The Impact of Large Grain Clay Minerals on X-ray Diffraction Quantitative Analysis of Clay Minerals
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ABSTRACT
BACKGROUNDCurrent X-ray Diffraction analysis of clay minerals is used to detect the clay mineral assemblages and contents of suspended solution with a particle size of less than 2 μm, but the content data is sometimes inconsistent with other test data. The clay minerals with grain sizes larger than 2 μm in the Ordos Basin were observed by Polarizing Microscope and Scanning Electron Microscope (SEM). The kaolinite has grain sizes ranging from 3 μm to 10 μm, which would result in imprecise content data of clay minerals.OBJECTIVETo evaluate the influence of large particle clay minerals on the relative content of clay minerals by designing a comparative test of extracts from different particle size.METHODS267 samples were selected randomly, and each sample was prepared by extracting two suspension solutions according to the standards of 10 μm and 2 μm, respectively. The clay mineral assemblages and contents of 10 μm and 2 μm extracts were obtained using the analytical method in the SY/T 5163-2010 industry standard.RESULTSThrough comparison, it is found that large-grained clay minerals have a significant effect on the relative contents of various types of clay minerals. The clay minerals in 10 μm extracts have a higher content of kaolinite than the 2 μm extracts. Illite/montmorillonite interlayer mineral contents decrease significantly. The change in the illite content is small and irregular. The overall change in chlorite content is small, and the chlorite content in minor samples deviates significantly, which is related to the occurrence of large-particle kaolinite. The standard for extracting grain size should be carefully selected in combination with the geological conditions.CONCLUSIONSIt is proved by this experiment that large particle kaolinite has a significant influence on the relative content of clay minerals. Furthermore, the extraction of particle size standards for clay minerals should be carefully chosen by the actual geological conditions and the purpose of the work. It is also suggested that the industry standard SY/T 5163-2010 should be revised.
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