Study on the Extraction Mechanism of Metal Ions on Small Molecular Phase of Tar-Rich Coal under Ultrasonic Loading

Abstract

This study aims to elucidate the mechanism by which the ultrasonic loading of metal affects the extraction of small molecular phase substances (low molecular compounds) in tar-rich coal. Tar-rich coal samples were collected from the Huangling mining area in the southeastern Ordos Basin, China. The coal, the leaching solution of the coal, the extraction products, and the extraction residual coal samples with different metal ions loaded by ultrasound were analyzed using field emission scanning electron microscopy, pH detection, gas chromatography–mass spectrometry, a Fourier transform infrared spectrometer, and an X-ray diffractometer. The obtained results indicated that the ultrasonic loading of coal samples with different metal ions (Mn2+, Co2+, Cu2+, Fe2+, and Ni2+) promoted the extraction of small molecular phase substances in coal and increased the proportion of extracted aliphatic hydrocarbons, alkylbenzene, naphthalene, phenanthrene, and other compounds. The extraction rate of Mn2+ was the highest. Compared with the control group, the extraction rate was increased by 212%. After the ultrasonic loading of metal ions, the physical structure of the coal was loose and the contact area of the solvent increased; the degree of branching and the hydrogen enrichment of the residual coal decreased, the aromaticity increased, the interlayer spacing and stacking layers decreased, and the stacking degree and ductility increased. Metal ions exchanged with hydrogen ions in the coal molecules. At the same time, the metal ions were adsorbed in the coal molecules and effectively combined with free electrons in the coal molecules to catalyze; thus, the extraction effect of the small molecular phase of tar-rich coal was improved. This provides a new method for the clean and efficient utilization of tar-rich coal.