Reduction Mechanism Of Hg²⁺ By Humic Acid Based On Fractional Difference

Natural lakes are roughly classified into silicate-carbonate,chloride-sulfate,and sulfate-chloride water stages according to their natural evolution.The mechanism of abiotic reduction of Hg²⁺by different Humic acid?HA?fractions in different types of water has not been fully investigated.Based on the different HA fractions of Wuliangsuhai obtained by continuous alkali extraction method,the reduction process of Hg²⁺under different environmental conditions?different pH,different ion type and strength?was studied as the main line,combined with elemental analysis,fourier infrared spectroscopy,three-dimensional fluorescence and other characterization methods,in order to provide a theoretical basis for the prevention and control of Hg pollution in lake ecosystems.The main conclusions are as follows:?1?The Hg²⁺reduction rate of different HA fractions decreased gradually with the natural evolution of the water ion environment?type 1 to type 2 and type 3?.As the lake water body evolves naturally,the increasing concentration of cations would block the negative charge of HA,which would hinder the binding of Hg²⁺to the reduction site in HA.The increase of anion concentration and the type change would enhance the degree of complexation between major anions and Hg²⁺.It caused anions to compete with the reducing sites in HA for Hg²⁺in water.Results showed that with the acceleration of the natural evolution of natural lake waters,the Hg elements entering the gas phase from the water phase were less and less,and the risk of Hg pollution was gradually increasing.?2?Fourier transform infrared spectroscopy analysis showed that the infrared characteristic peak area of phenolic and carboxyl groups in different HA fractions had a good correlation with the reduction rate of Hg²⁺.Three-dimensional fluorescence spectroscopy analysis before and after the reaction showed that the phenolic group was probably the chromophore of the fluorescent peak A,the carboxyl group was the chromophore of the fluorescent peak B,and both fluorescent peaks were fluorescence quenched after the reaction.Both characterization methods showed that phenolic and carboxyl groups play an important role in the reduction of Hg²⁺.?3?Correlation analysis showed that the sulfhydryl group in HA inhibited the reduction of Hg²⁺.The Hg²⁺could form a strong complex compound directly with sulfhydryl groups.After Hg²⁺was reduced to Hg⁰,part of Hg⁰ was adsorbed on sulfhydryl groups.Then,Hg⁰ was oxidized again by electron conduction,and further formed a complex having a strong binding force with the sulfhydryl group.The strong complex would hinder the binding of other reducing sites in HA to Hg²⁺,and reduced the reduction rate of Hg²⁺.Correlation analysis also showed that both phenolic and carboxyl groups played a positive role in the reduction of Hg²⁺.?4?As the pH of the system rised,the reduction rate of Hg²⁺by different HA fractions increased,and the increasing pH of the system would gradually open the HA molecules and increase the contact chance of the reduction sites with Hg²⁺.The research results have accumulated basic data for further understanding about the abiotic reduction process of HA in water in the natural evolution of natural lake,and have certain significance for the prevention and control of Hg pollution in natural lake.