Adsorption Of Arsenic Ions On Activated Carbon Fiber Supported Metal Oxide

With the development of China’s chemical industry,the effective utilization of fluorine-containing resources has been paid more and more attention.Fluorosilicic acid is an important raw material for the production of fluorine-containing products.However,arsenite（As（III））and arsenate（As（V））ions in fluorosilicic acid will affect the quality of fluorosilicic acid.Therefore,the effective removal of arsenic ions in fluorosilicic acid has broad industrial application value.Activated carbon fiber（ACF）was prepared from absorbent cotton by pre-carbonization,acid-base modification and carbonization.The ACF was characterized by scanning electron microscopy（SEM）,Fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）and BET&BJH;On this basis,titanium tetrachloride and zirconium oxychloride were used as raw materials to load titanium dioxide and zirconia onto activated carbon fiber by hydrothermal method.The elemental composition of the materials was investigated by energy dispersive X-ray spectrometry（EDX）.The two materials were applied to the adsorption experiment of arsenic solution under acidic conditions,and the adsorption mechanism was preliminarily studied.The main contents are as follows:（1）A series of activated carbon fibers（ACFs）were prepared by calcining absorbent cotton in a high temperature box resistance furnace filled with nitrogen with pre-carbonization temperature,pre-carbonization time,volume concentration of sulfuric acid,carbonization temperature and carbonization time as experimental variables by orthogonal test.The iodine value and yield of ACFs were compared,and the best preparation conditions were discussed.The optimum preparation conditions were as follows:concentrated sulfuric acid 40%,pre carbonization temperature 350℃,pre carbonization time 1 h,carbonization temperature 900℃,carbonization time 2 h.The yield of ACF was 13.341%and the iodine value was 1322.100 mg/g.The results show that the average adsorption pore size of ACF is 2.671 nm,the specific surface area is 759.482 m²/g,and the total pore volume is 0.523 cm³/g.Electron microscope analysis showed that the activated carbon fiber kept the original fiber structure of degreasing cotton,but there was a slight fiber fracture.Thermogravimetric analysis showed that there might be chemical reaction between Na OH and absorbent cotton,and there were dehydration reaction,fracture reaction and polymerization reaction in the process of conversion from absorbent cotton to activated carbon fiber.FTIR spectra showed that ACF mainly contained C-H and C≡C functional groups.The XRD patterns show that the fiber structure of absorbent cotton and ACF is different（2）L₉（3⁵）was used to load titanium dioxide and zirconia onto activated carbon fiber with titanium tetrachloride and zirconium oxychloride as raw materials.SEM results show that zirconia and titanium dioxide are loaded on ACF in amorphous form.XRD results show that the crystals are Zr O₂ and Ti O₂,respectively.In the solution with initial arsenic concentration of 20 ppm,p H of 2 and temperature of 27℃,the adsorption experiment was carried out.The preparation conditions of Zr O₂-ACF-3 are as follows:p H of solution is 11,alkaline reagent is ammonia,heating temperature is 200℃,heating time is 0.5 h.Zr O₂-ACF-3 can reach the adsorption equilibrium of arsenous acid radical in 40 min,and the adsorption capacity is 4.880 mg·g^-1;The adsorption equilibrium of pentavalent arsenic was achieved in 20 min,and the adsorption capacity was 5.410 mg·g^-1.The preparation conditions of Ti O₂-ACF-5 are as follows:p H of solution is 11,Na OH is the basic reagent,heating temperature is 150℃,heating time is 6 h.Ti O₂-ACF-5 can reach the adsorption equilibrium of arsenous acid radical and arsenate in 60 min,and the adsorption capacity is 4.412 mg·g^-1 and 6.032 mg·g^-1,respectively（3）The effects of different temperature,feeding amount,initial arsenic concentration and initial p H value on arsenic removal efficiency of Zr O₂-ACF-3 and Ti O₂-ACF-5 were further studied.The results show that the higher the temperature,the larger the feed amount and the initial concentration of arsenic ions,the more favorable the adsorption.At the same time,at different p H values,the greater the zeta potential,the greater the adsorption capacity.The data fitting showed that the adsorption capacity data was more consistent with the second-order kinetic equation model,the adsorption isotherm was more consistent with the Langmuir adsorption isotherm model,and the Weber Morris model had better fitting effect.The results show that the adsorption process is monolayer adsorption and chemical reaction exists.Intra particle diffusion and liquid film diffusion are the speed controlling steps of the adsorption process.After adsorption,the as peak was detected by energy spectrum;The content of titanium and zirconium was less than 0.050 mg·L^-1,which indicated that the material had a certain arsenic adsorption capacity and good stability.Zr O₂-ACF-3 and Ti O₂-ACF-5 were used to adsorb arsenic from fluorosilicic acid containing wastewater（fluorosilicic acid concentration 16.734%,arsenic content 42 ppm,p H=1）.The results showed that the adsorption effect of Ti O₂-ACF-5 was better than that of Zr O₂-ACF-3.