Electrolysis With Hydrotalcite As Three-dimensional Electrode Applied For Treatment Of Desulfurization Wastewater Containing Chloride

Limestone gypsum wet flue gas desulfurization?WFGD?process is the most popular and widely-used flue gas desulfurization technology in the world.However,a great amount of desulfurization wastewater is often produced in this process.The composition of desulfurization wastewater is very complicated and it also contain high concentration of Cl^-,which is generally 5000-20000 mg/L.Such high concentration of Cl^-corrodes pipeline and equipments,and degrades the desulfurization efficiency and the quality of gypsum and so on.The traditional chemical precipitation method is difficult to remove Cl^-in desulfurization wastewater.In order to solve this problem,an electrolysis technology was investigated for treatment of high concentration of Cl^-in desulfurization wastewater,in which three-dimensional granule electrodes based on layered double hydroxides?LDHs?were prepared in this thesis.In this paper,the structure and physical characterization of six kinds of granule electrode materials of iron-carbon granules,Zn Al-NO₃ LDHs,Mg Al-CO₃ LDHs,Mg Al-CO₃calcined layered double hydroxides?Mg Al-CO₃CLDHs?,Fe₃O₄@Zn Al-NO₃ LDHs,Fe₃O₄@Mg Al-CO₃CLDHs were conducted by XRD,FT-IR,TG-DSC,SEM and magnetic property analysis.As a result,four kinds of materials,iron-carbon granules,Zn Al-NO₃ LDHs,Mg Al-CO₃CLDHs,Fe₃O₄@Zn Al-NO₃ LDHs were selected as the three-dimensional granule electrodes used in electrolysis.Under the optimal experimental parameters of current density,electrode spacing,granule electrode dosage,circulating water flow rate,initial Cl^-concentration,the maximum Cl^-removal efficiencies for these four different granule electrodes,iron-carbon granules,Zn Al-NO₃ LDHs,Mg Al-CO₃CLDHs,Fe₃O₄@Zn Al-NO₃ LDHs are 81.81%,83.01%,83.78%and 87.70%respectively.Among the four kinds of granule electrodes,iron-carbon granules and Fe₃O₄@Zn Al-NO₃ LDHs can be recycled.After recycling three times,Cl^-removal efficiency is still 60%and a stable Cl^-removal efficiency is achieved for Fe₃O₄@Zn Al-NO₃ LDHs.Finally,linear scanning voltammetry?LSV?and cyclic voltammetry?CV?experiments prove that oxygen evolution reaction and chlorine evolution reaction occur during electrolysis of desulfurization wastewater,and that the chlorine evolution reaction is completely reversible.The removal mechanisms of Cl^-in wastewater involve electrochemical oxidation,microelectrolysis of granule electrodes,surface adsorption,ion exchange,and memory effects.At the same time,the Cl^-is transformed into a certain amount of Cl₂,HCl O,Cl O^-,Cl O₂,Cl O₂^-and other related substances in the electrolysis of desulfurization wastewater.