| Coal dust reduction is critical for the building of modern anthracite coal mines that are both efficient and environmentally friendly.Spray dust removal is a common approach for preventing and controlling coal dust disasters,however anthracite has a high degree of coalification,high hydrophobicity,and a poor dust removal effect.The addition of surfactants to water can improve water’s ability to moisten coal dust,resulting in a more effective dust reduction effect.For the selection of surfactants for wetting anthracite and the development of high-efficiency anthracite dust suppression technology,the adsorption characteristics of surfactants on the surface of anthracite,as well as the interaction mechanism between surfactants,water,and anthracite macromolecules,are critical.This paper took Jincheng anthracite as the research object,adopted molecular dynamics simulation and experimental methods,selected the linear alkylbenzene sulfonate（LAS）series of octaalkylbenzene sulfonate（8C）,sodium dodecylbenzene sulfonate（10C）,sodium dodecylbenzenesulfonate（12C）,sodium tetradecylbenzenesulfonate（14C）,four isomers of sodium hexadecyl benzene sulfonate（m-C16,m=2,4,6,8;m represents the attachment site of the benzene ring in the skeleton）,octadecyl benzene sulfonate Sodium（18C）,to study the effects of the attachment site of benzene ring structure on the main carbon chain and the length of hydrophobic tail chain on the adsorption characteristics of anionic surfactants on the surface of anthracite.Dodecyl polyoxyethylene ether(C12（EO）7,C12（EO）15,C12（EO）20,C12（EO）23)with different numbers of ethoxy groups and Tween 20 were selected to study the influence of the length and branched chain structure of the hydrophilic head group in nonionic surfactants on the adsorption characteristics on the surface of anthracite.Three anthracite models were constructed,namely:two-component anthracite surface model;anthracite model characterized by graphene modified with oxygen-containing functional groups;55-component large-scale anthracite model.Among them,the large-scale coal model with 55 components(C7730H3916O133N123S25)is closer to the real situation in terms of the richness of the components and the molecular weight of the coal model.The surfactant-anthracite,surfactant-graphene,water-anthracite binary system models and water-surfactant-anthracite ternary system models were constructed.Through the extraction of parameters such as interaction energy,diffusion coefficient,relative concentration distribution,adsorption configuration,radial distribution function,coordination number,molecular orientation and order parameters,mean square displacement,roughness,number of hydrogen bonds,etc,the influence of surfactant structure on its adsorption characteristics on the surface of anthracite was analyzed and compared from multiple perspectives,and the microscopic mechanism of the difference in adsorption characteristics was clarified.The simulation conclusions were verified by surface tension,X-ray photoelectron spectroscopy（XPS）,and infrared spectroscopy（FTIR）.The main conclusions are as follows:（1）The 4-16C/anthracite system has the lowest total interaction energy and the largest contact surface area;It shows that 4-16C has the highest adsorption strength on the surface of anthracite;4-16C has the highest aggregation degree and the highest adsorption strength near the oxygen-containing functional groups on the surface of anthracite;4-16C can densely cover the ketone groups on the surface of anthracite in solution,and the covering effect is the best near the hydroxyl group,which is much stronger than the other three isomers;The long chain branch of 4-16C has the smallest angle with the Z axis and the highest order degree in the Z axis direction,which is an important reason for the denser layered structure and higher adsorption strength formed by 4-16C.（2）The total interaction energy of the 12C/anthracite system is the lowest,and the diffusion coefficient of 12C is the smallest,indicating that the adsorption strength of 12C on the surface of anthracite is the highest;12C has the highest aggregation degree and the highest adsorption strength near the oxygen-containing functional groups on the surface of anthracite;The layered structure formed by 12C in solution is the densest;The order parameter of 12C is the closest to 0,indicating that its isotropy is the strongest,this also enables its molecules to combine from different directions,intertwined better,and form a denser layered structure,so as to better cover the coal surface.（3）As the length of the hydrophilic group of the dodecyl polyoxyethylene ether surfactant increases the adsorption strength between the surfactant layer and the anthracite becomes stronger,and the hydrophilic head group of the surfactant is more uniformly distributed in the whole distribution range;After adsorption of C12（EO）n on the surface of anthracite,the number of hydrogen bonds between coal and water increased significantly,and the surface of the modified coal became stronger for binding water molecules,indicating that C12（EO）n can well improve the hydrophilicity of anthracite,And the higher the degree of ethoxylation,the stronger the ability to improve the hydrophilicity of coal;Surface tension experiments confirmed that the hydrophilicity order of surfactants was C12（EO）7<C12（EO）15<C12（EO）23;XPS experiment and FTIR experiment proved that:after the adsorption of surfactant and anthracite,with the increase of ethoxylation degree,the content of carbon element on the surface decreased and the content of oxygen element increased,resulting in enhanced hydrophilicity.（4）The anthracite after adsorption of Tween 20 is more hydrophilic;due to the existence of the branched structure of polyoxyethylene,the adsorption conformation of Tween 20 on the surface of anthracite is that the hydrophilic head group covers the hydrophobic tail chain.The C12（EO）20 adsorption conformation of the linear polyoxyethylene unit is that the hydrophobic tail chain covers the hydrophilic head group;The layered structure formed by the adsorption of anthracite by Tween 20 is relatively loose and the surface is rougher;Water molecules are more aggregated,more permeable,and form more hydrogen bonds near Tween 20;The existence state of carbon and oxygen elements on the surface of modified coal was analyzed by XPS experiment,which confirmed the adsorption structure obtained by molecular simulation. |
