Removal Of Gaseous Elemental Mercury By Liquid Phase Absorption Combined With Electrochemistry

China’s energy structure is dominated by coal.The combustion of coal is the main source of atmospheric mercury pollution,and the zero-valent mercury（Hg~0）in coal-fired flue gas is difficult to be removed by the existing flue gas purification equipment due to its characteristics of insoluble in water,slow dry sedimentation rate,and low reaction activity.Therefore,it is urgent to study the removal and recovery technology of mercury in the coal-fired flue gas.This study mainly uses electrochemical oxidation and KI/I₂ absorption solution to remove Hg~0 from simulated flue gas,discusses the influence of various factors on Hg~0 removal efficiency,compares the removal efficiency of Hg~0 under different cathode conditions,explores the removal mechanism of Hg~0,and solves the technical problem that Hg~0 is difficult to be effectively removed by existing purification devices.Preparation of titanium-based metal oxide coated electrode（DSA）.DSA electrode was prepared by coating thermal decomposition method with titanium plate as a matrix.The morphology,structure,and electrochemical properties of the electrode were analyzed by SEM,XRD,EDS,CV,and LSV.The results show that the doping of noble metal element platinum has a great influence on the surface morphology of the DSA electrode.It can not only change the grain size of the active layer on the electrode surface but also affect the stability of the coating and promote the formation and agglomeration of crystals on the coating surface.Platinum particles are evenly dispersed on the DSA electrode with small particle size and many active points.The electrochemical activity of platinum doped DSA electrode is significantly higher than that of undoped DSA electrode,and the DSA electrode with 10%platinum doping has the best performance.Study on Influencing Factors of Hg~0 removal.K₂S₂O₈,KI/I₂,K₂Cr₂O₇,KMn O₄,Na Cl O,and other oxidizing absorbers meeting the requirements were screened.The results showed that the absorption effect of KI/I₂absorption solution on Hg~0 was the best,which could reach 36.82%.Using KI/I₂ solution as absorbent,DSA electrode as the anode,titanium electrode as a cathode,and DSA electrode as anode and cathode respectively,it is used for electrochemical synergistic catalytic oxidation of Hg~0 in simulated flue gas with KI/I₂ absorption solution.It is found that the performance of the electrode is stable and the effect is good.The effects of the ratio of KI/I₂,I₂ concentration,electrolytic voltage,current density,plate spacing,and platinum doping of DSA electrode on Hg~0 removal efficiency were investigated.The results show that when the DSA electrode is used as anode and the titanium electrode is used as the cathode,with the decrease of the ratio of KI/I₂,the removal efficiency of Hg~0 first increases and then decreases.When the ratio is 12:1,the effect is the best,which can reach28%.The concentration of I₂ has a great impact on the removal efficiency of Hg~0.The concentration of I₂ is too low and the reaction cannot be carried out completely,resulting in the reduction of Hg~0 removal efficiency;If the concentration of I₂ is too high,the generation of complexions such as I₃^-or I₃（I₂^-）will be inhibited,and the removal effect of Hg~0 will also be affected.When the voltage is from 0V to 6V,the removal efficiency of Hg~0 first increases and then decreases.The effect is the best at 6V,which can reach more than 90%.The current density has little effect on the removal efficiency of Hg~0,but the increase of current density will promote the removal of Hg~0 to a certain extent.The platinum content of the anode electrode increased from 0%to 60%,and the removal efficiency of Hg~0increased first and then decreased,and the effect was the best at 10%;The plate spacing has a great impact on the removal efficiency of Hg~0.If the spacing is too large,the cell voltage increases,and the power consumption also decreases the removal efficiency.When DSA electrode is anode and cathode,it is found that the ratio of KI/I₂,I₂ concentration,electrolytic voltage,and platinum doping of DSA electrode have a great influence on the removal efficiency of Hg~0,which first increases and then decreases;The effect of current density and plate spacing on Hg~0 removal efficiency is not obvious.Comparing the two different cathodes,it is found that when the two electrodes are cathodes,they can achieve good Hg~0 removal efficiency.However,there will be slight differences under different conditions,which also provides some help for the subsequent selection of the most appropriate electrode under different flue gas conditions.Although the DSA electrode is an anode electrode,it can also achieve good results when used as a cathode.Study on Hg~0 removal mechanism and I₂ recovery mechanism.The preliminary analysis of Hg~0 removal mechanism includes six paths:one is to form[Hg I₄]^2-after absorption by KI/I₂ absorption solution,the other is to form Pt Hg₄ with Pt on the electrode,the third is to indirectly oxidize·OH generated on the anode,the fourth is to be directly oxidized to Hg²⁺on the DSA electrode,the fifth is to be directly adsorbed on the DSA anode,and the sixth is to be possibly oxidized by strong oxidizing substances such as O·,O₃,IO₃·and IO₄·etc;The recovery mechanism of I₂ includes two paths:one is that I^-forms I₂ through electrochemical redox,and the other is that I^-is first adsorbed on Pt and then oxidized to form I₂.At the same time,the stability of the electrode is also studied.The results show that DSA electrode has a good effect on the removal of Hg~0,and has good stability and repeatability.