Effect of pre-wetting time on oxidized coal flotation

•The pre-wetting time is 1 min, 2 min, 3 min, 4 min and 5 min, respectively.•The pre-wetting time has a significant effect on oxidized coal flotation.•XPS and SEM were used to indicate surface properties of oxidized coal.

In this investigation, we discussed the flotation behavior of oxidized coal treated by different pre-wetting times. The pre-wetting time is 1 min, 2 min, 3 min, 4 min and 5 min, respectively. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and contact angle measurements were used to indicate the surface properties of oxidized coal. XPS results show that the hydrophobicity of oxidized coal is very low and the oxidized coal should be pre-wetted quickly as there are many hydrophilic functional groups and few hydrophobic functional groups on the oxidized coal surface. In addition, there are also many cracks and holes on the oxidized coal surface from SEM pictures. The cracks and holes should be covered or filled up with water during pre-wetting process. Contact angle measurement results show that the contact angle between the water drop and oxidized coal surface decreases rapidly with the increase of measurement time. Both of the combustible matter recovery and concentrate ash content decrease with the increase of pre-wetting time.

Graphical abstractXPS, SEM and contact angle measurements indicate why oxidized coal is difficult to float. Oxidized coal has many hydrophilic functional groups, such as C═O, C―O and COOH. There are few hydrophobic functional groups, such as C―H and C―C. There are also lots of cracks and holes on oxidized coal surface which can be filled with the water.Figure optionsDownload full-size imageDownload as PowerPoint slide