The Mechanism Study Of Adsorption And Modification Of Gemini Surfactant On Low-rank Coal

Energy is an important material basis for the survival and development of human society.High-quality coal resources have been developed on a large scale to meet the demand of rapid economic development,therefore,the reserve of high-quality coal is decreasing,therefore,it is an inevitable trend to increase the development and utilization of low-rank coal resources.Low-rank coal is featured by a number of oxygen-containing functional groups on surface and long side chains,which result in strong hydrophilicity and poor floatability and then the upgrading and utilization of low rank coal is limits.In this paper,Shendong long-flame coal was taken as the research object,and nonionic Gemini surfactant was taken as modifier to regulate the surface wettability of low-rank coal.The surface wettability and adsorption modification mechanism of Gemini surfactant on low-rank coal were systematically studied by adsorption experiment,X-ray photoelectron spectroscopy(XPS),flotation kinetics and other research methods,which provided theoretical foundation and technical support for effective upgrading and utilization of low-rank coal.Nonionic surfactant S465 is a Gemini structure containing-CH3、-CH2、C-O-C、-OH functional groups.The surface tension of S465 was 30.10 mN/m at cmc,which has higher surface activity than traditional surfactant.And the cloud point of surfactant was 66℃(±1℃)when its concentration was 1.00%.The adsorption of Gemini surfactant on low-rank coal surface was well fitted by the Langmuir equation,and the maximum absorptive capacity was 14.49 mg/g,18.15 mg/g,22.94 mg/g respectively at 30℃,40℃,50℃.Gibbs free energy ΔG were negative and the enthalpy change ΔH were greater than 0,so the adsorption was spontaneous endothermic process.The adsorption of Gemini surfactant on low-rank coal surface was physical adsorption driven by hydrogen bonding,conforming with pseudo-second order kinetics model,and following the intergranular diffusion and the liquid film diffusion,and the liquid film diffusion was a limiting factor in the rate of adsorption.The contact angle of low-rank coal after adsorbing surfactant reached the maximum,which was 13° higher than the value without the surfactant.After adsorbing a certain amount of surfactant,both the adhesion force of low coal-water system and surface free energy of low-rank coal were reduced.Compared with that before adsorbing surfactant,the oxygen element content of low-order coal after adsorbing surfactant decreased by 1.51%and the content of oxygen-containing groups decreased by 10.39%,which improved the hydrophobicity of low-rank coal.Adsorbing Gemini surfactant could increase Zeta potential and reduced the negatively charged functional groups on the surface of the low-rank coal.After adding Gemini surfactant,the flotation process followed the classical first order dynamics model,and the combustible material recovery was 70.67%.