CN113151865B - Method for extracting and separating rare earth and preparing multi-element rare earth alloy by molten salt pulse electrolysis of Pb-Bi alloy cathode - Google Patents

Method for extracting and separating rare earth and preparing multi-element rare earth alloy by molten salt pulse electrolysis of Pb-Bi alloy cathode Download PDF

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CN113151865B
CN113151865B CN202110205682.XA CN202110205682A CN113151865B CN 113151865 B CN113151865 B CN 113151865B CN 202110205682 A CN202110205682 A CN 202110205682A CN 113151865 B CN113151865 B CN 113151865B
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李著尧
唐丹丹
刘峙嵘
张雪莹
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East China Institute of Technology
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Abstract

A method for extracting and separating rare earth and preparing a multi-element rare earth alloy by molten salt pulse electrolysis of a Pb-Bi alloy cathode. The invention belongs to the technical field of nuclear fuel dry post-processing. The invention aims to solve the technical problems of low extraction efficiency and low separation efficiency of the existing method for extracting and separating actinides and rare earth elements. The method comprises the following steps: silver/silver chloride is used as a reference electrode, a spectral pure graphite rod is used as an anode, a liquid Pb-Bi alloy is used as a cathode, cyclic voltammetry is carried out in an electrochemical workstation, the reduction peak potential of rare earth ions on the Pb-Bi alloy cathode is obtained, the reduction potential of rare earth can be changed by changing the composition of the alloy, the electrochemical workstation or a pulse power supply is used for carrying out electrolytic extraction and separation on rare earth under different set pulse conditions, and the uniform segregation-free lead-bismuth-rare earth multi-element alloy is obtained. The method has the advantages of simple cathode preparation, high extraction and separation efficiency, high rare earth extraction rate up to 98.9 percent and high two rare earth separation factors up to 786.

Description

Method for extracting and separating rare earth and preparing multi-element rare earth alloy by molten salt pulse electrolysis of Pb-Bi alloy cathode
Technical Field
The invention belongs to the technical field of nuclear fuel dry post-treatment, and particularly relates to a method for extracting and separating rare earth and preparing a multi-element rare earth alloy by molten salt pulse electrolysis of a Pb-Bi alloy cathode.
Background
The living environment of human beings is becoming worse, and particularly, in recent years, the development of clean energy such as nuclear energy is rapidly progressing worldwide due to the fact that mountain fires are being continued all over the world. For China with increasingly severe environmental pollution, nuclear energy has irreplaceable attraction. According to the strategic action plan of energy development, china adheres to the sustainable development of nuclear power, and the nuclear energy cause enters a new rapid development period. Spent fuel reprocessing is an important industry which limits future nuclear power industries in China and is in urgent need of being promoted and developed. The spent fuel dry post-treatment has the advantages of radiation resistance, less radioactive waste, low critical risk and the like, and can meet the separation requirement of the spent fuel in the advanced nuclear fuel cycle. Among dry post-treatment technologies, the molten salt electrolysis technology is currently the most promising technology recognized by countries in the world to be compatible with fourth-generation reactor systems. The rare earth elements have higher thermal neutron capture cross sections and are very unfavorable for the proliferation and transmutation of fuel in the future closed cycle of nuclear fuel, so that the selection of proper cathode electrolysis for extracting the rare earth has important significance for the sustainable development of nuclear energy in China.
The liquid metal such as Pb, bi, zn and the like is used as the cathode, and the method has the advantages of wide experimental temperature range, low working temperature, simplified process flow and equipment, low steam pressure and the like. At present, the actinides and the rare earth elements are extracted and separated by adopting a single liquid cathode in the world, and the problems of low extraction efficiency and low separation efficiency exist all the time, so that the development of an economic molten salt electrolysis extraction process with a simple flow and a potential liquid cathode material is urgent for efficiently extracting and separating the actinides and the rare earth elements.
Disclosure of Invention
The invention aims to solve the technical problems of low extraction efficiency and low separation efficiency of the existing method for extracting and separating actinides and rare earth elements, and provides a method for extracting and separating rare earth and preparing a multi-element rare earth alloy by molten salt pulse electrolysis of a Pb-Bi alloy cathode.
The method for extracting and separating rare earth and preparing the multi-element rare earth alloy by molten salt pulse electrolysis of the Pb-Bi alloy cathode comprises the following steps:
step one, putting anhydrous LiCl and anhydrous KCl into an alumina crucible, uniformly mixing, performing drying pretreatment, then putting the alumina crucible into an electrolytic cell, introducing high-purity argon, and heating to 380-550 ℃ to obtain a molten salt of LiCl and KCl;
secondly, adding the cleaned elemental Pb and elemental Bi into a crucible, then putting the crucible filled with the elemental Pb and elemental Bi into the LiCl and KCl molten salt obtained in the first step for smelting, continuously stirring by using an aluminum oxide bar in the smelting process, and obtaining a Pb-Bi alloy after smelting;
thirdly, adding rare earth chloride into the molten salt of the LiCl and the KCl obtained in the first step, taking the Pb-Bi alloy obtained in the second step as a working electrode, taking the spectrally pure conductor graphite as an anode, taking a silver/silver chloride electrode as a reference electrode, inserting the anode and the reference electrode into the molten salt of the LiCl and the KCl obtained in the first step and connecting the anode and the reference electrode with an electrochemical workstation, inserting a W wire sleeved with an aluminum oxide protection tube into the Pb-Bi alloy obtained in the second step and connecting the Pb-Bi alloy and the electrochemical workstation as a lead to form a pulse electrolysis system;
performing cyclic voltammetry by using an electrochemical workstation to determine the reduction potential of the rare earth ions on the Pb-Bi alloy electrode;
and step five, on the basis of the reduction potential of the rare earth ions determined in the step four, applying pulse voltage between the working electrode and the anode by using an electrochemical workstation or a pulse power supply for pulse electrolysis, and washing and drying the electrolyzed product at low temperature to obtain the multi-element Pb-Bi-rare earth alloy.
Further limiting, in the step one, the mass ratio of the anhydrous LiCl to the anhydrous KCl is 46: (53 to 55).
Further, the specific process of the drying pretreatment in the step one is as follows: drying and dehydrating at 150 to 300 ℃ for 5 to 30 hours.
Further limiting, in the second step, the mass fraction of Pb in the Pb-Bi alloy is 55.2% -98.5%.
Further limiting, the smelting parameters in the step two are as follows: the temperature is 380 to 550 ℃, and the time is 1 to 3 hours.
Further limiting, in the third step, the rare earth chloride is lanthanum trichloride (LaCl) 3 ) Cerium trichloride (CeCl) 3 ) Praseodymium trichloride (PrCl) 3 ) Neodymium trichloride (NdCl) 3 ) Samarium trichloride (SmCl) 3 ) Europium trichloride (EuCl) 3 ) Gadolinium trichloride (GdCl) 3 ) Terbium trichloride (TbCl) 3 ) Dysprosium trichloride (DyCl) 3 ) Holmium trichloride (HoCl) 3 ) Erbium trichloride (ErCl) 3 ) Ytterbium trichloride (YbCl) 3 ) One or a mixture of three of them according to any ratio.
Further limiting, the mass ratio of the Pb-Bi alloy to the rare earth chloride in the third step is (5 to 50): 1.
further limiting, in the third step, the mass fraction of the rare earth chloride in the LiCl and KCl molten salt is 0.2% -10%.
Further limiting, the pulse electrolysis in the fifth step is divided into four stages, the first stage is enrichment: the pulse electrolytic potential is-1.2V to-1.7V, the time is 1s to 10s, and the second-stage electrolytic deposition: the pulse electrolytic potential is-1.2V to-1.6V, the time is 5s to 200s, and the third stage is dissolution: the pulse electrolytic potential is-1V-0.1V, the time is 1 s-20 s, and the fourth stage is stable: the pulse electrolysis potential is-1.60V-0V, and the time is 1 s-10 s.
Further limiting, the specific process of washing in the step five is as follows: washing 3~5 times by acetone, and then washing 3~5 times by absolute ethyl alcohol, wherein the parameters of low-temperature drying are as follows: the temperature is 200 to 300 ℃, and the time is 5 to 24 hours.
Compared with the prior art, the invention has the advantages that:
1) The chloride molten salt system and the liquid Pb-Bi alloy cathode adopted by the invention can be electrolyzed at a lower temperature (380 ℃ to 550 ℃).
2) The invention takes the liquid Pb-Bi alloy as the cathode, changes the rare earth precipitation potential by controlling the alloy composition, and can increase the rare earth precipitation potential difference, thereby being easier to separate and purify various rare earths.
3) The invention adopts pulse electrolysis to extract and separate rare earth, and achieves the high-efficiency extraction and separation of the rare earth by adjusting the potential of the pulse electrolysis stage of the four stages of enrichment, electrolytic deposition, dissolution and stabilization.
4) The depolarization value of the rare earth ions on the liquid Pb-Bi alloy electrode is as high as about 0.98V, which is beneficial to improving the extraction rate of the rare earth and can solve the problem of current loss of the divalent and trivalent rare earth ions in the reciprocating circulation process in the electrolysis process.
5) The method adopts a pulse electrolysis method, has shorter process flow than the traditional electrolysis extraction of rare earth, can reduce the deposition of impurities, can obtain Pb-Bi-rare earth ternary or multi-element rare earth alloy by one-step electrolysis, and the obtained rare earth alloy has uniform structure and no segregation; concentration polarization is reduced, the extraction rate is high, the extraction efficiency is high, and the extraction rate of rare earth is up to 98.9%; the separation effect of the two rare earths is good, and the separation factor is as high as 786.
Drawings
FIG. 1 is a schematic diagram of an experimental apparatus for extracting and separating rare earth and preparing a multi-element rare earth alloy by molten salt pulse electrolysis of a Pb-Bi alloy cathode according to the present invention;
wherein, 1-an electrochemical workstation, 2-an alumina sleeve, 3-an electrolytic bath, 4-a liquid Pb-Bi alloy electrode, 5-a chlorine outlet, 6-an auxiliary electrode, 7-a reference electrode and 8-an auxiliary electrode;
FIG. 2 shows LiCl-KCl-CeCl at 500 deg.C 3 (1.62×10 -4 mol cm -3 ) Cyclic voltammetry curves of different termination potentials on a liquid Pb-Bi (44.8 wt%) alloy cathode in molten salt;
FIG. 3 shows LiCl-KCl-CeCl at 500 deg.C 3 SEM-EDS analysis of the alloy surface is obtained by pulse electrolysis on a molten salt liquid Pb-Bi (44.8 wt%) alloy cathode, wherein a is an SEM picture, and b, c and d are EDS element surface distribution;
FIG. 4 shows LiCl-KCl-GdCl at 500 deg.C 3 (1.14×10 -4 mol cm -3 ) Cyclic voltammetry curves of different termination potentials on a liquid Pb-Bi (44.8 wt%) alloy cathode in molten salt;
FIG. 5 shows LiCl-KCl-GdCl at 500 deg.C 3 SEM-EDS analysis of the alloy surface is obtained on a Pb-Bi (44.8 wt%) alloy cathode in a molten salt through pulse electrolysis, wherein a is an SEM picture, and b, c and d are EDS element surface distribution;
FIG. 6 shows LiCl-KCl-SmCl at 500 deg.C 3 The XRD pattern of the alloy is obtained on a liquid Pb-Bi (44.8 wt%) alloy cathode in the molten salt through pulse electrolysis;
FIG. 7 shows LiCl-KCl-DyCl at 500 deg.C 3 (7.43×10 -5 mol cm -3 ) Cyclic voltammetry curves of different termination potentials and different sweep rates on a liquid Pb-Bi (40 wt%) alloy cathode in the molten salt;
FIG. 8 is a 500 ℃ LiCl-KCl-DyCl 3 (7.43×10 -5 mol cm -3 ) Cyclic voltammetry curves of different termination potentials and different sweep rates on a liquid Pb-Bi (44.8 wt%) alloy cathode in the molten salt;
FIG. 9 shows LiCl-KCl-SmCl at 500 deg.C 3 (7.43×10 -5 mol cm -3 )-DyCl 3 (7.43×10 -5 mol cm -3 ) Cyclic voltammetry curves of different termination potentials on a liquid Pb-Bi (44.8 wt%) alloy cathode in molten salt;
FIG. 10 shows LiCl-KCl-SmCl at 500 deg.C 3 -DyCl 3 Obtaining an SEM picture of the alloy surface on a liquid Pb-Bi (44.8 wt%) alloy cathode in the molten salt through pulse electrolysis;
FIG. 11 shows LiCl-KCl-SmCl at 500 deg.C 3 -DyCl 3 Pulse electrolysis curve on liquid Pb-Bi (44.8 wt%) alloy cathode in molten salt;
FIG. 12 shows LiCl-KCl-SmCl at 500 deg.C 3 -DyCl 3 The XRD pattern of the alloy is obtained by extracting and separating Sm and Dy on a liquid Pb-Bi (44.8 wt%) alloy cathode in the molten salt through pulse electrolysis.
Detailed Description
Example 1: the method for extracting and separating rare earth and preparing the multi-element rare earth alloy by molten salt pulse electrolysis of the Pb-Bi alloy cathode comprises the following steps:
step one, putting 83 g (mass ratio of anhydrous LiCl to anhydrous KCl is 45.8, 54.2) of anhydrous LiCl and anhydrous KCl into an alumina crucible, uniformly mixing, drying and dehydrating 25 h at 300 ℃ for drying pretreatment, then putting the alumina crucible into an electrolytic cell, introducing high-purity argon with the purity of 99%, and heating to 500 ℃ to obtain molten salt of LiCl and KCl;
step two, adding the cleaned 11.04 g elementary substance Pb and 8.96 g elementary substance Bi into a crucible, then putting the crucible containing the elementary substance Pb and the elementary substance Bi into the LiCl and KCl molten salt obtained in the step one for smelting at 500 ℃, continuously stirring by using an alumina rod in the smelting process, and smelting 2 h to obtain a Pb-Bi alloy with the Pb content of 55.2 wt%;
step three, adding cerium trichloride (CeCl) into the LiCl and KCl molten salt obtained in the step one 3 ) 2 g, using Pb-Bi alloy obtained in the second step as a working electrode, using spectrally pure conductive graphite as an anode, using a silver/silver chloride electrode as a reference electrode, inserting the anode and the reference electrode into LiCl and KCl molten salt obtained in the first step and connecting the anode and the reference electrode with an electrochemical workstation, inserting a W wire sleeved with an alumina protective tube into the Pb-Bi alloy obtained in the second step as a lead wireConnecting the Pb-Bi alloy and the electrochemical workstation to form a pulse electrolysis system (shown in figure 1);
step four, performing cyclic voltammetry test by using an electrochemical workstation, determining that the reduction potential of Ce (III) on the Pb-Bi alloy electrode is-0.96V, and forming a Pb-Bi-Ce alloy at-1.22V (shown in figure 2);
and step five, on the basis of the reduction potential of the rare earth ions determined in the step four, applying pulse voltage between the working electrode and the anode by using an electrochemical workstation to perform pulse electrolysis, wherein the pulse electrolysis is divided into four stages, and the first stage is enriched: pulse electrolytic potential is-1.25V, time is 10s, and second-stage electrolytic deposition: the pulse electrolysis potential is-1.22V, the time is 80 s, and the third stage is dissolution: the pulse electrolytic potential is-0.8V, the time is 20s, and the fourth stage is stable: the pulse electrolysis potential is-1.10V, the time is 10s, the four stages are a period, the cycle is 750 periods, the product after electrolysis is washed by acetone for 3 times, then is washed by absolute ethyl alcohol for 3 times, and then is dried at the low temperature of 200 ℃ for 24h, so that the Pb-Bi-Ce ternary alloy is obtained.
SEM-EDS analysis of the obtained Pb-Bi-Ce ternary alloy proves that the alloy mainly consists of three elements of Pb, bi and Ce, as shown in figure 3, and as can be seen from figure 3, the generated Pb-Bi-Ce ternary alloy has certain refining effect on a Pb-Bi alloy matrix, so that the matrix is refined into rod-shaped grains with the diameter of 1 mu m. The upper salt was detected by ICP-MS and calculated to have a Ce extraction of 98.7%.
Example 2: the method for extracting and separating rare earth and preparing the multi-element rare earth alloy by molten salt pulse electrolysis of the Pb-Bi alloy cathode comprises the following steps:
firstly, putting anhydrous LiCl and anhydrous KCl which are 83 g (the mass ratio of the anhydrous LiCl to the anhydrous KCl is 45.8 and 54.2) into an alumina crucible, uniformly mixing, drying and dehydrating 25 h at 300 ℃ for drying pretreatment, then putting the alumina crucible into an electrolytic cell, introducing high-purity argon with the purity of 99%, and heating to 500 ℃ to obtain molten salt of the LiCl and KCl;
step two, adding the cleaned 11.04 g elementary substance Pb and 8.96 g elementary substance Bi into a crucible, then putting the crucible containing the elementary substance Pb and the elementary substance Bi into the LiCl and KCl molten salt obtained in the step one for smelting at 500 ℃, continuously stirring by using an alumina rod in the smelting process, and smelting 2 h to obtain a Pb-Bi alloy with the Pb content of 55.2 wt%;
step three, adding gadolinium trichloride (GdCl) into the molten salt of LiCl and KCl obtained in the step one 3 ) 1.5 g, using the Pb-Bi alloy obtained in the second step as a working electrode, using a spectrally pure conductor graphite as an anode, using a silver/silver chloride electrode as a reference electrode, inserting the anode and the reference electrode into the LiCl and KCl molten salt obtained in the first step and connecting the anode and the reference electrode with an electrochemical workstation, inserting a W wire sleeved with an alumina protective tube into the Pb-Bi alloy obtained in the second step and connecting the Pb-Bi alloy and the electrochemical workstation as a lead to form a pulse electrolysis system (as shown in FIG. 1);
step four, performing cyclic voltammetry by using an electrochemical workstation, determining that the reduction potential of Gd (III) on the Pb-Bi alloy electrode is-1.11V, and forming a Pb-Bi-Gd alloy at-1.32V (shown in figure 4);
and step five, on the basis of the reduction potential of the rare earth ions determined in the step four, applying pulse voltage between the working electrode and the anode by using an electrochemical workstation to perform pulse electrolysis, wherein the pulse electrolysis is divided into four stages, and the first stage is enrichment: pulse electrolytic potential is-1.40V, time is 10s, and second stage electrolytic deposition: the pulse electrolysis potential is-1.32V, the time is 80 s, and the third stage is dissolution: the pulse electrolytic potential is-0.6V, the time is 20s, and the fourth stage is stable: the pulse electrolysis potential is-1.12V, the time is 10s, the four stages are a period, the cycle is 540 periods, the product after electrolysis is washed by acetone for 3 times, then washed by absolute ethyl alcohol for 3 times, and then dried at the low temperature of 250 ℃ for 10 h, so that the Pb-Bi-Gd ternary alloy is obtained.
SEM-EDS analysis of the obtained Pb-Bi-Gd ternary alloy proves that the alloy mainly consists of three elements of Pb, bi and Gd, as shown in figure 5, and as can be seen from figure 5, the generated ternary alloy has a certain refining effect on a Pb-Bi alloy matrix and is refined into grains with the size of about 200 nm; the upper salt was detected by ICP-MS and the calculated extraction of Gd was 98.5%.
Example 3: the method for extracting and separating rare earth and preparing the multi-element rare earth alloy by molten salt pulse electrolysis of the Pb-Bi alloy cathode comprises the following steps:
step one, putting anhydrous LiCl and anhydrous KCl which are 83 g (the mass ratio of the anhydrous LiCl to the anhydrous KCl is 45.8;
step two, adding the cleaned 11.04 g elementary substance Pb and 8.96 g elementary substance Bi into a crucible, then putting the crucible containing the elementary substance Pb and the elementary substance Bi into the LiCl and KCl molten salt obtained in the step one for smelting at 500 ℃, continuously stirring by using an alumina rod in the smelting process, and smelting 2 h to obtain a Pb-Bi alloy with the Pb content of 55.2 wt%;
step three, adding samarium trichloride (SmCl) into the molten salt of LiCl and KCl obtained in the step one 3 ) 0.95 g, using the Pb-Bi alloy obtained in the second step as a working electrode, using a spectrally pure conductor graphite as an anode, using a silver/silver chloride electrode as a reference electrode, inserting the anode and the reference electrode into the LiCl and KCl molten salt obtained in the first step and connecting the anode and the reference electrode with an electrochemical workstation, inserting a W wire sleeved with an alumina protection tube into the Pb-Bi alloy obtained in the second step and connecting the Pb-Bi alloy and the electrochemical workstation as a lead, and forming a pulse electrolysis system (as shown in figure 1);
step four, performing cyclic voltammetry by using an electrochemical workstation to determine that the reduction potential of Sm (III) on the Pb-Bi alloy electrode is-1.56V;
and step five, on the basis of the reduction potential of the rare earth ions determined in the step four, applying pulse voltage between the working electrode and the anode by using an electrochemical workstation to perform pulse electrolysis, wherein the pulse electrolysis is divided into four stages, and the first stage is enrichment: pulse electrolytic potential is-1.60V, time is 3 s, and second stage electrolytic deposition: the pulse electrolysis potential is-1.55V, the time is 53 s, and the third stage is dissolution: the pulse electrolytic potential is-1.0V, the time is 3 s, and the fourth stage is stable: the pulse electrolysis potential is-1.39V, the time is 3 s, the four stages are one period, 600 periods are circulated, the electrolyzed product is washed by acetone for 3 times, then is washed by absolute ethyl alcohol for 3 times, and then is dried at the low temperature of 150 ℃ for 15 h, so that the Pb-Bi-Sm ternary alloy is obtained.
XRD analysis of the obtained Pb-Bi-Sm ternary alloy proves that the alloy consists of BiSm and Pb 7 Bi 3 And a Bi phase, as shown in fig. 6; the upper salt was detected by ICP-MS and the Sm extraction was calculated to be 98.6%.
Example 4: the method for extracting and separating rare earth and preparing the multi-element rare earth alloy by molten salt pulse electrolysis of the Pb-Bi alloy cathode comprises the following steps:
step one, putting 83 g (mass ratio of anhydrous LiCl to anhydrous KCl is 45.8, 54.2) of anhydrous LiCl and anhydrous KCl into an alumina crucible, uniformly mixing, drying and dehydrating 12 h at 200 ℃ for drying pretreatment, then putting the alumina crucible into an electrolytic cell, introducing high-purity argon with the purity of 99%, and heating to 500 ℃ to obtain molten salt of LiCl and KCl;
the processes of the second step to the fourth step are respectively carried out in three situations, and the specific processes are as follows:
the first situation is as follows: step two, adding the cleaned 12 g elementary substance Pb and 8 g elementary substance Bi into a crucible, then putting the crucible containing the elementary substance Pb and the elementary substance Bi into the LiCl and KCl molten salt obtained in the step one for smelting at 500 ℃, continuously stirring by using an alumina rod in the smelting process, and obtaining a Pb-Bi alloy with the Pb content of 60 wt% after smelting 3h;
step three, adding dysprosium trichloride (DyCl) into the molten salt of LiCl and KCl obtained in the step one 3 ) 1 g, using the Pb-Bi alloy obtained in the second step as a working electrode, using a spectrally pure conductor graphite as an anode, using a silver/silver chloride electrode as a reference electrode, inserting the anode and the reference electrode into the LiCl and KCl molten salt obtained in the first step and connecting the anode and the reference electrode with an electrochemical workstation, inserting a W wire sleeved with an alumina protective tube into the Pb-Bi alloy obtained in the second step and connecting the Pb-Bi alloy and the electrochemical workstation as a lead to form a pulse electrolysis system (as shown in FIG. 1);
and step four, performing cyclic voltammetry by using an electrochemical workstation, determining that the reduction potential of Dy (III) on the Pb-Bi alloy electrode is-1.18V, and forming the Pb-Bi-Dy alloy at-1.40V (shown in figure 7).
Case two: step two, adding the cleaned 11.04 g elementary substance Pb and 8.96 g elementary substance Bi into a crucible, then putting the crucible containing the elementary substance Pb and the elementary substance Bi into the LiCl and KCl molten salt obtained in the step one for smelting at 500 ℃, continuously stirring by using an alumina rod in the smelting process, and obtaining a Pb-Bi alloy with the Pb content of 55.2wt% after smelting 3h;
step three, adding dysprosium trichloride (DyCl) into the molten salt of LiCl and KCl obtained in the step one 3 ) 1 g, using the Pb-Bi alloy obtained in the second step as a working electrode, using a spectrally pure conductor graphite as an anode, using a silver/silver chloride electrode as a reference electrode, inserting the anode and the reference electrode into the LiCl and KCl molten salt obtained in the first step and connecting the anode and the reference electrode with an electrochemical workstation, inserting a W wire sleeved with an alumina protective tube into the Pb-Bi alloy obtained in the second step and connecting the Pb-Bi alloy and the electrochemical workstation as a lead to form a pulse electrolysis system (as shown in FIG. 1);
step four, performing cyclic voltammetry by using an electrochemical workstation, determining that the reduction potential of Dy (III) on the Pb-Bi alloy electrode is-1.08V, and forming a Pb-Bi-Dy alloy at-1.31V (as shown in FIG. 8);
case three: step two, adding the cleaned 11.04 g elementary substance Pb and 8.96 g elementary substance Bi into a crucible, then putting the crucible containing the elementary substance Pb and the elementary substance Bi into the LiCl and KCl molten salt obtained in the step one for smelting at 500 ℃, continuously stirring by using an alumina rod in the smelting process, and smelting 2 h to obtain a Pb-Bi alloy with the Pb content of 55.2 wt%;
step three, adding samarium trichloride (SmCl) into the molten salt of LiCl and KCl obtained in the step one 3 ) 0.95 g, using Pb-Bi alloy obtained in the second step as a working electrode, using spectrally pure conductor graphite as an anode, using a silver/silver chloride electrode as a reference electrode, inserting the anode and the reference electrode into LiCl and KCl molten salt obtained in the first step and connecting the anode and the reference electrode with an electrochemical workstation, inserting a W wire sleeved with an alumina protection tube into Pb-Bi alloy obtained in the second step and connecting the Pb-Bi alloy and the electrochemical workstation as a lead, and forming a pulse electrolysis system (as shown in the figure)1) is shown in the specification;
step four, performing cyclic voltammetry test by using an electrochemical workstation, and determining that the reduction potential of Sm (III) on the Pb-Bi alloy electrode is-1.56V, namely, the Pb-Bi-Sm alloy is formed at the potential (shown in figure 9), so that the theoretical separation coefficient of Sm and Dy is 99.99%;
the Dy and Sm determined according to the three situations are subjected to pulse electrolysis to separate the Dy and the Sm on the reduction potential of the liquid Pb-Bi eutectic alloy electrode, and the specific process is shown in the step five;
and step five, on the basis of the determined reduction potential of Dy and Sm on the liquid Pb-Bi eutectic alloy electrode, applying pulse voltage between a working electrode and an anode by using an electrochemical workstation for pulse electrolysis, wherein the pulse electrolysis is divided into four stages, and enrichment is performed in the first stage: pulse electrolytic potential is-1.40V, time is 2 s, and second stage electrolytic deposition: the pulse electrolytic potential is-1.31V, the time is 55 s, and the third stage is dissolution: the pulse electrolytic potential is-0.4V, the time is 2 s, and the fourth stage is stable: the pulse electrolysis potential is-1.2V, the time is 1s, the four stages are one period, the cycle is 840 periods, the pulse electrolysis curve is shown in figure 11, the deposition of Li and Sm is avoided by controlling the pulse potential, and the current of the electrodeposition stage in each period of pulse electrolysis is increased and then gradually stabilized. With the progress of pulse electrolysis, dysprosium ions in the molten salt are rapidly reduced and deposited on the liquid Pb-Bi alloy electrode, samarium ions are left in the molten salt because the samarium ions do not reach the reduction potential, the electrolyzed product is washed by acetone for 3 times, then is washed by absolute ethyl alcohol for 3 times, and then is dried at the low temperature of 200 ℃ for 20 hours to obtain the Pb-Bi-Dy ternary alloy.
SEM-EDS analysis of the obtained Pb-Bi-Dy ternary alloy proves that the alloy mainly consists of three elements of Pb, bi and Dy as shown in figure 10; the pulse electrolysis curve on the alloy cathode is shown in FIG. 11, and XRD analysis of the alloy proves that the alloy is composed of Pb 3 Dy、BiDy、Pb 7 Bi 3 And Bi phase, which shows that both liquid Pb and liquid Bi participate in pulse electrolysis extraction and separation of Sm and Dy, as shown in figure 12, the generated ternary alloy has certain refining effect on a Pb-Bi alloy matrix and is refined into rod-shaped crystals with the size of about 30 nm; upper layer ofThe salt is detected by ICP-MS, the extraction rate of Dy is calculated to be 98.9%, and the separation factor of Dy and Sm is as high as 786.

Claims (6)

1. A method for extracting and separating rare earth and preparing a multi-element rare earth alloy by Pb-Bi alloy cathode molten salt pulse electrolysis is characterized by comprising the following steps:
step one, placing anhydrous LiCl and anhydrous KCl into an alumina crucible to be uniformly mixed, carrying out drying pretreatment, then placing the alumina crucible into an electrolytic cell, introducing high-purity argon, heating to 380-550 ℃, and obtaining a molten salt of LiCl and KCl;
secondly, adding the cleaned elemental Pb and elemental Bi into a crucible, then putting the crucible filled with the elemental Pb and elemental Bi into the LiCl and KCl molten salt obtained in the first step for smelting, continuously stirring by using an alumina rod in the smelting process, and obtaining a Pb-Bi alloy after smelting; the mass fraction of Pb in the Pb-Bi alloy is 55.2% -98.5%, and the smelting parameters are as follows: the temperature is 380-550 ℃, and the time is 1-3 h;
thirdly, adding rare earth chloride into the molten salt of the LiCl and the KCl obtained in the first step, taking the Pb-Bi alloy obtained in the second step as a working electrode, taking the spectrally pure conductor graphite as an anode, taking a silver/silver chloride electrode as a reference electrode, inserting the anode and the reference electrode into the molten salt of the LiCl and the KCl obtained in the first step and connecting the anode and the reference electrode with an electrochemical workstation, inserting a W wire sleeved with an aluminum oxide protection tube into the Pb-Bi alloy obtained in the second step and connecting the Pb-Bi alloy and the electrochemical workstation as a lead to form a pulse electrolysis system; the rare earth chloride is LaCl 3 、CeCl 3 、PrCl 3 、NdCl 3 、SmCl 3 、EuCl 3 、GdCl 3 、TbCl 3 、DyCl 3 、HoCl 3 、ErCl 3 、YbCl 3 One or a mixture of three of (a);
performing cyclic voltammetry by using an electrochemical workstation to determine the reduction potential of the rare earth ions on the Pb-Bi alloy electrode;
step five, on the basis of the reduction potential of the rare earth ions determined in the step four, applying pulse voltage between a working electrode and an anode by using an electrochemical workstation or a pulse power supply for pulse electrolysis, washing and drying the electrolyzed product at low temperature to obtain the multi-element Pb-Bi-rare earth alloy, wherein the pulse electrolysis is divided into four stages, and enrichment is performed in the first stage: the pulse electrolytic potential is-1.2V to-1.7V, the time is 1s to 10s, and the second stage electrolytic deposition: the pulse electrolytic potential is-1.2V to-1.6V, the time is 5s to 200s, and the third stage is dissolution: the pulse electrolytic potential is-1V-0.1V, the time is 1 s-20 s, the fourth stage is stable: the pulse electrolytic potential is-1.60V-0V, and the time is 1 s-10 s.
2. The method for separating rare earth and preparing multi-element rare earth alloy by Pb-Bi alloy cathode molten salt pulse electrolysis extraction according to claim 1, wherein the mass ratio of anhydrous LiCl to anhydrous KCl in the first step is 46: (53 to 55).
3. The method for extracting and separating rare earth and preparing multi-element rare earth alloy according to the Pb-Bi alloy cathode molten salt pulse electrolysis method of claim 1, wherein the drying pretreatment in the first step comprises the following specific processes: drying and dehydrating for 5-30 h at 150-300 ℃.
4. The method for extracting and separating rare earth and preparing multi-element rare earth alloy by Pb-Bi alloy cathode molten salt pulse electrolysis according to claim 1, wherein the mass ratio of the Pb-Bi alloy to the rare earth chloride in the third step is (5-50): 1.
5. the method for extracting and separating rare earth and preparing multi-element rare earth alloy by Pb-Bi alloy cathode molten salt pulse electrolysis according to claim 1, wherein the mass fraction of the rare earth chloride in the molten salt of LiCl and KCl in the third step is 0.2-10%.
6. The method for extracting and separating rare earth and preparing multi-element rare earth alloy by Pb-Bi alloy cathode molten salt pulse electrolysis according to claim 1, wherein the concrete process of washing in the fifth step is as follows: washing with acetone for 3-5 times, and then washing with absolute ethyl alcohol for 3-5 times, wherein the low-temperature drying parameters are as follows: the temperature is 200-300 ℃, and the time is 5-24 h.
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