| Excessive fluoride will cause pollution to surface water,excessive intake of fluoride will cause dental fluorosis,fluorosis bone disease and other diseases.Reducing the impact of fluoride on the environment is of great significance.In many fluoride removal/reduction methods,adsorption method is widely used,due to simple operation,economic and environmental protection.Aluminum-based adsorbents such as alumina are commonly used in the market to remove fluorine from water,but the disadvantages of the adsorption process are low adsorption capacity,narrow pH response range and low adsorption rate.In order to improve the performance of aluminum-based adsorbents,the polymerized aluminum-based adsorbents Al5·7.5H2O were prepared and characterized by XRD,XPS,SEM and FT-IR in this thesis.The adsorption performance,thermodynamic calculation,adsorption isotherm model and adsorption dynamics model of Al5·7.5H2O on fluorine ions were investigated,and the adsorption mechanism was investigated and verified from three perspectives of pHzpc,coordination structure and anion exchange.The conclusions are as follows:（1）The indirect synthesis method was used to prepare the adsorbent Al5·7.5H2O:First,the ternary phase diagram theory was used to prepare the precursor high-purity P-Al13 crystals,then dissolved into distilled water at 0 oC as saturation concentration.After the hydrothermal synthesis reaction,the adsorbent Al5·7.5H2O was successfully prepared.The agent Al5·7.5H2O was characterized and analyzed by XRD,SEM,BET,FT-IR.The results showed that the as-prepared Al5·7.5H2O had high purity,rhombohedral shape and mesoporous shape,and Al-OH coordination bonds,so that its adsorption performance has a theoretical guarantee.（2）The adsorption performance of Al5·7.5H2O for fluorine was investigated,including the dosage,initial pH of the solution,coexisting ions,temperature,initial concentration,contact time,thermodynamic calculation,adsorption isotherm model,adsorption kinetic model,and renewable recycling test.The results show that Al5·7.5H2O can have a response range of pH 2-9 under a low dosage（1.0g/L）,and the fluorine removal rate can reach 99%.Compared with other types of adsorbents,the fluorine removal rate was excellent.When the pH of the solution was at 5.0,the F-concentration was 100 mg/L,and the dosage of Al5·7.5H2O was 0.25g/L,the adsorption capacity was as high as 276.1 mg/g.When the pH was at 5.0,the F-concentration was 10mg/L,and the dosage of Al5·7.5H2O was 0.25g/L,the entire adsorption process reached 92.4%of the fluorine removal rate in 37s,the adsorption equilibrium was stable in 2 minutes,and the removal rate was up to 99%,to achieve rapid adsorption,high adsorption rate.（3）Thermodynamic calculations show that the adsorption process was a spontaneous and exothermic reaction.The fitting of Freundlich isotherm equation and PSO kinetic model revealed that the active sites of the adsorbent were not uniformly distributed,and the adsorption of fluoride was mainly chemical adsorption and multilayer adsorption.The presence of Cl-,NO3-,SO42-did not cause competitive adsorption and had no significant nagative effect on the removal of F-,the removal rate remained above 95%,while CO32-,PO43-had a disturbing effect on the fluorine removal performance.The regenerated Al5·7.5H2O adsorbent maintained a high adsorption capacity of more than 90%even after 4 desorption-adsorption cycles,and the fluorine concentration of the effluent reached the drinking water standard,indicating that the Al5·7.5H2O adsorbent had a good fluoride removal and reuse.（4）Exploration of the adsorption mechanism was carried out,comparing with the heat treatment products of Al5·7.5H2O at 245℃,300℃,450℃,900℃.Fluorine adsorption performance experiment and related characterization verified the Al5·7.5H2O coordination structure played the most roles on the adsorption performance.By comparing the change of chlorine content before and after adsorption to infer whether there is ion exchange adsorption,the results show that the product after different temperature treatment,the adsorption performance was negatively affected by high temperature treatment.The analysis results of XRD,FT-IR,XPS indicated that the high temperature causes Al5·7.5H2O to collapse its own structure,Al-OH and Al-OH2 coordination bonds disappeared.Combined with the adsorption effect,the effect of coordination structure on the adsorption performance was verified,in other words,coordination adsorption was one of the adsorption mechanisms of Al5·7.5H2O defluorination.XPS characterization was performed on Al5·7.5H2O after adsorption of fluorine at different concentrations.The increase in fluorine and the decrease in chlorine were sufficient to indicated that the exchange of chloride anion in the Al5·7.5H2O solid with fluoride ions in the solution is also one of the adsorption mechanisms.Combined with the effect of pH value on the adsorption effect of Al5·7.5H2O and the corresponding pHzpc,it was concluded that the adsorption mechanism of electrostatic interaction also exist.Adsorption mechanism was contain three aspects:firstly,electrostatic interaction:fluoride ions are adsorbed on the surface of Al5·7.5H2O by electrostatic interaction;sencondly,the anion exchange mechanism:fluoride ions and chloride ions are exchanged,and fluoride ions enter the structure;finnaly,ligand exchange:Al-OH or Al-OH2 react with fluoride ion and converted to Al-F.After retreatment operation of hydrochloric acid and sodium hydroxide,Al-OH or Al-OH2 can be regenerated,and a new round of adsorption experiment can be continued.All in all,Al5·7.5H2O as a new type of polymeric aluminum-based adsorbent had advantages of rapid adsorption,large adsorption capacity,wide pH response range,easly reproducible utilization and various adsorption mechanisms.Al5·7.5H2O can solve the disadvantages of aluminum-based adsorbents such as alumina and expected to be used in the market to remove fluorine from water. 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