Adsorption Of Heavy Metal Ions On Chelated Fibers And Activated Carbon Fibers Based On Polyacrylonitrile

The large amount of industrial wastewater discharge has increased the content of heavy metals in water,which caused serious harm to the environment and humans.Adsorption has been widely used in the field of heavy metal wastewater treatment because of its advantages of large adsorption capacity,high selectivity,wide range of raw materials and easy regeneration.Polyacrylonitrile(PAN)fibers have received extensive attention in the field of heavy metal wastewater treatment since they can be transformed into chelated fibers,carbon fibers,activated carbon fiber and other adsorbents by modification,carbonization,activation and other treat processes to achieve selective adsorption of heavy metal ions.The adsorption of heavy metal ions in water solutions by chelated fibers and activated carbon fibers based on polyacrylonitrile(PAN)was investigated,the samples before and after adsorption were characterized by SEM,FT-IR,XRD and XPS.And the main results of this research can be summarized as follows:1、The nitrile groups in preoxidated PAN electrospun fibers were transformed into amide groups after sulfuric acid modification,those can combine with Cu(II)and Pb(II)ions.The adsorption capacities of the chelated fibers(PANS)was significantly affected by the increasing initial concentration of heavy metal ions and reaction time.The optimum pH value for adsorption was around 5,meanwhile the adsorption quantity of Cu(II)and Pb(II)ions were 12.0mg/g and 28.8mg/g at 25℃,respectively.The adsorption of the two ions were both fitted well with Langmuir isotherm,and pesudo-second-order.The adsorption capacity of PANS to Cu(II),Pb(II),Cr(VI),Cd(II)ions was higher than that of PAN crude fibers under the same modification conditions,and it can carry out multiple adsorption and desorption cycles.2、It was found that the activation degree of the activated carbon fibers(ACF-P and ACF-250)prepared by KOH activation of PAN fibers and preoxidated PAN fibers,respectively,were similar with those of the activated carbon fibers(ACF-700)prepared by PAN carbon fibers in the same activation manner.ACF-700 showed advantages in adsorption capacity and removal rate with the increase of ions concentration,which was related to the agglomeration of ACF-P and ACF-250 fibers.The adsorption capacity of Cu(II)ions on ACF-P,ACF-250 and ACF-700 were 24.5 mg/g,25.4 mg/g and 25.6 mg/g respectively,and Pb(II)ions were 81.0 mg/g,82.6 mg/g and 82.7 mg/g respectively.The adsorption equilibriums of the two ions were both fitted well with Langmuir isotherm,and the adsorption of the two ions on the three fibers were all fitted well with pesudo-second-order.The ion exchange of K~+played a role in the adsorption process.3、The four activated carbon fibers(ACF-600,ACF-700,ACF-800,ACF-900)were prepared by carbonization of PAN preoxidized fibers at 600,700,800 and 900℃,respectively,and activation of KOH in the same way.It was more diffcult to activate after carbonization at higher temperature,and the capacity was ACF-600>ACF-700>ACF-800>ACF-900.The adsorption capacity of ACF-600,ACF-700,ACF-800 and ACF-900 were70.4mg/g,62.8mg/g,47.2mg/g and 35.4mg/g at 25℃,respectively.The adsorption of Ba(II)ions on the four fibers were all fitted well with pesudo-second-order.The adsorption equilibriums of ACF-600 and ACF-700 were both fitted well with Langmuir isotherm,while ACF-800 and ACF-900 were both fitted well with Frendlich isotherm.