1、Designation: E 1335 04e1Standard Test Methods forDetermination of Gold in Bullion by Cupellation1This 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 of last revision.
2、 A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEEditorial changes were made throughout the text in February 2006.1. Scope1.1 These test methods cover cupellation analysis of bullionhavi
3、ng chemical compositions within the following limits:Element Concentration Range, %Gold 0.5 to 4.0 and 20.0 to 99.0Silver 1.0 to 99.5Total gold plus silver 75.0 to 100.01.2 These test methods appear in the following order:Sections20.099.0 % gold 10-160.54.0 % gold 17-2198.999.8 % gold 22-281.3 This
4、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. For specific safetyhaza
5、rds, see Section 8.2. Referenced Documents2.1 ASTM Standards:2B 562 Specification for Refined GoldE 29 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
6、, andRelated MaterialsE 135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE 173 Practice for Conducting Interlaboratory Studies ofMethods for Chemical Analysis of Metals3E 882 Guide for Accountability and Quality Control in theChemical Analysis LaboratoryE 1601 P
7、ractice for Conducting an Interlaboratory Study toEvaluate the Performance of an Analytical MethodE 1763 Guide for Interpretation and Use of Results fromInterlaboratory Testing of Chemical Analysis Methods3. Terminology3.1 Definitions:3.1.1 annealinga thermal treatment to change the proper-ties or g
8、rain structure of the product.3.1.2 cupela small, shallow, porous cup, usually made ofbone ash or magnesite.3.1.3 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 an
9、d tin, are oxidized as well. The oxidized metals areabsorbed into the cupel, leaving a gold and silver dor bead onthe cupel surface.3.1.4 dor beada gold and silver alloy bead which resultsfrom cupellation.3.1.5 inquartationthe addition of silver to an assaysample to facilitate parting.3.1.6 partings
10、eparating silver from gold by selectivelydissolving the silver in acid, usually nitric acid.3.1.7 proofa synthetic standard having a compositionsimilar to the test sample.3.1.8 proof correctionanalyzing the proof concurrentlywith the test sample and using the results to correct the finalassay.3.1.9
11、For definitions of other terms, refer to TerminologyE 135.4. Significance and Use4.1 These test methods 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 of1These test methods are under the
12、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 Oct. 1, 2004. Published November 2004. Originallyapproved in 1990. Last previous edition approved in 20
13、03 as E 1335 03.2For 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.1Copyright ASTM International, 10
14、0 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.performing common fire assay procedures skillfully and safely.It is expected that work will be performed in a properlyequipped laboratory.5. Interferences5.1 If the bullion contains any of the following elements inexce
15、ss 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, Pd, Pt, Rh, Ru) 0.01Selenium 2.0Tellurium 2.0Thallium 2.0Tungsten 0.5Zinc 5.06.
16、Apparatus6.1 Assay FurnaceCapable of temperatures up to 1100C,accurate to 610C, with draft controls.6.2 CupelsMagnesite (MgCO3) or bone ash.6.3 Hammer.6.4 Hammering Block.6.5 Rolling Mill.6.6 Analytical BalanceCapable of weighing to 0.01 mg.6.7 Parting BasketPlatinum basket of porcelain goochcrucibl
17、es in stainless steel basket/vessel.6.7.1 Gooch Porcelain Crucible13 mL capacity, bottomID 18 mn, top ID 29 mn.6.7.2 Stainless Steel Basket316 stainless steel6.7.2.1 parting basket (99 X69 X 1.259)6.7.2.2 parting vessel (109 X 6.759 X49)6.7.2.3 parting vessel lid7. Reagents7.1 Copper Metal, 99.9 % p
18、urity, minimum.7.2 Gold Metal, 99.99 % purity, minimum.7.2.1 Gold metal, 99.999 % purity, minimum for Method Conly.7.3 Lead Foil, 99.99 % purity, min (0.001 % silver, maxi-mum).7.4 Silver Metal, 99.9 % purity, min (0.001 % gold, maxi-mum).8. Hazards8.1 For precautions to be observed in the use of ce
19、rtainreagents and equipment 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 toxic materials and arevolatile at low temperatures. Avoid inhalation, ingest
20、ion, 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 and 3 mm indiameter.9.3 Pin tube samples are prepared from molten metal drawninto
21、 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 (0.005 in.), then clean them with alcohol.9.3.2 Cut the strip into horizontal s
22、lices to obtain the desiredsample weight.9.4 Drillings are not usually representative of a melt. If bardrillings are to be analyzed, obtain them as directed inSpecification B 562.TEST METHOD A10. Scope10.1 This test method covers cupellation analysis of gold inbullion containing 20.0 to 99.0 % gold
23、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 XRF, ICP, DCP or AAS canalso be used for a preliminary assay if they have been shownto have an accuracy of b
24、etter than 6 1 % forAu and 6 2 % forAg. The sample is weighed and silver or copper, or both, addedif necessary. The sample is wrapped in lead foil and cupelled toremove base metals, then parted in nitric acid. The insolubleportion is weighed to determine the gold content. Proofstandards are used for
25、 correction of systematic gravimetricerrors.12. Approximate 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 6 2-mg sample to the nearest 0.1
26、mg. Weigh a portion oflead foil in accordance with the following:Estimated Total Gold Plus Silver, % Weight of Lead Foil, g95.0100.0 5.075.095.0 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 temperatur
27、egradient. After the lead foil packets are prepared, place them inthe assay furnace on cupels which have been preheated to900C for 10 min with the draft slightly open. The furnacetemperature is correct if the dark crust which forms over themelted lead packet disappears within a few minutes. A typica
28、ltemperature to produce such reasonably rapid “opening up” ofthe samples is 900C.12.2.3 After the lead packets have opened up adjust theairflow through the furnace. The temperature must be main-tained high enough to prevent the button from freezing (thesolidification of molten litharge on the button
29、 surface).E133504e1212.2.4 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 slowly cool them to room temperatureeither by placing cupels at the entrance of the
30、 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 release of thelatent heat of fusion as the lead-free bead solidifies.12.2.5 Remove t
31、he test sample dor beads from the cupelsand clean any adhering cupel material from them with a stiffbrush. (see 14.4.)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! 3 100 (1)where:Ta= approximate total gold plus silver, %,D =
32、 weight of the dor bead, g, andV = weight of the sample, g.12.3 Approximate Gold ContentWeigh one 500 6 2-mgtest sample to the nearest 0.1 mg. Add 1.25 6 0.05 g ofinquarting silver and 0.05 6 0.010 g copper. Wrap the samplewith additions in lead foil as directed in 12.2.12.3.1 Cupel as directed in 1
33、2.2.2-12.2.4.12.3.2 Remove the test samples and any proof beads fromthe cupels, place them on edge and tap them lightly 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
34、 on an anvil with a hammer and taper the edges tofacilitate rolling.12.3.4 Anneal the flattened beads to a temperature of 650 to700C. Pass the beads through a rolling mill to form anelongated strip about 10 cm long and 0.005 to 0.01 cm inthickness, maintaining a uniform thickness throughout thebatch
35、 of samples. Reanneal the strips and then roll 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 HNO3(1 + 2) and he
36、at at justbelow the boiling point for 45 min, or until the evolution ofNOx fumes has ceased. The coronet must remain completelyimmersed throughout the parting process. Decant and discardthe solution.12.3.5.2 Add 25 mL of HNO3(2 + 1) and heat at just belowthe boiling point for 45 min. The coronet mus
37、t 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 and 700C. Cool the gold and weigh to the nearest0.1 mg.12.3.5.4 Calculate the approximate gold content as follows:Ga5
38、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)where:Sa= approximate silver, %,Ta= approximate total gold plus silver, % (12.2.6), andGa= approximate gold,
39、% (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 silver, % (12.2.6).13. Proof Standard Preparation13.1 Prepare two proof standards, each containing gold,silv
40、er, 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 65mgofthe approximate gold content (12.3). Weigh the gold to thenearest 0.01 mg and use this weight for calculating the proofcorrecti
41、on (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(12.5) of the sample is less than 1 %, add 0.056 0.01 g ofcopper metal to each proof. If the approximate base
42、 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 the final assay for thegold, incorporating corrections for any material losses.14.2 Test Sample PreparationWeigh
43、three 500 6 2-mgtest samples to the nearest 0.01 mg. Add weighed portions ofinquarting silver as follows:Sw5 2.5 3 Ga! 2 Sa# 3 X/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 %
44、of base metals are present in the unknown,add 0.05 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 portion of the foil.14.3 Cupel as directed in 12.2.2. Alternate the three testsamples with the two proof standards in each ro
45、w.14.4 Remove the test samples and any proof beads from thecupels, place them on edge and tap them lightly with a hammerE133504e13to loosen any adhering cupel material. Remove the remainingtraces of cupel material with a stiff brush.14.5 Form the coronets as directed in 12.3.3.14.6 Part the test sam
46、ples 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.NOTE 2Parting solutions
47、may be retained to check the gold content byinstrumental methods.15. Calculation (Proof-Corrected Assay)15.1 Calculate the average percent gold. For each golddetermination sample calculate as follows:Gu5 O/Z! 3 100 (6)where:Gu= gold, uncorrected, %,O = weight of gold found, g, andZ = weight of sampl
48、e, g.15.2 Average the three replicates Gu.15.3 Calculate the proof correction, P, for each gold deter-mination proof standard as follows:P 5 Q/O (7)where:P = proof correction,Q = weight of gold added, g, andO = weight of gold found, g.A successful analysis should have proof corrections fallingbetwee
49、n 0.99XX and 1.00XX. (See supporting data RR:E01-1010 and ASTM proficiency test program for Au in bullion.)15.4 Average the two proof standard corrections, P.15.5 Calculate the proof-corrected gold percent as follows:Gc5 Gu3 P(8)where Gc= gold, corrected, %.16. Precision and Bias16.1 PrecisionTen laboratories cooperated in testingSamples 1 through 4 and seven laboratories in Samples 5 and6.4Their data is summarized in Table 1. Testing and statisticalanalysis were performed in accordance with Practice E 173.16.1.1 ReproducibilityT
