The Study On Modification And Adsorption Mechanism Of NaA Zeolite Synthesized From Coal Gangue

Coal gangue is a kind of solid waste accompanied with the production operations of various mining areas.In recent years,a large number of accumulated solid waste have caused serious natural environmental disasters,which has aroused widespread concern.Although there are many cases of exploying coal gangue comprehensively at present,this problem has not been solved from the root cause,because most of them are very simple,low economic benefits and high labor cost.The main components of coal gangue are Al₂O₃ and Si O₂,which are the raw materials for the preparation of zeolites,so this article uses coal gangue as the main raw material to synthesize a high value-added chemical product zeolite by the one-step hydrothermal method.Then,it is modified by a consecutive alkaline and ultrasonic post-treatment to prepare hierarchical porous NaA zeolite,and its micromorphology,crystal structure,phase composition,specific surface area,etc.are characterized by SEM,TEM,XRD,BET and other characterization methods.Finally,adsorption experiments are carried out on untreated and treated zeolites,and the adsorption mechanism is initially explored.（1）Using coal gangue as raw material,the NaA zeolite with an average size of2 um,high integrity and uniform distribution is synthesized by hydrothermal method.Through XRD and SEM,the impact of n（Na₂O）/n（Si O₂）（0.5-3.5）,n（H₂O）/n（Na₂O）（20-50）,crystallization time（1-4 h）,crystallization temperature（70-100°C）on the crystal structure and morphology of there zeolites are studied systematically to determine the best synthesis parameters.The prepared samples are tested by FT-IR and BET to study it’s framework structure and specific surface area,what’s more,the synthesis mechanism was preliminary explored in this article.（2）The NaA zeolite prepared with coal gangue as raw material has a small specific surface area and pore volume,and poor adsorption capacity,so the physical-chemical method of combining with alkaline and ultrasonic post-treatment is used to tune the pore structure of the zeolites.Studies have shown that the skeleton structure of the treated zeolite has not changed.The impact of concentration of Na OH solution（0-5.0 mol/L）,alkaline treatment time（0.5-6 h）,alkaline treatment temperature（70-100°C）and ultrasonic time duration（0-60 min）influence on the phase composition,micro-morphology and adsorption performance of those zeolites.Compared with the untreated zeolite（64.28 m²/g）,the specific surface area of the treated zeolite（162.29 m²/g）increased significantly.From the adsorption experiment date,it is obviously that the removal efficiency of treated zeolite for Cu²⁺and Rhodamine B（Rh-B）has been greatly improved to 83.5%and 95.1%,respectively.The untreated and treated zeolites are tested by TEM and other methods to explore the modification mechanism.The study of post-treatment suggests that the erosion of some Al-OH bonds and Si-OH bonds and parts of structures in the zeolite fell off to Na OH solution,thus forming the hierarchical porous structure which increases the specific surface area and pore volume.（3）In this paper,adsorption experiments are carried out on the untreated and treated zeolites,metal cations(Cu²⁺)and organic compounds Rhodamine B（Rh-B）are selected as adsorbates,and the initial solution concentration(Cu²⁺:10-400 mg/L,Rh-B:2-14 mg/L),adsorption time(Cu²⁺:0-1 h,Rh-B:0-1 h)and the amount of adsorbent(Cu²⁺:0-4 g/L,Rh-B:0-4 g/L)affect on the adsorption capacity of zeolite.The adsorption isotherm is fitted by the adsorption experiment data,and the best fitting correlation coefficient（R²）is used to judge that the adsorption process is consistent with the Langmuir adsorption isotherm.Through the study of adsorption kinetics and adsorption thermodynamics,it is found that the adsorption of Cu²⁺and Rh-B by the treated zeolite is physical adsorption,and the whole adsorption process is a spontaneous endothermic reaction.