1、Designation: E463 09E463 14Standard Test Method forDetermination of Silica in Fluorspar by Silico-MolybdateVisible Spectrometry1This standard is issued under the fixed designation E463; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisio
2、n, 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 in fluorspar in concentrations from 0.5 % to 10 %.1
3、.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish ap
4、propriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterE50 Practices forApparatus, Reagents, and Safety Considerations for ChemicalAnalysis of Metals, Ores, and Relate
5、d MaterialsE135 Terminology Relating to Analytical Chemistry for Metals, Ores, and Related MaterialsE276 Test Method for Particle Size or Screen Analysis at No. 4 (4.75-mm) Sieve and Finer for Metal-Bearing Ores and RelatedMaterialsE882 Guide for Accountability and Quality Control in the Chemical An
6、alysis Laboratory3. Terminology3.1 DefinitionsFor definitions of terms used in this test method, refer to Terminology E135.4. Summary of Test Method4.1 The sample is fused with anhydrous sodium borate and the melt is dissolved in dilute HCl. Silica is determinedphotometrically after extraction of th
7、e silico-molybdate complex with normal butyl alcohol. Photometric measurement of theextract is made at 400 nm.5. Significance and Use5.1 This test method is intended as a referee method for compliance with compositional specifications for impurity content. Itis assumed that all who use this procedur
8、e will be trained analysts capable of performing common laboratory practices skillfullyand safely. It is expected that work will be performed in a properly equipped laboratory and that proper waste disposal procedureswill be followed. Follow appropriate quality control practices such as those descri
9、bed in Guide E882.6. Interferences6.1 The elements ordinarily present in commercial fluorspars do not interfere in this test method.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allreagents conform t
10、o the specifications of the Committee on Analytical Reagents of the American Chemical Society where such1 This test method is under the jurisdiction of ASTM Committee E01 on Analytical Chemistry for Metals, Ores, and Related Materials and is the direct responsibility ofSubcommittee E01.02 on Ores, C
11、oncentrates, and Related Metallurgical Materials.Current edition approved May 1, 2009Aug. 15, 2014. Published June 2009September 2014. Originally approved in 1972. Last previous edition approved in 20082009 asE463 08.E463 09. DOI: 10.1520/E0463-09.10.1520/E0463-14.2 For referencedASTM standards, vis
12、it theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standa
13、rd an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM
14、is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1specifications are available.3 Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purityto perm
15、it its use without lessening the accuracy of the determination.7.2 Purity of WaterUnless otherwise indicated, references to water shall be understood to mean reagent water as defined byconforming to Type I or II of Specification D1193. Type III or IV may be used if they effect no measurable change i
16、n the blankor sample.7.3 Ammonium Molybdate Solution (100 gL)Dissolve 100 g of ammonium-heptamolybdate (NH4)6Mo7O244H2O in500 mL of water, dilute to 1 L, and mix.7.4 Silica (SiO2)Heat pure silicic acid in a platinum crucible to expel combined water by gradually increasing temperatureto 1050 C. Maint
17、ain 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 the reagent as follows: Transfer 247 g of boric acid to a large platinum dish. Expel waterby gradually
18、 increasing the temperature to about 1000 C. When effervescence ceases, gradually introduce 106 g of sodium carbonate into the moltenmass. Maintain at a temperature of about 1000 C until a clear melt is obtained.8. Hazards8.1 For precautions to be observed in this method, refer to Practices E50.9. S
19、ample Preparation9.1 The analytical sample shall be pulverized, if necessary, to pass a 150-m sieve (see Test Method E276). Dry at 105 C to110 C for a minimum of 1 h.10. Procedure10.1 Transfer 7 g of Na2B4O7 to each of six 25-mL platinum crucibles. Form a cavity in the center of the flux.10.2 Into C
20、rucibles 1 and 2, weigh 0.100 g to 1 g of the dry sample. Choose sample weights to provide from 5 mg to 10 mgof SiO2.10.3 Into Crucibles 3 and 4, weigh 10.0 mg of SiO2 reagent.10.4 Crucibles 5 and 6 serve as blanks.10.5 Mix the contents of the crucibles with a platinum or polyethylene rod. Transfer
21、adhering particles to the crucible.10.6 Cover the crucible and heat gently until moisture is expelled. Increase the temperature until complete fusion results.NOTE 2A Meker burner or a muffle furnace maintained at 1000 C may be used for this purpose.10.7 Transfer the platinum crucible and cover to a
22、400-mL polyethylene or TFE-fluorocarbon beaker containing 150 mL waterand 25 mL HCl (1 + 1). Cool the crucible for about 3 s, then pour the melt dropwise into the beaker so that most of the flux settleson the crucible cover (Note 3). Transfer the cooled crucible to the beaker. Cover the beaker with
23、a polyethylene sheet and secureit to the beaker with a rubber band.NOTE 3Hold the crucible while cooling to avoid contamination problems. This prevents damage to the beaker.10.8 Place the beaker on a steam bath and swirl occasionally until the melt is completely dissolved (Note 4). Cool, remove andr
24、inse the platinum crucible and cover, and add the washings to the beaker. Transfer the solution to a 250-mLvolumetric flask. Rinsethe beaker and add the rinsings to the flask. Dilute to volume, mix, and examine the solution for any insoluble material (Note 4).Transfer the solution to a dry polyethyl
25、ene bottle.NOTE 4Complete dissolution of the melt requires about 2 h. In cases of incomplete dissolution, a new sample must be taken.10.9 Transfer 50-mL aliquots of the blank and sample solutions to 200-mL polyethylene or TFE-fluorocarbon beakers.10.10 Transfer (10.0, 20.0, 30.0, 40.0, and 50.0)-mL
26、aliquots of the standard solutions to 200-mL polyethylene orTFE-fluorocarbon beakers. Dilute, if necessary, to a 50-mL volume with the remaining blank solution.NOTE 5Since commercially available Na2B4O7 frequently contains appreciable amounts of silica, each standard and sample solution must contain
27、the same amounts of this reagent. The dilution of the aliquots to a 50-mL volume should, therefore, be carried out using a buret.10.11 Determine the pH of the blank, standard, and sample solutions using a pH meter. If the pH of the solutions lies between0.5 and 0.9 and within 0.1 units of each other
28、, proceed to 10.12. If the pH lies outside these parameters, adjust the pH with HCl(1 + 1).3 Reagent Chemicals, American Chemical Society Specifications, , American Chemical Society, Washington, DC, http:/www.chemistry.org. DC. For suggestions on thetesting of reagents not listed by the American Che
29、mical Society, see Annual Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., http:/, andthe United States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD, http:/www.usp.org. MD.E463 142NOTE 6Accurate pH adjustments are essential for maxi
30、mum color development and color stability.10.12 Add, while stirring, 10 mL of ammonium molybdate solution. Allow 10 min for color development, then dilute to100 mL. Transfer the solution to a 250-mL separatory funnel and add 25 mL of cool H2SO4 (1 + 1).10.13 Add 75 mL of normal butyl alcohol and sha
31、ke vigorously for 1 min. Allow the phases to separate and discard the acid(lower) layer. Add 20 mL of H2SO4 (1 + 99) to the separatory funnel, shake for 30 s, allow the phases to separate, and discard theacid layer. Repeat the washing twice more.10.14 Transfer the butyl alcohol phase to a dry 100-mL
32、 volumetric flask. Wash the separatory funnel twice with 1-mL or 2-mLportions of butyl alcohol, and add the washings to the volumetric flask. Add 1 mL of ethyl alcohol, dilute to volume with butylalcohol, and mix.11. Photometry11.1 Concentration Range:11.1.1 The recommended concentration range is fr
33、om 0.2 mg to 2.0 mg of silica per 100 mL of solution, using a 1-cm cell.NOTE 7Cells having other dimensions may be used, provided suitable adjustments can be made in the amounts of sample and reagent used.11.2 Adjust the photometer to the initial setting using water as the reference solution. While
34、maintaining this setting, takephotometric readings of the blank, standard, and sample solutions using a light band centered at approximately 400 nm.11.3 Stability of Color:11.3.1 After the addition of the ammonium molybdate, color is fully developed within 10 min and is stable after extraction withb
35、utyl alcohol12. Preparation of Calibration Curve12.1 Subtract the average absorbance of the blank solution from the average absorbance of each standard solution and plot thenet absorbances against milligrams of silica per 100 mL of solution.13. Calculation13.1 Subtract the average absorbance of the
36、blank solutions from absorbances of the sample solutions. Convert the netabsorbance of the sample solution to milligrams of SiO2 by means of the calibration curve. Calculate the percentage of SiO2 asfollows:Silica,%5A/B 310! (1)A = silica found in the aliquot used, mg, andB = sample represented by t
37、he aliquot, g.14. Precision and Bias14.1 PrecisionTable 1 indicates the precision of the test method between laboratories.14.2 BiasNo information on the accuracy of this test method is known. The accuracy of this test method may be judged bycomparison of accepted values for standard reference materi
38、als with the mean determined through interlaboratory testing.TABLE 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 6A Each concentration represents a different grade of fluorspar.B Rel
39、ative Standard Deviation (RSD), in this test method is calculated as follows:RSD5s100/Xdod 2/sn21d (2)where:X = average concentration, %,d = difference of the determination from the mean, andn = number of determinations.E463 14315. Keywords15.1 fluorspar; photometric; silica; silico-molybdate magnes
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