CN114908381A - Method for removing rare earth ions in waste molten salt - Google Patents

Method for removing rare earth ions in waste molten salt Download PDF

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CN114908381A
CN114908381A CN202210482091.1A CN202210482091A CN114908381A CN 114908381 A CN114908381 A CN 114908381A CN 202210482091 A CN202210482091 A CN 202210482091A CN 114908381 A CN114908381 A CN 114908381A
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rare earth
molten salt
earth ions
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CN114908381B (en
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杨明帅
沈振芳
晏太红
许恒斌
王长水
叶国安
贾艳虹
肖益群
何辉
宋文臣
孟照凯
胡小飞
陈辉
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China Institute of Atomic of Energy
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    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25CPROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C5/00Electrolytic production, recovery or refining of metal powders or porous metal masses
    • C25C5/04Electrolytic production, recovery or refining of metal powders or porous metal masses from melts
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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

一种废熔盐中稀土离子的去除方法A method for removing rare earth ions in waste molten salt

技术领域technical field

本发明涉及核电乏燃料后处理领域,具体涉及一种废熔盐中稀土离子的去除方法,尤其是电解精炼法产生的废熔盐中稀土离子的去除方法。The invention relates to the field of post-processing of nuclear power spent fuel, in particular to a method for removing rare earth ions in waste molten salt, in particular to a method for removing rare earth ions in waste molten salt produced by an electrolytic refining method.

背景技术Background technique

发展清洁高效的绿色能源已经迫在眉睫。核电代表了绿色能源的重要的发展方向,目前正蓬勃发展,有望在未来成为主流能源之一。The development of clean and efficient green energy is imminent. Nuclear power represents an important development direction of green energy, is currently booming, and is expected to become one of the mainstream energy sources in the future.

仅依靠天然铀资源难以保证核电的可持续性发展,高效利用铀资源,尤其是核电燃料成为必然。目前核电工业多采用水法后处理工艺对核电工业产生的乏燃料进行处理。It is difficult to ensure the sustainable development of nuclear power only by relying on natural uranium resources, and efficient utilization of uranium resources, especially nuclear power fuel, is inevitable. At present, the nuclear power industry mostly adopts the water reprocessing process to treat the spent fuel produced by the nuclear power industry.

与水法后处理工艺相比,干法后处理工艺具有乏燃料冷却期短、步骤少、废料体积小等明显的优势。干法后处理工艺主要有氟化挥发法、熔盐液-液萃取法和以熔盐为介质的高温化学法(如电解精炼法)等。其中,电解精炼法最有发展前景。电解精炼法仍产生大量带有稀土离子的废熔盐,为使核废料的量最小化,需要将废熔盐净化复用。Compared with the water reprocessing process, the dry reprocessing process has obvious advantages such as short cooling period of spent fuel, few steps, and small waste volume. Dry post-treatment processes mainly include fluorination volatilization method, molten salt liquid-liquid extraction method and high temperature chemical method (such as electrolytic refining method) using molten salt as a medium. Among them, electrolytic refining is the most promising. Electrolytic refining still produces a large amount of waste molten salt with rare earth ions. In order to minimize the amount of nuclear waste, the waste molten salt needs to be purified and reused.

目前各国开发出的去除废熔盐中稀土离子的方法有磷酸盐沉淀法、沸石吸附法、氧气沉淀法等。磷酸盐沉淀法中磷酸根难以除去,在反应体系中引入了杂质离子。沸石吸附法使用大结构的4A型沸石,产生大量的废物,而且也难以将废熔盐中的稀土离子去除干净。虽然氧气沉淀法在去除稀土离子时不引入杂质离子,稀土离子去除率也较好,但该法产生大量的废气,污染环境;同时该法为气液反应,反应物接触不完全,反应速率慢。At present, the methods developed by various countries to remove rare earth ions in waste molten salt include phosphate precipitation, zeolite adsorption, and oxygen precipitation. Phosphate radicals are difficult to remove in the phosphate precipitation method, and impurity ions are introduced into the reaction system. The zeolite adsorption method uses 4A-type zeolite with a large structure, which produces a large amount of waste, and it is also difficult to remove the rare earth ions in the waste molten salt. Although the oxygen precipitation method does not introduce impurity ions when removing rare earth ions, and the removal rate of rare earth ions is also good, this method produces a large amount of waste gas and pollutes the environment; at the same time, this method is a gas-liquid reaction, the contact of the reactants is incomplete, and the reaction rate is slow .

因此,需要开发一种反应速率快、对环境污染少的废熔盐中稀土离子的去除方法。Therefore, it is necessary to develop a method for removing rare earth ions in waste molten salt with fast reaction rate and less environmental pollution.

发明内容SUMMARY OF THE INVENTION

有鉴于此,本发明的主要目的在于提供一种能解决上述问题中至少部分问题放射性废熔盐中稀土离子的去除方法。In view of this, the main purpose of the present invention is to provide a method for removing rare earth ions in radioactive waste molten salt which can solve at least part of the above problems.

根据本公开,提供一种放射性废熔盐中稀土离子的去除方法,包括向300℃~800℃的所述废熔盐中加入Li2O进行反应以去除所述稀土离子。According to the present disclosure, a method for removing rare earth ions in radioactive waste molten salt is provided, which includes adding Li 2 O to the waste molten salt at 300° C.˜800° C. for reaction to remove the rare earth ions.

根据一些实施方式,Li2O是逐步加入的。According to some embodiments, Li 2 O is added gradually.

根据一些实施方式,所述方法还包括在所述反应过程中,利用电化学方法测试反应体系,获得电化学曲线图,并根据所获得的电化学曲线图判断反应进程。According to some embodiments, the method further includes, during the reaction, testing the reaction system by an electrochemical method, obtaining an electrochemical curve, and judging the reaction progress according to the obtained electrochemical curve.

根据一些实施方式,所述电化学方法包括循环伏安法、方波伏安法或开路计时电位法。According to some embodiments, the electrochemical method comprises cyclic voltammetry, square wave voltammetry, or open circuit chronopotentiometry.

根据一些实施方式,所述电化学曲线图中出现Li2O的氧化和/或还原峰时,判断所述反应进程为所述稀土离子已去除,停止加入Li2O并结束反应。According to some embodiments, when the oxidation and/or reduction peaks of Li 2 O appear in the electrochemical curve, it is determined that the reaction progress is that the rare earth ions have been removed, the addition of Li 2 O is stopped, and the reaction is terminated.

根据一些实施方式,测试所述反应体系的多个不同区域,获得多张所述电化学曲线图,其中,According to some embodiments, a plurality of different regions of the reaction system are tested to obtain a plurality of the electrochemical graphs, wherein,

所述多张电化学曲线图中均未出现Li2O的氧化和/或还原峰,则判断所述反应进程为反应体系中仍有所述稀土离子未去除,继续加入Li2O;If no oxidation and/or reduction peaks of Li 2 O appear in the multiple electrochemical curves, it is judged that the reaction progress is that the rare earth ions are still not removed in the reaction system, and Li 2 O is continued to be added;

所述多张电化学曲线图中至少有一张电化学曲线图未出现Li2O的氧化和/ 或还原峰,且至少有一张电化学曲线图出现Li2O的氧化和/或还原峰,则判断所述反应进程为所述反应体系中仍存在所述稀土离子尚未去除的区域以及所述稀土离子已完全去除且Li2O过量的区域,停止加入Li2O,继续反应;或If at least one of the electrochemical curves does not show the oxidation and/or reduction peaks of Li 2 O, and at least one of the electrochemical curves shows the oxidation and/or reduction peaks of Li 2 O, then It is judged that the reaction progress is a region in the reaction system where the rare earth ions have not been removed and a region where the rare earth ions have been completely removed and Li 2 O is excessive, stop adding Li 2 O, and continue the reaction; or

所述多张电化学曲线图中均出现Li2O的氧化和/或还原峰,则判断所述反应进程为所述反应体系中所述稀土离子已完全去除,停止加入Li2O并结束反应。If the oxidation and/or reduction peaks of Li 2 O appear in the multiple electrochemical curves, it is judged that the reaction progress is that the rare earth ions in the reaction system have been completely removed, the addition of Li 2 O is stopped and the reaction is terminated .

所述多个不同区域包括反应体系的上部、中部和下部。所述多张电化学曲线图至少为3张。The plurality of different zones include upper, middle and lower parts of the reaction system. The plurality of electrochemical graphs are at least three.

根据一些实施方式,进行所述电化学方法测试前,将所述废熔盐静置2~10min,例如3、4、5、6、7分钟。According to some embodiments, before performing the electrochemical method test, the spent molten salt is allowed to stand for 2-10 minutes, such as 3, 4, 5, 6, 7 minutes.

根据一些实施方式,在所述电化学方法中使用三电极体系,其中工作电极为钨丝或钼丝,辅助电极为石墨棒、钼棒或钨棒;参比电极为Ag/AgCl。According to some embodiments, a three-electrode system is used in the electrochemical method, wherein the working electrode is a tungsten wire or a molybdenum wire, the auxiliary electrode is a graphite rod, a molybdenum rod or a tungsten rod; and the reference electrode is Ag/AgCl.

根据一些实施方式,所述方法还包括在反应结束后,采用真空蒸馏法或熔盐过滤法将反应体系中的沉淀物去除获得去除稀土离子的熔盐。任选地,当去除稀土离子的熔盐中存在过量的Li2O时,所述方法还包括对所述去除稀土离子的熔盐在400℃~800℃进行电解以去除过量的Li2O。According to some embodiments, the method further includes, after the reaction is completed, using vacuum distillation or molten salt filtration to remove the precipitate in the reaction system to obtain a molten salt from which rare earth ions are removed. Optionally, when there is excess Li 2 O in the rare earth ion-removing molten salt, the method further includes electrolyzing the rare earth ion-removing molten salt at 400° C.˜800° C. to remove the excess Li 2 O.

根据一些实施方式,所述电解采用恒电位法,当电解电流达到1mA时,停止电解。According to some embodiments, the electrolysis adopts a potentiostatic method, and when the electrolysis current reaches 1 mA, the electrolysis is stopped.

根据一些实施方式,所述电解使用三电极体系,其中工作电极为钨丝或钼丝,辅助电极为石墨棒、钼棒或钨棒;参比电极为Ag/AgCl。According to some embodiments, the electrolysis uses a three-electrode system, wherein the working electrode is a tungsten wire or a molybdenum wire, the auxiliary electrode is a graphite rod, a molybdenum rod or a tungsten rod; and the reference electrode is Ag/AgCl.

通过向300℃~800℃的放射性废熔盐中加入Li2O进行液相反应,避免了大量废气的产生,具有反应速率快、对环境污染少的优点。同时该方法还保证了稀土离子去除效果,也并未引入难以除去的杂质离子或产生大量的废物。By adding Li 2 O to the radioactive waste molten salt at 300°C to 800°C to carry out the liquid phase reaction, the generation of a large amount of waste gas is avoided, and the reaction rate is fast and the environmental pollution is less. At the same time, the method also ensures the removal effect of rare earth ions, and does not introduce impurity ions that are difficult to remove or generate a large amount of waste.

附图说明Description of drawings

图1示出了实施例中使用方波伏安法分别测试未加入Li2O的熔盐以及在熔盐中累计加入0.20g、0.40g Li2O并反应后的反应体系获得的电化学曲线图;Fig. 1 shows the electrochemical curves obtained by using square wave voltammetry to test the molten salt without adding Li 2 O and the reaction system after accumulatively adding 0.20g and 0.40g Li 2 O to the molten salt and reacting respectively in the embodiment. picture;

图2示出了实施例中使用方波伏安法分别测试在熔盐中累计加入0.50g、 0.60g、0.65g、0.70g Li2O并反应后的反应体系获得的电化学曲线图;Figure 2 shows the electrochemical curves obtained by using square wave voltammetry to test the reaction system obtained by accumulatively adding 0.50g, 0.60g, 0.65g, 0.70g Li 2 O to molten salt and reacting respectively in the embodiment;

图3示出了实施例中使用方波伏安法分别测试在熔盐中累计加入0.75g、 0.80g、0.85g、0.90g Li2O并反应后的反应体系获得的电化学曲线图;3 shows the electrochemical curves obtained by using square wave voltammetry to test the reaction system obtained by accumulatively adding 0.75g, 0.80g, 0.85g, 0.90g Li 2 O in molten salt and reacting respectively in the embodiment;

图4示出了实施例中使用方波伏安法测试在熔盐中累计加入0.70g Li2O并反应后的反应体系获得的电化学曲线图;Fig. 4 shows the electrochemical curve obtained by using square wave voltammetry to test the reaction system after accumulatively adding 0.70g Li 2 O in molten salt and reacting in the embodiment;

图5示出了实施例中使用方波伏安法测试在熔盐中累计加入0.75g Li2O并反应后的反应体系获得的电化学曲线图;Fig. 5 shows the electrochemical curve obtained by using square wave voltammetry to test the reaction system after accumulatively adding 0.75g Li 2 O to molten salt and reacting in the embodiment;

图6示出了实施例中使用方波伏安法测试在熔盐中累计加入0.90g Li2O并反应后的反应体系获得的电化学曲线图;Fig. 6 shows the electrochemical curve obtained by using square wave voltammetry to test the reaction system after accumulatively adding 0.90g Li 2 O to molten salt and reacting in the embodiment;

图7示出了实施例中使用循环伏安法测试过滤后的熔盐经电解后获得的电化学曲线图;Fig. 7 shows the electrochemical graph obtained after electrolysis of the filtered molten salt using cyclic voltammetry in the embodiment;

图8示出了实施例中使用方波伏安法测试过滤后的熔盐经电解后获得的电化学曲线图。FIG. 8 shows an electrochemical curve obtained by using square wave voltammetry to test the filtered molten salt after electrolysis.

具体实施方式Detailed ways

下面将结合本申请实施方式及附图,对本申请实施方式中的技术方案进行清楚、完整地描述,显然,所描述的实施方式仅仅是本申请的一部分实施方式,而不是全部的实施方式。基于本申请中的实施方式,本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施方式,都属于本申请保护的范围。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. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

在整个说明书中,除非另有特别说明,本文使用的术语应理解为如本领域中通常所使用的含义。因此,除非另有定义,本文使用的所有技术和科学术语具有与本申请所属领域技术人员的一般理解相同的含义。若存在矛盾,本说明书优先。Throughout the specification, unless specifically stated otherwise, terms used herein are to be understood as commonly used in the art. Therefore, unless otherwise defined, 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. In case of conflict, the present specification takes precedence.

本公开意在提供一种反应速率快、对环境污染少的废熔盐中稀土离子的去除方法,以应用于核电乏燃料后处理领域,尤其是核电乏燃料干法后处理领域,更尤其是电解精炼法产生的废熔盐的净化领域。其中,电解精炼时产生的废熔盐中含有诸如LiCl-KCl共熔盐和大量稀土元素,例如,总含量>1000ppm的 La、Ce、Pr、Nd、Y等稀土元素。The present disclosure is intended to provide a method for removing rare earth ions in waste molten salt with fast reaction rate and less environmental pollution, so as to be applied in the field of nuclear power spent fuel reprocessing, especially in the field of dry reprocessing of nuclear power spent fuel, more particularly The field of purification of waste molten salt produced by electrolytic refining. Among them, the waste molten salt produced during electrolytic refining contains such as LiCl-KCl eutectic salt and a large amount of rare earth elements, such as La, Ce, Pr, Nd, Y and other rare earth elements with a total content of >1000ppm.

为实现上述目的,本申请提供一种放射性废熔盐中稀土离子的去除方法,包括向300℃~800℃,优选450℃~550℃的废熔盐中加入Li2O进行反应以去除稀土离子。In order to achieve the above purpose, the present application provides a method for removing rare earth ions in radioactive waste molten salt, comprising adding Li 2 O to the waste molten salt at 300°C to 800°C, preferably 450°C to 550°C for reaction to remove rare earth ions .

发明人发现通过向含有熔盐和大量稀土元素(例如,总含量>1000ppm的 La、Ce、Pr、Nd、Y等元素)的放射性废熔盐中加入Li2O,边搅拌边进行置换反应,将废熔盐中可溶性的稀土氯离子转化为不溶的氯氧稀土或者氧化稀土沉淀物以去除稀土离子。该反应速度较快,反应彻底,稀土元素去除率高,且不引入其他离子,也不会产生废气。而且即使有过量的氧化锂,也可方便地通过电解除去。The inventors found that by adding Li 2 O to the radioactive waste molten salt containing molten salt and a large amount of rare earth elements (for example, elements such as La, Ce, Pr, Nd, Y, etc., with a total content of >1000 ppm), the displacement reaction is carried out while stirring, The soluble rare earth chloride ions in the waste molten salt are converted into insoluble rare earth oxychloride or rare earth oxide precipitates to remove rare earth ions. The reaction speed is fast, the reaction is thorough, the removal rate of rare earth elements is high, and no other ions are introduced, and no waste gas is generated. And even if there is excess lithium oxide, it can be easily removed by electrolysis.

本公开对放射性废熔盐没有特别限制,任何由核电乏燃料电解精炼后处理产生的废熔盐均可适用于本发明的方法。熔盐通常是两种或更多种混合盐,典型地,可以是LiCl-KCl共熔盐,但不限于此。The present disclosure has no particular limitation on the radioactive waste molten salt, and any waste molten salt produced by the post-processing of the electrolytic refining of nuclear power spent fuel can be applied to the method of the present invention. The molten salt is usually two or more mixed salts, typically, it may be a LiCl-KCl eutectic salt, but not limited thereto.

以下示例性地说明本方法的具体步骤。以下示例性说明仅为了方便理解,而本方法并不限于以下描述的内容。The specific steps of the method are exemplified below. The following exemplary description is only for the convenience of understanding, and the present method is not limited to the content described below.

由于本方法涉及放射性物质的处理,因此采用无人自动化装置进行远程控制反应进程。所述方法使用装有自动升降系统、可远程控制的搅拌装置的反应系统进行反应。搅拌桨的材质可为刚玉、不锈钢、镍基合金、钨等耐高温耐辐射腐蚀的材质。Since the method involves the handling of radioactive materials, an unmanned automated device is used to remotely control the reaction process. The method uses a reaction system equipped with an automatic lifting system and a remotely controllable stirring device to carry out the reaction. The material of the stirring paddle can be corundum, stainless steel, nickel-based alloy, tungsten and other materials that are resistant to high temperature and radiation corrosion.

将放射性废熔盐引入上述反应系统中,升温至300℃~800℃,在搅拌下加入Li2O进行反应。优选地,反应温度为450℃~550℃,例如500℃。反应的时间为0.1~2h。需要说明的是,可以根据废熔盐的量及反应温度调整反应时间,本申请对反应时间不作特别限制。The radioactive waste molten salt is introduced into the above reaction system, the temperature is raised to 300°C to 800°C, and Li 2 O is added under stirring to carry out the reaction. Preferably, the reaction temperature is 450°C to 550°C, for example 500°C. The reaction time is 0.1~2h. It should be noted that the reaction time can 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.

由于本方法的反应是液相反应,避免了废气的产生,具有反应速率快、对环境污染少的优点。此外,在保证稀土离子去除效果的前提下,该方法并未引入难以除去的杂质离子,也不产生大量的废物。Since the reaction of the method is a liquid-phase reaction, the generation of waste gas is avoided, and the reaction rate is fast and the environmental pollution is less. In addition, on the premise of ensuring the removal effect of rare earth ions, the method does not introduce impurity ions that are difficult to remove, and does not generate a large amount of waste.

根据一些实施方式,Li2O是逐步加入的。即在反应开始时,Li2O的加入量低于化学反应当量,随反应进行不断补充加入Li2O。例如,可以在反应中依次加入等量的Li2O;也可以随反应进行不断减少Li2O的加入量,例如以加入量梯度减少的方式加入Li2O,但不限于此。这种方式可以在一定程度上避免Li2O 的过量。According to some embodiments, Li 2 O is added gradually. That is, at the beginning of the reaction, the amount of Li 2 O added is lower than the chemical reaction equivalent, and Li 2 O is continuously added as the reaction proceeds. For example, the same amount of Li 2 O may be added in sequence during the reaction; the addition amount of Li 2 O may also be continuously reduced as the reaction proceeds, for example, Li 2 O may be added in a manner of decreasing the addition amount in a gradient manner, but not limited to this. In this way, the excess of Li 2 O can be avoided to a certain extent.

根据优选的实施方式,所述方法还包括在反应过程中,利用电化学方法测试反应体系中的反应进程,以便能够实时判断反应终点,及时终止反应。由于Li2O的氧化还原电位低,因此一旦反应体系中存在过量的Li2O,就能够检测到 Li2O的氧化和/或还原峰,从而确定反应完成。以这样的方式可以减少试剂,即 Li2O的使用量,且能够避免Li2O过量后的后处理步骤。According to a preferred embodiment, the method further includes, during the reaction, using an electrochemical method to test the reaction progress in the reaction system, so that the reaction end point can be judged in real time, and the reaction can be terminated in time. Due to the low redox potential of Li 2 O, once excess Li 2 O exists in the reaction system, the oxidation and/or reduction peaks of Li 2 O can be detected, thereby confirming the completion of the reaction. In this way, the amount of reagent, ie, Li 2 O, can be reduced, and post-processing steps after an excess of Li 2 O can be avoided.

具体地,根据一些实施方式,监测反应进程的电化学方法可为循环伏安法、方波伏安法或开路计时电位法。因监测前后电极表面变化程度小,循环伏安法较常用。使用开路计时电位法监测可获得较高的准确性,但时间较长。方波伏安法对电化学信号的响应较为灵敏,可快速获得电化学曲线图,为优选的电化学监测方法。通过电化学方法获得电化学曲线图,并据此判断反应进程。Specifically, according to some embodiments, the electrochemical method for monitoring the progress of the reaction may be cyclic voltammetry, square wave voltammetry, or open circuit chronopotentiometry. Cyclic voltammetry is more commonly used due to the small change in the electrode surface before and after monitoring. Monitoring with open-circuit chronopotentiometry can achieve higher accuracy, but for longer periods of time. Square wave voltammetry is more sensitive to electrochemical signals and can quickly obtain electrochemical curves, which is the preferred electrochemical monitoring method. The electrochemical curve is obtained by electrochemical method, and the reaction progress is judged accordingly.

具体地,根据一些实施方式,在判断反应进程时,电化学曲线图中出现Li2O 的氧化和/或还原峰时,判断反应进程为稀土离子已去除,停止加入Li2O并结束反应。现有的以金属电位判断反应终点的方式,因电化学检测限的存在,判断常有误差。以Li2O的氧化和/或还原峰出现与否判断反应终点的方式更准确,可更精准的避免Li2O的过量。Specifically, according to some embodiments, when judging the progress of the reaction, when the oxidation and/or reduction peaks of Li 2 O appear in the electrochemical curve, it is judged that the reaction progress is that rare earth ions have been removed, the addition of Li 2 O is stopped and the reaction is terminated. In the existing method of judging the reaction end point by metal potential, there are often errors in judgment due to the existence of the electrochemical detection limit. It is more accurate to judge the end point of the reaction by the presence or absence of the oxidation and/or reduction peaks of Li 2 O, and the excess of Li 2 O can be avoided more accurately.

更进一步地,根据优选实施方式,测试反应体系的多个不同区域,获得多张电化学曲线图。在判断反应进程时,多张电化学曲线图中均未出现Li2O的氧化和/或还原峰,则判断反应进程为反应体系中仍有稀土离子未去除,继续加入 Li2O;多张电化学曲线图中至少有一张电化学曲线图未出现Li2O的氧化和/或还原峰,且至少有一张电化学曲线图出现Li2O的氧化和/或还原峰,则判断反应进程为反应体系中仍存在稀土离子尚未去除的区域以及稀土离子已完全去除且Li2O过量的区域,停止加入Li2O,继续搅拌进行反应;或多张电化学曲线图中均出现Li2O的氧化和/或还原峰,则判断反应进程为反应体系中稀土离子已完全去除,停止加入Li2O并结束反应。Further, according to a preferred embodiment, a plurality of different regions of the reaction system are tested to obtain a plurality of electrochemical curves. When judging the progress of the reaction, if no oxidation and/or reduction peaks of Li 2 O appeared in the multiple electrochemical curves, it was judged that the reaction progress was that there were still rare earth ions in the reaction system that had not been removed, and Li 2 O was continued to be added; If there is no oxidation and/or reduction peak of Li 2 O in at least one of the electrochemical curves, and there is an oxidation and/or reduction peak of Li 2 O in at least one of the electrochemical curves, the reaction process is judged as There are still areas in the reaction system where the rare earth ions have not been removed and areas where the rare earth ions have been completely removed and the Li 2 O is excessive, stop adding Li 2 O, and continue to stir for the reaction; or Li 2 O appears in multiple electrochemical curves. Oxidation and/or reduction peaks, it is judged that the reaction progress is that the rare earth ions in the reaction system have been completely removed, the addition of Li 2 O is stopped and the reaction is terminated.

例如,测试反应体系的三个不同区域(如反应体系的上、中、下部),获得三张电化学曲线图。在判断反应进程时,若三张图中均未出现Li2O的氧化和/ 或还原峰,说明反应体系中仍有稀土离子未去除,继续加入Li2O,并搅拌;若三张图中至少有一张出现了Li2O的氧化和/或还原峰,同时至少有一张未出现 Li2O的氧化和/或还原峰,说明反应时间不足,继续反应;若三张图中均出现了Li2O的氧化和/或还原峰,说明稀土离子已完全去除,停止加入Li2O并结束反应。也可以对其它数目的反应体系的区域进行测试,获得相应数目的电化学曲线图。本公开对测试区域及电化学曲线图的数目不作限制。这种测试反应体系的多个区域以获得多张电化学曲线图的判断方式能够避免因不同区域反应进程不一致而仅基于某一个或部分区域的电化学曲线图做出局限性或有偏差的判断的问题。因此,对反应体系进行多区域测试的方式不仅能够确保将整个反应体系的稀土离子完全去除,而且更精准的避免了Li2O的过量。For example, three different regions of the reaction system (eg, upper, middle, and lower parts of the reaction system) are tested, and three electrochemical curves are obtained. When judging the progress of the reaction, if the oxidation and/or reduction peaks of Li 2 O do not appear in the three pictures, it means that there are still rare earth ions in the reaction system that have not been removed. Continue to add Li 2 O and stir; if at least one of the three pictures appears The oxidation and/or reduction peaks of Li 2 O are detected, and at least one of the oxidation and/or reduction peaks of Li 2 O does not appear, indicating that the reaction time is insufficient and the reaction continues; if the oxidation and/or reduction of Li 2 O appears in all three figures Or the reduction peak, indicating that the rare earth ions have been completely removed, stop adding Li 2 O and end the reaction. Other numbers of regions of the reaction system can also be tested to obtain a corresponding number of electrochemical plots. The present disclosure does not limit the number of test areas and electrochemical graphs. This judgment method of testing multiple regions of the reaction system to obtain multiple electrochemical graphs can avoid making limited or biased judgments based only on the electrochemical graphs of a certain or part of the regions due to inconsistent reaction processes in different regions. The problem. Therefore, the method of multi-regional testing of the reaction system can not only ensure the complete removal of rare earth ions in the entire reaction system, but also more accurately avoid the excess of Li 2 O.

根据一些实施方式,进行电化学方法测试前,暂时停止搅拌,使反应体系静置一段时间,如2-10min,例如3、4、5、6、7min,优选5min。According to some embodiments, before the electrochemical method test, the stirring is temporarily stopped, and the reaction system is allowed to stand for a period of time, such as 2-10 min, such as 3, 4, 5, 6, 7 min, preferably 5 min.

根据一些实施方式,所述方法还包括在反应结束后,采用减压蒸馏法或熔盐过滤法将反应体系中的沉淀物去除获得去除稀土离子的熔盐。具体地,减压蒸馏法利用氯化物与氧化物或氯氧化物的饱和蒸气压差将其分离,所用蒸馏装置体积大且蒸馏时间长,但是所得分离物纯度较高。过滤法虽对滤材有较高要求,但可快速将氯化物与沉淀物分离,为优选的分离方法。According to some embodiments, the method further includes removing the precipitate in the reaction system by a vacuum distillation method or a molten salt filtration method after the reaction ends to obtain a molten salt from which rare earth ions are removed. Specifically, the vacuum distillation method utilizes the saturated vapor pressure difference between chlorides and oxides or oxychlorides to separate them, and the used distillation apparatus is bulky and the distillation time is long, but the purity of the obtained separation product is relatively high. Although the filtration method has higher requirements on the filter material, it can quickly separate the chloride and the precipitate, which is the preferred separation method.

根据一些实施方式,所述方法还包括,对去除稀土离子的熔盐在400℃~800,优选450℃~550℃(例如500℃)下进行电解以去除过量的Li2O,如果有的话。具体地,电解采用恒电位法,当电解电流达到1mA时,停止电解。利用Li2O 的分解电压小于熔盐的分解电压的特点,以1mA的电解电流为判断终点,采用恒电位法电解法很好的去除了废熔盐中过量的Li2O,使得废熔盐不仅得到净化,还可循环使用,实现了核电乏燃料后处理废物的最小化。According to some embodiments, the method further comprises electrolyzing the rare earth ion-removing molten salt at 400°C to 800°C, preferably 450°C to 550°C (eg 500°C) to remove excess Li 2 O, if any . Specifically, the electrolysis adopts a potentiostatic method, and when the electrolysis current reaches 1 mA, the electrolysis is stopped. Taking advantage of the fact that the decomposition voltage of Li 2 O is lower than that of molten salt, the electrolytic current of 1 mA is used as the judgment end point, and the potentiostatic electrolysis method is used to remove the excess Li 2 O in the waste molten salt well, making the waste molten salt Not only is it purified, but it can also be recycled, which minimizes the reprocessing waste of nuclear power spent fuel.

根据一些实施方式,其中,获取电化学曲线图的电化学方法或去除废熔盐中过量Li2O的电解均可使用三电极体系,其中工作电极为钨丝或钼丝(例如,将三根长度不同的工作电极组装在一起,并通过陶瓷隔开,将工作电极插入熔盐中,三根工作电极分别处于熔盐上部、中部和底部,控制三根电极的导通状态,以依次获取熔盐不同区域的电化学曲线图),辅助电极为石墨棒、钼棒或钨棒;参比电极为Ag/AgCl。优选地,工作电极的材质为钼,在稀土浓度比较高时,仍可获得较为准确的电化学信号。远程使用与电化学工作站相配合且可自动升降的三电极体系在线获得电化学曲线图,操作方便,无需中断废熔盐的处理进程,也无需取出废熔盐的样品,很好的避免了操作人员遭受核辐射的危险。According to some embodiments, the electrochemical method for obtaining the electrochemical graph or the electrolysis for removing excess Li 2 O in the spent molten salt can use a three-electrode system, wherein the working electrode is a tungsten wire or a molybdenum wire (for example, three lengths of Different working electrodes are assembled together and separated by ceramics. The working electrodes are inserted into the molten salt. The three working electrodes are located at the upper, middle and bottom of the molten salt, respectively. The conduction state of the three electrodes is controlled to obtain different areas of the molten salt in turn. The electrochemical curve), the auxiliary electrode is a graphite rod, a molybdenum rod or a tungsten rod; the reference electrode is Ag/AgCl. Preferably, the material of the working electrode is molybdenum, and when the rare earth concentration is relatively high, a relatively accurate electrochemical signal can still be obtained. Remotely use the three-electrode system that cooperates with the electrochemical workstation and can be automatically raised and lowered to obtain the electrochemical curve online. It is easy to operate, and there is no need to interrupt the treatment process of the waste molten salt, and it is not necessary to take out the sample of the waste molten salt, which avoids the operation. risk of exposure to nuclear radiation.

以下,通过具体实施例来进一步说明本申请。Hereinafter, the present application will be further described through specific examples.

实施例Example

依次称量38g LiCl、45g KCl、2g LaCl3、2g CeCl3和2g NdCl3用于制备模拟废熔盐(以下简称熔盐);另依次称取0.2g、0.2g、0.1g、0.1g、0.05g、0.05g、 0.05g、0.05g、0.05g、0.05g的Li2O备用。Weigh 38g LiCl, 45g KCl, 2g LaCl 3 , 2g CeCl 3 and 2g NdCl 3 in turn for the preparation of simulated waste molten salt (hereinafter referred to as molten salt); 0.05g, 0.05g, 0.05g, 0.05g, 0.05g, 0.05g of Li 2 O were used for later use.

将LiCl和KCl放入刚玉坩埚中,加热到500℃使两种氯化物熔融,随后加入LaCl3、CeCl3和NdCl3,并加热搅拌至500℃使后加入的3种氯化物熔融,以制备熔盐。Put LiCl and KCl in a corundum crucible, heat to 500 ° C to melt the two chlorides, then add LaCl 3 , CeCl 3 and NdCl 3 , and heat and stir to 500 ° C to melt the three chlorides added later, to prepare molten salt.

加热保持熔盐的熔融状态,静置5分钟,利用与电化学工作站相连接的三电极体系(Mo工作电极,石墨辅助电极,Ag/AgCl参比电极)进入熔盐中部,以方波伏安法进行测试,获取方波伏安曲线,如图1中曲线1所示。Heating to maintain the molten state of the molten salt, let stand for 5 minutes, use the three-electrode system (Mo working electrode, graphite auxiliary electrode, Ag/AgCl reference electrode) connected to the electrochemical workstation to enter the middle of the molten salt, and use square wave voltammetry to enter the middle of the molten salt. The test method is used to obtain the square wave voltammetry curve, as shown in curve 1 in Figure 1.

边搅拌边按顺序加入上述依次称取的Li2O,每次加入Li2O后让体系反应 1min,随后静置5min,按上述方法获取的方波伏安曲线,如图1-6所示。Add the above Li 2 O weighed in sequence while stirring, let the system react for 1 min after each addition of Li 2 O, and then let it stand for 5 min. The square wave voltammetry curve obtained by the above method is shown in Figure 1-6 .

以熔盐过滤法分离熔盐与沉淀物。The molten salt and the precipitate were separated by molten salt filtration.

以铂为阳极,以钼为阴极,对分离得到的熔盐进行恒电位电解,直至电流小于1mA,以去除过量的Li2O。随后,以循环伏安法和方波伏安法(两种方法均使用Mo工作电极,石墨辅助电极,Ag/AgCl参比电极)电化学测试熔盐,获得循环伏安曲线和方波伏安曲线,结果如图7(循环伏安曲线)、图8(方波伏安曲线)所示。Using platinum as the anode and molybdenum as the cathode, the separated molten salt is electrolyzed at a constant potential until the current is less than 1 mA to remove excess Li 2 O. Subsequently, the molten salt was electrochemically tested by cyclic voltammetry and square wave voltammetry (both methods used Mo working electrode, graphite counter electrode, Ag/AgCl reference electrode) to obtain cyclic voltammetry curves and square wave voltammetry The results are shown in Figure 7 (cyclic voltammetry curve) and Figure 8 (square wave voltammetry curve).

其中,在各图中,各曲线中峰A为Li离子的氧化和/或还原峰(A1为Li 离子的氧化峰,A2为Li离子的还原峰),峰B为La离子、Ce离子和Nd离子的共熔还原峰,峰C为Li2O的还原峰,峰D代表Nd3+浓度高时,其两步3电子转移过程中的其中一步的还原峰。Among them, in each figure, peak A in each curve is the oxidation and/or reduction peak of Li ion (A1 is the oxidation peak of Li ion, A2 is the reduction peak of Li ion), and peak B is La ion, Ce ion and Nd ion The eutectic reduction peak of ions, peak C is the reduction peak of Li 2 O, and peak D represents the reduction peak of one of the two-step 3-electron transfer process when the Nd 3+ concentration is high.

图1-3中曲线1-11分别对应以上未加入和逐步加入Li2O后测定的方波伏安曲线。具体参考图1和图2,曲线1-7中峰B随着Li2O的加入而不断降低直至消失,说明随着Li2O的加入,熔盐中的La离子、Ce离子和Nd离子的浓度不断降低直至低到超出电化学工作站的检测下限。图3中曲线8-11中峰C的强度随着Li2O的加入不断增大,说明随着Li2O的加入,熔盐中的Li2O浓度越来越高,但是峰强度增加的幅度越来越小,说明当熔盐中Li2O达到一定浓度时,开始推动REClO(其中RE代表La离子、Ce离子或Nd离子)向RE2O3的转化。需要说明的是,与曲线2对比,曲线3中峰B随着Li2O的加入并未发生明显的降低,出现了反常,归因于熔盐中生成的一部分REClO漂浮在熔盐表面,加入 Li2O首先与其接触、反应,生成RE2O3,被消耗了很大一部分。Curves 1-11 in Fig. 1-3 correspond to the square wave voltammetry curves measured above without adding Li 2 O and gradually adding Li 2 O respectively. Referring specifically to Figures 1 and 2, the peak B in curves 1-7 decreases continuously until disappearing with the addition of Li 2 O, indicating that with the addition of Li 2 O, the concentration of La ion, Ce ion and Nd ion in the molten salt increases. The concentration is continuously decreased until it falls below the detection limit of the electrochemical workstation. The intensity of peak C in curves 8-11 in Fig. 3 increases continuously with the addition of Li 2 O, indicating that with the addition of Li 2 O, the concentration of Li 2 O in the molten salt is higher and higher, but the peak intensity increases with the addition of Li 2 O. The amplitude becomes smaller and smaller, indicating that when Li 2 O in the molten salt reaches a certain concentration, it starts to promote the conversion of REClO (where RE represents La ion, Ce ion or Nd ion) to RE 2 O 3 . It should be noted that, compared with curve 2, the peak B in curve 3 did not decrease significantly with the addition of Li 2 O, and an abnormality occurred, which was attributed to a part of REClO generated in the molten salt floating on the surface of the molten salt. Li 2 O first contacts and reacts with it to generate RE 2 O 3 , and a large part of it is consumed.

进一步参考图4-6。图4单独示出了图2中曲线7,在曲线7中峰B刚刚消失;图5单独示出了图3中曲线8,在曲线8中峰C刚出现;和图5单独示出了图3中曲线11,在曲线11中出现较大的峰C。分别对曲线7、8和11对应的反应体系取样,对所获样品进行ICP(电感耦合等离子体)测试。结果表明峰B 消失时,废盐中稀土离子的总残余量为1458ppm,曲线中刚出现峰C时,废盐中稀土离子的总残余量为294ppm,而出现较大的峰C时,稀土离子的总残余量降至47ppm。可见在曲线中刚出现峰C时,稀土离子总残余量仅约300ppm,即基本彻底除去了稀土离子,同时Li2O仅稍过量,此时结束反应可以更精准的避免Li2O的过量。若继续加入Li2O,即使Li2O明显过量时,虽峰C的强度继续增大,但稀土离子的总残余量仅略有下降,无疑增加了后续电解的负担。Further reference is made to Figures 4-6. Fig. 4 shows curve 7 in Fig. 2 alone, in which peak B has just disappeared; Fig. 5 shows curve 8 in Fig. 3 alone, in which peak C has just appeared; and Fig. 5 alone shows the graph In curve 11 in 3, the larger peak C appears in curve 11. The reaction systems corresponding to curves 7, 8 and 11 were sampled respectively, and the obtained samples were subjected to ICP (Inductively Coupled Plasma) test. The results show that when peak B disappears, the total residual amount of rare earth ions in the waste salt is 1458 ppm, when peak C just appears in the curve, the total residual amount of rare earth ions in the waste salt is 294 ppm, and when a larger peak C appears, rare earth ions The total residual amount dropped to 47ppm. It can be seen that when the peak C just appeared in the curve, the total residual amount of rare earth ions was only about 300 ppm, that is, the rare earth ions were basically completely removed, and Li 2 O was only slightly excessive. At this time, the reaction can be more accurately avoided. Li 2 O excess. If Li 2 O is continued to be added, even when Li 2 O is obviously excessive, although the intensity of peak C continues to increase, the total residual amount of rare earth ions only decreases slightly, which undoubtedly increases the burden of subsequent electrolysis.

进一步参考图7-8,Li2O的还原峰C消失了,两图中只有Li离子的氧化和 /或还原峰A,说明熔盐中Li2O已完全去除。Further referring to Figures 7-8, the reduction peak C of Li 2 O disappears, and only the oxidation and/or reduction peak A of Li ions in the two figures indicates that Li 2 O in the molten salt has been completely removed.

以上所述,仅为本发明的较佳实施例而已,并非用于限定本发明的保护范围。The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the protection 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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KR20180098916A (en) * 2017-02-27 2018-09-05 한국원자력연구원 Pyroprocessing
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KR20180098916A (en) * 2017-02-27 2018-09-05 한국원자력연구원 Pyroprocessing
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