Preparation Of Biochar Loaded Nano Iron And Its Removal And Detection Of Heavy Metal Cr(Ⅵ)

With the rapid development of industry,chromium metal is widely used in electroplating,mining,textile and other industries.The chromium pollution in water is becoming more and more serious,and it is also a serious threat to human health.In recent years,Nano zero iron（nZVI）has been widely used to repair pollutants in groundwater due to its strong reducing ability and large specific surface area.However,nZVI is unstable and easy to agglomerate,which reduces the reaction activity and limits the adsorption of pollutants.Biochar is widely used in adsorption because of its large specific surface area and abundant functional groups.The biochar loaded encapsulation method can protect nZVI from oxidation and agglomeration,and give full play to the advantages of both,making biochar loaded nano iron become a new green and environmental friendly adsorbent.In this thesis,the mangosteen shell was prepared into biochar,which was coated with nZVI load to prepare biochar supported nano-iron for the removal of heavy metal Cr（Ⅵ）.Firstly,the morphology,functional groups,element content and thermal stability of mangosteen shell were analyzed by SEM,FTIR,XRF,EDS,ICP-OES and TGA.EDS and XRF determined that the elements contained in mangosteen shell were C,O,Cl,P,Si,S,K,Ca,Na,Mg,Al,Mn,Cu.The contents of metal elements in ICP-OES were K（1.361%）,Ca（0.3045%）,Na（0.2275%）,Mg（0.0928%）,Al（0.0277%）,Mn（0.0041%）and Cu（0.0036%）.Biochar was prepared from mangosteen shell.The results show that mangosteen shell biochar（BC）has abundant functional groups and good thermal stability.Then,in this thesis,biochar supported nano-iron（BC@nZVI）was prepared by the traditional liquid phase reduction method,the adsorption performance of BC@nZVI on Cr（Ⅵ）was optimized by changing the preparation conditions,and BC@nZVI was characterized by SEM,EDS and FTIR.The results show that BC@nZVI has the best adsorption performance for Cr（Ⅵ）when the carbonization temperature of mangosteen shell is 400℃,FeCl3·6H2O is the iron source and the iron-carbon ratio is 1:1.Through characterization,it is found that the porous structure is present on the surface,and the number of oxygen-containing functional groups not only increases,but also new oxygen-containing functional groups appear.XRD characterization demonstrated that BC and nZVI were successfully loaded together.Finally,the adsorption properties of Cr（Ⅵ）on BC@nZVI were studied by static adsorption experiments.The adsorption mechanism of Cr（Ⅵ）by BC@nZVI has been studied by means of adsorption kinetics,adsorption isotherm and adsorption thermodynamics.The results show that at 25℃,pH=2,adsorbent dosage of 0.5 g L^-1,concentration of 50 mg L-1 and volume of 50 m L Cr（Ⅵ）solution reach the equilibrium state when the rotation speed is 150 r min-1 and the reaction time is 120min.The adsorption capacity of Cr（Ⅵ）by BC@nZVI is up to 99.68 mg g-1;The adsorption process accords with the quasi second-order kinetic model,the intramaterial diffusion model,the Yelovich model and the Langmuir model,indicating that the adsorption is mainly a multi-step controlled chemisorption.The thermodynamic model shows that the adsorption process of Cr（Ⅵ）on BC@nZVI is a spontaneous endothermic reaction.During the adsorption of Cr（Ⅵ）by BC@nZVI,a REDOX reaction occurs between nZVI and Cr（Ⅵ）to form Cr（Ⅲ）,which is combined to form Cr（Ⅲ）-Fe（Ⅲ）hydroxide precipitation,indicating that there is not only adsorption reaction but also REDOX reaction in the reaction process.