Preparation Of Activated Carbon Derived From Corncob And The Adsorption Characteristics For Organic Arsenic Compounds

Roxarsone?ROX?and Arsanilic acid?ASA?were widely used as livestock feed additives over the world.Those organic arsenic compounds would be discharged into the environment with livestock feces and converted into inorganic arsenic with strong toxicity and fluidity by microorganismor photodegradation,posing a great threat to the ecological environment and human health.Adsorption was one of the effective methods to remove organic arsenic contamination.Corncob was an ideal material for preparation of activated carbon due to abundant resources,reproducibility and low ash content.In this paper,the activated carbon?AC?derived from corncob was prepared with steam activation for the removal of ROX and ASA from aqueous solution.Using the corncob as raw material,the Box-Behnken design?BBD?model of response surface methodology?RSM?was used to optimize the preparation conditions of activated carbon by steam activation.The optimum process conditions were found to be activation temperature of 892?,activation time of 40 min and the mass ratio of char to H₂O of 1:1.6.Iodine adsorption capacity of AC was 1216.74mg/g and S_BET was 1183.31 m²/g.The adsorption performance of ROX was studied.The adsorption operation variables of ROX on AC were optimized by the central composite design?CCD?model of RSM.The optimum adsorption conditions of ROX were adsorption time of260 min,adsorbent dosage of 0.4 g/L,pH 2.5 and ROX initial concentration of 240mg/L.Thermodynamic studies showed that the ROX adsorption equilibrium data was fitted well to the the Langmuir and Sips isotherm models.At 298K,the maximum monolayer adsorption of ROX on AC was 309.62 mg/g from Langmuir model.The adsorption process of ROX on AC was spontaneous and exothermic.It was favorable for adsorption at low temperature.Kinetic studies showed that the adsorption process of ROX on AC could be well described by the pseudo-second order kinetic model.It also found that the adsorption rate was affected by both intra-particle diffusion and membrane diffusion.The adsorption performance of ASA was studied.The adsorption operation variables of ASA on AC were optimized by the CCD model of RSM.The optimum adsorption conditions of ASA were adsorption time of 280 min,adsorbent dosage of0.4 g/L,pH 2.0 and ASA initial concentration of 120 mg/L.Thermodynamic studies showed that the equilibrium data of ASA fitted well to the Freundlich,Sips and Redlich-Peterson adsorption isotherm models.The maximum adsorption capacity of ASA was 200.35 mg/g from Sips model.Adsorption process of ASA on AC was spontaneous and exothermic.It was favorable for adsorption at low temperature.Kinetic studies found that the adsorption process of ASA on AC could be well described by pseudo-second order kinetic model.The adsorption process was not only controlled by intra-particle diffusion,but also by membrane diffusion.The results indicated that activated carbon derived from corncob was the promising adsorbent for removal of ROX and ASA because of the large adsorption capacity.