Preliminary Study On The Treatment Progress Of Arsenic Pollutants By Electrochemistry Combined With In-situ Infrared Technology

In recent years,the excessive discharge of industrial arsenic-containing wastewater has caused a serious arsenic pollution crisis in the world.It is urgent to adopt scientific and effective strategies to repair arsenic-contaminated wastewater.Adsorption and oxidation are the two main technologies currently used to treat arsenic pollution.However,the lack of scientific understanding,especially the understanding of the long-term adsorption mechanism,prevents us from scientifically and effectively designing the adsorbent and achieving removal of arsenic adsorption.The lack of in-situ real-time monitoring means prevents us from timely and effectively controlling the amount of oxidant added and the degree of reaction in the oxidation process.Most of the existing characterization and analysis methods are complicated to operate and require high environmental conditions,which cannot realize in-situ real-time analysis and monitoring,resulting in waste of agents and prolonged treatment cycle.Electrochemical technology has the advantages of simple operation,high sensitivity,strong environmental applicability and portability,which undoubtedly provides a new idea for in-situ real-time analysis of long-term adsorption mechanism and real-time monitoring of the degree of oxidation reaction.At the same time,in-situ infrared spectroscopy technology has the advantages of fast analysis speed,high resolution,high sensitivity and wide application range,which provides the possibility for real-time in-situ online analysis and monitoring.The research work of this paper aims to use electrochemical technology to explore the changes of electrochemical signals in the process of long-term adsorption and arsenic removal by oxidation and use in-situ infrared spectroscopy to analyze the internal mechanism of electrochemical signal changes,which lays a theoretical foundation for the application of electrochemical combined with in-situ infrared technology in the field of environment.The main research contents of the paper is as follows:1.Taking the adsorption process of As(V)(H2AsO4-)on hematite as the research object,we tracked and analyzed the change of open circuit potential(OCP)during the adsorption of As(V)to hematite by electrochemical means.The experimental results showed that the open circuit potential presented a stepwise change,that is,the open circuit potential increased at 0-lh,and decreased at 1-6 h,and fell below the initial equilibrium potential.Subsequently,we used in-situ attenuated total reflection Fourier transform infrared spectroscopy(ATR-FTIR)to detect the infrared signal on the surface of the hematite during the adsorption process,and found that the infrared signals in the early and late stage of adsorption were significantly different,indicating that the adsorption pattern of arsenic on the hematite surface was not unchanged.The experimental results showed that arsenic was initially adsorbed on the surface of hematite in a mixed mode of inner-sphere coordination and outer-sphere coordination.However,as the adsorption time was prolonged,the adsorption mode of arsenic eventually changed to the dominant inner-sphere coordination.The time coordinate corresponding to the adsorption mode transformation was consistent with the electrochemical signal evolution process observed before,indicating that the transition of the arsenic adsorption mode was the internal cause of the staged change of the open circuit potential.Subsequently,we combined X-ray photoelectron spectroscopy(XPS)and solid infrared(FTIR)analysis methods,and found that the essence of the potential drop to below the equilibrium potential in the later period was the transformation from outer-sphere coordination to inner-sphere coordination promotes the resorption of free OH" in solution on the surface of hematite.This chapter clarifies the inherent conversion mechanism of the long-term adsorption process of As(V)on hematite through electrochemical combined with in-situ infrared technology,which provides a theoretical basis for us to better understand the adsorption and removal mechanism of As(V)and scientific design of adsorption materials.2.Taking the reaction between arsenic contaminated aqueous solution and hydrogen peroxide simulated in the laboratory as the research object,we tracked and analyzed the change of open circuit potential during the oxidation of As(?)by hydrogen peroxide by electrochemical means,and found that the change of open circuit potential direction can be used to determine the real-time repair state and reaction degree.When the redox reaction was not completed,hydrogen peroxide could continuously oxidize trivalent arsenic and the direction of the open circuit potential was decreased,and once the redox reaction was complete,the potential direction was increased.This suggested that the change in the direction of the open circuit potential could be used to determine the real-time repair state and reaction process.In this chapter,we uses electrochemical technology to realize real-time monitoring of the reaction process between the arsenic-contaminated aqueous solution and the oxidant and uses in-situ infrared spectroscopy technology to analyze the inherent chemical changes,which provides a new direction for the deficiency of the current oxidation method in the real-time analysis and detection of arsenic pollution in water.