Electrocatalytic Reduction Treatment Of Simulated Liquid Radioactive Waste Containing Methyl Iodide In Nuclear Power Plants

In this paper,non-radioactive isotope methyl iodide(CH3I)was used to simulate radioactive CH3131I as pollutant to treat by electrocatalytic reduction.The electrocatalytic reduction of CH3I(1mg/L)with copper electrode(Cu),Cu/carbon felt electrode(Cu/CF)and Cu/Ni/carbon felt electrode(Cu/Ni/CF)was studied.We chose copper metal electrode as cathode to degradate CH3I by comparing the electrocatalytic properties of copper,nickel and iron metal electrodes for CH3I.The effects of experimental conditions such as reaction temperature,quaternary ammonium salt,current density,initial pH and electrolyte concentration on the degradation of CH3I were investigated.The results show that under the optimal electrolysis conditions:Tetrabutylammonium chloride(TBAC 0.05%,mass fraction vs CH3I),current density(3 mA/cm2),reaction temperature(20 ?),initial pH(4.5),electrolyte(0.5 M Na2S04)and electrolysis time(120 min),the degradation efficiency of CH3I was 89%.The reduction mechanism of CH3I on the surface of copper electrode was studied by cyclic voltammetry(CV).The dissociative electron transfer(DET)leading to the scission of the carbon-halogen,and the active hydrogen atoms generated during the electrolysis process can promote the reduction process.A nano-Cu/CF electrode was successfully prepared by pulse potential deposition process with low concentration of Cu2+ and high current density.X-ray diffraction(XRD)and scanning electron microscope(SEM)characterization were performed on a Cu/CF electrode prepared under optimal electrodeposition conditions(1 mM Cu2+,4 mM C6H5O73-,20mM KNO3,pH=5,deposition potential-2.5 V,deposition temperature 45 ?,deposition time 300 s).It can be seen that the copper particles are uniiformly dispersed on the carbon felt substrate.The specific surlface area was determined by the BET method,the specific surface area of the Cu/CF electrode(2.252 m2/g)was increased by 44%compared with the CF electrode(1.563 m2/g),which helped to improve electrocatalytic activity of the electrode.The optimum electrolysis conditions of constant current electrolysis:copper loading was 6.98 mg/g,current density was 2.5 mA/cm2,initial pH was 5.5,and the degradation efficiency of CH3I was 98.8%within 90 min.CV results show that the electrochemical reduction of CH3I is a diffusion-control process.The optimal deposition conditions of Cu/Ni/CF electrode were determined by orthogonal experiments:1 mM Cu2+,2 mM Ni2+,2 mM C6H5073-,20 mM KNO3,pH=6,plating temperature 45 ?,deposition potential-2.5 V and deposition time 300 s.We can see that the copper and nickel nano metal particles are dispersed on carbon felt electrode by SEM and EDS.The coated particles uniformly cover the surface of the carbon fibers.The electrode has the highest electrocatalytic activity when the copper and nickel loading was 4.56 mg/g and 6.07 mg/g respectively in the Cu/Ni/CF electrode.The optimum electrolysis conditions were obtained as follows:current density 2.0 mA/cm2,electrolyte 0.4 M Na2SO4,and initial pH 3.5.The degradation efficiency of CH3I was up to 99.5%within 90 min.