The effect of saline water on the critical degree of coal surface oxidation for coal flotation

In this work, the effects of water with different salinities on the flotation of oxidized coals were studied and the underlying mechanisms were revealed. Flotation tests were conducted using coal samples with different degrees of surface oxidation and in water of different salinities. A critical degree of coal surface oxidation, above which the coal particles cannot be recovered by true flotation, was observed in flotation with all types of water. It is interesting to find that the critical degree of surface oxidation increased with water salinity, suggesting that coal flotation in saline water had a better tolerance for surface oxidation. The effects of water salinity on the flotation of oxidized coals were studied by investigating the change of coal surface properties and froth stability. On one hand, the surface hydrophobicity of oxidized coals decreased in saline water, which was unfavorable for coal flotation. On the other hand, the compression of the electric double layer in saline water could increase the flotation efficiency by reducing the electrostatic repulsion between particle and bubble. In addition, smaller bubbles and a higher stability froth were generated in saline water, which could also increase the flotation efficiency