ASTM E1805-96
(Test Method)Standard Test Method for Fire Assay Determination of Gold in Copper Concentrates by Gravimetry
Standard Test Method for Fire Assay Determination of Gold in Copper Concentrates by Gravimetry
SCOPE
1.1 This test method is for the determination of gold in copper concentrates in the concentration range from 0.2 to 17 μg/g (0.007 to 0.500 Troy oz/short ton).
Note 1—The lower scope limit is set in accordance with Practice E 1601.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific warning statements, see 11.3.1, 11.5.4, and 11.6.5.
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Designation: E 1805 – 96
Standard Test Method for
Fire Assay Determination of Gold in Copper Concentrates
by Gravimetry
This standard is issued under the fixed designation E 1805; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope remove the lead. The remaining doré bead is parted with nitric
acid to remove the silver and other impurities from the gold.
1.1 This test method is for the determination of gold in
The gold then is cleaned, and weighed on a microbalance.
copper concentrates in the concentration range from 0.2 to 17
μg/g (0.007 to 0.500 Troy oz/short ton).
5. Significance and Use
NOTE 1—The lower scope limit is set in accordance with Practice
5.1 In the metallurgical process used in the mining indus-
E 1601.
tries, gold is often carried along with copper during the
1.2 This standard does not purport to address all of the
flotation concentration process. Metallurgical accounting, pro-
safety concerns, if any, associated with its use. It is the
cess control, and concentrate evaluation procedures for this
responsibility of the user of this standard to establish appro-
type of material depend on an accurate, precise measurement
priate safety and health practices and determine the applica-
of the gold in the copper concentrate. This test method is
bility of regulatory limitations prior to use.
intended to be a reference method for metallurgical laborato-
ries and a referee method to settle disputes in commercial
2. Referenced Documents
transactions.
2.1 ASTM Standards:
5.2 It is assumed that all who use this test method will be
D 1193 Specification for Reagent Water
trained analysts capable of performing common laboratory
E 29 Practice for Using Significant Digits in Test Data to
operations skillfully and safely. It is expected that the work will
Determine Conformance with Specifications
be performed in a properly equipped laboratory under appro-
E 50 Practices for Apparatus, Reagents, and Safety Precau-
priate quality control practices such as those described in
tions for Chemical Analysis of Metals
Guide E 882.
E 135 Terminology Relating to Analytical Chemistry for
6. Interferences
Metals, Ores, and Related Materials
E 691 Practice for Conducting an Interlaboratory Test Pro-
6.1 Elements normally found in copper concentrates do not
gram to Determine the Precision of Test Methods
interfere. High concentrations of arsenic, antimony, tellurium,
E 882 Guide for Accountability and Quality Control in the
bismuth, nickel, and platinum group metals (and, in some
Quality Control Laboratory
instances, copper), however, may interfere with the fusion and
E 1601 Practice for Conducting an Interlaboratory Study to
cupellation steps.
Evaluate the Performance of an Analytical Method
7. Apparatus
3. Terminology
7.1 Analytical Balance, capable of weighing to 0.1 g.
3.1 For definitions of terms used in this test method, refer to
7.2 Semi-Microbalance, capable of weighing to 0.001 mg.
Terminology E 135.
7.3 Assay Mold, 100-mL capacity.
7.4 Cube or Cone Mixer, 1000-g capacity.
4. Summary of Test Method
7.5 Cupel, magnesite or bone ash—40-g lead capacity.
4.1 A test sample of copper concentrate is fused in a clay
7.6 Dry Oven, forced air circulation with temperature con-
crucible. The precious metals are reduced, collected in a lead
trol, 104°C.
button, and then cupelled in a bone ash crucible, (cupel), to
7.7 Fire Assay Bead Brush.
7.8 Fire Assay Bead Pliers.
7.9 Fire Assay Clay Crucible, 20 to 30-sample capacity.
This test method is under the jurisdiction of ASTM Committee E-1 on
Analytical Chemistry for Metals, Ores, and Related Materials and is the direct
7.10 Fire Assay Tongs, crucible and cupel.
responsibility of Subcommittee E01.02 on Ores, Concentrates, and Related Metal-
7.11 Fire Assay Tumble Mixer, an industrial mixer-crucible
lurgical Materials.
tumbler.
Current edition approved April 10, 1996. Published June 1996.
7.12 Hot Plate, with variable temperature control and ven-
Annual Book of ASTM Standards, Vol 03.05.
Annual Book of ASTM Standards, Vol 14.02.
tilation controls for acid fumes.
Annual Book of ASTM Standards, Vol 03.06.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 1805
try again. Increasing the KNO produces a smaller lead button, and
7.13 Fire Assay Muffle Furnace, gas-fired or elec-
decreasing the KNO produces a larger one.
tricequipped with air circulation systems and with draft con-
trols capable of temperatures to 1100°C, accurate to 610°C,
9. Hazards
and with ventilation controls for acid and lead fumes.
9.1 For precautions to be observed in the use of certain
7.14 Jaw Crusher, capable of reducing cupels and slag to 60
reagents in this test method, refer to Practice E 50.
mesh.
7.15 Ring Pulverizer, capable of 250-g minimal capacity.
10. Sampling and Sample Preparation
7.16 Steel Hammer.
10.1 Collect, store, and handle gross samples in accordance
8. Reagents and Materials
with the safety and materials guidelines in Practice E 50. Gross
samples must be free of all extraneous materials.
8.1 Purity of Reagents—Use reagent grade chemicals in all
10.2 Dry the laboratory sample to constant weight at 104°C.
tests. Unless otherwise indicated, all reagents conform to the
10.3 Pass the laboratory sample through a No. 100 (150-
specifications of the Committee on Analytical Reagents of the
μm) sieve, grind the oversize material in a ring mill until it also
American Chemical Society where such specifications are
passes the sieve, and blend the prepared sample in a cube or
available. Other grades may be used provided it is first
cone blender. Obtain the test samples by incremental division
ascertained that the reagents are of sufficiently high purity to
by mixing the prepared sample and spreading it on a flat
permit their use without lessening the accuracy of the deter-
nonmoisture-absorbing surface so that the prepared sample
mination.
forms a rectangle of uniform thickness. Divide into at least 20
8.2 Purity of Water—Unless otherwise indicated, references
segments of equal area. With a flat bottom, square-nose tool,
to water shall be understood to mean reagent water as defined
take scoopfuls of approximately equal size from each segment
by Type T of Specification D 1193.
from the full depth of the bed. Combine the scoopfuls to form
8.3 Ammonium Hydroxide (NH OH).
the test sample.
8.4 Borax Glass (Na B O ).
2 4 7
8.5 Lead Oxide, Litharge, (PbO)—Containing less than
11. Procedure
0.02μ g/g gold and less than 0.40 μg/g silver.
11.1 Crucible Preparation:
8.6 Potassium Carbonate, Potash (K CO ).
2 3
11.1.1 Add 106 g of fire assay flux mixture to each clay fire
8.7 Potassium Nitrate, Niter (KNO ).
assay crucible.
8.8 Silica Sand (SiO )—95 % minimum purity, particle size
11.1.2 Weigh duplicate test samples: 14.583 6 0.001 g ( ⁄2
less than 80 mesh.
assay ton). Record the test sample weights. Transfer the test
8.9 Sodium Chloride, salt (NaCl).
samples to the fire-assay crucibles.
8.10 Silver Foil, 99.9 % purity with less than 0.10-ppm gold
11.1.3 Mix the contents of the crucible for 2 min in a
content.
crucible tumble mixer.
8.11 Silver Solution (1 g/L)—Add 1.557 g silver nitrate to
11.1.4 Inquartation—Based on the preliminary assay or an
1000 mL of water containing 5 mL of nitric acid. Store in a
estimate, dispense the silver solution over the top portion of the
dark bottle.
mixed fire assay clay crucible to achieve an Au to Ag ratio of
8.12 Sodium Carbonate, Soda Ash (Na CO ), anhydrous
2 3
10 to 1. Alternatively, add silver foil in small chips to make the
technical grade.
same ratio.
8.13 Cupel Correction Flux—Blend the following ingredi-
11.1.5 Place 55 g of litharge (PbO) on top of the mixed fire
ents in the listed proportions:
assay clay crucible. Top with 3 g salt, (NaCl).
Borax glass 15 g
11.2 Fusion:
Flour, white wheat 2 g
Lead oxide 30 g 11.2.1 Primary—Place the prepared crucibles carefully into
Potassium carbonate 45 g
a room temperature fire assay furnace. Raise the temperature as
Silica 12 g
rapidly as possible to 600°C and hold at that point until the salt
8.14 Fire Assay Flux Mixture—Blend the following ingre-
cover melts. Elapsed time should be approximately 25 min.
dients in the listed proportions:
11.2.2 Secondary—Increase temperature to 950°C and hold
Borax glass (Na B 0)15g
until slag formation is completed. Time required is about 10
2 4 7
Lead oxide (PbO) 55 g
min.
Potassium carbonate 6g
11.2.3 Tertiary—Increase temperature to 1100°C and let the
(K CO )
2 3
Potassium nitrate (KNO)13g
fusion material liquify completely. Total time in the fire assay
Silica (SiO)6g
furnace for all three fusion stages should be about 45 min.
Sodium carbonate (Na CO)20g
2 3
11.3 Pouring:
NOTE 2—Perform a preliminary fusion to determine lead button weight.
11.3.1 When the fusion is completed, remove the crucible
If a 30 to 40-g lead button is not obtained, adjust the amount of KNO and
with the crucible tongs. Slowly swirl the crucible several times,
tap the crucible lightly on an iron plate or table, then pour the
Reagent Chemicals, American Chemical Society Specifications, American
contents in the fusion assay m
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