Study on the effects of oxidation on coal surface properties and floatability

Coal inevitably undergoes oxidation reactions during transportation, leading to increased hydrophilicity and reduced flotation recovery rate. In this study, one‑third coking coal was used, and coal samples with different oxidation degrees were prepared using a time-moisture dual-factor design. Various characterization techniques were employed to investigate the influence law of the oxidation process on coal surface functional groups, chemical bonds, wettability, and flotation performance. The results show that as the oxidation degree increased from 14.52% to 26.32%, the surface morphology of the samples evolved from flat agglomerates to porous and fragmented structures, with a decrease in carbon content and an increase in oxygen content. The functional groups exhibited an oxidative upgrading law from – OH to C–O/C=O and finally to –COO–. The contact angle decreased from 63.24 ° to 49.46 °, the flotation clean coal yield dropped from 100.00% to 6.76%, the combustible matter recovery rate decreased from 69.66% to 19.43%, and the floatability grade declined from “extremely easy to float” to nearly “unfloatable” . The study confirms that the effect of oxidation on coal floatability stems from the synergistic effect of physical pore formation and chemical enrichment of oxygen-containing polar functional groups.