Effect Of Electric-flow Field On Oxide Particle Melting In 6kA Rare Earth Electrolyzer

Molten salt electrolysis is the main method for industrial production of rare earth metals and their alloys which has the advantages of high yield,low cost and less waste residue.In industrial production,rare earth oxides need to be continuously added into the electrolytic cell.There are two feeding methods that are manual feeding and machine feeding.But there is no scientific and theoretical basis for the control of oxide feeding position and feeding time.The temperature of rare earth electrolysis is kept at about 1000℃,which belongs to high temperature environment.It is difficult to study the changes of the melting and diffusion of rare earth oxides in molten salt.The gas produced by electrolysis will affect the molten salt flow field.The change of current density will affect the electrolysis rate and gas generation and further affect the change of flow field.In this thesis,the melting and diffusion process of lanthanum oxide in molten salt is studied for the first time by using commercial software.For 6k A rare earth electrolytic cell,the optimal blanking time and optimal blanking position of lanthanum oxide are analyzed.Combined with the research of electric field and flow field,the optimization scheme of electrolytic cell structure is put forward,which provides a theoretical basis for the basic theoretical research and large-scale development of electrolytic cell.Firstly,the electric field of 6ka rare earth electrolytic cell is studied by numerical simulation.It is found that the current density increases gradually from anode to cathode and reaches the maximum on the cathode surface.The potential decreases gradually from the inner surface of the anode to the surface of the cathode and the potential at the bottom of the electrode presents a fan-shaped distribution.It is found that the current density difference between the bottom of the anode and the side of the anode is too large,resulting in tip discharge and other problems.The difference between the two sides is too large,resulting in uneven anode consumption and falling graphite particles,polluting the electrolytic cell.The improvement measures for the chamfering of the bottom of the anode are put forward.It is found that the current density gradient of the chamfered surface is uniform after chamfering.In addition,it is found that when the chamfering Angle increases by 10mm,the potential of the electrolytic cell increases by 0.0055V and the current density of the chamfering surface of the electrolytic cell increases by about 1000A/m~2.When the insertion depth of the electrode increases by 20mm,the voltage of the electrolytic cell decreases by about 0.1V.Secondly,the flow field of 6k A rare earth electrolytic cell is simulated by calculating the gas velocity through the distribution of current density.It is found that the fluid velocity on the inner surface of the anode is greater than the molten salt velocity on the cathode surface.The farther away from the anode surface,the fluid velocity will gradually decrease.There is a vortex in the molten salt between the anode and cathode.The velocity value reaches the minimum at 230mm away from the molten salt liquid level,and the molten salt has the best fluidity at the130mm to 400mm away from the liquid level.By analyzing the cloud diagram of gas proportion,it is found that the gas mainly exists on the anode surface,the closer to the liquid surface,the thicker the gas layer,and the less the gas away from the anode surface.Through the analysis of four insertion depths,it is found that the optimal electrode insertion depth is 470mm.This electrode depth makes the molten salt outside of the anode reflux downward and drives the molten salt flow at the bottom,which is conducive to the drop of rare earth metal into the metal collector and has a benign impact on electrolysis.Finally,the diffusion law of lanthanum oxide in molten salt is explored.It is found that the blanking time of lanthanum oxide is controlled at about 60s,which is conducive to electrolysis.When the blanking position is corresponding to the anode gap in the middle of the anode pole,which is easy to cause inconsistent anode consumption.Through the movement analysis of lanthanum oxide particles,it is found that the molten salt formed eddy current near the anode gap,which leads to the concentration of lanthanum oxide here being higher than that of other positions and aggravates the anode consumption.In order to solve the problem of uneven distribution of lanthanum oxide concentration,three blanking schemes are proposed to improve:blanking near the anode,symmetrical blanking on both sides of the anode and symmetrical blanking on four sides of the anode.By comparing the lanthanum oxide diffusion concentration distribution and lanthanum oxide movement track of the three blanking schemes,it is found that symmetrical blanking on four sides of the anode makes the lanthanum oxide concentration distribution in the electrolytic cell uniform,which is conducive to electrolysis and is the best blanking position.In this thesis,the optimization of the anode structure of the electrolytic cell is proposed and the electric field law under different working conditions is summarized.It provides a theoretical basis for the oxide blanking time and blanking position of the rare earth electrolytic cell,and also provides a practical research method for the large-scale development of the rare earth electrolytic cell.