Quantitative phase analysis of bentonites by the rietveld method

Thirty six bentonite samples from 16 different locations were examined in order to demonstrate the applicability of a new Rietveld description approach for quantitative phase analysis. X-ray diffraction patterns of the bulk material were obtained and analyzed by the Rietveld method. The samples contain up to ten different minerals, with dioctahedral smectite as the major component. A model for turbostratic disorder of smectites was formulated inside a structure-description file of the Rietveld program BGMN. The quality of the refinements was checked using an internal standard mineral (10.0 or 20.0 wt.% corundum) and by cross-checking results with X-ray fluorescence (XRF) data. The corundum content was reproduced with only small deviations from the nominal values. A comparison of the chemical composition obtained by XRF and the composition as re-calculated from quantitative Rietveld results shows a satisfactory agreement, although X-ray amorphous components such as volcanic glasses were not considered. As a result of this study, the Rietveld method combined with the new structure model for turbostratic disorder has proven to be a suitable method for routine quantitative analysis of bentonites with smectites as the dominant clay minerals.

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