Study Of Preparation,modification And Adsorption Performance Of Activated Carbon From Astragalus Residue

The traditional Chinese medicine resources of China is very rich,the consumption of a large number of Chinese herbal medicine leads to quantities of Traditional Chinese medicine waste residue.Astragalus residue(AS)is a kind of Traditional Chinese medicine residues,its annual output is big with widespread source.At present,a large amount of AS is disposed of through land filling or combustion as industrial waste or the living garbage,not only causing serious resource waste,but also serious environmental pollution.At the same time,with the rapid development of modern industry,all kinds of heavy metals and organic matter pollution has become increasingly serious,a shortage of world resources has also become gradually apparent,so the secondary utilization of AS and reaching the purpose of using waste treat waste is becoming a hot spot of research.In this paper,astragalus residue activated carbons(ASC)was prepared from AS using KOH as activator,and then ASC was modified by KMnO4 and cetyl trimethyl ammonium bromide(CTAB).The activated carbons before and after modification were applied for the adsorption of Cu2+? Cd2+? toluene and aniline in aqueous media.The best preparation conditions of ASC were obtained from single factor experiments which contained the concentration of KOH,impregnation ratio,activation time,activation temperature on the adsorption properties and yield of activated carbon.Through the study of modifier concentration and modified time on the surface properties and adsorption properties of ASC,the optimum modification conditions were determined.The changes of before and after modification of activated carbon were investigated by scanning electron microscope(SEM),N2 adsorption,X-ray diffraction(XRD),Fourier transform infrared(FTIR).By using batchadsorption experiments,the influence of pH value,adsorbent dosage,adsorption time on adsorption effect was investigated;in addition,adsorption kinetic and adsorption isotherms were analyzed;then go into the adsorption ability of activated carbons before and after modification on heavy metal ions and organic compound.The experimental results showed that the optimum process conditions of preparation of ASC was: the concentration of KOH was 20%,the ratio of liquid to solid was 3:1,activation temperature was 600?,and the activation time was 80 min.After carbonization and activation,the BET surface area of ASC was 1519.53m2/g;the results of SEM showed that its surface was coarse,porous and presented honeycomb structure;the XRD spectra presented that ASC produced graphite crystallite structure which can increase the stability of ASC.The best conditions modifying ASC with KMnO4 was: the concentration of KMnO4 was0.15mol/L,the ratio of solid to liquid was 10:1,the modification temperature was 98?,and the modification time was 90 min.The activated carbon before modification(ASC)and the activated carbon modified by KMnO4(ASC-Mn)were applied for the adsorption of Cd2+ and Cu2+ in aqueous media.When the solution concentration of Cd2+ was 100mg/L,the solution pH value was 6.0,the adsorption time was 60 min,and the adsorbent dosage was 2g/L,the adsorption rate of ASC and ASC-Mn for Cd2+ was 73.10%,97.24% respectively.Based on Langmuir equation,the maximum adsorption capacity of ASC and ASC-Mn for Cd2+ was116.96mg/g and 217.86mg/g separately.When the solution concentration of Cu2+was63.5mg/L,the solution pH value was 5.0,the adsorption time was 60 min,and the adsorbent dosage was 2g/L,the adsorption rate of ASC and ASC-Mn for Cu2+ was 98.20%,100%respectively.Based on Langmuir equation,the maximum adsorption capacity of ASC and ASC-Mn for Cu2+ was 125.73mg/g and 196.46mg/g separately.The kinetic adsorption could be described by a pseudo-second order model very well.After oxidation modification,the saturated adsorption capacity of modified product to Cd2+and Cu2+increased significantly,because MnO2 was almost uniformly deposited on the surface of ASC-Mn,the amount ofoxygen containing functional groups was significantly increased after modification,too.The best conditions modifying ASC with CTAB was: the concentration of CTAB was0.05mol/L,the ratio of solid to liquid was 10:1,the modification temperature was 70?,and the modification time was 7h.ASC and the activated carbon modified by CTAB(ASC-N)were applied for the adsorption of toluene and aniline in aqueous media.When the solution concentration of toluene was 200mg/L,the solution pH value was 7.5,the adsorption time was 60 min,and the adsorbent dosage was 2g/L,the adsorption rate of ASC and ASC-N for toluene was 54.79%,80.05% respectively.Based on Langmuir equation,the maximum adsorption capacity of ASC and ASC-N for toluene was 178.88mg/g and 266.18mg/g differently.When the solution concentration of aniline was 200mg/L,the solution pH value was 6.5,the adsorption time was 60 min,and the adsorbent dosage was 2g/L,the adsorption rate of ASC and ASC-N for aniline was 27.92%,82.45% respectively.Based on Langmuir equation,the maximum adsorption capacity of ASC and ASC-N for aniline was 74.51mg/g and 121.54mg/g separately.The kinetic adsorption could be described by a pseudo-second order model very well.After modification,the saturated adsorption capacity of modified product to toluene and aniline increased significantly,because oxygen-containing functional groups of ASC reduced and nonpolar groups increased by modification,modified products increased affinity to the weak polar and nonpolar substances.By employing AS as raw material to prepare activated carbon can reduce the cost of the preparation of activated carbon,saving resource,finding a reasonable way for the utilization of astragalus residue;The activated carbons before and after modification were applied for the adsorption of heavy metal ions and organic matter,not only control and manage environmental pollution effectively,but also lay a good foundation for pollution control technology.