An iodine removal process for iodine-containing solutions
The iodine removal process, which is enhanced by the synergistic effect of gas-liquid mass transfer and chemical reaction, has solved the problem of efficient removal of radioactive iodine isotopes in nuclear fuel reprocessing. It achieves high iodine removal rate and stable operation, and is suitable for engineering applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA INSTITUTE OF ATOMIC ENERGY
- Filing Date
- 2026-02-04
- Publication Date
- 2026-06-05
AI Technical Summary
Existing technologies are insufficient to efficiently remove radioactive iodine isotopes, especially 129I and 131I, generated during nuclear fuel reprocessing, which pose a threat to the environment and human health.
By employing the principle of synergistic enhancement of gas-liquid mass transfer and chemical reaction, and by controlling key process parameters such as temperature, gas-liquid ratio, and nitrogen oxide concentration, the efficient conversion and removal of iodine is achieved. The reaction is carried out in an iodine removal tower using a nitric acid solution containing iodate and trace amounts of organic iodine, mixed with nitrogen oxides and air.
It achieves an iodine removal rate of over 96%, operates stably, is suitable for engineering applications, has strong adaptability, and can operate stably within a wide range of iodine concentrations, ensuring the closed treatment of iodine.
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Figure CN122158220A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of spent fuel reprocessing, specifically relating to a process for removing iodine from iodine-containing solutions. Background Technology
[0002] During nuclear fuel reprocessing, substances including... 129 I and 131-135 I, 138-141 A large number of radioactive iodine isotopes, including I. 138 I arrive 141 I has an extremely short half-life, and its potential harm is negligible; while 129 I and 131 I, on the other hand, has an extremely long half-life (approximately 1.57 × 10⁻⁶). 7 With its high specific activity and high concentration (in years), radioactive iodine in spent fuel is one of the most hazardous radioactive isotopes. Direct release into the atmosphere would pollute the environment and seriously threaten human health. Therefore, in the context of the active development of nuclear energy, the effective treatment of radioactive iodine in spent fuel is of paramount importance.
[0003] To improve the efficiency of iodine removal and realize its engineering application, it is necessary to develop an efficient, stable and easy-to-operate iodine removal process. Summary of the Invention
[0004] To address the technical deficiencies in existing technologies, the present invention aims to provide an iodine removal process for iodine-containing solutions. Based on the principle of synergistic enhancement of gas-liquid mass transfer and chemical reaction, this process achieves efficient conversion and removal of iodine by controlling key process parameters such as temperature, gas-liquid ratio, and nitrogen oxide concentration. This process enables efficient removal of iodine from solutions and has the technical advantages of high iodine removal rate, stable operation, and suitability for engineering applications.
[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention discloses an iodine removal process for iodine-containing solutions, the method comprising the following steps:
[0006] S1. Introduce the iodine-containing solution from the bottom of the tower into the iodine removal tower;
[0007] S2. The purging gas is introduced into the iodine removal tower from the middle and bottom, and comes into contact with the iodine-containing solution in parallel flow through the gas distributor to carry out the iodine removal reaction.
[0008] The iodine-containing solution is a nitric acid solution containing iodate and trace amounts of organic iodine, and the gases to be removed include nitrogen oxides and air.
[0009] Furthermore, in step S1, the concentration of nitric acid in the iodine-containing solution is 3.5-4.0 mol / L, preferably 4.0 mol / L.
[0010] Furthermore, in step S1, the total iodine content in the iodine-containing solution is 0.03-0.5 g / L, preferably 0.5 g / L.
[0011] Furthermore, the volume concentration of nitrogen oxides in the purge gas in step S1 is 5%–50%.
[0012] Furthermore, the operating temperature of the iodine removal tower is 75-98℃, preferably 98℃.
[0013] Furthermore, the working pressure of the iodine removal tower is from atmospheric pressure to slightly positive pressure, preferably 0.05 MPa.
[0014] Furthermore, the gas-liquid ratio of the volume of the purging gas to the volume of the iodine-containing solution is 60:1-160:1, preferably 160:1.
[0015] Furthermore, the intake temperature of the purge gas is 120°C.
[0016] Furthermore, the average residence time of the solution in the iodine removal tower is 2.5-4 hours, preferably 3 hours.
[0017] Furthermore, in step S1, the iodine-containing solution is introduced from the bottom of the tower into the iodine removal tower at a preset flow rate using an inlet pump.
[0018] The beneficial technical effects of the present invention are as follows: The iodine removal process for iodine-containing solutions disclosed in the present invention is based on the principle of synergistic enhancement of gas-liquid mass transfer and chemical reaction, and achieves efficient removal of iodine from the solution by optimizing process parameters.
[0019] Furthermore, the process has a wide process window and stable operation. Through systematic research, the optimal range and influence of key parameters such as liquid-to-gas ratio, temperature, and average residence time of the dissolved solution in the iodine removal tower have been clarified. Operating within this optimal range, the process exhibits strong resistance to fluctuations, and the iodine capture rate can be stably maintained above 96%.
[0020] Furthermore, based on the verification test of the engineering prototype, the iodine removal process disclosed in this invention for iodine-containing solutions has strong process adaptability and can operate stably within a wide range of total iodine concentrations. The iodine-containing exhaust gas after removal can be connected to an iodine capture system to achieve closed-loop treatment of iodine throughout the entire process. Attached Figure Description
[0021] Figure 1 This is a flowchart illustrating an iodine removal process for iodine-containing solutions, as shown in Embodiment 1 of the present invention. Detailed Implementation
[0022] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.
[0023] Example 1
[0024] like Figure 1 As shown, this embodiment of the invention provides an iodine removal process for iodine-containing solutions, the method comprising the following steps:
[0025] S1. The iodine-containing solution is introduced into the iodine removal tower and enters from the bottom of the tower.
[0026] The iodine-containing solution is a nitric acid solution containing iodate and trace amounts of organic iodine, wherein the nitric acid concentration is 3.5-4.0 mol / L, preferably 4.0 mol / L; and the total iodine content in the solution is 0.03-0.5 g / L, preferably 0.5 g / L.
[0027] The operating temperature of the iodine removal tower is 75-98℃, preferably 98℃. The operating pressure of the iodine removal tower is atmospheric pressure to slightly positive pressure, preferably 0.05 MPa.
[0028] The average residence time of the solution in the iodine removal tower is 2.5-4 h, preferably 3 h.
[0029] S2. The purging gas is introduced from the middle and bottom of the iodine removal tower and comes into contact with the iodine-containing solution in parallel flow through the gas distributor to carry out the iodine removal reaction.
[0030] The purge gas includes nitrogen oxides and air, wherein the concentration of nitrogen oxides (calculated as NO2) in the purge gas is 5%-50% (volume fraction), preferably 50%.
[0031] The gas-liquid ratio of the volume of the purging gas to the volume of the iodine-containing solution is 60:1-160:1, preferably 160:1.
[0032] The intake temperature of the purging gas is 120°C.
[0033] The iodine-containing exhaust gas after removal is sent to an iodine capture system for further treatment.
[0034] This invention discloses an iodine removal process for iodine-containing solutions. The simulated iodine solution enters the removal tower from the bottom, and the removal gas is obtained by premixing several gases. It then enters the first gas distributor at the bottom. Under certain temperature and pressure, the removal gas contacts the iodine-containing solution in the simulated spent fuel through the gas distributors in the middle and bottom sections. The removal gas reacts with a 3.5 mol / L nitric acid solution in the iodine-containing solution to generate nitrous acid. Simultaneously, under certain temperature and pressure, the nitrous acid reacts with IO3 in the iodine-containing solution in the simulated spent fuel. - The reaction produces I₂ and nitric acid. I₂ has low solubility in 3.5 mol / L nitric acid (less than 1 × 10⁻⁶). -3 (mol / L), generating I2 which enters the hot air blowing section, transferring I2 from the liquid phase to the gas phase. After passing through the gas-liquid separation and defoaming device, the iodine removal is completed.
[0035] In this embodiment, the gas delivery pipeline is connected to a gas distributor to ensure that the purging gas is evenly dispersed at the bottom of the iodine removal tower, where it fully contacts and reacts with the iodine-containing solution to form bubbles. Since solid particles in the iodine-containing solution can easily clog the gas distributor, it is removed from the top of the iodine removal tower for easier maintenance. The gas delivery pipeline then enters the iodine removal tower from the top. The purging gas enters the iodine removal tower from the gas delivery pipeline at the top, which extends to the bottom of the tower. The purging gas is then released from the bottom of the tower.
[0036] Using the iodine removal process for iodine-containing solutions disclosed in this invention, the iodine removal rate is not less than 96%, and the residual amount of HNO2 in the outlet solution is less than 4 × 10⁻⁶. -3 mol / L.
[0037] Iodate (IO3) in liquid phase - The method for testing the concentration of IO3 is as follows: under acidic conditions, IO3... - Will I - It is oxidized to I2, and I2 forms a blue complex with starch. The absorbance is measured at 580 nm using a UV-Vis spectrophotometer (model UV1901PCS). The concentration is calculated according to the standard curve, and the detection accuracy is 0.0001 g / L.
[0038] The method for testing the concentration of elemental iodine (I2) in the liquid phase is as follows: I2 is extracted from the liquid phase using CCl4, and after separating the organic phase, the absorbance is measured at a wavelength of 517 nm using a UV-Vis spectrophotometer. The concentration is calculated according to the standard curve, and the detection accuracy is 0.0001 g / L.
[0039] The method for testing the concentration of elemental iodine (I2) and nitrogen oxides (NO2) in the gas phase is as follows: online sampling and analysis are performed using a gas chromatograph (model GC-9890) equipped with a TCD detector, and the corresponding concentrations are calculated based on their respective standard curves.
[0040] The formula for calculating the iodine removal rate is:
[0042] Where X is the iodine removal rate; I in To simulate the total iodine concentration at the inlet of the solution, g / L; I out The total iodine concentration at the outlet of the solution is measured in g / L.
[0043] Example 2
[0044] S1. Prepare a simulated solution with a total iodine concentration of 0.07 g / L (of which iodate accounts for 99.5% and organic iodine accounts for 0.5%) and a nitric acid concentration of 3.5 mol / L. Introduce the solution from the bottom into the iodine removal tower through a feed pump at a flow rate of 1000 L / h. Control the average residence time in the iodine removal tower to be 3 h and maintain the working temperature in the iodine removal tower at 85℃.
[0045] S2. A purging gas with a NO2 volume concentration of 10% (made by mixing high-purity NO2 with air heated to 120°C) is introduced into the iodine purging tower from the bottom at a flow rate of 120 m³ / h. The operating pressure inside the iodine purging tower is controlled at 0.05 MPa(G), and the gas-liquid ratio is 120:1.
[0046] S3. After the system has been running stably for 4 hours, it reaches a steady state. Samples of the dissolved solution at the inlet and outlet of the iodine removal tower are then taken for analysis. The total iodine concentration in the outlet dissolved solution is measured to be 0.0022 g / L, and the calculated iodine removal rate is 96.8%.
[0047] Example 3
[0048] A similar method to that in Example 2 was used, with the only difference being that the NO2 volume concentration of the purging gas in S2 was 50%, and the gas flow rate was 120 m³ / h (gas-liquid ratio 120:1). The total iodine concentration in the outlet solution was measured to be 0.0011 g / L, and the calculated iodine removal rate was 98.4%.
[0049] Example 4
[0050] A similar method to that in Example 2 was used, the only difference being that the operating temperature of the iodine removal tower in S2 was 98°C. The total iodine concentration in the outlet solution was measured to be 0.0012 g / L, and the calculated iodine removal rate was 98.3%.
[0051] Example 5
[0052] A similar method to that in Example 2 was used, with the only difference being that the gas-liquid ratio in S2 was 160:1 (gas flow rate 160 m³ / h, liquid flow rate 1000 L / h). The total iodine concentration in the outlet solution was measured to be 0.0016 g / L, and the calculated iodine removal rate was 97.7%.
[0053] Example 6
[0054] S1. Prepare a simulated solution with a total iodine concentration of 0.09 g / L and a nitric acid concentration of 3.5 mol / L. Introduce the solution from the bottom of the iodine removal tower using a feed pump at a flow rate of 750 L / h. Control the average residence time in the tower to be 4 h and maintain the operating temperature in the tower at 75℃.
[0055] S2. A purging gas with a NO2 volume concentration of 20% is introduced into the iodine purging tower from the bottom at a flow rate of 120 m³ / h (gas-liquid ratio 160:1), and the operating pressure inside the tower is controlled at 0.05 MPa(G).
[0056] S3. After 4 hours of stable operation, the system reached steady state. The total iodine concentration in the outlet solution was measured to be 0.0035 g / L, resulting in an iodine removal rate of 96.1%. Under these optimized conditions, the system operated continuously and stably for 80 hours, maintaining an iodine removal rate consistently above 96% and a stable nitrite residue concentration of 10 g / L. -4 The mol / L level verified the long-term stability of the process.
[0057] Comparative Example 1
[0058] The method of Example 2 was used, with the only difference being that the gas-liquid ratio in S2 was 60:1 (gas flow rate 60 m³ / h, liquid flow rate 1000 L / h). The total iodine concentration in the outlet solution was measured to be 0.0046 g / L, and the calculated iodine removal rate was 93.4%, which failed to meet the technical target of 96%.
[0059] Comparative Example 2
[0060] The method of Example 2 was used, with the only difference being that the operating temperature of the iodine removal tower in S2 was 75°C. The total iodine concentration in the outlet solution was measured to be 0.0043 g / L, and the calculated iodine removal rate was 93.8%, which failed to meet the technical target of 96%.
[0061] Comparative Example 3
[0062] The method of Example 2 was used, with the only difference being that the total iodine concentration in the solution in S1 was 0.03 g / L. The total iodine concentration in the outlet solution was measured to be 0.0033 g / L, and the calculated iodine removal rate was 89.1%, which failed to reach the technical target of 96%.
[0063] The process conditions and iodine removal rates of Examples 2-6 and Comparative Examples 1-3 are summarized in the table below:
[0064]
[0065] A comparison of the data from Example 2 and Comparative Examples 1-3 shows that the gas-liquid ratio, operating temperature, and total iodine concentration all have a significant impact on the removal rate. When the parameters are below the lower limit required by the embodiments of the present invention, a removal rate of 96% cannot be guaranteed. Example 6 demonstrates that by optimizing the combination of process parameters (appropriately increasing the gas-liquid ratio, NO concentration, and residence time), stable operation meeting the standards can still be achieved even at a relatively low operating temperature of 75°C.
[0066] As can be seen from the above embodiments, the iodine removal process for iodine-containing solutions disclosed in this invention uses hot air containing nitrogen oxides as the removal gas. Under optimized reaction conditions, the iodine-containing solution is bubbled and removed in an iodine removal tower. By controlling the reaction conditions, the conversion of iodine from the liquid phase to the gas phase is achieved, with a removal rate of over 96%. The process is stable and reliable, and suitable for the treatment of iodine-containing radioactive solutions in nuclear fuel reprocessing plants. It has technical advantages such as clear operating parameters, high iodine removal efficiency, stable operation, and suitability for industrial engineering applications. It enables control over the iodine flow in reprocessing plants, improves product quality, increases solvent reuse times, and enhances the stability, economy, and safety of plant operation.
[0067] The method described in this invention is not limited to the embodiments described in the specific implementation. Other implementation methods derived by those skilled in the art based on the technical solution of this invention also fall within the scope of technical innovation of this invention.
Claims
1. An iodine removal process for iodine-containing solutions, characterized in that: The method includes the following steps: S1. Introduce the iodine-containing solution from the bottom of the tower into the iodine removal tower; S2. The purging gas is introduced into the iodine removal tower from the middle and bottom, and comes into contact with the iodine-containing solution in parallel flow through the gas distributor to carry out the iodine removal reaction. The iodine-containing solution is a nitric acid solution containing iodate and trace amounts of organic iodine, and the gases to be removed include nitrogen oxides and air.
2. The iodine removal process for iodine-containing solutions according to claim 1, characterized in that: In step S1, the concentration of nitric acid in the iodine-containing solution is 3.5-4.0 mol / L, preferably 4.0 mol / L.
3. The iodine removal process for iodine-containing solutions according to claim 1, characterized in that: In step S1, the total iodine content in the iodine-containing solution is 0.03-0.5 g / L, preferably 0.5 g / L.
4. The iodine removal process for iodine-containing solutions according to claim 1, characterized in that: In step S1, the volume concentration of nitrogen oxides in the purge gas is 5%-50%.
5. The iodine removal process for iodine-containing solutions according to claim 1, characterized in that: The operating temperature of the iodine removal tower is 75-98℃, preferably 98℃.
6. The iodine removal process for iodine-containing solutions according to claim 1, characterized in that: The working pressure of the iodine removal tower is from atmospheric pressure to slightly positive pressure, preferably 0.05 MPa.
7. The iodine removal process for iodine-containing solutions according to claim 1, characterized in that: The gas-liquid ratio of the volume of the purging gas to the volume of the iodine-containing solution is 60:1-160:1, preferably 160:
1.
8. The iodine removal process for iodine-containing solutions according to claim 1, characterized in that: The intake temperature of the purging gas is 120℃.
9. The iodine removal process for iodine-containing solutions according to claim 1, characterized in that: The average residence time of the solution in the iodine removal tower is 2.5-4 hours, preferably 3 hours.
10. The iodine removal process for iodine-containing solutions according to claim 1, characterized in that: In step S1, the iodine-containing solution is introduced from the bottom of the tower into the iodine removal tower at a preset flow rate using an inlet pump.