Preparation,Characterization Of Immobilized Nano Zero Valent Iron And Its Application In The Removal Of Typical Pollutent

As the important supplement of water supply resource,the pollution prevention,control and governance of groundwater has attracted much attention.Recently,the permeable reactive barrier(PRB)technology is widely used in the in situ removal of pollutant for groundwater in many developed countries.With nano zero-valent iron as the active material in PRB,chemical reactions such as precipitation,adsorption,catalytic reduction or catalytic oxidation were introduced in repairing processes.Pollutants can be transformed or degraded to low activity of material or non-toxic ingredients,which is convenient and relatively low cost.However,pure nano zero-valent iron is unstable and easily to be deactivated and agglomerate in groundwater pollution remediation process.The hydrophilic nano iron and hydrophobic organic contaminant moleculars were also difficult to contact in pollution repairing process.The supported zero-valent iron nanoparticles can improve the performance of the reaction,increase the contacting surface area and dispersion of nanoparticles,which is convenient to the practical application in environmental pollution control.Acid-activated attapulgite,biochar and cetyl-trimethyl ammonium bromide(CTAB)modified attapulgite were selected as the supporter for preparing nanoscale zero valent iron(nZVI)in this research.The removal behaviors and kinetics of typical pollutants includeing chromium(Ⅵ),acid orange 7 and 2,4,6-trichlorophenol by these supported nZVI were discussed in detail.Three parts were composed of this thesis.Part Ⅰ:Preparation and characterization of nanoscale zero valent iron supported on the surface of acid-activated attapulgite(A-nZVI)for the removal efficiency of Cr(Ⅵ).A-nZVI was prepared by a liquid-phase reduction method and used for Cr(Ⅵ)removal from solution with enhanced efficiency.The specific surface area of A-nZVI was 30.63 m2 g-1.EDX and element analysis results showed that the nZVI was uniformly dispersed on the surface of attapulgite and the loading content is about 2.94%.nZVI was well dispersed on the surface of acid-treated attapulgite and no obvious aggregation was observed due to the support of rod-like structure of attapulgite,which is beneficial to Cr(Ⅵ)removal.Batch experiments revealed that the removal of Cr(Ⅵ)using A-nZVI was consistent with pseudo first-order reaction kinetics,and removal efficiency was up to 98.73%within 60 min for 100 mL 20 mg L-1 Cr(Ⅵ)at the initial pH 7.0 and 4.0 gL-1 A-nZVI.The pseudo-first order rate constant kobs was independent of initialCr(Ⅵ)concentration,but there was a good linearity(R2 = 0.95)between kobs and the A-nZVI dosage.For the column experiment of treatment of hexavalent chromium by A-nZVI,a trend of rise in the pH value of the effluent was observed,and the breakdown effect happened in 65th PV.Part Ⅱ:Preparation and characterization of biochar supported nanoscale zero valent iron(B-nZVI)and its application in the degradation behavior and mechnanism of acid orange 7(AO7).nZVI was well dispersed on the surface of biochar with a specific surface area 52.21 m2g-1,and no obvious aggregation was observed due to the support of biochar.The surface of B-nZVI was coated by 2-4 nm amorphous iron oxides(FeOOH)film with clusters structure.The internal stability of nanometer zero-valent iron was increased due to the core-shell structure.The synergistic effect between the Fe0 and the substrate biochar and the functional groups on the surface of biochar are beneficial to A07 molecules adsorption,which can promote the reduction and degradation of A07 and thus enhance the removal rate.Batch experiments revealed that the removal of A07 by B-nZVI was fast and consistent with pseudo first-order kinetics.At pH 2.0,the degradation of A07(20 mg L-1)by B-nZVI(2 gL-1)reached to 98.3%within 10 min.There was a good linearity(R2 = 0.99)between kobs and B-nZVI dosage.The reductive cleavage of the azo group in AO7to amino groups may be the dominated stage.The removal rate of A07 was promoted in a certain extent with the coexistence of low concentration of electrolyte.For the column experiment of treatment of A07 by B-nZVI,the breakdown effect occurrenced at 110th PV,the removal capacity was found to be lower than the batch experiment due tomass transfer resistance.Part Ⅲ:nZVI supported on organic modified attapulgite and its application.The cationic cetyl-trimethyl ammonium bromide(CTAB)modified attapulgite was well prepared,and the optimum conditions for preparation are as follow.The dosing quantity ratio is 2:1,processing time is 4h,and modification temperature is 60℃.The removal of A07 experimental study of organic modified attapulgite nano zero-valent iron(M-A-nZVI)showed that A07 and TOC removal rate increased with the increasing of the dosage of M-A-nZVI and the modification temperature.The reaction process conformed the first order kinetics with good correlation coefficient.The rate constants for decolorization and TOC were between 0.0369～0.0392 min-1 and 0.0055～0.0082 min-1 at pH in 3.0～7.0,respectively.The rate constants of decolorization were 0.0215,0.0308,0.0369 and 0.0581 min-1 for 20 mg L-1 of A07 by adding M-A-nZVI0.5,1.0,2.0 and 4.0 g L-1,respectively.And theintermediate productsin the reaction process were analyzed byUPLC&Q-TOF MS,the possible degradation pathwayof removing A07 by modified attapulgite nano zero-valent iron was proposal,and the reaction mechanism was illustrated.Compared with A-nZVI,the removal rate of TOC by M-A-nZVI increased significantly.The removal of 2,4,6-trichlorophenolwas in the order:iron<attapulgite<A-nZVI<M-A-nZVI.Based on the synergistic effect of surface adsorption and iron reduction,nanoscalezero iron supported on the surface of biochar,attapulgite and organic modified attapulgite with different hydrophilic/hydrophobic properties hasbetter resistance to aggregationand higher reduction activities,and iseffectivelyused in wastewater treatment.