Transport Behavior And Metallurgical Effect Of Copper Electrolysis Process Under Inter-Electrode Jet Conditions

Copper electrorefining and copper powder electrolysis are two representative electrochemical deposition processes,the former for purifying crude copper and the latter for obtaining powdered copper products.The development direction of copper electrorefining is to further increase the current density to increase the output.The development direction of copper powder electrolysis is to further reduce the direct current?DC?power consumption to enhance the competitiveness of products,and the inter-electrode jet is an important means to achieve the two goals.In this paper,based on the characteristics of copper electrorefining process,a mathematical model describing the macroscopic transport phenomenon in the electrolytic cell is established.Through the numerical simulation,the natural convection phenomenon between electrodes in the conventional electrolyte inlet mode is studied,and the influence of the jet flow on the concentration boundary layer was analyzed.Through the experimental research,the variation characteristics of the cathode quality in copper electrorefining with high current density are clarified,and the effect of jet flow on the power consumption and performance of electrolytic copper powders is investigated.The research content and main achievements of this paper are as follows:?1?According to the characteristics of electrolyte transport behavior in copper electrorefining process,based on Boussinesq approximation,a mathematical model describing the flow and mass transfer of electrolyte and the trajectory of floating anode slime was established.The unit experiment of turbulent natural convection in copper electrorefing process was designed.The experimental data is used to verify the correctness of the mathematical model and its solution method.By comparing the adaptability of four typical turbulence models to solve the natural convection in copper electrorefining process,it is found that the calculation results of SST k-?turbulence model are the most accurate and the calculation cost is low.?2?Based on the established mathematical model of flow and mass transfer in copper electrorefining process,the numerical simulation study was carried out.The correctness of the mathematical model and the solution method was verified by the measured data of industrial electrolytic cell,and the grid independence was verified.The results showed that in the conventional inlet mode,the concentration of copper ions near the cathode is low,and the electrolyte flows upward.The concentration of copper ions near the anode is high,and the electrolyte flows downward.The electrolyte flow between the cathode and the anode is mainly controlled by this natural convection.The thickness of concentration boundary layer of both the cathode and the anode decreases with the increase of the current density.The characteristic number equations of the turbulent natural convection in copper electrorefining process are Sh_x=0.592Ra_x^*1/5,??_C?/x=3.32Ra_x^*-1/5,?u_mx?/D=0.856Ra_x^*2/5,?/x=1.68Ra_x^*-1/5?3?Based on the mathematical model of electrolyte transport behavior in copper electrorefining process,the effects of the jet flow on electrolyte flow and mass transfer and floating anode slime trajectory at high current density were investigated.The results show that when the velocity of the jet flow is 2.0m/s,the copper concentration near the cathode above the nozzle position increases significantly,and the thickness of the cathode concentration boundary layer reduces obviously.In the jet inlet mode,the distance of the nozzle to the cathode becomes smaller as the electrolysis reaction progresses,and some of the jet flow is blocked by the cathode and fails to enter the inter-electrode gap,which weakens the stirring effect,resulting in the copper concentration near the cathode becoming smaller and the thickness of the concentration boundary layer gradually becomeing thicker.Under the jet flow,the anode slime particles float upward with the main stream,and the closer the jet position is to the bottom,the more difficult anode slime is to float.?4?The surface quality and uniformity of cathode copper were measured by surface roughness and its standard deviation.The effect of the jet flow on the surface quality of cathode copper in copper electrorefining process at high current density was studied under experimental conditions.The results show that in the conventional inlet mode,the surface roughness of the cathode copper increases sharply with the extension of the electrolysis time.The electrolysis time increases from 1h to 5h,and the surface roughness of the cathode copper increases from 1.3?m to 8.2?m.Increasing the circulation flow rate of the electrolyte has a limited effect on the surface quality of the cathode copper.In the single-side single-row inlet mode,as the circulating flow rate of the electrolyte increases,and the burr on the surface of the cathode copper decreases,the surface becomes flat and the crystal grains decrease.When the nozzle position is at the middle of the height of the effective area of the cathode,the surface roughess and its standard deviation is the smallest,and the electrolyte is most fully stirred near the cathode.?5?The copper powder was prepared by electrolysis method.The influence of process parameters on DC power consumption was studied by single factor experiment and response surface analysis.The results show that increasing the copper concentration and the temperature of the electrolyte and prolonging the electrolysis time are beneficial to reduce the cell voltage and improve the current efficiency in copper powder electrolysis process,thereby reducing the DC power consumption.Five significant factors affecting the DC power consumption of copper powder electrolysis selected by Plackett–Burman method are:electrolyte temperature?A?,copper ion concentration?B?,sulfuric acid concentration?C?,interelectrode gap?D?,current density?E?.Using the Box Behnken experimental design,the prediction model of DC power consumption(Y_PC)of copper powder electrolysis was constructed by response surface analysis as follows:Y_PC?28?1112.67-1.9687A-88.709B-6.5444C?10?29.391D?10?0.6328E-0.1688AD-0.00399AE-0.46701BD-0.01055BE-0.10CD-0.001058CE?10?0.00634937DE?10?4.14837B²?10?0.033301C²?6?The effects of inter-electrode jet on the DC power consumption,morphology and apparent density of electrolytic copper powders were studied under experimental conditions.The results show that in the conventional inlet mode,when the circulating flow rate is increased,the power consumption and apparent density change a little.The obtained cathode copper powder has a honeycomb appearance and the particle morphology is dispersed dendritic shape.The inter-electrode jet can greatly reduce the power consumption of electrolytic copper powder,which is up to 37%compared with the conventional inlet mode.However,the jet flow makes the copper powder in the jet zone close to the cathode,and no longer has a honeycomb appearance.On the microstructure,the copper powder changes from a dendritic to a compact,rounded,and less dendritic bulk dendrites.And the apparent density of copper powder increases significantly.In summary,based on numerical simulation and experimental research,the influence of inter-electrode jet on copper electrolysis process is analyzed.The variation of the surface quality of the cathode copper in copper electrorefining process with jet flow is clarified.The influence of the jet flow on DC power consumption,copper powder morphology and apparent density of electrolytic copper powders is studied.The research of the thesis provides a theoretical basis and practical basis for improving the current density in copper electrorefining and reducing the DC power consumption in copper powder electrolysis.