1、Designation: D 6721 01 (Reapproved 2006)Standard Test Method forDetermination of Chlorine in Coal by Oxidative HydrolysisMicrocoulometry1This standard is issued under the fixed designation D 6721; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、 of revision, the year of last 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 totalchlorine in coal.2. Referenced Documents2
3、.1 ASTM Standards:2D 2013 Practice for Preparing Coal Samples for AnalysisD 3173 Test Method for Moisture in theAnalysis Sample ofCoal and CokeD 3180 Practice for Calculating Coal and Coke Analysesfrom As-Determined to Different BasesD 4621 Guide for Quality Management in an OrganizationThat Samples
4、 or Tests Coal and CokeD 5142 Test Methods for Proximate Analysis of the Analy-sis Sample of Coal and Coke by Instrumental ProceduresE 29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE 691 Practice for Conducting an Interlaboratory Study toDetermine t
5、he Precision of a Test Method2.2 Other StandardsISO 5725-6:1994 Accuracy of measurement methods andresults-Part 6: Use in practice of accuracy values33. Summary of Test Method3.1 A 5.00 to 40.00 mg sample of coal is combusted withtungsten accelerator in a humidified oxygen gas flow, at 900C.Halogens
6、 are oxidized and converted to hydrogenated halides,which are flushed into a titration cell where they accumulate.Chlorine is converted to hydrochloric acid. Once the chloride iscaptured in the electrolyte of the titration cell, it can bequantitatively determined by microcoulometery, where chlo-ride
7、 ions react with silver ions present in the electrolyte. Thesilver ion thus consumed is coulometrically replaced and thetotal electrical work needed to replace it is proportional to thechloride in the test sample.4. Significance and Use4.1 This test method permits measurements of the chlorinecontent
8、 of coals.5. Interferences5.1 Bromides and iodides, if present are calculated aschloride. However, fluorides are not detected by this testmethod.6. Apparatus6.1 Hydrolysis Furnace, which can maintain a minimumtemperature of 900C.6.2 Hydrolysis Tube, made of quartz and constructed suchthat when the s
9、ample is combusted in the presence of tungstenaccelerator and humidified oxygen, the byproducts of combus-tion are swept into a humidified hydrolysis zone. The inlet endshall allow for the introduction and advancement of the sampleboat into the heated zone. The inlet shall have a side arm for theint
10、roduction of the humidified oxygen gas. The hydrolysis tubemust be of ample volume, and have a heated zone with quartzwool so that complete hydrolysis of the halogens is ensured.6.3 Titration Cell, containing a reference electrode, a work-ing electrode, and a silver sensor electrode, a magnetic stir
11、reras well as an inlet from the hydrolysis tube.6.4 Microcoulometer, capable of measuring the potential ofthe sensing-reference electrode pair, comparing this potentialwith a bias potential, and amplifying the difference to theworking electrode pair to generate current. The microcoulom-eter output v
12、oltage should be proportional to the generatingcurrent.6.5 Controller, with connections for the reference, working,and sensor electrodes, for setting operating parameters and fordata integration.1This test method is under the jurisdiction of ASTM Committee D05 on Coaland Coke and is the direct respo
13、nsibility of Subcommittee D05.29 on MajorElements in Ash and Trace Elements of Coal.Current edition approved April 1, 2006. Published April 2006. Originallyapproved in 2001. Last previous edition approved in 2001 as D 6721 01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orco
14、ntact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from International Organization for Standardization 1 Rue deVaremb, Case Postale 56, CH-1211, Geneva 20, Switzerland1Copyrig
15、ht ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6.6 Hydration Tube, containing water, positioned before thegas inlet on the side arm of the combustion tube, through whichoxygen gas bubbles to provide a hydrated gas flow.6.7 Dehydration Tube,
16、 positioned at the end of the hydroly-sis tube so that effluent gases are bubbled through a 95 %sulfuric acid solution. Water vapor is subsequently trappedwhile other gases flow into the titration cell.6.8 Gas-Tight Sampling Syringe, having a 50 L capacity,capable of accurately delivering 10 to 40 L
17、 of standardsolution.6.9 Sample Boats, made of quartz, ceramic or platinum.6.10 Balance, analytical, with a sensitivity to 0.00001 g.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall con
18、form to the specification of the Committeeon Analytical Reagents of the American Chemical Society,where such specifications are available. Other grades may beused, provided that the reagent is of sufficiently high purity topermit its use without lessening the accuracy of the determi-nation.7.2 Purit
19、y of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Specification D 1193, Type II or Type III.7.3 Acetic Acid (sp gr. 1.05), glacial acetic acid(CH3COOH).7.4 Argon or Helium, carrier gas, minimum 99.9 % purity.7.5 Sodium Acetate, anhydrous,
20、 (NaCH3CO2), fine granular.7.6 Cell Electrolyte SolutionDissolve 1.35 g sodium ac-etate (NaCH3CO2) in 100 mL water. Add to 850 mL of aceticacid (CH3COOH) and dilute to 1000 mL with water.7.7 Tungsten Powder, combustion accelerator, (-100 mesh)minimum 99.9 % purity.7.8 Oxygen, combustion gas minimum
21、99.6 % purity.7.9 Gas RegulatorsUse two-stage gas regulators for thecarrier and combustion gases.7.10 Potassium Nitrate (KNO3), fine granular.7.11 Potassium Chloride (KCl), fine granular.7.12 Working Electrode Solution (10 % KNO3), Dissolve50 g potassium nitrate (KNO3) in 500 mL of water.7.13 Inner
22、Chamber Reference Electrode Solution (1 MKCl)Dissolve 7.46 g potassium chloride (KCl) in 100 mL ofwater.7.14 Outer Chamber Reference Electrode Solution (1 MKNO3)Dissolve 10.1 g potassium nitrate (KNO3) in 100 mLof water.7.15 Sodium Chloride (NaCl), fine granular.7.16 Sulfuric Acid (sp gr. 1.84), (H2
23、SO4), concentrated.7.17 2,4,6-Trichlorophenol (TCP) (C6H3OCl3), fine granu-lar.7.18 Methanol (MeOH) (CH3OH), 99.9 % minimum purity.7.19 Working Chlorine Standard (1g/L)Weigh accu-rately 0.1856 g of 2,4,6-Trichlorophenol to the nearest 0.1 mg.Transfer to a 100 mL volumetric flask. Dilute to the mark
24、withmethanol.WSCI5 gofTCP 3 0.5386 3 1000/100! (1)where:TCP = 2,4,6-Trichlorophenol, andWSCI= the working chlorine standard concentration.8. Hazards8.1 Consult the current version of OSHA regulations, sup-pliers Material Safety Data Sheets, and local regulations forall materials used in this test me
25、thod.9. Sampling9.1 Prepare the analysis sample in accordance with MethodD 2013 to pass a 250-m (60 mesh) sieve.9.2 Analyze a separate portion of the analysis sample formoisture content in accordance with Test Method D 3173 orTest Methods D 5142.10. Preparation of Apparatus10.1 Fill the hydration to
26、wer with water and connect it tothe quartz furnace tube inlet.10.2 Set the furnace temperature to 900C.10.3 Adjust the gas flows according to manufacturers speci-fication, typically 200 mL/min for oxygen and 100 mL/min forthe carrier gas.10.4 Prepare the sulfuric acid dehydration scrubber, andconnec
27、t it to the outlet of the quartz furnace combustion tube.10.5 Clean and prepare the electrode system for the titrationcell per instrument specifications.10.6 Fill the titration cell with fresh electrolyte solution tojust above the top fill mark.10.7 Place the titration cell on the magnetic stirring
28、deviceand connect the electrode system to the controller. Do notconnect the gas flow from the dehydration scrubber to thetitration cell.10.8 Initiate a conditioning run of the titration cell toestablish titration gain and endpoint values.10.9 Once the titration cell is properly conditioned, connectt
29、he gas flow from the dehydration scrubber to the titration cell.10.10 Let the titration cell stabilize to a background poten-tial of less then 1.0 mv.10.11 To ensure quality data, care must be taken to avoidcontaminating the sample boats during the course of theanalytical procedure. Do not touch the
30、 boats with fingers.Handle and transfer the boats using tongs and store said boatsin a sealed container such as a glass desiccator, containing nodesiccant. Prepare the combustion boats by heating them in thecombustion tube with oxygen flow for a minimum of five min.11. Recovery Factor11.1 Confirm th
31、e instrument carrier gas and time delaysettings. Typical delays for solvent injections are 2.0 min forcarrier gas and 2.5 min to titration start.11.2 Inject 10 L of chlorine standard solution through theinjection port into a prepared combustion boat. Advance thecombustion boat slowly into the heated
32、 zone of the furnace.Record the recovered g Chlorine as RC.11.3 Repeat this recovery measurement a minimum of threetimes.11.4 Calculate the Recover Factor (RF) for each measure-ment according to Eq 2.D 6721 01 (2006)2RF 5WSCl3 10!RC(2)where:RF = the recover factor,WSCl= the working chlorine standard
33、 concentration, andRC = the recovered chlorine value.11.5 Calculate the average recovery factor.11.6 If the average recovery factor is from 0.95 to 1.05, therecovery factor shall be assumed to be 1.0 and the instrumentcan be used for sample analysis.11.7 If the average recovery factor is less than 0
34、.95 orgreater than 1.05, then the instrument shall be re-calibrated byrunning 5 L, 10 L, 20 L, 30 L and 50 L volumes of theChlorine working standard, after confirming that the apparatusis in proper working condition and after setting up theapparatus in accordance with Section 10 Preparation of Appa-
35、ratus (Note 1).NOTE 1A low recovery factor is usually indicative of leaks in thecombustion system or improper packing of the combustion tube. Highrecovery factors are generally indicative of contamination.12. Blank Determination12.1 Carry out a conditioning run with 100 mg 6 10 mg oftungsten powder.
36、 Note the value of chlorine recovered but donot use this value in any blank calculations.12.2 Weigh 100 mg 6 10 mg of tungsten into the preparedcombustion boat and record the g of chlorine in 100 mgtungsten.12.3 Repeat the blank measurement until three successivemeasurements of less than 0.1 g of ch
37、lorine are obtained.12.4 Calculate the average blank value from the threemeasurements less than 0.1 g chlorine and record as B.13. Procedure13.1 Follow the manufacturers instructions to program thecarrier gas to switch to oxygen immediately after the sampleboat is completely inside the combustion fu
38、rnace. Delay thestart of the titration for a time sufficient to collect thebyproducts of the sample combustion in the titration cell,typically 2.0 min.13.2 Weigh approximately 10 mg of sample into a preparedcombustion boat. Record the weight to the nearest 0.01 mg asW. The recommended sample sizes f
39、or coals with higher andlower chlorine respectively are outlined in the following table.Chlorine Range, mg/kg Sample Size, mg20.0 to 100 40100 to 300 20300 1013.3 Cover the specimen with approximately 100 mg oftungsten powder accelerator.13.4 Proceed with the combustion titration analysis by firstst
40、arting the controller count down and then advancing thesample boat directly into the combustion furnace hot zone.Record the measured Chlorine value as M.14. Calculation14.1 The as determined chlorine concentration is calculatedas follows:Chlorine, mg/kg 5 1000 3 MB!/W! (3)where:M = measured chloride
41、 value, g,B = blank chloride value, g, andW = weight of sample, mg.15. Report15.1 The results of the chlorine analysis can be reported toother bases, differing from each other in the manner by whichmoisture is treated.15.2 Use the percent moisture, as determined by TestMethod D 3173 or Test Method D
42、 5142, in the analysis samplepassingaN60(250 m) sieve, to calculate the results of theanalysis to a dry basis.15.3 Procedures for converting the values obtained on theanalysis sample to other bases are described in PracticeD 3180.16. Precision and Bias416.1 The precision of this test method for the
43、determinationof Chlorine in coal, is shown in Table 1. The precisioncharacterized by the repeatability (Sr, r) and reproducibility(SR, R) is described in Table A1.1 in Annex A1.16.1.1 Repeatability Limit (r)The value below which theabsolute difference between two test results of separate andconsecut
44、ive test determinations, carried out on the samesample in the same laboratory by the same operator using thesame apparatus on samples taken at random from a singlequantity of homogeneous material, may be expected to occurwith a probability of approximately 95 %.16.1.2 Reproducibility Limit (R)The va
45、lue below whichthe absolute difference between two test results, carried out indifferent laboratories using samples taken at random from asingle quantity of material that is as nearly homogeneous aspossible, may be expected to occur with a probability ofapproximately 95 %.4Supporting data have been
46、filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR: D05-1030.TABLE 1 Concentration Range and Limits for Repeatability andReproducibility for Chlorine in CoalConcentrationRange, ppmRepeatability LimitrReproducibility LimitR22 11361.92 + 0.06 x6.13 + 0.07 xD 6
47、721 01 (2006)316.2 BiasNIST Standard Reference Material NIST 1630awas included in the interlaboratory study to ascertain possiblebias between reference material values and those determinedby this method. A comparison of the NIST values and thoseobtained in the interlaboratory study are given in Tabl
48、e 2.NOTE 2When possible , the analysis of several reference materials ,spanning the concentration range of interest, is the most meaningful wayto investigate measurement bias. When a matrix match is possible theuncertainty in sample measurements can be equatable to that observed inmeasurement of the
49、 Certified Reference Material (CRM). When such amatch is not possible, but a CRM with a related matrix is available, the testsample uncertainty may be related to those observed when measuring theCRM. Different methods of measurement of a property may not becapable of equal repeatability. Accordingly, instances could arise wherethe method of measurement has greater variability than that or those usedin certification of the CRM.516.3 An interlaboratory study, designed consistent withASTM Practice E 691, was conducted in the year 2000. Sixla
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