Mechanism of conditioning on improving fine coal flotation

Flotation is an effective method for the separation of fine coal slime.Conditioning has a significant effect on the flotation performance when used as a pre⁃treatment process before flotation.The effects of kerosene dosage and stirring speed on combustible recovery，ash and flotation kinetics were studied by using a difficult⁃to⁃float coal sample with high fine particle content from a surface mining.The changes in the hydrophobicity of the particle surface un⁃ der different stirring speeds were analyzed by film flotation.The distributions of kerosene droplets and coal particles un⁃ der different stirring speeds and stirring time in the conditioning process were measured in real time by using the focused beam reflectance measurement(FBRM).The kerosene adsorption on the coal surface under different stirring speeds were studied by the infrared spectrum analyzer(FTIR).The effects of different stirring speeds on particle flocs were observed by microscopy，and the collision probability between oil droplets and coal particles was calculated theo⁃ retically.The results showed that the combustible recovery and flotation rate constant increased gradually while the ash decreased with the increase of stirring speed from 900 to 1 800 r/min. The results of film flotation indicated that the hydrophobicity of particle surface was improved with the increase of stirring speed.The dispersion ef⁃ ficiency of kerosene was relatively low at a stirring speed of 900 r / min.However，the dispersion efficiency of kerosene was improved significantly with the increase of stirring speed，and the dispersion could be achieved in a relatively short time.The flocs of fine particles were formed through shear flocculation after conditioning verified by FBRM and floc image analysis.When stirring speed increased from 900 to 1 800 r / min，the number of -50 μm coal particles de⁃ creased gradually，especially for the -20 μm particles.The kerosene adsorption on coal surface increased gradually with the increase of stirring speeds.Theoretical calculation revealed the collision probability between kerosene droplets and coal particles increased with the increase of kerosene dispersion when the coal particle size was constant.