SIST ISO 10378:2006
(Main)Copper, lead and zinc sulfide concentrates -- Determination of gold and silver -- Fire assay gravimetric and flame atomic absorption spectrometric method
Copper, lead and zinc sulfide concentrates -- Determination of gold and silver -- Fire assay gravimetric and flame atomic absorption spectrometric method
This International Standard specifies a fire assay gravimetric and flame atomic absorption spectrometric method for the determination of the mass fraction of gold and silver in copper, lead and zinc sulfide concentrates as follows: - Copper concentrates: The method is applicable to the determination of mass fractions of gold from 0,5 g/t to 300 g/t and of mass fractions of silver from 25 g/t to 1 500 g/t in copper sulfide concentrates containing mass fractions of copper from 15 % to 60 %. - Lead concentrates The method is applicable to the determination of mass fractions of gold from 0,1 g/t to 25 g/t and of mass fractions of silver from 200 g/t to 3 500 g/t in lead sulfide concentrates containing mass fractions of lead from 10 % to 80 %. - Zinc concentrates The method is applicable to the determination of mass fractions of gold from 0,1 g/t to 12 g/t and of mass fractions of silver from 10 g/t to 800 g/t in zinc sulfide concentrates containing mass fractions of zinc up to 60 %.
Concentrés de sulfure de cuivre, de plomb et de zinc -- Dosage de l'or et de l'argent -- Méthode gravimétrique par essai au feu et spectrométrie d'absorption atomique dans la flamme
Koncentrati bakrovih, svinčevih in cinkovih sulfidov – Določevanje zlata in srebra – Plamenska analizna gravimetrijska in plamenska atomska absorpcijska spektrometrijska metoda
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INTERNATIONAL ISO
STANDARD 10378
Second edition
2005-07-01
Copper, lead and zinc sulfide
concentrates — Determination of gold
and silver — Fire assay gravimetric and
flame atomic absorption spectrometric
method
Concentrés sulfurés de cuivre, de plomb et de zinc — Dosage de l'or et
de l'argent — Méthode gravimétrique par essai au feu et spectrométrie
d'absorption atomique dans la flamme
Reference number
ISO 10378:2005(E)
©
ISO 2005
---------------------- Page: 1 ----------------------
ISO 10378:2005(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
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Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
© ISO 2005
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2005 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 10378:2005(E)
Contents Page
Foreword. v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Principle. 2
3.1 Fusion . 2
3.2 Cupellation . 2
3.3 Parting. 2
3.4 Retreatment . 2
3.5 Correction for blank contamination. 2
4 Reagents. 2
5 Apparatus . 4
6 Sample . 5
6.1 Test sample . 5
6.2 Test portion . 5
7 Procedure . 5
7.1 Number of determinations . 5
7.2 Trial fusion. 5
7.3 Blank tests. 5
7.4 Charge preparation. 6
7.5 Primary fusion. 7
7.6 Cupellation . 7
7.7 Retreatment of residues. 8
7.8 Determination of gold in the primary bead . 8
7.9 Determination of gold and silver in secondary beads and blanks, and of silver in prills. 9
7.10 Determination of silver in the parting solution. 11
8 Expression of results . 11
8.1 Mass fraction of gold. 11
8.2 Mass fraction of silver. 12
9 Precision. 13
9.1 Expression of precision . 13
9.2 Method for obtaining the final result (see Annex H) . 14
9.3 Precision between laboratories. 15
9.4 Check of trueness. 17
9.4.1 General. 17
9.4.2 Type of certified reference material (CRM) or reference material (RM) . 17
10 Test report . 18
Annex A (normative) Procedure for the preparation and determination of the mass of a predried
test portion . 19
Annex B (normative) Trial fusion. 21
Annex C (normative) Blank determination . 22
Annex D (normative) Inquartation .23
Annex E (normative) Determination of vaporization loss of silver during the cupellation process . 24
Annex F (normative) Sulfuric acid - Parting . 25
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ISO 10378:2005(E)
Annex G (normative) Determination of impurities in parting solutions and washings. 27
Annex H (normative) Flowsheet of the procedure for the acceptance of analytical values for test
samples (see 9.2) . 31
Annex I (informative) Flowsheet of the method. 32
Annex J (informative) Roasting method. 33
Annex K (informative) Guide to the preparation of dilutions for the determination of silver in
parting solutions and residues. 34
Annex L (informative) Derivation of precision equations. 35
Bibliography . 52
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ISO 10378:2005(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 10378 was prepared by Technical Committee ISO/TC 183, Copper, lead, zinc and nickel ores and
concentrates.
This second edition cancels and replaces the first edition (ISO 10378:1994), which has been technically
revised.
© ISO 2005 – All rights reserved v
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ISO 10378:2005(E)
Introduction
This International Standard describes a method for the determination of the mass fraction of gold and silver in
copper, lead and zinc sulfide concentrates. This International Standard was prepared to enable laboratories to
determine the mass fraction of gold and silver in suitable samples using instrumental methods.
vi © ISO 2005 – All rights reserved
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INTERNATIONAL STANDARD ISO 10378:2005(E)
Copper, lead and zinc sulfide concentrates — Determination of
gold and silver — Fire assay gravimetric and flame atomic
absorption spectrometric method
WARNING — This International Standard may involve hazardous materials, operations and equipment.
It is the responsibility of the user of this International Standard to establish appropriate health and
safety practices and determine the applicability of regulatory limitations prior to use.
1 Scope
This International Standard specifies a fire assay gravimetric and flame atomic absorption spectrometric
method for the determination of the mass fraction of gold and silver in copper, lead and zinc sulfide
concentrates as follows:
Copper concentrates:
The method is applicable to the determination of mass fractions of gold from 0,5 g/t to 300 g/t and of
mass fractions of silver from 25 g/t to 1 500 g/t in copper sulfide concentrates containing mass fractions of
copper from 15 % to 60 %.
Lead concentrates
The method is applicable to the determination of mass fractions of gold from 0,1 g/t to 25 g/t and of mass
fractions of silver from 200 g/t to 3 500 g/t in lead sulfide concentrates containing mass fractions of lead
from 10 % to 80 %.
Zinc concentrates
The method is applicable to the determination of mass fractions of gold from 0,1 g/t to 12 g/t and of mass
fractions of silver from 10 g/t to 800 g/t in zinc sulfide concentrates containing mass fractions of zinc up to
60 %.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 385-1:1984, Laboratory glassware — Burettes — Part 1: General requirements
ISO 648:1977, Laboratory glassware — One-mark pipettes
ISO 1042:1998, Laboratory glassware — One-mark volumetric flasks
ISO 3696:1987, Water for analytical laboratory use — Specification and test methods
ISO 4787:1984, Laboratory glassware — Volumetric glassware — Methods for use and testing of capacity
ISO 9599:1991, Copper, lead and zinc sulfide concentrates — Determination of hygroscopic moisture in the
analysis sample — Gravimetric method
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ISO 10378:2005(E)
3 Principle
Fire assaying for the determination of gold and silver comprises a series of steps to separate firstly the
precious metals from most of the associated metals, followed by separation of the gold from silver and other
metals preconcentrated into a precious-metal alloy.
The stages that comprise the determinations are described in 3.1 to 3.5 inclusive.
3.1 Fusion
The samples are fused in a crucible after mixing with a litharge-based flux which, under reducing conditions,
collects the precious metals in a metallic lead button.
3.2 Cupellation
The base metals present in the lead button are substantially separated from the precious metals by oxidizing
fusion. Cupellation produces a bead largely comprising a silver-gold alloy with small quantities of other metals.
3.3 Parting
Gold is separated from the primary bead by treatment with nitric acid. The gold prill is weighed. Gold prills
having a mass less than 50 µg are dissolved in aqua regia and the gold is determined by atomic absorption
spectrometry (AAS). Silver is determined in the parting solution by AAS.
3.4 Retreatment
All residues are retreated to maximize the recovery of gold and silver. The addition of collectors for either gold
or silver is not required, as both metals are present in sufficient amounts to be readily visible after the
cupellation stage. The second bead is dissolved in acids followed by analysis of both metals by AAS.
3.5 Correction for blank contamination
Contamination by gold and silver impurities in the reagents is corrected for by fusing the reagents without the
test portion.
4 Reagents
During the analysis, use only reagents of recognized analytical grade and water that complies with grade 2 of
ISO 3696.
4.1 Sodium carbonate, anhydrous.
4.2 Litharge (PbO), assay grade having a mass fraction of gold of less than 0,01 g/t and a mass fraction of
silver of less than 0,2 g/t.
4.3 Silica, precipitated.
4.4 Potassium nitrate or sodium nitrate
NOTE If sodium nitrate is used, the masses specified for potassium nitrate will have to be modified:
85,0
gof KNO×= gof NaNO
33
101,1
4.5 Flour
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ISO 10378:2005(E)
4.6 Borax, fused anhydrous sodium tetraborate (borax glass powder).
4.7 Nitric acid, concentrated (ρ 1,42 g/ml), chloride concentration < 0,5 µg/ml.
20
4.8 Nitric acid, diluted 1+1.
Slowly add 500 ml of concentrated nitric acid (4.7) to 500 ml of water, while stirring.
4.9 Lead, foil, having a mass fraction of gold of less than 0,01 g/t and a mass fraction of silver of less than
0,2 g/t.
4.10 Silver, of minimum purity 99,99 %.
4.11 Hydrochloric acid (ρ 1,16 g/ml to 1,19 g/ml).
20
4.12 Thiourea, 10 g/l solution.
Add 1 g of thiourea to 100 ml of water.
4.13 Aqua regia
Mix 3 parts of hydrochloric acid (4.11) with 1 part of nitric acid (4.7). Prepare freshly as required.
4.14 Standard solutions
Standard solutions should be prepared at the same ambient temperature as that at which the determinations
will be conducted.
4.14.1 Silver, standard stock solution A (500 µg of Ag/ml).
Weigh 0,500 0 g of silver metal to the nearest 0,1 mg. Transfer to a 100 ml beaker, add 20 ml of diluted nitric
acid (4.8) and warm to dissolve. Cool and add 20 ml of concentrated nitric acid (4.7). Transfer to a 1 000 ml
volumetric flask, fill up with water nearly to the mark, mix and cool to room temperature; then fill up exactly to
the mark and mix again.
4.14.2 Silver, standard solution B (50 µg of Ag/ml).
Pipette 10,00 ml of silver standard stock solution A (4.14.1) into a 100 ml volumetric flask, fill up with water
nearly to the mark, mix and cool to room temperature; then fill up exactly to the mark and mix again.
Prepare a fresh solution per batch.
4.14.3 Gold, standard solution (1000 µg of Au/ml).
Weigh 1,000 g of gold metal to the nearest 0,1 mg. Transfer to a 200 ml beaker, add 25 ml of aqua regia
solution (4.13) and warm to dissolve. Cool and transfer to a 1 000 ml volumetric flask. Add 75 ml of
hydrochloric acid (4.11), fill up nearly to the mark with water, mix and cool to room temperature; then fill up
exactly to the mark and mix again.
4.14.4 Gold and silver, standard solution (100 µg of Au/ml + 50 µg of Ag/ml).
Pipette 10,00 ml of silver standard stock solution A (4.14.1) into a 100 ml volumetric flask. Add 40 ml of
hydrochloric acid (4.11). Pipette 10,00 ml of gold standard solution (4.14.3) into the volumetric flask. Fill up
nearly to the mark with water, mix and cool to room temperature; then fill up exactly to the mark and mix again.
4.15 Calibration solutions
Calibration solutions should be prepared at the same ambient temperature as that at which the determinations
will be conducted.
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ISO 10378:2005(E)
4.15.1 Gold/silver calibration solutions
Pipette 0,0 ml, 1,00 ml, 2,00 ml, 5,00 ml and 10,00 ml of gold and silver standard solution (4.14.4) into a
series of 100 ml one-mark volumetric flasks.
Add 40 ml of hydrochloric acid (4.11) to each flask, fill up nearly to the mark with water, mix and cool to room
temperature; then fill up exactly to the mark and mix again.
These solutions contain 0,0 µg of Au/ml, 1,00 µg of Au/ml, 2,00 µg of Au/ml, 5,00 µg of Au/ml and 10,00 µg of
Au/ml; and 0,0 µg of Ag/ml, 0,50 µg of Ag/ml, 1,00 µg of Ag/ml, 2,50 µg of Ag/ml and 5,00 µg of Ag/ml and
shall be freshly prepared.
4.15.2 Silver calibration solutions
Pipette 0,0 ml, 1,00 ml, 2,00 ml, 4,00 ml, 6,00 ml, 8,00 ml and 10,00 ml of silver standard solution B (4.14.2)
into a series of 100 ml volumetric flasks. Add 10 ml of nitric acid (4.7), fill up nearly to the mark with water, mix
and cool to room temperature; then fill up exactly to the mark and mix again.
These solutions contain 0,0 µg of Ag/ml, 0,50 µg of Ag/ml, 1,00 µg of Ag/ml, 2,00 µg of Ag/ml, 3,00 µg of
Ag/ml, 4,00 µg of Ag/ml and 5,00 µg of Ag/ml, and shall be freshly prepared.
Contamination by gold and silver impurities in the reagents is corrected for by fusing the reagents without the
test portion.
5 Apparatus
5.1 Assay crucible furnace, with a maximum required operating temperature of 1 200 °C.
5.2 Muffle furnace, with a maximum required operating temperature of 1 100 °C. Temperature indication,
automatic temperature control and controlled air flow are preferable.
5.3 Assay crucibles, made of fire clay, of nominal capacity 200 ml to 600 ml, capable of withstanding
corrosion by the samples and fluxes at 1 100 °C. The crucible shall be of such a size that the charge does not
fill the crucible to a depth greater than 3/4 the depth of the crucible.
5.4 Cupels, made of magnesium oxide, or bone-ash cupels having a nominal capacity of 50 g of molten
lead. The inside bottom of the cupel shall be concave, as recommended in the fire assay texts referred to in
the Bibliography.
5.5 Conical mould, made of cast iron, of sufficient capacity to contain all of the molten lead plus slag from
the crucible fusion.
5.6 Analytical balance, sensitive to 1 mg.
5.7 Microbalance, sensitive to 1 µg or less.
5.8 Ordinary laboratory glassware, washed free of chlorides.
5.9 Volumetric glassware, of class A complying with ISO 385-1, ISO 648 and ISO 1042, and used in
accordance with ISO 4787.
5.10 Atomic absorption spectrometer (AAS), equipped with background correction and a glass bead in
the spray chamber.
5.11 Inductively coupled plasma (ICP) atomic emission spectrometer
5.12 Pulverizer
5.13 Hotplate
4 © ISO 2005 – All rights reserved
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ISO 10378:2005(E)
6 Sample
6.1 Test sample
Prepare an air-equilibrated test sample in accordance with ISO 9599.
NOTE A test sample is not required if predried test portions are to be used (see Annex A).
6.2 Test portion
Taking multiple increments, extract a test portion from the test sample in such a manner that it is
representative of the whole contents of the dish or tray. Weigh to the nearest 1 mg approximately 10 g to 20 g
of the test sample. At the same time as test portions are being weighed for analysis, weigh test portions for
the determination of hygroscopic moisture in accordance with ISO 9599.
Alternatively, the method specified in Annex A may be used to prepare predried test portions directly from the
laboratory sample.
If a mass fraction of arsenic above 2 % is present in the sample, this element should be removed by following
the procedure in Annex J; otherwise, interference with the cupellation stage may occur.
NOTE If the mass fraction of copper is greater than 30 %, a 10 g or 15 g test portion is preferable (see the fourth
paragraph of 7.4).
For lead concentrates, the test portion should be 10 g to ensure an adequate supply of lead.
7 Procedure
7.1 Number of determinations
Carry out the determinations at least in duplicate, as far as possible under repeatability conditions, on each
test sample.
NOTE 1 Repeatability conditions exist where mutually independent test results are obtained with the same method on
identical test material in the same laboratory by the same operator using the same equipment, within short intervals of
time.
NOTE 2 In the case where the ratio of silver to gold does not exceed 2,5 to 1 and the procedure specified in 7.10 is
carried out for the silver determination, separate determinations for gold and silver will be necessary (see Annex D). Four
test portions, therefore, are required, i.e. two for determinations of gold and two for silver.
7.2 Trial fusion
Carry out a trial fusion as described in Annex B, to ensure that the mass of the lead button is between 30 g
and 45 g.
7.3 Blank tests
Carry out a reagent blank test as described in Annex C in parallel with the analysis, using the same quantities
of all reagents, with the addition of sufficient flour (4.5) to the flux to give a lead button of between 30 g and
45 g. Omit the test portion and the potassium nitrate. The total blank should not exceed 5 µg of gold or 100 µg
of silver.
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ISO 10378:2005(E)
7.4 Charge preparation
Determine the mass of potassium nitrate (4.4) and flour (4.5) required in the charge, as indicated by the trial
fusion (see Annex B), and include this reagent in the flux mixture. Typical masses of the flux components for
copper, lead and zinc concentrates are shown in Tables 1 to 3 respectively.
Thoroughly mix the test portion with a flux.
Intimate mixing of flux components and the test portion is very important. All flux components should be in a
finely divided state with a preferred particle size of less than 0,5 mm.
Table 1 — Typical masses of flux components for copper concentrates
Mass
Flux components
g
Sodium carbonate (4.1) 30
Litharge (4.2) 210
Silica (4.3) 25
Potassium nitrate (4.4) —
Flour (4.5) —
Test portion 20
NOTE If the mass fraction of copper is greater than 30 %, the mass of litharge should be 30 times that of copper plus
35 g for the lead button. Alternatively, a 10 g or 15 g test portion can be used while retaining the flux composition given in
Table 1. If there are difficulties experienced in achieving a fluid melt, the amount of silica recommended in Table 1 can be
reduced to 19 g, while including 6 g borax.
Table 2 — Typical masses of flux components for lead concentrates
Mass
Flux components
g
Sodium carbonate (4.1) 30
Litharge (4.2) 100
Silica (4.3) 10
Borax (4.6) 10
Potassium nitrate (4.4) —
Flour (4.5) —
Test portion 10
Table 3 — Typical masses of flux components for zinc concentrates
Mass
Flux components
g
Sodium carbonate (4.1) 30
Litharge (4.2) 120
Silica (4.3) 10
Borax (4.6) 10
Potassium nitrate (4.4) —
Flour (4.5) —
Test portion 20
Place the mixture in an assay crucible (5.3).
6 © ISO 2005 – All rights reserved
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ISO 10378:2005(E)
7.5 Primary fusion
Place the crucibles in the furnace (5.1) preheated to approximately 900 °C.
If oil-fired or gas-fired furnaces are used, the fuel should be turned off immediately before opening the furnace.
Slowly raise the furnace temperature to 1 000 °C to 1 050 °C. Maintain this temperature until the fusion has
been tranquil for at least 10 min.
The optimum furnace setting temperature depends on the furnace structure and the position of the
thermometer. If unfused material remains in the bottom of assay crucibles, the setting temperature of the
furnace should be raised and the assay repeated.
To minimize crucible corrosion and build-up of impurities in the lead button, the overall fusion time should not
exceed 40 min. However, should the fusion take an extended time to settle, the fusion time may need to
exceed 40 min.
It is recommended that a fire-clay lid or a layer of salt or borax approximately 12 mm thick be used with this
fusion to prevent loss of material by dusting or ebullition. If borax is used as a cover, the amount used in the
flux may be reduced accordingly. If some ‘shotting’ of the lead is noted in the slag (this is common for zinc
concentrates), it is recommended that the extra borax be retained.
Pour the mixture into a dry conical mould (5.5), taking care that no loss of lead or slag occurs. Reserve the
crucible for retreatment fusion.
Allow the mixture to cool and carefully separate the lead button from the slag. Hammer the lead button as
necessary to remove any small particles of adhering slag. Reserve the slag for retreatment.
Weigh the lead button. If the button weighs less than 30 g or more than 45 g, discard the button and slag and
repeat the assay after appropriate adjustment of the oxidizing agent (see Annex B).
NOTE Buttons weighing less than 30 g may show poor collection efficiencies, whereas those exceeding 45 g may
contain higher amounts of copper and other base metals.
7.6 Cupellation
Place the lead button obtained in 7.5 into a preheated cupel (5.4) in a muffle furnace (5.2) at 900 °C. Allow the
cupellation to proceed at the lower muffle temperature of approximately 860 °C with a steady air flow.
Variations depend on the cupel type and furnace conditions. In the case of cupels made of bone ash, a
cupellation temperature of 820 °C is recommended.
NOTE 1 In the case where only gold is being determined, it could be effective to raise the furnace temperature to
900 °C to finish the cupellation after the visible lead melt on the cupel is approximately 10 mm in diameter [approximately
80 % (mass fraction) of lead absorbed].
High cupellation temperatures will cause higher silver losses and low temperatures can cause “freezing” of the
bead and incomplete cupellation. It is recommended that loss of silver during the cupellation process be
determined, to decide upon the furnace conditions (see Annex E).
Remove the cupel from the furnace and cool.
Carefully extract the primary bead and remove any adhering cupel material with a brush. Flatten the bead
slightly and place in a 30 ml porcelain crucible.
NOTE 2 A test tube can be used instead of a porcelain crucible.
NOTE 3 If the ratio of silver to gold in the primary bead is greater than 2,5 to 1, the silver can be determined by the
gr
...
SLOVENSKI STANDARD
SIST ISO 10378:2006
01-oktober-2006
.RQFHQWUDWLEDNURYLKVYLQþHYLKLQFLQNRYLKVXOILGRY±'RORþHYDQMH]ODWDLQVUHEUD
±3ODPHQVNDDQDOL]QDJUDYLPHWULMVNDLQSODPHQVNDDWRPVNDDEVRUSFLMVND
VSHNWURPHWULMVNDPHWRGD
Copper, lead and zinc sulfide concentrates -- Determination of gold and silver -- Fire
assay gravimetric and flame atomic absorption spectrometric method
Concentrés de sulfure de cuivre, de plomb et de zinc -- Dosage de l'or et de l'argent --
Méthode gravimétrique par essai au feu et spectrométrie d'absorption atomique dans la
flamme
Ta slovenski standard je istoveten z: ISO 10378:2005
ICS:
73.060.99 Druge rude Other metalliferous minerals
SIST ISO 10378:2006 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST ISO 10378:2006
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SIST ISO 10378:2006
INTERNATIONAL ISO
STANDARD 10378
Second edition
2005-07-01
Copper, lead and zinc sulfide
concentrates — Determination of gold
and silver — Fire assay gravimetric and
flame atomic absorption spectrometric
method
Concentrés sulfurés de cuivre, de plomb et de zinc — Dosage de l'or et
de l'argent — Méthode gravimétrique par essai au feu et spectrométrie
d'absorption atomique dans la flamme
Reference number
ISO 10378:2005(E)
©
ISO 2005
---------------------- Page: 3 ----------------------
SIST ISO 10378:2006
ISO 10378:2005(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
© ISO 2005
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2005 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 10378:2006
ISO 10378:2005(E)
Contents Page
Foreword. v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Principle. 2
3.1 Fusion . 2
3.2 Cupellation . 2
3.3 Parting. 2
3.4 Retreatment . 2
3.5 Correction for blank contamination. 2
4 Reagents. 2
5 Apparatus . 4
6 Sample . 5
6.1 Test sample . 5
6.2 Test portion . 5
7 Procedure . 5
7.1 Number of determinations . 5
7.2 Trial fusion. 5
7.3 Blank tests. 5
7.4 Charge preparation. 6
7.5 Primary fusion. 7
7.6 Cupellation . 7
7.7 Retreatment of residues. 8
7.8 Determination of gold in the primary bead . 8
7.9 Determination of gold and silver in secondary beads and blanks, and of silver in prills. 9
7.10 Determination of silver in the parting solution. 11
8 Expression of results . 11
8.1 Mass fraction of gold. 11
8.2 Mass fraction of silver. 12
9 Precision. 13
9.1 Expression of precision . 13
9.2 Method for obtaining the final result (see Annex H) . 14
9.3 Precision between laboratories. 15
9.4 Check of trueness. 17
9.4.1 General. 17
9.4.2 Type of certified reference material (CRM) or reference material (RM) . 17
10 Test report . 18
Annex A (normative) Procedure for the preparation and determination of the mass of a predried
test portion . 19
Annex B (normative) Trial fusion. 21
Annex C (normative) Blank determination . 22
Annex D (normative) Inquartation .23
Annex E (normative) Determination of vaporization loss of silver during the cupellation process . 24
Annex F (normative) Sulfuric acid - Parting . 25
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Annex G (normative) Determination of impurities in parting solutions and washings. 27
Annex H (normative) Flowsheet of the procedure for the acceptance of analytical values for test
samples (see 9.2) . 31
Annex I (informative) Flowsheet of the method. 32
Annex J (informative) Roasting method. 33
Annex K (informative) Guide to the preparation of dilutions for the determination of silver in
parting solutions and residues. 34
Annex L (informative) Derivation of precision equations. 35
Bibliography . 52
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Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 10378 was prepared by Technical Committee ISO/TC 183, Copper, lead, zinc and nickel ores and
concentrates.
This second edition cancels and replaces the first edition (ISO 10378:1994), which has been technically
revised.
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Introduction
This International Standard describes a method for the determination of the mass fraction of gold and silver in
copper, lead and zinc sulfide concentrates. This International Standard was prepared to enable laboratories to
determine the mass fraction of gold and silver in suitable samples using instrumental methods.
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INTERNATIONAL STANDARD ISO 10378:2005(E)
Copper, lead and zinc sulfide concentrates — Determination of
gold and silver — Fire assay gravimetric and flame atomic
absorption spectrometric method
WARNING — This International Standard may involve hazardous materials, operations and equipment.
It is the responsibility of the user of this International Standard to establish appropriate health and
safety practices and determine the applicability of regulatory limitations prior to use.
1 Scope
This International Standard specifies a fire assay gravimetric and flame atomic absorption spectrometric
method for the determination of the mass fraction of gold and silver in copper, lead and zinc sulfide
concentrates as follows:
Copper concentrates:
The method is applicable to the determination of mass fractions of gold from 0,5 g/t to 300 g/t and of
mass fractions of silver from 25 g/t to 1 500 g/t in copper sulfide concentrates containing mass fractions of
copper from 15 % to 60 %.
Lead concentrates
The method is applicable to the determination of mass fractions of gold from 0,1 g/t to 25 g/t and of mass
fractions of silver from 200 g/t to 3 500 g/t in lead sulfide concentrates containing mass fractions of lead
from 10 % to 80 %.
Zinc concentrates
The method is applicable to the determination of mass fractions of gold from 0,1 g/t to 12 g/t and of mass
fractions of silver from 10 g/t to 800 g/t in zinc sulfide concentrates containing mass fractions of zinc up to
60 %.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 385-1:1984, Laboratory glassware — Burettes — Part 1: General requirements
ISO 648:1977, Laboratory glassware — One-mark pipettes
ISO 1042:1998, Laboratory glassware — One-mark volumetric flasks
ISO 3696:1987, Water for analytical laboratory use — Specification and test methods
ISO 4787:1984, Laboratory glassware — Volumetric glassware — Methods for use and testing of capacity
ISO 9599:1991, Copper, lead and zinc sulfide concentrates — Determination of hygroscopic moisture in the
analysis sample — Gravimetric method
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3 Principle
Fire assaying for the determination of gold and silver comprises a series of steps to separate firstly the
precious metals from most of the associated metals, followed by separation of the gold from silver and other
metals preconcentrated into a precious-metal alloy.
The stages that comprise the determinations are described in 3.1 to 3.5 inclusive.
3.1 Fusion
The samples are fused in a crucible after mixing with a litharge-based flux which, under reducing conditions,
collects the precious metals in a metallic lead button.
3.2 Cupellation
The base metals present in the lead button are substantially separated from the precious metals by oxidizing
fusion. Cupellation produces a bead largely comprising a silver-gold alloy with small quantities of other metals.
3.3 Parting
Gold is separated from the primary bead by treatment with nitric acid. The gold prill is weighed. Gold prills
having a mass less than 50 µg are dissolved in aqua regia and the gold is determined by atomic absorption
spectrometry (AAS). Silver is determined in the parting solution by AAS.
3.4 Retreatment
All residues are retreated to maximize the recovery of gold and silver. The addition of collectors for either gold
or silver is not required, as both metals are present in sufficient amounts to be readily visible after the
cupellation stage. The second bead is dissolved in acids followed by analysis of both metals by AAS.
3.5 Correction for blank contamination
Contamination by gold and silver impurities in the reagents is corrected for by fusing the reagents without the
test portion.
4 Reagents
During the analysis, use only reagents of recognized analytical grade and water that complies with grade 2 of
ISO 3696.
4.1 Sodium carbonate, anhydrous.
4.2 Litharge (PbO), assay grade having a mass fraction of gold of less than 0,01 g/t and a mass fraction of
silver of less than 0,2 g/t.
4.3 Silica, precipitated.
4.4 Potassium nitrate or sodium nitrate
NOTE If sodium nitrate is used, the masses specified for potassium nitrate will have to be modified:
85,0
gof KNO×= gof NaNO
33
101,1
4.5 Flour
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4.6 Borax, fused anhydrous sodium tetraborate (borax glass powder).
4.7 Nitric acid, concentrated (ρ 1,42 g/ml), chloride concentration < 0,5 µg/ml.
20
4.8 Nitric acid, diluted 1+1.
Slowly add 500 ml of concentrated nitric acid (4.7) to 500 ml of water, while stirring.
4.9 Lead, foil, having a mass fraction of gold of less than 0,01 g/t and a mass fraction of silver of less than
0,2 g/t.
4.10 Silver, of minimum purity 99,99 %.
4.11 Hydrochloric acid (ρ 1,16 g/ml to 1,19 g/ml).
20
4.12 Thiourea, 10 g/l solution.
Add 1 g of thiourea to 100 ml of water.
4.13 Aqua regia
Mix 3 parts of hydrochloric acid (4.11) with 1 part of nitric acid (4.7). Prepare freshly as required.
4.14 Standard solutions
Standard solutions should be prepared at the same ambient temperature as that at which the determinations
will be conducted.
4.14.1 Silver, standard stock solution A (500 µg of Ag/ml).
Weigh 0,500 0 g of silver metal to the nearest 0,1 mg. Transfer to a 100 ml beaker, add 20 ml of diluted nitric
acid (4.8) and warm to dissolve. Cool and add 20 ml of concentrated nitric acid (4.7). Transfer to a 1 000 ml
volumetric flask, fill up with water nearly to the mark, mix and cool to room temperature; then fill up exactly to
the mark and mix again.
4.14.2 Silver, standard solution B (50 µg of Ag/ml).
Pipette 10,00 ml of silver standard stock solution A (4.14.1) into a 100 ml volumetric flask, fill up with water
nearly to the mark, mix and cool to room temperature; then fill up exactly to the mark and mix again.
Prepare a fresh solution per batch.
4.14.3 Gold, standard solution (1000 µg of Au/ml).
Weigh 1,000 g of gold metal to the nearest 0,1 mg. Transfer to a 200 ml beaker, add 25 ml of aqua regia
solution (4.13) and warm to dissolve. Cool and transfer to a 1 000 ml volumetric flask. Add 75 ml of
hydrochloric acid (4.11), fill up nearly to the mark with water, mix and cool to room temperature; then fill up
exactly to the mark and mix again.
4.14.4 Gold and silver, standard solution (100 µg of Au/ml + 50 µg of Ag/ml).
Pipette 10,00 ml of silver standard stock solution A (4.14.1) into a 100 ml volumetric flask. Add 40 ml of
hydrochloric acid (4.11). Pipette 10,00 ml of gold standard solution (4.14.3) into the volumetric flask. Fill up
nearly to the mark with water, mix and cool to room temperature; then fill up exactly to the mark and mix again.
4.15 Calibration solutions
Calibration solutions should be prepared at the same ambient temperature as that at which the determinations
will be conducted.
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4.15.1 Gold/silver calibration solutions
Pipette 0,0 ml, 1,00 ml, 2,00 ml, 5,00 ml and 10,00 ml of gold and silver standard solution (4.14.4) into a
series of 100 ml one-mark volumetric flasks.
Add 40 ml of hydrochloric acid (4.11) to each flask, fill up nearly to the mark with water, mix and cool to room
temperature; then fill up exactly to the mark and mix again.
These solutions contain 0,0 µg of Au/ml, 1,00 µg of Au/ml, 2,00 µg of Au/ml, 5,00 µg of Au/ml and 10,00 µg of
Au/ml; and 0,0 µg of Ag/ml, 0,50 µg of Ag/ml, 1,00 µg of Ag/ml, 2,50 µg of Ag/ml and 5,00 µg of Ag/ml and
shall be freshly prepared.
4.15.2 Silver calibration solutions
Pipette 0,0 ml, 1,00 ml, 2,00 ml, 4,00 ml, 6,00 ml, 8,00 ml and 10,00 ml of silver standard solution B (4.14.2)
into a series of 100 ml volumetric flasks. Add 10 ml of nitric acid (4.7), fill up nearly to the mark with water, mix
and cool to room temperature; then fill up exactly to the mark and mix again.
These solutions contain 0,0 µg of Ag/ml, 0,50 µg of Ag/ml, 1,00 µg of Ag/ml, 2,00 µg of Ag/ml, 3,00 µg of
Ag/ml, 4,00 µg of Ag/ml and 5,00 µg of Ag/ml, and shall be freshly prepared.
Contamination by gold and silver impurities in the reagents is corrected for by fusing the reagents without the
test portion.
5 Apparatus
5.1 Assay crucible furnace, with a maximum required operating temperature of 1 200 °C.
5.2 Muffle furnace, with a maximum required operating temperature of 1 100 °C. Temperature indication,
automatic temperature control and controlled air flow are preferable.
5.3 Assay crucibles, made of fire clay, of nominal capacity 200 ml to 600 ml, capable of withstanding
corrosion by the samples and fluxes at 1 100 °C. The crucible shall be of such a size that the charge does not
fill the crucible to a depth greater than 3/4 the depth of the crucible.
5.4 Cupels, made of magnesium oxide, or bone-ash cupels having a nominal capacity of 50 g of molten
lead. The inside bottom of the cupel shall be concave, as recommended in the fire assay texts referred to in
the Bibliography.
5.5 Conical mould, made of cast iron, of sufficient capacity to contain all of the molten lead plus slag from
the crucible fusion.
5.6 Analytical balance, sensitive to 1 mg.
5.7 Microbalance, sensitive to 1 µg or less.
5.8 Ordinary laboratory glassware, washed free of chlorides.
5.9 Volumetric glassware, of class A complying with ISO 385-1, ISO 648 and ISO 1042, and used in
accordance with ISO 4787.
5.10 Atomic absorption spectrometer (AAS), equipped with background correction and a glass bead in
the spray chamber.
5.11 Inductively coupled plasma (ICP) atomic emission spectrometer
5.12 Pulverizer
5.13 Hotplate
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6 Sample
6.1 Test sample
Prepare an air-equilibrated test sample in accordance with ISO 9599.
NOTE A test sample is not required if predried test portions are to be used (see Annex A).
6.2 Test portion
Taking multiple increments, extract a test portion from the test sample in such a manner that it is
representative of the whole contents of the dish or tray. Weigh to the nearest 1 mg approximately 10 g to 20 g
of the test sample. At the same time as test portions are being weighed for analysis, weigh test portions for
the determination of hygroscopic moisture in accordance with ISO 9599.
Alternatively, the method specified in Annex A may be used to prepare predried test portions directly from the
laboratory sample.
If a mass fraction of arsenic above 2 % is present in the sample, this element should be removed by following
the procedure in Annex J; otherwise, interference with the cupellation stage may occur.
NOTE If the mass fraction of copper is greater than 30 %, a 10 g or 15 g test portion is preferable (see the fourth
paragraph of 7.4).
For lead concentrates, the test portion should be 10 g to ensure an adequate supply of lead.
7 Procedure
7.1 Number of determinations
Carry out the determinations at least in duplicate, as far as possible under repeatability conditions, on each
test sample.
NOTE 1 Repeatability conditions exist where mutually independent test results are obtained with the same method on
identical test material in the same laboratory by the same operator using the same equipment, within short intervals of
time.
NOTE 2 In the case where the ratio of silver to gold does not exceed 2,5 to 1 and the procedure specified in 7.10 is
carried out for the silver determination, separate determinations for gold and silver will be necessary (see Annex D). Four
test portions, therefore, are required, i.e. two for determinations of gold and two for silver.
7.2 Trial fusion
Carry out a trial fusion as described in Annex B, to ensure that the mass of the lead button is between 30 g
and 45 g.
7.3 Blank tests
Carry out a reagent blank test as described in Annex C in parallel with the analysis, using the same quantities
of all reagents, with the addition of sufficient flour (4.5) to the flux to give a lead button of between 30 g and
45 g. Omit the test portion and the potassium nitrate. The total blank should not exceed 5 µg of gold or 100 µg
of silver.
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7.4 Charge preparation
Determine the mass of potassium nitrate (4.4) and flour (4.5) required in the charge, as indicated by the trial
fusion (see Annex B), and include this reagent in the flux mixture. Typical masses of the flux components for
copper, lead and zinc concentrates are shown in Tables 1 to 3 respectively.
Thoroughly mix the test portion with a flux.
Intimate mixing of flux components and the test portion is very important. All flux components should be in a
finely divided state with a preferred particle size of less than 0,5 mm.
Table 1 — Typical masses of flux components for copper concentrates
Mass
Flux components
g
Sodium carbonate (4.1) 30
Litharge (4.2) 210
Silica (4.3) 25
Potassium nitrate (4.4) —
Flour (4.5) —
Test portion 20
NOTE If the mass fraction of copper is greater than 30 %, the mass of litharge should be 30 times that of copper plus
35 g for the lead button. Alternatively, a 10 g or 15 g test portion can be used while retaining the flux composition given in
Table 1. If there are difficulties experienced in achieving a fluid melt, the amount of silica recommended in Table 1 can be
reduced to 19 g, while including 6 g borax.
Table 2 — Typical masses of flux components for lead concentrates
Mass
Flux components
g
Sodium carbonate (4.1) 30
Litharge (4.2) 100
Silica (4.3) 10
Borax (4.6) 10
Potassium nitrate (4.4) —
Flour (4.5) —
Test portion 10
Table 3 — Typical masses of flux components for zinc concentrates
Mass
Flux components
g
Sodium carbonate (4.1) 30
Litharge (4.2) 120
Silica (4.3) 10
Borax (4.6) 10
Potassium nitrate (4.4) —
Flour (4.5) —
Test portion 20
Place the mixture in an assay crucible (5.3).
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7.5 Primary fusion
Place the crucibles in the furnace (5.1) preheated to approximately 900 °C.
If oil-fired or gas-fired furnaces are used, the fuel should be turned off immediately before opening the furnace.
Slowly raise the furnace temperature to 1 000 °C to 1 050 °C. Maintain this temperature until the fusion has
been tranquil for at least 10 min.
The optimum furnace setting temperature depends on the furnace structure and the position of the
thermometer. If unfused material remains in the bottom of assay crucibles, the setting temperature of the
furnace should be raised and the assay repeated.
To minimize crucible corrosion and build-up of impurities in the lead button, the overall fusion time should not
exceed 40 min. However, should the fusion take an extended time to settle, the fusion time may need to
exceed 40 min.
It is recommended that a fire-clay lid or a layer of salt or borax approximately 12 mm thick be used with this
fusion to prevent loss of material by dusting or ebullition. If borax is used as a cover, the amount used in the
flux may be reduced accordingly. If some ‘shotting’ of the lead is noted in the slag (this is common for zinc
concentrates), it is recommended that the extra borax be retained.
Pour the mixture into a dry conical mould (5.5), taking care that no loss of lead or slag occurs. Reserve the
crucible for retreatment fusion.
Allow the mixture to cool and carefully separate the lead button from the slag. Hammer the lead button as
necessary to remove any small particles of adhering slag. Reserve the slag for retreatment.
Weigh the lead button. If the button weighs less than 30 g or more than 45 g, discard the button and slag and
repeat the assay after appropriate adjustment of the oxidizing agent (see Annex B).
NOTE Buttons weighing less than 30 g may show poor collection efficiencies, whereas those exceeding 45 g may
contain higher amounts of copper and other base metals.
7.6 Cupellation
Place the lead button obtained in 7.5 into a preheated cupel (5.4) in a muffle furnace (
...
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