Interfacial Mechanism Of Coal Chemical Wastewater Components And Dispersants In Lignite Water Slurry

Coal chemical wastewater（CCW）contains various complex components,and is difficult to degrade,treat and achieve the goal of near-zero-liquid-discharge.Using coal water slurry（CWS）technology for CCW treatment is an efficient and simple way to achieve both CCW treatment and resource utilization.The macroscopic properties of the slurry are related to the nature of the coal particles and the liquid phase,whether it is a clear water slurry or a wastewater slurry.At present,the kinetics and thermody-namics of liquid phase components adsorption on the coal surface have been extensive-ly studied.However,the information about the effect of CCW components on the ad-sorption structure of dispersant on coal surface and the microscopic mechanism of the dispersant effect on coal/water interface properties is not available.To study the ad-sorption mechanism of CCW components on coal surface at the atomic scale,to reveal the microscopic mechanism of the influence of CCW components on coal/water inter-face,and to analyze the influence of the change of coal/water interface properties in CWWS on the macroscopic properties of the slurry,the results of this work can pro-vide theoretical reference for CCW treatment by CWS technology.This thesis characterized the structural features of de-ash lignite with the support of various analytical testing techniques.For the lignite,the microcrystalline structure was loose,the content of oxygen elements on the surface was high,and the aromaticity was 52.61%calculated by solid NMR ¹³C NMR.The model of the macromolecular structure of lignite was constructed and validated,and the molecular formula of the model was C₁₄₈H₁₄₀O₄₈N₂.The macroscopic adsorption characteristics of coal chemical wastewater and components and dispersants NNO on lignite surfaces were investigated based on adsorption tests.The results showed that the adsorption rates of lignite for NH₄⁺-N,phenol and NNO were site-dependent and the adsorption was heterogeneous.The addition of NH₄⁺-N increased the adsorption of phenol and NNO,phenol had less effect on the adsorption of NH₄⁺-N but inhibited the adsorption of NNO.The surface properties of lignite after adsorption of NH₄⁺-N,phenol and NNO were analyzed using contact angle,zeta potential and XPS.The contact angle of lignite was found to become larger after adsorption of CCW,while those for NH₄⁺-N had no significant effect,whereas phenol and NNO reduced the contact angle.Compared to the deionized water environment,the absolute values of zeta potential of lignite parti-cles in CCW and NH₄⁺-N solution decreased.but increased in phenol and NNO solu-tion.The contents of C-C/C-H and C-O groups on lignite increased weakly after the adsorption of phenol.And the contents of quaternary nitrogen（N-Q）,pyridine nitrogen（N-6）and pyrrole nitrogen（N-5）on the surface of lignite increased after the adsorption of NH₄⁺-N.The percentage of surface S element increased from 0.08%to 0.42%after the adsorption of NNO.The microscopic adsorption structure and kinetic properties of water molecules,ammonia nitrogen,phenol and dispersant NNO on lignite surface were simulated by molecular dynamics,and the microscopic regulation mechanism of the lignite interface after adsorption of ammonia nitrogen,phenol and NNO was investigated.It was shown that the water molecules on the surface of lignite formed the first and second coordina-tion layers.The diffusion coefficient of interfacial water was lower than that of bulk phase water.The lignite molecules had strong binding to the water molecules,and thus forming a more stable hydrogen bonding network near the hydroxyl,carboxyl,and carboxyl groups.There were hydrogen bonding interactions between lignite and NH₄⁺,while hydrogen bonding andπ-πstacking interactions with phenol and NNO anions.The NNO anion formed multilayer adsorption on the lignite surface with increasing bound water,and the diffusion coefficient of interfacial water was further reduced in the presence of phenol.Quantum chemical calculations were used to investigate the interaction mecha-nisms between lignite structural units on water molecules,NH₄⁺-N,phenol and NNO.The results indicated that the interactions between lignite structural units and water molecules were mainly driven by electrostatic interactions,while dispersion and polar-ization interactions were not negligible.The hydrogen bonding energies estimated in the AIM analysis were carboxyl group>hydroxyl group>ether bond>carbonyl group in descending order.Hydrogen bonding between lignite structural units and NH₄⁺was dominated by electrostatic interactions,andπ-πstacking with phenol and NNO anions was mainly a dispersion interaction.The mechanism of the influence of the microscopic interfacial structure of lig-nite/water on the macroscopic properties of the slurry was analyzed by combining ad-sorption tests,theoretical calculation results and slurry production tests.The results showed that the viscosity concentration of CWWS was higher than that of deionized water.When NH₄⁺-N solution was used for slurry,the solid concentration was de-creased While phenol was adsorbed in the pores of lignite,more free water was re-leased,and the viscosity of the slurry was reduced.The slurries all exhibited yield pseudo-plasticity,with an overall weaker pseudo-plasticity for the NH₄⁺-N solution slurry compared to CWWS,and overall lower yield stress for the phenol solution slurry.The lignite particles showed an overall settling phenomenon under the action of gravity,and the stability of the CWS prepared from wastewater and phenol solutions was better compared to the slurry prepared from the deionized water,while the addition of NH₄⁺-N deteriorated the stability of the slurry.