1、Designation: E342 11 (Reapproved 2016)Standard Test Method forDetermination of Chromium Oxide in Chrome Ores byPermanganate Titrimetry1This standard is issued under the fixed designation E342; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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 composi
3、tional range from25%to60%.NOTE 1As used in this test method, “%” refers to a mass fraction(wt/wt %) (g/100g).1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety conc
4、erns, 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. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterE5
5、0 Practices for Apparatus, Reagents, and Safety Consid-erations for Chemical Analysis of Metals, Ores, andRelated MaterialsE135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE276 Test Method for Particle Size or ScreenAnalysis at No.4 (4.75-mm) Sieve and Finer fo
6、r Metal-Bearing Ores andRelated MaterialsE882 Guide for Accountability and Quality Control in theChemical Analysis Laboratory3. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology E135.4. Summary of Test Method4.1 The sample is decomposed by fusion with s
7、odiumperoxide. After leaching in water and boiling to decomposeperoxides, the solution is acidified with HNO3and H2SO4.Residual chromium is oxidized to chromate with silver nitrate,potassium permanganate, and peroxydisulfate. The excess ofpermanganate is destroyed by the addition of NaCl. Aftercooli
8、ng, the chromate is reduced by the addition of a measuredexcess of a ferrous ammonium sulfate, and the excess is titratedwith a permanganate solution.5. Significance and Use5.1 This test method is intended to be used for compliancewith compositional specifications for chromium oxide contentin chromi
9、um-bearing ores. It is assumed that all who use theseprocedures will be trained analysts capable of performingcommon laboratory procedures skillfully and safely. It isexpected that work will be performed in a properly equippedlaboratory and that proper waste disposal procedures will befollowed. Appr
10、opriate quality control practices must be fol-lowed such as those described in Guide E882.6. Interferences6.1 None of the elements normally found in chrome oresinterfere with this test method.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless oth
11、erwise 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 used,provided it is first ascertained that the reagent is of sufficientlyhigh purity to
12、 permit its use without lessening the accuracy ofthe determination.1This test method is under the jurisdiction of ASTM Committee E01 onAnalytical Chemistry for Metals, Ores, and Related Materials and is the directresponsibility of Subcommittee E01.02 on Ores, Concentrates, and Related Metal-lurgical
13、 Materials.Current edition approved Nov. 15, 2016. Published December 2016. Originallyapproved in 1967. Last previous edition approved in 2011 as E342 11. DOI:10.1520/E0342-11R16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org.
14、 For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical
15、 Society, see the United States Pharmacopeia andNational Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,MD.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States17.2 Purity of WaterUnless otherwise indicated, referencesto
16、water shall be understood to mean reagent water conformingto Type I or II of Specification D1193. Type III or IV may beused if they effect no measurable change in the blank orsample.7.3 Ammonium Peroxydisulfate Solution (250 g/L)Dissolve 25 g of ammonium persulfate (ammonium peroxy-disulfate) (NH4)2
17、S2O8) in water, and dilute to 100 mL.Prepare fresh as needed.7.4 Ferrous Ammonium Sulfate Solution (0.2 N)Dissolve78.4 g of ferrous ammonium sulfate (FeSO4(NH4)2SO46H2O)in 1 L of cool H2SO4(5 + 95). Because the ferrous ammoniumsulfate solution gradually weakens in reducing power, it isnecessary to s
18、tandardize the ferrous ammonium sulfate solu-tion daily or at the same time that the chrome ore is analyzed.To standardize, transfer 100 mL of FeSO4(NH4)2SO46H2Otoa 600-mL beaker, dilute to 300 mL with cold H2SO4(5 + 95),add2mLofH3PO4and 2 drops of ortho-phenanthrolineferrous sulfate (ferroin). Titr
19、ate immediately with 0.2 NKMnO4solution (7.8) to a faint, 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 Ortho-Phenanthroline Ferrous Sulfate IndicatorSolution(0.025 M)Dissolve 1.485 g of 1,10-phenanthro
20、line monohydrate in 100 mL of ferrous sulfatesolution (FeSO47H2O) prepared in 7.5.7.7 Potassium Permanganate Solution (20 g/L)Dissolve20 g of potassium permanganate (KMnO4) in water and diluteto1L.7.8 Potassium Permanganate Solution (0.2 N)Dissolve6.4 g of KMnO4in 1 L of water. Standardize against a
21、 NationalInstitute of Standards and Technology Reference Material forsodium oxalate (Na2C2O4) or equivalent.7.9 Silver Nitrate Solution (8 g/L)Dissolve8gofsilvernitrate (AgNO3) in water and dilute to 1 L.7.10 Sodium Chloride Solution (100 g/L)Dissolve 10 g ofNaCl in water and dilute to 100 mL.7.11 S
22、odium Peroxide (Na2O2).8. Hazards8.1 For precautions to be observed in this method, refer toPractices E50.9. Sampling, Test Specimens, and Test Units9.1 The test material shall be pulverized so that at least 95% passes a No. 100 (150-m) sieve in accordance with TestMethod E276 and shall be dried at
23、105 C to 110 C 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 (Note2)andadd8gofdryNa2O2(Note 3). Thoroughly mix thecontents of the crucible and cover the mixture with anadditional1gto2gofNa2O2.10.2 Cover the
24、 crucible with an iron or nickel cover andcarefully fuse the contents at 600 C to 700 C, preferably inan electric muffle furnace. After the mix has melted, fuse forseveral minutes at a low red heat while giving a slight rotarymotion to the crucible to ensure complete decomposition.NOTE 2Ordinary iro
25、n crucibles that may contain significant amountsof chromium should be avoided. Crucibles made of ingot iron aresatisfactory.NOTE 3Only about 5 g of Na2O2is required if about 0.2 g of very finepulverized sugar charcoal is mixed with the Na2O2.After heating for about30 s, ignition of the charcoal take
26、s place, and the crucible will suddenlybecome a dull red on the outside. The total time required to complete thefusion is about 2 min. By shortening the time for fusion and contact withthe flux, the life of the crucible is extended.10.3 Place the cool crucible and its cover into a 600-mLcovered beak
27、er, leach the melt with 150 mL of water, removethe crucible and cover, and rinse the crucible and cover into thebeaker. Boil 10 min to destroy the residual peroxide.10.4 Add to the cooled solution 60 mL of H2SO4(1+1)and 5 mL of HNO3and boil for several minutes until any ironscale from the crucible i
28、s dissolved.10.5 Add 15 mL of AgNO3solution, 2 drops of KMnO4solution (7.7), and 10 mL of (NH4)2S2O8solution and boil for5 min.10.6 Add 10 mL of NaCl solution and boil for 5 min to 10min after the KMnO4or any MnO2has completely disap-peared.10.7 Cool, and if necessary, dilute with cold water to 350m
29、L, then add 3 mL to 5 mL of H3PO4.10.8 Add a measured excess of FeSO4(NH4)2SO46H2O.The point at which reduction is complete can be detected by thedevelopment of deep green color. The FeSO4(NH4)2SO46H2Omay be added either as the 0.2 N prepared solution (7.4)oraweighed amount of the salt (Note 4). Add
30、 2 drops of ortho-phenanthroline ferrous sulfate (ferroin) as an indicator.10.9 Titrate the excess FeSO4(NH4)2SO46H2O with 0.2 NKMnO4solution (7.8). The end point is reached whenever thesolution becomes clear green in color.NOTE 4Approximately 70 mL of 0.2 N FeSO4(NH4)2SO46H2Osolution (7.4) containi
31、ng 5.5 g of the salt is required for a chrome orecontaining 65 % Cr2O3(Note 1).11. Calculation11.1 Calculate the chromium oxide content as follows:Chromium oxide Cr2O3!,%5A 2 B! 3 C 32.534#D(1)where:A = millilitres of KMnO4solution (7.8) equivalent to thetotal amount of FeSO4(NH4)2SO46H2O added to t
32、hesample solution,B = millilitres of KMnO4solution (7.8) required to titratethe excess FeSO4(NH4)2SO46H2O,C = normality of KMnO4solution, andD = grams of sample used (Note 1).12. Precision and Bias12.1 PrecisionThe precision of this test method betweenlaboratories is indicated in Table 1.E342 11 (20
33、16)212.2 BiasNo information on the bias of this test method 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 acceptedreference materials, if available, and to judge the bias of themet
34、hod from the difference between the accepted value for thechromium oxide content and the mean value from interlabora-tory testing of the reference material.13. Keywords13.1 chromium ores; chromium oxide content; permangan-ate titrimetry; titrimetryASTM International takes no position respecting the
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37、quarters. Your comments will receive careful consideration at a meeting of theresponsible 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 sta
38、ndard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, 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 s
39、erviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 1 Precision DataAverageConcentration,A%RelativeStandard Deviation, %Number ofParticipatingLaboratories51.52 0.21 442.11 0.19 5AEach value represents a different kind of chrome ore (see Note 1).E342 11 (2016)3
