Research Of Treatment On Cyanide Absorption By Electrodialysis And Electrodeionization Based Technology

The polyacrylonitrile-based carbon fiber?PAN-CF?industry has being tremendously developed in recent years,and produced huge amount of waste gas containing 14%of HCN at a concentration of 100 mg/m³.HCN is highly toxic even at very low concentration.Electro-oxidation of HCN is simple,cost effective and highly efficient for HCN removal,therefore has huge application potential.Meaning while,the electrochemical hydrogen evolution reaction?HER?can generate hydrogen from water.The hydrogen cyanide was treated with electro-electrodialysis?ED?and electrodeionization?EDI?to produce the active chlorine and generate hydrogen gas simultaneously.A two-compartment electrodialysis was used to investigate the removal of aqueous cyanide.The effects of environmental factors such as electrolyte,applied potential,reaction temperature,aqueous pH and concentration of cyanide were also studied.According to the results of data fitting,the reaction could be divided into two processes.Scanning electron microscopy?SEIM?showed that no obvious breakage was found on thenon-homogeneous cation-exchange membrane.Finally,comparative analysis on current efficiency and energy consumption was conducted between the ED and EDI devices.Results of the research showed that the optimum reaction conditions of active chlorine production were at the room temperature,under a potential of 5 V,with 2.5moL/L sodium chloride and aqueous initial pH of 7.Finally,846.57 mg/L of active chlorine were produced.Through linear match in two segments respectively,it was found that ED was not suitable for a very low concentration of CN^-.EDI could avoid concentration polarization and was suitable for a very low concentration of CN^-treatment.The current efficiency and energy consumption of ED were 5?66.7%and 1.674?2.067 MJ/g?CN^-?respectively.The current efficiency and energy consumption of EDI were 5.2-29%and 1.541-2.74 MJ/g?CN^-?respectively.Energy consumption of ED was not high when it treat medium concentration of CN^-absorption liquid and the EDI has low energy consumption on low concentration of CN^-treatment.Thus,the two-compartment electrodialysis could not only oxidize CN^-by activating chlorine,but also generate hydrogen.Meanwhile,alkaline solution can be generated in situ to absorb HCN contained waste gases continuously and CN^-can be ultimately converted to harmless CO₂ and N₂.Two-compartment electrodialysis is expected to become an innovative and environmental friendly treatment technology for HCN.