1、Designation: E463 14aStandard Test Method forDetermination of Silica in Fluorspar by Silico-MolybdateVisible Spectrophotometry1This standard is issued under the fixed designation E463; 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 This test method covers the determination of silica influorspar in concentrations from 0.5 % to 10 %.1.2
3、 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 concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-p
4、riate 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 WaterE50 Practices for Apparatus, Reagents, and Safety Consid-erations for Chemical Analysis of Metals, Ores, andRelate
5、d 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 for Metal-Bearing Ores andRelated MaterialsE882 Guide for Accountability and Quality Control in theChemical Analys
6、is Laboratory3. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology E135.4. Summary of Test Method4.1 The sample is fused with anhydrous sodium borate andthe melt is dissolved in dilute HCl. Silica is determinedphotometrically after extraction of the sili
7、co-molybdate com-plex with normal butyl alcohol. Photometric measurement ofthe extract is made at 400 nm.5. Significance and Use5.1 This test method is intended as a referee method forcompliance with compositional specifications for impuritycontent. It is assumed that all who use this procedure will
8、 betrained analysts capable of performing common laboratorypractices skillfully and safely. It is expected that work will beperformed in a properly equipped laboratory and that properwaste disposal procedures will be followed. Follow appropriatequality control practices such as those described in Gu
9、ideE882.6. Interferences6.1 The elements ordinarily present in commercial fluor-spars do not interfere in this test method.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents conform to the spec
10、ifications of the Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are available.3Other grades may be 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
11、 Unless otherwise indicated, references to water shall beunderstood to mean reagent water conforming to Type I or II ofSpecification D1193. Type III or IV may be used if they effectno measurable change in the blank or sample.7.3 Ammonium Molybdate Solution (100 g L)Dissolve100 g of ammonium-heptamol
12、ybdate (NH4)6Mo7O244H2Oin 500 mL of water, dilute to 1 L, and mix.7.4 Silica (SiO2)Heat pure silicic acid in a platinumcrucible to expel combined water by gradually increasing1This test method is under the jurisdiction of ASTM Committee E01 onAnalytical Chemistry for Metals, Ores, and Related Materi
13、als and is the directresponsibility of Subcommittee E01.02 on Ores, Concentrates, and Related Metal-lurgical Materials.Current edition approved Oct. 1, 2014. Published November 2014. Originallyapproved in 1972. Last previous edition approved in 2014 as E463 14. DOI:10.1520/E0463-14A.2For referenced
14、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.3Reagent Chemicals, American Chemical Society Specifications, AmericanChemica
15、l Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see the United States Pharmacopeia andNational Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West
16、 Conshohocken, PA 19428-2959. United States1temperature to 1050 C. Maintain at 1050 C for at least 5 min.Cool to room temperature in a desiccator.7.5 Sodium Borate(Na2B4O7)Anhydrous powder, low-silica content.NOTE 1If low silica sodium borate is not available, prepare thereagent as follows: Transfer
17、 247 g of boric acid to a large platinum dish.Expel water by gradually increasing the temperature to about 1000 C.When effervescence ceases, gradually introduce 106 g of sodium carbon-ate into the molten mass. Maintain at a temperature of about 1000 C untila clear melt is obtained.8. Hazards8.1 For
18、precautions to be observed in this method, refer toPractices E50.9. Sample Preparation9.1 The analytical sample shall be pulverized, if necessary,to pass a 150-m sieve (see Test Method E276). Dry at 105 Cto 110 C for a minimum of 1 h.10. Procedure10.1 Transfer7gofNa2B4O7to each of six 25-mL platinum
19、crucibles. Form a cavity in the center of the flux.10.2 Into Crucibles 1 and 2, weigh 0.100 g to 1 g of the drysample. Choose sample weights to provide from 5 mg to 10 mgof SiO2.10.3 Into Crucibles 3 and 4, weigh 10.0 mg of SiO2reagent.10.4 Crucibles 5 and 6 serve as blanks.10.5 Mix the contents of
20、the crucibles with a platinum orpolyethylene rod. Transfer adhering particles to the crucible.10.6 Cover the crucible and heat gently until moisture isexpelled. Increase the temperature until complete fusion re-sults.NOTE 2A Meker burner or a muffle furnace maintained at 1000 Cmay be used for this p
21、urpose.10.7 Transfer the platinum crucible and cover to a 400-mLpolyethylene or TFE-fluorocarbon beaker containing 150 mLwater and 25 mL HCl (1 + 1). Cool the crucible for about 3 s,then pour the melt dropwise into the beaker so that most of theflux settles on the crucible cover (Note 3). Transfer t
22、he cooledcrucible to the beaker. Cover the beaker with a polyethylenesheet and secure it to the beaker with a rubber band.NOTE 3Hold the crucible while cooling to avoid contaminationproblems. This prevents damage to the beaker.10.8 Place the beaker on a steam bath and swirl occasionallyuntil the mel
23、t is completely dissolved (Note 4). Cool, removeand rinse the platinum crucible and cover, and add thewashings to the beaker. Transfer the solution to a 250-mLvolumetric flask. Rinse the beaker and add the rinsings to theflask. Dilute to volume, mix, and examine the solution for anyinsoluble materia
24、l (Note 4). Transfer the solution to a drypolyethylene bottle.NOTE 4Complete dissolution of the melt requires about 2 h. In casesof incomplete dissolution, a new sample must be taken.10.9 Transfer 50-mL aliquots of the blank and samplesolutions to 200-mL polyethylene or TFE-fluorocarbon bea-kers.10.
25、10 Transfer (10.0, 20.0, 30.0, 40.0, and 50.0)-mL ali-quots of the standard solutions to 200-mL polyethylene orTFE-fluorocarbon beakers. Dilute, if necessary, to a 50-mLvolume with the remaining blank solution.NOTE 5Since commercially available Na2B4O7frequently containsappreciable amounts of silica
26、, each standard and sample solution mustcontain the same amounts of this reagent. The dilution of the aliquots toa 50-mL volume should, therefore, be carried out using a buret.10.11 Determine the pH of the blank, standard, and samplesolutions using a pH meter. If the pH of the solutions liesbetween
27、0.5 and 0.9 and within 0.1 units of each other, proceedto 10.12. If the pH lies outside these parameters, adjust the pHwith HCl (1 + 1).NOTE 6Accurate pH adjustments are essential for maximum colordevelopment and color stability.10.12 Add, while stirring, 10 mL of ammonium molybdatesolution. Allow 1
28、0 min for color development, then dilute to100 mL. Transfer the solution to a 250-mL separatory funneland add 25 mL of cool H2SO4(1 + 1).10.13 Add 75 mL of normal butyl alcohol and shake vigor-ously for 1 min. Allow the phases to separate and discard theacid (lower) layer. Add 20 mL of H2SO4(1 + 99)
29、 to theTABLE 1 Precision DataAverageConcentration,A%StandardDeviation,%RelativeStandardDeviation,B%Numberof ParticipatingLaboratories0.71 0.03 4.2 62.16 0.11 5.1 76.94 0.10 1.4 6AEach concentration represents a different grade of fluorspar.BRelative Standard Deviation (RSD), in this test method is c
30、alculated as follows:RSD5 s100/Xdod2/sn 2 1d (2)where:X= average concentration, %,d = difference of the determination from the mean, andn = number of determinations.E463 14a2separatory funnel, shake for 30 s, allow the phases to separate,and discard the acid layer. Repeat the washing twice more.10.1
31、4 Transfer the butyl alcohol phase to a dry 100-mLvolumetric flask. Wash the separatory funnel twice with 1-mLor 2-mL portions of butyl alcohol, and add the washings to thevolumetric flask. Add 1 mL of ethyl alcohol, dilute to volumewith butyl alcohol, and mix.11. Photometry11.1 Concentration Range:
32、11.1.1 The recommended concentration range is from0.2 mg to 2.0 mg of silica per 100 mL of solution, using a 1-cmcell.NOTE 7Cells having other dimensions may be used, provided suitableadjustments can be made in the amounts of sample and reagent used.11.2 Adjust the photometer to the initial setting
33、using wateras the reference solution. While maintaining this setting, takephotometric readings of the blank, standard, and samplesolutions using a light band centered at approximately 400 nm.11.3 Stability of Color:11.3.1 After the addition of the ammonium molybdate, coloris fully developed within 1
34、0 min and is stable after extractionwith butyl alcohol12. Preparation of Calibration Curve12.1 Subtract the average absorbance of the blank solutionfrom the average absorbance of each standard solution and plotthe net absorbances against milligrams of silica per 100 mL ofsolution.13. Calculation13.1
35、 Subtract the average absorbance of the blank solutionsfrom absorbances of the sample solutions. Convert the netabsorbance of the sample solution to milligrams of SiO2bymeans of the calibration curve. Calculate the percentage ofSiO2as follows:Silica, % 5 A/B 310! (1)A = silica found in the aliquot u
36、sed, mg, andB = sample represented by the aliquot, g.14. Precision and Bias14.1 PrecisionTable 1 indicates the precision of the testmethod between laboratories.14.2 BiasNo information on the accuracy of this testmethod is known. The accuracy of this test method may bejudged by comparison of accepted
37、 values for standard refer-ence materials with the mean determined through interlabora-tory testing.15. Keywords15.1 fluorspar; photometric; silica; silico-molybdate magne-siumASTM International takes no position respecting the validity of any patent rights asserted in connection with any item menti
38、onedin this standard. 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 a
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