1、Designation: E 1335 08Standard Test Methods forDetermination of Gold in Bullion by Fire Assay CupellationAnalysis1This standard is issued under the fixed designation E 1335; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、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 following limits:El
3、ement 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 10-170.5 % 4.0 % gold 18-2398.9 % 99.8 % gold 24-301.3 The values stated in SI units are to be regarded as
4、standard. 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 determine the
5、applica-bility of regulatory limitations prior to use. For specific safetyhazards, see Section 8.2. Referenced Documents2.1 ASTM Standards:2B 562 Specification for Refined GoldE50 Practices for Apparatus, Reagents, and Safety Consid-erations for Chemical Analysis of Metals, Ores, andRelated Material
6、sE 135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE 173 Practice for Conducting Interlaboratory Studies ofMethods for Chemical Analysis of Metals3E 1601 Practice for Conducting an Interlaboratory Study toEvaluate the Performance of an Analytical Method3. Termi
7、nology3.1 DefinitionsFor definitions of terms used in these testmethods, refer to Terminology E 135.3.2 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 small, shallow, porous cup, usually made ofbon
8、e 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. The oxidized metals areabsorbed into the cupel, l
9、eaving 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 assaysample to enable parting.3.2.6 partthe separation of silver from gold by selectivelydissolving the silver in acid, usuall
10、y 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.4. Significance and Use4.1 These test methods are intended for the determinat
11、ion 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.1These test methods are under t
12、he jurisdiction of ASTM Committee E01 onAnalytical Chemistry for Metals, Ores, and Related Materials and are the directresponsibility of Subcommittee E01.03 on Precious Metals.Current edition approved Nov. 1, 2008. Published December 2008. Originallyapproved in 1990. Last previous edition approved i
13、n 2004 as E 1335 04e1.2For 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 Document Summary page onthe ASTM website.3Withdrawn. The last approved version o
14、f this historical standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Interferences5.1 If the bullion contains any of the following elements inexcess of the concentrations shown, the accuracy and
15、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, Pd, Pt, Rh, Ru) 0.01Selenium 2.0Tellurium 2.0Thallium 2.0Tungsten 0.5Zinc 5.06. Apparatus6.1 Assay FurnaceCapable of temperatures
16、 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, capable 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 porcel
17、ain 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 Basket316 stainless steel.7. Reagents47.1 Copper Metal, 99.9 % purity, minimum; 0.0005 % gold,maximum.7.2 Gold Metal, 99.99 % purity,
18、 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 Silver Metal, 99.9 % purity, minimum (0.0005 % gold,maximum).7.5 Nitric Acid, 0.0002 % chloride, maximum.7.6 CupelsMagnesium oxide or
19、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 hot crucibles and operatingfurnaces to avoid personal injury by either burn or electricalshock.8.3 Lead and litharge (PbO) are toxi
20、c 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 adhering glass or flux.9.2 Prepare shot samples from molten metal poured intowater. Use only whole single pieces between 1 mm and 3
21、 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 not hollow and that they arefree from slag and inclusions.9.3.1 Roll the samples lengthwise on a clean rolling mill to0.127 mm, th
22、en 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 tube or shot samples. If bar drillings are to be analyzed,obtain them as directed in Specification B 562.TEST METHOD A10. Scope10.1
23、 This test method covers cupellation analysis of gold inbullion containing 20.0 % to 99.0 % gold and 1.0 % to 80.0 %silver.11. Summary of Test Method11.1 A preliminary assay is performed to estimate theapproximate gold content and approximate gold plus silvercontent. Other methods such as X-ray fluo
24、rescence (XRF),inductively coupled plasma emission (ICP), direct currentplasma emission (DCP), or atomic absorption spectroscopy(AAS) can also be used 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 silve
25、r orcopper, or both, added if necessary. The sample is wrapped andcompacted in lead foil and cupelled to remove base metals,then parted in nitric acid. The insoluble portion is weighed todetermine the gold content. Proof standards are used forcorrection of systematic gravimetric errors.12. Approxima
26、te Assay12.1 Perform a preliminary assay first on the test sample toestablish a suitable 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
27、 following:Estimated Total Gold Plus Silver, % Weight of Lead Foil, g95.0 100.0 5.075.0 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,
28、 place them in4Reagent Chemicals, American Chemical Society Specifications, 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,
29、 U.K., http:/, and the United States Pharmacopeia and National Formulary, U.S.Pharmacopeial Convention, Inc. (USPC), Rockville, MD, http:/www.usp.org.E1335082the assay furnace on cupels which have been preheated to900 C for 20 min with the draft slightly open. The furnacetemperature is correct if th
30、e 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 theairflow through the furnace. The temperature must be main-tained high
31、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 furnace temperature, and the airflow (Note 1).Remove the cupels and
32、 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 beadswill visibly brighten or “flash.” This is a result of the sudden
33、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. Remove theremaining traces of cupel material with a stiff brush.12.2.6 W
34、eigh the dor bead to the nearest 0.1 mg andcalculate the approximate gold plus silver content as follows:Ta5 D/V! 3 100 (1)where:Ta= approximate total gold plus silver, %,D = weight of the dor bead, g, andV = weight of the sample, g.12.3 Approximate Gold ContentWeigh one 500 mg 62-mg test sample to
35、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 proof beads fromthe cupels, place them on edge and tap them lightly
36、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 tofacilitate rolling.12.3.4 Anneal the flattened beads to a temperature o
37、f 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 each into aloose spiral (or coronet) with the bottom side facing ou
38、tward.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 for 45 min. The coronetmust remain completely immersed throughout the
39、 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. If a coronet breaks apart,it will contaminate the other parted sampl
40、es.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 the gold on a hotplate, then anneal it tobetween 650 C and 700 C. C
41、ool the gold and weigh to thenearest 0.1 mg.12.3.5.4 Calculate the approximate gold content as follows:Ga5 C/W! 3 100 (2)where:Ga= approximate gold, %,C = weight of gold, g, andW = weight of sample, g.12.4 Approximate Silver ContentCalculate the approxi-mate silver content as follows:Sa5 Ta2 Ga(3)wh
42、ere: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= approximate base metal content, %, andTa= approximate gold plus s
43、ilver, % (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 to12.2.2.13.1.1 GoldThe weight of gold must be within 6 5mgofthe approximate gol
44、d 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 the silver to thenearest 10 mg.13.1.3 CopperIf the approximate base metal content(
45、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. Weigh the copper to thenearest 10 mg.14. Procedure14.1 Proof Corrected AssayThis is th
46、e 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:Sw5 2.5 3 Ga! 2 Sa# 3 X/100 (5)E1335083where:Sw= weight of silver to be added, g
47、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 unknown,add 0.05 g 6 0.010 g of copper metal to each sample. Weighthree portions of lead foil in accordance with 12.2 and wrapeach sample in a p
48、ortion of the foil.14.3 Cupel as directed in 12.2.2. Alternate the three testsamples with the two proof standards in each row.14.4 Remove the test samples and any proof beads from thecupels, place them on edge and tap them lightly with a hammerto loosen any adhering cupel material. Remove the remain
49、ingtraces of cupel material with a stiff brush.14.5 Form the coronets as directed in 12.3.3.14.6 Part the test samples and proofs as directed in 12.3.5.For accurate results, the parting conditions for the proofs andsamples must be as close as possible. To this end, use of aparting basket or use of individual Bunsen Burners to controlthe time and temperature of the parting is recommended.15. Calculation (Proof-Corrected Assay)15.1 Calculate the average percent gold. For each golddetermination sample calculate as follow
