1、Designation: E1335 08 (Reapproved 2017)Standard Test Methods forDetermination of Gold in Bullion by Fire Assay CupellationAnalysis1This standard is issued under the fixed designation E1335; the number immediately following the designation indicates the year oforiginal adoption or, in the case of rev
2、ision, 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 These test methods cover cupellation analysis of bullionhaving chemical compositions within the fol
3、lowing limits:Element Concentration Range, %Gold 0.5 to 4.0 and 20.0 to 99.8Silver 1.0 to 99.5Total gold plus silver 75.0 to 100.01.2 These test methods appear in the following order:Sections20.0 % 99.0 % gold 10170.5 % 4.0 % gold 182398.9 % 99.8 % gold 24301.3 The values stated in SI units are to b
4、e regarded asstandard. No other units of measurement are included in thisstandard.1.4 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 d
5、etermine the applica-bility of regulatory limitations prior to use. For specific safetyhazards, see Section 8.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of In
6、ternational Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2B562 Specification for Refined GoldE50 Practices for Apparatus, Reagents, and Safety Consid-erations for Chemical Analysis o
7、f Metals, Ores, andRelated MaterialsE135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE173 Practice for Conducting Interlaboratory Studies ofMethods for Chemical Analysis of Metals (Withdrawn1998)3E1601 Practice for Conducting an Interlaboratory Study toEvaluate
8、 the Performance of an Analytical Method3. Terminology3.1 DefinitionsFor definitions of terms used in these testmethods, refer to Terminology E135.3.2 Definitions of Terms Specific to This Standard:3.2.1 anneala thermal treatment to change the propertiesor grain structure of the product.3.2.2 cupela
9、 small, shallow, porous cup, usually made ofbone ash or from magnesium oxide.3.2.3 cupellationan oxidizing fusion of lead, sample basemetals and gold, and silver in a cupel. The lead is oxidized tolitharge (PbO); other base metals which may be present, suchas copper and tin, are oxidized as well. Th
10、e oxidized metals areabsorbed into the cupel, leaving a gold and silver dor bead onthe cupel surface.3.2.4 dor beada gold and silver alloy bead which resultsfrom cupellation.3.2.5 inquartationthe addition of silver to an assay sampleto enable parting.3.2.6 partthe separation of silver from gold by s
11、electivelydissolving the silver in acid, usually nitric acid (HNO3).3.2.7 proofa synthetic standard having a compositionsimilar to the test sample.3.2.8 proof correctionanalyzing the proof concurrentlywith the test sample and using the results to correct the finalassay.1These test methods are under
12、the jurisdiction of ASTM Committee E01 onAnalytical Chemistry for Metals, Ores, and Related Materials and are the directresponsibility of Subcommittee E01.05 on Cu, Pb, Zn, Cd, Sn, Be, Precious Metals,their Alloys, and Related Metals.Current edition approved Jan. 15, 2017. Published March 2017. Orig
13、inallyapproved in 1990. Last previous edition approved in 2008 as E1335 08. DOI:10.1520/E1335-08R17.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Do
14、cument Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with int
15、ernationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.14. Significance and Use4.1 These test methods
16、are intended for the determination ofthe gold content of gold and silver bullion. It is assumed that allwho use these test methods are trained assayers capable ofperforming common fire assay procedures skillfully and safely.It is expected that work will be performed in a properlyequipped laboratory.
17、5. Interferences5.1 If the bullion contains any of the following elements inexcess of the concentrations shown, the accuracy and precisionrequirements of these test methods may not be achieved.Element Maximum Level, %Arsenic 2.0Antimony 2.0Bismuth 2.0Iron 2.0Nickel 2.0Platinum group, total (Ir, Os,
18、Pd, Pt, Rh, Ru) 0.01Selenium 2.0Tellurium 2.0Thallium 2.0Tungsten 0.5Zinc 5.06. Apparatus6.1 Assay FurnaceCapable of temperatures up to1100 C, accurate to 6 10 C, with draft controls and fumehood.6.2 Hammer.6.3 Hammering Block.6.4 Rolling Mill.6.5 Analytical Balance.6.5.1 For Test Methods A and B, c
19、apable of weighing to0.01 mg.6.5.2 For Test Method C, capable of weighing to 0.002 mg.6.6 Parting BasketPlatinum basket or porcelain goochcrucibles in stainless steel basket/vessel.6.6.1 Gooch Porcelain Crucible13 mL capacity, bottominside diameter (ID) 18 mn, top ID 29 mn.6.6.2 Stainless Steel Bask
20、et316 stainless steel.7. Reagents47.1 Copper Metal, 99.9 % purity, minimum; 0.0005 % gold,maximum.7.2 Gold Metal, 99.99 % purity, minimum.7.2.1 Gold metal, 99.999 % purity, minimum for TestMethod C only.7.3 Lead Foil, 99.99 % purity, minimum (0.001 % silver,maximum; 0.0005 % gold, maximum).7.4 Silve
21、r Metal, 99.9 % purity, minimum (0.0005 % gold,maximum).7.5 Nitric Acid, 0.0002 % chloride, maximum.7.6 CupelsMagnesium oxide or bone ash.8. Hazards8.1 For precautions to be observed in the use of certainreagents and equipment in these test methods refer to PracticesE50.8.2 Use care when handling ho
22、t crucibles and operatingfurnaces to avoid personal injury by either burn or electricalshock.8.3 Lead and litharge (PbO) are toxic materials and arevolatile at low temperatures. Avoid inhalation, ingestion, orskin contact.9. Sampling9.1 Use shot or pin tube samples. Brush the samples toremove any ad
23、hering glass or flux.9.2 Prepare shot samples from molten metal poured intowater. Use only whole single pieces between 1 mm and 3 mmin diameter.9.3 Pin tube samples are prepared from molten metal drawninto vacuum-evacuated glass tubes. Break the glass and inspectthe samples to ensure that they are n
24、ot hollow and that they arefree from slag and inclusions.9.3.1 Roll the samples lengthwise on a clean rolling mill to0.127 mm, then clean them with alcohol.9.3.2 Cut the strip into horizontal slices to obtain the desiredsample weight.9.4 Drillings are not usually as representative of a melt aspin tu
25、be or shot samples. If bar drillings are to be analyzed,obtain them as directed in Specification B562.TEST METHOD A10. Scope10.1 This test method covers cupellation analysis of gold inbullion containing 20.0 % to 99.0 % gold and 1.0 % to 80.0 %silver.10.2 This international standard was developed in
26、 accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.11. Summary of Test Metho
27、d11.1 A preliminary assay is performed to estimate theapproximate gold content and approximate gold plus silvercontent. Other methods such as X-ray fluorescence (XRF),inductively coupled plasma emission (ICP), direct currentplasma emission (DCP), or atomic absorption spectroscopy(AAS) can also be us
28、ed for a preliminary assay if they havebeen shown to have an accuracy of better than 6 1 % for goldand 6 2 % for silver. The sample is weighed and silver orcopper, or both, added if necessary. The sample is wrapped andcompacted in lead foil and cupelled to remove base metals,4Reagent Chemicals, Amer
29、ican Chemical Society Specifications, AmericanChemical Society, Washington, DC, www.chemistry.org. For suggestions on thetesting of reagents not listed by the American Chemical Society, see the UnitedStates Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention,Inc. (USPC), Rockville, MD
30、, http:/www.usp.org.E1335 08 (2017)2then parted in nitric acid. The insoluble portion is weighed todetermine the gold content. Proof standards are used forcorrection of systematic gravimetric errors.12. Approximate Assay12.1 Perform a preliminary assay first on the test sample toestablish a suitable
31、 composition for the proof correctionstandard and inquarting silver.12.2 Approximate Gold Plus Silver ContentWeigh one500 mg 6 2-mg sample to the nearest 0.1 mg. Weigh a portionof lead foil in accordance with the following:Estimated Total Gold Plus Silver, % Weight of Lead Foil, g95.0 100.0 5.075.0
32、95.0 10.012.2.1 Wrap the sample in the lead foil.12.2.2 CupellationThe cupels are placed in rows in thesection of the furnace having the most uniform temperaturegradient. After the lead foil packets are prepared, place them inthe assay furnace on cupels which have been preheated to900 C for 20 min w
33、ith the draft slightly open. The furnacetemperature is correct if the dark crust which forms over themelted lead packet disappears within a few minutes. A typicaltemperature to produce such reasonably rapid “opening up” ofthe samples is 900 C.12.2.3 After the lead packets have opened up adjust theai
34、rflow through the furnace. The temperature must be main-tained high enough to prevent the button from freezing (thesolidification of molten litharge on the button surface).12.2.4 Keep the cupels in the furnace until all traces of leadhave disappeared. This time depends on the amount of leadused, the
35、 furnace temperature, and the airflow (Note 1).Remove the cupels and slowly cool them to room temperatureeither by placing cupels at the entrance of the furnace with thedoor open or by placing a warmed metal spatula on top of thecupels.NOTE 1Occasionally at the end of the cupellation process, the be
36、adswill visibly brighten or “flash.” This is a result of the sudden release of thelatent heat of fusion as the lead-free bead solidifies.12.2.5 Remove the test samples and any proof beads fromthe cupels, place them on edge and tap them lightly with ahammer to loosen any adhering cupel material. Remo
37、ve theremaining traces of cupel material with a stiff brush.12.2.6 Weigh the dor bead to the nearest 0.1 mg andcalculate the approximate gold plus silver content as follows:Ta5 D/V! 3100 (1)where:Ta= approximate total gold plus silver, %,D = weight of the dor bead, g, andV = weight of the sample, g.
38、12.3 Approximate Gold ContentWeigh one 500 mg 62-mg test sample to the nearest 0.1 mg.Add 1.25 g 6 0.05 g ofinquarting silver and 0.05 g 6 0.010 g copper. Wrap thesample with additions in lead foil as directed in 12.2.12.3.1 Cupel as directed in 12.2.2 12.2.4.12.3.2 Remove the test samples and any p
39、roof beads fromthe cupels, place them on edge and tap them lightly with ahammer to loosen any adhering cupel material. Remove theremaining traces of cupel material with a stiff brush.12.3.3 Form CoronetFlatten the beads for the gold deter-mination on an anvil with a hammer and taper the edges tofaci
40、litate rolling.12.3.4 Anneal the flattened beads to a temperature of 650 Cto 700 C. Pass the beads through a rolling mill to form anelongated strip about 10 cm long and 0.015 cm to 0.03 cm inthickness, maintaining a uniform thickness throughout thebatch of samples. Reanneal the strips and then roll
41、each into aloose spiral (or coronet) with the bottom side facing outward.12.3.5 Parting:12.3.5.1 Place each coronet in a suitable parting container(50-mL porcelain crucible, 50-mL Florence flask, or 50-mLErlenmeyer flask). Add 25 mL of preheated HNO3(1 + 2) andheat at just below the boiling point fo
42、r 45 min. The coronetmust remain completely immersed throughout the partingprocess. Decant and discard the solution. If the coronet breaksapart, care must be taken not to lose any gold pieces.NOTE 2Parting baskets should not be used when determining theapproximate gold content of multiple samples. I
43、f a coronet breaks apart,it will contaminate the other parted samples.12.3.5.2 Add 25 mL of HNO3(2 + 1) and heat at just belowthe boiling point for 45 min. The coronet must remaincompletely immersed throughout the parting process. Decantand wash the gold three times with 25 mL of water.12.3.5.3 Dry
44、the gold on a hotplate, then anneal it tobetween 650 C and 700 C. Cool the gold and weigh to thenearest 0.1 mg.12.3.5.4 Calculate the approximate gold content as follows:Ga5 C/W! 3100 (2)where:Ga= approximate gold, %,C = weight of gold, g, andW = weight of sample, g.12.4 Approximate Silver ContentCa
45、lculate the approxi-mate silver content as follows:Sa5 Ta2 Ga(3)where:Sa= approximate silver, %,Ta= approximate total gold plus silver, % (12.2.6), andGa= approximate gold, % (12.3).12.5 Approximate Base Metal Content Calculate the ap-proximate base metal content, as follows:Ma5 100 2 Ta(4)where:Ma=
46、 approximate base metal content, %, andTa= approximate gold plus silver, % (12.2.6).13. Proof Standard Preparation13.1 Prepare two proof standards, each containing gold,silver, and copper in the amounts listed as follows. Wrap eachproof in lead foil in accordance with 12.2 and proceed to12.2.2.E1335
47、 08 (2017)313.1.1 GoldThe weight of gold must be within 6 5mgofthe approximate gold content (12.3). Weigh the gold to thenearest 0.01 mg and use this weight for calculating the proofcorrection (15.3).13.1.2 SilverThe weight of inquarting silver is 2.5 timesthe approximate gold content (12.3). Weigh
48、the silver to thenearest 10 mg.13.1.3 CopperIf the approximate base metal content(12.5) of the sample is less than 1 %, add 0.05 g 6 0.01 g ofcopper metal to each proof. If the approximate base metalcontent is greater than 1 %, the amount of copper is equal to theapproximate base metal content. Weig
49、h the copper to thenearest 10 mg.14. Procedure14.1 Proof Corrected AssayThis is the final assay for thegold, incorporating corrections for any material losses.14.2 Test Sample PreparationWeigh three 500mg 6 2-mg test samples to the nearest 0.01 mg. Add weighedportions of inquarting silver as follows:Sw52.5 3Ga!2 Sa#3X/100 (5)where:Sw= weight of silver to be added, g 6 0.05 g,Ga= approximate gold, % (12.3),Sa= approximate silver, % (12.4), andX = sample weight, g (14.2).If less than 1 % of base metals are present in the unk
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