Effect of roughness on the wettability of lean coal surfaces
Surface roughness plays an important role in the floatability of coal.So the coal surface was roughened with four different grits of sandpaper and the surface properties were characterized by a roughness meter.A contact angle and interaction meter was used to analyze the effect of surface roughness on the wettability of coal with or without sodium oleate modification.The results show that the contact angle decreases as the surface roughness of natural coal increases.The diffusion force between water droplets and coal surface increases due to the increase of contact line.When the roughness is 0.32,1.02,1.82,and 2.38 μm,the diffusion force between water and coal surface is 159.00,177.82,200.99,and 209.60 μN,respectively.Whereas,after modification with low concentration(120 mg/L)of sodium oleate,the contact angle of the coal surface increases with the increase of roughness,and the diffusion force decreases,and the diffusion force is 149.11,146.40,134.06,and 124.27 μN.However,when the concentration of sodium oleate reaches 320 mg/L,the contact angle decreases rapidly with the increase of roughness,and the diffusion force also increases rapidly,and the diffusion force is 174.21,211.05,244.37,and 288.51 μN,respectively.The increase of roughness enhances the coal wettability,and low concentrations of sodium oleate modification and surface roughening can increase the hydrophobicity of the coal surface,however,too much of the agent will increase the wettability of the coal surface again.
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