Study On Binding Characteristics Of Coal-based Fulvic Acid With Fe²⁺,Pb²⁺ And Cr⁶⁺

In this thesis,fulvic acid（FA）was extracted from Yunnan lignite,and then its binding properties with Fe²⁺,Pb²⁺and Cr⁶⁺were investigated.The kinetic model and isothermal model were used to explore the action mechanism of FA binding metal ions.The sites of FA binding metal ions were characterized and analyzed by modern instruments.And the action mechanism of FA binding metal ions was further explored by molecular simulation.It provides a theoretical reference for the application of FA in water treatment and also provides new ideas for studying the characteristics of FA binding other metal ions.In the experiment of FA binding metal ions,the amount of FA binding Cr⁶⁺and Fe²⁺gradually increased with the increase of temperature,while the amount of FA binding Pb²⁺gradually decreased with the increase of temperature.Under low p H conditions,the amount of FA binding to metal ions was Pb²⁺>Fe²⁺>Cr⁶⁺in sequence,while under high p H conditions,the amounts of FA binding metal ions followed the order of Pb²⁺>Cr⁶⁺>Fe²⁺.Meanwhile,the amount of FA binding metal ions increased with the increase of FA dosage.With the increase of Fe³⁺and Cu²⁺concentrations in the solution,the amount of FA binding Pb²⁺and Fe²⁺gradually decreased,but the amount of FA binding Cr⁶⁺gradually increased.The amount of FA binding Fe²⁺,Pb²⁺and Cr⁶⁺decreased with the increase of Na⁺concentration.The fitting results of the kinetic model and isothermal model revealed that the process of FA binding metal ions was controlled by chemical adsorption mechanism and diffusion,and the whole process was a multi-layer adsorption process with an uneven surface,which was easy to carry out.The elemental analysis revealed that the main elements of FA were C,O,N and H.The infrared spectrum showed that the aromatic structure of FA was mainly tetra-substituted benzene and penta-substituted benzene,and connected with a large number of oxygen-containing functional groups such as carboxylic acid,amino group and anhydride.Besides FA also had a small number of nitrogen-containing and sulfur-containing functional groups.NMR results showed that FA C skeleton was mainly aromatic structure,indicating the aromatic degree of FA was high.From the characterization analysis of FA before and after binding metal ions,it can be seen that carboxyl,carbonyl and anhydride were the main binding sites,and hydroxyl was the secondary binding site.Meanwhile,nitrogen-containing and sulfur-containing functional groups also contributed to the process of FA binding metal ions.The FA characterization data was used to construct a reasonable molecular model of FA.And it concluded that the molecular weight of FA is 865 and its molecular formula is C₃₈H₃₁O₂₁NS.According to the simulation calculation of the sorption module in Materials Studio,the number of FA adsorbing Fe²⁺Pb²⁺and Cr⁶⁺are 12,15and 5 molecular/u.c.,respectively.Based on the molecular simulation results of FA,it was found that the main site of FA adsorbing metal ions was carboxyl or carbonyl,and hydroxyl is the secondary site.The affinity of hydroxyl to Fe²⁺,Pb²⁺and Cr⁶⁺is greater than that of carboxyl or carbonyl.There are 93 figures,51 tables,and 106 references in this thesis.