Synthesis Of Humic Acid Supported Nano-zero Valent Iron For The Removal Of Cr(?)

Hexavalent chromium,as a common heavy metal pollutant,is teratogenic,carcinogenic and genotoxic to organisms.Nano zero-valent iron(nZVI)is a pollutant removal material that can effectively control Cr(?)pollution.However,nZVI is easy to be deactivated and agglomerated,which decrease its efficiency.Therefore,it is of great significance to improve the performance of nZVI for water treatment.In this paper,humic acid(HA)was used as supporting material,and HA supported nZVI(HA-nZVI)was successfully prepared for Cr(?)removal.The characteristics of HA-nZVI,the removal of Cr(?)under different conditions and the corresponding kinetics were studied.The possible mechanism of Cr(?)removal was proposed.The main results of this research are as follows:1.HA-nZVI was sucessfuly prepared by pre-adsorption and liquid phase reduction.The best Cr(?)removal efficiency was achieved for HA-nZVI with the ratio of HA/Fe2+at 3/4.The removal efficiency of 25 mg/L Cr(?)can reach 97.46%by 0.5 g/L of HA-nZVI after reacted at pH 6.5 for 180 min.Successful synthesis of HA-nZVI could be proved by SEM,XRD and XPS analysis.nZVI was dispersed on the outer surface of the material.Compared with unsupported nZVI,HA can effectively enhance the dispersibility and oxidation resistance of the material.2.All changes in conditions had effects on the adsorption reaction.Under different conditions,the removal of Cr(?)conforms to the pseudo-second adsorption kinetics,indicating that chemical adsorption was the rate-controlling step in the reaction.The removal of Cr(?)by HA-nZVI was easier at low pH.Compared with other materials,the removal efficiency of HA-nZVI was higher under alkaline condition.The removal efficiency and adsorption capacity at pH 10.0 were 83.68%and 45.871 mg/g,respectively.The adsorption rate increased with the increase of background ion concentration,but when the ion concentration reaches a certain level,the increase of ion concentration had little effect on the adsorption process.The addition of different kinds of ions would affect the removal efficiency,and the overall adsorption rate was in the order of cation>blank>anion.The addition of cation could increase the adsorption capacity,while anion would reduce the adsorption capacity.PO43-also reduced the adsorption rate.3.Compared with nZVI,loading with HA could increase the adsorption rate of Cr(?),increase the adsorption capacity of unit mass of Fe in the material,and promote the conversion of Cr(?)to Cr(?).According to the change of the surface properties of HA-nZVI,we speculated that the mechanism of Cr(?)removal by HA-nZVI includes adsorption,reduction and complexation.Cr(?)was adsorbed by HA-nZVI,and redox reactions took place to produce FeCr2O4,Cr(?)and Fe(?).Fe(?)may be complexed with HA to accelerate the reduction of Cr(?),and the complexation of HA may also reduce the concentration of Cr(?)and Fe(T)in the solution.The formation of FeOOH on the surface of the material was favorable for the adsorption of Cr(?)and Cr(?).