A method and system for processing a uranium-containing organic phase

Abstract

The present application relates to the technical field of nuclear fuel cycle and radioactive waste treatment, in particular to a method and system for treating uranium-containing organic phase, the system comprises pretreatment washing tank, pyrolysis reactor, phase separation tank, uranium recovery device, vacuum distillation device, tail gas treatment device and solidification device connected in sequence; the method first removes acid by water washing pretreatment of uranium-containing organic phase at 40-50 DEG C, then adds phosphoric acid to catalyze pyrolysis to decompose TBP and transfer uranium to phosphoric acid phase, recovers uranium and n-dodecane after phase separation, simultaneously treats tail gas and solidifies residual waste, and further provides online monitoring and control subsystem to realize automatic control and safety interlocking; the present application has mild reaction condition, avoids strong corrosive substance generation, total uranium recovery rate reaches more than 90%, about 80% of n-dodecane can be recycled, greatly reduces radioactive waste production amount, is safe and reliable in operation, and is suitable for radioactive waste organic extractant reduction and resourceful treatment in nuclear fuel cycle.

Description

Technical Field

[0001] This invention relates to the field of nuclear fuel cycle and radioactive waste treatment technology, specifically a method and system for treating uranium-containing organic phases. Background Technology

[0002] In the upstream uranium purification and conversion process and the downstream spent fuel reprocessing process of the nuclear fuel cycle, 30% TBP / kerosene is widely used as an extractant for the extraction and separation of radioactive elements such as uranium. Because the extractant gradually degrades and becomes ineffective during irradiation and use, it needs to be replaced periodically, resulting in a large amount of radioactive waste organic phase. The main components are 30% tributyl phosphate (TBP) and 70% kerosene, as well as degradation products such as dibutyl phosphate (DBP) and monobutyl phosphate (MBP). Direct long-term storage of these uranium-containing waste organic extractants poses environmental safety hazards and requires "inorganicification" treatment to convert them into small-molecule inorganic substances for final disposal.

[0003] Currently, the inorganic treatment of radioactive organic phases mainly includes direct solidification and incineration, supercritical water oxidation, and high-temperature steam reforming. However, phosphorus-containing organic extractants generate highly corrosive substances such as phosphoric acid and phosphorus pentoxide during these processes, making it difficult for treatment equipment to operate safely for extended periods. Furthermore, supercritical water oxidation requires operation under high temperature and pressure conditions, is complex, and carries safety risks, failing to meet the stringent safety requirements for radioactive waste treatment in the nuclear industry. Therefore, given these shortcomings, there is an urgent need to develop a method and system for treating uranium-containing organic phases to overcome the deficiencies in current practical applications. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for processing uranium-containing organic phases to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A system for processing uranium-containing organic phases includes a pretreatment washing tank, a pyrolysis reactor, a phase separation tank, and a uranium recovery device that are fluidly connected in sequence, and also includes a vacuum distillation device and an online monitoring and control subsystem; The vacuum distillation apparatus is in fluid communication with the uranium recovery apparatus, and the vacuum distillation apparatus is used to recover and purify n-dodecane from the organic phase; The pretreatment washing tank is used to wash and remove acid from uranium-containing organic phases with water; The pyrolysis reactor is used to add phosphoric acid to catalytically decompose TBP in the organic phase and transfer uranium to the phosphoric acid phase. Its tail gas outlet is connected to the inlet of the tail gas treatment device. The phase separation tank is used to separate the uranium-containing phosphate phase from the organic phase; The uranium recovery device is used to recover uranium products from uranium-containing phosphate phase, and the waste liquid outlet of the uranium recovery device and the residue outlet of the vacuum distillation device are both connected to the feed inlet of the solidification device. The online monitoring and control subsystem is electrically connected to the pretreatment washing tank, pyrolysis reactor, phase separation tank, uranium recovery device, vacuum distillation device, tail gas treatment device, and solidification device, respectively, and is used to monitor process parameters in real time and realize automatic control and safety interlock.

[0006] As a further aspect of the present invention: the pretreatment washing tank is a mixing and clarification tank structure, with a stirring and mixing zone and a clarification and stratification zone inside, for realizing multi-stage series washing operations.

[0007] As a further aspect of the present invention: the pyrolysis reactor is made of acid-resistant and radiation-resistant materials and is equipped with a stirring device, a heating device and a temperature control device; Furthermore, the feed inlet of the pyrolysis reactor is connected to a feed pump for adding phosphoric acid.

[0008] As a further embodiment of the present invention: the phase separation tank is a gravity settling tank with a feed inlet at the top, baffles or mesh covers inside to promote droplet coalescence, and phosphoric acid phase outlet and organic phase outlet at the bottom and top respectively, with online radioactivity detectors at both outlets.

[0009] As a further aspect of the present invention: the uranium recovery device includes an acidification reactor and a precipitation reactor connected in series; The acidification reactor is used to convert uranyl phosphate into uranyl nitrate, and the precipitation reactor is used to precipitate uranium as ammonium diuranate.

[0010] A method for processing uranium-containing organic phases, using the system for processing uranium-containing organic phases described above, includes the following steps: S1. Pretreatment: The uranium-containing organic phase is sent into a pretreatment washing tank and heated with water to remove free acid and nitrate, thus obtaining a deacidified organic phase. S2. Catalytic pyrolysis: The deacidified organic phase is fed into the pyrolysis reactor, phosphoric acid is added as a catalyst, and the pyrolysis reaction is carried out under normal pressure, so that TBP is decomposed into hydrocarbon gas and phosphoric acid, and uranium is transferred to the phosphoric acid phase to form a uranium-containing mixture. S3. Phase separation: The uranium-containing mixture is sent into a phase separation tank and allowed to stand and separate into layers to obtain a lower uranium-containing phosphoric acid phase and an upper organic phase. S4. Uranium Recovery: The uranium-containing phosphate phase is fed into the uranium recovery unit, and uranium products are recovered by chemical precipitation. S5. Solvent recovery: The organic phase is fed into a vacuum distillation unit for vacuum distillation to recover purified n-dodecane. S6. Waste treatment: The tail gas generated by the pyrolysis reaction is sent to the tail gas treatment device for harmless treatment, and the waste liquid generated by uranium recovery and the residue generated by vacuum distillation are sent to the solidification device for stabilization and solidification.

[0011] As a further aspect of the present invention: in step S1, a multi-stage series water washing is performed using warm water at 40-50°C until the separated washing liquid is neutral and free of nitrate residue.

[0012] As a further aspect of the present invention: in step S2, the molar ratio of phosphoric acid to TBP is greater than 2:1, the pyrolysis reaction temperature is controlled at 190-250°C, and the reaction time is determined based on the online monitoring results of the organic component content of the tail gas.

[0013] As a further aspect of the present invention: step S4 specifically comprises: First, concentrated nitric acid is added to the uranium-containing phosphate phase to carry out an acid hydrolysis reaction, converting uranyl phosphate into uranyl nitrate; Then, ammonia water is added to the acid hydrolysis solution to adjust the pH to 7.5-8.0, so that uranium precipitates out in the form of ammonium diuranate. Uranium product is obtained by solid-liquid separation (9).

[0014] As a further aspect of the present invention: in step S5, vacuum distillation is carried out under absolute pressure below 10 kPa, and the purified n-dodecane (10) recovered has a purity of not less than 99% and a recovery rate of not less than 80%.

[0015] Compared with the prior art, the beneficial effects of the present invention are: First, the reaction conditions of the process of this invention are mild, with a pyrolysis temperature of about 190 to 250°C, and it can be carried out under normal pressure without the need for ultra-high temperature and high pressure conditions, which greatly reduces the corrosion and operational risks of the equipment. Secondly, the formation of phosphorus pentoxide is effectively avoided by the autocatalytic pyrolysis of phosphoric acid, which reduces the corrosivity of the system and ensures that the treatment device can operate stably for a long time. Furthermore, this invention quantitatively transfers and enriches uranium in the waste organic phase into the phosphoric acid aqueous phase, achieving a total uranium recovery rate of over 90%, and ultimately recovering it in the form of uranium products, thus realizing the reuse of radioactive precious elements. In addition, the process of this invention can recover about 80% of the diluent n-dodecane in the waste organic phase. After purification by a vacuum distillation unit, it can be reused as an extractant, which greatly reduces the amount of radioactive organic waste generated and the treatment cost. At the same time, the residual waste liquid and residue that are not recycled are stabilized by a solidification unit, resulting in small volume and stable morphology, which facilitates safe storage and disposal. Finally, by using an online monitoring and automatic control system to adjust and interlock key parameters in real time, the safety and reliability of the process are improved. Therefore, the processing method and system provided by this invention have the advantages of high safety, high recovery rate and environmental economy, and are suitable for the treatment needs of radioactive waste organic extractants in the nuclear fuel cycle. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the uranium-containing organic phase treatment process in an embodiment of the present invention.

[0017] In the diagram: 1-Pretreatment washing tank, 2-Pyrolysis reactor, 3-Phase separation tank, 4-Uranium recovery device, 5-Vacuum distillation device, 6-Tail gas treatment device, 7-Solidification device, 8-Nitric acid-containing washing liquid, 9-Uranium product, 10-Purified n-dodecane. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0020] Please see Figure 1 The present invention provides a method and system for processing uranium-containing organic phases. The overall process includes a main process of pretreatment → pyrolysis reaction → phase separation → uranium recovery → organic phase distillation, as well as auxiliary processes of tail gas treatment and solidification treatment.

[0021] The pretreatment stage is carried out in the pretreatment washing tank 1, which adopts a mixed clarification tank structure and is used to wash and denitrate the uranium-containing waste organic phase.

[0022] Specifically, the uranium-containing TBP / kerosene waste liquid to be treated is added to the pretreatment washing tank 1, pure water is added in a certain proportion, heated to about 45°C, and stirred for a certain time to allow the residual nitric acid and nitrates in the waste organic phase to be fully transferred to the aqueous phase. Then, stirring is stopped and the mixture is allowed to stand and separate into layers. The lower layer, which is rich in nitric acid and contains washing liquid 8, is separated, thus obtaining the upper organic phase from which acidic impurities have been removed.

[0023] To ensure complete removal of nitric acid, the organic phase can undergo multi-stage series water washing pretreatment until the separated washing liquid is monitored to be neutral and free of nitrate residue. The pretreated organic phase mainly consists of 30% TBP degradation products (containing trace amounts of residual TBP) and approximately 70% hydrocarbon diluent (kerosene), and can proceed to the next pyrolysis reaction.

[0024] This step involves pretreatment with warm water at 40–50°C, which can efficiently remove residual free acid and nitrates from the organic phase, avoid the generation of corrosive nitrogen oxides in the subsequent pyrolysis reaction, and reduce the entrainment loss of uranium.

[0025] In one embodiment of the invention, the pyrolysis reaction stage is carried out in a pyrolysis reactor 2. The pyrolysis reactor 2 is preferably made of acid- and radiation-resistant materials (such as Hastelloy or stainless steel containers lined with tetrafluoroethylene) and is equipped with stirring, heating and temperature control devices as well as a feed pump.

[0026] The organic phase outlet of the pretreatment washing tank 1 is connected to the feed inlet of the pyrolysis reactor 2 via a corrosion-resistant conveying pipe. After the pretreated organic phase is conveyed from the pretreatment washing tank 1 to the pyrolysis reactor 2, stirring is started and a certain amount of phosphoric acid (H3PO4) solution is slowly added as a catalyst.

[0027] The molar ratio of phosphoric acid to TBP is greater than 2:1 to ensure sufficient autocatalysis. The reactor is then sealed and heated to approximately 200°C with stirring to carry out the pyrolysis reaction.

[0028] The presence of phosphoric acid significantly reduces the decomposition activation energy of TBP, enabling TBP to decompose rapidly and completely into gaseous and liquid small molecule products at relatively low temperatures: the organic part is mainly converted into low-carbon olefin gases such as butene (C4H8), and the phosphate ester part is converted into phosphoric acid (H3PO4).

[0029] The organic waste gases, such as butene, generated during the reaction are discharged from the top of the reactor and sent to the waste gas treatment device 6 via pipeline. Temperature and organic gas concentration sensors are installed on the waste gas pipeline. When a significant decrease in gas yield is detected, it indicates that the organic compounds, such as TBP, have been essentially completely decomposed. At this point, heating is stopped, and the pyrolysis reaction ends.

[0030] After approximately 1–2 hours of reaction (the exact time can be adjusted based on online monitoring results), the TBP and its degradation products in the original uranium-containing organic phase have been completely converted into phosphoric acid and gaseous hydrocarbons, while the radioactive uranium metal, along with the phosphoric acid, forms a soluble uranyl phosphate complex that remains in the liquid phase. The resulting reaction mixture consists of an aqueous phosphoric acid phase and an organic phase, and then proceeds to the phase separation stage.

[0031] This step uses phosphoric acid autocatalytic pyrolysis technology, which requires a reaction temperature of only 190-250℃ and is carried out at normal pressure. It does not require ultra-high temperature and high pressure conditions, and avoids the generation of highly corrosive substances such as phosphorus pentoxide, which greatly reduces the risk of equipment corrosion and operational safety.

[0032] In one embodiment of the invention, the phase separation stage utilizes the density difference between the phosphate phase and the organic phase to perform liquid-liquid separation in the phase separation tank 3. The liquid phase outlet of the pyrolysis reactor 2 is connected to the top feed inlet of the phase separation tank 3 via an insulated conveying pipe. The phase separation tank 3 is a gravity settling tank with sufficient volume. Its design features include top feeding at the liquid inlet to reduce disturbance, internal baffles or mesh covers to promote droplet coalescence, and sufficient space at the top for the two liquid phases to separate.

[0033] After the pyrolysis reaction is completed, the mixture at the bottom of pyrolysis reactor 2 is slowly transported under pressure to the top inlet of phase separation tank 3 and allowed to settle. After an appropriate residence time (which can be determined by calculating the droplet rise / fall rate), the high-density phosphoric acid phase (containing uranium) gradually sinks to the bottom, while the low-density organic phase rises to the top, and a clear interface between the two phases is formed. After the stratification stabilizes, the lower phosphoric acid phase is first discharged through the bottom drain valve and sent to uranium recovery unit 4; then the upper clear organic phase is exported and sent to the subsequent vacuum distillation unit 5.

[0034] To minimize cross-contamination between the two phases, an online radioactivity detector can be installed at the outlet of phase separation tank 3: the upper organic phase is tested for radioactivity, and if abnormal uranium activity is found, the settling time is extended or a washing step is added; the lower aqueous phase is tested for organic content, and if a large amount of organic phase is entrained, it can be returned to the tank for re-separation or auxiliary separation measures such as centrifugation can be taken.

[0035] This step achieves efficient separation of the uranium-containing phosphate phase and the organic phase through gravity-driven natural phase separation without additional energy consumption. The phase transfer rate of uranium can reach over 99%, laying the foundation for subsequent uranium recovery and organic solvent purification.

[0036] In one embodiment of the invention, the uranium recovery stage is carried out in a uranium recovery unit 4, which includes an acidification reactor and a precipitation reactor connected in series. The aqueous phase outlet of the phase separation tank 3 is connected to the feed inlet of the acidification reactor of the uranium recovery unit 4. The lower phosphoric acid phase (generally a concentrated phosphoric acid solution containing uranyl phosphate complexes, with a uranium concentration of up to 40-50 g / L) is first fed into the acidification reactor.

[0037] Concentrated nitric acid (HNO3) is slowly added with stirring, controlling the acid concentration to approximately 3–6 mol / L, and the temperature is maintained at 50–60°C. The following reaction occurs: UO2HPO4+2HNO3→UO2(NO3)2+H3PO4; Through the above acidolysis reaction, the uranyl complex in the phosphoric acid medium is converted into soluble uranyl nitrate. Uranium exists in the solution in the form of UO2(NO3)2, while the generated phosphoric acid remains in the solution.

[0038] After acidification, the feed solution is transferred to a precipitation reactor. The temperature is maintained at 50–60°C in the precipitation reactor with vigorous stirring, and then 25% ammonia solution (or gaseous ammonia) is slowly added dropwise to gradually neutralize the solution to a weakly alkaline state. As the pH rises to approximately 7.5–8.0, uranium is quantitatively precipitated as sparingly soluble ammonium diuranate. The main reactions are as follows: 2UO2(NO3)2+6NH3+3H2O→(NH4)2U2O7·xH2O↓+ 4NH4NO3; H3PO4 + 3NH3 → (NH4)3PO4; It can be seen that uranium quantitatively precipitates from the solution as a yellow solid (NH4)2U2O7・xH2O (ammonium diuranate, abbreviated as ADU), while soluble ammonium nitrate and ammonium phosphate are produced as byproducts in the solution.

[0039] To obtain larger particles and lower water content, the precipitate can be stirred and matured for approximately 30 minutes after formation. Then, the process is stopped to allow solid-liquid separation, using vacuum filtration to separate the precipitated solid from the mother liquor. The filter cake is uranium product 9, which can be further calcined and reduced to obtain uranium trioxide (U3O8) or other uranium compounds for subsequent uranium fuel recycling. The filtered mother liquor mainly contains ammonium nitrate, ammonium phosphate, and trace amounts of residual uranium, and can be incorporated into the waste liquid for solidification treatment or recycled after treatment.

[0040] In the system of the present invention, in order to ensure a high uranium recovery rate, an online monitoring system can be set to detect the uranium concentration in the mother liquor after precipitation: if the uranium content is higher than a set threshold (e.g., >0.05 g / L), the acidolysis or precipitation conditions can be adjusted (e.g., extending the reaction time or reprecipitating) until the uranium content in the mother liquor drops to an extremely low level.

[0041] This step, through acidification-ammonia precipitation, achieves a total uranium recovery rate of over 90%, realizing the efficient recycling and utilization of radioactive precious uranium resources.

[0042] In one embodiment of the invention, the organic phase distillation stage is carried out in a vacuum distillation apparatus 5. The organic phase outlet of the phase separation tank 3 is connected to the feed inlet of the vacuum distillation apparatus 5. The upper organic phase from the phase separation tank 3 is mainly composed of alkane diluents (approximately 80% n-dodecane) and a small amount of low-boiling-point impurities, since phosphate esters such as TBP have been decomposed and phosphoric acid has been separated and removed.

[0043] To recover and utilize valuable solvent components, the organic phase is purified by vacuum distillation. Vacuum distillation apparatus 5 includes a heating vessel, a condenser, a vacuum pump, and a distillate collector. During operation, the organic phase feed is first added to the distillation flask and evacuated to a low pressure (e.g., below 10 kPa), then heating and distillation are initiated at a gentle rate.

[0044] The initial temperature was set at approximately 30°C and maintained for a period of time to remove trace amounts of light components (moisture or very low-boiling substances) remaining in the system. The temperature was then gradually increased by approximately 2°C each time, and the condensation and distillation rate was monitored. After heating to approximately 45°C and maintaining this temperature for a period of time, if no more distillate was observed, the temperature increment was adjusted to 1°C per step, and heating continued. At approximately 47°C (corresponding to a condensation temperature of approximately 29°C), a small amount of distillate began to appear, and after approximately 30 minutes, no more liquid evaporated. This initial fraction contained a small amount of low-boiling-point impurities.

[0045] The temperature was then slowly increased to above 50°C, with the main fraction continuously distilling off within the 50–100°C range. The collected condensate, mostly distilled off in the approximately 50–60°C range, was colorless and transparent; analysis revealed that its main component was purified n-dodecane 10. When the distillation rate became extremely slow and no more condensate dripped off within 10 minutes, it indicated that the main organic solvent had been almost completely distilled off. At this point, heating was stopped and the vacuum was released.

[0046] The distillate and residue were removed and their volume and weight measured. The main distillate was purified n-dodecane 10, accounting for approximately 80% of the original organic phase volume, with a purity exceeding 99%, which could be reused as an extractant. The remaining unvaporized heavy organic matter accounted for approximately 20%, which may contain impurities such as high-boiling-point phosphate polymers produced by TBP degradation. This material has a certain degree of radioactivity and needs to be treated as solid waste. After being discharged from the distillation vessel, this residue was sent to solidification unit 7 for stabilization and solidification treatment together with the uranium recovery mother liquor.

[0047] This step utilizes vacuum distillation technology to recover approximately 80% of the n-dodecane solvent from the waste organic phase, significantly reducing the amount of radioactive organic waste generated and the treatment costs. At the same time, the purity of the recovered solvent meets the requirements of the extraction process.

[0048] In one embodiment of the present invention, the exhaust gas treatment stage is carried out in the exhaust gas treatment device 6. The exhaust gas outlet of the pyrolysis reactor 2 is connected to the inlet of the exhaust gas treatment device 6. The hydrocarbon gases such as butene produced by the pyrolysis reaction are combustible gases at normal temperature and pressure, and may carry trace amounts of radioactive components (such as radioactive particles in the form of aerosols).

[0049] This invention preferably employs incineration to treat exhaust gases to render them harmless: the exhaust gases first enter an incineration chamber equipped with a burner and combustion air, where hydrocarbon gases are completely oxidized and decomposed into inorganic small molecules such as carbon dioxide and water in a high-temperature flame. The high-temperature flue gas produced by combustion then enters post-treatment equipment, such as a scrubbing tower or a high-efficiency filter, to remove acidic gases and particulate matter. Finally, the clean and compliant gas is safely discharged through an exhaust stack.

[0050] The combustion temperature and residence time of the exhaust gas treatment device 6 are maintained and monitored by setting parameters of the control system to ensure that hydrocarbon organic matter is completely oxidized and radioactive aerosols are efficiently intercepted.

[0051] This step, through high-temperature incineration combined with exhaust gas purification, can achieve complete harmless treatment of organic exhaust gas, and the emitted waste gas meets the national radioactive waste emission standards.

[0052] In one embodiment of the invention, the solidification stage is carried out in the solidification device 7. The waste liquid outlet of the uranium recovery device 4 and the residue outlet of the vacuum distillation device 5 are both connected to the feed inlet of the solidification device 7 to treat the residual waste from the uranium recovery and distillation steps.

[0053] The mother liquor produced in the uranium recovery process contains large amounts of ammonium nitrate and phosphate, as well as trace amounts of unrecovered uranium and other radioactive impurities, and should not be discharged directly. The heavy residue produced in the organic distillation process is a viscous organic substance, which also contains radioactive contaminants and is chemically unstable.

[0054] The curing device 7 can employ methods such as cement curing, asphalt curing, or glass curing to uniformly mix the aforementioned waste liquid and residue and then add it to the matrix material to form a stable cured form. For example, in this embodiment, the uranium recovery mother liquor is concentrated and then mixed with materials such as cement and sand in a certain proportion, poured into molds, and cured into stable cement blocks; organic residues are mixed into hot-melt asphalt, stirred and dispersed, and then cooled and cured into solid asphalt blocks.

[0055] Solidified waste exhibits regular shape, high strength, and low leaching rate, allowing for safe storage and final disposal. The solidification unit 7 is equipped with a radioactivity monitoring instrument and a solidifying agent dosing control system to ensure that the solidified products meet the requirements for radioactive waste management.

[0056] This step, through stabilization and solidification treatment, transforms residual radioactive waste into a stable solid form, significantly reducing the risk of radionuclide leaching and facilitating long-term safe storage and final disposal.

[0057] In one embodiment of the present invention, in order to achieve automatic control and safe operation of the entire process, the system of the present invention is equipped with a complete online monitoring and control subsystem.

[0058] Specifically, temperature and pH sensors are installed in the pretreatment washing tank 1 to monitor the washing temperature and aqueous phase acidity to ensure thorough washing; temperature, pressure and tail gas organic component sensors are installed on the pyrolysis reactor 2 to monitor the reaction temperature and decomposition process in real time. When the temperature or pressure rises abnormally, the heating power is automatically adjusted or the cooling system is started or stopped. When the organic content of the tail gas drops to a low value, feedback is triggered to end the reaction. A solution pH sensor and a liquid level detector are installed on the precipitation reactor of uranium recovery unit 4 to achieve precise control of the ammonia addition rate and prevent overflow; a radioactive dose monitor is installed at the condensation outlet of vacuum distillation unit 5 to detect the radioactivity of the distilled solvent and ensure that it meets the radiological safety standards for reuse.

[0059] All monitoring data is transmitted in real time to a central programmable logic controller (PLC) or distributed control system (DCS). The control system automatically adjusts relevant equipment according to preset process parameter ranges, such as controlling the start and stop of the feed pump, heater temperature, and vacuum pump pressure, to achieve closed-loop control. Simultaneously, when any monitored parameter exceeds the safety limit, the system will issue an alarm signal and can implement interlock shutdown to ensure the safety and stability of the process operation.

[0060] Example 1: Pyrolysis and Uranium Recovery Experiment of Uranium-Containing Waste TBP / Kernel Oil Organic Phase One liter of 30% TBP / kerosene extractant was taken from the nuclear fuel reprocessing process (of which TBP volume fraction is 30%, kerosene is about 70%, and uranium concentration is about 5 g / L, mainly existing in the form of uranyl complex in the organic phase).

[0061] First, pretreatment washing is performed: the waste organic phase is added to a 2L glass mixing and clarification tank, an equal volume of pure water is added, and the mixture is stirred at 45℃ for 15 minutes, then allowed to stand and separate into layers. The lower acidic aqueous phase is then discharged. This washing process is repeated 3 times until the pH of the aqueous phase is close to neutral and free of nitrates, yielding approximately 0.9L of pretreated organic phase.

[0062] Then, phosphoric acid catalytic pyrolysis was carried out: the pretreated organic phase was transferred to a 2L reactor (stainless steel lined with tetrafluoroethylene) equipped with a stirrer and condenser recovery device, 150mL of 85% phosphoric acid (approximately 2.2 times the molar amount of TBP) was added, the device was sealed, and nitrogen was purged to purge the air before stirring and heating began. When the temperature reached 200℃, the reaction was maintained at a constant temperature of 200±5℃ for 1 hour.

[0063] During the reaction, a continuous release of gas was observed, which was then condensed and collected. Initially, a small amount of water and light organic matter were generated. After the temperature rose to approximately 180°C or higher, a large amount of hydrocarbon gas (mainly butene) was produced, totaling approximately 20 L (standard conditions). After about one hour of reaction, the tail gas collection rate decreased significantly, indicating that TBP had been almost completely decomposed. Heating was stopped and the mixture was cooled to below 100°C. The reaction product liquid was released from the bottom of the vessel while still hot and quickly transferred to a separatory funnel for static cooling and separation.

[0064] After cooling, two distinct phases were observed: the lower layer was a brownish-yellow viscous liquid (phosphoric acid phase), approximately 210 mL, and the upper layer was a light yellow, clear liquid (organic phase), approximately 720 mL. Analysis of small samples from both phases revealed: the uranium concentration in the lower aqueous phase was approximately 45 g / L, almost entirely containing all the uranium from the initial waste liquid; the phosphorus content in the upper organic phase was <50 mg / L, essentially free of phosphate esters, and the alpha radioactivity was <1 × 10⁻⁶. 3 The concentration of Bq / L indicates that most radioactive impurities have entered the aqueous phase. The lower phosphoric acid phase was transferred to a 1000 mL beaker, and 50 mL of concentrated nitric acid (HNO3) was added. The mixture was stirred and heated to approximately 60°C for 0.5 hours, causing the solution to change from viscous to clear, forming uranyl nitrate. This acidified solution was then transferred to a 500 mL beaker and placed in a water bath at 55°C with stirring. Approximately 120 mL of 25% ammonia solution was slowly added using a titration funnel, gradually increasing the pH from 1 to approximately 8. At pH ≈ 8, a large amount of yellow precipitate appeared in the solution. The reaction was stopped after stirring and maintaining the temperature for 30 minutes. After filtration, the filter cake was washed with a small amount of deionized water and dried at 50°C to obtain 7.0 g of a light yellow solid. Analysis showed that this solid was ammonium diuranate (ADU), containing approximately 4.8 g of uranium, equivalent to 96% of the total uranium in the initial waste liquid. The filtrate volume is approximately 350 mL, with a uranium concentration below 0.02 g / L, and can be directly treated as a Class II low-level radioactive waste liquid.

[0065] This demonstrates that the method of the present invention can efficiently transfer and recover uranium from the organic phase of waste TBP, while simultaneously inorganicating the organic phase.

[0066] Example 2: Organic phase vacuum distillation and solvent recovery experiment 720 mL of the upper organic phase obtained from phase separation in Example 1 was placed in a 1 L three-necked distillation flask, and a reflux condenser and a vacuum pump were connected to evacuate the flask to an absolute pressure of approximately 5 kPa.

[0067] Turn on the electric heating mantle at approximately 200W to slowly raise the liquid temperature to 30°C and maintain it for 10 minutes; no distillate will form at this point. Then, gradually increase the temperature at intervals of approximately 2°C, holding each target temperature for about 10 minutes to observe the distillation process. If no significant condensate drips after heating to 45°C and maintaining it for a period, continue increasing the temperature by 1°C each time. When the temperature reaches approximately 50°C, droplets begin to flow from the condenser outlet, indicating that the main solvent components have begun distillation. Adjust the vacuum to maintain the condensation temperature at approximately 30°C and slowly collect the distillate. As distillation continues, to ensure a stable distillation rate, gradually increase the flask temperature from 50°C to approximately 100°C. When the temperature reaches 100°C, almost no more liquid will distill; stop heating and the vacuum pump, and return to atmospheric pressure.

[0068] The collected distillate and residue were poured out and their volumes measured separately: approximately 580 mL of distillate and approximately 140 mL of residue. The distillate was clear and transparent, with no irritating odor. Gas chromatography analysis showed that the main component was n-dodecane, with a purity greater than 99%. The residue was a dark brown viscous liquid containing a small amount of high-molecular-weight organic matter and suspended solids.

[0069] The specific activity of the distillate was measured, and the total alpha radioactivity was <5 Bq / mL and the total beta radioactivity was <10 Bq / mL, indicating that most radioactive impurities did not enter the distillate. This distillate can be reused directly as an extraction solvent, while the remaining 140 mL of heavy organic matter, still containing radioactivity, requires solidification treatment. This residue was mixed with Portland cement and slaked lime in a mass ratio of 1:5:1, and an appropriate amount of water was added to form a mud-like consistency. This mixture was then poured into a mold and solidified for 28 days to form a solid block.

[0070] The leaching toxicity test results of the solidified block showed that the uranium leaching rate was far below the national standard limit, indicating that the residue could safely and stably seal radioactive materials after being solidified with cement, meeting the final disposal requirements.

[0071] In summary, this invention achieves safe and efficient treatment of the organic phase of uranium-containing waste TBP through phosphoric acid catalytic pyrolysis combined with wet chemical precipitation. Under mild conditions, the organic components in the organic phase are converted into inorganic small molecules for recycling, while simultaneously enabling efficient recovery and fixation of radioactive uranium, significantly reducing the hazards and disposal difficulties of radioactive organic waste.

[0072] The method and system of this invention have the advantages of simple process flow, high equipment integration and safe and reliable operation, and are suitable for the reduction and resource utilization of uranium-containing extractant waste liquid generated in the nuclear fuel cycle process.

[0073] It should be noted that, in this invention, although the specification describes the embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A system for processing uranium-containing organic phases, comprising a pretreatment washing tank (1), a pyrolysis reactor (2), a phase separation tank (3), and a uranium recovery device (4) in sequential fluid communication, characterized in that, It also includes a vacuum distillation unit (5) and an online monitoring and control subsystem; The vacuum distillation apparatus (5) is in fluid communication with the uranium recovery apparatus (4), and the vacuum distillation apparatus (5) is used to recover and purify n-dodecane (10) from the organic phase; The pretreatment washing tank (1) is used to wash and remove acid from the uranium-containing organic phase with water; The pyrolysis reactor (2) is used to add phosphoric acid to catalytically decompose TBP in the organic phase and transfer uranium to the phosphoric acid phase. Its tail gas outlet is connected to the inlet of the tail gas treatment device (6). The phase separation tank (3) is used to separate the uranium-containing phosphate phase from the organic phase; The uranium recovery device (4) is used to recover uranium products (9) from uranium-containing phosphoric acid phase, and the waste liquid outlet of the uranium recovery device (4) and the residue outlet of the vacuum distillation device (5) are both connected to the feed inlet of the solidification device (7). The online monitoring and control subsystem is electrically connected to the pretreatment washing tank (1), pyrolysis reactor (2), phase separation tank (3), uranium recovery device (4), vacuum distillation device (5), tail gas treatment device (6) and solidification device (7), respectively, and is used to monitor process parameters in real time and realize automatic control and safety interlock.

2. The system for processing uranium-containing organic phases according to claim 1, characterized in that, The pretreatment washing tank (1) is a mixing and clarification tank structure, with a stirring and mixing zone and a clarification and stratification zone inside, which is used to realize multi-stage series water washing operation.

3. The system for processing uranium-containing organic phases according to claim 1, characterized in that, The pyrolysis reactor (2) is made of acid-resistant and radiation-resistant materials and is equipped with a stirring device, a heating device and a temperature control device. Furthermore, the feed inlet of the pyrolysis reactor (2) is also connected to a feed pump for adding phosphoric acid.

4. The system for processing uranium-containing organic phases according to claim 1, characterized in that, The phase separation tank (3) is a gravity settling tank with a feed inlet at the top and baffles or mesh covers inside to promote droplet aggregation. The bottom and upper parts are respectively provided with phosphate phase outlet and organic phase outlet, and both outlets are equipped with online radioactivity detectors.

5. The system for processing uranium-containing organic phases according to claim 1, characterized in that, The uranium recovery unit (4) includes an acidification reactor and a precipitation reactor connected in series; The acidification reactor is used to convert uranyl phosphate into uranyl nitrate, and the precipitation reactor is used to precipitate uranium as ammonium diuranate.

6. A method for processing uranium-containing organic phases, comprising processing using the system for processing uranium-containing organic phases as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Pretreatment: The uranium-containing organic phase is sent into the pretreatment washing tank (1) and heated with water to remove the free acid and nitrate, thus obtaining the deacidified organic phase; S2, Catalytic pyrolysis: The deacidified organic phase is fed into the pyrolysis reactor (2), phosphoric acid is added as a catalyst, and the pyrolysis reaction is carried out under normal pressure, so that TBP is decomposed into hydrocarbon gas and phosphoric acid, and uranium is transferred to the phosphoric acid phase to form a uranium-containing mixture. S3, phase separation: The uranium-containing mixture is sent into the phase separation tank (3) and allowed to stand and separate into layers to obtain the lower uranium-containing phosphoric acid phase and the upper organic phase; S4. Uranium recovery: The uranium-containing phosphate phase is fed into the uranium recovery unit (4), and uranium products (9) are recovered by chemical precipitation. S5, Solvent recovery: The organic phase is fed into a vacuum distillation apparatus (5) for vacuum distillation to recover purified n-dodecane (10); S6. Waste treatment: The tail gas generated by the pyrolysis reaction is sent to the tail gas treatment device (6) for harmless treatment, and the waste liquid generated by uranium recovery and the residue generated by vacuum distillation are sent to the solidification device (7) for stabilization and solidification.

7. The method for processing uranium-containing organic phases according to claim 6, characterized in that, In step S1, a multi-stage series water wash is performed using warm water at 40-50°C until the separated washing liquid is neutral and free of nitrate residue.

8. The method for processing uranium-containing organic phases according to claim 6, characterized in that, In step S2, the molar ratio of phosphoric acid to TBP is greater than 2:1, the pyrolysis reaction temperature is controlled at 190-250℃, and the reaction time is determined based on the online monitoring results of the organic component content in the tail gas.

9. The method for processing uranium-containing organic phases according to claim 6, characterized in that, Step S4 is as follows: First, concentrated nitric acid is added to the uranium-containing phosphate phase to carry out an acid hydrolysis reaction, converting uranyl phosphate into uranyl nitrate; Then, ammonia water is added to the acid hydrolysis solution to adjust the pH to 7.5-8.0, so that uranium precipitates out in the form of ammonium diuranate. Uranium product is obtained by solid-liquid separation (9).

10. The method for processing uranium-containing organic phases according to claim 6, characterized in that, In step S5, vacuum distillation is carried out at an absolute pressure below 10 kPa, and the purified n-dodecane (10) recovered has a purity of not less than 99% and a recovery rate of not less than 80%.

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