Study Of Low Rank Coal Surface Wettability Regulation And Its Effect On Flotation Under Assistance Of Ultrasonic

The organic matter in low rank coal contains a large number of polar oxygen-containing groups and has poor hydrophobicity.It is difficult to utilize the difference in surface wet Tableility between organic matter and minerals in coal to achieve the purpose of flotation separation.By changing the solution environment and other factors can enhance the selective adsorption of surfactants on organic matter and increase the hydrophobicity of the organic matter on the surface of the coal.At the same time,the ultrasonic desorption method is used to remove the surfactants adsorbed on the minerals,which further expands the surface wet Tableility difference between the organic matter and the minerals in the low rank coal,and achieves the purpose of promoting the flotation effect of the low rank coal.In this paper,the non-ionic surfactant dodecyl alcohol polyoxyethylene ether(C₁₂EO₁₅)was selected to enhance the surface hydrophobicity of low rank coal.By changing the addition method of calcium ions and the pH of the solution,the effect of the changes of solution environment on the surface wet Tableility difference of organic matter and minerals and low rank coal flotation under the assistance of ultrasound were studied.The flotation performance index was used as evaluation index,an optimized plan for pretreatment before selection was obtained.With the help of adsorption capacity,Zeta potential,surface functional groups and wetting heat,the improving effect mechanism of surface wet Tableility regulation on low rank coal flotation under ultrasonic assisted was discussed.The three calcium ion addition methods(first CaCl₂ then C₁₂EO₁₅,first C₁₂EO₁₅ then CaCl₂,and simultaneous adsorption C₁₂EO₁₅ and CaCl₂)would promote the adsorption of C₁₂EO₁₅ on the surface of organic matter.C₁₂EO₁₅would be desorbed from the surface of organic matter by ultrasonic desorption treatmentFor minerals,when C₁₂EO₁₅ was adsorbed first,ultrasonic treatment had no significant effect on the desorption capacity,in the other two cases,ultrasonic treatment would promote the adsorption of C₁₂EO₁₅ on the surface of minerals to varying degrees.Under ultrasonic assistance,preferential adsorption of CaCl₂ or C₁₂EO₁₅ could both expand the wet Tableility difference between the surface of organic matter and minerals,and improve the flotation separation performance.While simultaneous adsorption of C₁₂EO₁₅ and CaCl₂ had no effect on expanding the difference in wet Tableility.Ultrasonic desorption would facilitate the separation of organic matter and minerals,and improved the flotation effect of low rank coal.Under the optimal treatment method,all three calcium ions addition methods could reduce the ash content of clean coal about 8%.The yield of clean coal obtained by simultaneous adsorption of C₁₂EO₁₅ and CaCl₂ was highest,followed by calcium ions preferential adsorption,and surfactant preferential adsorption.When pH=5,the adsorption capacity of surfactant on the surface of organic matter was lowest,and when pH was in range of 3～12,Ultrasonic treatment would cause desorption of surfactant.For minerals,in the range of pH less than 7,ultrasonic treatment could facilitate the surfactants adsorbed on the surface of minerals,while the pH was greater than 7,ultrasonic treatment facilitated desorption of surfactants from mineral surfaces.Under the assistance of ultrasonic,with the increase of pH,the yield of clean coal gradually increased,and the ash content increased first and then decreased and then increased.