Flotation behavior of raw and oxidized fine coal when mixed with coarse particles

It is well-known that ultra-fine particles, especially those with oxidized surface, are difficult to float using conventional methods. Flotation of oxidized ultra-fine particles has been a serious problem which should be well solved as the demand for energy is increasing. In this investigation, the flotation behaviors of fresh and oxidized fine coal (<45 μm) and the effect of mixing with coarse particles (250-500 μm) in equal proportions were discussed. Zeta potential and contact angle results indicated the surface hydrophobicity of oxidized fine coal was much lower than that of fresh fine coal. When floating alone, yields of fresh, moderately oxidized, deeply oxidized and very deeply oxidized fine coal were 77.88%, 62.36%, 34.66% and 16.67%, respectively. However, the yields for the above four fine coals were increased to 82.83%, 87.04%, 82.72% and 50.07%, respectively when mixed with coarse particles. The yield improvement indicator values for the four fine coals were 4.95%, 24.68%, 48.06% and 33.40%, respectively. Obviously, the yield improvement indicator values for oxidized fine coals were much higher than fresh fine coal. A similar trend was also observed in the experiments without collector. Throughout this research, mixing with hydrophobic coarse coal is proved to be an effective method to improve the flotation behavior of oxidized fine coal.