Effect Factors Of Activated Carbon Regeneration Efficiency In Ferrous Ion/Hydrogen Peroxide/Persulfate System

Activated carbon?AC?adsorption is a common water treatment technology,but the saturation AC has no adsorption capacity when pore structures were blocked with adsorbates.Filled with a large number of highly enriched pollutants,saturation AC will cause the waste of resources and secondary environmental pollution if the disposal was not proper or timely.Therefore,recycling of saturation AC by regeneration has high economic and environmental value.In this paper,we choose one of the Chemical Oxidation methods,ferrous ion(Fe²⁺)/hydrogen peroxide?H₂O₂?/sodium persulfate?Na₂S₂O₈?,to regenerate AC adsorbed by trichloroethylene?TCE?.It is an effective means of AC regeneration,and it can overcome the drawbacks of both the rapidly decomposes of H₂O₂,the low pH of traditional Fenton method and that the persulfate was too stable to react with the target contaminants'problem.Since the reaction mechanism of H₂O₂ and Na₂S₂O₈activated by Fe²⁺systems were poorly understood,and the factors that influence the efficiency of AC regeneration were not clear,this study focused on both the mechanism of Fe²⁺activated H₂O₂ and Na₂S₂O₈ method to regenerate AC adsorbed by TCE,and the factors that influenced the efficiency of AC regeneration.The main research results are as follows.When TCE/Fe²⁺/H₂O₂/S₂O₈^2-=1/9.20/59.79/77.52 in molar ratio was used and regeneration time was 12 h,the regeneration efficiency of AC was about 50%.After the regeneration,63.03%of adsorbed TCE was completely oxidized to chloridion?Cl^-?,and it can not be adsorbed again.In addition,27.51%of adsorbed TCE that can not be oxidized was stay on AC and occupy the adsorption sites.That will reduce the future adsorption efficiency of TCE.1,1-Dichloroethylene?1,1-DCE?and Vinyl Chloride?VC?were generated as by-products during the regeneration in the percentage of 0.02%and 0.1%of adsorbed TCE,respectively.Mass balance calculations,based on measured chlorine before and after AC regeneration,show95.78%chlorine balance.Changes of properties and structure of AC before and after regeneration were studied by using analytical instruments,including Scanning Electron Microscope?SEM?,Energy Dispersive Spectrometer?EDS?,X-ray Photoelectron Spectroscopy?XPS?,and Nitrogen Adsorption-Desorption Techniques.There was ferric iron precipitation on regenerated AC.Compared with original AC,the carbon loss of regenerated AC was about 11%,the surface area,pore volume,and aperture area of regenerated AC were decreased by 21.70%,19.57%,and 35.88%,respectively.Therefore,changes of properties and structure of AC can reduce the future adsorption efficiency of TCE.Using high performance liquid chromatography?HPLC?to test hydroxyl radicals?HO·?produced from reaction system indirectly.HO·produced from regeneration system was about 1.4 times of oxidation system,which proved AC can promote the generation of HO·.The increase of HO·can not remove the 27.51%of adsorbed TCE,which will enhance the damage to the surface and pore structure of AC.