Influence law of slime coating on coal floatability

The slime coating of gangue on the surface of hydrophobic coal particles is one of gangue contaminations to the flotation clean coal,and it is also a main reason for the deterioration of coal floatability and the decrease of clean coal recovery.The degree of slime coating and its influence law of three kinds of gangue minerals(quartz,kaolinite and illite) on the coal floatability were studied by a single bubble loading test in this study.The results showed that with the increase of the stirring time of coal and gangue mixture,the degree of slime coating between the gangue and coal particles increased with time and almost did not change after 40 minutes.The slime coating was fast at first and then slowed down.Under the condition that the fluid shear rate kept constant,the degree of slime coating of quartz was the weakest,kaolinite the second,and illite the strongest,which was consistent with the observation of cryogenic scanning electron microscope (Cryo-SEM) and the inter-particle force calculation based on the DLVO theory.With the increase of fluid shear rate,the degree of slime coating between the gangue and coal particles was inhibited and the floatability of coal was improved.The slime coating of quartz was almost eliminated at the shear rate of 58 s-1,but the slime coating of kaolinite and illite still existed at the shear rate of 116 s-1.The flotation experiments of coal-gangue mixture were carried out after the agitation with different shear rates.It was found that the high intensity agitation before flotation could mitigate the slime coating of quartz,kaolinite and illite on coal surface,and improve the flotation recovery of coal.But the high intensity agitation increased the dispersion of gangue,which resulted in the aggravation of water entrainment of gangue during flotation.It is necessary to combine other methods to restrain the contamination of gangue to the flotation clean coal.