Studies On Preparation Of Coal Gangue-based Porous Silicate Nanomaterials And Its Adsorption Of CO₂

Carbon dioxide（CO₂）is one of the most important greenhouse gases.Its excessive emissions cause serious consequences such as global warming.Therefore,the control of CO₂ emissions has become a research hotspot at home and abroad.Using solid adsorbents to capture CO₂ is one of the most important methods.However,some solid adsorbents present high cost and low selectivity for CO₂.Therefore,this paper tries to use solid waste coal gangue to prepare adsorbents to solve the problems of the solid adsorbents.Coal gangue is a large amount of solid waste discharged by coal mine in the production process,which brings a lot of pollution to water resources,land resources and air,but it contains a lot of SiO₂,which can be used in the preparation of chemical products.In this work,SiO₂ in coal gangue is extracted by roasting-caustic alkali leaching process.Silicon extraction liquid is prepared and reacted with some metal salts to prepare porous silicate nanomaterials（silicate and composite silicate）to adsorb CO₂.The main research contents are as follows:Firstly,the optimum preparation conditions for extracting SiO₂ from coal gangue were determined,and the silicon extraction rate could reach 77.69%.Four kinds of silicates（MgSiO₃,MnSiO₃,CuSiO₃ and ZrSiO₄）and three kinds of composite silicates(Mg_x-Mn_1-x-SiO₂,Mg_x-Cu_1-x-SiO₂ and Mn_x-Cu_1-x-SiO₂)were prepared by using silicon extraction solution as silicon source and the conditions determined by single factor and response surface experiments.Secondly,the structures of porous silicate nanomaterials were characterized systemly by the technologies of Fourier transform infrared spectroscopy（FTIR）,X-ray photoelectron spectroscopy（XPS）,specific surface area measurement（BET）,thermogravimetric analysis（TG-DSC）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.It could be seen that materials were basically amorphous structure,which were made up of nanometer-sized small particles with many pore structures,a relatively high specific surface area and higher thermal stability.Finally,adsorption phase equilibrium and thermodynamics of CO₂ on porous silicate nanomaterials were studied.Langmuir and Freundlich models were used to fit the adsorption isotherms at different temperatures.It was found that the adsorption of CO₂ on the material belonged to the multi-molecular layer adsorption,and the surface of the materials were not uniform.Through the analysis of thermodynamic parameters(?H_ads,?Sads,Q^st,and?G_ads),it could be seen that the adsorption of CO₂ on porous silicate nanomaterials belonged to physical adsorption,which was a process of exothermic,entropy reduction and spontaneous process.Ten cycles of adsorption and desorption indicated that porous silicate nanomaterials had relatively stable cycle performance.Porous silicate nanomaterials adsorbed N₂ at 25 ^o C,the adsorptive capacity was 1/39 of CO₂,indicating that the prepared porous silicon nanomaterials present high selectivity to CO₂.