1、Designation: E 463 03Standard Test Method forSilica in Fluorspar by the Silico-Molybdate VisibleSpectrometry1This standard is issued under the fixed designation E 463; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las
2、t 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 silica influorspar in concentrations from 0.5 to 10 %.1.2 This standard doe
3、s not purport to address all of thesafety problems, 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 Stan
4、dards:2D 1193 Specification for Reagent WaterE50 Practices for Apparatus, Reagents, and Safety Precau-tions for Chemical Analysis of MetalsE 135 Terminology Relating to Analytical Chemistry forMetals, Ores and Related MaterialsE 276 Test Method for Particle Size or Screen Analysis atNo. 4 (4.75-mm)
5、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 Terminology E 135.4. Summary of Test Method4.1 The sample is fused w
6、ith anhydrous sodium borate andthe melt is dissolved in dilute hydrochloric acid. Silica isdetermined photometrically after extraction of the silico-molybdate complex with normal butyl alcohol. Photometricmeasurement of the extract is made at 400 nm.5. Significance and Use5.1 This test method is int
7、ended as a referee method forcompliance with compositional specifications for impuritycontent. It is assumed that all who use this procedure will betrained analysts capable of performing common laboratorypractices skillfully and safely. It is expected that work will beperformed in a properly equippe
8、d laboratory and that properwaste disposal procedures will be followed. Follow appropriatequality control practices such as those described in GuideE 882.6. Interferences6.1 The elements ordinarily present in commercial fluor-spars do not interfere in this test method.7. Reagents and Materials7.1 Pu
9、rity 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 available.3Other grades may be used,provid
10、ed 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 1193.7.3 A
11、mmonium Molybdate Solution (100 g/L)Dissolve100 g of ammonium-heptamolybdate (NH4)6Mo7O244H2Oin 500 mL of water, dilute to 1 L, and mix.1This test method is under the jurisdiction of ASTM Committee E01 onAnalytical Chemistry for Metals, Ores, and Related Materials and is the directresponsibility of
12、Subcommittee E01.02 on Ores, Concentrates, and Related Metal-lurgical Materials.Current edition approved June 10, 2003. Published October 2003. Originallyapproved in 1972. Last previous edition approved in 1998 as E 463 72 (1998).2For referenced ASTM standards, visit the ASTM website, www.astm.org,
13、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, AmericanChemical Society, Washington, DC. For suggestions on the test
14、ing of reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.1Copyright ASTM International, 100 Barr Harbor D
15、rive, PO Box C700, West Conshohocken, PA 19428-2959, United States.7.4 Silica (SiO2)Heat pure silicic acid in a platinumcrucible to expel combined water by gradually increasingtemperature to 1050C. Maintain at 1050C for at least 5 min.Cool to room temperature in a desiccator.7.5 Sodium Borate (Na2B4
16、O7)Anhydrous powder, low-silica content.NOTE 1If low silica sodium borate is not available, prepare thereagent as follows: Transfer 247 g of boric acid to a large platinum dish.Expel water by gradually increasing the temperature to about 1000C.When effervescence ceases, gradually introduce 106 g of
17、sodium carbon-ate into the molten mass. Maintain at a temperature of about 1000C untila clear melt is obtained.8. Hazards8.1 For precautions to be observed in this method, refer toPractice E 50.9. Sample Preparation9.1 The analytical sample shall be pulverized, if necessary,to pass a No. 100 (150-m)
18、 sieve (see Test Method E 276). Dryat 105 to 110C for a minimum of 1 h.10. Procedure10.1 Transfer7gofNa2B4O7to each of six 25-mL platinumcrucibles. Form a cavity in the center of the flux.10.2 Into Crucibles 1 and 2 weigh 0.100 to1gofthedrysample. Choose sample weights to provide from 5 to 10 mg ofS
19、iO2.10.3 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 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 t
20、emperature until complete fusion re-sults.NOTE 2A Meker burner or a muffle furnace maintained at 1000Cmay be used for this purpose.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 abou
21、t 3 s,then pour the melt dropwise into the beaker so that most of theflux settles on the crucible cover (Note 3). Transfer the 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 contami
22、nationproblems. This prevents damage to the beaker.10.8 Place the beaker on a steam bath and swirl occasionallyuntil the melt 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.
23、 Rinse the beaker and add the rinsings to theflask. Dilute to volume, mix, and examine the solution for anyinsoluble material (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
24、 taken.10.9 Transfer 50-mL aliquots of the blank and samplesolutions to 200-mL polyethylene or TFE-fluorocarbon bea-kers.10.10 Transfer 10.0, 20.0, 30.0, 40.0, and 50.0-mL aliquotsof the standard solutions to 200-mL polyethylene or TFE-fluorocarbon beakers. Dilute, if necessary, to a 50-mL volumewit
25、h the remaining blank solution.NOTE 5Since commercially available Na2B4O7frequently containsappreciable amounts of silica, 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.
26、11 Determine the pH of the blank, standard, and samplesolutions using a pH meter. If the pH of the solutions liesbetween 0.5 and 0.9 and within 0.1 unit 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
27、for maximum colordevelopment and color stability.10.12 Add, while stirring, 10 mL of ammonium molybdatesolution. Allow 10 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
28、 shakevigorously for 1 min. Allow the phases to separate and discardthe acid (lower) layer. Add 20 mL of H2SO4(1 + 99) to theseparatory funnel, shake for 30 s, allow the phases to separate,and discard the acid layer. Repeat the washing twice more.10.14 Transfer the butyl alcohol phase to a dry 100-m
29、Lvolumetric flask. Wash the separatory funnel twice with 1 or2-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.E46303211. Photometry11.1 Concentration Range:11.1.1 The recommended concentration range is
30、 from 0.2 to2.0 mg of silica per 100 mL of solution, using a 1-cm cell.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 using wateras the reference solution. While mai
31、ntaining 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 10 min and is stable after extractionwith butyl
32、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 Subtract the average absorbance of the blank s
33、olutionsfrom 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/B3 10! (1)A = silica found in the aliquot used, mg, andB = sample represented by the aliqu
34、ot, 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 values for standard refer-ence materials with
35、the mean determined through interlabora-tory testing.15. Keywords15.1 fluorspar; photometric; silica; silico-molybdatemagnesiumASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are
36、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 reviewed every five years andif not re
37、vised, 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 technical committee, which you
38、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 Conshohocken, PA 19428-2959,United S
39、tates. 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 DataAverageConcen-tration,A%Standard
40、Deviation,%RelativeStandardDeviation,B%Numberof Par-ticipatingLabora-tories0.71 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 calculated as follows:RSD 5 100/X!= (d2/n 2 1! (2)where:X= average concentration, %,d = difference of the determination from the mean, andn = number of determinations.E463033
