Preparation Of Aluminum Oxide Medium And Its Adsorption Properties

Fluoride contamination of drinking water due to natural and human activities is considered to be one of the major threats to human health worldwide.Fluoride is an essential element in trace amounts in the body,but when ingested in humans at concentrations above 1.5 mg/L,it can cause organ damage to the body.The fluorine in the earth’s crust is about 0.06-0.09%,and is ranked 13 in the most abundant elemental order.Fluoride ions（F^-）are formed in water because of their electronegativity in an aqueous medium.Fluoride in contact with humans and animals comes mainly from water resources and plants.Accumulation of excess fluoride in the human body can lead to irreversible demineralization of teeth and bones,a condition known as fluorosis,which can cause varying degrees of damage to the brain,liver,thyroid and kidneys.Among several defluorination technologies,adsorption is the most commonly used technology because of its low cost efficiency and ease of operation.Aluminum oxide is currently the most widely studied fluorine removal adsorbent because of its advantages of good chemical resistance,high specific surface area and high recovery efficiency.In the study of this paper,different aluminum oxides were prepared by hydrothermal method,precipitation method and impregnation-calcination method,using scanning electron microscope（SEM）,infrared spectrometer（FT-IR）,and X-ray diffractometer（XRD）.,energy spectrum analyzer（EDS）,laser particle size analyzer,thermogravimetric analyzer（TGA）and X-ray photoelectron spectroscopy（XPS）and other instruments to characterize the composition and characteristics of aluminum oxide,analysis of different aluminum oxidation Adsorption model,adsorption effect and adsorption mechanism.The main research contents are as follows:1.The synthesis conditions of the sample play a key role in the physical and chemical properties of the sample.The effect of hydrothermal preparation conditions on the adsorption performance ofγ-Al₂O₃ was investigated by changing the hydrothermal preparation conditions.The two-step gradient heat preservation of the hydrothermal reaction（heating at 120°C for 2 h,then increasing to 180°C for 24 h）was changed to one-step heat preservation,that is,directly raised to 180°C for 24 h,and the adsorption was obtained under different preparation conditions.The performance of the agent.The results show that theγ-Al₂O₃ synthesized by one-step heat preservation has the best adsorption performance,which provides an important basis for optimizing the experimental process of hydrothermal preparation of adsorbents.2.The amorphous aluminum hydroxide was synthesized by precipitation method.Before the precipitant was added,a certain amount of ethanol reagent was added to the medium.Since the charge center could not overlap,it was a polar molecule,and it was beneficial to be mixed into the solution.The dispersion of the precipitate is such that the specific surface area of the amorphous aluminum hydroxide is enlarged.In the experiment,the influence of different molar ratio of aluminum source and precipitant on the adsorption capacity of the adsorbent was investigated.The results showed that the amorphous aluminum hydroxide prepared by the molar ratio of 1:1 had the maximum adsorption capacity.The kinetic study results show that the adsorption process follows a pseudo second-order model.Thermodynamic studies have shown that fluoride removal is an endothermic and spontaneous process,which confirms the potential value of amorphous aluminum hydroxide for fluorine removal.3.The utilization of natural resources is the eternal topic of human beings.Based on the poplar seed fluff,Mg-Al double metal oxide adsorbent was synthesized by desorption calcination.Firstly,the effects of different Mg/Al molar ratios and calcination temperatures on the fluorine removal performance of the samples were investigated,and then the optimized samples were characterized.The experimental results show that the maximum adsorption capacity of Mg-Al double metal oxide adsorbent is 53 mg/g,and the adsorption equilibrium time is 24 h,which has potential defluorination ability.The adsorption mechanism of Mg-Al bimetal oxide was characterized by infrared spectroscopy and X-ray photoelectron spectroscopy.The hydroxyl group on the surface of the sample was the key factor for adsorption.