1、Designation: E246 10Standard Test Methods forDetermination of Iron in Iron Ores and Related Materials byDichromate Titrimetry1This standard is issued under the fixed designation E246; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、 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 These test methods cover the determination of total ironin iron ores, concentrates, and agglomerates in t
3、he concentra-tion range 30 % to 95 % iron.1.2 The test methods in this standard are contained in thesections indicated as follows:Test Method AIron by the Hydrogen Sulfide Reduction Dichromate Ti-tration Method (30 % to 75 % Fe)Test Method BIron by the Stannous Chloride Reduction DichromateTitration
4、 Method (35 % to 95 % Fe)Test Method CIron by the Silver Reduction Dichromate TitrationMethod (35 % to 95 % Fe)1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety co
5、ncerns, 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. Specific hazardsstatements are given in Section 5 and in special “Warning”parag
6、raphs throughout these test methods.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterE50 Practices for Apparatus, Reagents, and Safety Consid-erations for Chemical Analysis of Metals, Ores, andRelated MaterialsE276 Test Method for Particle Size or Screen Analysis atNo.
7、 4 (4.75-mm) Sieve and Finer for Metal-Bearing Oresand Related MaterialsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE877 Practice for Sampling and Sample Preparation of IronOres and Related Materials for Determination of ChemicalCompositionE882 Gui
8、de for Accountability and Quality Control in theChemical Analysis LaboratoryE1028 Test Method for Total Iron in Iron Ores and RelatedMaterials by Dichromate Titrimetry33. Significance and Use3.1 The determination of the total iron content is theprimary means for establishing the commercial value of
9、ironores used in international trade.3.2 These test methods are intended as referee methods forthe determination of iron in iron ores. It is assumed that all whouse these test methods will be trained analysts capable ofperforming common laboratory procedures skillfully andsafely. It is expected that
10、 work will be performed in a properlyequipped laboratory and that proper waste disposal procedureswill be followed.Appropriate quality control practices must befollowed, such as those described in Guide E882.4. Apparatus, Reagents, and Instrumental Practices4.1 ApparatusSpecialized apparatus require
11、ments arelisted in the “Apparatus” Section in each test method.4.2 Reagents:4.2.1 Purity of ReagentsUnless otherwise indicated, allreagents used in these test methods shall conform to the reagentgrade specifications of the American Chemical Society.4Othergrades may be used provided it is first ascer
12、tained that they are1These test methods are under the jurisdiction of ASTM Committee E01 onAnalytical Chemistry for Metals, Ores, and Related Materials and are the directresponsibility of Subcommittee E01.02 on Ores, Concentrates, and Related Metal-lurgical Materials.Current edition approved June 15
13、, 2010. Published August 2010. Originallyapproved in 1964. Last previous edition approved in 2005 as E246 01 (2005).DOI: 10.1520/E0246-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume
14、information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC, www.chemistry.org. For s
15、uggestions on thetesting of reagents not listed by the American Chemical Society, see the UnitedStates Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention,Inc. (USPC), Rockville, MD, http:/www.usp.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken
16、, PA 19428-2959, United States.of sufficient purity to permit their use without adverselyaffecting the expected performance of the determination, asindicated in the “Precision and Bias” Section. Reagent watershall conform to Type II as described in Specification D1193.5. Hazards5.1 For precautions t
17、o be observed in the use of certainreagents and equipment in this test method refer to PracticesE50.6. Sampling and Sample Preparation6.1 Collect and prepare the test sample in accordance withPractice E877.6.2 The test sample shall be pulverized to pass a No. 100(150-m) sieve in accordance with Test
18、 Method E276.Tofacilitate decomposition some ores, such as specular hematite,require grinding to pass a No. 200 (75-m) sieve.TEST METHOD AIRON BY THE HYDROGENSULFIDE REDUCTION DICHROMATE TITRATIONMETHOD7. Scope7.1 This test method covers the determination of total ironin iron ores, concentrates, and
19、 agglomerates in the concentra-tion range from 30 % to 75 %.8. Summary of Test Method8.1 The sample is dissolved in HCl. The insoluble residue isremoved by filtration, ignited, treated for the recovery of iron,and added to the main solution. To this solution containing allof the iron, H2SO4is added
20、and the solution evaporated tofumes to expel chlorides. The salts are dissolved in water, thesolution heated to boiling, and the iron reduced by a rapidstream of hydrogen sulfide (H2S). The precipitated sulfides arefiltered and washed with an acid-sulfide wash solution untilfree of iron. The filtrat
21、e is then boiled to expel the H2S, cooled,and titrated with K2Cr2O7solution, using sodium dipheny-lamine sulfonate as the indicator.9. Interferences9.1 None of the elements normally found in iron oresinterfere with this test method. These include vanadium,copper, and small amounts of molybdenum, whi
22、ch occasion-ally occur in iron ores.10. Apparatus10.1 Hydrogen Sulfide GeneratorH2S shall be obtainedfrom a cylinder of the compressed gas or from a Kippgenerator.Aconsistent flow of 1 L/min shall be maintained andthe gas passed through a water trap to remove any salts.10.1.1 WarningH2S is extremely
23、 toxic. All proceduresinvolving its use must be performed in an efficient fume hood.Refer to Hazards section in Practices E50.10.2 Crucibles, platinum, 25-mL capacity.11. Reagents and Materials11.1 Ferrous Ammonium Sulfate Solution (approximately0.10 N)Dissolve 40 g of ferrous ammonium sulfate(FeSO4
24、(NH4)2SO46H2O) in H2SO4(1 + 19). Transfer to a1-L flask and dilute to volume with the same acid. When thesample solution is ready for titration, standardize theFeSO4(NH4)2SO46H2O solution against the standardK2Cr2O7(0.1000 N), as described in 12.5. Calculate themillilitres of standard K2Cr2O7equival
25、ent to 1 mL of theFeSO4(NH4)2SO46H2O solution.11.2 Potassium Dichromate, Standard Solution (0.1000N)Transfer 4.9031 g of primary standard grade potassiumdichromate (K2Cr2O7); previously ground in an agate mortar,and dried at 105 C to 110 C, to a 1-L volumetric flask.Dissolve in water and dilute to 1
26、 L. If preferred, this solutionmay be prepared from reagent grade K2Cr2O7, by purifying thesalt twice by recrystallizing from water, drying at 110 C,pulverizing in an agate mortar, and drying at 180 C to constantweight. The titer of this solution shall be confirmed by meansof standard sample similar
27、 in type and composition to the testsample.11.3 Potassium Permanganate Solution (25 g/L)Dissolve25 g of potassium permanganate (KMnO4) in water and diluteto 1 L.11.4 Sodium Diphenylamine Sulfonate Indicator SolutionDissolve 0.3 g of sodium diphenylamine sulfonate in 100 mLof water. Store in a dark-c
28、olored bottle.11.5 Sodium Pyrosulfate (Na2S2O7).11.6 Sulfuric Acid-Hydrogen Sulfide Wash SolutionAdd20 mL of concentrated H2SO4(H2SO4, sp gr 1.84) to 900 mLwater, cool, dilute to 1 L, and pass a rapid stream of H2Sthrough it for at least 10 min.12. Procedure12.1 Transfer approximately 0.50 g of the
29、test specimen to asmall weighing bottle previously dried at about 105 C. Drythe bottle and contents for 1 h at 105 C to 110 C (Note 1).Cap the bottle and cool to room temperature in a desiccator.Momentarily release the cap to equalize the pressure and weighthe capped bottle and sample to the nearest
30、 0.1 mg. Repeat thedrying and weighing until there is no further weight loss.Transfer the test specimen to a 250-mL beaker and reweigh thecapped bottle to the nearest 0.1 mg. The difference between thetwo weights is the weight of the sample taken for analysis.NOTE 1Most ores yield their hygroscopic
31、moisture at this tempera-ture. If a drying temperature other than that specified is required, this shallbe determined by mutual agreement between manufacturer and purchaser.12.2 Decomposition of the SampleMoisten the samplewith a few millilitres of water and add 25 mL of HCl. Coverthe beaker and hea
32、t, maintaining a temperature below boilinguntil most of the dark particles are dissolved and no furtherattack is apparent. Add 5 mL of HNO3and digest for another15 min. Remove from the source of heat, wash the sides andcover of the beaker, and dilute to 50 mL with warm water.Filter the insoluble res
33、idue on a fine-texture paper. Wash theresidue with warm HCl (1 + 50) until the yellow color of ferricchloride is no longer observed and then with warm water sixtimes to eight times. Collect the filtrate and washings in a600-mLbeaker and reserve as the main solution (Note 2). Placethe paper and resid
34、ue in a platinum crucible. Char the paper ata low temperature, then ignite at 950 C. Allow the crucible toE246 102cool, moisten the residue with H2SO4(1 + 1), add about 5 mLof HF, and heat gently to remove silica and H2SO4(Note 3).Cool the crucible, add 3 g of Na2S2O7, and heat until a clearmelt is
35、obtained. Cool, place the crucible in a 250-mL beaker,add about 25 mL of water and 5 mL of HCl, and warm todissolve the melt. Rinse and remove the crucible. Add thesolution and washings to the main solution.NOTE 2If the residue is small in amount and perfectly white, thefiltration, and treatment of
36、the residue may be omitted without causingsignificant error.NOTE 3The treatment of the residue depends upon the nature of theminerals present. Many ores require only an H2SO4HF treatment todecompose the residue.12.3 ReductionTo the combined solution add 10 mL ofH2SO4(1 + 1) and evaporate to copious
37、fumes of sulfurtrioxide (SO3)(Note 4). Cool, dilute to approximately 100 mLwith water, and heat to boiling.Add dropwise KMnO4solutionuntil the permanganate color persists. Dilute the solution to250 mL and again heat to boiling for several minutes. Removefrom the source of heat and pass a rapid strea
38、m of H2S throughthe solution for 15 min. (WarningHydrogen sulfide isextremely toxic. All procedures involving its use must beperformed in an efficient fume hood. Refer to Hazards sectionin Practices E50.) Digest at 60 C for 15 min and filter througha medium-texture paper, collecting the filtrate in
39、a 500-mLErlenmeyer flask. Wash the precipitated sulfides thoroughlywith the H2SO4H2S wash solution. Add 10 mL of H2SO4(1 + 1) to the solution in the flask and add glass beads toprevent bumping. Boil for 10 min to expel H2S (lead acetatetest paper) and continue boiling for an additional 10 min (Note5
40、). Remove from the source of heat, cover the flask with asmall watch glass, and cool in running water to 20 C.NOTE 4If the sample contains much calcium, prolonged fuming withH2SO4may lead to the formation of salts that are difficult to dissolve.Therefore, in the presence of considerable calcium, fum
41、e just long enoughto expel the chlorides and nitrates. Cool, wash the sides of the beaker withwater, and again evaporate to light fumes.NOTE 5If the sample contains an appreciable amount of molybde-num, further precipitation may occur in the filtrate when boiling out theH2S. The effect of residual m
42、olybdenum is not significant and may beneglected.12.4 TitrationAdd to the cooled solution 5 mL of phos-phoric acid (H3PO4) and five drops of the sodium dipheny-lamine sulfonate indicator solution. Dilute to 350 mL andtitrate with the standard K2Cr2O7solution to a distinct purpleendpoint.12.5 Determi
43、nation of BlankDetermine the blank value ofthe reagents concurrently with the test determination, using thesame amount of all reagents and following all the steps of theprocedure. Immediately before titrating with the K2Cr2O7solution, add 1.0 mL, accurately measured, of theFeSO4(NH4)2SO46H2O solutio
44、n. In another beaker place350 mLof cold H2SO4(1 + 9) and add an accurately measured1 mL of the FeSO4(NH4)2SO46H2O solution. Add 5 mL ofH3PO4and five drops of the sodium diphenylamine sulfonateindicator solution and titrate with the K2Cr2O7solution.Record this titration and subtract from the titratio
45、n of the blanksolution to obtain the corrected blank.NOTE 6In the absence of iron, the diphenylamine sulfonate indicatordoes not react with the K2Cr2O7solution. The addition of theFeSO4(NH4)2SO46H2O is, therefore, necessary to promote indicatorresponse in the blank solution. A correction must be mad
46、e in terms of itsequivalent in millilitres of K2Cr2O7solution.13. Calculation13.1 Calculate the percentage of iron as follows:iron, % 5 A 2 B! 3 C/D 3 100 (1)where:A = millilitres of K2Cr2O7required for titration of thesample,B = millilitres of K2Cr2O7required for titration of theblank,C = iron equi
47、valent of the K2Cr2O7, g/mL, andD = grams of sample used.14. Precision and Bias14.1 PrecisionFrom six to nine laboratories analyzed fouriron ore samples to determine iron. The replication made by thedifferent laboratories ranged from two to four, averaging threereplicates. The data was studied by th
48、e interlaboratory testprocedure of Practice E691 87 modified by weighting certainsums to accommodate the unequal replication.5Table 1 showsa summary of these results. From pooled standard deviations,the overall between-laboratory reproducibility coefficient, R,was calculated as being 0.38.14.2 The a
49、greement of the determination of iron in the NBSStandard Reference Material with the certified value shows noevidence of bias, well within a 95 % confidence level:(R2= 0.24)5Supporting data giving the results of cooperative testing have been filed atASTM International Headquarters and may be obtained by requesting ResearchReport RR:E16-63, dated April 23, 1968, with an amendment, dated July 27, 1993.TABLE 1 Precision DataSampleNumber ofLaboratoriesIron Found%Repeatability ReproducibilitysrRI(2.8 sr)sRR2(2.8 sR)Seine River Ore
