The Characteristics Of Different Fulvic Acid Fractions Combining With Copper

Three fulvic acid?FA?subgroups in the sediment of Potamogeton pectinatus plant specie plant species area?Pota.Area?in Lake Wuliangsuhai were obtained by continuous alkali extraction method.The experimental study on the combination of FA and Cu²⁺in different subgroups under the influence of different environmental factors was carried out.A variety of characterization methods and model simulation results were synthetized to reveal the characteristics of FA combining with Cu²⁺in order to accumulate basic data for the prevention and control of pollution from Cu²⁺in lake ecosystems.The main findings are as follows:?1?There were significant differences in the composition and structure of the three FA groups before the combination.The fatification degree and molecular weight of the former extracted FA was smaller than that of the later extracted FA,and the oxygen-containing functional group,aromatization degree and molecular polarity were relatively larger.Compared with the previous study on the FA in the Phragmites area?phra.Area?,the hydroxyl content of FA in this area was less than that in the phra.Area,the contents of carboxyl groups and nitrogen-containing functional groups were higher.?2?Within the set experimental conditions,the combining amount of diffierent FA subgroups with Cu²⁺gradually increased until saturation,and the combining amount of F1 with Cu²⁺was the largest;The combining amount of FA with Cu²⁺gradually decreased as grouped,revealing that the former extracted FA contained more carboxyl and phenolic hydroxyls.Electrostatic adsorption and surface complexation are the main apporaches of FA combining with Cu²⁺and weak sites are the main combining sites.Carboxyl groups and phenolic hydroxyl groups are the dominant functional groups of FA combining with Cu²⁺in each group.?3?Within the set pH range,the peak areas of hydroxyl and carboxyl groups showed a better response to the contribution of combining with Cu²⁺.When pH?5,the combining amount of FA with Cu²⁺increased with the increasing of pH;pH>5,he combining amount of FA with Cu²⁺decreased with the increasing of pH;With the increasing of pH,the fatty of FA increased after combining.Saturation and aromaticity are both reduced.Before the combination,each group of FA showed only Peak A?Ex/Em=380-400/450-500 nm?and Peak B?Ex/Em=330-370/450-500 nm?.With the increasing of p H,the fluorescence intensity of peak A gradually decreased until it quenches after combination,and the fluorescence intensity of peak B gradually weakened;When pH?6,a new Peak C appeared after combination?Ex/Em=300-350/400-440 nm?;When the pH?5,the phenolic hydroxyl group,carboxyl group and nitrogen-containing functional group gradually hydrolyzed as pH increased,the degree of deprotonation occured in the functional group increased,and a large amount of negative charges were generated to allow more phenolic hydroxyl groups,carboxyl groups and nitrogen-containing functional groups to participate in the adsorption reaction;At pH>5,although the hydrolysis of phenolic hydroxyl,carboxyl,and nitrogen-containing functional groups still existed,the OH^—content increased,the hydrolysis complexation between FA and Cu²⁺was enhanced,the hydrolysis and precipitation function dominated,and the Cu²⁺in the solution could bind to the adsorption sites.The amount of Cu²⁺that could combine with the combination sites in the solution dropped dramatically.which reduced the number of phenolic hydroxyl groups,carboxyl groups,and nitrogen-containing functional groups involved in the combination reaction.?4?Within the range of experimental condition,Cu²⁺had little effect on the FA combining with Pb²⁺,while Pb²⁺exhibited a strong competitive effect on Cu²⁺.?5?The phenolic hydroxyl group and carboxyl group were the dominant functional groups of FA combining with Cu²⁺in each group,and the carboxyl group contributedmorethan thephenolichydroxylgroup significantly.The nitrogen-containing functional group also participated in the combining reaction.The contribution of phenolic hydroxyl groups to combining with Cu²⁺in the phra.Area was much greater than that of the carboxyl group.As for the two plant types areas,there were some differences in the dominant functional groups of FA combining with Cu²⁺.