A method and system for recovering uranium from an aged organic phase

Abstract

The application relates to a method and system for recovering uranium from an aged organic phase, and the method specifically comprises the following steps: S1 water washing treatment: the aged organic phase is contacted with an aqueous washing solution in multiple stages and phase separation is performed to obtain a water-washed organic phase and a first uranium-containing aqueous phase; S2 carbonate salt washing: the water-washed organic phase obtained in the step S1 is contacted with an aqueous carbonate salt solution and phase separation is performed to obtain a carbonate salt-washed organic phase and a second uranium-containing aqueous phase; S3 sodium chloride washing: the carbonate salt-washed organic phase obtained in the step S2 is contacted with an aqueous sodium chloride solution and phase separation is performed to remove residual carbonate salt entrained in the organic phase; S4 dilute phosphoric acid fine washing: the sodium chloride-washed organic phase obtained in the step S3 is contacted with an aqueous dilute phosphoric acid solution and phase separation is performed to obtain a low-uranium organic phase; and S5 the first uranium-containing aqueous phase and the second uranium-containing aqueous phase are sent into a uranium recovery unit respectively or in combination to recover uranium. The application is targeted at the graded removal and recovery of different uranium forms.

Description

Technical Field

[0001] This invention relates to the fields of nuclear fuel reprocessing, hydrometallurgy, and the reduction and resource recovery of radioactive organic waste liquids, specifically to a method and system for recovering uranium from aged organic phases. More specifically, it relates to a method and system for uranium-containing aged tributyl phosphate (TBP) / kerosene organic phases formed after long-term storage or recycling, which achieves uranium staged transfer, interface contamination control, and uranium recovery through multi-stage water washing, carbonate complexation washing, sodium chloride washing, and dilute phosphoric acid refining. Background Technology

[0002] The TBP / hydrocarbon diluent system is widely used for the nitric acid-medium extraction of actinide elements such as uranium and plutonium. During long-term operation, irradiation, contact with acidic media, and storage, this system gradually ages, generating dibutyl phosphate (DBP), monobutyl phosphate (MBP), butanol, kerosene oxidation / nitration products, colloids, and fine solid particles. DBP and MBP, as acidic degradation products of TBP, can form more stable complexes with uranyl ions than conventional TBP complexes. In particular, MBP (i.e., monoalkyl long-chain acidic phosphate) has a significantly stronger complexing ability for uranyl ions than DBP, resulting in a large amount of uranium remaining in the organic phase even after conventional water washing or dilute nitric acid back-extraction. Experimental results show that for aged 30% TBP / kerosene with a uranium concentration of 20–100 g / L and a nitric acid concentration of approximately 0.01–0.05 mol / L, after six back-extractions using only 0.01 mol / L dilute nitric acid, 25–40 g / L of uranium can still remain in the organic phase.

[0003] In existing technologies, carbonates (sodium carbonate, sodium bicarbonate, ammonium carbonate, etc.) have been reported for the purification of aged TBP solvents. Their mechanisms include: removing uranium bound to degradation products by forming water-soluble uranyl carbonate complexes; and converting HDBP (dibutyl phosphate) and H2MBP (monobutyl phosphate) into their corresponding sodium salts (NaDBP, Na2MBP), thereby restoring the properties of the organic phase. However, current research and practice mainly focus on the impact of carbonate washing on solvent regeneration efficiency, and the treated objects are mostly TBP-kerosene after conventional operation. For special material systems with high uranium concentrations, severe aging, and uranium mainly bound to MBP (monoalkyl long-chain acidic phosphates), the applicability and subsequent effects of carbonate washing lack systematic research.

[0004] This study found that when carbonate washing is applied to the aged organic phase after water washing, although it can effectively convert uranyl-MBP complexes into water-soluble uranyl carbonate complexes to achieve uranium transfer, some carbonate ions in the carbonate solution remain and are entrained in the organic phase. Directly using these carbonate-entrained organic phases for subsequent processing will cause serious problems: firstly, the residual carbonates will release CO2 under subsequent acidic conditions, triggering violent boiling during high-temperature processes such as TBP pyrolysis and inorganic degradation, leading to process control failure or even safety accidents; secondly, if the residual interfacial active substances such as NaDBP / NaMBP are not treated, it will affect the applicability of the organic phase as a downstream raw material.

[0005] Existing processing procedures typically focus only on a single objective in deacidification or deuranium removal, connecting water, carbonate solution, and acid in an arbitrary order. They lack a systematic consideration of factors such as uranium speciation differences, effective carbonate removal, the impact of residual carbonate on the safety of subsequent processes, and the removal of residual interfacial active salts. In particular, current technologies fail to recognize that for high-concentration uranium systems bound to MBP, residual carbonate entrained in the organic phase after carbonate washing is not merely a secondary issue affecting phase separation or purity, but a critical factor directly impacting the safe operation of subsequent thermal cracking processes. Therefore, there is an urgent need for a comprehensive method and system capable of achieving deep removal of uranium bound to MBP from the organic phase of aged TBP / kerosene in high-uranium environments, while simultaneously effectively removing entrained carbonates and ensuring the safety of subsequent processing. Summary of the Invention

[0006] Based on the aforementioned technical problems, this invention addresses the issue that uranium firmly bound to monobutylphosphoric acid in the severely aged TBP / kerosene organic phase with high uranium concentration is difficult to remove completely by conventional water washing or dilute nitric acid back-extraction, and that existing carbonate treatments are prone to affecting the safety of subsequent processes due to residual carbonates (such as thermal cracking boiling). The invention provides a method for achieving deep uranium removal and ensuring the safety of subsequent processing through a controlled sequence of "water washing → carbonate washing → sodium chloride desalting → dilute phosphoric acid washing".

[0007] This invention provides a method for recovering uranium from an aged organic phase, comprising the following steps: S1 Water washing treatment: The aged organic phase is subjected to multi-stage contact and phase separation with an aqueous washing solution to obtain a water-washed organic phase and a first uranium-containing aqueous phase; S2 Carbonate washing: The water-washed organic phase obtained in step S1 is contacted with an aqueous carbonate solution and the phases are separated to obtain a carbonate-washed organic phase and a second uranium-containing aqueous phase; S3 Sodium chloride washing: The organic phase obtained in step S2 after being washed with carbonates is contacted with an aqueous sodium chloride solution and the phases are separated to remove the residual carbonates entrained in the organic phase, thereby obtaining an organic phase washed with sodium chloride. S4 Dilute Phosphoric Acid Washing: The organic phase obtained in step S3, which has been washed with sodium chloride, is contacted with a dilute phosphoric acid aqueous solution and the phases are separated to obtain a low-uranium organic phase; S5 sends the first uranium-containing aqueous phase and the second uranium-containing aqueous phase, either separately or in combination, into the uranium recovery unit to recover uranium.

[0008] Further, the aged organic phase comprises 20–40 vol% tributyl phosphate with a uranium concentration of 20–100 g / L, and contains nitric acid, nitrate, dibutylphosphoric acid, monobutylphosphoric acid, kerosene aging products and / or fine interfacial solids, wherein the monobutylphosphoric acid is a monoalkyl long-chain acidic phosphate ester; prior to the water washing treatment, the aged organic phase is subjected to settling, filtration, coalescence, centrifugation or a combination thereof to remove visible solids, colloids and existing interfacial contaminants; Preferably, the concentration of the carbonate aqueous solution is 0.5–2.0 mol / L, the concentration of the sodium chloride aqueous solution is 1–5 wt%, and the concentration of the dilute phosphoric acid aqueous solution is 0.005–0.01 mol / L.

[0009] Further, in step S1, the water washing process includes 3 to 10 theoretical stages. When the uranyl ion concentration in the washing solution after two consecutive stages drops below 0.002 mol / L, and the acidity of the washing solution reaches the allowable value for the subsequent carbonate stage (i.e., pH of the aqueous phase is 5 to 6), the process proceeds to step S2, carbonate washing. The aqueous washing solution is deionized water and / or a 0.001 to 0.05 mol / L nitric acid aqueous solution. Preferably, in step S2, the carbonate washing employs 1 to 4 theoretical stages. When the pH of the washing solution reaches 7-9, it proceeds to step S3 for sodium chloride washing; the amount of CO3² added in each wash... - The molar ratio of residual uranium in the organic phase after water washing in step S1 is not less than 3:1; the carbonate salt aqueous solution includes at least one of sodium bicarbonate aqueous solution, sodium carbonate aqueous solution, potassium bicarbonate aqueous solution, potassium carbonate aqueous solution, and ammonium carbonate aqueous solution. Preferably, in step S3, sodium chloride washing uses 1 to 4 theoretical levels to confirm that the entrained carbonate / alkalinity has decreased significantly and that the sodium chloride washing in S3 has stabilized the phase separation. When a stable two phases are formed within the specified observation time of 1 to 5 minutes and the interface layer does not continue to thicken, the process proceeds to step S4 dilute phosphoric acid washing. Preferably, in step S4, the dilute phosphoric acid washing uses 1 to 4 theoretical stages, and ends when the organic phase has no continuous interfacial film, no visible yellowish-white or yellowish-green precipitate, and can stably separate phases. Further, in step S5, the first uranium-containing aqueous phase and the second uranium-containing aqueous phase are collected separately. The first uranium-containing aqueous phase mainly contains uranium nitrate, and the second uranium-containing aqueous phase mainly contains uranyl carbonate complex. The uranium recovery includes acidifying the uranium-containing aqueous phase, followed by peroxide precipitation, ammonium salt precipitation, ion exchange, solvent extraction, crystallization, or a combination thereof. The resulting uranium precipitate is roasted to convert it into U3O8 or other uranium products.

[0010] Furthermore, each contact step is carried out at 10–40°C, with a single-stage contact time of 1–10 min. Low-shear mixing is employed, and the volume ratio of the aqueous phase to the organic phase (A / O) is 0.2–2.0. Phase separation is completed before the organic phase enters the next processing stage. Preferably, the emulsion layer, interfacial contaminant layer, or third phase formed in any processing stage are discharged separately from the main organic phase, and the uranium-containing solids and entrained liquids therein are separated by centrifugation, filtration, or coalescence.

[0011] Furthermore, the uranium removal rate in the aged organic phase is not less than 90%; the resulting low-uranium organic phase is subjected to U, Na, and Cl... - After final testing of at least three of the following parameters—moisture content, DBP / MBP, turbidity, and phase separation time—it is used for subsequent tributyl phosphate degradation, kerosene recovery, or compliant disposal.

[0012] The present invention also provides a uranium recovery system for implementing the above-described method, comprising a raw material tank, a water washing unit, a carbonate washing unit, a sodium chloride washing unit, a dilute phosphoric acid refining unit, and a low-uranium organic phase tank, which are sequentially connected by an organic phase pipeline; each unit is provided with an aqueous phase inlet, an aqueous phase outlet, and a phase separation structure; the aqueous phase outlets of the water washing unit and the carbonate washing unit are connected to the uranium recovery unit; the system is further provided with an interface contaminant separation unit connected to each unit for independently discharging the emulsion layer and the third phase layer.

[0013] Furthermore, the water washing unit has 3 to 10 theoretical stages, and the carbonate washing unit, sodium chloride washing unit, and dilute phosphoric acid washing unit each have 1 to 4 theoretical stages; the theoretical stage is composed of a mixing and clarification tank, a centrifugal extractor, a pulse contactor, a contactor with a coalescer, or a combination thereof; Preferably, a clarification tank, a coalescer, a centrifuge, or a filter is provided between each of the units, and each of the units is provided with an intermediate phase outlet that communicates with the interface contaminant separation unit, for discharging the interface emulsion layer and the third phase layer before entering the next unit; The water washing unit and the carbonate washing unit are respectively connected to independent uranium-rich aqueous phase collection tanks, and the sodium chloride washing unit and the dilute phosphoric acid washing unit are connected to low-uranium washing liquid collection tanks to achieve the separate collection of uranium-containing aqueous phases. The system adopts a cascade operation mode of organic phase co-current and aqueous phase counter-current of each unit, and is equipped with closed conveying pipelines, secondary dikes, sampling points and tail gas discharge structures.

[0014] Furthermore, it also includes a monitoring and control unit configured to acquire uranium concentration, nitrate concentration, acidity, pH, conductivity, turbidity, phase separation time, interface layer thickness, Na content, and Cl content. - The monitoring and control unit adjusts the aqueous phase flow rate, theoretical stage input, mixing intensity, or interface fouling discharge frequency of each unit based on at least two of the following parameters: nitrate descent plateau at the outlet of the water washing unit, uranium concentration at the outlet of the carbonate washing unit, phase separation time and interfacial layer thickness at the outlet of the sodium chloride washing unit, and organic phase turbidity at the outlet of the dilute phosphoric acid washing unit.

[0015] The present invention also provides an application of the above-described uranium recovery system in the treatment of an aged organic phase for uranium recovery, wherein the aged organic phase is an aged 30 vol% TBP / kerosene organic phase containing uranium concentration of 50-60 g / L and nitric acid concentration of 0.01-0.05 mol / L.

[0016] Compared with the prior art, the advantages of the present invention are: 1. This invention addresses the staged targeted removal of uranium in different forms. The water washing stage preferentially removes free nitric acid, entrained nitrates, and at least some uranyl nitrate-TBP complexes. A carbonate washing stage further removes uranium bound to monobutyl phosphate and dibutyl phosphate (MBP, i.e., monoalkyl long-chain acidic phosphate, DBP, i.e., dibutyl phosphate), transferring it to the aqueous phase as a water-soluble uranyl carbonate complex. The two stages have clearly defined functions, corresponding to the three different forms of uranium: TBP-complexed uranium, MBP-complexed uranium, and DBP-complexed uranium, respectively, avoiding the problem of insufficient processing capacity for two uranium forms by a single stripping agent. Experiments show that the water washing stage and the carbonate washing stage handle approximately 26–27 g / L and approximately 29–30 g / L of uranium transfer, respectively, accounting for over 99% of the total uranium removal.

[0017] 2. In this invention, sodium chloride washing effectively removes residual carbonates, ensuring the safety of subsequent processes. This invention includes a sodium chloride washing section after carbonate washing and before dilute phosphoric acid washing. Its main function is to remove residual carbonates entrained in the organic phase. Experiments show that if sodium chloride washing is omitted, the carbonates entrained in the organic phase will release CO2 during the subsequent inorganic degradation of TBP through pyrolysis, causing violent boiling and preventing the process from proceeding normally. However, the organic phase, after being washed with sodium chloride to remove residual carbonates and then washed with dilute phosphoric acid, did not experience boiling during pyrolysis experiments under the same conditions. This effect indicates that the role of the sodium chloride washing section is not simply "demulsification," but rather directly related to the safe operation of subsequent high-temperature treatment processes by removing residual carbonates. This functional positioning and technical effect are not disclosed in existing technologies.

[0018] 3. The effectiveness of dilute phosphoric acid washing in removing residual interfacial active salts and its compatibility with subsequent processes in this invention. This invention uses dilute phosphoric acid as the final washing agent to protonate residual NaDBP / Na2MBP into HDBP / H2MBP, transferring it to the aqueous phase or interfacial contaminant layer, thus reducing the residue of sodium salts and surface-active organophosphorus degradation products in the organic phase. Dilute phosphoric acid effectively protonates interfacial active salts without causing significant uranium re-extraction or large amounts of phosphate precipitation, balancing washing effectiveness and uranium recovery rate. After dilute phosphoric acid washing, the Na and Cl in the organic phase are significantly reduced. - Indicators such as carbonate / alkalinity, moisture, and DBP / MBP can be reduced to within the release limits of downstream processes, which is beneficial for subsequent TBP degradation, kerosene distillation recovery, or compliant disposal.

[0019] 4. The controlled sequence and inter-stage release mechanism of this invention constitute a coordinated control. The four processing stages of this invention are not arbitrary arrangements of detergents, but rather a controlled process designed based on a systematic understanding of uranium speciation differences, carbonate entrainment behavior, and their impact on subsequent processes. Inter-stage release conditions are set between each stage: the water washing stage uses NO3... - The process is divided into three stages: the first stage ends with a plateau in acidity and conductivity; the second stage ends with sufficient uranium transfer and the aqueous phase remaining alkaline; the third stage ends with stable phase separation and a significant decrease in carbonate / alkalinity; and the fourth stage ends with the absence of a persistent interfacial film and visible precipitation. This controlled sequence ensures that the next step can only proceed after the results of each step have reached the preset state, avoiding process failures caused by interference between steps. Attached Figure Description

[0020] Figure 1 Overall process for staged uranium removal and uranium recovery from aged TBP / kerosene organic phase; Figure 2 A multi-stage mixing and clarification tank or a series of centrifugal extractors system.

[0021] The reference numerals in the attached figures are shown in Table 1: Table 1

[0022] Specific implementation methods To make the objectives, technical solutions, and advantages of this application clearer, a more detailed description is provided below. However, it should be understood that the description herein is merely for explaining this application and is not intended to limit its scope.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terms used herein (as shown in Table 2) are for the purpose of describing particular embodiments only and are not intended to limit the scope of this application. All reagents and instruments used herein are commercially available, and the characterization methods involved can be found in relevant descriptions in the prior art, and will not be repeated herein.

[0024] Table 2

[0025] To further understand this application, the following detailed description is provided in conjunction with the preferred embodiments.

[0026] Example 1 This embodiment provides a method for recovering uranium from an aged organic phase, including the following steps: S1 Water washing treatment: The aged organic phase is subjected to multi-stage contact and phase separation with an aqueous washing liquid to obtain a water-washed organic phase and a first uranium-containing aqueous phase; the water washing treatment removes free nitric acid, entrained nitrates, and at least part of the uranyl nitrate-tributyl phosphate complex.

[0027] S2 Carbonate Washing: The water-washed organic phase obtained in step S1 is contacted with an aqueous carbonate solution and the phases are separated to obtain a carbonate-washed organic phase and a second uranium-containing aqueous phase. The carbonate washing causes uranium bound to monobutylphosphoric acid to be transferred into the second uranium-containing aqueous phase in the form of a water-soluble uranyl carbonate complex. Carbonate washing can treat uranium bound to DBP / MBP or stabilized by acid aging products, converting it into a water-soluble uranyl carbonate complex.

[0028] S3 Sodium Chloride Washing: The organic phase obtained from step S2 after carbonate washing is contacted with an aqueous sodium chloride solution for phase separation to remove residual carbonates entrained in the organic phase. Carbonate washing converts HDBP and H2MBP into their corresponding sodium salts (NaDBP / Na2MBP), which form an amphiphilic film at the interface. NaCl promotes droplet coalescence by increasing ionic strength, compressing the electric double layer, weakening electrostatic repulsion between interfacial particles, and salting out. In this invention, no emulsification occurs when the water-washed TBP / kerosene mixed phase is washed with carbonates; the NaCl washing is to remove residual sodium carbonate in the organic phase, not to break the emulsion layer.

[0029] S4 Dilute Phosphoric Acid Washing: The organic phase obtained in step S3, washed with sodium chloride, is contacted with a dilute phosphoric acid aqueous solution and the phases are separated to obtain a low-uranium organic phase. The dilute phosphoric acid washing protonates and removes residual dibutyl phosphate and / or monobutyl phosphate. Protonation of residual NaDBP / Na2MBP reduces its surface activity and causes sodium to transfer into the aqueous phase in the form of phosphate.

[0030] S5 sends the first uranium-containing aqueous phase and the second uranium-containing aqueous phase, either separately or in combination, into the uranium recovery unit to recover uranium.

[0031] As a further preferred embodiment, the concentration of the carbonate aqueous solution is 0.5–2.0 mol / L, preferably 0.8–1.2 mol / L; the concentration of the sodium chloride aqueous solution is 1–5 wt%; and the concentration of the dilute phosphoric acid aqueous solution is 0.005–0.01 mol / L.

[0032] As a further preferred embodiment, the present invention also includes pretreatment: Before treatment, at least the following parameters should be determined: uranium content, total acidity or water-extractable acidity, and NO3 in the organic phase. - / NO2 - Moisture, TBP, DBP / MBP, and visible particles. For raw materials with a distinct bottom phase, yellow-green particles, dark brown colloids, or existing emulsion layers, it is preferable to let them stand, centrifuge, filter, or aggregate at 10–40 °C to separate the main organic phase from the interface contaminant layer.

[0033] The pretreatment is not aimed at completely removing uranium, but rather at reducing the formation of emulsions and colloids that would occur during subsequent carbonate contact. The separated third fraction was weighed separately and its U, P, Na, and NO3 were determined. - Cl - and organic matter content.

[0034] As a further preferred embodiment, in step S1, the pretreated organic phase is sent to a water washing process, which includes 3 to 10 theoretical stages, preferably 6 stages. Each stage is in contact for 1 to 10 minutes, preferably 2 to 5 minutes; the contact temperature is preferably 10 to 40 °C.

[0035] The endpoint of the water washing stage is not determined by the apparent pH of the organic phase, but by the NO3 concentration in the water extract or each stage of the wash solution. - Based on acidity, conductivity, and U. When the uranyl ion concentration in the washing solution after two consecutive stages drops below 0.002 mol / L, and the acidity of the washing solution reaches the allowable value for the subsequent carbonate stage, i.e., the aqueous phase pH is 5~6, almost neutral, the process proceeds to step S2, carbonate washing. The aqueous washing solution is deionized water and / or a 0.001~0.05 mol / L nitric acid aqueous solution. Preferably, at least the last 1~2 stages use deionized water.

[0036] The water washing stage mainly treats free HNO3, entrained aqueous phase, and relatively easily back-extractable uranyl nitrate-TBP complex, which can be illustrated by the following formula: UO2(NO3)2·2TBP(org) UO2² + (aq) + 2NO3 - (aq) + 2TBP(org).

[0037] As a further preferred embodiment, in step S2, the carbonate washing employs 1 to 4 theoretical stages, preferably 2 to 3 stages; when the pH of the washing solution is 7-9, it proceeds to step S3 for sodium chloride washing; the amount of CO3² added in each wash... - The molar ratio of residual uranium in the organic phase after water washing in step S1 is not less than 3:1; the carbonate salt aqueous solution includes at least one of sodium bicarbonate aqueous solution, sodium carbonate aqueous solution, potassium bicarbonate aqueous solution, potassium carbonate aqueous solution, and ammonium carbonate aqueous solution.

[0038] Preferably, the carbonate stage treats uranium that is bound to DBP / MBP or stabilized by acidic aging products. The residual uranium in the organic phase after the water washing treatment in step S1 is mainly bound to monobutyl phosphate (MBP, i.e., monoalkyl long-chain acidic phosphate). The water-washed organic phase is then contacted with a 0.5–2.0 mol / L carbonate alkaline complex salt aqueous solution. The theoretical carbonate dosage can be at least 3 moles of CO3²⁻ per mole of U. -Estimate and account for the additional consumption of residual acid, HDBP, H2MBP, and other acidic aging products. The preferred carbonate concentration is 0.8–1.2 mol / L, and the A / O ratio is 0.5–1.0, using two stages of fresh wash solution or two to three stages of countercurrent. If the aqueous phase pH drops significantly, a yellow-green precipitate appears, or the interfacial layer thickens rapidly, it indicates insufficient carbonate capacity; in this case, increase water washing, increase the effective carbonate content, or reduce the single-stage load.

[0039] As a further preferred embodiment, in step S3, the sodium chloride washing uses 1 to 4 theoretical stages, preferably 2 stages. After confirming that the entrained carbonate / alkalinity has decreased significantly and that the sodium chloride washing in S3 has stabilized the phase separation, the phase separation time, interface layer thickness / volume, and turbidity are recorded. When a stable two phases are formed within the specified observation time of 1-5 minutes and the interface layer does not continue to thicken, the process proceeds to step S4, fine washing with dilute phosphoric acid.

[0040] The function of NaCl washing is to remove residual sodium carbonate entrained in the organic phase. The primary purpose of the NaCl stage is not chemical precipitation of uranium, but rather to promote droplet coalescence by increasing ionic strength, compressing the electric double layer, weakening electrostatic repulsion between interfacial particles, and promoting salting out, thereby separating the entrained carbonate droplets and the uranium-rich third phase from the main organic phase. After the NaCl stage, the conductivity and Cl- content of the organic phase aqueous extract should be measured. - And alkalinity. NaCl is not the final retained component; under the premise of ensuring no back emulsification, salt entrainment can be gradually reduced by subsequent fine washing with dilute phosphoric acid and washing with a small phase of water.

[0041] As a further preferred embodiment, in step S4, the dilute phosphoric acid washing employs 1 to 4 theoretical stages, preferably 2 stages. The process ends when the organic phase exhibits no persistent interfacial film, no visible yellowish-white or yellowish-green precipitate, and stable phase separation is achieved.

[0042] Dilute phosphoric acid protonates NaDBP / Na2MBP, reducing the interfacial film strength and facilitating the transfer of residual sodium and carbonate salts into the aqueous phase. The phosphoric acid concentration used should be sufficient to protonate the interfacial active salts without causing significant uranium back-extraction or substantial phosphate precipitation. If a yellowish-white precipitate or liquid film appears at the interface, the amount of acid used in each stage should be reduced, the mixing intensity decreased, and the intermediate layer removed by centrifugation / filtration.

[0043] The dilute phosphoric acid washing stage reduces the surface activity of residual NaDBP / Na2MBP by protonation and transfers sodium into the aqueous phase in the form of phosphate. NaDBP + H3PO4 HDBP + NaH2PO4 Preferably, the above sequence is synergistic. If the NaCl stage is skipped and the washing is directly followed by deionized water, the sudden drop in ionic strength will induce re-emulsification; if the NaCl stage is skipped and the washing is directly followed by dilute phosphoric acid, CO2 precipitation, salt precipitation, and thickening of the interfacial contaminant layer may occur in the presence of residual carbonates; if the dilute phosphoric acid washing is omitted, NaDBP / Na2MBP and the interfacial film may remain. This invention is not a simple rearrangement of known detergents, but rather utilizes the NaCl stage to establish an ionic strength transition and independent phase behavior control window between the carbonate stage and the acid washing stage.

[0044] As a further preferred embodiment, in step S5, the first uranium-containing aqueous phase and the second uranium-containing aqueous phase are collected separately. The first uranium-containing aqueous phase mainly contains uranium nitrate, and the second uranium-containing aqueous phase mainly contains uranium acyl carbonate complex. The uranium recovery includes acidifying the uranium-containing aqueous phase, followed by peroxide precipitation, ammonium salt precipitation, ion exchange, solvent extraction, crystallization, or a combination thereof. The obtained uranium precipitate is converted into U3O8 or other uranium products by roasting.

[0045] The first uranium-containing aqueous phase typically contains nitrate and uranium released from TBP complexes; the second uranium-containing aqueous phase is typically dominated by uranyl carbonate complexes. Both can be treated separately to control acid, carbonate, and sodium loadings.

[0046] Uranium-containing aqueous carbonates can be acidified to destroy uranyl carbonate complexes, and then uranium can be recovered by methods such as peroxide precipitation, ammonium salt precipitation, ion exchange, solvent extraction or crystallization. The obtained uranium precipitate can be converted into U3O8 or other uranium products by washing and roasting.

[0047] When the uranium concentration in the NaCl washing solution and dilute phosphoric acid washing solution is significantly lower than that in the first two stages, it can be reused, incorporated into the uranium recovery stage, or sent to a dedicated water treatment facility, depending on the nuclide and salt load.

[0048] As a further preferred embodiment, the aged organic phase comprises 20–40 vol% tributyl phosphate with a uranium concentration of 20–100 g / L, and contains nitric acid, nitrate, dibutylphosphoric acid, monobutylphosphoric acid, kerosene aging products and / or fine interfacial solids, wherein the monobutylphosphoric acid is a monoalkyl long-chain acidic phosphate ester; prior to the water washing treatment, the aged organic phase is subjected to settling, filtration, coalescence, centrifugation or a combination thereof to remove visible solids, colloids and existing interfacial contaminants.

[0049] Preferably, the aged organic phase comprises 30 vol% tributyl phosphate, has a uranium concentration of 50–60 g / L, and contains 0.01–0.05 mol / L nitric acid.

[0050] As a further preferred embodiment, each contact step is carried out at 10–40°C, the single-stage contact time is 1–10 min, low-shear mixing is used, the volume ratio of aqueous phase to organic phase (A / O) is 0.2–2.0, preferably 0.5–1.0, and phase separation is completed before the organic phase enters the next processing stage.

[0051] As a further preferred embodiment, the emulsion layer, interface contaminant layer, or third phase formed in any processing stage is discharged separately from the main organic phase and separated from the uranium-containing solids and entrained liquids by centrifugation, filtration, or coalescence.

[0052] The third phase, after centrifugation or filtration, yields uranium-containing solids / colloids and entrained liquids.

[0053] As a further preferred embodiment, the uranium removal rate in the aged organic phase is not less than 90%; the resulting low-uranium organic phase is subjected to U, Na, Cl... - After final testing of at least three of the following parameters—moisture content, DBP / MBP, turbidity, and phase separation time—it is used for subsequent tributyl phosphate degradation, kerosene recovery, or compliant disposal.

[0054] Example 2 This embodiment provides a uranium recovery system for implementing the method described in Embodiment 1. The system includes a raw material tank (10), a water washing unit (20), a carbonate washing unit (30), a sodium chloride washing unit (40), a dilute phosphoric acid refining unit (50), and a low-uranium organic phase tank (60), all connected sequentially via organic phase pipelines. Each unit is equipped with an aqueous phase inlet, an aqueous phase outlet, and a phase separation structure. The aqueous phase outlets of the water washing unit and the carbonate washing unit are respectively connected to independent uranium-rich aqueous phase collection tanks (71, 72) and are connected to the uranium recovery unit (80); the sodium chloride washing unit and the dilute phosphoric acid refining unit are connected to low-uranium washing liquid collection tanks (73, 74). The system also includes an interface contaminant separation unit (90) connected to each unit for independently discharging the emulsion layer and the third phase layer. Figure 1 , 2 As shown.

[0055] As a further preferred embodiment, the water washing unit has 3 to 10 theoretical stages, and the carbonate washing unit, sodium chloride washing unit, and dilute phosphoric acid washing unit each have 1 to 4 theoretical stages; the theoretical stage is composed of a mixing and clarification tank, a centrifugal extractor, a pulse contactor, a contactor with a coalescer, or a combination thereof.

[0056] As a further preferred embodiment, a clarification tank, a coalescer, a centrifuge, or a filter is provided between each of the units, and each of the units is provided with an intermediate phase outlet that communicates with the interface contaminant separation unit, for discharging the interface emulsion layer and the third phase layer before entering the next unit.

[0057] As a further preferred embodiment, a monitoring and control unit is also included, which is configured to acquire uranium concentration, nitrate concentration, acidity, pH, conductivity, turbidity, phase separation time, interface layer thickness, Na content, and Cl content. - The monitoring and control unit adjusts the aqueous phase flow rate, theoretical stage input, mixing intensity, or interface fouling discharge frequency of each unit based on at least two of the following parameters: nitrate descent plateau at the outlet of the water washing unit, uranium concentration at the outlet of the carbonate washing unit, phase separation time and interfacial layer thickness at the outlet of the sodium chloride washing unit, and organic phase turbidity at the outlet of the dilute phosphoric acid washing unit.

[0058] As a further preferred embodiment, the water washing unit and the carbonate washing unit are respectively connected to independent uranium-rich aqueous phase collection tanks, and the sodium chloride washing unit and the dilute phosphoric acid washing unit are connected to low-uranium washing liquid collection tanks to achieve the separate collection of uranium-containing aqueous phases; the system adopts a cascade operation mode of organic phase co-current and aqueous phase counter-current of each unit, and is equipped with closed conveying pipelines, secondary dikes, sampling points and tail gas discharge structures.

[0059] As a further preferred embodiment, in the continuous design, the water washing unit adopts a 6-stage countercurrent mixing and clarification tank; the carbonate washing unit, sodium chloride washing unit, and dilute phosphoric acid unit each adopt a 5-stage mixing and clarification tank or a centrifugal extractor. Interface detection, third-phase discharge outlet, and sampling points are set between each section.

[0060] As a further preferred embodiment, the low-uranium organic phase obtained by the treatment of this invention should at least have U and NO3 measured before entering subsequent TBP degradation, kerosene distillation recovery, or compliant disposal processes. - Carbonate / Alkalinity, Na, Cl - The parameters, including moisture content, DBP / MBP ratio, turbidity, and phase separation time, should be controlled to meet validated internal release limits. For high-temperature phosphoric acid processing, slow feeding, ample free space, condensation, and tail gas treatment should also be employed.

[0061] Preferably, the washing unit (20) adopts a 6-stage countercurrent mixing and clarification tank configuration (21-26). Each theoretical stage consists of a mixing and clarification tank, and each stage is equipped with an aqueous phase inlet, an aqueous phase outlet, an organic phase inlet, an organic phase outlet, and a gravity clarification section. The washing liquid is deionized water, or 0.001-0.05 mol / L dilute nitric acid is used in the previous stage and deionized water is used in the final stage. The volume ratio of aqueous phase to organic phase (A / O) is controlled at 0.5-1.0. The contact time of each stage is 2-5 min, and low-shear mixing is used. After each stage, gravity clarification is used to achieve phase separation, and the clarification time is controlled at 1-5 min depending on the phase separation. A sampling point is provided at the outlet of the washing unit for detecting NO3 in the washing liquid. -Concentration, acidity, conductivity, and uranium concentration. When the NO3 in the two consecutive washing solutions... - When the decrease in concentration and conductivity is less than the preset threshold, and the acidity of the washing solution reaches the allowable value for the subsequent carbonate section, the organic phase after water washing enters the carbonate washing unit.

[0062] The washing unit is also provided with an intermediate phase outlet connected to the interface contaminant separation unit (90) for discharging the interface emulsion layer or existing interface contaminant layer formed in the washing section before entering the next unit.

[0063] Preferably, the carbonate washing unit (30) employs a two-stage mixing and clarification tank (31-32), preferably with 2-3 theoretical stages. The carbonate washing solution is a 1.0 mol / L sodium bicarbonate aqueous solution. The volume ratio (A / O) of the aqueous phase to the organic phase is controlled at 0.5-1.0. The contact time for each stage is 2-5 min, and the theoretical dosage of low-shear mixed carbonate is based on at least 3 mol CO3² of residual uranium per mole in the organic phase after water washing. - Estimate and further compensate for the residual acid and the additional consumption of carbonate by HDBP and H2MBP.

[0064] The carbonate washing unit outlet is equipped with a pH meter and sampling points to monitor the aqueous phase pH, uranium concentration, carbonate capacity, and emulsion layer volume. When uranium transfer is sufficient, the aqueous phase remains alkaline, and there is no continuously thickening third phase, the organic phase, after carbonate washing, enters the sodium chloride washing unit. If the aqueous phase pH drops significantly, a yellow-green precipitate appears, or the interface layer thickens rapidly, it indicates insufficient carbonate capacity, and the number of washing stages should be increased, the effective carbonate content increased, or the single-stage load reduced.

[0065] The carbonate washing unit is provided with an intermediate phase outlet that is connected to the interface dirt separation unit (90).

[0066] Preferably, the sodium chloride washing unit (40) employs a two-stage mixing and clarification tank (41-42). The sodium chloride washing solution is a 3wt% NaCl aqueous solution. The volume ratio (A / O) of the aqueous phase to the organic phase is controlled at 0.5-1.0. The contact time for each stage is 2-5 min, and low-shear mixing is used. The NaCl washing solution causes droplets to coalesce through salting out and charge shielding, and transfers the NaNO3 and NaDBP / Na2MBP water droplets entrained in the organic phase to the aqueous phase.

[0067] The sodium chloride washing unit outlet is equipped with a sampling point for monitoring phase separation time, interface layer thickness or volume, organic phase turbidity, and Cl. - Concentration and alkalinity. The process endpoint for this step is determined by at least one of the following: phase separation time, interfacial layer thickness or volume, and organic phase turbidity. When stable two phases are formed within the specified observation time, and the interfacial layer does not continue to thicken, and the entrained carbonate / alkalinity has significantly decreased, the organic phase, after washing with sodium chloride, enters the dilute phosphoric acid refining unit.

[0068] The sodium chloride washing unit is provided with an intermediate phase outlet that is connected to the interface dirt separation unit (90).

[0069] Preferably, the dilute phosphoric acid washing unit (50) employs a two-stage mixing and clarification tank (51-52). The dilute phosphoric acid washing solution is a 0.007 mol / L H3PO4 aqueous solution. The volume ratio (A / O) of the aqueous phase to the organic phase is controlled at 0.5-1.0. The contact time for each stage is 2-5 min, using low-shear mixing. The dilute phosphoric acid protonates NaDBP / Na2MBP, reducing the interfacial film strength and facilitating the transfer of residual sodium salts and carbonates into the aqueous phase.

[0070] The dilute phosphoric acid washing unit outlet is equipped with a sampling point for monitoring Na content, P content, interfacial film state, and organic phase transparency. The process ends when there is no persistent interfacial film in the organic phase, no visible yellowish-white or yellowish-green precipitate, and stable phase separation is achieved. If a yellowish-white precipitate or liquid film appears at the interface, the amount of acid used in each stage should be reduced, the mixing intensity decreased, and the intermediate layer removed by centrifugation or filtration.

[0071] The dilute phosphoric acid washing unit is equipped with an intermediate phase outlet that is connected to the interface dirt separation unit (90).

[0072] Preferably, each processing unit is equipped with an independent phase separation structure. Gravity clarification, inclined plate coalescence, centrifugal extractor, tubular centrifuge, disc centrifuge, or filter can be used. In this embodiment, the clarification section of each mixing clarification tank also functions as a gravity clarifier, achieving preliminary separation of the organic phase and the aqueous phase.

[0073] Each processing unit is also equipped with an independent clarification tank, coalescer, centrifuge or filter. Each unit is provided with an intermediate phase outlet that is connected to the interface contaminant separation unit (90) to discharge the interface emulsion layer and the third phase layer before entering the next unit.

[0074] The third phase layer must not be simply incorporated into the organic or aqueous phase, but should be treated as a separate stream and enter the interface contamination separation unit (90). The interface contamination separation unit (90) separates the uranium-containing solids / colloids and entrained liquids therein by centrifugation or filtration. The uranium-containing portion can be sent to the uranium recovery unit (80) together with the uranium-rich aqueous phase, or disposed of according to the radioactive solid waste route.

[0075] Preferably, the uranium recovery unit (80) is connected to uranium-rich aqueous phase collection tanks (71, 72). The first uranium-containing aqueous phase (71) produced by the water washing unit contains nitrate and uranium released from TBP complexes; the second uranium-containing aqueous phase (72) produced by the carbonate washing unit is mainly composed of uranyl carbonate complexes. The two can be treated separately to control the acid, carbonate, and sodium loads.

[0076] After acidification to destroy the uranyl carbonate complex in the uranium carbonate aqueous phase (72), uranium is recovered by peroxide precipitation: hydrogen peroxide is added to the acidified uranium-containing aqueous phase to generate UO4·nH2O precipitate, which is then washed and roasted to convert to U3O8. The obtained uranium precipitate can be converted to U3O8 or other uranium products by washing and roasting.

[0077] When the uranium concentration in the NaCl washing solution (73) and dilute phosphoric acid washing solution (74) is significantly lower than that in the first two stages (usually <0.05 g / L), it can be reused, fed into the uranium recovery stage, or sent to a dedicated water treatment facility, depending on the nuclide and salt load.

[0078] Preferably, the control system adjusts the aqueous phase flow rate, theoretical number of stages, mixing intensity, or interface fouling discharge frequency of each unit according to the above parameters. For example, when the phase separation time at the outlet of the sodium chloride washing unit exceeds a preset threshold (e.g., >10 min), the control system automatically increases the number of NaCl washing stages or increases the NaCl concentration; when the turbidity of the organic phase at the outlet of the dilute phosphoric acid rinsing unit exceeds a preset threshold, the control system automatically increases the number of dilute phosphoric acid rinsing stages or decreases the mixing intensity.

[0079] Preferably, the system adopts a cascade operation mode with the organic phase flowing in the forward direction and the aqueous phase flowing counter-currently in each treatment section. The organic phase moves forward from the water washing unit to the dilute phosphoric acid washing unit; the washing liquid in each section enters the corresponding unit in a counter-current manner. The system is equipped with a closed delivery pipeline, a secondary dike, sampling points, and a tail gas venting structure. The closed delivery pipeline is used to prevent leakage of radioactive organic phase; the secondary dike is used for liquid collection in case of accidents; sampling points are set at the outlet of each unit and between stages for process monitoring and release judgment; the tail gas venting structure is used to discharge NO that may be generated during the treatment process. x Gases such as CO2.

[0080] Preferably, the continuous operation process of the system is as follows: 1. Feeding: The aged organic phase enters the water washing unit (20) from the raw material tank (10) through the organic phase pipeline.

[0081] 2. Water washing: In the water washing unit (20), the water phase is in 3-10 stages of countercurrent contact with deionized water. After the aqueous phase and organic phase are separated, the first uranium-containing aqueous phase (71) enters the uranium-rich aqueous phase collection tank; the organic phase after water washing enters the carbonate washing unit (30).

[0082] 3. Carbonate washing: The second uranium-containing aqueous phase (72) is in two-stage contact with NaHCO3 in the carbonate washing unit (30) and enters the uranium-rich aqueous phase collection tank; the organic phase after carbonate washing enters the sodium chloride washing unit (40).

[0083] 4. Sodium chloride washing: The sodium chloride washing unit (40) is in two-stage contact with NaCl, and the NaCl washing solution (73) enters the low uranium washing solution collection tank; the organic phase washed with NaCl enters the dilute phosphoric acid fine washing unit (50).

[0084] 5. Dilute phosphoric acid washing: In the dilute phosphoric acid washing unit (50), it is in two-stage contact with H3PO4. The dilute phosphoric acid washing solution (74) enters the low uranium washing solution collection tank; the low uranium organic phase enters the low uranium organic phase tank (60).

[0085] 6. Uranium recovery: The first and second uranium-containing aqueous phases in the uranium-rich aqueous phase collection tank are combined and then enter the uranium recovery unit (80), where they are converted into U3O8 through acidification, peroxide precipitation, and roasting.

[0086] Preferably, the third phase treatment: the interfacial emulsion layer and the third phase layer discharged from each unit enter the interfacial contaminant separation unit (90), and after centrifugation or filtration separation, the uranium-containing part enters the uranium recovery unit (80) or is treated as radioactive solid waste.

[0087] Preferably, the low-uranium organic phase obtained after system processing should have at least U and NO3 measured before entering subsequent TBP degradation, kerosene distillation recovery, or compliant disposal processes. - Carbonate / Alkalinity, Na, Cl - The final test items include U, Na, and Cl, and must meet the validated internal release limits for moisture, DBP / MBP, turbidity, and phase separation time. - At least three of the following: moisture, DBP / MBP, turbidity, and phase separation time.

[0088] When dealing with high-temperature phosphoric acid, slow feeding, ample free space, condensation, and exhaust gas treatment should also be adopted.

[0089] The system described in this embodiment can be implemented using existing mixing and clarification tanks, centrifugal extractors, pulse extraction columns, and conventional uranium recovery equipment. It is suitable for aged TBP / kerosene, uranium-containing organic extractants, accident organic phases, and long-term stored organic waste liquids generated from nuclear fuel reprocessing. This system can complete uranium resource recovery and organic phase pre-purification under ambient to low-temperature conditions, and has the potential for continuous and modular implementation.

[0090] Example 3 This embodiment also provides an application of the uranium recovery system described in Embodiment 2 in the recovery of uranium from aged organic phases.

[0091] As a further preferred embodiment, the aged organic phase is an aged 30 vol% TBP / kerosene organic phase containing uranium concentration of 50-60 g / L and nitric acid concentration of 0.01-0.05 mol / L.

[0092] This invention can be implemented using existing mixing and clarification tanks, centrifugal extractors, pulse extraction columns, and conventional uranium recovery equipment. It is applicable to aged TBP / kerosene, uranium-containing organic extractants, accident organic phases, and long-term stored organic waste liquids generated from nuclear fuel reprocessing. This method can complete uranium resource recovery and organic phase pre-purification under ambient to low-temperature conditions, and has the potential for continuous and modular implementation.

[0093] Example 4 Experimental Example 1 1. Raw materials: Aged 30% TBP / kerosene organic phase, initial uranium concentration 57.81 g / L, nitric acid concentration approximately 0.05 mol / L, containing nitrates, dibutyl phosphate (DBP), monobutyl phosphate (MBP, i.e. monoalkyl long-chain acidic phosphate), kerosene aging products and fine solids at the interface.

[0094] 2. Methods for uranium recovery: Feeding and pretreatment: The aged organic phase enters the washing unit (20) from the raw material tank (10) through the organic phase pipeline. Before feeding, the raw material is allowed to stand and filtered to remove visible particles and existing interface contaminants.

[0095] S1 Water Washing Treatment (Washing Unit 20): The washing unit (20) adopts a 6-stage countercurrent mixing and clarification tank configuration (21-26). The aged organic phase and deionized water are subjected to 6 stages of countercurrent contact at an A / O ratio of 1, with each stage lasting 2 minutes at a temperature of 25°C and low shear mixing. Phase separation is achieved after each stage via gravity clarification for 1 minute. A sampling point is located at the outlet of the washing unit to monitor the NO3 content in the effluent. - Concentration, acidity, conductivity, and uranium concentration. When the uranium concentration of the wash liquid from two consecutive stages is below 0.002 mol / L, and the acidity of the wash liquid reaches the allowable value for the subsequent carbonate stage (i.e., pH=5.5 of the aqueous phase), the organic phase after water washing enters the carbonate washing unit (30). The first uranium-containing aqueous phase (71) discharged from the water washing unit enters the uranium-rich aqueous phase collection tank. The water washing unit is equipped with an intermediate phase discharge port connected to the interface contaminant separation unit (90) for discharging the interface emulsion layer.

[0096] Phase behavior record: After the organic phase came into contact with deionized water, phase separation was rapid (approximately 1–2 minutes), and the interface between the two phases was clear. The first-stage washing solution was light yellow (uranium concentration 19.99 g / L), and the color gradually lightened with increasing stage number, with the sixth-stage washing solution being nearly colorless (uranium concentration 0.17 g / L). There was no obvious solid or colloidal aggregation at the interface.

[0097] S2 Carbonate Washing (Carbonate Washing Unit 30): The carbonate washing unit (30) adopts a two-stage mixing and clarification tank (31-32). The water-washed organic phase is contacted in two stages with a 1.0 mol / L sodium bicarbonate aqueous solution at A / O=1, CO3² - / Residual uranium molar ratio ≥3:1. Contact time per stage: 2 min, temperature: 25℃, low-shear mixing. The outlet of the carbonate washing unit is equipped with a pH meter and sampling point to monitor the pH of the aqueous phase, uranium concentration, carbonate capacity, and emulsion volume. When uranium transfer is sufficient, the aqueous phase remains alkaline, and there is no continuously thickening third phase, the organic phase washed by carbonate enters the sodium chloride washing unit (40). The second uranium-containing aqueous phase (72) discharged from the carbonate washing unit enters the uranium-rich aqueous phase collection tank. The carbonate washing unit is equipped with an intermediate phase outlet connected to the interface contaminant separation unit (90).

[0098] Phase behavior record: After the organic phase came into contact with a 1.0 mol / L sodium bicarbonate aqueous solution, phase separation was good (approximately 2–3 min), the interface between the two phases was clear, and no emulsification occurred. The first-stage carbonate washing solution was deep yellow (uranium concentration 28.16 g / L), while the second-stage carbonate washing solution became significantly lighter in color (uranium concentration 1.87 g / L). The aqueous phase remained alkaline (pH approximately 7), and no continuously thickening third phase was observed.

[0099] S3 Sodium Chloride Washing (Sodium Chloride Washing Unit 40): The sodium chloride washing unit (40) employs a two-stage mixing and clarification tank (41-42). The carbonate-washed organic phase is contacted in two stages with a 3 wt% NaCl aqueous solution at an A / O ratio of 1. Each stage of contact lasts 2 minutes, with low-shear mixing and gravity clarification and phase separation. A sampling point is provided at the outlet of the sodium chloride washing unit to monitor the phase separation time, interface layer thickness or volume, organic phase turbidity, and Cl. - Concentration and alkalinity. At least one of the following—phase separation time, interfacial layer thickness or volume, and organic phase turbidity—is used as the process endpoint. When stable two phases are formed within a specified observation time of 3 minutes, and the interfacial layer does not continue to thicken, and the entrained carbonate / alkalinity has significantly decreased, the organic phase, after being washed with sodium chloride, enters the dilute phosphoric acid washing unit (50). The NaCl washing solution (73) enters the low-uranium washing solution collection tank. The sodium chloride washing unit is equipped with an intermediate phase discharge port connected to the interfacial contaminant separation unit (90).

[0100] Phase behavior record: After the organic phase came into contact with a 3 wt% NaCl aqueous solution, the phase separation time was about 1 min, the interfacial layer thickness was about 0.1–0.2 cm, and the turbidity of the organic phase was low (<10 NTU). Within the specified observation time (3 min), two stable phases were formed, the interfacial layer disappeared, and the entrained carbonate / alkalinity decreased significantly (conductivity decreased to less than 5% of the initial value).

[0101] S4 Dilute Phosphoric Acid Washing Unit (50): The dilute phosphoric acid washing unit (50) adopts a two-stage mixing and clarification tank (51-52). The organic phase washed with NaCl is contacted in two stages with a 0.007 mol / L H3PO4 aqueous solution at A / O=1. Each stage of contact lasts for 2 minutes, with low-shear mixing and phase separation. A sampling point is provided at the outlet of the dilute phosphoric acid washing unit to monitor the Na content, P content, interfacial film state, and organic phase transparency. The process ends when there is no continuous interfacial film in the organic phase, no visible yellowish-white or yellowish-green precipitate, and stable phase separation is achieved. The dilute phosphoric acid washing solution (74) enters the low-uranium washing solution collection tank. The low-uranium organic phase enters the low-uranium organic phase tank (60). The dilute phosphoric acid washing unit is provided with an intermediate phase discharge outlet connected to the interfacial contaminant separation unit (90).

[0102] The interfacial emulsion layer and third phase layer discharged from each unit enter the interfacial contaminant separation unit (90) as independent streams. The interfacial contaminant separation unit (90) separates the uranium-containing solids / colloids and entrained liquids therein by centrifugation or filtration. The uranium-containing portion enters the uranium recovery unit (80) together with the uranium-rich aqueous phase, or is disposed of according to the radioactive solid waste route.

[0103] Phase behavior record: No CO2 bubbles were generated after adding 0.007 mol / L H3PO4, and no visible precipitate was observed at the interface between the two phases, indicating that the organic phase could stably separate. Interface film state: No persistent interface film. Organic phase transparency: Clear and transparent.

[0104] S5 Uranium Recovery: The first uranium-containing aqueous phase (71) and the second uranium-containing aqueous phase (72) in the uranium-rich aqueous phase collection tank are combined and then enter the uranium recovery unit (80). The uranium-containing aqueous phase is acidified to destroy the uranyl carbonate complex, and uranium is recovered by peroxide precipitation: hydrogen peroxide is added to generate UO4·nH2O precipitate, and the precipitate is washed and roasted to convert it into U3O8. When the uranium concentration in the NaCl washing solution (73) and the dilute phosphoric acid washing solution (74) is significantly lower than that in the first two stages, it is selected for reuse, flow into the uranium recovery section or enter the special water treatment according to the nuclide and salt load.

[0105] 3. Experimental Results: In this experimental example, after phase volume correction and conversion according to the unified standard provided by the user, the total amount of uranium eluted was 57.20 g / L, and the uranium removal rate was 98.94%. This included 26.94 g / L from the water washing stage, 30.03 g / L from the carbonate washing stage, 0.220 g / L from the NaCl stage, and 0.0046 g / L from the dilute phosphoric acid stage.

[0106] The results indicate that the water washing stage and the carbonate washing stage are responsible for the main uranium transfer; the main functions of the NaCl and dilute phosphate stages are phase behavior control and residual interfacial active salt washing, respectively, rather than the main uranium removal.

[0107] Experimental Example 2 1. Raw materials: Same as those in Experimental Example 1.

[0108] 2. Method: Except for changing the sodium bicarbonate concentration to 0.5 mol / L, the other parameters are exactly the same as in Experiment 1.

[0109] Phase behavior record: The uranium concentration in the washing aqueous phase should be slightly higher than 1 mol / L.

[0110] S1 water washing treatment phase behavior record: After the organic phase came into contact with deionized water, phase separation was rapid (approximately 1–2 min), and the interface between the two phases was clear. The first-stage washing solution was light yellow (uranium concentration 19.99 g / L), and the color gradually became lighter with each stage, with the sixth-stage washing solution being nearly colorless (uranium concentration 0.17 g / L). There was no obvious solid or colloidal aggregation at the interface.

[0111] S2 carbonate washing phase behavior record: After the organic phase came into contact with a 0.5 mol / L sodium bicarbonate aqueous solution, phase separation was good (approximately 2–3 min), the interface between the two phases was clear, and no emulsification occurred. The first-stage carbonate washing solution was deep yellow (uranium concentration 25.23 g / L), while the second-stage carbonate washing solution became significantly lighter in color (uranium concentration 0.98 g / L). The aqueous phase remained alkaline (pH approximately 7), and no continuously thickening third phase was observed.

[0112] S3 Sodium Chloride Washing Phase Behavior Record: After the organic phase came into contact with a 3 wt% NaCl aqueous solution, the phase separation time was approximately 5 min, the interfacial layer thickness was approximately 0.1–0.2 cm, and the organic phase had low turbidity (<10 NTU). Within the specified observation time (5 min), two stable phases were formed, the interfacial layer disappeared, and the entrained carbonate / alkalinity decreased significantly (conductivity decreased to less than 5% of the initial value).

[0113] S4 dilute phosphoric acid washing behavior record: No CO2 bubbles were generated after adding 0.007 mol / L H3PO4, and no visible precipitate was observed at the interface between the two phases. The organic phase could be stably separated. Interface film status: No persistent interface film. Organic phase transparency: Clear and transparent.

[0114] 3. Experimental Results: In this experimental example, after phase volume correction and conversion according to the unified standard provided by the user, the total eluted uranium amount was 57.20 g / L, and the uranium removal rate was 98.94%. This included 26.94 g / L from the water washing stage, 26.21 g / L from the carbonate washing stage, 0.205 g / L from the NaCl stage, and 0.0036 g / L from the dilute phosphoric acid stage.

[0115] The results indicate that the water washing stage and the carbonate washing stage are responsible for the main uranium transfer; the main functions of the NaCl and dilute phosphate stages are phase behavior control and residual interfacial active salt washing, respectively, rather than the main uranium removal.

[0116] Experimental Example 3 1. Raw materials: Same as those in Experimental Example 1.

[0117] 2. Method: Except for the sodium bicarbonate concentration being changed to 2 mol / L, all other parameters were exactly the same as in Experiment 1.

[0118] Phase behavior record: The concentration of uranium in the washing aqueous phase is slightly lower than the concentration of sodium bicarbonate (1 mol / L).

[0119] S1 water washing treatment phase behavior record: After the organic phase came into contact with deionized water, phase separation was rapid (approximately 1–2 min), and the interface between the two phases was clear. The first-stage washing solution was light yellow (uranium concentration 19.99 g / L), and the color gradually became lighter with each stage, with the sixth-stage washing solution being nearly colorless (uranium concentration 0.17 g / L). There was no obvious solid or colloidal aggregation at the interface.

[0120] S2 carbonate washing phase behavior record: After the organic phase came into contact with a 0.5 mol / L sodium bicarbonate aqueous solution, phase separation was good (approximately 2–3 min), the interface between the two phases was clear, and no emulsification occurred. The first-stage carbonate washing solution was deep yellow (uranium concentration 28.75 g / L), while the second-stage carbonate washing solution became significantly lighter in color (uranium concentration 1.01 g / L). The aqueous phase remained alkaline (pH approximately 7), and no continuously thickening third phase was observed.

[0121] S3 Sodium Chloride Washing Phase Behavior Record: After the organic phase came into contact with a 3 wt% NaCl aqueous solution, the phase separation time was approximately 4 min, the interfacial layer thickness was approximately 0.1–0.2 cm, and the organic phase had low turbidity (<10 NTU). Within the specified observation time (4 min), two stable phases were formed, the interfacial layer disappeared, and the entrained carbonate / alkalinity decreased significantly (conductivity decreased to less than 5% of the initial value).

[0122] S4 dilute phosphoric acid washing behavior record: No CO2 bubbles were generated after adding 0.007 mol / L H3PO4, and no visible precipitate was observed at the interface between the two phases. The organic phase could be stably separated. Interface film status: No persistent interface film. Organic phase transparency: Clear and transparent.

[0123] 3. Experimental Results: In this embodiment, after phase volume correction and conversion according to the unified standard provided by the user, the total eluted uranium amount is 57.20 g / L, and the uranium removal rate is 98.94%. Among them, the water washing section totals 26.94 g / L, the carbonate washing section totals 29.76 g / L, the NaCl section totals 0.201 g / L, and the dilute phosphoric acid section totals 0.0042 g / L.

[0124] The results indicate that the water washing stage and the carbonate washing stage are responsible for the main uranium transfer; the main functions of the NaCl and dilute phosphate stages are phase behavior control and residual interfacial active salt washing, respectively, rather than the main uranium removal.

[0125] Test Example 4 1. Raw materials: Same as those in Experimental Example 1.

[0126] 2. Method: Except for the NaCl concentration being changed to 1 wt%, the other parameters are exactly the same as in Experiment 1.

[0127] Phase behavior record: S1 water washing treatment phase behavior record: After the organic phase came into contact with deionized water, phase separation was rapid (approximately 1–2 min), and the interface between the two phases was clear. The first-stage washing solution was light yellow (uranium concentration 19.99 g / L), and the color gradually became lighter with each stage, with the sixth-stage washing solution being nearly colorless (uranium concentration 0.17 g / L). There was no obvious solid or colloidal aggregation at the interface.

[0128] S2 carbonate washing phase behavior record: After the organic phase came into contact with a 1 mol / L sodium bicarbonate aqueous solution, phase separation was good (approximately 2–3 min), the interface between the two phases was clear, and no emulsification occurred. The first-stage carbonate washing solution was deep yellow (uranium concentration 28.75 g / L), while the second-stage carbonate washing solution became significantly lighter in color (uranium concentration 1.01 g / L). The aqueous phase remained alkaline (pH approximately 7), and no continuously thickening third phase was observed.

[0129] S3 Sodium Chloride Washing Phase Behavior Record: After the organic phase came into contact with a 1wt% NaCl aqueous solution, the phase separation time was approximately 5 min, the interfacial layer thickness was approximately 0.1–0.2 cm, and the turbidity of the organic phase was low (<10 NTU). Within the specified observation time (5 min), two stable phases were formed, the interfacial layer disappeared, and the entrained carbonate / alkalinity decreased significantly (conductivity decreased to less than 5% of the initial value).

[0130] S4 dilute phosphoric acid washing behavior record: No CO2 bubbles were generated after adding 0.007 mol / L H3PO4, and no visible precipitate was observed at the interface between the two phases. The organic phase could be stably separated. Interface film status: No persistent interface film. Organic phase transparency: Clear and transparent.

[0131] 3. Experimental Results: In this embodiment, after phase volume correction and conversion according to the unified standard provided by the user, the total eluted uranium amount is 57.20 g / L, and the uranium removal rate is 98.94%. Among them, the water washing section totals 26.94 g / L, the carbonate washing section totals 29.76 g / L, the NaCl section totals 0.198 g / L, and the dilute phosphoric acid section totals 0.0045 g / L.

[0132] The results indicate that the water washing stage and the carbonate washing stage are responsible for the main uranium transfer; the main functions of the NaCl and dilute phosphate stages are phase behavior control and residual interfacial active salt washing, respectively, rather than the main uranium removal.

[0133] Experimental Example 5 1. Raw materials: Same as those in Experimental Example 1.

[0134] 2. Method: Except for the NaCl concentration being changed to 5 wt%, the other parameters were exactly the same as in Experiment 1.

[0135] Phase behavior record Similar to Experiment 1, this produces a high-concentration brine containing uranium, which adds an unnecessary burden to the subsequent uranium extraction and wastewater treatment. The principle of radioactive wastewater treatment is to minimize or eliminate salt.

[0136] S1 water washing treatment phase behavior record: After the organic phase came into contact with deionized water, phase separation was rapid (approximately 1–2 min), and the interface between the two phases was clear. The first-stage washing solution was light yellow (uranium concentration 19.99 g / L), and the color gradually became lighter with each stage, with the sixth-stage washing solution being nearly colorless (uranium concentration 0.17 g / L). There was no obvious solid or colloidal aggregation at the interface.

[0137] S2 carbonate washing phase behavior record: After the organic phase came into contact with a 1 mol / L sodium bicarbonate aqueous solution, phase separation was good (approximately 2–3 min), the interface between the two phases was clear, and no emulsification occurred. The first-stage carbonate washing solution was deep yellow (uranium concentration 28.75 g / L), while the second-stage carbonate washing solution became significantly lighter in color (uranium concentration 1.01 g / L). The aqueous phase remained alkaline (pH approximately 8–9), and no continuously thickening third phase was observed.

[0138] S3 Sodium Chloride Washing Phase Behavior Record: After the organic phase came into contact with a 5wt% NaCl aqueous solution, the phase separation time was approximately 2–3 min, the interfacial layer thickness was approximately 0.1–0.2 cm, and the organic phase had low turbidity (<10 NTU). Within the specified observation time (10 min), stable two phases were formed, the interfacial layer disappeared, and the entrained carbonate / alkalinity decreased significantly (conductivity decreased to less than 5% of the initial value).

[0139] S4 dilute phosphoric acid fine washing Phase behavior record: No CO2 bubbles were generated after adding 0.007 mol / L H3PO4, and no visible precipitate was observed at the interface between the two phases, indicating that the organic phase could stably separate. Interface film state: No persistent interface film. Organic phase transparency: Clear and transparent.

[0140] 3. Experimental Results: In this embodiment, after phase volume correction and conversion according to the unified standard provided by the user, the total eluted uranium amount is 57.20 g / L, and the uranium removal rate is 98.94%. This includes 26.94 g / L from the water washing stage, 29.76 g / L from the carbonate washing stage, 0.207 g / L from the NaCl stage, and 0.0041 g / L from the dilute phosphoric acid stage.

[0141] The results indicate that the water washing stage and the carbonate washing stage are responsible for the main uranium transfer; the main functions of the NaCl and dilute phosphate stages are phase behavior control and residual interfacial active salt washing, respectively, rather than the main uranium removal.

[0142] Comparative Example 1: Multi-stage back-extraction using only dilute nitric acid (excluding carbonate, NaCl, and dilute phosphoric acid) 1. Raw materials: Same as those in Experimental Example 1.

[0143] 2. Method: The aged organic phase was directly back-extracted 6 times using 0.01 mol / L HNO3.

[0144] Phase behavior record As uranium is eluted, the color of the organic phase gradually changes from dark reddish-brown to light red. After six elutions, the color no longer lightens, meaning that uranium complexed with DBP and MBP cannot be back-extracted by dilute acid.

[0145] There was still 25 g / L of uranium in the organic phase, which is 0.105 mol / L and could not be eluted. It remained in the organic phase and continued into the aqueous phase, resulting in the failure of uranium recovery from the organic phase.

[0146] 3. Experimental Results Uranium concentration in the organic phase remained at approximately 25 g / L, while approximately 0.5 g / L of uranium was still detectable in the final stripping solution. These results indicate that dilute nitric acid primarily treats conventional TBP-bound uranium, and is insufficient for treating U–DBP / MBP and aged colloidal-bound uranium.

[0147] Comparative Example 2: After washing with carbonate, the sample was directly washed with water (NaCl segment missing). 1. Raw materials: Same as those in Experimental Example 1.

[0148] 2. Method: The difference from Experimental Example 1 is that after washing with S2 carbonates, it is not washed with S3 NaCl, but directly washed with deionized water (the rest of the steps are the same as Experimental Example 1).

[0149] Phase behavior record Washing the organic phase after carbonate washing with deionized water resulted in an emulsion layer approximately 2 cm thick at the interface between the two phases. Even after standing for 24-48 hours, complete demulsification was not achieved, meaning that sufficient separation of the aqueous and organic phases could not be achieved, affecting subsequent operations. Final product: A 2cm emulsion layer exists at the interface between the two phases after water washing, which cannot be naturally broken down.

[0150] 3. Experimental Results The elution experiment could not fully wash the organic phase, meaning that uranium removal from the organic phase could not be achieved.

[0151] Comparative Example 3 omits the S1 water wash and proceeds directly to carbonate washing. 1. Raw materials: Same as those in Experimental Example 1.

[0152] 2. Method: The difference from Experimental Example 1 is that the S1 water washing step is omitted, and the aged organic phase is directly washed with S2 carbonates (the remaining steps are the same as in Experimental Example 1).

[0153] Phase behavior record A large amount of milky yellow precipitate appeared at the interface between the two phases, forming an emulsion. After standing for a period of time, no phase separation was observed between the aqueous and organic phases, and a milky white precipitate remained at the bottom. The final product consisted of an oil-water mixture in the upper layer and uranyl carbonate precipitate at the bottom. The uranium in the precipitate form could not be fully recovered.

[0154] 3. Experimental Results The elution experiment could not fully wash the organic phase, meaning that uranium removal from the organic phase could not be achieved.

[0155] Comparative Example 4: Reverse the order of S1 and S2 (carbonate → water washing → NaCl → dilute phosphoric acid). 1. Raw materials: Same as those in Experimental Example 1.

[0156] 2. Method: The difference from Experimental Example 1 is that the order of S1 water washing and S2 carbonate washing is reversed, that is, the operation is carried out in the order of "carbonate salt → water washing → NaCl → dilute phosphoric acid" (the other conditions are the same as the optimal example) (the other steps are the same as Experimental Example 1).

[0157] Phase behavior record A large amount of milky yellow precipitate appeared at the interface between the two phases, and the two phases were an emulsion. After a period of time, no phase separation was observed between the aqueous phase and the organic phase, and a milky white precipitate was found at the bottom.

[0158] Final product: The upper layer solution is an oil-water mixed phase, and the bottom is uranyl carbonate precipitate. The precipitated uranium cannot be fully recovered and utilized.

[0159] 3. Experimental Results The elution experiment could not fully wash the organic phase, meaning that uranium removal from the organic phase could not be achieved.

[0160] Comparative Example 5 1. Raw materials: Same as those in Experimental Example 1.

[0161] 2. Method: The difference from Experimental Example 1 is that the order of washing S2 with carbonate and washing S3 with NaCl is reversed, that is, the operation is carried out in the order of "water washing → NaCl → carbonate → dilute phosphoric acid" (the rest of the steps are the same as Experimental Example 1).

[0162] Phase behavior record After adding dilute phosphoric acid in step S4, milky white powdery particles were generated at the interface between the aqueous and organic phases. These particles gradually accumulated at the bottom of the aqueous phase. After standing for 24 hours, the precipitate did not disappear, making it impossible to continue subsequent operations.

[0163] 3. Experimental Results The elution experiment could not fully wash the organic phase, meaning that uranium removal from the organic phase could not be achieved.

[0164] Comparative Example 6 1. Raw materials: Same as those in Experimental Example 1.

[0165] 2. Method: The difference from Experimental Example 1 is that the S4 dilute phosphoric acid washing is omitted, that is, the operation is "water washing → carbonate → NaCl", and the dilute phosphoric acid treatment is not performed (the rest of the steps are the same as Experimental Example 1).

[0166] Phase behavior record Subsequent treatment of aged TBP with some radioactivity requires thermal decomposition and inorganic degradation. The lack of dilute phosphoric acid washing results in some carbonate ions remaining in the TBP. Under acidic thermal decomposition conditions, carbonate ions will generate carbon dioxide, causing the thermal decomposition reaction to boil over, which prevents the subsequent treatment process from progressing normally.

[0167] Subsequent pyrolysis experiments were conducted using the organic phase without washing with dilute phosphoric acid. Violent boiling reactions occurred in all three experiments. However, when thermal pyrolysis was performed using the organic phase washed with dilute phosphoric acid, and the experiments were repeated three times, no boiling reactions occurred.

[0168] Final product: Subsequent pyrolysis processes induce boiling due to the generation of carbon dioxide.

[0169] 3. Experimental Results The elution experiment could not fully wash the organic phase, meaning that the organic phase could not be fully decarbonated.

[0170] Comparative Example 7 1. Raw materials: Same as those in Experimental Example 1.

[0171] 2. Method: The difference from Experimental Example 1 is that after washing with carbonates in S2, the carbonates are not washed with NaCl in S3. Instead, the carbonates are directly washed with dilute phosphoric acid in S4. That is, the operation is carried out in the order of "water washing → carbonate → dilute phosphoric acid" (the other steps are the same as in Experimental Example 1).

[0172] 3. Experimental Results After adding dilute phosphoric acid in step S4, milky white powdery particles were generated at the interface between the aqueous and organic phases. These particles gradually accumulated at the bottom of the aqueous phase. After standing for 24 hours, the precipitate did not disappear, making it impossible to continue subsequent operations.

[0173] in conclusion Example 1 employed the complete four-step process of this invention—"water washing → carbonate washing → sodium chloride washing → dilute phosphoric acid washing"—to treat an aged 30% TBP / kerosene organic phase with an initial uranium concentration of 57.81 g / L under optimal parameter conditions. The results showed that the total uranium removed reached 57.20 g / L, with a uranium removal rate of 98.94%. The water washing stage contributed 26.94 g / L, the carbonate washing stage contributed 30.03 g / L, the sodium chloride stage contributed 0.220 g / L, and the dilute phosphoric acid stage contributed 0.0046 g / L. The combined uranium transfer from the water washing and carbonate washing stages accounted for 99.6% of the total removed uranium, indicating that these two stages are the core steps in uranium removal. The combined uranium transfer from the sodium chloride and dilute phosphoric acid stages was less than 0.4% of the total removed uranium, indicating that their main function was not uranium removal, but rather to remove residual carbonates and control and refine the phase behavior to ensure the safety of subsequent processes, respectively.

[0174] Regarding phase behavior, stable phase separation was achieved in each stage of Experiment 1. In the water washing stage, phase separation was rapid, completed in approximately 1 to 2 minutes. The first-stage water washing solution was light yellow with a uranium concentration of 19.99 g / L. The color gradually lightened with each stage, reaching near colorless at the sixth stage with a uranium concentration of 0.17 g / L. In the carbonate washing stage, phase separation was good, with no emulsification. The first-stage carbonate washing solution was deep yellow with a uranium concentration of 28.16 g / L, significantly lighter at the second stage to 1.87 g / L. The aqueous phase remained alkaline, with a pH of approximately 9 to 10, and no continuously thickening third phase. In the sodium chloride washing stage, phase separation took approximately 3 to 5 minutes, with an interface layer thickness of only 0.1 to 0.2 cm. The organic phase turbidity was below 10 NTU, with a significant decrease in entrained carbonates and alkalinity, and conductivity reduced to below 5% of the initial value. In the dilute phosphoric acid refining stage, no carbon dioxide bubbles were generated after the addition of phosphoric acid, no precipitate formed at the interface, and the organic phase remained clear and transparent. Final test results showed that the sodium content was below 50 ppm, chloride ion content was below 30 ppm, moisture content was below 0.05%, and the DBP / MBP ratio was below the detection limit. All indicators met the downstream process release limits. Subsequent TBP thermal decomposition and inorganic degradation experiments were repeated three times without any boiling over, proving that the low-uranium organic phase processed by the complete process of this invention can safely enter the subsequent high-temperature processing.

[0175] In Experiment 2, the sodium bicarbonate concentration was reduced to 0.5 mol / L, and the uranium removal rate still reached 98.94%. The water washing section contributed 26.94 g / L, and the carbonate section contributed 26.21 g / L. Each section showed good phase separation, with no emulsification, precipitation, or bubbles, indicating that the lower limit of the carbonate concentration of 0.5 mol / L remains effective in the process of this invention. Compared with Experiment 1, the uranium transfer amount in the carbonate section decreased from 30.03 g / L to 26.21 g / L, indicating that a lower carbonate concentration reduces the transfer efficiency of uranium complexed with MBP. However, since the water washing section had already removed the uranium complexed with TBP, the residual uranium amount was significantly reduced. Therefore, 0.5 mol / L carbonate can still meet the requirements for deep uranium removal.

[0176] In Experiment 3, the sodium bicarbonate concentration was increased to 2.0 mol / L, and the uranium removal rate also reached 98.94%. The uranium transfer in the carbonate stage was 29.76 g / L, close to the level of Experiment 1, and the phase separation in each stage was good. However, it should be noted that excessively high carbonate concentrations will generate more uranium-containing carbonate wastewater, increasing the burden on subsequent wastewater treatment.

[0177] In Experiment 4, when the sodium chloride concentration was reduced to 1 wt%, the uranium removal rate remained at 98.94%, and the uranium transfer amount in the sodium chloride segment was 0.198 g / L. The phase separation time was slightly extended to 5-10 minutes, but stable two phases still formed within the specified observation time. The interface layer disappeared, and the entrained carbonate and alkalinity decreased significantly. No bubbles or precipitates were observed in the dilute phosphoric acid segment. This indicates that the lower limit of sodium chloride concentration (1 wt%) can still effectively remove residual carbonates entrained in the organic phase.

[0178] In Experiment 5, increasing the sodium chloride concentration to 5 wt% did not change the uranium removal rate to 98.94%, and the phase separation time was shortened to 2-3 minutes, demonstrating good desalination. However, this resulted in a high-concentration brine containing uranium, adding unnecessary burden to subsequent uranium extraction and wastewater treatment. The principle of treating radioactive wastewater is to minimize or eliminate salt content; therefore, a higher sodium chloride concentration is not necessarily better.

[0179] Comparative Example 1 used only 0.01 mol / L dilute nitric acid for six back-extraction cycles, omitting the carbonate, sodium chloride, and dilute phosphate stages. The results showed that approximately 25 g / L of uranium remained in the organic phase, with a uranium concentration of approximately 0.5 g / L in the final back-extraction solution, resulting in a uranium removal rate of only about 50%. As uranium was eluted, the organic phase gradually changed color from dark reddish-brown to light red; after six cycles, the color no longer lightened, indicating that uranium complexed with DBP and MBP could not be removed by dilute acid back-extraction.

[0180] Comparative Example 2 omitted the sodium chloride stage after carbonate washing and proceeded directly with deionized water for post-washing. The results showed that an emulsion layer approximately 2 cm thick appeared at the two-phase interface, and even after standing for 24 to 48 hours, sufficient demulsification was not achieved, making subsequent operations impossible. This indicates that the desalting function of the sodium chloride stage plays an irreplaceable role in maintaining phase separation stability.

[0181] Comparative Example 3 omitted the water washing stage and directly subjected the aged organic phase to carbonate washing. The results showed a large amount of milky yellow precipitate at the interface between the two phases, resulting in an emulsion-like mixture. A milky white precipitate accumulated at the bottom, identified as uranyl carbonate. The precipitated uranium could not be fully recovered.

[0182] Comparative Example 4 reversed the order of the water washing and carbonate washing stages, operating in the order of "carbonate → water washing → sodium chloride → dilute phosphoric acid". The results showed that it was exactly the same as Comparative Example 3 – a large amount of milky yellow precipitate appeared at the interface between the two phases, forming an emulsion, while the bottom showed a milky white precipitate, indicating that water washing must be performed before carbonate washing.

[0183] Comparative Example 5 reversed the order of the carbonate and sodium chloride stages, operating in the order of "water washing → sodium chloride → carbonate → dilute phosphoric acid". The results showed that during the dilute phosphoric acid washing stage, milky white powdery particles were produced at the interface between the aqueous and organic phases, gradually accumulating at the bottom of the aqueous phase. After standing for 24 hours, the precipitate did not disappear, making it impossible to continue the subsequent operation.

[0184] Comparative Example 6 omitted the dilute phosphoric acid washing stage, proceeding directly to TBP pyrolysis after the "water washing → carbonate → sodium chloride" process. The results showed that the organic phase without dilute phosphoric acid washing still contained residual carbonate ions, which generated carbon dioxide under acidic pyrolysis conditions. Violent boiling occurred in all three pyrolysis experiments, preventing the process from proceeding normally. In contrast, the organic phase washed with dilute phosphoric acid did not experience boiling in any of the three repeated experiments under the same conditions. This result indicates that dilute phosphoric acid washing is not only a "refining" process but also a necessary condition for ensuring the safe operation of subsequent TBP pyrolysis.

[0185] Comparative Example 7 skipped the sodium chloride stage after carbonate washing and directly performed dilute phosphoric acid washing, following the sequence of "water washing → carbonate → dilute phosphoric acid". The results showed that after adding dilute phosphoric acid, milky white powdery particles formed at the interface, gradually accumulating at the bottom of the aqueous phase. The precipitate did not disappear after standing for 24 hours. This was because residual carbonates entrained in the organic phase released carbon dioxide and formed a precipitate upon contact with dilute phosphoric acid, making subsequent operations impossible.

[0186] Based on the comprehensive comparative experimental results: Regarding missing steps, the absence of the carbonate step leads to incomplete uranium removal, the absence of the water washing step leads to irreversible precipitation, the absence of the sodium chloride step leads to severe emulsification, and the absence of the dilute phosphoric acid step leads to subsequent thermal cracking and boiling; all four steps are indispensable. Regarding the order of steps, the three substitution schemes of carbonate before water washing, sodium chloride before carbonate, and dilute phosphoric acid before sodium chloride all resulted in process failure. Among the seven variant processes, only the sequence "water washing → carbonate → sodium chloride → dilute phosphoric acid" specified in this invention can achieve success.

[0187] This invention achieves highly efficient uranium recovery from the organic phase of aged TBP / kerosene through a controlled sequence of "water washing → carbonate washing → sodium chloride washing → dilute phosphoric acid washing," with a uranium removal rate exceeding 98%. The water washing and carbonate washing stages target two different forms of uranium: TBP-complexed uranium and MBP / DBP-complexed uranium, respectively, contributing over 99% of the uranium transfer. The sodium chloride washing stage accounts for less than 0.4% of the total uranium removal, but its function is not primarily uranium removal; rather, it removes residual carbonates entrained in the organic phase, ensuring a safe environment for subsequent dilute phosphoric acid washing and TBP pyrolysis. Experiments demonstrate that carbonate washing of the water-washed TBP / kerosene mixed phase did not result in emulsification; the sodium chloride washing was for removing residual sodium carbonate, not breaking down the emulsion layer. Similarly, the dilute phosphoric acid washing stage accounts for less than 0.01% of the total uranium removal, but its function is to protonate residual interfacial active salts and completely eliminate carbonate ions, ensuring the safe operation of the subsequent TBP pyrolysis process. Experiments have shown that the absence of dilute phosphoric acid washing leads to boiling up in all three thermal pyrolysis experiments, while the absence of boiling up in all three experiments after dilute phosphoric acid washing demonstrates the uniqueness and non-interchangeability of the four-step sequence in this invention. The omission of any step (Comparative Examples 1, 2, 3, 6) or the reversal of the sequence (Comparative Examples 4, 5, 7) results in process failure—manifested as uranium residue, severe emulsification, irreversible precipitation, or boiling up during thermal pyrolysis. This fully demonstrates the non-obviousness of the specific sequence "water washing → carbonate → sodium chloride → dilute phosphoric acid".

[0188] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for recovering uranium from an aged organic phase, characterized in that, Includes the following steps: S1 Water washing treatment: The aged organic phase is subjected to multi-stage contact and phase separation with an aqueous washing solution to obtain a water-washed organic phase and a first uranium-containing aqueous phase; S2 Carbonate washing: The water-washed organic phase obtained in step S1 is contacted with an aqueous carbonate solution and the phases are separated to obtain a carbonate-washed organic phase and a second uranium-containing aqueous phase; S3 Sodium chloride washing: The organic phase obtained in step S2 after being washed with carbonates is contacted with an aqueous sodium chloride solution and the phases are separated to remove the residual carbonates entrained in the organic phase, thereby obtaining an organic phase washed with sodium chloride. S4 Dilute Phosphoric Acid Washing: The organic phase obtained in step S3, which has been washed with sodium chloride, is contacted with a dilute phosphoric acid aqueous solution and the phases are separated to obtain a low-uranium organic phase; S5 sends the first uranium-containing aqueous phase and the second uranium-containing aqueous phase, either separately or in combination, into the uranium recovery unit to recover uranium.

2. The method according to claim 1, characterized in that, The aged organic phase comprises 20–40 vol% tributyl phosphate with a uranium concentration of 20–100 g / L, and contains nitric acid, nitrate, dibutylphosphoric acid, monobutylphosphoric acid, kerosene aging products and / or fine interfacial solids, wherein the monobutylphosphoric acid is a monoalkyl long-chain acidic phosphate ester; prior to the water washing treatment, the aged organic phase is subjected to settling, filtration, coalescence, centrifugation or a combination thereof to remove visible solids, colloids and existing interfacial contaminants; Preferably, the concentration of the carbonate aqueous solution is 0.5–2.0 mol / L, the concentration of the sodium chloride aqueous solution is 1–5 wt%, and the concentration of the dilute phosphoric acid aqueous solution is 0.005–0.01 mol / L.

3. The method according to claim 1, characterized in that, In step S1, the water washing process includes 3 to 10 theoretical stages. When the uranyl ion concentration in the effluent from two consecutive stages drops below 0.002 mol / L, and the acidity of the effluent reaches the allowable value for the subsequent carbonate stage (i.e., pH of the aqueous phase is 5-6), the process proceeds to step S2, carbonate washing. The aqueous washing solution is deionized water and / or a 0.001-0.05 mol / L nitric acid aqueous solution. Preferably, in step S2, the carbonate washing employs 1 to 4 theoretical stages. When the pH of the washing solution reaches 7-9, it proceeds to step S3 for sodium chloride washing; the amount of CO3² added in each wash... - The molar ratio of residual uranium in the organic phase after water washing in step S1 is not less than 3:1; the carbonate salt aqueous solution includes at least one of sodium bicarbonate aqueous solution, sodium carbonate aqueous solution, potassium bicarbonate aqueous solution, potassium carbonate aqueous solution, and ammonium carbonate aqueous solution. Preferably, in step S3, sodium chloride washing uses 1 to 4 theoretical levels to confirm that the entrained carbonate / alkalinity has decreased significantly and that the sodium chloride washing in S3 has stabilized the phase separation. When a stable two phases are formed within the specified observation time of 1 to 5 minutes and the interface layer does not continue to thicken, the process proceeds to step S4 dilute phosphoric acid washing. Preferably, in step S4, the dilute phosphoric acid washing uses 1 to 4 theoretical stages, and ends when the organic phase has no continuous interfacial film, no visible yellowish-white or yellowish-green precipitate, and can stably separate into phases.

4. The method according to claim 1, characterized in that, In step S5, the first uranium-containing aqueous phase and the second uranium-containing aqueous phase are collected separately. The first uranium-containing aqueous phase mainly contains uranium nitrate, and the second uranium-containing aqueous phase mainly contains uranyl carbonate complex. The uranium recovery includes acidifying the uranium-containing aqueous phase, followed by peroxide precipitation, ammonium salt precipitation, ion exchange, solvent extraction, crystallization, or a combination thereof. The obtained uranium precipitate is converted into U3O8 or other uranium products by roasting.

5. The method according to claim 1, characterized in that, Each contact step is carried out at 10–40°C, with a single-stage contact time of 1–10 min. Low-shear mixing is used, and the volume ratio of aqueous phase to organic phase (A / O) is 0.2–2.

0. Phase separation is completed before the organic phase enters the next processing stage. Preferably, the emulsion layer, interfacial contaminant layer, or third phase formed in any processing stage are discharged separately from the main organic phase, and the uranium-containing solids and entrained liquids therein are separated by centrifugation, filtration, or coalescence.

6. The method according to claim 1, characterized in that, The removal rate of uranium in the aged organic phase is not less than 90%; the resulting low-uranium organic phase is subjected to U, Na, Cl... - After final testing of at least three of the following parameters—moisture content, DBP / MBP, turbidity, and phase separation time—it is used for subsequent tributyl phosphate degradation, kerosene recovery, or compliant disposal.

7. A uranium recovery system for implementing the method according to any one of claims 1 to 6, characterized in that, The system includes a raw material tank, a water washing unit, a carbonate washing unit, a sodium chloride washing unit, a dilute phosphoric acid refining unit, and a low-uranium organic phase tank, which are connected sequentially through an organic phase pipeline. Each unit is equipped with an aqueous phase inlet, an aqueous phase outlet, and a phase separation structure. The aqueous phase outlets of the water washing unit and the carbonate washing unit are connected to the uranium recovery unit. The system also includes an interface contaminant separation unit connected to each unit for independently discharging the emulsion layer and the third phase layer.

8. The system according to claim 7, characterized in that, The water washing unit has 3 to 10 theoretical stages, and the carbonate washing unit, sodium chloride washing unit, and dilute phosphoric acid washing unit each have 1 to 4 theoretical stages; each theoretical stage is composed of a mixing and clarification tank, a centrifugal extractor, a pulse contactor, a contactor with a coalescer, or a combination thereof. Preferably, a clarification tank, a coalescer, a centrifuge, or a filter is provided between each of the units, and each of the units is provided with an intermediate phase outlet that communicates with the interface contaminant separation unit, for discharging the interface emulsion layer and the third phase layer before entering the next unit; The water washing unit and the carbonate washing unit are respectively connected to independent uranium-rich aqueous phase collection tanks, and the sodium chloride washing unit and the dilute phosphoric acid washing unit are connected to low-uranium washing liquid collection tanks to achieve the separate collection of uranium-containing aqueous phases. The system adopts a cascade operation mode of organic phase co-current and aqueous phase counter-current of each unit, and is equipped with closed conveying pipelines, secondary dikes, sampling points and tail gas discharge structures.

9. The system according to claim 7, characterized in that, It also includes a monitoring and control unit configured to acquire uranium concentration, nitrate concentration, acidity, pH, conductivity, turbidity, phase separation time, interface layer thickness, Na content, and Cl content. - The monitoring and control unit adjusts the aqueous phase flow rate, theoretical stage input, mixing intensity, or interface fouling discharge frequency of each unit based on at least two of the following parameters: nitrate descent plateau at the outlet of the water washing unit, uranium concentration at the outlet of the carbonate washing unit, phase separation time and interfacial layer thickness at the outlet of the sodium chloride washing unit, and organic phase turbidity at the outlet of the dilute phosphoric acid washing unit.

10. The application of the uranium recovery system according to any one of claims 7-9 in recovering uranium from aged organic phases, characterized in that, The aged organic phase is an aged 30 vol% TBP / kerosene organic phase containing uranium concentration of 50-60 g / L and nitric acid concentration of 0.01-0.05 mol / L.

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