| The fluoride pollution in flue gas produced by electrolytic aluminium is seriously harmful to human health,the growth of plants and animals.In this paper,Na F solution was selected as a model wastewater containing fluoride,which was then adsorbed using alumina based adsorbent materials so as to achieve the aim of depth removing of fluoride containments.The results can offer some references to the secondary purification of fluoride pollutions in flue gas produced by electrolytic aluminium,and we also expect that which can be applied in the actual process of fluoride in the future.The synthesis methods,characterization,regulation of pore structural properties,adsorption thermodynamics,kinetics,selectivity and recycling performance were also carefuly studied in the experiments.The results indicated that alumina based adsorbents have simple prepared methods,controlled pore structures,large specific surface area,high selectivity and adsorption capacity toward F-,and fast adsorption rate,which is a kind of excellent defluorination agent.The concrete research contents include the following four aspects.?1?Several gamma-alumina adsorbents were successfully prepared by the hydrothermal synthesis and high temperature roasting technologies with low cost of inorganic aluminum sourcses and precipitation reagents.The effects of reaction conditions on the crystal type,morphology,microstructure and pore structural properties of products were studied detailedly.The experimental results indicated that the crystal structure the products were not controlled by the varieties of aluminum sourcses and precipitation reagents,but the morphologies were obvious influenced.The BET specific surface area,pore volume and pore diameter of gamma-alumina can be tuned by reaction raw materials to some extent.?2?Gamma-alumina was successfully synthesized by using double hydrolysis and high temperature roasting technology with glucose as a pore-controlling reagent.The adsorption performance and mechanism towards fluoride were studied detailed.The experimental results indicated that glucose dosage had no effect on the crystalline,but had important influences on the microstructure and pore structure properties of gamma-alumina.The adsorption speed of gamma-alumina towards fluoride is very quick,and the adsorption process conforms to the Langmuir monolayer adsorption and pseudo-second-order kinetic model,the maximum adsorption capacity is 8.34 mg?g-1.The zeta potential values of gamma-alumina and removing efficiency for fluoride were seriously controlled by solution p H values,but the optimum p H range is rather narrow.Coexisting anions have significant effectsrecycling performance of gamma-alumina is excellent.Fluoride removal mechanism mainly includes the electrostatic attraction,ligand exchange,ion exchange and hydrogen-bond interaction.?3?Mn O2-Al2O3 adsorbent was successfully fabricated using the in-situ growth technology with gamma-alumina as a precursor.The crystalline,morphology,pore structural characters,fluoride removal performance and defluorination mechanism of Mn O2-Al2O3were studied systematically.Compared with mesoporous gamma-alumina,Mn O2-Al2O3 has much larger specific surface area,pore volume,narrower pore size distribution and special bimodal mesoporous structure.The experimental results showed that the adsorption rate of Mn O2-Al2O3 was very quick,and the removal efficiency was better.Mn O2-Al2O3 has a wide defluorination range of p H?p H=410?,which is more suitable for actual conditions for industrial application.The adsorption process conformed to pseudo-second-order kinetic model,which indicated this was a chemical adsorption procedure.Coexisting anions experiments results indicated that some anions in the solution have significant effect on theHowever,the recycling utilization performance of Mn O2-Al2O3 is inferior to gamma-alumina,and the microstructures are needed to be improved furthermore.The adsorption mechanism is same as the adsorbing process of?-Al2O3.?4?GO-Al2O3 was successfully prepared by using hydrothermal technology as graphene oxide?GO?and?-Al2O3 as based materials,as well as the adsorption performance and mechanism for fluoride removal were also carried out thoroughly.The experimental results indicated that more active sites were increased,the specific surface area of GO-Al2O3was greatly enhanced and the pore structure properties was also improved after gamma-alumina nanoparticles were dispersed evenly onto the surface of GO layers.Based on much more active sites of gamma-alumina were exposure and some functional groups were provided by GO,the adsorption capacity of GO-Al2O3 increased to the value of 2 times of gamma-alumina.The optimum p H range of GO-Al2O3 for fluoride removal is rather wide,and the adsorption process conforms to pseudo-second-order kinetic model,which suggests the adsorption behavior is involved in chemistry reaction.Adsorption isotherm results indicated that the process of fluoride removal is a special pattern between monolayer adsorption and multilayer adsorption.Coexisting anions have significant effect on therecycling utilization performance of GO-Al2O3 is inferior to gamma-alumina,and the microstructures were needed to be improved furthermore.The adsorption mechanism is also same as the adsorbing process of ?-Al2O3. |
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