A method for separating thorium from a thorium, lanthanum mixture

Abstract

The present application relates to the nuclear technology field, specifically to a method for separating thorium from a thorium and lanthanum mixture. The method comprises the following steps: in a three-electrode system, pulse constant current controlled potential electrolysis is performed on a molten salt system containing mixed ions of thorium and lanthanum series elements, and the deposition rate difference of thorium and lanthanum series element ions during pulse constant current electrolysis and the electrolytic reaction limitation of the control potential on the lanthanum series element ions are utilized to achieve efficient separation of thorium from the thorium and lanthanum mixture. The molten salt system containing mixed ions of thorium and lanthanum series elements is obtained by adding the thorium and lanthanum mixture into a chloride molten salt, mixing uniformly, and passing in chlorine gas mixture to chlorinate the mixture and dissolve it into the chloride molten salt. The method has the advantages of simple process, strong radiation resistance, no additional radioactive waste, and low cost, and is suitable for industrial application of molten salt reactor spent fuel reprocessing.

Description

A method for separating thorium from a mixture of thorium and lanthanum Technical Field

[0001] This invention relates to the field of nuclear technology, and more specifically to a method for separating thorium from a mixture of thorium and lanthanum. Background Technology

[0002] Nuclear power, as a highly efficient and clean energy source that can be utilized on a large scale, has been gradually adopted and is replacing traditional fossil fuels due to its excellent economic benefits and extremely high energy density. However, with the widespread application of nuclear power technology, the low utilization rate of nuclear fuel has led to the accumulation of large amounts of spent fuel, posing serious safety risks to the environment. The sustainable development of nuclear power is constrained by two major challenges: the full utilization of fuel resources and the minimization of nuclear waste.

[0003] Thorium-based molten salt reactors, as fourth-generation advanced nuclear reactors, achieve stable operation through a thorium-uranium fuel cycle. They possess advantages such as high safety and conversion efficiency, low nuclear waste, and low toxicity of the unloaded radioactive products, making them considered the most competitive type of advanced reactor for sustainable development. Despite their promising application prospects, the related fuel processing technologies are not yet fully mature. The separation of thorium fuel from lanthanide neutron poisons is a key obstacle to the further development of thorium-based molten salt reactors.

[0004] Because lanthanides and actinides such as thorium have similar physicochemical properties, they have similar redox potentials in the dry post-processing of molten salt electrolysis. Therefore, it is impossible to effectively separate thorium and lanthanides in the mixture by means of the difference in deposition overpotential. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for separating thorium from a mixture of thorium and lanthanides. Using a molten salt system containing a mixture of thorium and lanthanide ions as a substrate, pulsed constant-current controlled-potential electrolysis is performed. By utilizing the difference in deposition rates of thorium and lanthanide ions and limiting the electrolytic reaction of lanthanide ions by setting a control potential, thorium is separated from the thorium-lanthanum mixture. This method is simple, highly radiation-resistant, does not generate additional radioactive waste, and is low-cost, making it suitable for industrial applications in the reprocessing of spent fuel from molten salt reactors.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The purpose of this invention is to provide a method for separating thorium from a mixture of thorium and lanthanum, comprising the following steps:

[0008] Using a molten salt system containing a mixture of thorium and lanthanide ions as a substrate, pulsed constant current controlled potential electrolysis was performed. By controlling the difference in deposition rates of thorium and lanthanide ions, the electrolytic reaction of lanthanide ions was limited by the controlled potential, which ranged from 0.56V to 0.78V, thus achieving the separation of thorium from the thorium-lanthanum mixture.

[0009] In a preferred embodiment of the present invention, the pulsed constant current controlled potential electrolysis is performed in multiple cycles with equilibrium-electrolysis-relaxation as one pulse unit until thorium is separated from the thorium-lanthanum mixture. The equilibrium-electrolysis-relaxation includes an equilibrium step, an electrolysis step, and a relaxation step. The equilibrium step involves balancing the system with zero current. The electrolysis step involves applying current to perform constant current electrolysis. The relaxation step involves setting the electrolysis current to zero and bringing the system back to equilibrium. In the electrolysis step, a control potential is set. When the potential is lower than the set potential during the pulse process, the pulse is directly cut off, and then the next pulse process begins.

[0010] In a preferred embodiment of the present invention, the balancing step lasts for 10s to 30s, the electrolysis step lasts for 100s to 300s, the relaxation step lasts for 50s to 250s, the current applied in the electrolysis step is -1mA to -10mA, and the pulsed constant current controlled potential electrolysis lasts for 1h to 3h.

[0011] In a preferred embodiment of the present invention, a three-electrode system is used in the pulsed constant current controlled potential electrolysis process, with a bismuth-lithium electrode as the reference electrode, a graphite rod as the anode, and a Ga, Zn, In, or Pb metal melt as the liquid cathode.

[0012] In a preferred embodiment of the present invention, the method for preparing a molten salt system containing a mixture of thorium and lanthanide elements includes the following steps: mixing a mixture of thorium and lanthanide with a chloride molten salt, and chlorinating the mixture of thorium and lanthanide under an inert gas atmosphere containing chlorine to obtain a molten salt system containing a mixture of thorium and lanthanide elements.

[0013] In a preferred embodiment of the present invention, the thorium-lanthanum mixture is a mixture of thorium dioxide and lanthanide oxides; the mixture of thorium dioxide and lanthanide oxides consists of the following components in the following mass ratio: 23.5%~53.5% thorium dioxide and 46.5%~76.5% lanthanide oxides, totaling 100%.

[0014] In a preferred embodiment of the present invention, the lanthanide oxides are La₂O₃, CeO₂, and Pr₆O. 11 At least one of Nd2O3, Gd2O3, and Dy2O3.

[0015] In a preferred embodiment of the present invention, the chloride molten salt is a LiCl-KCl mixture system molten salt, a LiCl-NaCl mixture system molten salt, or a KCl-NaCl mixture system molten salt.

[0016] In a preferred embodiment of the present invention, the temperature of the chloride molten salt is 400°C to 800°C.

[0017] In a preferred embodiment of the present invention, the volume content of chlorine in the inert gas is 55% to 75%.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. This invention provides a method for separating thorium from a mixture of thorium and lanthanides. Using a molten salt system containing a mixture of thorium and lanthanide ions as the substrate, pulsed constant-current controlled-potential electrolysis is performed. A dual strategy enhances the separation effect: firstly, sufficient diffusion time is provided for thorium atoms to restore the system equilibrium at the liquid electrode interface, reducing the reduction of lanthanide ions and widening the difference in deposition rates between the two. Secondly, the electrode potential is further limited by potential control, reducing the possibility of lanthanide ion reduction. Based on this, this invention controls the electrolytic reaction of lanthanide ions by controlling the potential based on the difference in deposition rates between thorium and lanthanide ions. The controlled potential is 0.56V~0.78V, achieving the separation of thorium from the thorium-lanthanide mixture. This overcomes the limitation of existing molten salt electrolysis methods that cannot achieve efficient separation of thorium and lanthanides from mixtures through deposition overpotential differences. Separation tests show that the separation factor of thorium and lanthanides using the above method can reach over 800, demonstrating excellent separation performance.

[0020] 2. The method of the present invention has a simple process flow, is easy to operate, has low equipment requirements, is green and environmentally friendly and radiation resistant, does not generate additional radioactive waste and is inexpensive, and is easy to apply to the industrialization of spent fuel reprocessing.

[0021] 3. This invention obtains thorium metal and its alloys through electrolytic control, eliminating the cumbersome processing and preparation process for subsequent thorium reuse and improving the economic efficiency of thorium recycling. Attached Figure Description

[0022] Figure 1 is a schematic diagram of a single pulse process of pulsed constant current controlled potential electrolysis in Embodiment 1 of the present invention.

[0023] Figure 2 is a potential change curve of pulsed constant current controlled potential electrolysis in Embodiment 1 of the present invention.

[0024] Figure 3 shows the separation effect of thorium and lanthanides after pulsed constant current controlled potential electrolysis in Example 1 of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0027] Although thorium-based molten salt reactors have very promising applications, the related fuel processing technologies are not yet fully mature. Among these, the separation of thorium nuclear fuel from lanthanide neutron poisons is a key obstacle to the further development of thorium-based molten salt reactors. Lanthanides and actinides such as thorium have similar physicochemical properties, and they exhibit similar redox potentials in molten salt electrolysis dry reprocessing. Existing molten salt electrolysis methods cannot effectively separate thorium and lanthanides from the mixture by utilizing differences in deposition overpotential.

[0028] Based on this, the present invention provides a method for separating thorium from a mixture of thorium and lanthanum, comprising the following steps:

[0029] Using a molten salt system containing a mixture of thorium and lanthanide ions as a substrate, pulsed constant current controlled potential electrolysis was performed. By controlling the difference in deposition rates of thorium and lanthanide ions, the electrolytic reaction of lanthanide ions was limited by the controlled potential, which ranged from 0.56V to 0.78V, thus achieving the separation of thorium from the thorium-lanthanum mixture.

[0030] It should be noted that during electrolysis, according to the electrolysis sequence of thorium and lanthanides, thorium ions preferentially undergo electrode reactions. However, influenced by the reaction rate and the diffusion rate of reduced particles in the liquid electrode, reduced thorium atoms accumulate on the electrode surface, causing the liquid electrode interface to transform into a solid electrode, leading to further reduction of lanthanides. Furthermore, as the electrolysis proceeds, reduced thorium atoms continuously dissolve into the liquid electrode, gradually shifting the electrode potential negative, further intensifying the electrolytic reduction of lanthanides. Pulsed constant-current controlled potential electrolysis provides sufficient diffusion time for thorium atoms, restoring the system equilibrium at the liquid electrode interface, reducing the reduction of lanthanides, and widening the difference in deposition rates between thorium and lanthanides. In addition, the potential control setting further limits the electrode potential, reducing the possibility of lanthanides reduction. Pulsed constant-current controlled potential electrolysis achieves efficient separation of thorium in thorium-lanthanum mixtures through multiple strategies, including widening the deposition rate difference and limiting the electrolysis reaction.

[0031] The pulsed constant current controlled potential electrolysis uses equilibrium-electrolysis-relaxation as a pulse unit for multiple cycles until thorium is separated from the thorium-lanthanum mixture. The equilibrium-electrolysis-relaxation includes an equilibrium step, an electrolysis step, and a relaxation step. The equilibrium step involves balancing the system with zero current. The electrolysis step involves applying current for constant current electrolysis. The relaxation step involves setting the electrolysis current to zero and bringing the system back to equilibrium. In the electrolysis step, a control potential is set. If the potential is lower than the set potential during the pulse process, the pulse is directly cut off, and then the next pulse process begins.

[0032] The balancing step lasts for 10s to 30s, the electrolysis step lasts for 100s to 300s, the relaxation step lasts for 50s to 250s, the current applied during the electrolysis step is -1mA to -10mA, and the pulsed constant current controlled potential electrolysis lasts for 1h to 3h.

[0033] In the pulsed constant current controlled potential electrolysis process, a three-electrode system is employed: a bismuth-lithium electrode as the reference electrode, a graphite rod as the anode, and a Ga, Zn, In, or Pb molten metal as the liquid cathode. The choice of a liquid electrode in this invention significantly reduces the electrolysis potential. The three-electrode system is used to accurately obtain the actual reaction potential of the working electrode, avoiding potential deviations caused by electrode polarization in a two-electrode system, thereby enabling subsequent control of the set potential and ensuring efficient separation of thorium and lanthanides.

[0034] The method for preparing the molten salt system containing a mixture of thorium and lanthanide elements includes the following steps: after thoroughly stirring the thorium and lanthanide mixture with chloride molten salt, an inert gas containing chlorine is introduced into the molten salt to chlorinate the mixture, thereby obtaining a molten salt system containing a mixture of thorium and lanthanide elements.

[0035] The thorium-lanthanum mixture is a mixture of thorium dioxide and lanthanide oxides; the mixture of thorium dioxide and lanthanide oxides consists of the following components in the following mass ratio: 23.5%~53.5% thorium dioxide and 46.5%~76.5% lanthanide oxides, totaling 100%.

[0036] The lanthanide oxides mentioned are La2O3, CeO2, and Pr6O. 11 At least one of Nd2O3, Gd2O3, and Dy2O3.

[0037] The chloride molten salt is a LiCl-KCl mixture system molten salt, a LiCl-NaCl mixture system molten salt, or a KCl-NaCl mixture system molten salt.

[0038] During the mixing process, the temperature of the chloride molten salt is 400℃~800℃.

[0039] In the inert gas, the volume content of chlorine is 55% to 75%. Chlorine causes the mixed oxides to chlorinate and dissolve into the chloride molten salt. The 55% to 75% volume content of chlorine is used because at low concentrations, the chlorination effect of the chlorine mixture is not significant; at high concentrations, a large amount of unreacted chlorine will escape. Furthermore, since nitrogen reacts with chlorine at high temperatures, the inert gas can be any inert gas other than nitrogen. In a preferred embodiment of the invention, argon is used as the inert gas. In a specific embodiment, the chlorine-containing inert gas consists of the following components in the following volume ratio: 55% to 75% chlorine and 25% to 45% argon.

[0040] The method provided by this invention overcomes the limitation of existing molten salt electrolysis methods, which cannot effectively separate thorium and lanthanides from a mixture through deposition overpotential differences. Separation tests show that by controlling the potential electrolysis with pulsed constant current, the separation factor of thorium and lanthanides can reach over 800, demonstrating excellent separation performance. This invention features a simple process flow, convenient operation, low equipment requirements, is environmentally friendly and radiation-resistant, produces no additional radioactive waste, and is low-cost, making it suitable for industrial application in spent fuel reprocessing. This invention obtains thorium metal and its alloys through controlled electrolysis, eliminating cumbersome processing steps for subsequent thorium reuse and improving the economics of thorium recycling.

[0041] The following specific examples will provide further explanation.

[0042] In this invention, the chemical formula of thorium dioxide is ThO2.

[0043] Example 1

[0044] A method for separating thorium from a mixture of thorium and lanthanum includes the following steps:

[0045] S1. A mixture of thorium and lanthanum (consisting of 23.5% ThO2 and 76.5% Nd2O3) is added to a LiCl-KCl chloride molten salt at 450℃. After thorough stirring, a mixture of chlorine and argon gas with a volume ratio of 11:9 is introduced into the molten salt, causing the mixture to chlorinate and dissolve into the molten salt, thus obtaining a molten salt system containing a mixture of thorium and lanthanide ions.

[0046] S2. A three-electrode system is used, with a bismuth-lithium electrode as the reference electrode, a graphite rod as the anode, and Ga metal melt as the liquid cathode. In the molten salt system obtained in S1, a pulsed constant current controlled potential electrolysis is performed with an equilibrium step time of 10s, an electrolysis step time of 100s, a relaxation step time of 50s, an electrolysis current of -1mA, a control potential of 0.56V, and an electrolysis time of 1h, to achieve the separation of thorium from the thorium-lanthanum mixture.

[0047] Example 2

[0048] A method for separating thorium from a mixture of thorium and lanthanum includes the following steps:

[0049] S1. A mixture of thorium and lanthanum (consisting of 25% ThO2 and 75% Nd2O3) is added to a LiCl-KCl chloride molten salt at 500℃. After thorough stirring, a mixture of chlorine and argon gas with a volume ratio of 3:2 is introduced into the molten salt to chlorinate the mixture and dissolve it into the molten salt, thus obtaining a molten salt system containing a mixture of thorium and lanthanide ions.

[0050] S2. A three-electrode system is used, with a bismuth-lithium electrode as the reference electrode, a graphite rod as the anode, and Ga metal melt as the liquid cathode. Pulsed constant current controlled potential electrolysis is performed in the molten salt system obtained in S1. The equilibrium step time is 20s, the electrolysis step time is 150s, the relaxation step time is 100s, the electrolysis current is -2mA, the control potential is 0.6V, and the electrolysis time is 1.5h to achieve the separation of thorium in the thorium-lanthanum mixture.

[0051] Example 3

[0052] A method for separating thorium from a mixture of thorium and lanthanum includes the following steps:

[0053] S1, a mixture of thorium and lanthanum (composed of 40% ThO2, 15.36% La2O3, 20.1% CeO2, and 9.55% Pr6O3). 11 (Composed of 14.99% Nd2O3) is added to a LiCl-NaCl chloride molten salt at 600℃. After thorough stirring, a mixture of chlorine and argon gas with a volume ratio of 13:7 is introduced into the molten salt, causing the mixture to chlorinate and dissolve into the molten salt, resulting in a molten salt system containing a mixture of thorium and lanthanide ions.

[0054] S2. A three-electrode system is used, with a bismuth-lithium electrode as the reference electrode, a graphite rod as the anode, and Pb metal melt as the liquid cathode. Pulsed constant current controlled potential electrolysis is performed in the molten salt system obtained in S1. The equilibrium step time is 15s, the electrolysis step time is 100s, the relaxation step time is 100s, the electrolysis current is -5mA, the control potential is 0.67V, and the electrolysis time is 2h to achieve the separation of thorium in the thorium-lanthanum mixture.

[0055] Example 4

[0056] A method for separating thorium from a mixture of thorium and lanthanum includes the following steps:

[0057] S1, a mixture of thorium and lanthanum (composed of 51.2% ThO2, 8.43% La2O3, 13.17% CeO2, and 20.3% Pr6O3). 11(Composed of 6.9% Nd2O3) is added to a NaCl-KCl chloride molten salt at 750℃. After thorough stirring, a mixture of chlorine and argon in a volume ratio of 3:1 is introduced into the molten salt, causing the mixture to chlorinate and dissolve into the molten salt, resulting in a molten salt system containing a mixture of thorium and lanthanide ions.

[0058] S2. A three-electrode system is used, with a bismuth-lithium electrode as the reference electrode, a graphite rod as the anode, and In metal melt as the liquid cathode. Pulsed constant current controlled potential electrolysis is performed in the molten salt system obtained in S1. The equilibrium step time is 30s, the electrolysis step time is 200s, the relaxation step time is 250s, the electrolysis current is -3mA, the control potential is 0.73V, and the electrolysis time is 3h to achieve the separation of thorium in the thorium-lanthanum mixture.

[0059] Comparative Example 1

[0060] A method for separating thorium from a mixture of thorium and lanthanum includes the following steps:

[0061] S1. A mixture of thorium and lanthanum (consisting of 23.5% ThO2 and 76.5% Nd2O3) is added to a LiCl-KCl chloride molten salt at 500℃. After thorough stirring, a mixture of chlorine and argon gas with a volume ratio of 13:7 is introduced into the molten salt, causing the mixture to chlorinate and dissolve into the molten salt, thus obtaining a molten salt system containing a mixture of thorium and lanthanide ions.

[0062] S2. Using a three-electrode system with a bismuth-lithium electrode as the reference electrode, a graphite rod as the anode, and Ga metal melt as the liquid cathode, constant current electrolysis with a current of -1mA is performed in the molten salt system obtained in S1 for 1 hour to achieve the separation of thorium from the thorium-lanthanum mixture.

[0063] Comparative Example 2

[0064] A method for separating thorium from a mixture of thorium and lanthanum includes the following steps:

[0065] S1. A mixture of thorium and lanthanum (consisting of 23.5% ThO2 and 76.5% Nd2O3) is added to a LiCl-KCl chloride molten salt at 500℃. After thorough stirring, a mixture of chlorine and argon gas with a volume ratio of 13:7 is introduced into the molten salt, causing the mixture to chlorinate and dissolve into the molten salt, thus obtaining a molten salt system containing a mixture of thorium and lanthanide ions.

[0066] S2. Using a three-electrode system with a bismuth-lithium electrode as the reference electrode, a graphite rod as the anode, and Ga metal melt as the liquid cathode, constant potential electrolysis with a voltage of 0.6V is performed in the molten salt system obtained in S1 for 1 hour to achieve the separation of thorium from the thorium-lanthanum mixture.

[0067] The separation efficiency of Examples 1-4 and Comparative Examples 1-2 was tested. The separation factor for thorium and lanthanides was calculated using the following formula:

[0068] .

[0069] Where, is the separation factor, D Th and D Ln X represents the distribution coefficients of thorium and lanthanides in molten salt and M-metal melt. Th,M X Ln,M X Th,melt X Ln,melt This indicates the molar ratio of thorium and lanthanides in both molten salt and molten metal media.

[0070] Calculations using the above formulas show that the thorium / neodymium separation factor in Example 1, Example 2, Example 3, and Example 4 all exceeded 800. In contrast, the separation factor for thorium and lanthanides in Comparative Example 1 (constant current electrolysis) was only 73, and in Comparative Example 2 (constant voltage electrolysis), the separation factor was only 132. This indicates that the above examples (pulsed constant current controlled potential electrolysis) all achieved efficient separation of thorium from the thorium-lanthanide mixture.

[0071] Figure 1 is a schematic diagram of a single pulse process of pulsed constant current controlled potential electrolysis in Embodiment 1 of the present invention. As shown in Figure 1, a single pulse goes through three stages: equilibrium, electrolysis, and relaxation. The relaxation stage allows the electrolysis system to return to equilibrium, reducing particle enrichment on the surface of the liquid electrode and thus increasing the deposition rate difference.

[0072] Figure 2 is a potential change curve of pulsed constant current controlled potential electrolysis in Embodiment 1 of the present invention. The small graph in the upper right corner of Figure 2 is a potential change curve for electrolysis time from 0s to 700s. As can be seen from Figure 2, the working electrode potential decreases slowly during electrolysis under the control of the electrode potential; by limiting the electrode potential, the increase in lanthanide ion reduction caused by sudden changes in electrode potential during each pulse is reduced.

[0073] Figure 3 shows the separation effect of thorium and lanthanides after pulsed constant current controlled potential electrolysis in Example 1 of the present invention. As can be seen from Figure 3, the separation factor of thorium / neodymium in Example 1 is above 800, and the separation effect is significant.

[0074] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended scope of protection is intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0075] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of protection of this invention and its equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for separating thorium from a mixture of thorium and lanthanum, characterized in that, The process includes the following steps: using a molten salt system containing a mixture of thorium and lanthanide ions as a substrate, pulsed constant current controlled potential electrolysis is performed. By controlling the difference in deposition rates of thorium and lanthanide ions, the electrolytic reaction of the lanthanide ions is limited by the controlled potential. The controlled potential is 0.56V~0.78V relative to the bismuth-lithium reference electrode, achieving the separation of thorium from the thorium-lanthanum mixture. The pulsed constant current controlled potential electrolysis is performed in multiple cycles, with equilibrium-electrolysis-relaxation as one pulse unit, until the separation of thorium from the thorium-lanthanum mixture is achieved. The equilibrium-electrolysis-relaxation step includes an equilibrium step, an electrolysis step, and a relaxation step. The process involves three steps: equilibration, electrolysis, and relaxation. The equilibrium step involves achieving zero-current system equilibrium; the electrolysis step involves applying current for constant-current electrolysis; and the relaxation step involves setting the electrolysis current to zero to bring the system back to equilibrium. In the electrolysis step, a control potential is set. If the potential during the pulse process is lower than the set potential, the pulse is immediately stopped, and the next pulse process begins. The equilibrium step lasts 10-30 seconds, the electrolysis step lasts 100-300 seconds, and the relaxation step lasts 50-250 seconds. The current applied during the electrolysis step is -1 mA to -10 mA, and the pulsed constant-current controlled-potential electrolysis lasts 1-3 hours.

2. The method for separating thorium from a mixture of thorium and lanthanum according to claim 1, characterized in that, In the pulsed constant current controlled potential electrolysis process, a three-electrode system is adopted, with a bismuth-lithium electrode as the reference electrode, a graphite rod as the anode, and a Ga, Zn, In, or Pb metal melt as the liquid cathode.

3. The method for separating thorium from a mixture of thorium and lanthanum according to claim 1, characterized in that, The preparation method of a molten salt system containing a mixture of thorium and lanthanide elements includes the following steps: mixing a mixture of thorium and lanthanide with a chloride molten salt, and chlorinating the mixture of thorium and lanthanide under an inert gas atmosphere containing chlorine to obtain a molten salt system containing a mixture of thorium and lanthanide elements.

4. The method for separating thorium from a mixture of thorium and lanthanum according to claim 3, characterized in that, The thorium-lanthanum mixture is a mixture of thorium dioxide and lanthanide oxides; the mixture of thorium dioxide and lanthanide oxides consists of the following components in the following mass ratio: 23.5%~53.5% thorium dioxide and 46.5%~76.5% lanthanide oxides, totaling 100%.

5. The method for separating thorium from a mixture of thorium and lanthanum according to claim 4, characterized in that, Lanthanide oxides include La₂O₃, CeO₂, and Pr₆O. 11 At least one of Nd2O3, Gd2O3, and Dy2O3.

6. The method for separating thorium from a mixture of thorium and lanthanum according to claim 3, characterized in that, Chloride molten salts are molten salts of LiCl-KCl mixture system, molten salts of LiCl-NaCl mixture system, or molten salts of KCl-NaCl mixture system.

7. The method for separating thorium from a mixture of thorium and lanthanum according to claim 3, characterized in that, When mixing, the temperature of the chloride molten salt is 400℃~800℃.

8. The method for separating thorium from a mixture of thorium and lanthanum according to claim 3, characterized in that, In inert gases, the volume content of chlorine is 55% to 75%.

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