Study On The Performance Of Graphene Oxide-based Membrane For The Separation Of Mercury Ions In Desulfurization Wastewater

Graphene Oxide（GO）,as an important derivative of graphene,which has excellent mechanical properties and stable two-dimensional pore structure.It shows great potential in sewage treatment,desalination and energy engineering.At present,the triple-tank neutralization and sedimentation were widely used in the coal-fired power plant to treat Hg²⁺in desulfurization wastewater.However,due to the large number of chemical reagents added in this process,resulting in the high suspended solids and salt content in the discharged wastewater,and may cause secondary pollution to surface water,which cannot meet the increasingly stringent discharge standards.Based on this background,this paper carried out"Study on the separation performance of graphene oxide-based membranes for mercury ions in desulfurization wastewater",which laid the foundation and provided the basis for future industrial applications.First,the Hummers method was used to prepare GO,and the polyethersulfone（PES）microfiltration membrane filter membrane was severed as a supporting layer.The GO membrane was prepared under the assistance of pressure.The Scanning electron microscope（SEM）,X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FTIR）,X-ray photoelectron spectroscopy（XPS）,and atomic force microscope（AFM）were used to characterize the physical and chemical properties of GO membranes.The results show that the GO prepared in this paper has a large number of hydroxyls,carboxyl,and oxygen-containing functional groups.Besides,the GO membrane was brittle by liquid nitrogen to observe the cross-sectional view of the membrane.It could be found that the membrane was in a layered state,and the membrane was dense and uniform.Secondly,the membrane performance evaluation device was designed in this paper.The GO loading,temperature,p H value,initial Hg²⁺concentration and ion component of wastewater were investigated.Besides,the separation mechanism of GO membrane was studied.The results indicate that the higher temperature of desulfurization wastewater was beneficial for the improvement of Hg²⁺rejection rate.The optimum rejection rate of Hg²⁺could be obtained at the GO loading of 246 mg·m^-2.In addition,the p H value has a great impact on the separation performance,and the optimum separation performance could be obtained at the p H value of 9,which was mainly related to the protonation and deprotonation effect of carboxyl groups in the membrane.Moreover,the influence of Ca²⁺,Mg²⁺and K⁺on Hg²⁺removal was unobvious,and rejection rate was higher than 65%.While the existence of Na⁺will inhibit the separation effect of the separation membrane on Hg²⁺.The separation mechanism of GO membrane mainly depended on the effect of adsorption,size sieving and Donnan effect.In order to enhance the separation performance of GO membranes,the Tannin Acid（TA）was severed as the reducing agent to prepare Tannin Acid Reduced Graphene Oxide（rGO-TA）membrane.Besides,the SEM,XPS,XRD and FTIR were carried out to analyze the rGO-TA membrane.It was found that the large number of polyphenolic hydroxyl groups in TA shows excellent reducing performance forGO membrane,which could eliminate some oxygen-containing functional groups in GO membrane and reduce the layer spacing.Moreover,the study found that the degree of reduction of the rGO-TA membrane could be adjusted by the amount of TA added and the reduction time.On this basis,the Hg²⁺separation performances of the rGO-TA membrane in different conditions,such as rGO-TA loading,temperature and initial Hg²⁺concentration,were investigated.The results show that the resistance of the rGO-TA membrane to water molecules was reduced so that the water flux could be increased to56.5 L·m^-2·h^-1.Moreover,the rGO-TA membrane exhibited an excellent rejection rate of more than 91.61%.Besides,the rGO-TA membrane could maintain good separation performance under different separation conditions.This was mainly due to the relatively stable membrane structure of the rGO-TA membrane and the enhancement of the screening effect of the separation membrane size.