Preparation And Modification Of Adsorbents Based On Activated Alumina And Biochar And Their Adsorption Performance For Fluoride Ion

Adsorption method is a common method for treating fluoride ions in water.For the adsorption defluorination method,activated alumina was selected as the fluorine removal adsorbent in this thesis,and two modification methods of rare earth elements and non-ferrous metal elements were used to modify it,and two new types of modified activated alumina were successfully prepared.The material characterization was carried out to analyze the adsorption performance of fluoride ion under different adsorption conditions.For the adsorption defluorination method,this thesis also proposes a new design idea of adsorbent:porphyrin carbon adsorption material.It is planned to retain the porphyrin ring structure in the raw material during the preparation of carbon-based adsorption materials,hoping that it can have a more prominent fluoride ion adsorption capacity.The specific research results are as follows:（1）A new modified activated alumina method was designed,using lanthanum nitrate and concentrated nitric acid as the main modified substances.Activated alumina was first prepared by alkali precipitation method,and then acidified with concentrated nitric acid,and the acidified activated alumina was modified by lanthanum nitrate impregnation modification method to obtain lanthanum-modified nitric acid acidified activated alumina adsorbent（La-HNO₃-AA）.In addition,magnesium nitrate and nitric acid were used as modified substances,and the magnesium-modified nitric acid acidified activated alumina adsorbent（Mg-HNO₃-AA）was prepared by the same method.Two adsorbents,La-HNO₃-AA and Mg-HNO₃-AA,were characterized and analyzed.The infrared spectra（FTIR）of the two adsorbents before and after modification were analyzed,and the scanning electron microscope（SEM）test was also carried out to observe the surface morphology.Finally,X-ray powder diffraction（XRD）was carried out to analyze the crystallinity of the adsorbent.phase structure.（2）The adsorption experiments of La-HNO₃-AA and Mg-HNO₃-AA showed that when the La³⁺/Mg²⁺modification concentration was 5%,the adsorption time was 2 h,and the p H was adjusted to 6,the adsorption performance could reach the best.The removal rate of fluoride ion under the optimal fluoride removal process conditions of La-HNO₃-AA can reach 93%.The best fluoride ion removal rate of Mg-HNO₃-AA under the same experimental conditions was 90%.The adsorption isotherm analysis showed that the isotherm fittings of La-HNO₃-AA and Mg-HNO₃-AA were in line with the Langmuir isotherm.Macroscopic adsorption kinetics analysis both belong to the pseudo-secondary reaction.Taking La-HNO₃-AA as an example,the effect of anion coexistence on fluoride ion adsorption is as follows:Br^->PO₄^3->NO₃^->Cl^->SO₄^2-.The regeneration experiment of La-HNO₃-AA shows that the primary regeneration rate of La-HNO₃-AA is 60.36%,and the secondary regeneration rate is 38.05%.（3）Using the four substances of the plant leaves,pig blood clots,chlorophyll,and heme as raw materials,porphyrin carbon was prepared by hydrothermal synthesis,direct pyrolysis,and alkali-activated pyrolysis,and alkali-modified It can be modified by nature method,Ca-doped and Mg-doped modification method.The raw materials were analyzed by thermogravimetric analysis,and part of the prepared porphyrin carbon was analyzed by FTIR and solid ultraviolet.The characterization results showed that the prepared porphyrin carbon retained the porphyrin ring structure.（4）The fluorine removal adsorption experiment was carried out by using the prepared porphyrin carbon adsorbent.The experimental results show that the directly prepared porphyrin carbon has weak adsorption performance on fluoride ions,and the porphyrin carbon treated with alkali can achieve a fluorine removal rate of more than18%,but the alkali treatment will affect the porphyrin structure of the carbon material.The adsorption performance of porphyrin carbon was not significantly improved by Ca-doped modification,but the defluorination performance of porphyrin carbon was better improved by Mg-doped modification,and the best Mg-doped heme carbon defluoridation reached 13.96%.