01388].

Kuligiewicz A, et al., 2015. Measuring the layer charge of dioctahedral smectite by O-D vibrational spectroscopy. Clay Clay Miner. 63: 443–456.

Skiba M, 2013. Evolution of diotahedral vermiculite in geological environments- An experimental approach. Clay Clay Miner. 61: 290-302.