1、Designation: E2296 03 (Reapproved 2013)Standard Practice forSilver Corrections in Metal Bearing Ores, Concentrates, andRelated Metallurgical Materials by Fire Assay Slag Recyclingand Cupel Proof Gravimetry1This standard is issued under the fixed designation E2296; the number immediately following th
2、e designation indicates the year oforiginal adoption or, in the case 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 practice covers the
3、 silver loss correction, utilizingslag recycling and cupellation of proof silver during the fireassay of metal bearing ores, concentrates, and related metal-lurgical materials.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.
4、1.3 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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. (See Practices
5、 E50and ISO 35:1989.)2. Referenced Documents2.1 ASTM Standards:2E29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE50 Practices for Apparatus, Reagents, and Safety Consid-erations for Chemical Analysis of Metals, Ores, andRelated MaterialsE135 Terminol
6、ogy Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE882 Guide for Accountability and Quality Control in theChemical Analysis Laboratory2.2 ISO Documents:3ISO 35:1989 Certification of Reference MaterialsGeneraland Statistical PrinciplesISO 10378:1994 Copper Sulfide Concentrate
7、sDetermination of Gold and Silver ContentsFire AssayGravimetric and Atomic Absorption SpectrometricMethod3. Terminology3.1 DefinitionsFor definitions of terms used in thispractice, refer to Terminology E135.4. Summary of Practice4.1 In the process of fire assay fusion, the slag is retainedfrom the i
8、nitial fusion and reprocessed through the fusionprocedure. The resulting lead button is combined with thepreliminary lead button during cupellation. Proof silver iscarried through the cupellation procedure to determine thesilver losses. (See ISO 10378:1994, Bugbee,4and Smith5.)5. Significance and Us
9、e5.1 This practice is primarily intended to be used for thecorrection of silver loss in the fire assay process. Silvercontents are determined by fire assay for the purpose ofmetallurgical exchange between buyer and seller. It is assumedthat all who use this practice will be trained analysts capable
10、ofperforming skillfully and safely. It is expected that work willbe performed in a properly equipped laboratory under appro-priate quality control practices such as those described inGuide E882.6. Apparatus6.1 Assay Furnace, capable of temperatures up to 1100 C,accurate to 6 5 C with draft controls.
11、6.2 Analytical Balance, capable of weighing to 0.001 mg.6.3 Hammer, blacksmith type.6.4 Hammering Block, flat steel or iron.1This practice is under the jurisdiction of ASTM Committee E01 on AnalyticalChemistry for Metals, Ores, and Related Materials and is the direct responsibility ofSubcommittee E0
12、1.02 on Ores, Concentrates, and Related Metallurgical Materials.Current edition approved Oct. 1, 2013. Published October 2013. Originallyapproved in 2003. Last previous edition approved in 2008 as E2296 03 (2008)1.DOI: 10.1520/E2296-03R13.2For referenced ASTM standards, visit the ASTM website, www.a
13、stm.org, orcontact 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 (ISO), 1, ch. dela Voie-Creuse, CP 56, CH-1211 Geneva 20, S
14、witzerland, http:/www.iso.org.4Bugbee, E. E., A Textbook of Fire Assaying, Third Ed., John Wiley and Sons,Inc., Hoboken, NJ, 1946.5Smith, E. A., The Sampling and Assay of the Precious Metals, Second Ed.,Charles Griffin and Co., Ltd., 1947.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C
15、700, West Conshohocken, PA 19428-2959. United States17. Reagents and Materials7.1 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 American Chem
16、ical Society wheresuch specifications are available.6Other grades may be used,provided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determination.7.2 Borax, sodium tetraborate (Na2B4O7), technical grade.7.3 Crucibles, s
17、tandard fire assay clay.7.4 Cupels, magnesite (MgCO3) or bone ash, size deter-mined by lead button weight.NOTE 1Cupel size is determined by the weight of the lead button.Cupels must be large enough to hold all the molten lead from the primaryfire assay fusion and slag re-fusion.7.5 Lead Foil (99.99
18、% purity min; 1 ppm silver max).7.6 Litharge (PbO), technical grade, precious metal free.7.7 Potassium Bitartrate (K2C4H4O6), technical grade.7.8 Silica Sand (SiO2), technical grade.7.9 Silver Metal (99.99 % purity), foil.7.10 Sodium Carbonate (Na2CO3), technical grade.7.11 Wax Paper Flux Bag, 25 cm
19、2by 25 cm2.8. Hazards8.1 For precautions to be observed in this method, refer toPractice E50.9. Procedure9.1 Perform the initial fire assay according to proper ac-cepted procedures to produce the initial lead button. (SeeBugbee4and Smith5.)9.2 Collect the fire assay fusion slag from the original fus
20、ionand place back into the original fire assay crucible.9.3 Add 50 g of the slag re-fusion flux to the crucible. Thecomposition is shown in Table 1.9.4 Place crucible in the fire assay furnace. Raise thetemperature to 1060 C. After the furnace obtains thattemperature, hold for at least 30 min. In mo
21、st instances, thetotal furnace time will be approximately 1 h. Fusion must be ina liquid state.NOTE 2In most cases, the best way to add re-fusion flux is with a waxpaper bag. Place the re-fusion flux into the bag, twist the top, and place ontop of the original fusion slag material in the original fi
22、re assay crucible.9.5 After 1 h, carefully pour the melt into fire assay moulds,taking care to ensure that no portion is lost.9.6 After cooling, break off slag and retain lead button.9.7 Place the re-fusion lead button with the original fusionlead button for each test sample.9.8 Weight two proof sil
23、ver foil samples to match thetypical weight of the expected dor bead and record theweights. If the weight of the dor bead is unknown, weigh twoproof silver samples approximately 75 mg to 100 mg and250 mg to 350 mg.9.9 Wrap the proof silver beads in lead foil, and pound intoa lead square with a hamme
24、r.NOTE 3The weight of the lead foil should approximate the weigh ofthe combined lead buttons collected in 9.1 and 9.6.9.10 Transfer the lead square (9.9) and the combined leadbuttons (9.7) into the cupellation furnace into three cupels withthe silver proofs on two sides of the combined test samplebe
25、ads.9.11 Cupel to obtain dor beads by normal fire assaycupellation procedures.9.12 After cupellation, re-weigh the silver proofs on thebalance and record the weights.NOTE 4The loss of silver due to the original fire assay fusiontechnique is recovered by the slag recycling and re-fusion steps.10. Cal
26、culation10.1 Calculate the silver ratio as follows:Silver Ratio 5BA(1)where:A = initial weight of proof silver, mg, andB = final weight of proof silver, mg.10.2 Round the silver ratio to the nearest 0.0001 in accor-dance with Practice E29.10.3 To correct a silver fire assay result, divide the weight
27、 ofthe silver in the test sample, determined by the difference inweight before and after parting, by the average silver ratio forthe two proofs to obtain the corrected silver weight.11. Keywords11.1 cupellation; fire assay; silver; silver correction6Reagent Chemicals, American Chemical Society Speci
28、fications, AmericanChemical Society, Washington, DC, http:/www.chemistry.org. For suggestions onthe testing of reagents not listed by the American Chemical Society, see AnnualStandards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., http:/, and the United States Pharmacopeia and National Fo
29、rmulary, U.S.Pharmacopeial Convention, Inc. (USPC), Rockville, MD, http:/www.usp.org.TABLE 1 Slag Re-Fusion Fluxlitharge 55.4 gsodium carbonate 9.3 gsilica sand 9.4 gpotassium bitartrate 7.3 gborax 18.7 gE2296 03 (2013)2ASTM International takes no position respecting the validity of any patent right
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