1、Designation: E945 12Standard Test Method forDetermination of Zinc in Zinc Ores and Concentrates byEDTA Complexometric Titrimetry1This standard is issued under the fixed designation E945; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisi
2、on, 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 zinc inores, concentrates, and related materials having c
3、hemicalcomposition within the following limits:Element Application Range, %Zinc 5.0 to 70.0Lead 0.5 to 50.0Copper 0.1 to 3.0Iron 0.5 to 16.0Sulfur 4.0 to 30.0Calcium 0.1 to 20.0Magnesium 0.1 to 10.0Cadmium 0.1 to 8.0Arsenic 0.01 to 1.0Antimony 0.01 to 0.005Bismuth 0.001 to 0.1Cobalt 0.1 to 0.5Nickel
4、 0.3 to 3.0Silver 0.00 to 150 oz/tonGold 0.00 to 1.0 oz/tonNOTE 1As used in this test method, percent or “%” refers to a massfraction.1.2 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 esta
5、blish appro-priate 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 WaterE29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE50
6、 Practices for Apparatus, Reagents, and Safety Consid-erations for Chemical Analysis of Metals, Ores, andRelated MaterialsE135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE173 Practice for Conducting Interlaboratory Studies ofMethods for Chemical Analysis of Me
7、tals3E663 Practice for Flame Atomic Absorption Analysis3E882 Guide for Accountability and Quality Control in theChemical Analysis LaboratoryE1601 Practice for Conducting an Interlaboratory Study toEvaluate the Performance of an Analytical Method3. Terminology3.1 DefinitionsFor definitions of terms u
8、sed in this testmethod, refer to Terminology E135.4. Summary of Test Method4.1 The sample, after appropriate acid decomposition, isevaporated to near dryness. The salts are dissolved in acid,interfering elements are removed, and the zinc is extracted asthiocyanate complex into MIBK. Zinc is determin
9、ed in theextract by titrating with EDTA, using an internal indicator.5. Significance and Use5.1 This test method is primarily intended to test materialsfor compliance with compositional specifications. It is assumedthat all who use this test method will be trained analystsworking in properly equippe
10、d laboratories.5.2 Appropriate quality control practices shall be followedsuch as those described in Guide E882.6. Interferences6.1 With the exception of cadmium and cobalt, elements donot interfere if their compositional ranges are under themaximum limits shown in 1.1.6.2 When the cadmium content i
11、s above 5.0 % in thematerial to be analyzed, some of the cadmium is extracted and1This test method is under the jurisdiction of ASTM Committee E01 onAnalytical Chemistry for Metals, Ores, and Related Materials and is the directresponsibility of Subcommittee E01.02 on Ores, Concentrates, and Related
12、Metal-lurgical Materials.Current edition approved June 1, 2012. Published July 2012. Originally approvedin 1983. Last previous edition approved in 2007 as E945 07. DOI: 10.1520/E0945-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceas
13、tm.org. For Annual Book of ASTMStandards volume 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshoho
14、cken, PA 19428-2959, United States.will titrate as zinc. The addition of potassium iodide before thetitration serves to prevent the interference of cadmium. Theamount of potassium iodide solution to add in order to preventthe interference of cadmium is listed in 13.10.3.6.3 Cobalt is extracted and t
15、itrated with the zinc. If thecobalt content of the material to be analyzed is less than0.05 %, the interference is negligible. For cobalt contentsgreater than 0.05 %, the cobalt must be extracted as outlined in13.9.5.7. Apparatus7.1 Magnetic Stirrer, with TFE-fluorocarbon covered mag-netic stirring
16、bar. A magnetic stirrer provided with illuminationis preferred.8. Reagents and Materials8.1 Purity 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 Ame
17、rican Chemical Society wheresuch specifications are available.4Other grades may be used,provided it is first ascertained that the reagent is of sufficienthigh purity to permit its use without lessening the accuracy ofthe determination.8.2 Purity of WaterUnless otherwise indicated, referencesto water
18、 shall be understood to mean reagent water as definedby Type I or II of Specification D1193. Type III or IV may beused if they effect no measurable change in the blank or sample8.3 Ammonium Fluoride Solution (250 g/L)Dissolve 250g of ammonium fluoride (NH4F) in water and dilute to 1 L.Store in a pol
19、yethylene bottle.8.4 Ammonium Chloride Solution (250 g/L)Dissolve 250g of ammonium chloride (NH4Cl) in water and dilute to 1 L.8.5 Ammonium Thiocyanate (500 g/L)Dissolve 500 g ofammonium thiocyanate (NH4SCN) in distilled water and diluteto1L.8.6 Buffer Solution (pH 5.5)Dissolve 250 g of hexameth-yle
20、netetramine (C6H12N4) in 750 mL of water. Add 57 mL ofacetic acid, dilute to 1 L, and mix.8.7 Chloroform (CHCl3).8.8 Disodium Ethylenedinitrilo Tetraacetate Dihydrate(EDTA) Standard SolutionPrepare a solution as follows:8.8.1 PreparationDissolve disodium ethylenedinitrilo tet-raacetate (EDTA) dihydr
21、ate in water, transfer to a 1L volu-metric flask, dilute to volume, and mix. The solution is stablefor several months when stored in plastic or borosilicate glassbottles.Use the following table as a guide for the specific weight ofEDTA 2H2O to use.NOTE 2The use of varying concentrations of EDTA solu
22、tion allowsthe volume of the titrant to be between 30 mL and 50 mL.Amount ofEDTA 2H2O EDTA Standard ZincIf the expectedzinc is:Mass, g/L Concentration Solution toUse5%to20% 6.642 6g/L 10mL20 % to 40 % 13.29 12 g/L 30 mL40 % to 56 % 17.71 16 g/L 40 mL56 % to 70 % 22.14 20 g/L 50 mL8.8.2 Standardize t
23、he EDTA solution by pipetting the sug-gested amount of standard zinc solution into a 250-mLseparatory funnel.Add 10 drops of ferric chloride solution, adddistilled water to adjust volume to 50 mL, mix, and proceed asdirected in 13.9.2. It is recommended that replicate standard-izations be made to en
24、sure better accuracy.8.8.3 Calculate the zinc equivalent of the EDTA solution asfollows:Zinc Equivalent mg/mL!5AB(1)where:A = zinc in the chosen aliquot, mg andB = EDTA solution (8.8) used, mL8.9 Ethanol (CH3CH2OH)Certain denatured ethanols in-terfere with the color of the indicator during the titra
25、tion. Pureethanol is recommended for this reason.8.10 Ferric Chloride Solution (140 g/L)Dissolve 14 g offerric chloride (FeCl36H2O) in water and dilute to 100 mL.8.11 4-Methyl-2-Pentanone (MIBK)CH3COCH2CH(CH3)2.8.12 2-Nitroso-1-Naphthol Solution (10 g/L)Dissolve 0.5g of 2-nitroso-1-naphthol (NOC10H6
26、OH) in 50 mL of aceticacid. Prepare fresh as needed.8.13 Potassium Iodide (1000 g/L)Dissolve 100 g ofpotassium iodide (KI) in distilled water and dilute to 100 mL.8.14 Sodium Fluoride Solution (20 g/L)Dissolve 10 g ofsodium fluoride (NaF) in water and dilute to 500 mL. Store ina polyethylene bottle.
27、8.15 Thiourea Solution (100 g/L)Dissolve 50 g of thio-urea (NH2CSNH2) in water and dilute to 500 mL.8.16 Xylenol Orange Tetrasodium Salt Indicator Solution (2g/L)Dissolve 100 mg of xylenol orange tetrasodium salt inwater and dilute to 50 mL.8.17 Zinc, Standard Solution (1 mL3.50 mg)Dissolve3.50 g of
28、 zinc (minimum purity 99.99 %) in 10 mL of HNO3and 25 mL of water. Heat gently; when dissolution is complete,boil. Cool. Transfer to a 1-L flask. Dilute to the mark and mixthoroughly.9. Hazards9.1 For precautions to be observed in the use of certainreagents in this test method, refer to Practices E5
29、0.10. Sampling and Sample Preparation10.1 The gross sample shall be collected and prepared so asto be representative of the material to be analyzed.10.2 Pulverize the laboratory sample to pass a No. 100(150-m) sieve. The repeatability, R1, of Practice E173 corre-sponds to the repeatability index, r,
30、 of Practice E1601.11. Rounding Calculated Values11.1 Calculated values shall be rounded to the desirednumber of places as directed in the Rounding-Off Proceduresection of Practice E29.4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggest
31、ions 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.E945 12212. Interlaboratory Studies12.1 This test method has been evaluated in accordancewith Practice E173.
32、 For those methods tested according toPractice E173, the reproducibility, R2, of Practice E173 corre-sponds to the reproducibility index, R, of Practice E1601.13. Procedure13.1 Weigh approximately 2.5 g of sample into a weighingbottle. Dry the bottle and contents at least1hat105C,butnotmore than 3 h
33、. Cap the bottle and cool to room temperature ina desiccator.13.1.1 Momentarily release the cap to equalize the pressureand weigh the capped bottle and sample to the nearest 0.1 mg.13.1.2 Transfer all of the sample into a 250-mL to 300-mLErlenmeyer flask or Phillips beaker. Reweigh the capped bottle
34、to the nearest 0.1 mg. The difference between the massrecorded in 13.1.1 and the mass recorded in 13.1.2 is the massof the sample.13.2 Moisten the sample in the Erlenmeyer flask withapproximately 5 mL of water and add 2 mL to 3 mL bromine.Allow to stand for 15 min with occasional stirring.13.3 Add 1
35、0 mL of HNO3cautiously and allow to stand for5 min with occasional stirring.13.4 Cautiously add 15 mL of H2SO4(1 + 1), mix, and heatgently to remove the brown bromine and nitric oxide fumes.Do not boil.13.5 Remove from the heat, add 3 drops to 5 drops of HF,5 mL of HClO4, replace on the hotplate, an
36、d evaporate thesolution until the volume is reduced to approximately 5 mL.13.6 Remove from the heat, wash down the sides withwater, add 5 mLof H2SO4(1 + 1), add 1 mLof HCl (1 + 4), anddilute to 40 mL. Mix and bring to a boil.13.6.1 For samples containing more than 10 % SiO2, pro-ceed as directed in
37、13.7. For samples containing less than 10 %SiO2, proceed as directed in 13.8.13.7 Filter the solution into a 500-mL volumetric flask,using a Whatman #1 or equivalent paper. Wash the residuethoroughly to remove soluble precipitate.13.7.1 Transfer the paper plus residue into a platinumcrucible. Char t
38、he paper at a low temperature and then ignite ina muffle furnace at 800 C. Remove from the furnace and cool.13.7.2 Add 5 mL of HF, add 5 mL of HClO4, mix, and heatuntil dense fumes are being given off. Remove from the heatand cool.13.7.3 Dilute with water and transfer to the 500-mL volu-metric flask
39、, which contains the filtrate from 13.7. Dilute tovolume and mix. Allow any remaining residue to settle.Proceed to 13.9.13.8 Transfer the solution obtained in 13.6 to a 500-mLvolumetric flask. Dilute to volume and mix. Allow anyremaining residue to settle.13.9 Extraction:13.9.1 Pipet 50 mL of the cl
40、ear solution obtained in 13.7.3or 13.8 into a 250-mL separatory funnel.Add 10 drops of ferricchloride solution (8.10) and mix.NOTE 3Ferric chloride is added to aid the analyst in setting the pH ofthe solution. If iron is present in the sample already, the addition of theferric chloride solution can
41、be eliminated.13.9.2 Add 20 mL of NH4Cl solution (8.4) and mix.13.9.3 Add NH4OH, dropwise, until a slight turbidity de-velops. Then add 5 mL of HCl (1 + 4) and mix.13.9.4 Add 20 mL of NH4F solution and mix.13.9.4.1 If the cobalt content of the sample is known to beless than 0.05 %, proceed as direct
42、ed in 13.9.6. When thecobalt content is higher than 0.05 %, the cobalt must beremoved. Proceed as directed in 13.9.5.13.9.5 Adjust the pH using pH paper to between 3 and 4 bythe dropwise additions of HCl (1 + 1) or NH4OH (1 + 1)solution. Add 5 drops of H2O2(30 %) and 2 mL of 2-nitroso-1-napthol solu
43、tion (8.12). Allow to stand 30 min with occa-sional stirring.13.9.5.1 Add 20 mL of CHCl3, shake for 30 s, and allow thephases to separate. Discard the lower phase.13.9.5.2 Add another 20 mL of CHCl3(8.7) and repeat theextraction again discarding the lower phase.13.9.5.3 Extract a third time using 10
44、 mL of CHCl3(8.7) anddiscard the lower phase. Proceed as directed in 13.9.6.13.9.6 Add 5 mL of thiourea (8.15) solution and 25 mLNH4SCN solution (8.5), mixing after each addition.13.9.7 Add 80 mL of MIBK (8.11) and shake vigorously for1 min. Allow the phases to separate, and then draw off thelower a
45、queous phase into a second separatory funnel. Retainthe upper organic phase.13.9.8 Add 20 mL of MIBK (8.11) to the second separatoryfunnel and shake for 1 min. Allow the phases to separate anddiscard the lower aqueous phase. Retain the upper organicphase.13.9.9 Transfer the portions from both separa
46、tory funnels toa 400-mL beaker. To each separatory funnel add 1 mL of HCl(1 + 4) and 50 mL of ethanol and shake for 5 s. Transfer bothof these solutions to the 400-mL beaker. Cover the beaker untilthe titration is to begin.13.10 Titration:13.10.1 Place a stirring bar into the solution in the 400-mLb
47、eaker and place the beaker on a magnetic stirrer. Begin to stirat a moderate rate.13.10.2 While stirring, add 10 mL of NaF solution (8.14),10 mL of thiourea solution (8.15), and 20 mL of buffer solution(8.6).13.10.3 If the cadmium content of the original sample isbelieved to be from 5 % to 10 % add
48、10 mL of KI solution(8.13).13.10.4 Add 10 drops of xylenol orange indicator solution(8.16) and 0.25 g to 0.30 g ascorbic acid, and continue to stir.Titrate with the appropriate EDTA solution (8.8) chosen asprescribed in 8.8 to a yellow end point.NOTE 4The reaction between EDTA and zinc is slowed dow
49、n in thepresence of organic solvents. On approaching the equivalence point, it isnecessary to work more slowly than usual. Wait 10 s after each additionof EDTA. Should a phase separation occur or the sample become cloudy,add 20 mL of ethanol and proceed with the titration.NOTE 5If the end-point is inadvertently passed, add 1.00 mL of zincstandard solution (8.17) by means of a microburet. Complete the titrationas usual. Correct the final result for the quantity of zinc added.E945 12314. Calculation14.1 Calculate the percentage of zinc as follows:Zi
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