1、Designation: E508 09E508 13Standard Test Method forDetermination of Calcium and Magnesium in Iron Ores byFlame Atomic Absorption Spectrometry1This standard is issued under the fixed designation E508; the number immediately following the designation indicates the year oforiginal adoption or, in the c
2、ase of 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 calcium and magnesium in iron ores, concentr
3、ates, and agglomerates in themass fraction (%) range from 0.05 % to 5 % of calcium and 0.05 % to 3 % of magnesium.1.2 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 saf
4、ety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent Wa
5、terE50 Practices forApparatus, Reagents, and Safety Considerations for ChemicalAnalysis of Metals, Ores, and Related MaterialsE135 Terminology Relating to Analytical Chemistry for Metals, Ores, and Related MaterialsE276 Test Method for Particle Size or ScreenAnalysis at No. 4 (4.75-mm) Sieve and Fin
6、er for Metal-Bearing Ores and RelatedMaterialsE663 Practice for Flame Atomic Absorption Analysis (Withdrawn 1997)3E882 Guide for Accountability and Quality Control in the Chemical Analysis Laboratory3. Terminology3.1 DefinitionsFor definitions of terms used in this test method, refer to Terminology
7、E135.4. Summary of Test Method4.1 The sample is dissolved in HCl with the addition of a small amount of HNO3. After evaporation and dehydration, anyinsoluble residue is filtered, treated for the recovery of calcium and magnesium, and added to the main solution. The solution isaspirated into the flam
8、e of the atomic absorption spectrometer. For calcium, a nitrous oxide-acetylene burner is used, formagnesium, an air-acetylene burner is preferred (Note 1). The absorbed energy at the resonance line of the spectrum of calciumor magnesium, or both, is measured by atomic absorption spectrometry and co
9、mpared with that of the calibration solutions of thetwo elements.NOTE 1If a nitrous oxide burner is used for the determination of magnesium, the sensitivity is decreased by a factor of about three.If an air-acetylene burner is used for the determination of calcium, several elements, if present in a
10、mass fraction (%) of 1.0 or greater, interfere withthe calcium determination. Also, lanthanum chloride (LaCl3) must be employed and the sensitivity is decreased by a factor of about two.5. Significance and Use5.1 This test method is intended as a referee method for compliance with compositional spec
11、ifications for impurity content. Itis assumed that all who use this procedure will be trained analysts capable of performing common laboratory practices skillfully1 This test method is under the jurisdiction of ASTM Committee E01 on Analytical Chemistry for Metals, Ores, and Related Materials and is
12、 the direct responsibility ofSubcommittee E01.02 on Ores, Concentrates, and Related Metallurgical Materials.Current edition approved May 1, 2009Oct. 1, 2013. Published June 2009November 2013. Originally approved in 1973. Last previous edition approved in 20082009 asE50E508 09.8 08. DOI: 10.1520/E050
13、8-09.10.1520/E0508-13.2 For referencedASTM standards, visit 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.3 The last approved version of this his
14、torical standard is referenced on www.astm.org.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accuratel
15、y, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1a
16、nd 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 described in Guide E882.6. Interferences6.1 None of the elements normally found in iron ores i
17、nterfere with this test method (Note 1).7. Apparatus7.1 Atomic Absorption Spectrometer, meeting the following criteria:7.1.1 Minimum SensitivityThe absorbance of the highest calibration solution (see 8.4) must be at least 0.3.7.1.2 Curve-LinearityThe difference between the readings of the highest ca
18、libration solutions must be more than 1.4 times thedifference between the readings for the zero solutions and the lowest calibration solution.7.1.3 Minimum StabilityThe coefficient of variation of a number of measurements of the highest calibration solution and ofthe zero calibration solution must b
19、e less than 1.5 %1.5 % and 0.5 %0.5 % respectively.NOTE 2Use of digital readout devices or printers, or both, is advisable.NOTE 3Instrument parameters will vary with each instrument. The following parameters were successfully used in several laboratories and they canbe used as guidelines. In the cas
20、e of calcium, solutions were aspirated into a nitrous oxide-acetylene flame of a premix burner. For magnesium anair-acetylene burner was used.Ca MgHollow cathode lamp, mA 15 15Wavelength, nm 422.7 285.2Nitrous oxide flow rate, L/min 13.8 .Air flow rate, L/min . 22Acetylene flow rate, L/min 6.6 4.28.
21、 Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allreagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where suchspecifications are available.4
22、 Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purityto permit its use without lessening the accuracy of the determination.8.2 Purity of WaterUnless otherwise indicated, references to water shall be understood to mean reagent water as defined byc
23、onforming to Type I or Type II of Specification D1193. Type III or Type IV may be used if they effect no measurable change inthe blank or sample.8.3 Calcium, Standard Solution (1 mL = 25 g Ca)Dissolve 1.2487 g of anhydrous calcium carbonate (CaCO3) in 100 mL ofdilute HCl (1 + 3). When solution is co
24、mplete, cool and dilute to 1 L in a volumetric flask. Transfer 10 mL of this solution to a200-mL volumetric flask. Dilute to volume and mix.8.4 Calcium and Magnesium Calibration SolutionsUsing pipets, transfer, (5.0, 10.0, 20.0, 40.0, and 50.0)-mL portions of thestandard calcium and magnesium soluti
25、ons to 200-mL volumetric flasks (Note 4). Dilute to 90 mL and add 6 mL of HCl, 60 mLof background solution, and 40 mL of LaCl3 solution. Dilute to volume and mix.8.5 Iron, Background Solution (10 g/L )Dissolve 10 g of high-purity iron in 50 mL of HCl, and oxidize by the dropwiseaddition of HNO3. Eva
26、porate to a syrupy consistency. Add 20 mL of HCl and dilute to 200 mL with water. Add 20 g of sodiumchloride dissolved in 200 mL water and dilute to 1 L with water.8.6 Lanthanum Chloride Solution (50 g/L)Dissolve 50 g of LaCl3 in 50 mL of HCl and 300 mL of hot water. Cool and diluteto 1 L.8.7 Magnes
27、ium, Standard Solution (1 mL = 17.5 g Mg)Dissolve 0.3500 g of high-purity magnesium by slowly adding75 mL of HCl (1 + 3). When dissolved, dilute with water to 1 L in a volumetric flask. Transfer 10 mL of this solution to a 200-mLvolumetric flask, dilute to volume, and mix.8.8 Zero Calibration Soluti
28、onTransfer 60 mL of the background solution to a 200-mL volumetric flask, add 6 mL of HCl,40 mL of LaCl3 solution, dilute to volume, and mix.NOTE 4The range of calcium or magnesium that can be covered may vary from instrument to instrument. Attention should be paid to the minimumcriteria given in 7.
29、1.9. Hazards9.1 For precautions to be observed in this method, refer to Practices E50.4 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 Chemical
30、 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.E508 13210. Sample Preparation10.1 The analytical sample shall be
31、 pulverized to pass a 150-m sieve (see Test Method E276).NOTE 5To facilitate decomposition, some ores, such as specular hematite, require grinding to pass a 75-m sieve.11. Procedure11.1 Transfer approximately 1.0 g of the sample to a small weighing bottle previously dried at about 150 C. Dry the bot
32、tle andcontents for 1 h at 105 C to 110 C. Cap the bottle and cool to room temperature in a desiccator. Momentarily release the cap toequalize the pressure and weigh the capped bottle and sample to the nearest 0.1 mg. Repeat the drying and weighing until thereis no further weight loss. loss of mass.
33、 Transfer the sample to a 250-mLbeaker and reweigh the capped bottle to the nearest 0.1 mg.The difference between the two weightsmasses is the weightmass of the sample taken for analysis.11.2 Carry a reagent blank through all steps of the procedure starting with 11.3.11.3 Decomposition of SampleMois
34、ten the sample with a few milliliters of water, add 25 mL of HCl, cover, and digest belowthe boiling point until no further attack is apparent. Add 2 mL of HNO3 and digest for several minutes. Remove the cover andevaporate the solution to dryness. Heat the salts on a hot plate at 105 C to 110 C for
35、15 min.Add 5 mL of HCl, cover the beaker,and warm for several minutes. Add 50 mL of water and warm until soluble salts are in solution. Filter on a fine-textured paper,and collect the filtrate in a 250-mL beaker. Transfer the residue quantitatively to the filter paper. Wash alternately three times w
36、ithhot HCl (1 + 9) and hot water until the yellow color of ferric chloride is no longer apparent. Transfer the paper and residue to aplatinum crucible. Reserve the filtrate.11.4 Treatment of ResidueIgnite the paper and residue in the platinum crucible. Cool, moisten with several drops of water,add t
37、hree or four drops of dilute H2SO4 (1 + 1) and 10 mL of HF. Evaporate slowly to expel silica and then fume off the excessof H2SO4. Finally ignite at about 700 C.Add 1 g of anhydrous sodium carbonate to the residue, cover the crucible, and fuse overa burner or in a muffle furnace until a clear melt i
38、s obtained. Dissolve the cool melt in the reserved filtrate from 11.3, remove andwash the crucible and cover. Transfer the solution to a 200-mLvolumetric flask, dilute to volume, and mix. If the solution is cloudyat this stage, indicating the presence of titania, filter a portion of the solution thr
39、ough a dry paper into a dry beaker. Transfer aproper aliquot of this solution (see Table 1) to a 200-mL volumetric flask and add 40 mL of the LaCl3 solution. Add the amountof background solution and HCl indicated in Table 1, dilute to volume, and mix.NOTE 6Dilutions shown in Table 1 will provide con
40、centrations of calcium and magnesium falling within the range of the calibration solutions.11.5 Adjustment of Atomic Absorption SpectrometerIn accordance with Practice E663, set the initial instrument parametersto the values in Note 3. Light the burner and aspirate water until the instrument comes t
41、o thermal equilibrium. Optimize instrumentresponse by adjusting the wavelength, fuel, air, burner, and nebulizer while aspirating the highest calibration solution to obtainmaximum absorption or absorbance. Aspirate water until a steady signal is obtained and adjust the instrument readout system toob
42、tain zero absorption or absorbance.NOTE 7The manufacturers instructions for igniting and extinguishing the nitrous oxide-acetylene burner should be strictly followed to avoid possibleexplosion hazards. Tinted safety glasses should be worn by the operator whenever the flame is burning.11.6 Measuremen
43、tsAspirate water until the initial reading is again obtained. Aspirate the calibration solutions in the order ofincreasing absorption or absorbance starting with the zero calibration solution. When a stable response is obtained for eachsolution, record the readings. Aspirate the test solutions at th
44、e proper points in the calibration series. Aspirate water between eachcalibration and test solution. Repeat all measurements at least two more times.12. Calculation12.1 Only if necessary, convert the average of the readings for each calibration solution to absorbance. Obtain the netabsorbance of eac
45、h calibration solution by subtracting the average absorbance of the zero calibration solution. In a similar manner,obtain the net absorbance of the test solution by subtracting the absorbance of the reagent blank solution.12.2 Prepare calibration curves for calcium and magnesium by plotting the net
46、absorbance values of the calibration solutionsagainst micrograms of calcium or magnesium per millilitre.TABLE 1 Dilution Guide for Test SolutionElement Expected Percentage ofElement in Sample Aliquot, mL Equivalent WeightMass ofSample, g Background Solution toBe Added, mL Hydrochloric AcidAdded, mLC
47、alcium 0.05 to 0.5 50 0.25 45 4Calcium 0.5 to 2.5 10 0.05 60 6Calcium 2.5 to 10.0 2 0.01 60 6Magnesium 0.05 to 0.25 40 0.20 50 4Magnesium 0.25 to 1.25 10 0.05 60 6Magnesium 1.25 to 5.00 2 0.01 60 6E508 13312.3 Convert the net absorbance values of the sample solution to micrograms of calcium and magn
48、esium per millilitre by meansof the calibration curves.12.4 Calculate the mass fraction (%) of calcium and magnesium as follows:Calcium or magnesium,%5A 3200!/B 310000! (1)where:A = calcium or magnesium per mL, g, andB = sample represented in the 200-mL volume of the final test solution, g.13. Preci
49、sion and Bias513.1 PrecisionTable 2 indicates the precision of the test method within and between laboratories when applied to a numberof samples of iron ore.13.2 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 certified reference materials with the mean determined through interlaboratory testing.14. Keywords14.1 atomic absorption spectrometry; calcium; iron ores; magnesiumASTM International takes no position respecting the val
