Synthesis Of Wrapped NZVI Patricles Via Rheological Phase Reaction Method And Removal Of Heavy Metal From Aqueous Solution

In recent years, all countries treat the environmental protection as a toppriority,because, these years people focus their eyes on economicdevelopment which lead the human society appear a series of environmentalpollution problems and human living environment is facing a serious test.The nanoscale zero valent iron （nZVI） was used for the removal of avariety of environmental pollutants of ground water due to their high specificsurface area and reactive surface sites. However, nZVI were easily oxidizedby air, and thereby significantly lost their main advantage of a very highsurface reactivity. Freshly synthesized nZVI often ignited spontaneously uponexposure to air. When slowly exposed to air, a coating of iron oxide wasformed on the surface of particles. Furthermore, many methods have beenused for the preparation of nZVI, such as evaporation condensation method,hot plasma method, high energy ball milling method, solid phase reductionmethod, liquid phase reduction method, etc. Among them, the liquid phasereduction method has been wide attention due to its relatively simplepreparation technology. But this method needs inert gas to protect the processof preparation, greatly increasing the difficulty of preparation and costs.These problems affect the actual application of nZVI.To solve above problems, in this study, wrapped nanoscale zero-valentiron was synthesized using a rheological phase reaction method. The structureand morphology of wrapped nanoscale zero-valent iron were investigated byX-ray powder diffraction （XRD）, scanning electron microscopy （SEM）,transmission electron microscopy （TEM）. In addition, their performances,reaction kinetics and reaction mechanism were researched about the removalof Cr （VI） and Pb （Ⅱ） with wrapped nanoscale zero-valent iron.The main conclusions of this work are made as follows:1. Wrapped nanoscale zero-valent iron was synthesized using arheological phase reaction method, and the surface modification agents wererespectively agar, CMC and starch. Optimum condition for synthesis ofmaterials: FeSO₄·7H₂O and KBH4（molar ratio of1:3） were used assolid-phase media, and wrapped materials solution （0.06g/mL） was used asliquid medium. The ratio of solid/liquid was1:2. NZVI was prepared with areaction time of2h.2. The characterization results of synthetic materials showed that the distribution of particle size of Agar-Fe⁰is wide spread ranging from60to120nm, and has good dispersion and stability against oxidation; CMC-Fe⁰particle size of about50-100nm,and has uniform distribution, the CMC-Fe⁰particles were encapsulated into the microspheres by CMC and were isolatedfrom each other. CMC has been successfully used as an effective stabilizer inthe preparation of nanoparticles; The distribution of particle size ofStarch-Fe⁰is spread ranging from8to20nm, iron particles surrounded bystarch parcel layer, uniform thickness and presents obvious core-shellstructure, found no chains or reunion piles composite particles, particles hasgood dispersibility;3. The results of reduction of Cr（VI） with synthetic materials showed theeffect factors of Cr（VI） removal contain the initial concentration of Cr （VI）,pH value and the dosage of synthetic materials. The removal efficiencyincreased with the increasing of the dosage of synthetic materials addition.Low pH value could accelerate the rate of Cr（VI） removal. The reactionkinetic followed pseudo-first-order reaction model. In addition, first-orderrate coefficient kobsincreased with increasing the dosage of syntheticmaterials addition but inversely with initial concentration of Cr（VI） and pHvalue.4. The results of reduction of Pb（II） with synthetic materials showed theeffect factors of Pb（II） removal contain the initial concentration of Pb（II）, pHvalue and the dosage of synthetic materials. Experimental results show thatthe reaction optimum pH value is5, and lower initial concentration of Pb （Ⅱ）and higher the dosage of synthetic materials addition is good for the removalof Pb （Ⅱ）; The reaction kinetic followed pseudo-first-order reaction model.