1、Designation: E 1805 07Standard Test Method forFire Assay Determination of Gold in Copper Concentratesby Gravimetry1This standard is issued under the fixed designation E 1805; 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method is for the determination of gold incopper concentrates in the concentration range from 0.2 to 17
3、g/g (0.007 to 0.500 Troy oz/short ton).NOTE 1The lower scope limit is set in accordance with PracticeE 1601.1.2 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
4、and health practices and determine the applica-bility of regulatory limitations prior to use. For specificwarning statements, see 11.3.1, 11.5.4, and 11.6.5.2. Referenced Documents2.1 ASTM Standards:2D 1193 Specification for Reagent WaterE29 Practice for Using Significant Digits in Test Data toDeter
5、mine Conformance with SpecificationsE50 Practices for Apparatus, Reagents, and Safety Consid-erations for Chemical Analysis of Metals, Ores, andRelated MaterialsE 135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE 691 Practice for Conducting an Interlaboratory S
6、tudy toDetermine the Precision of a Test MethodE 882 Guide for Accountability and Quality Control in theChemical Analysis LaboratoryE 1601 Practice for Conducting an Interlaboratory Study toEvaluate the Performance of an Analytical Method3. Terminology3.1 For definitions of terms used in this test m
7、ethod, refer toTerminology E 135.4. Summary of Test Method4.1 A test sample of copper concentrate is fused in a claycrucible. The precious metals are reduced, collected in a leadbutton, and then cupelled to remove the lead. The remainingdor bead is parted with nitric acid to remove the silver andoth
8、er impurities from the gold. The gold then is cleaned, andweighed on a microbalance.5. Significance and Use5.1 In the metallurgical process used in the mining indus-tries, gold is often carried along with copper during theflotation concentration process. Metallurgical accounting, pro-cess control, a
9、nd concentrate evaluation procedures for thistype of material depend on an accurate, precise measurementof the gold in the copper concentrate. This test method isintended to be a reference method for metallurgical laborato-ries and a referee method to settle disputes in commercialtransactions.5.2 It
10、 is assumed that all who use this test method will betrained analysts capable of performing common laboratoryoperations skillfully and safely. It is expected that the work willbe performed in a properly equipped laboratory under appro-priate quality control practices such as those described inGuide
11、E 882.6. Interferences6.1 Elements normally found in copper concentrates do notinterfere. High concentrations of arsenic, antimony, tellurium,bismuth, nickel, and platinum group metals (and, in someinstances, copper), however, may interfere with the fusion andcupellation steps.7. Apparatus7.1 Analyt
12、ical Balance, capable of weighing to 0.1 g.7.2 Semi-Microbalance, capable of weighing to 0.001 mg.7.3 Assay Mold, 100-mL capacity.7.4 Cube or Cone Mixer, 1000-g capacity.7.5 Cupel, magnesite or bone ash40-g lead capacity.7.6 Dry Oven, forced air circulation with temperature con-trol, 104 C.7.7 Fire
13、Assay Bead Brush.7.8 Fire Assay Bead Pliers.7.9 Fire Assay Clay Crucible, 20 to 30-g sample capacity.1This test method is under the jurisdiction of ASTM Committee E01 onAnalytical Chemistry for Metals, Ores and Related Materials and is the directresponsibility of Subcommittee E01.02 on Ores, Concent
14、rates, and Related Metal-lurgical Materials.Current edition approved June 1, 2007. Published June 2007. Originallyapproved in 1996. Last previous edition approved in 2002 as E 1805 - 02.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceas
15、tm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.7.10 Fire Assay Tongs, crucible and cupel.7.11 Fire Assay Tu
16、mble Mixer, an industrial mixer-crucibletumbler.7.12 Hot Plate, with variable temperature control and ven-tilation controls for acid fumes.7.13 Fire Assay Muffle Furnace, gas-fired or elec-tricequipped with air circulation systems and with draft con-trols, capable of temperatures to 1100 C 6 10 C, a
17、nd withventilation controls for acid and lead fumes.7.14 Jaw Crusher, capable of reducing cupels and slag to 60mesh.7.15 Ring Pulverizer, capable of 250-g minimal capacity.7.16 Steel Hammer.8. Reagents and Materials8.1 Purity of ReagentsUse reagent grade chemicals in alltests. Unless otherwise indic
18、ated, all reagents conform to thespecifications of the Committee on Analytical Reagents of theAmerican Chemical Society where such specifications areavailable. Other grades may be used provided it is firstascertained that the reagents are of sufficiently high purity topermit their use without lessen
19、ing the accuracy of the deter-mination.38.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water as definedby Type T of Specification D 1193.8.3 Ammonium Hydroxide (NH4OH).8.4 Borax Glass (Na2B4O7).8.5 Lead Oxide, Litharge, (PbO)Containing less than
20、0.02 g/g gold and less than 0.40 g/g silver.8.6 Potassium Carbonate, Potash (K2CO3).8.7 Potassium Nitrate, Niter (KNO3).8.8 Silica Sand (SiO2)95 % minimum purity, particle sizeless than 80 mesh.8.9 Sodium Chloride, salt (NaCl).8.10 Silver Foil, 99.9 % purity with less than 0.10-ppm goldcontent.8.11
21、Silver Solution (1 g/L)Add 1.557 g silver nitrate to1000 mL of water containing 5 mL of nitric acid. Store in adark bottle.8.12 Sodium Carbonate, Soda Ash (Na2CO3), anhydroustechnical grade.8.13 Cupel Correction FluxBlend the following ingredi-ents in the listed proportions:Borax glass 15 gFlour, wh
22、ite wheat 2 gLead oxide 30 gPotassium carbonate 45 gSilica 12 g8.14 Fire Assay Flux MixtureBlend the following ingre-dients in the listed proportions:Borax glass (Na2B407)15gLead oxide (PbO) 55 gPotassium carbonate(K2CO3)6gPotassium nitrate (KNO3)13Silica (SiO2)6Sodium carbonate (Na2CO3)20gNOTE 2Per
23、form a preliminary fusion to determine lead button weight.If a 30 to 40-g lead button is not obtained, adjust the amount of KNO3andtry again. Increasing the KNO3produces a smaller lead button, anddecreasing the KNO3produces a larger one.9. Hazards9.1 For precautions to be observed in the use of cert
24、ainreagents in this test method, refer to Practice E50.10. Sampling and Sample Preparation10.1 Collect, store, and handle gross samples in accordancewith the safety and materials guidelines in Practice E50. Grosssamples must be free of all extraneous materials.10.2 Dry the laboratory sample to const
25、ant weight at 104C.10.3 Grind the laboratory sample in a ring mill so that100 % passes through a No. 100 (150-m) sieve and blend theprepared sample in a cube or cone blender, if necessary tofurther reduce the heterogeneity of the laboratory sample.Obtain the test samples by incremental division by m
26、ixing theprepared sample and spreading it on a flat non moisture-absorbing surface so that the prepared sample forms a rectangleof uniform thickness. Divide into at least 20 segments of equalarea. With a flat bottom, square-nose tool, take scoopfuls ofapproximately equal size from each segment from
27、the fulldepth of the bed. Combine the scoopfulls to form the testsample.NOTE 3Verify the adequacy of the grind on a separate sub-sample, donot pass the laboratory sample through the No. 100 sieve.11. Procedure11.1 Crucible Preparation:11.1.1 Add 106 g of fire assay flux mixture to each clay fireassa
28、y crucible.11.1.2 Weigh duplicate test samples: 14.583 6 0.001 g (12assay ton). Record the test sample weights. Transfer the testsamples to the fire-assay crucibles.11.1.3 Mix the contents of the crucible for 2 min in acrucible tumble mixer.11.1.4 InquartationBased on the preliminary assay or anesti
29、mate, dispense the silver solution over the top portion of themixed fire assay clay crucible to achieve an Ag to Au ratio of10 to 1. Alternatively, add silver foil in small chips to make thesame ratio.11.1.5 Place 55 g of PbO on top of the mixed fire assay claycrucible. Top with 3 g NaCl.11.2 Fusion
30、:3Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Reagent Chemicals and Standards,byJosepdh Rosin, D. Nostrand Co., Inc., New York, NY, and the United St
31、atesPharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc.(USPC), Rockville, MD.TABLE 1 Troy ConversionDesired Units Conversion Factorppm, mg/kg or g/metric ton 1Troy oz/short ton 0.02917E180507211.2.1 PrimaryPlace the prepared crucibles carefully intoa room temperature fire assay
32、furnace. Raise the temperature asrapidly as possible to 600 C and hold at that point until the saltcover melts. Elapsed time should be approximately 25 min.11.2.2 SecondaryIncrease temperature to 950 C and holduntil slag formation is completed. Time required is about 10min.11.2.3 TertiaryIncrease te
33、mperature to 1100 C and letthe fusion material liquefy completely. Total time in the fireassay furnace for all three fusion stages should be about 45min.11.3 Pouring:11.3.1 When the fusion is completed, remove the cruciblewith the crucible tongs. Slowly swirl the crucible several times,tap the cruci
34、ble lightly on an iron plate or table, then pour thecontents in the fusion assay mold. (Warning Rapidlycooling slag may eject sharp flying fragments. Cover the moldwith a wire screen immediately after pouring.)11.3.2 Save the crucible from the fusion for the slag andcupel correction procedure (see 1
35、1.8.1).11.4 Lead Separation:11.4.1 After cooling, separate the lead button from the slagby tapping with a steel hammer. Save the slag for correctionprocedure (see 11.8). Carefully hammer the lead button into asquare shape, completely removing any adhering slag from thesurface.11.4.2 Save the slag fr
36、om the fusion for the slag and cupelcorrection procedure (see 11.8.1).11.5 Cupellation:11.5.1 Place cupels into the furnace and preheat at 900 Cfor 30 min.11.5.2 Quickly place a lead button prepared as described in11.4.1 onto each cupel. The lead button will melt into a brightlead puddle that will s
37、oon form a dark crust with the formationof surface PbO. The furnace temperature must be greater than888 C, the melting point of PbO. This step should beaccomplished within 1 to 2 min.11.5.3 After 5 min, open the draft to the furnace, anddecrease the temperature to 820 C. The ventilation should bereg
38、ulated. If the temperature and draft conditions are correct, afringe of PbO crystals, known as “feathers” will appear aroundthe upper edge of the bone ash cupel.11.5.4 When the process of cupellation is near the end, oilyappearing drops of PbO can be seen to collect on the surface ofthe remaining do
39、r bead. These cause a rainbow color band tomove swiftly over the surface of the dor bead giving theillusion that the bead is revolving on a shifting axis. When thelast trace of PbO has been removed, this play of colorsdisappears and the dor bead becomes duller than a normalmetallic luster. At this p
40、oint remove the cupels from thefurnace and allow them to cool. (WarningHot cupels emitlead fumes. Use proper ventilation.)11.5.5 Remove the dor bead containing the precious metalfrom the cool cupel with bead pliers or tongs.11.5.5.1 Save the cupel from the cupellation for the slag andcupel correctio
41、n procedure (see 11.8.1).11.5.6 Brush the dor bead with a bead brush to remove anyadhering cupel material.11.6 Parting:11.6.1 Flatten the dor bead with a hammer, then place it ina 50-mL porcelain crucible.411.6.2 Add 25 mL HNO3(1 + 7) to the crucible with thedor bead. Place the crucible on a hot pla
42、te at 95 C and heatfor 30 min. Carefully decant the spent parting solution anddispose of properly.11.6.3 Repeat the parting and decanting step of 11.6.2 asecond time.11.6.4 Add 25 mL of HNO3(3 + 1) to the crucible. Heat for25 min. Carefully decant the spent parting solution and discard.11.6.5 Wash t
43、he bead twice with NH4OH (1 + 9) to dissolveany sliver chloride (AgCl2). Discard the liquid. (WarningStronger NH4OH solutions left in the porcelain crucible to“soak” the bead can form ammonium nitrates which mayexplode under certain conditions.)11.6.6 Dry beads in porcelain cups on a hot plate.11.6.
44、7 Anneal the remaining gold at 650 C, then cool.Black or other colored deposits remaining inside the crucibleindicate inadequate washing. Off-colored gold indicates thepresence of impurities.11.7 WeighingWeigh the remaining gold bead to thenearest 0.001 mg and record.11.8 Corrections:11.8.1 Combine
45、the slag and cupels from the duplicatefusions for each test sample, weigh the total, and record.11.8.2 Crush the slag-cupel mixture for each test sampleuntil 100 % passes a No. 60 (250-m) sieve.4Bugbee, E. E., “A Textbook of Fire Assaying,” John Wiley 0.0, ;0.1, or ; 0.2g/g Au as appropriate).13.3 R
46、eport results that are within the range in accordancewith 1.1 as the average of the duplicates rounded to the nearest0.1 g/g Au in accordance with Practice E29, roundingmethod.13.4 Conversion to other measurement units can be made bymultiplying the result by the appropriate number using Table 1.Troy
47、 ounce per ton results are rounded to the nearest 0.001oz/short ton, in accordance with Practice E29, roundingmethod.14. Precision and Bias514.1 PrecisionAn interlaboratory study on this testmethod was conducted with three materials analyzed by sevencooperating laboratories. The interlaboratory test
48、 data wasevaluated using Practice E 691 and is summarized in Table 2.14.1.1 Repeatability increases with gold content for thethree materials tested, in the range from 0.05 to 0.41 g/g gold.14.1.2 Reproducibility also increases with the gold contentfor the three materials tested, in the range from 0.
49、12 to 0.64g/g gold. The lower scope limit for the method was set at twotimes R for Material A, at 0.24 g/g gold.14.2 BiasThe bias of this test method was determined byanalysis of two certified reference materials in a single labo-ratory on two separate days, and the results are shown in Table3. The average values determined were slightly lower than thecertified values of the reference materials tested, but thedifferences were within the reproducibility limits of the methoddetermined in the interlaboratory study, thus no significant bia
