Preparation And Application Of Titanium SnO₂-MnO₂ Double Coated Oxygen Evolution Anode For Manganese Recovery By Electrolysis

At present,most electrolytic manganese enterprises only produce manganese-containing wastewater with simple chemical treatment,resulting in the production of a large amount of solid manganese residue and causing secondary pollution to the environment.The treatment methods for manganese-containing wastewater mainly focus on membrane electrolytic recovery.At present,the lead-based alloy anode and titanium-based coated anode used in wet electrolysis have problems such as large internal resistance,easy dissolution,high oxygen evolution potential,and easy corrosion and shedding of the coating.Therefore,seeking an anode material with low oxygen evolution potential,excellent chemical stability and economic efficiency in an acidic electrolysis environment is the key to completely getting rid of additives such as selenite to improve oxygen evolution efficiency.Based on these current conditions,titanium-based electrode samples with intermediate layers of 2,3,4 and 5 layers were prepared.Electrode samples with calcination temperature of 300°C,350°C,400°C,450°C,500°C;Electrode specimens with loads of 2.5 g/m²,5.0 g/m²,7.5 g/m²,10.0 g/m²,12.5 g/m²,In this way,the influence of different parameters on the performance of Ti/Sn O2+Mn O2 electrode was explored,and the optimal preparation conditions were obtained.The morphology and phase composition of the active coating prepared by electron scanning microscope（SEM）and X-ray diffraction instrument（XRD）were analyzed.At the same time,with the help of electrochemical workstation,the electrochemical performance of self-made Ti/Sn O₂+Mn O₂anodic polarization curve（LSV）,cyclic voltammetry curve（CV）and AC impedance spectroscopy（EIS）was analyzed,and the electrolytic manganese small experiment was designed,and the current efficiency,energy consumption and other economic indicators in the electrolytic manganese experiment were analyzed by comparing with the commercial titanium-based ruthenium electrode,and the specific research conclusions are as follows:（1）An appropriate increase in the number of intermediate layers of Sn O₂will make the electrode surface smooth and a small number of cracks conducive to electrochemistry,but when the number of intermediate layers exceeds 3,there will be aggregates composed of a large number of grains on the electrode surface.After adding the intermediate layer,the contact resistance of Ti/Sn O₂+Mn O₂anode is effectively reduced,and the amount of electron transfer is increased.At the same time,the polarization porosity factor generally increased,and the porosity reached a maximum when the middle layer of three layers was introduced.Secondly,the number of electrocatalytic active sites of the anode introduced into the Sn O₂intermediate layer increases,which improves the electrocatalytic activity of the anode,but too many intermediate layers will also increase the resistance value of the electrode itself.In addition,when the number of intermediate layers is 3,the oxygen evolution activity of Ti/Sn O₂+Mn O₂electrode is stronger than that of other electrodes,and the oxygen evolution reaction is more likely to occur,and the oxygen evolution rate is the best.（2）When the calcination temperature is lower than 350°C,the thermal decomposition reaction is insufficient,and there will be a large number of cracks on the electrode surface.The porosity factor of the electrode surface at 450°C is very close to the porosity factor corresponding to 500°C,but the diffraction peak of Mn O₂in the XRD pattern is significantly stronger than that of 350°C and 500°C at a calcination temperature of 450°C,and the mass transfer resistance of the electrode is the smallest at a temperature of 450°C,indicating that the oxygen evolution reaction is most likely to occur in the preparation of the electrode under these conditions.（3）When the loading amount of manganese dioxide（Mn O₂）is higher than 7.5g/m²,grain precipitation will begin to occur on the electrode surface,resulting in rough surface and high and sharp Mn O₂diffraction peaks.When the load is 7.5 g/m²,the corresponding cyclic voltammetry curve contour area is the largest,and at the same time,the voltammetry charge capacity Q^*reaches the maximum value（0.01618A）,so it is best to choose manganese dioxide（Mn O₂）with a load higher than7.5 g/m².（4）Based on the influence of various factors on Ti/Sn O₂+Mn O₂electrode,the best preparation electrode for Ti/Sn O₂+Mn O₂electrode obtained by orthogonal optimization of each factor was:3 layers in the middle layer,450°C-500°C calcination temperature,and 7.5 g/m²loading of Mn O₂active coating.Compared with commercial electrodes,the current efficiency of self-made Ti/Sn O₂+Mn O₂electrode increased from 50.61%to 64.86%,and the energy consumption decreased from12158.01 k Wht/t to 8417.71 k Wht/t,so the oxygen evolution potential of Ti/Sn O₂+Mn O₂electrode introduced into the middle layer was significantly reduced,and the working service life was extended by 7000 h compared with that of commercial Ti/Mn O₂electrode,and its passivation inactivation time could reach25000 h.