1、Designation: C 1267 06Standard Test Method forUranium by Iron (II) Reduction in Phosphoric Acid Followedby Chromium (VI) Titration in the Presence of Vanadium1This standard is issued under the fixed designation C 1267; the number immediately following the designation indicates the year oforiginal ad
2、option or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method, commonly referred to as the ModifiedDavies and Gray
3、 technique, covers the titration of uranium inproduct, fuel, and scrap materials after the material is dis-solved. The test method is versatile and has been ruggednesstested. With appropriate sample preparation, this test methodcan give precise and unbiased uranium assays over a widevariety of mater
4、ial types (1, 2).2Details of the titrationprocedure in the presence of plutonium with appropriatemodifications are given in Test Method C 1204.1.2 Uranium levels titrated are usually 20 to 50 mg, but upto 200 mg uranium can be titrated using the reagent volumesstated in this test method.1.3 This sta
5、ndard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For specificsafeguard and
6、safety precaution statements, see Section 4.2. Referenced Documents2.1 ASTM Standards:3C 696 Test Methods for Chemical, Mass Spectrometric, andSpectrochemical Analysis of Nuclear-Grade Uranium Di-oxide Powders and PelletsC 799 Test Methods for Chemical, Mass Spectrometric,Spectrochemical, Nuclear, a
7、nd Radiochemical Analysis ofNuclear-Grade Uranyl Nitrate SolutionsC 1128 Guide for Preparation of Working Reference Mate-rials for Use in the Analysis of Nuclear Fuel CycleMaterialsC 1204 Test Method for Uranium in the Presence of Pluto-nium by Iron(II) Reduction in Phosphoric Acid Followedby Chromi
8、um(VI) TitrationC 1346 Practice for Dissolution of UF6from P-10 TubesC 1347 Practice for Preparation and Dissolution of UraniumMaterials for Analysis2.2 NIST Standard:4SRM 136e Potassium Dichromate (Oxidimetric Standard)2.3 NBL Standard:5CRM 112A Uranium Metal Standard3. Summary of Test Method3.1 Sa
9、mples are prepared by dissolution techniques detailedin Practices C 1346, C 1347, or Refs (2), (3), and (4). Appro-priate uncertainties for sampling and weight determinationshould be applied to the overall precision and bias calculationsfor the final result. Aliquants containing 20 to 200 mg ofurani
10、um are prepared by weight. The sample is fumed todryness after the appropriate acid treatment. The sample isdissolved in dilute nitric acid or water prior to titration.3.2 Uranium is reduced to uranium(IV) by excess iron(II) inconcentrated phosphoric acid (H3PO4) containing sulfamicacid. The excess
11、iron(II) is selectively oxidized by nitric acid(HNO3) in the presence of a molybdenum(VI) catalyst. Afterthe addition of a vanadium(IV) solution, the uranium(IV) istitrated with chromium(VI) to a potentiometric end point.3.3 The chromium(VI) titrant may be delivered manually ona weight or on a volum
12、etric basis as specified by the facilitytitration procedure.3.3.1 If the titrant is delivered on a volumetric basis,corrections to the volume of titrant may be needed to adjust forthe difference between the temperature of preparation and theambient temperature.3.3.2 Automated titrators are facility
13、specific and are notexplicitly addressed in this test method. However, automatedtitrators which have comparable bias and precision may beused.3.3.3 There is an alternate, high precision (;0.005 % RSD)modified Davies and Gray titration, which is similar to the1This test method is under the jurisdicti
14、on ofASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods ofTest.Current edition approved July 1, 2006. Published July 2006. Originally approvedin 1994. Last previous edition approved in 2000 as C 1267 00.2The boldface numbers in parentheses refe
15、r to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Avail
16、able from National Institute of Standards and Technology (NIST), 100Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http:/www.nist.gov.5New Brunswick Laboratory (NBL) Certified Reference Materials Catalog (U.S.Department of Energy), http:/www.nbl.doe.gov.1Copyright ASTM International, 100 Barr H
17、arbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.method covered in this procedure. In the high precisionmethod, the amount of uranium titrated is increased and about90 % of the titrant is delivered on a solid weight basis followedby titration to the end point with a dilute t
18、itrant. Details of thisalternate method are available in Ref (5).4. Significance and Use4.1 Factors governing selection of a method for the deter-mination of uranium include available quantity of sample,homogeneity of material sampled, sample purity, desired levelof reliability, and facility availab
19、le equipment.4.2 This uranium assay method is referenced in the TestMethods for Chemical, Mass Spectrometric, and Spectro-chemical Analysis of Nuclear-Grade Uranium Dioxide Pow-ders and Pellets (Test Methods C 696) and in the Test Methodsfor Chemical, Mass Spectrometric, and Spectrochemical,Nuclear,
20、 and RadiochemicalAnalysis of Nuclear-Grade UranylNitrate Solutions (Test Methods C 799). This uranium assaymethod may also be used for uranium hexafluoride anduranium ore concentrate. This test method determines 20 to200 mg of uranium; is applicable to product, fuel, and scrapmaterial after the mat
21、erial is dissolved; is tolerant towards mostmetallic impurity elements usually specified in product andfuel; and uses no special equipment.4.3 The ruggedness of the titration method has been studiedfor both the volumetric (6) and the weight (7) titration ofuranium with dichromate.4.4 Committee C26 S
22、afeguards Statement:4.4.1 The materials (nuclear grade uranium in product, fuel,and scrap) to which this test method applies are subject tonuclear safeguard regulations governing their possession anduse. The analytical method in this standard meets U.S. Depart-ment of Energy guidelines for acceptabi
23、lity of a measurementmethod for generation of safeguards accountability measure-ment data.4.4.2 When used in conjunction with the appropriate certi-fied reference materials (SRM6or CRM), this procedure candemonstrate traceability to the national measurement base.However, use of the test method does
24、not automaticallyguarantee regulatory acceptance of the resulting safeguardsmeasurements. It remains the sole responsibility of the user ofthis test method to assure that its application to safeguards hasthe approval of the proper regulatory authorities.5. Interferences5.1 Interfering elements are n
25、ot generally present in productand fuel material in quantities which cause interference in thetitration.5.1.1 Of the metallic impurity elements usually included inspecifications for product and fuel, silver, manganese, andvanadium (in the V oxidation state) interfere when present inamounts of 10 mg
26、or greater of impurity per 100 mg ofuranium (2, 8).5.1.2 Silver and vanadium (in the V oxidation state) causepositive bias when present in milligram quantities in thesample. The aliquant treatment adjusts the oxidation state ofany vanadium(V) present in the sample (2). To remove silver,the sample mu
27、st be treated prior to titration (8).5.1.3 Manganese was originally found to cause a negativebias (2), but this bias is eliminated when the titration aliquantpreparation procedure is followed as given (9, 10) in thistitrimetric method.5.2 Interferences with the Modified Davies and Gray titra-tion, w
28、hich may be present in some uranium materials, havebeen systematically studied.5.2.1 The non-interference of copper, titanium, cobalt,nickel, cerium, and samarium was demonstrated (11) at the 50mg impurity level for 100 mg of uranium.5.2.2 The effects of the following elements in milligramquantities
29、 were studied: silver, gold, lead, iodine, arsenic,antimony, and bismuth (8).5.2.2.1 Gold, lead, arsenic(V), antimony(V), and bismuthdo not interfere when present in amounts of 10 mg for 100 mgof uranium.5.2.2.2 Silver, iodine, arsenic(III), and antimony(III) inter-fere seriously in the determinatio
30、n of uranium and must beeliminated prior to titration.5.2.3 The effects of impurities on the titration of uraniumcontinued with the platinum metals (ruthenium, rhodium,palladium, osmium, iridium, and platinum), chloride, bromide(12), fluoride (13), and technetium (14).5.2.3.1 Ruthenium, palladium, o
31、smium, iridium, and plati-num cause serious positive errors in the determination ofuranium. Rhodium alone among the platinum metals does notcause any significant error.5.2.3.2 Chloride and bromide interfere with the assaythrough their effect on the platinum indicator electrode.5.2.3.3 Small amounts
32、of fluoride, less than 400 mg ashydrofluoric acid (HF) or 600 mg if HNO3is present, can betolerated by the titration.5.2.3.4 Technicium, found in high temperature reactor graderecycle (htgr) fuel, interferes with the titration and must beremoved before titration.5.3 The removal of certain interferen
33、ces in the modifiedDavies and Gray titration has also been studied.5.3.1 The initial fuming of titration aliquants with sulfuricacid removes impurity elements such as the halides and volatilemetallic elements (2, 12, 13).5.3.2 Arsenic(III) and antimony(III) can be eliminated inthe H3PO4by potassium
34、dichromate (K2Cr2O7) oxidation priorto its addition to the titration medium (8).5.3.3 Elimination of interferences in the titration by mer-cury, platinum, and palladium by means of a copper columnwas evaluated (15).5.3.4 Elimination of interferences by solvent extraction ofthe uranium from the impur
35、ities has also been studied (16).5.4 A list of impurities with brief references to their treat-ment for elimination is given in Table A1.1 in Annex A1, andthe details are given in Refs 2, 8, 9, 10, and 12-16.6. Apparatus6.1 Buret, polyethylene bottle (preparation instructions canbe found in Appendix
36、 X1), glass weight, or glass volumetric.6SRM is a registered trademark.C12670626.2 pH Meter, with indicator (a 16-gauge platinum wire hasbeen found to be satisfactory) and reference (saturated calomelhas been found to be satisfactory) electrodes.6.2.1 The indicator electrode should be changed or cle
37、anedif there is a titration problem such as less distinct than normalend point break or end point drift, or, if desired, prior to usewhen more than a week has passed since its last use. Suggestedcleaning procedures for platinum wire electrodes are detailedin Appendix X2.6.2.2 Asbestos and glass bead
38、 tipped saturated calomelelectrodes can be placed directly in the titration solution. Glassfrit tipped saturated calomel electrodes may have a faster leakrate and may need to be used with a separator tube containingthe electrolyte to prevent titration problems due to chloride.6.2.3 The reference ele
39、ctrode should be covered with arubber tip or submerged in a solution (saturated potassiumchloride solution for the calomel electrode) for overnightstorage.6.3 Magnetic Stirrer and TFE-Fluorocarbon Coated Mag-net.7. Reagents7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unle
40、ss otherwise indicated, it is intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are available.7Other grades of reagentsmay be used, provided it is first ascertained that the reagent isof sufficient
41、ly high purity to permit its use without lesseningthe accuracy of the determination.7.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean laboratory accepteddemineralized or deionized water.7.3 Ferrous Sulfate Heptahydrate (FeSO47 H2O, 1.0 M)Add 100 mL of sulf
42、uric acid (H2SO4, sp gr 1.84) to 750 mL ofwater as the solution is stirred.Add 280 g of FeSO47 H2O, anddilute the solution to 1 L with water. Prepare the FeSO47 H2Oreagent fresh, weekly. See the Note 5 in 10.8 on combinationof this reagent with the H3PO4.7.4 Nitric Acid (HNO3, 8 M)Add 500 mL of HNO3
43、(sp gr1.42) to 10 % Au Reduce the gold to metal and separate (8).Am, Sb, As, Br, Cl, Fe, Au, Pb, Ir, Mn, Hg, Mo,Np, Os, Pd, Pt, Pu, Ru, Ag, Th, Sn, V, ZrUse the tributyl phosphate/carbon tetrachloride extraction technique (16). Alternate solvents such as dodecaneare now used.AThe potassium dichromat
44、e oxidizes these elements to a non-interfering oxidation state which the ferrous ion is not capable of reducing.C1267068X3. DICHROMATE SOLUTION STANDARDIZATIONX3.1 Standardize reagent grade or better potassium dichro-mate against CRM 112-A uranium metal or its equivalent (seeAppendix X4).X3.2 The st
45、andard deviation of the mean for the potassiumdichromate standardization (s/=n ) should be well within theaccepted laboratory error limits for the uranium titration whenn = 10. Example: To maintain an accepted laboratory precisionon the uranium titration of s = 0.10, the recommended accept-able prec
46、ision on the potassium dichromate standardization iss = 0.05 for n = 10 so that the accuracy of the potassiumdichromate standard solution will have a minimal effect on thetitration results.X4. DISSOLUTION OF URANIUM METALX4.1 The following method has been used successfully forthe dissolution of appr
47、oximately 40 g of uranium metal forwhich the cleaned and dried weight of the uranium metal hasbeen accurately determined. The surface of the uranium metal(CRM 112-A or its equivalent) shall be cleaned following theinstructions on the certificate.X4.2 Place the metal in a dry weighed 2-L flask, or su
48、itablealternative, and add 100 mL of 8 M nitric acid.X4.2.1 Place a small funnel, sitting on a glass bend, in themouth of the flask, and place the flask on a hot plate at about75C until dark brown fumes are seen.X4.2.2 Lower the hot plate temperature to about 65C, andheat for 6 h. Swirl the mixture
49、occasionally during this stage ofdissolution.X4.3 Remove the flask from the hot plate, and add 50 mLof 8 M nitric acid.X4.4 Return the mixture to the hot plate with the funnel inthe mouth of the flask, turn the temperature of the hot plate toabout 75C, and leave the mixture for 8 h.X4.5 Add 50 mL of 8 M nitric acid to the flask, turn the hotplate to about 85C, leave the mixture on the hot plate for 4 hwith occasional swirling. Visually check for completeness ofdissolution.X4.5.1 If the dissolution is complete, dilute to 2 L withwater, and allow the solution to equilibrat
