Method for determining hexavalent neptunium in organic phase

Abstract

The invention relates to the technical field of spent fuel aftertreatment analysis, in particular to a method for determining hexavalent neptunium in an organic phase. A method for determining hexavalent neptunium in an organic phase comprises the following steps: preparing organic phase standard solutions of hexavalent neptunium with a series of concentrations, and determining absorption spectra of the standard solutions; performing second derivative treatment on the absorption spectrum of the standard solution to obtain a second-order guide spectrum of the standard solution; establishing a quantitative correction relation between the peak area of a characteristic absorption peak and the concentration of the hexavalent neptunium according to the second-order guide spectrum of the standard solution; measuring the absorption spectrum of the organic phase solution to be measured; performing second derivative treatment on the absorption spectrum of the to-be-detected solution to obtain a second-order guide spectrum of the to-be-detected solution; and substituting the peak area of the second-order guide spectrum of the solution to be detected at the characteristic absorption peak into the quantitative correction relation, and calculating to obtain the concentration of the hexavalent neptunium in the solution to be detected. The concentration of Np (VI) in an organic phase can be directly determined, the influence of acidity is eliminated or corrected, and the method is rapid and accurate.

Description

Technical Field

[0001] This invention relates to the field of spent fuel reprocessing analysis technology, specifically to a method for determining hexavalent neptunium (Np(VI)) in an organic phase. Background Technology

[0002] In nuclear fuel reprocessing, tributyl phosphate (TBP) extraction is a key process for separating and recovering uranium, plutonium, and minor actinides. Neptunium (Np), an important minor actinide element, exists primarily in three valence states during reprocessing: tetravalent (Np(IV)), pentavalent (Np(V)), and Np(VI). Np(VI) can be effectively extracted into the organic phase by TBP, while Np(V) is not extracted, and the extraction behavior of Np(IV) falls somewhere in between. Therefore, accurate determination of the Np(VI) concentration in the organic phase is crucial for monitoring the Neptunium trajectory and optimizing extraction process parameters.

[0003] In related technologies, CN117949400A discloses a method for determining neptunium in nitric acid solution. This method employs second-order guided spectroscopy, quantitatively analyzing the concentration and species state of neptunium by measuring the characteristic absorption peaks of different valence states of neptunium in the aqueous phase at specific wavelengths (e.g., Np(VI) at 1225 nm). However, this method is only applicable to aqueous systems and cannot be directly applied to the determination of Np(VI) in the organic phase after TBP extraction.

[0004] Aqueous phase determination methods typically require back-extraction of Np(VI) from the organic phase into the aqueous phase before analysis. This process is cumbersome and time-consuming. During this process, TBP and n-dodecane are easily lost due to volatilization, and losses may also occur due to incomplete phase separation and cross-contamination, increasing measurement errors. Direct determination of the organic phase, on the other hand, eliminates the back-extraction step, achieving "sample-on-demand measurement." For example, a fiber optic probe or flow cell can be directly installed at the extraction tank outlet for continuous monitoring. Measurement data can also be fed back to the process control system in real time, automatically adjusting the extractant flow rate or nitric acid concentration. Furthermore, since the organic phase is usually located in a closed extraction device, direct determination reduces the number of times operators come into contact with radioactive samples, thus reducing radiation exposure to the human body during the measurement process.

[0005] Therefore, there is an urgent need for a method to determine hexavalent neptunium in the organic phase, which can not only significantly shorten the determination time and enable continuous monitoring directly at the extraction tank outlet, but also reduce the determination errors caused by incomplete phase separation and cross-contamination, thereby improving accuracy and meeting the needs of online monitoring and process control in the post-processing flow. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention provides a method for determining hexavalent neptunium in an organic phase. It can directly determine the Np(VI) concentration in the organic phase and can eliminate or correct the influence of acidity on the measurement results. It is characterized by its simple operation, speed, and accuracy, and is beneficial for real-time monitoring and control in post-processing procedures.

[0007] A first aspect of the present invention provides a method for determining hexavalent neptunium in an organic phase, comprising: Prepare a series of organic phase standard solutions of hexavalent neptunium at different concentrations, and determine the absorption spectra of the standard solutions; The absorption spectrum of the standard solution is processed by second derivative to obtain the second derivative spectrum of the standard solution; Based on the second-order guide spectrum of the standard solution, a quantitative correction relationship between the peak area of ​​the characteristic absorption peak and the concentration of hexavalent neptunium was established. Determine the absorption spectrum of the organic phase test solution; The absorption spectrum of the test solution is processed by second derivative to obtain the second derivative spectrum of the test solution; The concentration of hexavalent neptunium in the test solution is calculated by substituting the peak area at the characteristic absorption peak of the second-order guide spectrum of the test solution into the quantitative correction relationship.

[0008] By adopting the above technical solution, the concentration of Np(VI) in the organic phase can be directly determined, filling the gap in the existing technology for Neptunium analysis in the organic phase. It overcomes the cumbersome operation of back-extracting Np(VI) to the aqueous phase required by traditional methods, significantly shortens the determination time, and avoids measurement errors caused by incomplete phase separation and cross-contamination, thereby improving accuracy. This is beneficial for meeting the needs of online monitoring and process control in the post-processing flow. In addition, second-derivative spectral processing can eliminate baseline interference and distinguish overlapping absorption peaks, and quantification is performed using the area of ​​characteristic absorption peaks rather than simply peak height, which is beneficial for improving the selectivity, accuracy and sensitivity of the determination.

[0009] According to an embodiment of the present invention, the concentration range of the series concentrations is 1.0~12.0 mmol / L.

[0010] According to an embodiment of the present invention, the number of concentration points in the series of concentrations is 5 to 7.

[0011] According to an embodiment of the present invention, the organic phase comprises 30 vt% tributyl phosphate-n-dodecane (30% TBP / n-DD).

[0012] According to an embodiment of the present invention, the organic phase is either a blank organic phase or a pre-equilibrium organic phase.

[0013] In some embodiments, the composition of the organic phase in the standard solution is completely identical to that in the test solution, except for the concentration of neptunium. According to an embodiment of the present invention, the method for preparing the pre-equilibrium organic phase is as follows: add an aqueous phase to the organic phase, shake, allow to stand and separate into layers, remove the aqueous phase, and repeat three times to obtain the pre-equilibrium organic phase.

[0014] In some embodiments, the ratio of the aqueous phase to the organic phase is (0.8~1.2):1.

[0015] According to an embodiment of the present invention, the aqueous phase includes a nitric acid solution; further, the concentration of nitric acid in the nitric acid solution is 0.1~8.0 mol / L.

[0016] Preferably, the concentration of nitric acid in the nitric acid solution is 1.0~8.0 mol / L.

[0017] According to an embodiment of the present invention, the acidity of the organic phase is ≥1.0 mol / L.

[0018] In some embodiments, the standard solution has the same acidity as the organic phase in the test solution.

[0019] According to an embodiment of the present invention, the absorption spectrum of the standard solution or the test solution is determined by a spectroscopic method.

[0020] According to an embodiment of the present invention, the spectroscopic measurement method satisfies at least one of the following conditions: The wavelength range is 200~1400 nm; The spectral wavelength interval is 0.1~1.0 nm; The scan rate is 60~600 nm / min.

[0021] According to an embodiment of the present invention, the second derivative processing includes taking a second derivative of the absorbance of the absorption spectrum.

[0022] According to an embodiment of the present invention, the formula for the second derivative is:

[0023] in, The absorbance of the second-order guided spectrum; A represents the absorbance of the absorption spectrum; λ is the wavelength of the absorption spectrum.

[0024] In some embodiments, the software used for second derivative processing is Origin software.

[0025] According to an embodiment of the present invention, the peak position of the characteristic absorption peak is at least one of 1200~1220 nm or 615~625 nm.

[0026] Preferably, the peak position of the characteristic absorption peak is 615~625nm.

[0027] According to an embodiment of the present invention, for the absorption peak at 615~625 nm, the quantitative correction relationship between the peak area and the neptunium concentration is: S = 0.25c, R 2 = 0.99, RSD = 4.0%.

[0028] Where S is the peak area of ​​the absorption peak, and c is the neptunium concentration (mol / L).

[0029] According to an embodiment of the present invention, for the absorption peak at 1200~1220 nm, the determination method includes an acidity correction step: establishing a quantitative correction relationship between the peak area at 1200~1220 nm and the concentration of nitric acid in the aqueous phase in advance, determining the nitric acid concentration by measuring the peak area at 1200~1220 nm in the test solution, and then correcting the hexavalent neptunium concentration; or establishing a series of quantitative correction relationships between the peak area at 1200~1220 nm and the concentration of hexavalent neptunium under different acidities in advance, and determining the concentration of hexavalent neptunium in the test solution by looking up a table or interpolation.

[0030] In some embodiments, for the absorption peak at 1200–1220 nm, when the neptunium concentration is 1.0 mol / L, the quantitative correction relationship between the peak area and the nitric acid concentration is: S = 0.015e (cA / 1.39) +0.15, R 2 = 0.98, RSD = 9.1%.

[0031] Where S is the peak area of ​​the absorption peak, and cA is the concentration of nitric acid (mol / L).

[0032] In some embodiments, for the absorption peak at 1200–1220 nm, when the nitric acid concentration is 8.0 mol / L, the quantitative correction relationship between the peak area and the neptunium concentration is: S = 0.63c, R 2 = 0.99, RSD = 1.6%.

[0033] Where S is the peak area of ​​the absorption peak, and c is the neptunium concentration (mol / L).

[0034] According to an embodiment of the present invention, the reference for determining the absorption spectrum of the standard solution or the test solution is any one of air, water, blank organic phase, or pre-equilibrium organic phase.

[0035] Preferably, the reference is a pre-equilibrium organic phase with the same acidity as the standard solution or the test solution.

[0036] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0037] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 The second-order guide spectrum of the standard solution described in Example 1 of this invention is shown below. Figure 1 (a) in the figure represents the characteristic peak of the second-order guided spectrum at 615-625 nm. Figure 1 (b) in the figure represents the characteristic peak of the second-order guided spectrum at 1200~1220 nm; Figure 1 (c) in the figure is the peak area-Np(VI) concentration curve; Figure 2 The second-order guide spectrum of the standard solution described in Example 6 of this invention is shown below. Figure 2 (a) in the figure represents the characteristic peak of the second-order guided spectrum at 615-625 nm. Figure 2 (b) in the figure is the peak area-Np(VI) concentration curve at 615~625 nm; Figure 3 The results of second-order spectral processing in the range of 1200~1220 nm under different acidities, as described in Example 7 of this invention, are shown below. Figure 3 In the figure, (a) is the peak area-Np(VI) concentration curve. Figure 3 (b) in the figure is the peak area-nitric acid concentration curve. Detailed Implementation

[0038] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0039] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0040] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0041] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this invention, but do not exclude other aspects.

[0042] In this document, the terms “optionally,” “optionally,” or “optionally” generally refer to an event or condition that may, but may not, occur, and the description includes both cases in which the event or condition occurs and cases in which the event or condition does not occur.

[0043] A first aspect of the present invention provides a method for determining hexavalent neptunium in an organic phase, comprising: Prepare a series of organic phase standard solutions of hexavalent neptunium at different concentrations, and determine the absorption spectra of the standard solutions; The absorption spectrum of the standard solution is processed by second derivative to obtain the second derivative spectrum of the standard solution; Based on the second-order guide spectrum of the standard solution, a quantitative correction relationship between the peak area of ​​the characteristic absorption peak and the concentration of hexavalent neptunium was established. Determine the absorption spectrum of the organic phase test solution; The absorption spectrum of the test solution is processed by second derivative to obtain the second derivative spectrum of the test solution; The concentration of hexavalent neptunium in the test solution is calculated by substituting the peak area at the characteristic absorption peak of the second-order guide spectrum of the test solution into the quantitative correction relationship.

[0044] By adopting the above technical solution, the concentration of Np(VI) in the organic phase can be directly determined, filling the gap in the existing technology for Neptunium analysis in the organic phase. It overcomes the cumbersome operation of back-extracting Np(VI) to the aqueous phase required by traditional methods, significantly shortens the determination time, and avoids measurement errors caused by incomplete phase separation and cross-contamination, thereby improving accuracy. This is beneficial for meeting the needs of online monitoring and process control in the post-processing flow. In addition, second-derivative spectral processing can eliminate baseline interference and distinguish overlapping absorption peaks, and quantification is performed using the area of ​​characteristic absorption peaks rather than simply peak height, which is beneficial for improving the selectivity, accuracy and sensitivity of the determination.

[0045] According to an embodiment of the present invention, the concentration range of the series of concentrations is 1.0~12.0 mmol / L, specifically such as 1.0 mmol / L, 3.0 mmol / L, 5.0 mmol / L, 7.0 mmol / L, 10.0 mmol / L, 12.0 mmol / L, etc.

[0046] According to an embodiment of the present invention, the number of concentration points in the series is 5 to 7, specifically 5, 6, 7, etc.

[0047] According to an embodiment of the present invention, the organic phase comprises 30 vt% tributyl phosphate-n-dodecane (30% TBP / n-DD).

[0048] By adopting the above technical solution, TBP, as an extractant, can form neutral complexes with substances such as uranyl nitrate and plutonium nitrate through coordination, transferring them from the aqueous phase to the organic phase. n-Dodecane can reduce the density and viscosity of the organic phase, improve the dispersion and aggregation of the two phases, reduce the amount of TBP used, and improve economic efficiency. Moreover, it is consistent with the composition of the organic phase used in the nuclear fuel reprocessing process for the extraction, separation and recovery of uranium, plutonium and minor actinides, and can be directly measured after extraction without changing the solvent system through back-extraction or other means, which is convenient, fast and easy to monitor the processing status in real time.

[0049] According to an embodiment of the present invention, the organic phase is either a blank organic phase or a pre-equilibrium organic phase.

[0050] It should be noted that the blank organic phase refers to an organic phase that does not contain neptunium; the pre-equilibrium organic phase refers to an organic phase in which the components of the system have reached equilibrium after extraction treatment such as shaking and separation with the aqueous phase. When extracted again with an aqueous phase of the same acidity, the solvent composition and acidity of the pre-equilibrium organic phase remain essentially unchanged. By using a pre-equilibrium organic phase, the interference of aqueous phase or acid concentration on the absorption spectrum during testing can be eliminated.

[0051] In some embodiments, the standard solution and the test solution have identical organic phase compositions except for the concentration of neptunium. This eliminates the interference of different organic phase compositions on the intensity of certain regions in the absorption spectrum, thus helping to reduce errors.

[0052] According to an embodiment of the present invention, the method for preparing the pre-equilibrium organic phase is as follows: add an aqueous phase to the organic phase, shake, allow to stand and separate into layers, remove the aqueous phase, repeat three times to obtain the pre-equilibrium organic phase.

[0053] In some embodiments, the ratio of the aqueous phase to the organic phase is (0.8~1.2):1, specifically such as 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, etc., preferably 1:1.

[0054] According to an embodiment of the present invention, the aqueous phase includes a nitric acid solution; further, the concentration of nitric acid in the nitric acid solution is 0.1~8.0 mol / L, specifically such as 0.1mol / L, 0.5mol / L, 1.0mol / L, 2.0mol / L, 3.0mol / L, 4.0mol / L, 5.0mol / L, 6.0mol / L, 7.0mol / L, 8.0mol / L, etc.

[0055] Preferably, the concentration of nitric acid in the nitric acid solution is 1.0~8.0 mol / L.

[0056] It should be noted that at low nitric acid concentrations, TBP primarily extracts water molecules. In the organic phase, TBP and H₂O form a complex via hydrogen bonds, resulting in the highest water content in the organic phase. As the nitric acid concentration increases, the HNO₃ extracted into the organic phase forms a ternary complex with TBP and H₂O, causing a slight decrease in water content. With further increases in nitric acid concentration, the activity of water molecules decreases, and the hydration product gradually transforms into the unhydrated complex TBP·HNO₃. Therefore, the water content in the organic phase decreases with increasing nitric acid concentration.

[0057] Therefore, the nitric acid concentration within the aforementioned range is beneficial for maintaining the acidity of the pre-equilibration organic phase within a suitable range. This allows hexavalent neptunium to be extracted into the organic phase as a single NpO2(NO3)2·2TBP complex, reducing the formation of hydration or hydroxylation byproducts. This significantly sharpens the peak shape and reduces the half-width at half-maximum (WHM) of the ff transition absorption peak at 1200–1220 nm, ensuring that a clear and quantifiable characteristic derivative peak can still be obtained after second-derivative processing. Simultaneously, the salting-out effect caused by high acidity increases the partition ratio, thereby improving extraction completeness and spectral signal-to-noise ratio, and enhancing the sensitivity and accuracy of the determination. If the concentration of nitric acid used for pre-equilibration is less than 4.0 mol / L, the second-derivative absorption peak at 1200–1220 nm may not be obtained due to the large WHM of the absorption peak in the absorption spectrum.

[0058] According to an embodiment of the present invention, the acidity of the organic phase is ≥1.0 mol / L.

[0059] By adopting the above technical solution, hexavalent neptunium can be extracted into the organic phase in the form of a single NpO2(NO3)2·2TBP complex, which helps to reduce the formation of hydration or hydroxylation byproducts and ensures that clear and quantifiable characteristic derivative peaks can still be obtained after second derivative processing. At the same time, the salting-out effect generated by high acidity can increase the partition ratio and enhance the sensitivity and accuracy of the determination.

[0060] In some embodiments, the standard solution has the same acidity as the organic phase in the test solution.

[0061] According to an embodiment of the present invention, the absorption spectrum of the standard solution or the test solution is determined by a spectroscopic method.

[0062] According to an embodiment of the present invention, the spectroscopic measurement method satisfies at least one of the following conditions: The wavelength range is 200~1400 nm; The spectral wavelength interval is 0.1~1.0 nm; The scan rate is 60~600 nm / min.

[0063] By employing the above technical solution, the aforementioned wavelength range can determine the absorption spectra of hexavalent neptunium in organic phases across various regions, including ultraviolet, visible, and near-infrared. It can simultaneously capture the characteristic absorption peaks of hexavalent neptunium in both the visible and near-infrared regions, enabling multi-wavelength cross-validation to improve measurement accuracy. Furthermore, coverage of the ultraviolet region facilitates the identification of organic phase degradation products and matrix interference. The wavelength spacing within this range balances spectral resolution and measurement efficiency, clearly capturing the fine structure of hexavalent neptunium's characteristic absorption peaks for accurate quantification using derivative spectroscopy while avoiding data redundancy. Too small an interval, while resolving fine structures, increases time consumption; too large an interval may lead to the loss of characteristic peak information. The scanning rate within this range provides a wide range of selection flexibility. Low-speed scanning ensures the high signal-to-noise ratio required for second-derivative processing, while high-speed scanning meets the needs of rapid on-site detection. Low-speed scanning may improve signal-to-noise ratio and peak shape accuracy, while high-speed scanning, although shortening analysis time, is prone to introducing noise or causing peak position shifts.

[0064] For example, the wavelength range of the absorption spectrum can be 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, etc.; the spectral wavelength interval can be 0.1nm, 0.2nm, 0.3nm, 0.4nm, 0.5nm, 0.6nm, 0.7nm, 0.8nm, 0.9nm, 1.0nm, etc.; the scanning rate can be 60nm / min, 80nm / min, 100nm / min, 150nm / min, 200nm / min, 300nm / min, 400nm / min, 500nm / min, 600nm / min, etc.

[0065] According to an embodiment of the present invention, the second derivative processing includes taking a second derivative of the absorbance of the absorption spectrum.

[0066] According to an embodiment of the present invention, the formula for the second derivative is:

[0067] in, The absorbance of the second-order guided spectrum; A represents the absorbance of the absorption spectrum; λ is the wavelength of the absorption spectrum.

[0068] In some embodiments, the software used for second derivative processing is Origin software.

[0069] According to an embodiment of the present invention, the peak position of the characteristic absorption peak is at least one of 1200~1220 nm or 615~625 nm; for example, the peak position of the characteristic absorption peak can be 1200 nm, 1202 nm, 1204 nm, 1206 nm, 1208 nm, 1210 nm, 1212 nm, 1214 nm, 1216 nm, 1218 nm, 1220 nm or 615 nm, 617 nm, 619 nm, 621 nm, 623 nm, 625 nm, etc.

[0070] By adopting the above technical solution, the peak area of ​​the above characteristic absorption peaks can be used to quantify hexavalent neptunium, which is beneficial to improving the selectivity, accuracy and sensitivity of the determination. At the same time, the complementary advantages of low concentration sensitivity and high selectivity can be achieved through dual-wavelength synergistic coverage, and the error can be further reduced by the ratio method.

[0071] Preferably, the peak position of the characteristic absorption peak is 615~625nm.

[0072] It should be noted that the absorbance in the 615–625 nm range remains largely unchanged with nitric acid concentration. Therefore, after second-derivative processing, the peak area of ​​the absorption spectrum obtained in organic phases with different acidities shows a consistent relationship with the quantitative correction for neptunium concentration, and this relationship is not significantly altered by acidity. Thus, the same quantitative correction relationship (calculation formula) can be used to calculate the neptunium concentration in organic phases with different acidities within the 615–625 nm range, eliminating the need to retest standard solutions at each different acidity and separately fit the quantitative correction relationship between peak area and neptunium concentration for each acidity level. This greatly simplifies the determination method for hexavalent neptunium, significantly shortens the measurement time, and facilitates real-time measurement. Simultaneously, it reduces the impact of acidity differences between the test solution and the standard solution on the measurement results, significantly improving measurement accuracy.

[0073] According to an embodiment of the present invention, for the absorption peak at 615~625 nm, the quantitative correction relationship between the peak area and the neptunium concentration is: S = 0.25c, R 2 = 0.99, RSD = 4.0%.

[0074] Where S is the peak area of ​​the absorption peak, and c is the neptunium concentration (mol / L).

[0075] According to an embodiment of the present invention, for the absorption peak at 1200~1220 nm, the determination method includes an acidity correction step: establishing a quantitative correction relationship between the peak area at 1200~1220 nm and the concentration of nitric acid in the aqueous phase in advance, determining the nitric acid concentration by measuring the peak area at 1200~1220 nm in the test solution, and then correcting the hexavalent neptunium concentration; or establishing a series of quantitative correction relationships between the peak area at 1200~1220 nm and the concentration of hexavalent neptunium under different acidities in advance, and determining the concentration of hexavalent neptunium in the test solution by looking up a table or interpolation.

[0076] It should be noted that the peak area of ​​the absorption peak in the range of 1200~1220 nm increases with the increase of nitric acid concentration. The relationship between peak area and nitric acid concentration can be used to determine the nitric acid concentration, which can be used for acidity correction or simultaneous determination of acidity and concentration, and improve accuracy.

[0077] In some embodiments, for the absorption peak at 1200–1220 nm, when the neptunium concentration is 1.0 mol / L, the quantitative correction relationship between the peak area and the nitric acid concentration is: S = 0.015e (cA / 1.39) +0.15, R 2 = 0.98, RSD = 9.1%.

[0078] Where S is the peak area of ​​the absorption peak, and cA is the concentration of nitric acid (mol / L).

[0079] In some embodiments, for the absorption peak at 1200–1220 nm, when the nitric acid concentration is 8.0 mol / L, the quantitative correction relationship between the peak area and the neptunium concentration is: S = 0.63c, R 2 = 0.99, RSD = 1.6%.

[0080] Where S is the peak area of ​​the absorption peak, and c is the neptunium concentration (mol / L).

[0081] According to an embodiment of the present invention, the reference for determining the absorption spectrum of the standard solution or the test solution is any one of air, water, blank organic phase, or pre-equilibrium organic phase.

[0082] Preferably, the reference is a pre-equilibrium organic phase with the same acidity as the standard solution or the test solution.

[0083] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0084] In the following examples, unless otherwise specified, all organic phases are 30% TBP / n-DD. The 30% TBP / n-DD is prepared by mixing tributyl phosphate and n-dodecane at a volume ratio of 3:7 for later use. In the following embodiments, unless otherwise specified, the Np(VI) concentration is calibrated using a low-background liquid scintillation counter.

[0085] In the following embodiments, unless otherwise specified, the absorption spectra of Np(VI) are measured using a quartz cuvette and a UV-Vis-NIR spectrophotometer equipped with a near-infrared detector.

[0086] Example 1 The organic phase was pre-equilibrated with 8.0 mol / L nitric acid to obtain pre-equilibrated organic phase I; Standard solutions with Np(VI) concentrations of 1.67 mM, 3.53 mM, 4.97 mM, 6.87 mM, 8.80 mM, and 10.46 mM were prepared using pre-equilibrium organic phase I, and the absorption spectra of the standard solutions were measured. The absorption spectrum of the standard solution was processed by second derivative to obtain the second-order derivative spectrum of the standard solution; the results of the second-order derivative spectrum at 615~625 nm are as follows. Figure 1 As shown in (a); the result of the second-order guide spectrum at 1212 nm is as follows Figure 1 As shown in (b); Based on the second-order guide spectrum of the standard solution, quantitative correction relationships between the peak areas of the two characteristic absorption peaks and the concentration of hexavalent neptunium were established, and the results are as follows. Figure 1 As shown in (c) and Table 1; An organic phase test solution with a concentration of 5.77 mmol / L was prepared, and the absorption spectrum of the test solution was measured. The absorption spectrum of the test solution is processed by second derivative to obtain the second derivative spectrum of the test solution; Substituting the peak area at the characteristic absorption peak of the second-order guide spectrum of the test solution into the quantitative correction relationship, the concentration of hexavalent neptunium in the test solution was calculated to be 5.40 mmol / L, with a relative error of [missing value]. 6.4%, the formula for calculating the relative error is: relative error = (measured concentration - prepared concentration) / prepared concentration × 100%.

[0087] Example 2 The organic phase was pre-equilibrated with 7.0 mol / L nitric acid to obtain pre-equilibrated organic phase II; A series of standard solutions with Np(VI) concentrations were prepared using pre-equilibrium organic phase-II, and the absorption spectra of the standard solutions were measured. The absorption spectrum of the standard solution is processed by second derivative to obtain the second derivative spectrum of the standard solution; Based on the second-order guide spectrum of the standard solution, a quantitative correction relationship between the peak area of ​​the characteristic absorption peak and the concentration of hexavalent neptunium was established, and the results are recorded in Table 1. An organic phase test solution is provided, and the absorption spectrum of the test solution is measured; The absorption spectrum of the test solution is processed by second derivative to obtain the second derivative spectrum of the test solution; The concentration of hexavalent neptunium in the test solution is calculated by substituting the peak area at the characteristic absorption peak of the second-order guide spectrum of the test solution into the quantitative correction relationship.

[0088] Example 3 The organic phase was pre-equilibrated with 6.0 mol / L nitric acid to obtain pre-equilibrated organic phase III; A series of standard solutions with Np(VI) concentrations were prepared using pre-equilibrium organic phase III, and the absorption spectra of the standard solutions were measured. The absorption spectrum of the standard solution is processed by second derivative to obtain the second derivative spectrum of the standard solution; Based on the second-order guide spectrum of the standard solution, a quantitative correction relationship between the peak area of ​​the characteristic absorption peak and the concentration of hexavalent neptunium was established, and the results are recorded in Table 1. An organic phase test solution with a concentration of 3.93 mmol / L was prepared, and the absorption spectrum of the test solution was measured. The absorption spectrum of the test solution is processed by second derivative to obtain the second derivative spectrum of the test solution; Substituting the peak area at the characteristic absorption peak of the second-order guide spectrum of the test solution into the quantitative correction relationship, the concentration of hexavalent neptunium in the test solution was calculated to be 3.88 mmol / L, with a relative error of [missing value]. 1.3%.

[0089] Example 4 The organic phase was pre-equilibrated with 5.0 mol / L nitric acid to obtain pre-equilibrated organic phase-Ⅳ; A series of standard solutions with Np(VI) concentrations were prepared using pre-equilibrium organic phase-Ⅳ, and the absorption spectra of the standard solutions were measured. The absorption spectrum of the standard solution is processed by second derivative to obtain the second derivative spectrum of the standard solution; Based on the second-order guide spectrum of the standard solution, a quantitative correction relationship between the peak area of ​​the characteristic absorption peak and the concentration of hexavalent neptunium was established, and the results are recorded in Table 1. An organic phase test solution is provided, and the absorption spectrum of the test solution is measured; The absorption spectrum of the test solution is processed by second derivative to obtain the second derivative spectrum of the test solution; The concentration of hexavalent neptunium in the test solution is calculated by substituting the peak area at the characteristic absorption peak of the second-order guide spectrum of the test solution into the quantitative correction relationship.

[0090] Example 5 The organic phase was pre-equilibrated with 4.0 mol / L nitric acid to obtain pre-equilibrated organic phase-V; A series of standard solutions with Np(VI) concentrations were prepared using a pre-equilibrium organic phase-V, and the absorption spectra of the standard solutions were measured. The absorption spectrum of the standard solution is processed by second derivative to obtain the second derivative spectrum of the standard solution; Based on the second-order guide spectrum of the standard solution, a quantitative correction relationship between the peak area of ​​the characteristic absorption peak and the concentration of hexavalent neptunium was established, and the results are recorded in Table 1. An organic phase test solution is provided, and the absorption spectrum of the test solution is measured; The absorption spectrum of the test solution is processed by second derivative to obtain the second derivative spectrum of the test solution; The concentration of hexavalent neptunium in the test solution is calculated by substituting the peak area at the characteristic absorption peak of the second-order guide spectrum of the test solution into the quantitative correction relationship.

[0091] Example 6 The organic phase was pre-equilibrated with 3.0 mol / L nitric acid to obtain pre-equilibrated organic phase-VI; Standard solutions with Np(VI) concentrations of 1.30 mM, 2.82 mM, 4.50 mM, 5.94 mM, and 10.50 mM were prepared using pre-equilibrium organic phase-VI, and the absorption spectra of the standard solutions were measured. The absorption spectrum of the standard solution was processed by second derivative to obtain the second-order derivative spectrum of the standard solution; the results of the second-order derivative spectrum at 615~625nm are as follows. Figure 2As shown in (a), the second-order absorption peak cannot be obtained in the range of 1200~1220 nm because the half width of the absorption peak is large. Based on the second-order guide spectrum of the standard solution, a quantitative correction relationship was established between the peak area of ​​the characteristic absorption peak at 621 nm and the concentration of hexavalent neptunium. The results are as follows: Figure 2 As shown in (b); Prepare an organic phase test solution with a concentration of 4.50 mmol / L, and measure the absorption spectrum of the test solution; The absorption spectrum of the test solution is processed by second derivative to obtain the second derivative spectrum of the test solution; Substituting the peak area at the characteristic absorption peak of the second-order guide spectrum of the test solution into the quantitative correction relationship, the concentration of hexavalent neptunium in the test solution was calculated to be 4.64 mmol / L, with a relative error of 3.1%.

[0092] Example 7 Organic phases with a neptunium concentration of 1.0 mol / L were pre-equilibrated with nitric acid at concentrations of 4.0 mol / L, 5.0 mol / L, 6.0 mol / L, 7.0 mol / L, and 8.0 mol / L, respectively, to obtain pre-equilibrated organic phases with a neptunium concentration of 1.0 mol / L and different acidities. Np(VI) standard solutions were prepared using pre-equilibrium organic phases with different acidities, and the absorption spectra of the standard solutions were measured. The absorption spectrum of the standard solution was processed using the second derivative to obtain the second-order derivative spectrum of the standard solution; the results of the second-order derivative spectrum at 1200~1220 nm are as follows. Figure 3 As shown in (a) in the figure, the solid line represents the actual measurement of the absorption spectrum of the organic phase with multiple different Np(VI) concentrations at the corresponding acidity, and the dashed line represents the measurement of the absorption spectrum of the organic phase with only one Np(VI) concentration at the corresponding acidity. Based on the second-order guide spectrum of the standard solution, a quantitative correction relationship was established between the peak area of ​​the characteristic absorption peak at 1200–1220 nm and the nitric acid concentration. The results are recorded as follows: Figure 3 As shown in (b); A pre-equilibrium organic phase solution is provided, and the absorption spectrum of the solution is measured. The absorption spectrum of the test solution is processed by second derivative to obtain the second derivative spectrum of the test solution; The concentration of nitric acid in the solution to be tested is calculated by substituting the peak area of ​​the second-order guide spectrum at the characteristic absorption peak into the quantitative correction relationship between the peak area and the nitric acid concentration.

[0093] Results Analysis Table 1. Slope of the Np(VI) second-leader peak area versus Np(VI) concentration curve at different nitric acid concentrations.

[0094] like Figure 1 (a) and Figure 1 As shown in (b), at a nitric acid concentration of 8.0 mol / L, the second-guide spectrum of Np(VI) in the organic phase of 30% TBP / n-DD exhibits distinct characteristic absorption peaks at 615–625 nm and 1200–1220 nm. With increasing NpO2 concentration in the organic phase... 2+ As the concentration increases, the absorbance at the aforementioned wavelengths also increases.

[0095] like Figure 2 As shown in (a), when the nitric acid concentration is 3.0 mol / L, the second-guide spectrum of Np(VI) in the organic phase of 30% TBP / n-DD shows a distinct characteristic absorption peak in the range of 615–625 nm. This peak decreases with increasing NpO2 concentration in the organic phase. 2+ As the concentration increases, the absorbance at the aforementioned wavelengths also increases.

[0096] Combination Figure 1 (c) Figure 2 As can be seen from (b) and Table 1, for the absorption peak of 615~625nm, the effect of nitric acid concentration on the slope of the peak area-Np(VI) concentration curve is relatively small. The absorbance at a fixed wavelength is compared with NpO2... 2+ As can be seen from the concentration plot, the absorbance at each wavelength is related to NpO2. 2+ The concentration is directly proportional; the slope of the peak area-Np(VI) concentration curve is approximately 0.25 for different nitric acid concentrations. For example, when the nitric acid concentration is 8.0 mol / L, the quantitative correction relationship between the peak area and neptunium concentration is: S = 0.24c, R 2 = 0.99, RSD = 4.2%, where S is the peak area of ​​the absorption peak and c is the neptunium concentration (mol / L); the quantitative correction relationship between the peak area and neptunium concentration when the nitric acid concentration is 3.0 mol / L is: S = 0.25c, R 2 =0.99, RSD =4.0%.

[0097] Therefore, for the peak area at 615~625nm, the quantitative correction relationship between the peak area and the concentration of hexavalent neptunium can be unified as S=0.25c under different acidities, where S is the peak area of ​​the characteristic absorption peak and c is the concentration of neptunium (mol / L).

[0098] This result demonstrates that the present invention can obtain absorption spectra at any acidity level within the aforementioned range. By fitting a standard curve to the second-guide spectrum at 615–625 nm, a quantitative correction relationship between the peak area of ​​the characteristic absorption peak and the hexavalent neptunium concentration can be obtained, applicable to all acidities, without the need to establish multiple quantitative correction relationships for each different acidity concentration. This proves that the measurement method described in this invention significantly reduces testing steps, shortens testing time, avoids interference from acidity, and reduces measurement errors, making it suitable for real-time monitoring in nuclear fuel reprocessing.

[0099] For the absorption peak in the 1200~1220 nm range, from Figure 1 As can be seen from (c), when the nitric acid concentration is 8.0 mol / L, the quantitative correction relationship between the peak area and the neptunium concentration is: S = 0.63c, R 2 =0.99, RSD = 1.6%.

[0100] From Table 1 and Figure 3 Further research can be conducted on the relationship between nitric acid concentration and the peak area at 1200–1220 nm. It is evident that... Figure 3 The slope of the peak area-Np(VI) concentration curve in (a) increases with the increase of nitric acid concentration, indicating that acidity has a significant impact on the absorption peak in the 1200~1220 nm range. Figure 3 In (b) of the paper, an exponential relationship was obtained through fitting, establishing a quantitative correction relationship between the peak area and the nitric acid concentration when the neptunium concentration was 1.0 mol / L: S = 0.015e (cA / 1.39) +0.15, R 2 =0.98, RSD = 9.1%, where S is the peak area of ​​the absorption peak and cA is the nitric acid concentration (mol / L). This indicates that the present invention can determine the nitric acid concentration by measuring the peak area of ​​1200~1220 nm in the test solution, and then correct the hexavalent neptunium concentration; or determine the hexavalent neptunium concentration in the test solution under different acidities by looking up a table or interpolation.

[0101] In the description of this specification, the references to terms such as "an embodiment," "some embodiments," "a method of implementation," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0102] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for determining hexavalent neptunium in an organic phase, characterized in that, include: Prepare a series of organic phase standard solutions of hexavalent neptunium at different concentrations, and determine the absorption spectra of the standard solutions; The absorption spectrum of the standard solution is processed by second derivative to obtain the second derivative spectrum of the standard solution; Based on the second-order guide spectrum of the standard solution, a quantitative correction relationship between the peak area of ​​the characteristic absorption peak and the concentration of hexavalent neptunium was established. Determine the absorption spectrum of the organic phase test solution; The absorption spectrum of the test solution is processed by second derivative to obtain the second derivative spectrum of the test solution; The concentration of hexavalent neptunium in the test solution is calculated by substituting the peak area at the characteristic absorption peak of the second-order guide spectrum of the test solution into the quantitative correction relationship.

2. The determination method according to claim 1, characterized in that, The characteristic absorption peak is located at at least one of 1200~1220 nm or 615~625 nm, preferably 615~625 nm.

3. The determination method according to claim 2, characterized in that, The organic phase comprises 30 wt% tributyl phosphate-n-dodecane; Optionally, the organic phase is either a blank organic phase or a pre-equilibrium organic phase; Optionally, the method for preparing the pre-equilibrium organic phase is as follows: add an aqueous phase to the organic phase, shake, allow to stand and separate into layers, remove the aqueous phase, repeat three times to obtain the pre-equilibrium organic phase.

4. The determination method according to claim 3, characterized in that, The aqueous phase includes a nitric acid solution, wherein the nitric acid concentration in the nitric acid solution is 0.1~8.0 mol / L, preferably 1.0~8.0 mol / L.

5. The determination method according to any one of claims 1 to 4, characterized in that, The concentration range of the series is 1.0~12.0 mmol / L.

6. The determination method according to any one of claims 1 to 4, characterized in that, The absorption spectrum of the standard solution or the test solution is determined by a spectroscopic method, wherein the spectroscopic method satisfies at least one of the following conditions: The wavelength range is 200~1400 nm; The spectral wavelength interval is 0.1~1.0 nm; The scan rate is 60~600 nm / min.

7. The determination method according to any one of claims 1 to 4, characterized in that, The second derivative processing includes taking a second derivative of the absorbance of the absorption spectrum, and the formula for the second derivative is: in, The absorbance of the second-order guided spectrum; A represents the absorbance of the absorption spectrum; λ is the wavelength of the absorption spectrum.

8. The determination method according to any one of claims 2 to 4, characterized in that, For the absorption peak at 615–625 nm, the quantitative correction relationship between the peak area and the neptunium concentration is: S = 0.25c, R 2 = 0.99, RSD = 4.0%, where S is the peak area of ​​the absorption peak and c is the neptunium concentration / mol / L.

9. The determination method according to any one of claims 2 to 4, characterized in that, For the absorption peak at 1200–1220 nm, with a nitric acid concentration of 8.0 mol / L, the quantitative correction relationship between the peak area and the neptunium concentration is: S = 0.63c, R 2 =0.99, RSD = 1.6%, where S is the peak area of ​​the absorption peak and c is the neptunium concentration / mol / L.

10. The determination method according to any one of claims 2 to 4, characterized in that, For the absorption peak at 1200–1220 nm, the quantitative correction relationship between the peak area and the nitric acid concentration is: S = 0.015e (cA / 1.39) +0.15, R 2 = 0.98, RSD = 9.1%, where S is the peak area of ​​the absorption peak and cA is the nitric acid concentration / mol / L.

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