Composition, purification, and identification of carbon matter in coal-series kaolin by COD analysis

Coal-series kaolin is a product of seam deposition in coal-accumulating basins and may contain rich reducing substances. Having high carbon matter content, the chemical oxygen demand (COD) of raw kaolin can range from 5000 to 30,000 μg/g, representing a serious disadvantage for use in clarification in the glass industry, etc. and having potential adverse effects on final product quality. In this study, solvent extraction and demineralization procedures were adopted to collect carbon matter from coal-series kaolin; the structure and mineralogical characteristics of the carbon matter were investigated by X-ray diffraction (XRD) analysis, Fourier-transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy, and pyrolysis–gas chromatography–mass spectrometry (Py–GC/MS). Results show that the main phase of the raw ore was kaolinite, with pyrite, quartz, anatase, and illite as impurities, with carbon matter accounting for quite a large proportion of the COD of the coal-series kaolin. The main structure of the carbon matter in the chloroform extract and demineralization residue was aromatic hydrocarbon, with oxygen-containing functional groups mainly consisting of phenolic compounds and amino acids. Therefore, the main composition and structure of carbon matter in the coal-series kaolin were identified, facilitating its purification and application. Graphical Abstract