Abstract
In order to ascertain the kaolinite crystallinity of Carboniferous Permian coal-measure kaolinite rocks, seven groups of fresh samples were collected from below the ground in the Xiaoyu mine, Datong coalfield. Microscopy, X-ray diffraction (XRD), differential thermal analysis (DTA), infrared (IR) spectroscopy and X-ray fluorescence (XRF) spectrometry methods were applied to the samples. The petrographic analysis results show that the kaolinite rocks are characterized as compact, phaneritic, clastic, sand-bearing, sandy and silty types; the kaolinite content in the Shanxi formation and upper Taiyuan formations was more than 95%, while it was 60–90% in the middle and lower Taiyuan formations. Based on the Hinckley index and the features of XRD, DTA and IR of kaolinites, crystallinity was classified as having three grades: ordered, slightly disordered and disordered. The kaolinites’ SiO2/Al2O3 molar ratio was about 1.9–5.7, with a chemical index of alteration (CIA) of about 95.4–99.5. This research suggests that the kaolinite crystallinity correlates positively to its clay mineral content, purity and particle size, which are also related to the SiO2/Al2O3 molar ratio and CIA. The original sedimentary environment and weathering have a direct influence on kaolinite crystallinity, and the existence of organic matter is conducive to the stable existence of kaolinite. The study results have significance for the extraction and utilization of coal-measure kaolinite and the development of kaolinite crystallography and mineralogy.
Highlights
Coal-measure kaolinite rocks in China occur in all major coal deposits from the latePaleozoic to Cenozoic eras, but especially in the Carboniferous Permian of the late Paleozoic [1]
Kaolinite rocks to identify the petrographic features using a microscope of Leica 2700
The petrological characteristics of kaolinite rocks to identify the petrographic features using a microscope of Leica 2700 kaolinite were described from top results, to bottom below
Summary
Coal-measure kaolinite rocks in China occur in all major coal deposits from the late. Earlier mineralogical and geochemical characterization of the coal-measure kaolinite from Datong indicated an acid plutonic (granitic) or volcanic (rhyolitic) precursor [2,3,4,20], with potential provenance from the Yinshan uplift orogenic belt to the north of NCC (Figure 1), which features shallow surface water with a weak oxidation condition diagenetic environment, formed by protolith in situ leaching and alteration [21,22]. The intercalation composites formed by kaolinite have shown unique properties in mechanics, adsorption, electricity and catalysis, and have broad application prospects in the fields of functional ceramics, nonlinear optical materials, polymer matrix composites and electrorheological fluids [14,17,24]. The study of kaolinite crystallinity would benefit the development of intercalated kaolinites for industrial applications [14,25]
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