Effect Of Anode Dissolution And Additives On Zinc Electrowinning By Hydrogen Diffusion Anode

Zinc metallurgy is an energy-intensive sector.Reducing the electrode potential by altering the anode reaction is a workable new solution to the issue of power consumption during zinc electrowinning.The anodic reaction can be changed from an oxygen evolution reaction to a hydrogen oxidation reaction with a theoretical potential reduction of 1.229 V when using a hydrogen diffusion anode（HDA）on zinc electrowinning.Currently,there have been few research on the new system of zinc electrowinning.In this thesis,the cathodic reaction of zinc electrowinning step was studied by a homemade Pt-Ti HDA.The main conclusions are as follows:（1）With the electrowinning process,HDA was dissolved.Ti and Pt dissolved as ions in the electrowinning solution and reduced at the cathode.To simulate the impact on the cathodic process of zinc electrowinning after anodic corrosion dissolution,various amounts of Ti⁴⁺and Pt⁴⁺were added to the electrowinning solution.The addition of Ti⁴⁺decreases the current efficiency（CE）and increases the power consumption（PC）.In addition,the microscopic morphology of zinc products changes from lamellar to dendritic,and the surface of zinc becomes rough.Pt⁴⁺decreases the overpotential of HER and CE simultaneously.Adding Mn²⁺to the electrowinning solution improves CE and lowers PC.Concentrations of Ti were efficiently lowered from 1.2×10^-4 wt.%to 5×10^-5 wt.%and Pt from 1.6×10^-5 wt.%to 7×10^-6 wt.%by the addition of Mn²⁺.Increasing the p H of the electrowinning solution can effectively inhibit the reduction process of Pt,which reduces the Pt concentration of zinc product to ppb.（2）Gelatin is a typical additive in zinc electrowinning with lead anodes.In this paper,the effect of gelatin additive in zinc electrowinning with HDA was investigated.The ideal gelatin addition was 10 mg L^-1,resulting in the lowest PC of 1104.22 k W·h t^-1 and the highest CE of 94.46%.The surface of the zinc product was rough without the addition of gelatin,and the HER was aggressive,which influenced the bonding strength between zinc and cathodic aluminum.The addition of gelatin improved cathodic polarization and stopped zinc and hydrogen from being reduced.The nucleation overpotential of zinc increases from 0.139 V to 0.189 V,which increases the nucleation rate and refines the zinc grains.（3）To reduce energy consumption,process parameters such as the concentration of sulfuric acid and Zn²⁺,current density,deposition temperature,and electrode spacing were optimized.The optimal process parameters were as follows:electrode spacing of 2 cm,deposition temperature of 40°C,zinc ion concentration of 70 g L^-1,sulfuric acid concentration of 150 g L^-1,current density of 400 A m^-2.The optimized zinc electrowinning step has significantly reduced the electrical energy consumption from 1158.51 k Wh·t^-1 to 963.53k Wh·t^-1,with an energy saving rate of 68.92%compared to conventional lead anode zinc electrowinning system.