A method for preparing rare earth by molten salt electrolysis with gradient pole distance

Abstract

A method for preparing rare earths by molten salt electrolysis with a gradient pole distance belongs to the field of rare earth molten salt electrolysis. The method of the present invention is that in a rare earth molten salt electrolytic cell, an upper plug-in anode is inserted into the inner edge of the cell shell at a certain angle, and an upper plug-in cathode is vertically inserted into the center of the electrolytic cell, and the electrolytic cell is filled with molten salt composed of fluoride and / or chloride. The rare earth molten salt electrolysis method with a gradient pole distance is formed by obliquely inserting the anode into the electrolytic cell, in which the pole distance between the anode and the cathode gradually decreases from the molten salt liquid surface to the inside of the molten salt, which is different from the current electrolysis method with uniform and equal pole distances. By adjusting the electric field distribution, increasing the current distribution inside the molten salt, weakening the surface current of the molten salt, and then weakening the chemical reaction at the three-phase interface, the service life of the anode and the efficiency of the electrolysis current can be improved.

Description

Technical Field

[0001] The invention belongs to the field of rare earth molten salt electrolysis, and in particular relates to a method for preparing rare earths by gradual pole distance molten salt electrolysis. Background Art

[0002] In recent years, with the widespread application of rare earths, the demand for rare earths has increased year by year, so the output of rare earths needs to increase gradually. However, the production process of rare earth metals consumes a lot of energy. Rare earth metals are mainly produced by molten salt electrolysis, using an open molten salt electrolytic cell, inserting the cathode in the middle of the electrolytic cell, and inserting the anode around it. The current efficiency is generally between 60% and 75%. In addition, in the traditional rare earth electrolysis method, the cathode and anode are electrolyzed at an equal distance, that is, the pole distance is equal; this causes the anode on the surface of the molten salt to be consumed faster, resulting in a higher residual pole rate.

[0003] In the existing method of preparing rare earths by molten salt electrolysis, an equal-pole-distance top-inserted rare earth molten salt electrolytic cell is used, and the distance between the cathode and cathode is equal, such as the rare earth electrolytic cell invented by patents CN101845641B and CN204174293U, in which the distance between the cathode and cathode is uniform and equal; patent CN105088284B invented an electrolytic cell with adjustable pole distance, but the pole distance is equal; there are also some that use a pole distance that is thick on the top and thin on the bottom, such as patents CN202626314U, CN103397350A, and CN209162215U, which invented a structure in which the upper part of the anode (the anode at the three-phase interface) is thick and the lower part is thin according to the actual consumption state of the anode, that is, the pole distance is small at the molten salt liquid surface and the pole distance is large inside the molten salt. Although this anode structure can increase the service life of the anode, it will further reduce the current efficiency and require additional adjustment and preparation of the anode structure. Summary of the invention

[0004] In view of the above shortcomings, the present invention provides a method for preparing rare earths by molten salt electrolysis with a gradient pole distance. A rare earth molten salt electrolysis method with a gradient pole distance is formed by obliquely inserting the anode into the electrolytic cell, in which the pole distance between the anode and the cathode gradually decreases from the molten salt liquid surface to the inside of the molten salt. The method can adjust the electric field distribution, increase the current distribution inside the molten salt, weaken the surface current of the molten salt, and then weaken the chemical reaction at the three-phase interface, which can improve the service life of the anode and the electrolysis current efficiency.

[0005] To achieve the purpose of the present invention, the technical solution adopted by the present invention is as follows:

[0006] The invention discloses a method for preparing rare earth by molten salt electrolysis with a gradient pole distance. In an upper plug-in rare earth molten salt electrolytic cell, an anode is obliquely inserted into the inner edge of a cell shell of the rare earth molten salt electrolytic cell, and a cathode is vertically inserted into the center of the rare earth molten salt electrolytic cell. The rare earth molten salt electrolytic cell is filled with electrolyte molten salt.

[0007] Among them, the pole distances between the cathode and the anode are not equal, and the pole distance gradually decreases from the molten salt liquid surface to the inside of the molten salt, and the pole distance between the two poles on the molten salt liquid surface is greater than the pole distance between the two poles inside the molten salt.

[0008] The electrolyte molten salt is a molten salt formed by heating fluoride and / or chloride, the fluoride mainly includes rare earth fluoride and lithium fluoride, and the chloride mainly includes rare earth chloride, alkali metal chloride and alkaline earth metal chloride. When the electrolyte molten salt is entirely fluoride, the mass percentage of rare earth fluoride in the electrolyte molten salt is ≥50%, and when the electrolyte molten salt is entirely chloride, the mass percentage of rare earth chloride in the electrolyte molten salt is 20%-60%.

[0009] The angle between the anode inclination angle and the vertical direction is 0° to 45°, excluding 0°, wherein 0° is vertical insertion;

[0010] The pole distance is between 5cm and 80cm;

[0011] The current efficiency of the rare earth molten salt electrolytic cell is greater than 80%, the anode utilization rate is increased by more than 10%, and the service life of the anode is increased by 10%.

[0012] Compared with the existing technology, the method for preparing rare earth by molten salt electrolysis with a gradient pole distance of the present invention has the following beneficial effects:

[0013] (1) It can significantly improve the current efficiency, which is between 80% and 95%, and the average current efficiency is greater than 80%, thereby reducing the energy consumption per unit mass of the product;

[0014] (2) It can improve the service life of the anode and reduce the residual pole rate. The tilted insertion of the anode reduces the degree of reaction at the three-phase interface and reduces the consumption at the interface, thereby improving the overall service life of the anode. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a front view of the top-insertion rare earth molten salt electrolytic cell used in an embodiment of the present invention;

[0016] 1—anode; 2—graphite crucible; 3—rare earth molten salt electrolytic cell; 4—electrolyte molten salt; 5—crucible for rare earth metals; 6—cathode. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below in conjunction with embodiments.

[0018] In the following embodiments, the anode used is an upper plug-in anode, and the cathode used is an upper plug-in cathode.

[0019] Example 1

[0020] A method for preparing rare earths by molten salt electrolysis with a gradient pole distance, wherein a graphite crucible 2 is arranged on the inner wall of the tank shell of an upper plug-in rare earth molten salt electrolytic cell, an anode 1 is obliquely inserted into the inner edge of the tank shell of a rare earth molten salt electrolytic cell 3, wherein the angle formed between the anode 1 and the tank shell of the rare earth molten salt electrolytic cell 3 is 3°, and the inclination direction satisfies that the distance between the anode and the cathode inside the molten salt is less than the distance between the anode and the cathode at the molten salt liquid surface, a cathode 6 is vertically inserted into the center of the rare earth molten salt electrolytic cell 3, and an electrolyte molten salt is contained in the rare earth molten salt electrolytic cell 3. In this embodiment, the electrolyte molten salt used is a mixture of cerium fluoride, lithium fluoride, and sodium chloride, wherein the mass percentage of cerium fluoride in the electrolyte molten salt is 50%, and a crucible 5 containing rare earth metals is placed directly below the cathode 6; its structural schematic diagram is shown in Figure 1 .

[0021] Electrolysis is performed with an electrolysis voltage of 9-10V, an electrolysis current of 6000A, and an electrode distance of 5-20cm, that is, an electrode distance of 20cm on the surface of the molten salt and an electrode distance of 5cm at the end of the electrode inside the molten salt, to obtain rare earth metals. The current efficiency of the rare earth molten salt electrolysis cell is 80%.

[0022] Example 2

[0023] A method for preparing rare earths by molten salt electrolysis with a gradient pole distance, wherein a graphite crucible 2 is arranged on the inner wall of a cell shell of an upper plug-in rare earth molten salt electrolytic cell, an anode 1 is obliquely inserted into the inner edge of the cell shell of a rare earth molten salt electrolytic cell 3, wherein the angle formed between the anode 1 and the cell shell of the rare earth molten salt electrolytic cell 3 is 15°, and the inclination direction satisfies that the distance between the anode and the cathode inside the molten salt is less than the distance between the anode and the cathode on the surface of the molten salt, a cathode 6 is vertically inserted into the center of the rare earth molten salt electrolytic cell 3, and an electrolyte molten salt is contained in the rare earth molten salt electrolytic cell 3. In this embodiment, the electrolyte molten salt used is a mixture of neodymium chloride, sodium chloride, and magnesium chloride, wherein the mass percentage of neodymium chloride in the electrolyte molten salt is 40%, and a crucible 5 containing rare earth metals is placed directly below the cathode 6.

[0024] Electrolysis is performed with an electrolysis voltage of 9-10V, an electrolysis current of 10000A, and an electrode distance of 20-30cm, that is, an electrode distance of 30cm on the surface of the molten salt and an electrode distance of 20cm at the end of the electrode inside the molten salt, to obtain rare earth metals. The current efficiency of the rare earth molten salt electrolysis cell is 85%.

[0025] Example 3

[0026] A method for preparing rare earths by molten salt electrolysis with a gradient pole distance, wherein a graphite crucible 2 is arranged on the inner wall of a cell shell of an upper plug-in rare earth molten salt electrolytic cell, an anode 1 is obliquely inserted into the inner edge of the cell shell of a rare earth molten salt electrolytic cell 3, wherein the angle formed between the anode 1 and the cell shell of the rare earth molten salt electrolytic cell 3 is 30°, and the inclination direction satisfies that the distance between the anode and the cathode inside the molten salt is less than the distance between the anode and the cathode on the surface of the molten salt, a cathode 6 is vertically inserted into the center of the rare earth molten salt electrolytic cell 3, and an electrolyte molten salt is contained in the rare earth molten salt electrolytic cell 3. In this embodiment, the electrolyte molten salt used is a mixture of neodymium chloride, sodium chloride, and lithium fluoride, wherein the mass percentage of neodymium chloride in the electrolyte molten salt is 50%, and a crucible 5 containing rare earth metals is placed directly below the cathode 6.

[0027] Electrolysis is performed with an electrolysis voltage of 9-10V, an electrolysis current of 15000A, and an electrode distance of 25-40cm, that is, an electrode distance of 40cm on the surface of the molten salt and an electrode distance of 25cm at the end of the electrode inside the molten salt, to obtain rare earth metals. The current efficiency of the rare earth molten salt electrolysis cell is 90%.

[0028] Example 4

[0029] A method for preparing rare earths by molten salt electrolysis with a gradient pole distance, wherein a graphite crucible 2 is arranged on the inner wall of a cell shell of an upper plug-in rare earth molten salt electrolytic cell, an anode 1 is obliquely inserted into the inner edge of the cell shell of a rare earth molten salt electrolytic cell 3, wherein the angle formed between the anode 1 and the cell shell of the rare earth molten salt electrolytic cell 3 is 45°, and the inclination direction satisfies that the distance between the anode and the cathode inside the molten salt is less than the distance between the anode and the cathode on the surface of the molten salt, a cathode 6 is vertically inserted into the center of the rare earth molten salt electrolytic cell 3, and an electrolyte molten salt is contained in the rare earth molten salt electrolytic cell 3. In this embodiment, the electrolyte molten salt used is a mixture of neodymium fluoride and lithium fluoride, wherein the mass percentage of neodymium fluoride in the electrolyte molten salt is 60%, and a crucible 5 containing rare earth metals is placed directly below the cathode 6.

[0030] Electrolysis is performed with an electrolysis voltage of 9-10V, an electrolysis current of more than 20,000A, and an electrode distance of 30-80cm, that is, an electrode distance of 80cm on the surface of the molten salt and an electrode distance of 30cm at the end of the electrode inside the molten salt, to obtain rare earth metals. The current efficiency of the rare earth molten salt electrolysis cell is 95%.

[0031] Example 5

[0032] A method for preparing rare earths by molten salt electrolysis with a gradient pole distance, wherein a graphite crucible 2 is arranged on the inner wall of a cell shell of an upper plug-in rare earth molten salt electrolytic cell, an anode 1 is obliquely inserted into the inner edge of the cell shell of a rare earth molten salt electrolytic cell 3, wherein the angle formed between the anode 1 and the cell shell of the rare earth molten salt electrolytic cell 3 is 7°, and the inclination direction satisfies that the distance between the anode and the cathode inside the molten salt is less than the distance between the anode and the cathode on the surface of the molten salt, a cathode 6 is vertically inserted into the center of the rare earth molten salt electrolytic cell 3, and an electrolyte molten salt is contained in the rare earth molten salt electrolytic cell 3. In this embodiment, the electrolyte molten salt used is a mixture of cerium fluoride and lithium fluoride, wherein the mass percentage of cerium fluoride in the electrolyte molten salt is 70%, and a crucible 5 containing rare earth metals is placed directly below the cathode 6.

[0033] Electrolysis is performed with an electrolysis voltage of 9-10V, an electrolysis current of more than 10000A, and an electrode distance of 10-15cm, that is, an electrode distance of 15cm on the surface of the molten salt and an electrode distance of 10cm at the end of the electrode inside the molten salt, to obtain rare earth metals. The current efficiency of the rare earth molten salt electrolysis cell is 91%.

[0034] Comparative Example 1

[0035] A method for preparing rare earths by molten salt electrolysis is the same as that of Example 1, except that: in the rare earth molten salt electrolytic cell used, the pole distances of the cathode and the anode are equidistant, that is, the angle formed between the anode 1 and the cell shell of the rare earth molten salt electrolytic cell 3 is 0°. Compared with Example 1, the method of the present invention reduces the anode utilization rate by 10%, reduces the service life of the anode by 10%, and the current density is less than 80%, generally 70-75%.

[0036] Comparative Example 2

[0037] A method for preparing rare earths by molten salt electrolysis is the same as that of Example 1, except that: in the rare earth molten salt electrolytic cell used, after the anode is tilted and inserted, the distance between the anode and the cathode is such that the distance between the two electrodes on the molten salt surface is less than the distance between the two electrodes inside the molten salt, then the current efficiency is reduced, generally 70%-75%; the anode utilization rate is reduced, and the service life is also reduced.

[0038] Comparative Example 3

[0039] A method for preparing rare earth by molten salt electrolysis is the same as Example 1, except that: the anode used is thick at the top and thin at the bottom. Although the service life of the anode can be improved to a certain extent, the current efficiency will be reduced. The current efficiency is generally 70%-75%.

[0040] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application. The above are only preferred implementations of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present application. For example, the anode is placed on the upper part of the molten salt and the cathode is placed on the lower part. These improvements and modifications should also be regarded as the protection scope of the present application.

Claims

1. A method for preparing rare earth by molten salt electrolysis with a gradient pole distance, characterized in that: In the top-insertion rare earth molten salt electrolytic cell, the anode is obliquely inserted into the inner edge of the cell shell of the rare earth molten salt electrolytic cell, and the cathode is vertically inserted into the center of the rare earth molten salt electrolytic cell, and the rare earth molten salt electrolytic cell is filled with electrolyte molten salt; The distances between the cathode and the anode are not equal; The inter-electrode distance gradually decreases from the molten salt surface to the inside of the molten salt, and the inter-electrode distance between the two electrodes on the molten salt surface is greater than the inter-electrode distance between the two electrodes inside the molten salt. The pole distance is between 5cm and 80cm; The current efficiency of the rare earth molten salt electrolytic cell is greater than 80%, the anode utilization rate is increased by more than 10%, and the service life of the anode is increased by 10%; The angle between the anode inclination angle and the vertical direction is 0° to 45°, excluding 0°, wherein 0° is vertical insertion.

2. The method for preparing rare earth by molten salt electrolysis with a gradient pole pitch according to claim 1, characterized in that: The electrolyte molten salt is a molten salt formed by heating fluoride and / or chloride.

3. The method for preparing rare earth by molten salt electrolysis with a gradient pole pitch according to claim 2, characterized in that: The fluorides mainly include rare earth fluorides and lithium fluoride, wherein when the electrolyte molten salt is entirely fluorides, the mass percentage of the rare earth fluorides in the electrolyte molten salt is ≥50%.

4. The method for preparing rare earth by molten salt electrolysis with a gradient pole pitch according to claim 2, characterized in that: The chlorides mainly include rare earth chlorides, alkali metal chlorides and alkaline earth metal chlorides. When the electrolyte molten salt is entirely chlorides, the mass percentage of rare earth chlorides in the electrolyte molten salt is 20%-60%.

Images