Abstract
Oxidation processes of coal surfaces are both fundamental and interesting from academic and engineering points of view. In this work, we comprehensively analyzed the mechanism of heating oxidation at 200 °C on the surface/interface characters and the floatability of anthracite coal. The variations of surface/interface characters were studied using SEM (scanning electron microscopy), FTIR (Fourier transform infrared spectroscopy), and XPS (X-ray photoelectron spectroscopy). The floatability was further identified using Induction Time and Bubble-Particle Wrap Angle. It was found that, after heating oxidation at 200 °C, both surface ravines and oxygen-containing groups were increased. The degradation of hydroxyl on anthracite could be neglected during the heating, while the oxidation of hydrocarbon chains dominated the balance of hydrophobicity and hydrophilicity on coal surface. The induction time significantly increased from 200 ms to 1200 ms and 2000 ms after 10 h and 20 h of heating oxidation at 200 °C, respectively. Additionally, raw coal exhibited the fastest kinetics of bubble-particle attachment and the largest wrap angle, directly proving that the floatability decreased after oxidation.
Highlights
In China, the coal is currently the important energy source
An SEM system was used to study the changes on surface morphology and elemental composition of coal before and after heating oxidation at 200 ◦ C
More time surface ravines were filled by water, preventing the bubble-particle attachment
Summary
In China, the coal is currently the important energy source. Flotation is one of the most common methods for fine coal de-ashing that cannot be achieved by gravity separation [1,2,3,4]. One opposite finding is that, for low-ranked coal, the contact angle increased after oxidation by heating after decreasing in hydrophilic functional groups [15,18,19]. It is well known that two opposing phenomena occur that influence the hydrophobicity at the coal surface during oxidation processes with heat treatment. The other is the oxidation of hydrocarbon chains on the coal surface, producing new carboxyl and phenol groups. This in turn makes coal more hydrophilic [18,20]. An open question is whether the hydrophobicity of high-ranked coal such as anthracite could be enhanced by oxidation by heating. The floatability of coal particles was further identified using induction time and the bubble-particle wrap angle
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
