CN113030225A - Judgment and automatic response method for molten salt purification end point - Google Patents
Judgment and automatic response method for molten salt purification end point Download PDFInfo
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- PUDIUYLPXJFUGB-UHFFFAOYSA-N praseodymium atom Chemical compound [Pr] PUDIUYLPXJFUGB-UHFFFAOYSA-N 0.000 description 1
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
- G01N27/4163—Systems checking the operation of, or calibrating, the measuring apparatus
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- Molecular Biology (AREA)
- Analytical Chemistry (AREA)
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Abstract
The invention provides a method for judging and automatically responding a molten salt purification end point, which comprises the following steps: inserting an inert metal cathode and an inert anode into molten salt, and respectively connecting a cathode and an anode of a direct current constant current power supply to form a detection loop; step two: connecting a voltage comparator module with a power supply, wherein the input end of the voltage comparator module is connected with the inert metal cathode and the inert metal anode in parallel, and the voltage comparator module and the direct-current power supply form an input loop; step three: the voltage comparator module is connected with the input loop and the output loop, the output loop comprises a normally open switch and an independent power supply, and the response module can select devices such as an indicator lamp, a buzzer alarm and an electromagnetic relay according to actual needs to realize automatic response and automatic control. The method provides convenience for the molten salt purification process, is simple to operate, has low learning cost in the application process, and is convenient to popularize and apply in the actual production process.
Description
Technical Field
The invention relates to a judgment and automatic response method, in particular to a judgment and automatic response method of a molten salt purification end point, belonging to the field of molten salt electrolysis and the field of spent fuel dry-process post-treatment.
Background
Nuclear energy is a clean energy source, and today, the traditional fossil energy source is increasingly consumed, and the nuclear energy has the unique advantage of being difficult to replace. In order to recycle nuclear fuel, it is necessary to perform post-treatment of spent fuel generated after nuclear reaction to remove impurity elements and recover the nuclear fuel. The spent fuel dry post-treatment technology based on the molten salt system has the advantages of radiation resistance, simple steps, small critical accident risk and the like, and is one of the most promising choices at present.
The spent fuel contains many nuclear fuels such as uranium (U) and plutonium (Pu) and many Fission Products (FP) generated by nuclear fission, and the presence of these Fission Products (FP) reduces the efficiency of the nuclear fission reaction and increases the risk of the reaction, wherein the rare earth element accounts for about 25% of the total amount of the fission products. After uranium and transuranic elements in the molten salt are recovered through a high-temperature chemical process, fission products such as rare earth elements and the like can remain in the molten salt, so that the pollution of the melt is caused. Therefore, the molten salt must be purified to remove fission products such as rare earth elements, and the molten salt can be recycled.
For the purification of the fused salt, Huangwei et al used an electrochemical method to remove impurity ions by controlling the electrolytic potential (Huangwei, Jianfeng, Tianlifang, Yufeng, Zheng ocean, Longdefu, Liqing-Lu. electrochemical purification method of fused salt, China, 201510237627.3[ P ]. 2017-01-04.). Yung-Zun Cho et al achieved some degree of purification of the melt by adding phosphate to the melt to convert La, Ce, Pr, Nd, etc. into phosphate precipitates In LiCl-KCl melts (Yung-Zun Cho, Tae-Kyo Lee, Hee-Chul Eun, Jung-Hoon Choi, In-Tae Kim, Geun-Il park. purification of used electrolytic (LiCl-KCl) salt electrolytic from processing [ J ] Journal of Nuclear Materials,2013,437: 47-54). However, in practical application, methods and technologies for judging and automatically responding to the molten salt purification endpoint are lacked.
Disclosure of Invention
The invention aims to provide a method for judging and automatically responding a purification end point in a molten salt purification process. The purification endpoint is monitored by an electrochemical method, the voltage comparator module is utilized to realize automatic response at the purification endpoint, and the response mode can be realized by selecting a proper module according to actual needs, such as: lighting indication, buzzing alarm, stopping feeding and the like.
The purpose of the invention is realized as follows:
heating the molten salt containing impurity ions to be purified to melt and stabilize the molten salt, inserting an inert metal cathode (3) and an inert anode (4) into the molten salt, and respectively connecting a cathode and an anode of a direct-current constant-current power supply (1) to form a detection loop;
the voltage comparator module (2) is connected with a power supply, the input end of the voltage comparator module is connected with the inert metal cathode (3) and the inert anode (4) in parallel, and the voltage comparator module (2) and the direct current power supply (1) form an input loop;
the voltage comparator module (2) is connected with the input loop and the output loop, the output loop comprises a normally open switch (5) and an independent power supply (6), and the response module (7) can select devices such as an indicator light, a buzzer alarm, an electromagnetic relay and the like according to actual needs to realize automatic response and automatic control;
before monitoring, a voltage comparator module is calibrated by using a serial port, so that the deviation of the measured voltage is accurate to +/-0.1V;
the method is suitable for judging the purification end point of the impurity ions of which the oxidation-reduction potential is just equal to the decomposition voltage of the solvent salt, measuring the oxidation-reduction potential of the ions to be purified and the decomposition voltage of the solvent salt by using an electrochemical workstation, and setting the set voltage of a voltage comparator module between the two values;
the method is used for monitoring while purifying the melt;
the method adopts a constant current electrolysis mode for monitoring, and the monitoring current is selected according to the actual condition;
when the melt contains impurity ions, the voltage at two ends of the detection loop is positioned near the oxidation-reduction potential of the impurity ions, the voltage is lower than the set voltage of the voltage comparator module, a normally open switch in the output loop is in an open state, the output loop is not electrified, and the response module does not respond;
when the purification end point is reached, the impurity ions in the melt are consumed, the voltage at the two ends of the detection loop rises to be close to the decomposition voltage of the solvent salt, the voltage is greater than the set voltage of the voltage comparator module, the normally open switch in the output loop is changed into a closed state, the output loop is electrified, and the response module starts to work, so that the automatic response or automatic control at the purification end point of the molten salt is realized.
Compared with the prior art, the invention has the beneficial effects that:
1. the method can realize automatic judgment and response of the molten salt purification end point, does not introduce other elements into a molten salt system in the using process, and does not cause secondary pollution;
2. the method is not limited to rare earth ions, and can be used for monitoring the removal of impurity ions with any deposition potential being positive to the decomposition voltage of the solvent salt;
3. the method is not limited to a certain molten salt, and the method can be suitable for most molten salt systems by adjusting the set voltage of the voltage comparator module;
4. the method is suitable for judging the purification end point of most molten salt purification processes such as an electrochemical method, a phosphate precipitation method and the like;
5. compared with the prior art, the method can select the response module according to the actual requirement to realize the required automatic response or automatic control;
6. the method has the advantages of simple working principle, less required elements and low operation and industrialization cost, and is favorable for popularization and utilization in the actual production process.
Drawings
FIG. 1 is a schematic diagram of the application process of the method, (1) a DC power supply; (2) a voltage comparator module; (3) an inert cathode; (4) an inert anode; (5) a normally open switch; (6) an independent power supply; (7) a response module selected according to actual needs; (8) liquid electrolyte reactor
FIG. 2 shows Pr-containing for determining potential in the examples3+Cyclic voltammetry of LiCl-KCl melt of ionic impurities;
FIG. 3 shows examples containing Pr3+A relation curve of potential change along with time in the LiCl-KCl melt purification process of ionic impurities;
FIG. 4 shows examples containing Pr3+The change curve of the potential with time when LiCl-KCl melt of ionic impurities approaches the purification end point is marked with an alarm point in the figure.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
The invention relates to a method for judging and automatically responding a molten salt purification end point based on electrochemistry. The application range of the invention includes but is not limited to judgment and response of purification endpoint in the purification process of the molten salt rare earth ions mentioned in the embodiment.
The application process schematic diagram of the method is shown in a figure I, wherein (1) a direct current power supply is shown in the figure; (2) a voltage comparator module; (3) an inert metal cathode; (4) an inert anode; (5) a normally open switch; (6) an independent power supply; (7) a response module selected according to actual needs; (8) a liquid electrolyte reactor.
The operation process of judging the molten salt purification end point and automatically responding by using the method comprises the following steps:
(1) first, the oxidation-reduction potential of the ions to be purified and the decomposition voltage of the solvent salt are determined.
(2) And the voltage comparator module is connected with a computer through a serial port to carry out voltage calibration, so that the voltage deviation is accurate to +/-0.1V.
(3) The upper threshold of the voltage comparator module is set between the oxidation-reduction potential of the impurity ions and the decomposition voltage of the solvent salt, and the lower threshold of the voltage comparator module is set below the oxidation-reduction potential of the impurity ions. The response mode of the voltage comparator module is set to an off-threshold response (i.e., when the voltage exceeds the upper threshold setting voltage, the voltage comparator module responds to close the normally open switch).
(4) And selecting a response module such as an indicator lamp, a buzzer alarm, an electromagnetic relay and the like according to actual needs, and connecting the response module into an output loop.
(5) After the connection is finished, the inert metal cathode and the inert anode are inserted into the molten salt which is being purified, a power supply is started, and the constant current is selected according to actual conditions for monitoring.
(6) And (4) as the reaction proceeds, when the purification end point is reached, the selected response module automatically responds to complete judgment and automatic response of the molten salt purification process.
A molten salt purification end point judgment and automatic response method comprises the following steps
Step (1): determining the oxidation-reduction potential of the impurity ions and the decomposition voltage of the solvent salt, and adjusting the set voltage of the voltage comparator module between the oxidation-reduction potential of the impurity ions and the decomposition voltage of the solvent salt;
step (2): inserting a cathode and an anode into the purified molten salt, and electrifying the molten salt by using a direct current power supply to perform electrolysis monitoring;
and (3): when the melt contains impurity ions, the voltage at the two ends of the cathode and the anode is positioned near the oxidation-reduction potential of the impurity ions and is smaller than the set voltage of the voltage comparator module, and the response module does not work;
and (4): when the purification end point is reached, the voltage at the two ends of the cathode and the anode is increased to the decomposition voltage of the solvent salt and is greater than the set voltage of the voltage comparator module, the response module works, automatic response or automatic control occurs, and the judgment of the purification end point is completed.
The molten salt can be common chloride or fluoride molten salt such as LiCl-KCl, NaCl-CsCl, NaCl-KCl, FLiNaK, FLiBe-KF and the like;
the ions to be purified can be ions with oxidation-reduction potential being positive to the decomposition voltage of the solvent salt, such as one or more of lanthanum, cerium, praseodymium, neodymium, europium, gadolinium, terbium, dysprosium, holmium, erbium, lutetium, iron, cobalt, nickel, copper, lead, aluminum, zinc, tin and the like.
A method for judging and automatically responding the purification end point of molten salt is used for monitoring based on an electrochemical principle in the purification process of the molten salt containing impurity ions, automatically responding at the purification end point, and realizing automatic response and automatic control in different forms according to different selected response modules.
Example (b):
in the embodiment, the molten salt to be purified is LiCl-KCl eutectic salt, wherein LiCl is 38g, KCl is 45g, impurity ions in the molten salt are praseodymium ions (2.6 wt.%), and the purification method is a sodium phosphate precipitation method. The molten salt was dried in a muffle furnace at 473K for 72 hours to remove the water from the solvent salt initially before purification, and then transferred to a box-type resistance furnace in a vacuum glove box and heated to 773K to melt it. After the molten salt melts and stabilizes, purification is started.
The method is used for judging and automatically responding to the purification end point of the molten salt purification process, and the response module selects the indicator lamp and the buzzer alarm.
Before purification, an electrochemical workstation is used for carrying out cyclic voltammetry on LiCl-KCl molten salt to be purified, the oxidation-reduction potential of praseodymium ions and the decomposition voltage of LiCl-KCl solvent salt are determined, and the obtained curve is shown in figure 2. In the figure, the oxidation reduction peak A/A' is Li/Li+Redox peak, B/B' is Pr/Pr3+Redox peak. The deposition potential of praseodymium ion was found to be-3.2V (vs Cl)2/Cl-) The decomposition voltage of LiCl-KCl solvent salt was-3.6V.
And connecting the voltage comparator module with a computer by using a serial port to perform voltage calibration, so that the voltage deviation is not more than 0.1V.
The upper threshold of the voltage comparator block was set to-3.5V (vs Cl) based on the potential value measured by cyclic voltammetry2/Cl-) The lower threshold is set to 0V (vs Cl)2/Cl-) The response mode is set to an off-threshold response.
The cathode of the detection loop uses an inert tungsten electrode, the diameter of the inert tungsten electrode is 1.0mm, the purity of the inert tungsten electrode is 99.99%, before the tungsten wire is used, the tungsten wire needs to be subjected to whole-body grinding by coarse abrasive paper with the roughness of 800Cw to remove an oxide layer on the surface of the tungsten wire, then the tungsten wire is subjected to fine abrasive paper with the roughness of 2000Cw to be inserted into a molten salt part and the top end of the tungsten wire to be carefully ground until the tungsten wire is bright and free of scratches, and then the treated tungsten wire is subjected to ultrasonic cleaning by ethanol to remove impurities.
The anode used a spectrally pure graphite rod with a diameter of phi (6.0 mm). In order to prevent impurities in the graphite rod from entering a molten salt system and protect the graphite rod from being corroded by corrosive gas generated in an experiment, the graphite rod is protected by a quartz glass sleeve, and is firstly put into dilute hydrochloric acid to be boiled before the experiment, and then is put into a vacuum drying oven to be dried and stored after being washed clean by distilled water.
And inserting the treated inert tungsten electrode and graphite electrode into LiCl-KCl molten salt to be purified, wherein the immersion depth of the electrode is 1.0 cm.
The power supply is turned on, the detection loop is monitored by constant current of 8mA, and the potential is stabilized at praseodymium ion deposition potential (-3.2V (vs Cl) in the molten salt purification process2/Cl-) Near (B) as shown in fig. 3, where the platform B is a pr ion deposition platform.
Sodium phosphate was added to the molten salt stepwise and allowed to stand for 30 minutes after each addition to allow the praseodymium ions to precipitate sufficiently. After a period of time, praseodymium ions are nearly completely precipitated, and the potential at the end of the detection loop rises to be close to the decomposition voltage of LiCl-KCl solvolyte. The potential change process is shown in fig. 4, in which the platform B is a praseodymium ion deposition platform and the platform a is a lithium ion deposition platform, and the potential change indicates the arrival of the molten salt purification endpoint. The potential C in FIG. 4 is the upper threshold alarm point set by the method. The molten salt is purified, the voltage of the detection loop exceeds the set potential of the upper threshold alarm point C, the voltage comparator module responds, the normally open switch is closed, the indicator lamp is turned on, and the buzzer alarm gives an alarm to prompt that the external molten salt reaches the purification end point.
And when the purification end point is reached, the power supply is turned off, the sodium phosphate is stopped being added, and the molten salt supernatant is sampled to carry out ICP test, wherein the result shows that the purification rate can reach 98.70%.
The invention provides a method for judging and automatically responding a molten salt purification end point. The method is used for monitoring the molten salt purification process, can realize automatic judgment and response of the purification end point, and judges the purification end point by using the change of the terminal voltage during constant current electrification based on the electrochemical principle; and a voltage comparator module is utilized to realize automatic responses such as buzzing alarm, material feeding stopping and the like at the purification endpoint. The method is suitable for judging most fused salt purification end points, has sensitive indication and simple operation requirement, and can realize automatic response and automatic control in the practical application process.
In conclusion, the invention provides a method for judging and automatically responding the molten salt purification endpoint based on electrochemistry. The voltage change is monitored through constant current electrolysis, the voltage comparator module is used for analyzing and judging the voltage, when the molten salt purification end point is reached, the voltage comparator module controls the output loop to react, and the response module in the output loop automatically responds. The molten salt purification condition is converted into a visual signal, automatic control can be realized by adding the response module, and convenience is provided for the molten salt purification process. The method is simple to operate, low in learning cost in the application process and convenient to popularize and apply in the actual production process.
Claims (4)
1. A method for judging and automatically responding a molten salt purification end point is characterized by comprising the following steps:
the method comprises the following steps: heating the molten salt containing impurity ions to be purified to melt and stabilize the molten salt, inserting an inert metal cathode (3) and an inert anode (4) into the molten salt, and respectively connecting a cathode and an anode of a direct-current constant-current power supply (1) to form a detection loop;
step two: the voltage comparator module (2) is connected with a power supply, the input end of the voltage comparator module is connected with the inert metal cathode (3) and the inert anode (4) in parallel, and the voltage comparator module (2) and the direct current power supply (1) form an input loop;
step three: the voltage comparator module (2) is connected with the input loop and the output loop, the output loop comprises a normally open switch (5) and an independent power supply (6), and the response module (7) can select devices such as an indicator lamp, a buzzer alarm and an electromagnetic relay according to actual needs to realize automatic response and automatic control.
2. The molten salt purification end point judgment and automatic response method as claimed in claim 1, characterized in that before monitoring, the voltage comparator module is calibrated by using a serial port, so that the deviation of the measured voltage is accurate to ± 0.1V.
3. The molten salt purification end point judgment and automatic response method as claimed in claim 1, wherein when the melt contains impurity ions, the voltage across the detection loop is near the oxidation-reduction potential of the impurity ions, the voltage is lower than the set voltage of the voltage comparator module, the normally open switch in the output loop is in an open state, the output loop is not powered on, and the response module does not respond.
4. The molten salt purification endpoint judgment and automatic response method according to claim 1, wherein when the purification endpoint is reached, the impurity ions in the melt are depleted, the voltage across the detection loop rises to be close to the decomposition voltage of the solvent salt, the voltage is greater than the set voltage of the voltage comparator module, a normally open switch in the output loop is changed into a closed state, the output loop is electrified, and the response module starts to work, so that automatic response or automatic control at the purification endpoint of the molten salt is realized.
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