Study On Preparation And Adsorption For Heavy Metals Of Activated Carbon Based On Reed

The reed area is more than 1.3 million hm²in China,the annual output reaches 100,000 tons among Baiyangdian in Xiong’an New Area.Due to the decrease of demand in the reed market and the low economic value of the application of reeds,most of the withered reeds were unharvested in the wetlands,this is not only a waste of reed resources,but also accelerating the transformation of lakes towards swamp lakes by the biological filling effect.Therefore,in order to improve the economic value of reed,the preparation of activated carbon using reed as raw material and its adsorption performance are studied.The results are as follows:1.Using white reeds in Baiyangdian District as raw materials,a two-step carbonization method,combining single factor experiments and orthogonal experiments,the iodine adsorption value and methylene blue adsorption value and yield as the evaluation criteria were used in the study,the optimal conditions for preparing reed activated carbon under the action of KOH or K₂CO₃ or CO₂ were screened out:（1）The optimal conditions for the preparation of activated carbon（RAC-KOH）under the action of KOH are the dosage ratio of 4:1,immersion for 36 h,and activation for 1.5 h at 850℃;the iodine adsorption value and the methylene blue adsorption value of RAC-KOH are 1,227 mg/g and 244 mg/g,the yield of RAC-KOH is 31.4%;（2）The optimal conditions for the preparation of activated carbon（RAC-K₂CO₃）under the action of K₂CO₃ are the dosage ratio of 2.5:1,immersion for 12 h,activation for 1.5 h at 900℃;the iodine adsorption value and the methylene blue adsorption value of RAC-K₂CO₃ are 1089 mg/g and 62 mg/g,and the yield of RAC-K₂CO₃ is 42%;（3）The optimal conditions for the preparation of activated carbon（RAC-CO₂）under the action of CO₂ are CO₂ ventilation of 200 mL/min,heating rate of 20℃/min,activation for 0.5 h at900℃;the iodine adsorption value and the methylene blue adsorption value are 1129 mg/g and 76 mg/g,and the yield of RAC-CO₂ is 57.3%.2.A fully automatic specific surface area and porosity analyzer,X-ray powder diffractometer（XRD）,Scanning electron microscope（SEM）and Fourier infrared spectrometer（FT-IR）to RAC-KOH,RAC-K₂CO₃,RAC-CO₂ of optimal conditions for analysis and characterization were used in the study.The results show that the pore diameter of RAC-KOH is mainly concentrated in 0.4-0.5 nm,0.6-1.3 nm and 2.2-2.7 nm,the specific surface area is1674 m²/g,the proportion of micropores is 84%,and the volume of micropores is 0.610cm³/g;the pore size of RAC-K₂CO₃ is mainly distributed around 0.6-1.2 nm and 2.2 nm,the specific surface area is 1151 m²/g,the micropores account is 86%,and the micropore volume is 0.418 cm³/g;the pore size of RAC-CO₂ is mainly distributed around 0.5 nm,0.8-1.1 nm and 2.0-2.2 nm,the specific surface area is 1349 m²/g,the micropore content is 82%,and the micropore volume reaches 0.497 cm³/g.The XRD spectrum,SEM image and Infrared spectrum analysis of reed activated carbon proved it has a porous and stable structure;the hydroxyl,ether,carboxyl,aldehyde,carbonyl and amino groups are distributed on the surface of activated carbon.3.RAC-KOH is selected to adsorb a single heavy metal Pb²⁺or Cd²⁺in the each solution,in order to explore the process and mechanism of RAC-KOH adsorption of heavy metals,analyzing the effect of the dosage,pH,time,and temperature on the adsorption process multiple adsorption isotherm models and kinetic models to fit and analyze the adsorption data were studied,and study the effects of reuse.The results show that the process of RAC-KOH adsorbing heavy metals Pb²⁺and Cd²⁺in the solution is an endothermic reaction,The adsorption conditions of RAC-KOH for heavy metal Pb²⁺are dosage of 5 g/L,pH of 5.5,constant temperature oscillation for 2 h;the adsorption conditions for heavy metal Cd²⁺are dosage of 6 g/L,pH of 6 and constant temperature oscillation for 2 h.The removal rate of RAC-KOH in the solutions with heavy metal Pb²⁺concentration of 100 mg/L and Cd²⁺concentration of 10 mg/L is above 95%,and that of the solutions with heavy metal Pb²⁺concentration of 200 mg/L or Cd²⁺concentration of 50 mg/L is above 85%.Langmuir model,Freundlich model,D-R model,pseudo-first-order and second-order kinetic model,Elovich model,and intra-particle diffusion model are used to fit the adsorption data,it is proved that RAC-KOH has an uneven surface,its adsorption of Pb²⁺and Cd²⁺accords with pseudo-second-order kinetics,the adsorption rate is affected not only by intraparticle diffusion but also by membrane diffusion process.The adsorption process of RAC-KOH for Pb²⁺is monolayer adsorption dominated by chemical adsorption.The adsorption process of Cd²⁺is multi-layer adsorption,dominated by ion exchange adsorption.RAC-KOH pickled with nitric acid solution after adsorption still has good adsorption effect when reused.