| This work was using fulvic acid (FA) from sediment in lake Wuliangsuhai as absorbent, in order to study the binding characteristics of FA from both Phra. Area and Pota. Area, under various conditions include pH, ionic strength, concentration of FA and M2+ and temperature. It has applied Langmuir, Freundilich, Bi-Langmuir and Ligand binding models, as well as fluorescence spectra, FTIR before and after binding to reveal the mechanism of FA and M2+. It is important in providing theoretical evidence for controlling the heavy metal pollution such as Pb, Cu and Cd. The main findings are listed below:1. The aromaticity, molecular weight, humification degree and polarity of FA from Phra. Area were higher than FA from Pota. Area, and the contents of phenolic hydroxyl group, carboxyl and aliphatics were different among two areas.2. The binding process of FA from both Phra. Area and Pota. Area can be categorized into three stages, which are fast binding, slow binding and balancing. As the concentration of FA increased, the FA binding M2+ increased as well. The increasing ionic strength and decreasing M2+ concentration both contribute to the raise of binding rate. The mechanism of controlling FA binding M2+ was mainly in liquid film diffusion resistance and chemisorption.3. The total amount binding of FA from both Phra. Area and Pota. Area to M2+ was increased as the increasing of initial concentrations of both M2+ and FA; unit amount binding was decreased as the increasing of concentration of FA. It also found that the amount of binding was declined as the raise up in ionic strength; it was increased as increasing of pH and the decreasing of temperature (spontaneous exothermic reaction).4. The simulation results of Langmuir, Freundlich and Bi-Langmuir indicates that the FA from Phra. Area and Pota. Area binding M2+ was not monomolecular layer adsorption and heterogeneity. The FA from both areas was easier in binding M2+5. There were two types of binding sites of FA participated in the process, the strong site (KS,1) has 1-2 point higher in apparent constant than weak site (Ks,2), however, the maximum binding amount Bmax,1 is 1-3 higher than Bmax,2 which indicates the heterogenetiy and the limited number of strong sites.6. The fluorescence spectra results of before and after process showed heterogenetiy of FA from Phra. Area and Pota. Area binding M2+ which aromatic was the key factor in binding FA and M2+. The FTIR results of before and after process showed M2+ can react with amine groups, and can form bidentate chelate compound with carboxyl and phenolic hydroxyl.7. The amount of Phra. Area FA in binding M2+ follow the order of Pb2+> Cu2+>Cd2+, and binding rates:Cu2+>Pb2+>Cd2+;The amount of Pota. Area FA in binding M2+ follow the order of Pb2+>Cd2+>Cu2+, no difference in binding rate.8. The pH has no significant difference in Phra. Area FA binding M2+, however, to Pota. Area FA in binding M2+ follow the order of Cu2+> Pb2+>Cd2+. The concentration of FA in Phra. Area affecting Cu2+ was 1.12 times than Pb2+,3.86 times than Cd2+; the concentration of FA in Pota. Area affecting Pb2+ was 1.36 times than Cu2,3.05 times than Cd2+. The ionic strength affecting FA binding M2+ in Phra. Area and Pota. Area follow the order:Pb2+> Cd2+> Cu2+, Pb2+> Cu2+> Cd2+, respectively.9. Freundlich and Bi-Langmuir models have been well simulated the FA binding M2+. The Freundilich model results indicate the affinity binding Phra. Area and Pota. Area to M2+follow the order:Pb2+>Cd2+>Cu2+ (15℃,25℃),Pb2+>Cd2+>Cu2+(250C),Cu2+>Cd2+>Pb2+(15℃), respectively. Bi-Langmuir model has the similar conclusion, which the binding amount in weak site was 1 point higher, and the affinity coefficient is 1-2 points lower. Ligand binding model is similar to other models, and it is relied on experimental conditions. |
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