The Kaolinite Crystallinity and Influence Factors of Coal-Measure Kaolinite Rock from Datong Coalfield, China

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.

Highly reactive metakaolin: a multi-parameter optimization by response surface methodology

“…The three bands observed are associated with hydroxyl stretching, confirming kaolinite's presence in the raw sample [19,37,38]. The observed three peaks define the kaolinite material under study as low-order kaolinite (LOK) [37,40]. The bands detected at 1115, 1030, and 1006 cm −1 are related to the Si-O stretching vibrations band, and the one at 534 cm −1 depicts the presence of the Al-Si-O bond within the kaolinite under study.…”

Study of Metakaolinite Geopolymeric Mortar with Plastic Waste Replacing the Sand: Effects on the Mechanical Properties, Microstructure, and Efflorescence

“…From the XRD pattern shown in Figure 2 a for kaolinite, the Hinchley index (HI) was calculated using the following Equation (4): where A and B are the height of the diffraction peak at 2θ = 20.2° for ( plan and 2θ = 21.3° for (11 ), respectively, while the At is the height from the baseline to the peak. According to Liu et al [ 32 ], an HI of ≥1.3 indicates a highly ordered structure, an HI of 1.1–1.3 is characteristic of an ordered structure, an HI of 0.8–1.1 is relatively disordered, and an HI of <0.8 is disordered. However, several factors should be considered in the analysis of these results, such as the presence of structural defects, dopants, mix of the phase with other minerals, and the amount of water molecules in the layers of aluminum and silicon clusters [ 33 ].…”

Peak Cutting Force Estimation of Improved Projection Profile Method for Rock Fracturing Capacity Prediction with High Lithological Tolerance

“…To verify the accuracy and stability of the PCF theoretical model proposed in this paper for different lithologies of rocks and for different numbers of rock samples, some full-scale rock cutting experimental results reported previously are cited in this section. The mechanical properties of the 27 rock samples used in these experiments [7,11,[22][23][24] are summarized in Table 1, and these properties interact with each other during rock destruction [25][26][27][28]. The samples are divided into three groups, S (soft), M (medium) and H (hard), according to the different fracture toughness of type I in Table 1.…”