Preparation And Modification Of Activated Carbons From Rice Husk And Investigation On Its Adsorption Mechanisms Of Phenol

Phenol is a toxic substance,which will pollute the water environment and endanger human health without treatment.The effective removal of phenol in water has become an important topic of energy utilization and environmental protection.Activated carbon has the advantages of large surface area,good microporosity,large adsorption capacity,high purity and easy to obtain,so it is considered to be an effective method to remove phenol from waste liquid.Rice husk,as a kind of biomass with huge output and low cost,will waste resources and pollute the environment if it is directly discarded or burned.Rice husk is rich in lignin and has a high content of fixed carbon after carbonization,which has the potential to become activated carbon with rich structure.In this study,rice husk-based activated carbon with high adsorption performance was prepared from rice husk by two-step method,KOH activation and EDTA-4Na in-situ modification,and applied to the treatment of phenol wastewater to realize the resource utilization of rice husk.The main research contents are as follows:(1)Using rice husk as raw material,the process parameters of KOH activation method were optimized to prepare rice husk based activated carbon with developed pores and high yield.The effects of carbonization temperature,activation temperature and carbon-alkali ratio on the pore structure of activated carbon were discussed.Under the conditions of carbonization temperature 500?,activation temperature 750? and rice husk carbon:KOH=1:3,the pore structure of activated carbon was the most abundant,and the specific surface area was 2087 m2/g.The proportion of micropores in the adsorption material is very high,which can promote the adsorption of phenol,and the maximum adsorption capacity is 194.24 mg/g.The mechanism of phenol adsorption by activated carbon was studied.The whole adsorption process reached equilibrium at 12 min,and the pseudo-second-order kinetic model could well describe the whole adsorption process,indicating that chemical adsorption controls the interaction between activated carbon and phenol.The adsorption behavior can be described by Langmiur isothermal adsorption model,which shows that the adsorption is mainly monolayer adsorption.(2)When the carbonation temperature is 500? and the activation temperature is 750?,the nitrogen-containing functional groups of activated carbon doped with a certain amount of EDTA-4Na in situ are increased,which is beneficial to enhance the Pi-dispersion force of activated carbon and phenol.By changing the amount of EDTA-4Na and taking the adsorption performance of phenol as the index,it was obtained that the best doping amount was rice husk carbon:KOH:EDTA-4Na=1:3:1.The specific surface area of the modified activated carbon decreased to 1368 m2/g,while the adsorption performance was 215.27 mg/g,indicating that the introduction of nitrogen-containing functional groups promoted the adsorption of phenol.The adsorption isotherm accords with the Langmuir model,indicating that the adsorption of phenol belongs to monolayer adsorption.The adsorption process accords with the pseudo-second-order adsorption model,which shows that the interaction between activated carbon and phenol is controlled by chemical adsorption and the adsorption equilibrium can be reached in 10min.