Effect of short-term weathering on kaolin preparation from coal gangue via flotation decarburization

Coal-series kaolin flotation decarburization efficiency is greatly influenced by weathering. This study investigated the mechanisms by which three typical types of weathering (short-term natural weathering, low-temperature oxidation and freeze–thaw weathering) affect the surface characteristics and floatability of low-rank coal. Zeta potential measurements, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and contact angle analysis were performed to investigate these mechanisms. Results revealed the following: (1) after 20 months of natural weathering, cracks formed on the coal surface, accompanied by the gradual disappearance of –CH3 and –C–H functional groups. Continued weathering increased the ash content, reduced hydrophobicity and deteriorated floatability. (2) Freeze–thaw weathering for 60 days had a minimal impact on coal hydrophobicity and flotation performance, with only slight fluctuations observed in the flotation yield and ash content of the recovered coal. (3) Low-temperature oxidation over 15 days induced crack development, particle size refinement and complete disappearance of hydrophobic –CH2 and –C–H functional groups, leading to severe deterioration in floatability. Thus, this study confirms that low-temperature oxidation exerts the most pronounced negative impact on flotation decarburization efficiency.