CN114908381A - Method for removing rare earth ions in waste molten salt - Google Patents
Method for removing rare earth ions in waste molten salt Download PDFInfo
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- 238000005868 electrolysis reaction Methods 0.000 claims description 16
- 238000004365 square wave voltammetry Methods 0.000 claims description 16
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims description 12
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- 238000005292 vacuum distillation Methods 0.000 claims description 2
- 150000002500 ions Chemical class 0.000 abstract description 14
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- 238000011161 development Methods 0.000 description 4
- 238000004821 distillation Methods 0.000 description 4
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 description 4
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- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 3
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- RCJVRSBWZCNNQT-UHFFFAOYSA-N dichloridooxygen Chemical compound ClOCl RCJVRSBWZCNNQT-UHFFFAOYSA-N 0.000 description 1
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- FUJCRWPEOMXPAD-UHFFFAOYSA-N lithium oxide Chemical compound [Li+].[Li+].[O-2] FUJCRWPEOMXPAD-UHFFFAOYSA-N 0.000 description 1
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- 229910052759 nickel Inorganic materials 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C5/00—Electrolytic production, recovery or refining of metal powders or porous metal masses
- C25C5/04—Electrolytic production, recovery or refining of metal powders or porous metal masses from melts
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
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- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electrolytic Production Of Metals (AREA)
- Removal Of Specific Substances (AREA)
Abstract
The invention provides a method for removing rare earth ions in radioactive waste molten salt, which comprises the step of adding Li into the waste molten salt at the temperature of 300-800 DEG C 2 O reacts to remove the rare earth ions. By adding Li into the radioactive waste molten salt at 300-800 deg.C 2 The O is subjected to liquid phase reaction, so that the generation of a large amount of waste gas is avoided, and the method has the advantages of high reaction rate and less environmental pollution. In addition, the method also ensures the rare earth ion removal effect, and does not introduce impurity ions which are difficult to remove or generate a large amount of waste.
Description
Technical Field
The invention relates to the field of nuclear power spent fuel post-treatment, in particular to a method for removing rare earth ions in waste molten salt, and particularly relates to a method for removing rare earth ions in waste molten salt generated by an electrolytic refining method.
Background
The development of clean and efficient green energy is imminent. Nuclear power represents an important development direction of green energy, is developed vigorously at present, and is expected to become one of mainstream energy in the future.
The sustainable development of nuclear power is difficult to guarantee only by relying on natural uranium resources, and the efficient utilization of the uranium resources, especially nuclear power fuel, becomes inevitable. At present, the nuclear power industry mostly adopts a water method post-treatment process to treat spent fuel produced by the nuclear power industry.
Compared with the water method post-treatment process, the dry method post-treatment process has the obvious advantages of short spent fuel cooling period, less steps, small waste volume and the like. The dry post-treatment process mainly comprises a fluorination volatilization method, a molten salt liquid-liquid extraction method, a high-temperature chemical method (such as an electrolytic refining method) taking molten salt as a medium and the like. Among them, the electrolytic refining method has the most promising development prospect. The electrolytic refining method still produces a large amount of waste molten salt with rare earth ions, and in order to minimize the amount of nuclear waste, the waste molten salt needs to be purified and reused.
The methods developed in various countries at present for removing rare earth ions in waste molten salt include phosphate precipitation method, zeolite adsorption method, oxygen precipitation method and the like. Phosphate radical is difficult to remove in the phosphate precipitation method, and impurity ions are introduced into a reaction system. The zeolite adsorption method uses 4A type zeolite with a large structure, generates a large amount of waste, and is difficult to remove the rare earth ions in the waste molten salt cleanly. Although the oxygen precipitation method does not introduce impurity ions when removing rare earth ions, and the rare earth ion removal rate is also good, the method generates a large amount of waste gas and pollutes the environment; meanwhile, the method is a gas-liquid reaction, the contact of reactants is incomplete, and the reaction rate is slow.
Therefore, it is required to develop a method for removing rare earth ions from waste molten salt, which has a fast reaction rate and causes little environmental pollution.
Disclosure of Invention
In view of the above, the main object of the present invention is to provide a method for removing rare earth ions from radioactive waste molten salt, which can solve at least some of the above problems.
According to the disclosure, a method for removing rare earth ions in radioactive waste molten salt is provided, which comprises adding Li into the waste molten salt at 300-800 ℃ 2 O reacts to remove the rare earth ions.
According to some embodiments, Li 2 O is added stepwise.
According to some embodiments, the method further comprises testing the reaction system during the reaction using an electrochemical method to obtain an electrochemical profile, and determining the progress of the reaction based on the obtained electrochemical profile.
According to some embodiments, the electrochemical method comprises cyclic voltammetry, square wave voltammetry, or open-circuit chronopotentiometry.
According to some embodiments, Li appears in the electrochemical profile 2 When the oxidation and/or reduction peak of O, judging the reaction process is that the rare earth ions are removed, and stopping adding Li 2 O and finishing the reaction.
According to some embodiments, a plurality of different regions of the reaction system are tested to obtain a plurality of the electrochemical profiles, wherein,
in the multiple electrochemical graphsAll do not show Li 2 Judging that the rare earth ions are not removed in the reaction system when the reaction process is carried out by the oxidation and/or reduction peak of O, and continuously adding Li 2 O；
At least one electrochemical profile of the plurality of electrochemical profiles is free of Li 2 Oxidation and/or reduction peaks of O, and at least one electrochemical diagram showing Li 2 The oxidation and/or reduction peak of O, judging that the reaction process is the region in which the rare earth ions are not removed and the region in which the rare earth ions are completely removed and Li still exist in the reaction system 2 In the region where O is excessive, stopping the addition of Li 2 O, continuing the reaction; or
Li is present in all of the multiple electrochemical plots 2 The oxidation and/or reduction peak of O, the reaction process is judged to be that the rare earth ions in the reaction system are completely removed, and Li addition is stopped 2 O and finishing the reaction.
The plurality of different zones includes an upper portion, a middle portion, and a lower portion of the reaction system. The plurality of electrochemical graphs is at least 3.
According to some embodiments, the spent molten salt is allowed to stand for 2-10min, e.g. 3, 4, 5, 6, 7min, before performing the electrochemical method test.
According to some embodiments, a three-electrode system is used in the electrochemical process, wherein the working electrode is a tungsten or molybdenum wire and the auxiliary electrode is a graphite rod, a molybdenum rod or a tungsten rod; the reference electrode was Ag/AgCl.
According to some embodiments, the method further comprises removing precipitates in the reaction system by using a vacuum distillation method or a molten salt filtration method after the reaction is finished to obtain the molten salt with the rare earth ions removed. Optionally, when excess Li is present in the rare earth ion-depleted molten salt 2 When O is used, the method also comprises the step of electrolyzing the fused salt for removing the rare earth ions at 400-800 ℃ to remove excessive Li 2 O。
According to some embodiments, the electrolysis is performed by potentiostatic method, and the electrolysis is stopped when the electrolysis current reaches 1 mA.
According to some embodiments, the electrolysis uses a three-electrode system, wherein the working electrode is a tungsten or molybdenum wire and the auxiliary electrode is a graphite rod, a molybdenum rod or a tungsten rod; the reference electrode was Ag/AgCl.
By adding Li into the radioactive waste molten salt at 300-800 deg.C 2 The O is subjected to liquid phase reaction, so that the generation of a large amount of waste gas is avoided, and the method has the advantages of high reaction rate and less environmental pollution. Meanwhile, the method also ensures the rare earth ion removal effect, and does not introduce impurity ions which are difficult to remove or generate a large amount of waste.
Drawings
FIG. 1 shows that square wave voltammetry is used in the examples to separately test the absence of added Li 2 O molten salt and Li added to the molten salt in an amount of 0.20g and 0.40g 2 An electrochemical curve obtained by a reaction system after O parallel reaction;
FIG. 2 shows the cumulative addition of 0.50g, 0.60g, 0.65g, 0.70g Li to the molten salt using square wave voltammetry tests, respectively, in the examples 2 An electrochemical curve obtained by a reaction system after O parallel reaction;
FIG. 3 shows the cumulative addition of 0.75g, 0.80g, 0.85g, 0.90g Li to the molten salt using square wave voltammetry tests, respectively, in the examples 2 An electrochemical curve obtained by a reaction system after O parallel reaction;
FIG. 4 shows the cumulative addition of 0.70g Li to the molten salt using square wave voltammetry testing in the examples 2 An electrochemical curve obtained by a reaction system after the O-union reaction;
FIG. 5 shows the cumulative addition of 0.75g Li to the molten salt using square wave voltammetry testing in the examples 2 An electrochemical curve obtained by a reaction system after O parallel reaction;
FIG. 6 shows the cumulative addition of 0.90g Li to the molten salt using the square wave voltammetry test in the examples 2 An electrochemical curve obtained by a reaction system after O parallel reaction;
FIG. 7 shows a graph of the electrochemical curve obtained by electrolyzing filtered molten salt using cyclic voltammetry in the example;
FIG. 8 shows an electrochemical graph obtained by testing the filtered molten salt by square wave voltammetry after electrolysis in the example.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application and the accompanying drawings, and it is obvious that the described embodiments are only some embodiments of the present application, and not all embodiments. All other embodiments obtained by a person of ordinary skill in the art without any inventive work based on the embodiments in the present application are within the scope of protection of the present application.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. If there is a conflict, the present specification will control.
The disclosure aims to provide a method for removing rare earth ions in waste molten salt with high reaction rate and less environmental pollution, which is applied to the field of nuclear power spent fuel post-treatment, particularly the field of nuclear power spent fuel dry post-treatment, and more particularly the field of purification of waste molten salt generated by an electrolytic refining method. Among them, the waste molten salt generated in the electrolytic refining contains such as LiCl-KCl eutectic salt and a large amount of rare earth elements, for example, La, Ce, Pr, Nd, Y, etc., with a total content of > 1000 ppm.
In order to achieve the purpose, the application provides a method for removing rare earth ions in radioactive waste molten salt, which comprises the step of adding Li into the waste molten salt at 300-800 ℃, preferably 450-550 DEG C 2 O reacts to remove rare earth ions.
The inventors have found that by adding Li to a radioactive waste molten salt containing the molten salt and a large amount of rare earth elements (e.g., elements such as La, Ce, Pr, Nd, Y, etc., in a total content of > 1000 ppm) 2 And O, carrying out a displacement reaction while stirring, and converting soluble rare earth chloride ions in the waste molten salt into insoluble rare earth oxychloride or rare earth oxide precipitate to remove the rare earth ions. The reaction has the advantages of high speed, thorough reaction, high rare earth element removal rate, no introduction of other ions,exhaust gas is not generated. And even with excess lithium oxide, can be conveniently removed by electrolysis.
The radioactive waste molten salt is not particularly limited in the disclosure, and any waste molten salt generated by the electrolytic refining post-treatment of nuclear spent fuel can be applied to the method. The molten salt is generally two or more mixed salts, and typically, may be LiCl-KCl eutectic salt, but is not limited thereto.
The specific steps of the method are exemplarily described below. The following exemplary illustrations are for ease of understanding only, and the present method is not limited to what is described below.
Since the method involves the treatment of radioactive materials, an unmanned automation device is used to remotely control the reaction process. The method uses a reaction system which is provided with an automatic lifting system and a stirring device capable of being remotely controlled to carry out reaction. The stirring paddle can be made of corundum, stainless steel, nickel-based alloy, tungsten and other materials with high temperature resistance and radiation corrosion resistance.
Introducing the radioactive waste molten salt into the reaction system, heating to 300-800 ℃, and adding Li under stirring 2 And O is reacted. Preferably, the reaction temperature is from 450 ℃ to 550 ℃, e.g. 500 ℃. The reaction time is 0.1-2 h. The reaction time may be adjusted according to the amount of the waste molten salt and the reaction temperature, and the reaction time is not particularly limited in the present application.
The reaction of the method is a liquid phase reaction, thereby avoiding the generation of waste gas and having the advantages of high reaction rate and little environmental pollution. In addition, on the premise of ensuring the rare earth ion removal effect, impurity ions which are difficult to remove are not introduced, and a large amount of waste is not generated.
According to some embodiments, Li 2 O is added stepwise. I.e. at the beginning of the reaction, Li 2 The addition of O is lower than the chemical reaction equivalent, and Li is continuously added along with the reaction 2 And (O). For example, equal amounts of Li may be added sequentially to the reaction 2 O; also can continuously reduce Li along with the reaction 2 The amount of O added, e.g. Li added in such a way that the addition gradient decreases 2 O, but is not limited thereto. Such a methodFormula (II) can avoid Li to a certain extent 2 Excess of O.
According to a preferred embodiment, the method further comprises the step of testing the reaction progress in the reaction system by an electrochemical method during the reaction process, so that the reaction endpoint can be judged in real time, and the reaction can be terminated in time. Due to Li 2 O has a low redox potential, so that once an excessive amount of Li is present in the reaction system 2 O, Li can be detected 2 Oxidation and/or reduction peaks of O, thereby confirming completion of the reaction. In such a way that the amount of reagents, i.e. Li, can be reduced 2 O is used in an amount such that Li can be avoided 2 And (4) carrying out a post-treatment step after O is excessive.
Specifically, according to some embodiments, the electrochemical method of monitoring the progress of the reaction may be cyclic voltammetry, square wave voltammetry, or open-circuit chronopotentiometry. Because the change degree of the front and rear electrode surfaces is small, the cyclic voltammetry is more commonly used. Higher accuracy can be obtained by using open-circuit chronopotentiometry for monitoring, but for a longer time. The square wave voltammetry is sensitive to the response of electrochemical signals, can quickly obtain an electrochemical curve graph, and is a preferred electrochemical monitoring method. An electrochemical curve chart is obtained by an electrochemical method, and the reaction process is judged according to the electrochemical curve chart.
In particular, according to some embodiments, Li appears in the electrochemical profile when the reaction progress is judged 2 When the oxidation and/or reduction peak of O is detected, judging that the reaction process is that the rare earth ions are removed, and stopping adding Li 2 O and finishing the reaction. The existing method for judging the reaction end point by using the metal potential has errors in judgment due to the existence of an electrochemical detection limit. With Li 2 The method for judging the reaction end point according to the existence of the oxidation and/or reduction peak of O is more accurate, and can more accurately avoid Li 2 Excess of O.
Further, according to a preferred embodiment, a plurality of electrochemical profiles are obtained by testing a plurality of different regions of the reaction system. When the reaction process is judged, Li does not appear in a plurality of electrochemical graphs 2 The oxidation and/or reduction peak of O, judging that the reaction process is that the rare earth ions are still not removed in the reaction system, and continuously adding Li 2 O; multi-sheet electrochemical cellIn which at least one electrochemical curve shows no Li 2 Oxidation and/or reduction peaks of O, and at least one electrochemical diagram showing Li 2 The oxidation and/or reduction peak of O, the reaction process is judged to be the region in which the rare earth ions are not removed and the region in which the rare earth ions are completely removed and Li 2 In the region where O is excessive, stopping the addition of Li 2 O, continuously stirring for reaction; or Li in all of the electrochemical plots 2 The oxidation and/or reduction peak of O, the reaction process is judged to be that the rare earth ions in the reaction system are completely removed, and the Li addition is stopped 2 O and finishing the reaction.
For example, three different zones of the reaction system (e.g., upper, middle, and lower portions of the reaction system) are tested to obtain three electrochemical profiles. When the reaction process is judged, if Li does not appear in all three graphs 2 The oxidation and/or reduction peak of O indicates that rare earth ions are not removed in the reaction system, and Li is continuously added 2 O, and stirring; if Li appears in at least one of the three figures 2 Oxidation and/or reduction peaks of O, while at least one is free of Li 2 The oxidation and/or reduction peak of O indicates that the reaction time is insufficient, and the reaction is continued; if Li appears in all three figures 2 The oxidation and/or reduction peak of O indicates that the rare earth ions are completely removed, and the Li addition is stopped 2 O and finishing the reaction. Other numbers of zones of the reaction system may also be tested to obtain a corresponding number of electrochemical profiles. The present disclosure does not limit the number of test zones and electrochemical profiles. The judgment mode of testing the multiple regions of the reaction system to obtain multiple electrochemical graphs can avoid the problem that the reaction progress of different regions is inconsistent, and the limitation or deviation judgment is made only on the basis of the electrochemical graphs of one region or a part of regions. Therefore, the mode of carrying out multi-region test on the reaction system not only can ensure that the rare earth ions of the whole reaction system are completely removed, but also more accurately avoids Li 2 Excess of O.
According to some embodiments, the stirring is temporarily stopped and the reaction system is allowed to stand for a period of time, such as 2-10min, e.g. 3, 4, 5, 6, 7min, preferably 5min, before performing the electrochemical method test.
According to some embodiments, the method further comprises removing precipitates in the reaction system by using a reduced pressure distillation method or a molten salt filtration method after the reaction is finished to obtain the molten salt with the rare earth ions removed. Specifically, the reduced pressure distillation method utilizes the saturated vapor pressure difference of chloride and oxide or oxychloride to separate the chloride, and the used distillation device has large volume and long distillation time, but the obtained separated substance has high purity. Although filtration methods have high requirements for the filter medium, they can rapidly separate the chloride from the precipitate, and are the preferred separation method.
According to some embodiments, the method further comprises electrolyzing the rare earth ion-removed molten salt at 400 ℃ to 800 ℃, preferably 450 ℃ to 550 ℃ (e.g., 500 ℃) to remove excess Li 2 O, if any. Specifically, the electrolysis is performed by a potentiostatic method, and is stopped when the electrolysis current reaches 1 mA. Using Li 2 The decomposition voltage of O is less than that of fused salt, 1mA electrolytic current is used as an end point, and a potentiostatic electrolysis method is adopted to well remove excessive Li in the waste fused salt 2 And O, the waste molten salt is purified and can be recycled, and the minimization of the nuclear spent fuel post-treatment waste is realized.
According to some embodiments, the electrochemical method in which the electrochemical profile is obtained or the excess Li in the waste molten salt is removed 2 The electrolysis of O can use a three-electrode system, wherein the working electrode is a tungsten wire or a molybdenum wire (for example, three working electrodes with different lengths are assembled together and separated by ceramic, the working electrodes are inserted into the molten salt, the three working electrodes are respectively positioned at the upper part, the middle part and the bottom of the molten salt, the conduction states of the three electrodes are controlled so as to sequentially obtain electrochemical curves of different areas of the molten salt), and the auxiliary electrode is a graphite rod, a molybdenum rod or a tungsten rod; the reference electrode was Ag/AgCl. Preferably, the working electrode is made of molybdenum, and when the concentration of rare earth is higher, a more accurate electrochemical signal can still be obtained. The electrochemical curve graph is obtained remotely by using a three-electrode system which is matched with the electrochemical workstation and can be automatically lifted, the operation is convenient, the treatment process of the waste molten salt is not required to be interrupted, and the electrochemical curve graph is also obtained on lineAnd a sample of the waste molten salt is not required to be taken out, so that the danger of nuclear radiation to operators is well avoided.
The present application is further illustrated by the following specific examples.
Examples
38g LiCl, 45g KCl and 2g LaCl were weighed in this order 3 、2g CeCl 3 And 2g of NdCl 3 Used for preparing simulated waste molten salt (hereinafter referred to as molten salt); further, 0.2g, 0.1g, 0.05g, and 0.05g of Li were weighed in this order 2 And O is reserved.
Placing LiCl and KCl in a corundum crucible, heating to 500 deg.C to melt the two chlorides, and adding LaCl 3 、CeCl 3 And NdCl 3 And heated and stirred to 500 ℃ to melt 3 kinds of chlorides added later to prepare a molten salt.
Heating to keep the molten salt in a molten state, standing for 5 minutes, entering the middle part of the molten salt by using a three-electrode system (a Mo working electrode, a graphite auxiliary electrode and an Ag/AgCl reference electrode) connected with an electrochemical workstation, and carrying out test by using a square wave voltammetry to obtain a square wave voltammetry curve, as shown by a curve 1 in figure 1.
Sequentially adding the sequentially weighed Li while stirring 2 O, each addition of Li 2 And (3) reacting the system for 1min after O, standing for 5min, and obtaining a square wave voltammogram according to the method, wherein the square wave voltammogram is shown in figures 1-6.
And separating the fused salt from the precipitate by a fused salt filtration method.
Platinum is used as an anode, molybdenum is used as a cathode, constant potential electrolysis is carried out on the molten salt obtained by separation until the current is less than 1mA, so as to remove excessive Li 2 And (O). Subsequently, the molten salt was electrochemically tested by cyclic voltammetry and square wave voltammetry (both methods use a Mo working electrode, a graphite auxiliary electrode, and an Ag/AgCl reference electrode), and cyclic voltammetry and square wave voltammetry were obtained, and the results are shown in fig. 7 (cyclic voltammetry), fig. 8 (square wave voltammetry).
In each graph, the peak A is an oxidation and/or reduction peak of Li ion (A1 is an oxidation peak of Li ion, A2 is a reduction peak of Li ion), and the peak B is La ionEutectic reduction peak of Ce ion and Nd ion, peak C is Li 2 Reduction peak of O, peak D represents Nd 3+ When the concentration is high, the reduction peak of one step in the two-step 3 electron transfer process is obtained.
Curves 1-11 in FIGS. 1-3 correspond to the above non-addition and gradual addition of Li, respectively 2 Square wave voltammograms measured after O. With specific reference to FIGS. 1 and 2, peak B follows Li in curves 1-7 2 The addition of O is continuously reduced until the O disappears, which shows that the addition of O is accompanied by Li 2 And adding O, and continuously reducing the concentrations of La ions, Ce ions and Nd ions in the molten salt until the concentrations are lower than the detection lower limit of the electrochemical workstation. Intensity of peak C with Li in curves 8-11 of FIG. 3 2 The addition of O is increasing, which shows that with Li 2 Addition of O, Li in molten salt 2 The higher the O concentration, the smaller the increase of the peak intensity, indicating that Li in the molten salt 2 When the concentration of O reaches a certain value, REClO (wherein RE represents La ion, Ce ion or Nd ion) is driven to RE 2 O 3 The transformation of (3). Note that, in contrast to curve 2, peak B follows Li in curve 3 2 The addition of O did not undergo a significant decrease and an anomaly occurred due to the fact that a portion of REClO generated in the molten salt floated on the surface of the molten salt, and Li was added 2 O is firstly contacted with the catalyst to react to generate RE 2 O 3 A large portion is consumed.
Reference is further made to fig. 4-6. FIG. 4 shows curve 7 of FIG. 2 alone, where peak B has just disappeared; FIG. 5 shows curve 8 of FIG. 3 alone, with peak C just occurring in curve 8; and figure 5 shows curve 11 of figure 3 alone, with a larger peak C appearing in curve 11. The reaction systems corresponding to the curves 7, 8 and 11 were sampled, respectively, and the obtained samples were subjected to ICP (inductively coupled plasma) test. The results showed that the total residual amount of rare earth ions in the waste salt was 1458ppm when the peak B disappeared, 294ppm when the peak C appeared in the curve, and 47ppm when the larger peak C appeared. It can be seen that the total residual content of rare earth ions at the moment of the occurrence of the peak C in the curve is only about 300ppm, i.e. the rare earth ions are substantially completely removed, while Li is present 2 O is only slightly excessive, at which point the reaction can be terminatedTo more accurately avoid Li 2 Excess of O. If Li is continuously added 2 O, even if Li 2 When O is significantly excessive, the intensity of the peak C continues to increase, but the total residual amount of rare earth ions is only slightly decreased, which undoubtedly increases the burden of the subsequent electrolysis.
With further reference to FIGS. 7-8, Li 2 The reduction peak C of O disappears, and only the oxidation and/or reduction peak A of Li ions in the two figures shows that Li in the molten salt 2 O has been completely removed.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention.
Claims (10)
1. A method for removing rare earth ions from radioactive waste molten salt includes adding Li to the waste molten salt at 300-800 deg.C 2 O reacts to remove the rare earth ions.
2. The process of claim 1, wherein Li is added stepwise 2 O。
3. The method of claim 2, further comprising testing the reaction system during the reaction using an electrochemical method to obtain an electrochemical profile, and judging the progress of the reaction based on the obtained electrochemical profile.
4. The method of claim 3, wherein the electrochemical method comprises cyclic voltammetry, square wave voltammetry, or open-circuit chronopotentiometry.
5. The method of claim 3, wherein Li is present in the electrochemical plot 2 When the oxidation and/or reduction peak of O, judging the reaction process is that the rare earth ions are removed, and stopping adding Li 2 O and finishing the reaction.
6. The method of claim 3, wherein a plurality of different regions of the reaction system are tested to obtain a plurality of the electrochemical profiles, wherein,
absence of Li in none of the multiple electrochemical plots 2 Judging the reaction process is that the rare earth ions are not removed in the reaction system if the oxidation and/or reduction peak of O, and continuously adding Li 2 O；
At least one electrochemical profile of the plurality of electrochemical profiles is free of Li 2 Oxidation and/or reduction peaks of O, and at least one electrochemical diagram showing Li 2 The oxidation and/or reduction peak of O, judging that the reaction process is the region in which the rare earth ions are not removed and the region in which the rare earth ions are completely removed and Li still exist in the reaction system 2 In the region where O is excessive, stopping the addition of Li 2 O, continuing the reaction; or
Li is present in all of the multiple electrochemical plots 2 The oxidation and/or reduction peak of O, the reaction process is judged to be that the rare earth ions in the reaction system are completely removed, and Li addition is stopped 2 O and finishing the reaction.
7. The method of claim 3, wherein the waste molten salt is left to stand for 2-10min before the electrochemical method test is performed.
8. The method of claim 3, wherein the electrochemical process uses a three-electrode system in which the working electrode is a tungsten or molybdenum wire and the auxiliary electrode is a graphite rod, molybdenum rod or tungsten rod; the reference electrode was Ag/AgCl.
9. The method of any one of claims 1 to 8, wherein the method further comprises removing precipitates in the reaction system by using a vacuum distillation method or a molten salt filtration method after the reaction is finished to obtain a molten salt with rare earth ions removed; and optionally, electrolyzing the fused salt for removing the rare earth ions at 400-800 ℃ to remove excessive Li 2 O, preferably, the electrolysis uses a three-electrode system, wherein the working electrode is a tungsten wire or a molybdenum wire, and the auxiliary electrode is a graphite rod, a molybdenum rod or a tungsten rod; the reference electrode was Ag/AgCl.
10. The method of claim 9, wherein the electrolysis is performed by potentiostatic method, and the electrolysis is stopped when the electrolysis current reaches 1 mA.
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| CN108802159A (en) * | 2018-05-25 | 2018-11-13 | 哈尔滨工程大学 | A kind of method that electrochemical method monitors fused salt removal rare earth ion in real time |
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| CN108802159A (en) * | 2018-05-25 | 2018-11-13 | 哈尔滨工程大学 | A kind of method that electrochemical method monitors fused salt removal rare earth ion in real time |
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| 付海英 等: "乏燃料干法后处理中的熔盐减压蒸馏技术", 核技术, no. 04, pages 5 - 12 * |
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