Preparation Of Chelating Electrode And Study On The Process Of Adsorption–Desorption Of Uranium From Seawater

Terpolymer with N,N'-Dipropionitrile acrylamide (DPAAm) / acrylic acid(AA)/ ferrocene(Fc)were synthesized. KH-550, PAA and Poly(DPAAm-co-Fc-co- AA)were coated on the nickel by self-assembly in turn.Then the coating was reacted with hydroxylamine hydrochloride directly to make chelating electrode which contained amidoxime-groups. Chelating electrodes were placed in a certain concentration of uranyl nitrate solution to the adsorption of uranium experiment,and others were placed in seawater to the adsorption of uranium experiment, the desorption was by electrochemical methods. The composition of the copolymer was measured by FT-IR, the electrochemical behavior of the chelating electrode was discussed by cyclic voltammetry, and surface morphology of the electrodes were characterized by SEM.(1)Film electrodes containning P(DPAAm-co-Fc-co-AA) were prepared firstly.Solution of _KH-550 was prepared with volume ratio of _KH-550, H2O and C2H5OH was 1:1:18, pH was adjusted to 5.5 by glacial acetic acid,then the hydrolyzing time was detemined by conductivity meter. It was about 60h in room temperature. In actual experiment , V_KH-550:V_water:V_ethanol=1:1:100 was the best ratio by SEM, and the best ratio of chromic acid etching solution was V_water:V_{sulfuric acid}:m_{potassium dichromate}=90:10:1. The corrosion time in chromic acid etching solution was 30min. The assembly time in solution of KH-550 was 1.5 min, 35min in solution of PAA/DMF, 30min in solution of P(DPAAm-co-Fc-co-AA)/DMF.(2)With chelating electrodes as work electrodes, stainless steel electrodes made in the lab as counter electrodes, calomel electrodes as reference electrodes and phosphate buffer solutionas(pH=7) supporting electrolyte, the chelating electrodes showed good electrochemical activities. Desorption voltage of the electrode adsorbed uranium in seawater was 0.72V, and desorption voltage of the electrode adsorbed uranium in uranyl nitrate solutionwas 0.88V.(3)Adsorption of uranium on the chelating electrodes contained two ways: electrostatic adsorption and chelating adsorption, and adsorption capacity of chelating electrodes was determined by the latter. Adsorption isotherm of chelating electrodes was:Γ_t =2.96×10^-2c^0.37.(4)The adsorption of uranium in sea water on the chelating electrodes reached equilibrium after 8 days,and equilibrium adsorption capacity was 8.9mgU·g^-1. Adsorption capacity increased as the temperature rise in 5℃to 25℃, Arrhenius equation: k=0.11exp(-37.20/RT).(5) The surface of the chelating electrode was changed greatly in morphology characterized by SEM in front and behind of adsorption of uranium ,and the adsorption of uranium on the chelating electrodes had achieved good results.