1、Designation: E 342 04Standard Test Method forDetermination of Chromium Oxide in Chrome Ores byPermanganate Titrimetry1This standard is issued under the fixed designation E 342; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar 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 covers the determination of chromiumoxide (Cr2O3) in chrome ores in the concentration range fr
3、om25 to 60 %.1.2 This standard 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.2.
4、 Referenced Documents2.1 ASTM Standards:2D 1193 Specification for Reagent WaterE 50 Practices for Apparatus, Reagents, and Safety Precau-tions for Chemical Analysis of Metals, Ores, and RelatedMaterialsE 135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE 276 Tes
5、t Method for Particle Size or Screen Analysis atNo. 4 (4.75-mm) Sieve and Finer for Metal-Bearing Oresand Related MaterialsE 882 Guide for Accountability and Quality Control in theChemical Analysis Laboratory3. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Term
6、inology E 135.4. Summary of Test Method4.1 The sample is decomposed by fusion with sodiumperoxide. After leaching in water and boiling to decomposeperoxides, the solution is acidified with nitric and sulfuricacids. Residual chromium is oxidized to chromate with silvernitrate, potassium permanganate,
7、 and peroxydisulfate. Theexcess of permanganate is destroyed by the addition of sodiumchloride. After cooling, the chromate is reduced by the additionof a measured excess of a ferrous ammonium sulfate, and theexcess titrated with a standard permanganate solution.5. Significance and Use5.1 This test
8、method is intended to be used for compliancewith compositional specifications for chromium oxide content.It is assumed that all who use these procedures will be trainedanalysts capable of performing common laboratory proceduresskillfully and safely. It is expected that work will be performedin a pro
9、perly equipped laboratory and that proper wastedisposal procedures will be followed. Appropriate qualitycontrol practices must be followed such as those described inGuide E 882.6. Interferences6.1 None of the elements normally found in chrome oresinterfere with this test method.7. Reagents and Mater
10、ials7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are available3. Other grades may be
11、used,provided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determination.7.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water as definedby Type I of Specification D
12、 1193.7.3 Ammonium Peroxydisulfate Solution (250 g/L)Dissolve 25 g of ammonium persulfate (ammonium peroxy-disulfate) (NH4)2S2O8) in water, and dilute to 100 mL.Prepare fresh as needed.1This test method is under the jurisdiction of ASTM Committee E01 onAnalytical Chemistry for Metals, Ores, and Rela
13、ted Materials and is the directresponsibility of Subcommittee E01.02 on Ores, Concentrates, and Related Metal-lurgical Materials.Current edition approved May 1, 2004. Published June 2004. Originallyapproved in 1967. Last previous edition approved in 1999 as E 342 99.2For referenced ASTM standards, v
14、isit 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.3Reagent Chemical, American Chemical Society Specifications, AmericanChemical Society, Washing
15、ton, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole Dorset, U. K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmaceutical Convention, Inc., (USPC), Rockville,MD.1Copyright
16、 ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.7.4 Ferrous Ammonium Sulfate, Standard Solution (0.2N)Dissolve 78.4 g of ferrous ammonium sulfate(FeSO4(NH4)2SO46H2O) in 1 L of cool H2SO4(5+95). As theferrous ammonium sulfate solution gradually
17、 weakens inreducing power, it is necessary to standardize it daily, or at thesame time that the chrome ore is analyzed. To standardize,transfer 100 mL of FeSO4(NH4)2SO46H2O to a 600-mLbeaker, dilute to 300 mL with cold H2SO4(5+95), add 2 mL ofH3PO4and 2 drops of ortho-phenanthroline ferrous sulfate(
18、Ferroin). Titrate immediately with 0.2 N KMnO4solution to afaint, permanent pink color.7.5 Ferrous Sulfate Solution (0.025 M)Dissolve 6.95 g offerrous sulfate (FeSO47H2O) in 500 mL of water and dilute to1L.7.6 Nitric Acid (sp gr 1.42)Concentrated nitric acid(HNO3).7.7 Ortho-Phenanthroline Ferrous Su
19、lfate Indicator Solu-tion (0.025 M)Dissolve 1.485 g of 1,10-phenanthrolinemonohydrate in 100 mL of ferrous sulfate solution (FeSO47H2O).7.8 Phosphoric Acid (sp gr 1.69)Concentrated phosphoricacid (H3PO4).7.9 Potassium Permanganate Solution (20 g/L)Dissolve20 g of potassium permanganate (KMnO4) in wa
20、ter and diluteto1L.7.10 Potassium Permanganate, Standard Solution (0.2N)Dissolve 6.4 g of KMnO4in 1 L of water. Standardizeagainst the National Institute of Standards and TechnologyStandard sodium oxalate or equivalent.7.11 Silver Nitrate Solution (8 g/L)Dissolve8gofsilvernitrate (AgNO3) in water an
21、d dilute to 1 L.7.12 Sodium Chloride Solution (100 g/L)Dissolve 10 g ofsodium chloride (NaCl) in water and dilute to 100 mL.7.13 Sodium Peroxide (Na2O2).7.14 Sulfuric Acid (1+1)Carefully pour 1 volume ofconcentrated sulfuric acid (H2SO4, sp gr 1.84) into 1 volumeof water.7.15 Sulfuric Acid (5+95)Car
22、efully pour 5 volumes ofconcentrated H2SO4(sp gr 1.84) into 95 volumes of water.8. Hazards8.1 For precautions to be observed in this method, refer toPractices E 50.9. Sampling, Test Specimens, and Test Units9.1 The test unit shall be pulverized so that at least 95 %passes a No. 100 (150-m) sieve in
23、accordance with TestMethod E 276 and shall be dried at 105 to 110C for aminimum of 1 h.10. Procedure10.1 Transfer 0.50 g of the previously dried sample,weighed to the nearest 0.1 mg to a 30-mL iron crucible (Note1)andadd8gofdryNa2O2(Note 2). Thoroughly mix thecontents of the crucible and cover the m
24、ixture with anadditional 1 to2gofNa2O2. Cover the crucible with an ironor nickel cover and carefully fuse the contents at 600 to 700C,preferably in an electric muffle furnace. After the mix hasmelted, fuse for several minutes at a low red heat while givinga slight rotary motion to the crucible to en
25、sure completedecomposition.NOTE 1Ordinary iron crucibles which may contain significantamounts of chromium should be avoided. Crucibles made of ingot iron aresatisfactory.NOTE 2If about 0.2 g of very fine pulverized sugar charcoal is mixedwith the Na2O2, only about5goftheperoxide is required. After h
26、eatingfor about 30 s, ignition of the charcoal takes place, and the crucible willsuddenly become a dull red on the outside. The total time required tocomplete the fusion is about 2 min. By thus shortening the time for fusionand contact with the flux, the life of the crucible is extended.10.2 Place t
27、he cool crucible and cover in a 600-mL coveredbeaker, leach the melt with 150 mL of water, remove thecrucible and cover, and rinse. Boil 10 min to destroy theresidual peroxide. Add to the cooled solution 60 mL ofH2SO4(1+1) and 5 mL of HNO3and boil for several minutesuntil any iron scale from the cru
28、cible is dissolved. Add 15 mLof AgNO3solution, 2 drops of KMnO4solution (7.9), and 10mL of (NH4)2S2O8solution and boil for 5 min. Add 10 mL ofNaCl solution and boil for 5 to 10 min after the KMnO4or anyMnO2has completely disappeared.10.3 Cool, and if necessary, dilute with cold water to 350mL, then
29、add 3 to 5 mL of H3PO4(7.8). Add a measured excessof FeSO4(NH4)2SO46H2O. The point at which reduction iscomplete can be detected by the development of deep greencolor. The FeSO4(NH4)2SO46H2O may be added either as 0.2N solution (7.4) or a weighed amount of the salt (Note 3). Add2 drops of orthophena
30、nthroline ferrous sulfate (Ferroin) as anindicator. Titrate the excess FeSO4(NH4)2SO46H2O with 0.2N KMnO4solution. The end point is reached when the solutionbecomes clear green in color.NOTE 3Approximately 70 mL of 0.2 N FeSO4(NH4)2SO46H2Osolution of 5.5 g of the salt is required for a chrome ore co
31、ntaining 65 %Cr2O3.11. Calculation11.1 Calculate the percentage of chromium oxide as fol-lows:Chromium oxide Cr2O3!,%5 A 2 B! 3 C 3 0.02534/D 3 100(1)where:A = millilitres of standard KMnO4solution equivalent tothe total amount of FeSO4(NH4)2SO46H2O added tothe sample solution,B = millilitres of sta
32、ndard KMnO4solution required totitrate the excess FeSO4(NH4)2SO46H2O,C = normality of standard KMnO4solution, andD = grams of sample used.12. Precision and Bias12.1 PrecisionTable 1 indicates the precision of this testmethod between laboratories.12.2 BiasNo information on the bias of this test metho
33、d isknown. Accepted reference materials may not have beenincluded in the materials used in the interlaboratory study.Users of this test method are encouraged to employ acceptedE342042reference materials, if available, and to judge the bias of themethod from the difference between the accepted value
34、for thechromium oxide content and the mean value from interlabora-tory testing of the refrence material.13. Keywords13.1 chromium ores; chromium oxide contentASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standa
35、rd. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewe
36、d every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible
37、technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Consh
38、ohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).TABLE 1 Precision DataA
39、verageConcentration,A%RelativeStandard DeviationB%Number ofParticipatingLaboratories51.52 0.21 442.11 0.19 5AEach concentration represents a different kind of chrome ore.BRelative Standard Deviation, RSD, in this test method is calculated as follows:RSD 5 100/ X!=(d2/ n 2 1!where:X= average concentration, %d = difference of the determination from the mean, andn = number of determinations.E342043
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