Research And Design Of New Long Effective Oxygen Cathode In Electrolyzing Causticizing Carbonization-Precipitation Liquid

During the electrolysis and regeneration of a novel technology of alumina production named alkali-dissolution and carbonization-precipitation process, using oxygen cathode can reduce the cell voltage and energy consumption. Based on performance evaluation and analytical characterization of oxygen cathode sold on the market, silver based catalyst was the first choice as catalysts using in electrolyzing causticizing carbonization-precipitation liquid. At the same time, nickel system, platinum group and manganese oxide catalysts were catalyst materials making an analysis and comparison. The working conditions of a electrolytic cell with ion-exchange were evaluation. It was found that when1.7mol/L Na2CO3 and 6.5mol/L NaOH as anolyte and catholyte respectively, pumping oxygen as 8KPa-25KPa into cathode chamber as the working environment of oxygen electrode, the current density of 1000A/m2 and 75℃, the cell voltage could be reduced to 1.75V and the current efficiency could reach over 98%.Based on research design and optimization analysis of oxygen cathode whose main material is graphite, it was found that when the optimum proportion of gas diffusion layer was 4 portions of graphite,1 portion of activated carbon,1 portion of PTFE and 1 portionl of NH4NO3, the optimum proportion of catalyst layer was 4 portions of Ag2O,1 portion of activated carbon,4 portions of graphite and 1 portion of PTFE, the electrode performance was the best. When the current density was 1000A/m2, the electrode potential was-0.42V(vs HgO electrode). The voltage of this electrode using as cathode was 2.1-2.3 V. In addition, adding MnO2 to catalyst can improve the reaction rate of oxygen reduction reaction.According to long service life and good mechanical properties of electrode used in electrolysis process, oxygen cathodes used by fiber felt were studied. It was found that Pt plated on Ni fibers electrode has a good catalytic activity of oxygen reduction and stability of electrode compared with Ni fibers electrode. When the current density was 1000A/m2, the electrode potential of Pt plated on Ni fibers electrode was lower 0.35V than Ni fibers electrode.Ag/C electrodes were prepared by electrodeposition method and hydration hydrazine reduction respectively. Using electrodeposition method to prepare Ag/C electrode, it was found that when the electric quantity of electrodeposition was 2.0C, the reduction potential was-0.7V-0.8V, the testing temperature was 70℃, the electrode potential was-0.4V(vs HgO electrode). This electrode potential was lower over 0.8V. Using hydration hydrazine reduction, when the concentration of hydration hydrazine in H2O-C2H5OH solution which the volume ratio of H2O:C2H5OH was 1:1 was 2mol/L, the concentration of AgNO3 was 1mol/L, the Ag/C electrode had a good activity. Compared with hydration hydrazine reduction, Ag/C electrodes prepared by electrodeposition method have good electrode stability.