Study On The Adsorption Property Of Typical Organic Pollutants By Activated Carbon Prepared From Walnut Shell

There is valuable in society,environment and economy when discarded biomass can be exploited to use in wastewater control.In this paper,walnut shell(NS)was activated by ammonium oxalate through muffle furnace heating and activated carbon(CAC)was obtained with yield 44.1%.The CAC was characterized by isoelectric point,SEM,FT-IR,specific surface area measurement and surface functional measurement.Three typical pollutants,4-chloropHenol(4-CP),2,4-dichloropHenoxyacetic acid(2,4-D)and bright green(LG)were selected as adsorbates and adsorption property of CAC was performed.Under the experimental conditions,the adsorption capacity toward 4-CP,2,4-D and LG was up 73.2,104,120 mg.g-1,respectively.Compared to NS,adsorption capacity of CAC was significantly enhanced.The experimental results showed that CAC may be a promising adsorbent for removal of organic pollutants from wastewater.The effects of adsorbent dosage,solution pH,common salt,contact time,initial concentration of adsorbate,temperature on the adsorption quantity of CAC were studied in batch mode.The property of column adsorption was also carried out.The shapes of breakthrough curves were affected by column height,flow rate and initial concentration of adsorbate.The model analysis of adsorption isotherm,kinetic curve and dynamic adsorption penetration curve were carried out.The results showed as follows:(1)The adsorption capacity of 4-CP was not significant in the range of 6 to 8.The increase with pH was not favor of adsorption of 2,4-D and LG onto CAC and solution pH=2 was chosen.The effect of salinity on the adsorption of 4-CP and 2,4-D was not significant,and the increase of salinity was not beneficial to LG adsorption.At experimental conditions,higher temperature was favor of 4-CP and2,4-D adsorption while it was opposite for LG adsorption.(2)The Temkin model can be used to describe the isotherms of 4-CP and 2,4-D adsorption while the Koble-Corrigan model can be used to describe the isotherms of2,4-D and LG adsorption.The pseudo-second order kinetic equation can be used to describe the kinetic adsorption curves of three systems.It was speculated that the adsorption be a non-uniform surface of the multi-molecular layer chemical adsorption process.From the thermodynamic parameters and the activation energy calculation results,it was inferred that the adsorption process of 4-CP and 2,4-D be spontaneous,endothermic and entropy increase while it be spontaneous,exothermic and entropy reduction process for LG.The three adsorption processes include physical adsorption and chemical adsorption.(3)Column adsorption experiments showed that the higher the column,the slower the flow rate,the greater the concentration were conducive to the adsorption.Yan model can predict the breakthrough curves of 4-CP,2,4-D and LG.Desorption regeneration study found that ethanol solution had a good efficiency of desorption and regeneration about 4-CP or 2,4-D loaded CAC.NaOH solution was better to efficiency of desorption while HCl solution was better to efficiency of regeneration.The spent CAC can be reused.