CN117129623A - Method for determining neptunium content in neptunium dioxide standard substance - Google Patents
Method for determining neptunium content in neptunium dioxide standard substance Download PDFInfo
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- 229910052781 Neptunium Inorganic materials 0.000 title claims abstract description 92
- LFNLGNPSGWYGGD-UHFFFAOYSA-N neptunium atom Chemical compound [Np] LFNLGNPSGWYGGD-UHFFFAOYSA-N 0.000 title claims abstract description 92
- QKUTVYUEUPNRBO-UHFFFAOYSA-N [O--].[O--].[Np+4] Chemical compound [O--].[O--].[Np+4] QKUTVYUEUPNRBO-UHFFFAOYSA-N 0.000 title claims abstract description 46
- 229910000478 neptunium(IV) oxide Inorganic materials 0.000 title claims abstract description 46
- 238000000034 method Methods 0.000 title claims abstract description 37
- 239000000126 substance Substances 0.000 title claims abstract description 37
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims abstract description 82
- 238000010438 heat treatment Methods 0.000 claims abstract description 18
- 238000005259 measurement Methods 0.000 claims abstract description 14
- 229910052709 silver Inorganic materials 0.000 claims abstract description 13
- 239000004332 silver Substances 0.000 claims abstract description 13
- 238000006243 chemical reaction Methods 0.000 claims abstract description 8
- 239000007788 liquid Substances 0.000 claims abstract description 5
- 239000000243 solution Substances 0.000 claims description 89
- 238000005868 electrolysis reaction Methods 0.000 claims description 52
- 238000007254 oxidation reaction Methods 0.000 claims description 48
- 230000003647 oxidation Effects 0.000 claims description 44
- 239000000523 sample Substances 0.000 claims description 34
- 239000012488 sample solution Substances 0.000 claims description 32
- 239000012490 blank solution Substances 0.000 claims description 23
- 238000004364 calculation method Methods 0.000 claims description 21
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 17
- 229910017604 nitric acid Inorganic materials 0.000 claims description 17
- 239000008367 deionised water Substances 0.000 claims description 11
- 229910021641 deionized water Inorganic materials 0.000 claims description 11
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 11
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 10
- 239000012470 diluted sample Substances 0.000 claims description 10
- 239000003792 electrolyte Substances 0.000 claims description 10
- 230000001590 oxidative effect Effects 0.000 claims description 9
- 239000011259 mixed solution Substances 0.000 claims description 6
- NDVLTYZPCACLMA-UHFFFAOYSA-N silver oxide Chemical compound [O-2].[Ag+].[Ag+] NDVLTYZPCACLMA-UHFFFAOYSA-N 0.000 claims description 6
- 229910052786 argon Inorganic materials 0.000 claims description 5
- 238000009835 boiling Methods 0.000 claims description 4
- 238000001816 cooling Methods 0.000 claims description 4
- 230000005611 electricity Effects 0.000 claims description 4
- 238000007865 diluting Methods 0.000 claims description 3
- 239000007789 gas Substances 0.000 claims description 3
- 229910001923 silver oxide Inorganic materials 0.000 claims description 3
- 238000003756 stirring Methods 0.000 claims description 3
- 238000002791 soaking Methods 0.000 claims description 2
- 238000005406 washing Methods 0.000 claims description 2
- 238000005303 weighing Methods 0.000 claims 1
- 238000004458 analytical method Methods 0.000 abstract description 16
- 239000003153 chemical reaction reagent Substances 0.000 abstract description 6
- LNOPIUAQISRISI-UHFFFAOYSA-N n'-hydroxy-2-propan-2-ylsulfonylethanimidamide Chemical compound CC(C)S(=O)(=O)CC(N)=NO LNOPIUAQISRISI-UHFFFAOYSA-N 0.000 abstract description 4
- 238000004448 titration Methods 0.000 abstract description 3
- BNGXYYYYKUGPPF-UHFFFAOYSA-M (3-methylphenyl)methyl-triphenylphosphanium;chloride Chemical compound [Cl-].CC1=CC=CC(C[P+](C=2C=CC=CC=2)(C=2C=CC=CC=2)C=2C=CC=CC=2)=C1 BNGXYYYYKUGPPF-UHFFFAOYSA-M 0.000 abstract description 2
- 230000006378 damage Effects 0.000 abstract description 2
- 238000004090 dissolution Methods 0.000 abstract description 2
- 239000000463 material Substances 0.000 abstract description 2
- 230000005855 radiation Effects 0.000 abstract description 2
- HIFJUMGIHIZEPX-UHFFFAOYSA-N sulfuric acid;sulfur trioxide Chemical compound O=S(=O)=O.OS(O)(=O)=O HIFJUMGIHIZEPX-UHFFFAOYSA-N 0.000 abstract description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 abstract 2
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 8
- 230000007547 defect Effects 0.000 description 4
- 238000002360 preparation method Methods 0.000 description 4
- 230000001276 controlling effect Effects 0.000 description 3
- IMBKASBLAKCLEM-UHFFFAOYSA-L ferrous ammonium sulfate (anhydrous) Chemical compound [NH4+].[NH4+].[Fe+2].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O IMBKASBLAKCLEM-UHFFFAOYSA-L 0.000 description 3
- 238000012544 monitoring process Methods 0.000 description 3
- ZOMNIUBKTOKEHS-UHFFFAOYSA-L dimercury dichloride Chemical class Cl[Hg][Hg]Cl ZOMNIUBKTOKEHS-UHFFFAOYSA-L 0.000 description 2
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 2
- 229910052737 gold Inorganic materials 0.000 description 2
- 239000010931 gold Substances 0.000 description 2
- RUTXIHLAWFEWGM-UHFFFAOYSA-H iron(3+) sulfate Chemical compound [Fe+3].[Fe+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O RUTXIHLAWFEWGM-UHFFFAOYSA-H 0.000 description 2
- 229910000360 iron(III) sulfate Inorganic materials 0.000 description 2
- 230000000155 isotopic effect Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 239000003758 nuclear fuel Substances 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 238000003918 potentiometric titration Methods 0.000 description 2
- 239000000779 smoke Substances 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000033116 oxidation-reduction process Effects 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 238000013215 result calculation Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 239000012086 standard solution Substances 0.000 description 1
- 239000012085 test solution Substances 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
- G01N31/16—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using titration
- G01N31/162—Determining the equivalent point by means of a discontinuity
- G01N31/164—Determining the equivalent point by means of a discontinuity by electrical or electrochemical means
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
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- Health & Medical Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Physics & Mathematics (AREA)
- Electrochemistry (AREA)
- Molecular Biology (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
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Abstract
The invention relates to a method for setting neptunium content in neptunium dioxide standard substance, which adopts sulfuric acid to carry out fuming treatment on sample dissolution liquid to remove hydrofluoric acid, and simultaneously converts a system into a sulfuric acid measurement system; the added excessive oxidized high silver is destroyed by adopting a heating mode, and compared with the destruction by adding sulfamic acid, the introduction of an additional reagent is reduced; meanwhile, the operation of destroying the oxidized high silver by sulfuric acid fuming and heating is adopted, so that sulfamic acid and aluminum nitrate reagents are prevented from being added, the introduction of other reagents is reduced, a single reaction system is ensured, and the measurement accuracy is improved. The coulomb analysis method of neptunium content in neptunium dioxide standard substance established by the invention has wide application range, and can directly complete analysis and determination of neptunium content in neptunium dioxide standard substance and neptunium dioxide sample by adopting controlled potential titration. The instrument is simple and convenient to operate, the error of manual operation is reduced under the condition of guaranteeing radiation protection, the analysis result is high in accuracy, the analysis precision is good, the consumption of analysis materials is less, and the experimental cost is reduced.
Description
Technical Field
The invention relates to the technical research field of nuclear fuel cycle analysis, in particular to a method for determining the neptunium content in neptunium dioxide standard substances.
Background
In daily analysis and monitoring, the neptunium dioxide standard substance is required to be used for carrying out the work of analysis method research and development, standard curve drawing, standard disk preparation, instrument graduation, quality monitoring and the like, so that the accuracy of neptunium content-related analysis methods and analysis results is ensured. In addition, the neptunium standards are also in need of the domestic environmental monitoring fields.
The neptunium content in neptunium dioxide standard substances is a main index for controlling whether the neptunium dioxide standard substance content and uniformity reach standards, and is an analysis item which needs to be controlled and detected; the neptunium content in the neptunium dioxide standard substance with accurate fixed value plays a vital role in developing the neptunium dioxide standard substance. Therefore, the establishment of a method for accurately and precisely measuring the neptunium content in neptunium dioxide standard substances has extremely important significance.
The content of neptunium in various valence states is measured by a control potential coulomb method by Style et al, and the method has the defects that the oxidation on a counter electrode of platinum is slow, the absolute error of measurement is large, and the measurement process is complicated; bai Chunyi and the like, which measure 1mg to 3mg of neptunium by a constant current method, have the defects that titration is required by adopting ferric sulfate (III), but the preparation steps of the ferric sulfate (III) standard solution are complex; the constant-current coulomb method and the potentiometric titration method are respectively adopted by the China atomic energy science institute and the Lanzhou nuclear fuel plant to measure the neptunium content, and the method has poor precision; zhu Haiqiao et al of China atomic energy science institute establish the method for measuring neptunium content by automatic potentiometric titration, the method has the defects that before each measurement, the ferrous ammonium sulfate solution needs to be calibrated, and the ferrous ammonium sulfate solution needs to be prepared in an existing mode, if the ferrous ammonium sulfate calibration result has errors, the neptunium content measurement accuracy is directly reduced; sun Yuanyuan et al disclose a method for analyzing the neptunium content in a sample of neptunium dioxide, which uses a gold mesh as a working electrode, a saturated calomel electrode as a reference electrode, and controls the reduction potential and the oxidation potential to cause the neptunium to be oxidized and reduced between pentavalent and hexavalent, and the method has the disadvantage that the method relies on the preceding standard and cannot meet the inspection requirement of the first-level standard substance for the neptunium dioxide standard substance to measure the neptunium content.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a method for setting the neptunium content of neptunium dioxide standard substance; the added excessive oxidized high silver is destroyed by adopting a heating mode, and compared with the destruction by adding sulfamic acid, the introduction of an additional reagent is reduced; meanwhile, the operation of destroying the oxidized high silver by sulfuric acid fuming and heating is adopted, so that sulfamic acid and aluminum nitrate reagents are prevented from being added, the introduction of other reagents is reduced, a single reaction system is ensured, and the measurement accuracy is improved. The coulomb analysis method of neptunium content in neptunium dioxide standard substance established by the invention has wide application range, and can directly complete analysis and determination of neptunium content in neptunium dioxide standard substance and neptunium dioxide sample by adopting controlled potential titration. The instrument is simple and convenient to operate, the error of manual operation is reduced under the condition of guaranteeing radiation protection, the analysis result is high in accuracy, the analysis precision is good, the consumption of analysis materials is less, and the experimental cost is reduced.
The aim of the invention can be achieved by the following technical scheme:
the method for determining the neptunium content in neptunium dioxide standard substance comprises the following specific determination steps:
s1, preparing a low-concentration sulfuric acid solution and a high-concentration sulfuric acid solution;
s2, dissolving neptunium dioxide standard substances to obtain a mixed solution;
s3, adding the high-concentration sulfuric acid solution obtained in the step S1 into the mixed solution obtained in the step S2, and heating and concentrating to obtain a evaporated sample;
s4, diluting the low-concentration sulfuric acid solution obtained in the step S1 with the evaporated sample obtained in the step S3 to obtain a diluted sample solution;
s5, measuring the blank electric quantity in the electrolytic cell cup without the sample solution;
s6, measuring the electric quantity of the diluted sample solution obtained in the step S4;
and S7, calculating the neptunium content in the neptunium dioxide standard substance according to Faraday' S law based on the blank electric quantity obtained in the step S5 and the electric quantity of the sample solution obtained in the step S6.
Further, in step S1, a certain amount of analytically pure sulfuric acid is measured, added into deionized water while stirring, cooled, transferred into a volumetric flask, and fixed in volume with deionized water.
Further, in the step S1, the concentration of the low-concentration sulfuric acid solution is 0.4-0.6 mol/L.
Further, in the step S1, the concentration of the high-concentration sulfuric acid solution is 2.5-3.5 mol/L.
In step S2, a nitric acid solution and an HF solution are added to a certain amount of neptunium dioxide standard substance, and the mixture is heated and dissolved and cooled to obtain a mixed solution.
Further to the above, neptunium dioxide standard: nitric acid solution: HF solution=0.03 to 0.05g: 10-15 mL: 0.10-0.15 mL.
The above further, the nitric acid solution is an analytically pure nitric acid solution and the HF solution is an analytically pure HF solution.
The above further, the heating temperature is 160 to 180 ℃.
Further, in step S3, the heating temperature is 220 to 250 ℃.
Further, in step S4, the neptunium concentration in the sample solution is 1-3 mg/g.
Further, in step S5, the specific measurement steps of the blank electricity amount are as follows:
adding a low-concentration sulfuric acid solution into an electrolytic cell cup, adding excessive oxidized high silver, heating to eliminate the excessive oxidized high silver, adding a low-concentration sulfuric acid solution, submerging an electrode on the liquid level of the solution, introducing argon, reducing on a reduction potential, and stopping reducing when the residual current is reduced to be less than 10 mu A; oxidation is carried out on oxidation potential, when the residual current is reduced to below 10 mu A, the oxidation is stopped, and the electrolysis electric quantity Q of the blank solution is recorded 1 Electrolyte potential E 1 And E is 2 Time t of electrolysis 1 And residual current I r1 。
Further to the above, the oxidation Gao Yin is analytically pure oxidized high silver.
Further, in step S6, the specific measurement steps of the electric quantity of the diluted sample solution are as follows:
(1) Immersing the electrode in a nitric acid solution, soaking the electrode in the nitric acid solution overnight after boiling, and washing the electrode with deionized water before use, and performing redox treatment in an electrolyte until the background current meets the requirement;
(2) Transferring the diluted sample solution obtained in the step S4 into an electrolytic cell cup, and calculating the mass Ws of the neptunium sample in the electrolytic cell cup;
(3) Adding a low-concentration sulfuric acid solution into the electrolytic cell cup filled with the neptunium sample obtained in the step (2), adding excessive oxidized high silver, heating to eliminate the excessive oxidized high silver, then adding a low-concentration sulfuric acid solution to submerge an electrode on the liquid level of the solution, introducing argon, reducing on a reduction potential, and stopping reducing when the residual current is reduced to be less than 10 mu A; oxidation is carried out on oxidation potential, oxidation is stopped when residual current is reduced to below 10 mu A, and electrolytic electricity quantity Q of neptunium sample solution is recorded S Electrolysis potential E 3 And E is 4 Residual current I r2 And electrolysis time t 2 ；
(4) Measuring standard electrode potential E0: adding neptunium solution into the electrolytic cell cup, operating according to the step (3), controlling the potential to reduce to a residual current of less than 10 mu A at the reduction potential, stopping reduction, adjusting the control potential to oxidize to a residual current of less than 10 mu A at the oxidation potential, recording the oxidation electric quantity Q, stopping oxidation, controlling the potential to reduce at the reduction potential, stopping reduction when the electric quantity is close to Q/2, and measuring the standard electrode potential E 0 。
The above further, in step (1), the electrode includes a working electrode and a counter electrode.
The above-mentioned further, in the step (1), the concentration of the nitric acid solution is 8mol/L.
In the step (1), the boiling time is 20min.
In the step (1), the electrolyte is sulfuric acid electrolyte of 0.5mol/L.
The background current in step (1) is required to be 5-10 mu A.
In the step (2), the diluted sample solution obtained in the step S4 is transferred to a weighed sample separating bottle, and then the sample solution in the sample separating bottle is transferred to an electrolytic cell cup, the residual solution in the sample separating bottle is weighed, the mass difference is the mass of the solution in the electrolytic cell cup, and the mass Ws of neptunium in the electrolytic cell cup is calculated according to the concentration of the neptunium solution.
Further, in step S7, a specific calculation formula of the neptunium content in the neptunium dioxide standard substance is shown in formula i:
in formula I:
C Np (%) neptunium content (%) in neptunium dioxide standard substance;
Q s -the integrated charge of the coulometer, C, during the oxidation of the neptunium sample;
Q b -blank electricity quantity, C, this value hasThe volume calculation formula is shown as formula II;
c, an integral factor of the coulometer, wherein a specific calculation formula of the integral factor is shown in a formula III;
A r -the relative atomic weight of neptunium (calculated from the isotopic abundance);
f, reaction fraction, wherein the specific calculation formula of the value is shown in formula IV;
F-Faraday constant, 96485.34;
W s -mass of neptunium sample in cell cup, g;
the specific calculation formula of the blank electric quantity is shown as a formula II:
in formula II:
E 1 -the potential at the end of the electrolysis of the blank solution is reduced, V;
E 2 -the potential at the end of the oxidation electrolysis of the blank solution, V;
E 3 -the potential at the end of the reduction electrolysis of the neptunium sample solution, V;
E 4 -the potential at the end of the oxidative electrolysis of the neptunium sample solution, V;
Q 1 -integrated electric quantity of coulometer at the end of the oxidation electrolysis of the blank solution, C;
I r1 -residual current after oxidation and electrolysis of the blank solution, a;
t 1 -oxidation electrolysis time of the blank solution, s;
t 2 -time s of oxidative electrolysis of neptunium sample solution;
I r2 -residual current after oxidation electrolysis of neptunium sample solution, a;
the specific calculation formula of the integral factor of the coulometer is shown in formula III:
in formula III:
I c -constant current, a, used for initial calibration of the coulometer;
t c -actual calibration time, s;
Q c -the output electric quantity of the coulometer integrator in the calibration process, C;
the specific calculation formula of the reaction fraction is shown in formula IV:
in formula IV:
E 1 -the potential at the end of the electrolysis of the blank solution is reduced, V;
E 2 -the potential at the end of the oxidation electrolysis of the blank solution, V;
E 3 -the potential at the end of the reduction electrolysis of the neptunium sample solution, V;
E 4 -the potential at the end of the oxidative electrolysis of the neptunium sample solution, V;
E 0 -standard potential of Np (V)/Np (vi), V in a low concentration sulfuric acid solution medium;
r-molar gas constant, 8.3145 Jmol.L -1 K -1 ；
T—absolute temperature of solution during electrolysis, K (where t=t c +273.15)。
Compared with the prior art, the invention has the following beneficial effects:
the precision (RSD) of the method for determining the neptunium content fixed value of the neptunium dioxide standard substance by using the control potential coulomb method established by the invention is better than 0.1%, the requirement of the standard substance content fixed value can be met, and the method is accurate and reliable and has wide application range.
Detailed Description
The present invention will be described in detail with reference to specific examples. The present embodiment is implemented on the premise of the technical scheme of the present invention, and a detailed implementation manner and a specific operation process are given, but the protection scope of the present invention is not limited to the following examples.
Example 1
The embodiment provides a method for determining the neptunium content in neptunium dioxide standard substance, which comprises the following specific determination steps:
(1) Preparation of 0.5mol/L sulfuric acid solution
30 mL-35 mL of analytically pure sulfuric acid is measured by a 50mL measuring cylinder, added into 500 mL-550 mL of deionized water, cooled and transferred into a 1L volumetric flask, and the volume is fixed by the deionized water, and the concentration of the prepared sulfuric acid is 0.5mol/L.
(2) Preparation of 3mol/L sulfuric acid solution
165-170 mL of analytically pure sulfuric acid is measured by a 100mL measuring cylinder, added into 500-550 mL of deionized water, cooled and transferred into a 1L volumetric flask, and the volume is fixed by the deionized water, and the concentration of the prepared sulfuric acid is 3mol/L.
(3) Dissolution of the sample
0.03 g-0.05 g neptunium dioxide standard substance is accurately weighed by a balance with the precision of 0.01mg and placed in a 100mL beaker. 10 mL-15 mL of analytically pure nitric acid solution is added, and 2 drops-3 drops of analytically pure HF solution are added. Placing the beaker on an electric furnace (temperature adjusting range is 0-300 ℃), completely dissolving the sample at 160-180 ℃, and cooling to 20-25 ℃ after the solution is completely evaporated.
Adding 1-2 mL of 3mol/L sulfuric acid solution, continuously heating and concentrating at 220-250 ℃ until the sample is nearly dry, continuously heating until white smoke is emitted, cooling the evaporated sample solution to 20-25 ℃ after the white smoke is no longer emitted, adding a small amount of 0.5mol/L sulfuric acid solution, transferring the sample solution into a weighed sample separating bottle by a dropper, and diluting the sample to the neptunium concentration of 1-3 mg/g by 0.5mol/L sulfuric acid solution.
(4) Sample separation
The mass of neptunium solution transferred to the sample vial was weighed with a 0.01mg balance. The sample separating bottle is gently squeezed, so that the sample solution is dropwise dripped into the electrolytic cell cup, and the residual solution in the sample separating bottle is weighed. The mass difference is the mass of the solution in the electrolytic cell cup, and the mass of neptunium is 1 mg-2 mg according to the concentration of neptunium sample solution, namely the mass Ws of neptunium in the electrolytic cell cup.
(5) Electrode pretreatment
The working electrode and the counter electrode were immersed in an 8mol/L nitric acid solution, boiled for 20min, and immersed overnight in the 8mol/L nitric acid solution. Before use, the working electrode and the counter electrode are washed three times by deionized water, and then oxidation-reduction treatment is carried out in sulfuric acid electrolyte with the concentration of 0.5mol/L until the background current is 5 mu A-10 mu A for standby.
(6) Measurement of blank electric quantity
The coulometer is preheated for 30min, 10 mL-15 mL of sulfuric acid solution (1) is added into the electrolytic cell cup, analytically pure high silver oxide (Ag (II)) is added, and stirring is carried out while adding until excessive high silver oxide is added and black is not lost after 10min. And heating the test solution at 190-200 ℃ to completely eliminate excessive black oxidized high silver powder. After cooling, adding 15 mL-20 mL of sulfuric acid solution (1), so that the gold electrode is just completely submerged by the liquid surface of the sample, and introducing argon (the purity is 99.99%) for 10 min-15 min (the argon flow is 10 mL/min-15 mL/min) for 10min. Reducing under the reduction potential of 0.665V (abbreviated as SCE for saturated calomel electrode), and stopping reducing when the residual current is reduced to below 10 mu A; oxidation was performed at an oxidation potential of 1.025V (SCE), and when the residual current was reduced to 10. Mu.A or less, the oxidation was stopped, and the electrolytic power Q was recorded 1 Electrolyte potential E 2 Time t of electrolysis 1 And residual current I r1 。
(7) Determination of samples
In the separated sample of 1 mg-2 mg neptunium, the sample is measured according to the blank electric quantity measurement in the step (6), and the electrolytic electric quantity Q is recorded S Electrolysis potential E 4 Residual current I r2 And electrolysis time t 2 。
(8) Standard electrode potential E 0 Is (are) determined by
And (3) adding a certain amount of neptunium solution into the electrolytic cell cup, measuring the standard electrode potential according to the blank electric quantity measurement in the step (6), reducing the potential at 0.665V (SCE) until the residual current is less than 10 mu A, and stopping reduction. Regulating the control potential at 1.025V (SCE) to oxidize to residual current less than 10 μA, and recording oxidation electric quantityAnd Q, stopping oxidization. The control potential was reduced at 0.665V (SCE) and the reduction was stopped when the charge was near Q/2. At this time, the concentration of Np (V) in the solution was equal to that of Np (VI). Np is measured 6+ /Np 5+ Potential value E of electric pair 0 。
(9) Result calculation
The specific calculation formula of the neptunium content in the neptunium dioxide standard substance is shown as formula I:
in formula I:
C Np (%) neptunium content (%) in neptunium dioxide standard substance;
Q s -the integrated charge of the coulometer, C, during the oxidation of the neptunium sample;
Q b the specific calculation formula of the blank electric quantity C is shown in a formula II;
c, an integral factor of the coulometer, wherein a specific calculation formula of the integral factor is shown in a formula III;
A r -the relative atomic weight of neptunium (calculated from the isotopic abundance);
f, reaction fraction, wherein the specific calculation formula of the value is shown in formula IV;
F-Faraday constant, 96485.34;
W s -mass of neptunium sample in cell cup, g;
the specific calculation formula of the blank electric quantity is shown as a formula II:
in formula II:
E 1 -the potential at the end of the electrolysis of the blank solution is reduced, V;
E 2 -the potential at the end of the oxidation electrolysis of the blank solution, V;
E 3 neptunium sample solution reduction electricityThe potential at the end of the solution, V;
E 4 -the potential at the end of the oxidative electrolysis of the neptunium sample solution, V;
Q 1 -integrated electric quantity of coulometer at the end of the oxidation electrolysis of the blank solution, C;
I r1 -residual current after oxidation and electrolysis of the blank solution, a;
t 1 -oxidation electrolysis time of the blank solution, s;
t 2 -time s of oxidative electrolysis of neptunium sample solution;
I r2 -residual current after oxidation electrolysis of neptunium sample solution, a;
the specific calculation formula of the integral factor of the coulometer is shown in formula III:
in formula III:
I c -constant current, a, used for initial calibration of the coulometer;
t c -actual calibration time, s;
Q c -the output electric quantity of the coulometer integrator in the calibration process, C;
the specific calculation formula of the reaction fraction is shown in formula IV:
in formula IV:
E 1 -the potential at the end of the electrolysis of the blank solution is reduced, V;
E 2 -the potential at the end of the oxidation electrolysis of the blank solution, V;
E 3 -the potential at the end of the reduction electrolysis of the neptunium sample solution, V;
E 4 -the potential at the end of the oxidative electrolysis of the neptunium sample solution, V;
E 0 -standard potential of Np (V)/Np (vi), V in a low concentration sulfuric acid solution medium;
r-molar gas constant, 8.3145 Jmol.L -1 K -1 ；
T—absolute temperature of solution during electrolysis, K (where t=t c +273.15)。
The previous description of the embodiments is provided to facilitate a person of ordinary skill in the art in order to make and use the present invention. It will be apparent to those skilled in the art that various modifications can be readily made to these embodiments and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above-described embodiments, and those skilled in the art, based on the present disclosure, should make improvements and modifications without departing from the scope of the present invention.
Claims (10)
1. A method for determining neptunium content in neptunium dioxide standard substance, which is characterized by comprising the following specific measuring steps:
s1, preparing a low-concentration sulfuric acid solution and a high-concentration sulfuric acid solution;
s2, dissolving neptunium dioxide standard substances to obtain a mixed solution;
s3, adding the high-concentration sulfuric acid solution obtained in the step S1 into the mixed solution obtained in the step S2, and heating and concentrating to obtain a evaporated sample;
s4, diluting the low-concentration sulfuric acid solution obtained in the step S1 with the evaporated sample obtained in the step S3 to obtain a diluted sample solution;
s5, measuring the blank electric quantity in the electrolytic cell cup without the sample solution;
s6, measuring the electric quantity of the diluted sample solution obtained in the step S4;
and S7, calculating the neptunium content in the neptunium dioxide standard substance according to Faraday' S law based on the blank electric quantity obtained in the step S5 and the electric quantity of the sample solution obtained in the step S6.
2. A method for determining neptunium content in neptunium dioxide standard substance according to claim 1, characterized in that in step S1, a certain amount of analytically pure sulfuric acid is measured, added into deionized water while stirring, cooled and transferred into a volumetric flask, and deionized water is used for determining volume;
the concentration of the low-concentration sulfuric acid solution is 0.4-0.6 mol/L;
the concentration of the high-concentration sulfuric acid solution is 2.5-3.5 mol/L.
3. A method for determining neptunium content in neptunium dioxide standard substance according to claim 1, characterized in that in step S2, nitric acid solution and HF solution are added into a certain amount of neptunium dioxide standard substance, and mixed solution is obtained after heating and dissolving and cooling;
neptunium dioxide standard: nitric acid solution: HF solution=0.03 to 0.05g: 10-15 mL: 0.10-0.15 mL;
the nitric acid solution is an analytically pure nitric acid solution, and the HF solution is an analytically pure HF solution;
the heating temperature is 160-180 ℃.
4. A method for the determination of neptunium content in neptunium dioxide standard according to claim 1, characterized in that in step S3, the heating temperature is 220-250 ℃.
5. A method for determining the neptunium content of neptunium dioxide standard according to claim 1, characterized in that in step S4 the neptunium concentration in the sample solution is 1-3 mg/g.
6. A method for determining the neptunium content of neptunium dioxide standard according to claim 1, characterized in that in step S5, the specific measurement steps of the empty capacity are as follows:
adding low concentration sulfuric acid solution into electrolytic cell cup, adding excessive oxidized high silver, heating to remove excessive oxidized high silver, adding low concentration sulfuric acid solution to submerge electrode, introducing argonGas, reducing at the reduction potential, stopping reducing when the residual current is reduced to below 10 mu A; oxidation is carried out on oxidation potential, when the residual current is reduced to below 10 mu A, the oxidation is stopped, and the electrolysis electric quantity Q of the blank solution is recorded 1 Electrolyte potential E 1 And E is 2 Time t of electrolysis 1 And residual current I r1 ；
The oxidation Gao Yin is analytically pure high silver oxide.
7. A method for determining neptunium content in neptunium dioxide standard according to claim 6, characterized in that in step S6, the specific measurement steps of the electric quantity of the diluted sample solution are as follows:
(1) Immersing the electrode in a nitric acid solution, soaking the electrode in the nitric acid solution overnight after boiling, and washing the electrode with deionized water before use, and performing redox treatment in an electrolyte until the background current meets the requirement;
(2) Transferring the diluted sample solution obtained in the step S4 into an electrolytic cell cup, and calculating the mass Ws of the neptunium sample in the electrolytic cell cup;
(3) Adding a low-concentration sulfuric acid solution into the electrolytic cell cup filled with the neptunium sample obtained in the step (2), adding excessive oxidized high silver, heating to eliminate the excessive oxidized high silver, then adding a low-concentration sulfuric acid solution to submerge an electrode on the liquid level of the solution, introducing argon, reducing on a reduction potential, and stopping reducing when the residual current is reduced to be less than 10 mu A; oxidation is carried out on oxidation potential, oxidation is stopped when residual current is reduced to below 10 mu A, and electrolytic electricity quantity Q of neptunium sample solution is recorded S Electrolysis potential E 3 And E is 4 Residual current I r2 And electrolysis time t 2 ；
(4) Measuring standard electrode potential E0: adding neptunium solution into the electrolytic cell cup, operating according to step (3), controlling the potential to reduce to residual current less than 10 μA at reduction potential, stopping reduction, adjusting the control potential to oxidize to residual current less than 10 μA at oxidation potential, recording oxidation electric quantity Q, stopping oxidation, controlling the potential to reduce at reduction potential, stopping reduction when the electric quantity is close to Q/2,measuring standard electrode potential E 0 。
8. A method for determining the neptunium content of neptunium dioxide standard according to claim 7, characterized in that in step (1), said electrodes comprise a working electrode and a counter electrode;
the concentration of the nitric acid solution is 8mol/L;
the boiling time is 20min;
the electrolyte is sulfuric acid electrolyte with the concentration of 0.5 mol/L;
the background current is required to be 5-10 mu A.
9. A method for determining neptunium content in neptunium standard substance as claimed in claim 7, characterized in that in step (2), the diluted sample solution obtained in step S4 is transferred to a weighed sample separating bottle, weighing is performed, the sample solution in the sample separating bottle is transferred to an electrolytic cell cup, the residual solution in the sample separating bottle is weighed, the mass difference is the mass of the solution in the electrolytic cell cup, and the mass Ws of neptunium in the electrolytic cell cup is calculated according to the concentration of neptunium solution.
10. A method for determining neptunium content in neptunium dioxide standard according to claim 7, wherein in step S7, the specific calculation formula of neptunium content in neptunium dioxide standard is shown in formula i:
in formula I:
C Np (%) neptunium content (%) in neptunium dioxide standard substance;
Q s -the integrated charge of the coulometer, C, during the oxidation of the neptunium sample;
Q b the specific calculation formula of the blank electric quantity C is shown in a formula II;
c, an integral factor of the coulometer, wherein a specific calculation formula of the integral factor is shown in a formula III;
A r -relative atomic weight of neptunium;
f, reaction fraction, wherein the specific calculation formula of the value is shown in formula IV;
F-Faraday constant, 96485.34;
W s -mass of neptunium sample in cell cup, g;
the specific calculation formula of the blank electric quantity is shown as a formula II:
in formula II:
E 1 -the potential at the end of the electrolysis of the blank solution is reduced, V;
E 2 -the potential at the end of the oxidation electrolysis of the blank solution, V;
E 3 -the potential at the end of the reduction electrolysis of the neptunium sample solution, V;
E 4 -the potential at the end of the oxidative electrolysis of the neptunium sample solution, V;
Q 1 -integrated electric quantity of coulometer at the end of the oxidation electrolysis of the blank solution, C;
I r1 -residual current after oxidation and electrolysis of the blank solution, a;
t 1 -oxidation electrolysis time of the blank solution, s;
t 2 -time s of oxidative electrolysis of neptunium sample solution;
I r2 -residual current after oxidation electrolysis of neptunium sample solution, a;
the specific calculation formula of the integral factor of the coulometer is shown in formula III:
in formula III:
I c coulometer primaryConstant current used in initial calibration, A;
t c -actual calibration time, s;
Q c -the output electric quantity of the coulometer integrator in the calibration process, C;
the specific calculation formula of the reaction fraction is shown in formula IV:
in formula IV:
E 1 -the potential at the end of the electrolysis of the blank solution is reduced, V;
E 2 -the potential at the end of the oxidation electrolysis of the blank solution, V;
E 3 -the potential at the end of the reduction electrolysis of the neptunium sample solution, V;
E 4 -the potential at the end of the oxidative electrolysis of the neptunium sample solution, V;
E 0 -standard potential of Np (V)/Np (vi), V in a low concentration sulfuric acid solution medium;
r-molar gas constant, 8.3145 Jmol.L -1 K -1 ；
T-absolute temperature of solution during electrolysis, K.
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