Preparation Of Loaded Nanometer Zero-valent Iron And Its Removal Of Pb²⁺ In Water

Lead and its compounds are difficult to be biodegraded,which can be accumulated in organisms through food chain enrichment.Owing to this fact,the removal of lead ions from water is critical in terms of the protection of public health and the environment.Nano-zero-valent iron（nZVI）has been widely used in heavy metal wastewater remediation because of its special advantages.However,the features like magnetism,easy to be oxidized,and so on,have been a big gap to hinder its practical utilization.In this paper,carbon-loaded nZVI composites were prepared by using the corn straw,kapok biomass and melamine sponge as the carrier source of nZVI,which successfully overcome the shortcomings that nZVI is easy to reunite,cannot be stored in the air and is not easy to recycle.This thesis includes the following three parts:Hydrophilic biological carbon（HPB）nano-zero-valent iron composites（nZVI-HPB）were prepared by liquid phase reduction.The adsorption efficiency,influencing factors and mechanisms of the adsorbent were explored in this study.The results showed that adsorption process can reach equilibrium in 30 minutes.And the adsorption amount of the adsorbent per unit mass to Pb²⁺was 199.9 mg g^-1 under the condition that the mass ratio of HPB to nZVI was1:1,the amount of adsorbent added was 10 mg and the Pb²⁺solution volume is 40 m L(50 mg L^-1).The adsorption isotherm is more compatible with the Langmuir model,which indicates that the adsorption of Pb²⁺by nZVI-HPB is mainly monolayer adsorption.The XRD and XPS characterizations of the adsorbent residue was also performed after the adsorption experiment.And it was concluded that adsorption,reduction and precipitation are performed simultaneously during the removal of Pb²⁺.The combination of low temperature pyrolysis and Na BH₄ reduction were used to synthesize carbon-foam nano-zero-valent iron composites（CF-nZVI）.The adsorption efficiency,influencing factors and mechanisms of the adsorbent were explored in this study.The results showed that the maximum adsorption amount is 189.3 mg g^-1under the condition that the amount of adsorbent added was 10 mg,the solution p H was 6 and the Pb²⁺solution volume was 40 m L(50 mg L^-1).The adsorption isotherm was more compatible with the Freundlich model,which indicates that the removal of Pb²⁺by CF-nZVI is mainly multi-layer chemisorption with uneven adsorption sites.The XRD,SEM,TEM,and XPS characterization methods were used to explore the changes in material composition and micromorphology before and after adsorption.And it was concluded that during the removal of Pb²⁺,the adsorption of iron oxide and the reduction of nZVI play a major role.Based on the respective advantages of polyvinylidene fluoride,hydrophilic biological carbon and nano-zero-valent iron,the biological-carbon nano-zero-valent iron composite membrane（nZVI-BC membrane）was prepared.The XRD characterization demonstrated the successful preparation of the Fe⁰.The FTIR analysis revealed the presence of abundant active functional groups（-COOH,-OH）on the surface of the composite membrane.Furthermore,the Pb²⁺adsorption experiments showed that the adsorption process can be balanced within 3 h and the saturated adsorption amount is 118.6 mg g^-1 under the condition that the initial Pb²⁺concentration was 50 mg L^-1,the mass ratio of BC to nZVI was 1:3 and the solution p H was 6.The adsorption isotherm of Pb²⁺was more in accordance with Langmuir model,which indicates that the adsorption of Pb²⁺by nZVI-BC membrane is mainly monolayer adsorption.After four cycles of utilization,nZVI-BC membrane still owns an adsorption capacity of 74.7 mg g^-1 for Pb²⁺.