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INTERNATIONAL STANDARD

ISO 10378 Third edition 15

2016-02-

Copper, lead and zinc sulfide concentrates — Determination of gold and silver— Fireassay gravimetric and flame atomic absorption spectrometricmethod Concentrés de sulfurede cuivre,de plomb et de zinc— Dosage de l’oret de l’argent— Méthode gravimétriquepar essaiau feu et spectrométrie d’absorption atomique dans la flamme

Reference number ISO 10378:2016(E)

InternationalOrganization for Standardization

©

ISO 2016

ISO10378:2016(E)

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COPYRIGHT PROTECTED DOCUMENT © ISO 2016,Publishedin Switzerland Allrightsreserved.Unless otherwise specified,no part of thispublicationmay be reproduced or utilizedotherwise in any form or by any means, electronicor mechanical, includingphotocopying, or posting on the internetor an intranet,without prior written permission.Permission can be requested from eitherISO at the address below or ISO’smember body in the country of the requester. ISO copyright office Ch. de Blandonnet 8 • CP 401 CH-1214 Vernier,Geneva, Switzerland Tel.+41 22 749 01 11 Fax +41 22 749 09 47 [email protected] www.iso.org

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ISO10378:2016(E)

Contents Pag e

Foreword

..................

...................................................................................................

v

Introduction..................................................................................................................

vi

1

..................................................................................................................

1

Normative references...................................................................................................

1

Principle............................................................................................................... General ................................................................................................................... Fusion ........................................................................................................... Cupellation............................................................................................................ Parting.......................................................................................................... Retreatment .......................................................................................................... Correctionfor blank contamination.......................................................................

2 2 2 2 2 2 2

4

Reagents ...............................................................................................................

2

5

Apparatus .............................................................................................................

4

Sample ................................................................................................................. Test sample ........................................................................................................... Test portion ..........................................................................................................

5 5 5

Scope

2 3 3.1 3.2 3.3 3.4 3.5 3.6

6 6. 1 6. 2 7 7. 1 7. 2 7. 3 7. 4 7.5 7. 6 7. 7 7.8 7.9 7. 10

Procedure............................................................................................................................. 6 of determinations....................................................................................... 6 Trialfusion ............................................................................................................ 6 Blank tests............................................................................................................. 6 Charge preparation....................................................................................... 6 Primary fusion ..................................................................................................... 7 Cupellation............................................................................................................ 8 Retreatment of residues.................................................................................... 8 Determination of gold in the primary bead .................................................. 9 Determination of gold and silverin secondary beads and blanks,and of silver ....nprills10 Determinationof silverin the partingsolution................................................. 11

Number

8

Expressionof results.................................................................................................... 12 Mass fractionof gold ...................................................................................... 12 Mass fractionof silver.................................................................................... 13

8. 1 8. 2 9 9.1 9.2 9.3 9.4

Method

9.4.1 9.4.2 10

Precision.............................................................................................................................. Expressionof precision................................................................................... for obtainingthe finalresult(seeAnnex H) ............................................ Precisionbetween laboratories............................................................................ Check of trueness................................................................................................ General.......................................................................................................... Type of certified referencematerial(CRM) or referencematerial(RM) .................

14 14 15 15 17 17 18

Test report ............................................................................................................. 18

Annex A (normative)Procedure for the preparationand determinationof the mass of a predriedtestportion ................................................................................................... 19 Annex B (normative)Trialfusion ......................................................................................

21

Annex C (normative)Blank determination.............................................................................

22

Annex D (normative)Inquartation......................................................................................

23

Annex E (normative)Determinationof vaporizationlossof silverduring the cupellationprocess ....................................................................................................... 24 Annex F (normative)Sulfuricacid— Parting...................................................................................

25

Annex G (normative)Determinationof impuritiesin partingsolutionsand washings

27

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.....................

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ISO 10378:2016(E)

Annex H (normative) Flowsheet of the procedure for the acceptance of analyticalvalues for testsamples (see 9.2 ) .........................................................................................31 Annex I (informative) Flowsheet of the method

.......................................................................32

Annex J (informative)Roasting method

...............................................................33........

Annex K (informative) Guide to the preparationof dilutionsfor the determination of silver in partingsolutionsand residues .......................................................................34

... . ..........

........

Annex L (informative)Derivationof precisionequations ...............................................35 ............... Bibliography .....................................................................................................50

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ISO 10378:2016(E)

Foreword ISO (theInternationalOrganizationfor Standardization)isa worldwide federationof nationalstandards bodies (ISO member bodies).The work of preparing InternationalStandards is normally carried out through ISO technicalcommittees. Each member body interestedin a subject for which a technical committee has been establishedhas the right to be represented on that committee. International organizations,governmental and non-governmental, in liaisonwith ISO,also take part in the work. ISO collaboratescloselywith the InternationalElectrotechnicalCommission (IEC) on allmatters of electrotechnicalstandardization.

The procedures used to develop thisdocument and those intended for itsfurther maintenance are describedin the ISO/IEC Directives,Part 1.In particularthe differentapproval criterianeeded for the differenttypes of ISO documents should be noted. This document was drafted in accordance with the editorialrulesof the ISO/IEC Directives,Part 2 (see www.iso.org/directives).

Attention isdrawn to the possibilitythat some of the elements of thisdocument may be the subjectof patent rights.ISO shallnot be held responsiblefor identifyingany or allsuch patent rights.Detailsof any patent rightsidentified during the development of the document willbe in the Introductionand/or on the ISO listof patent declarationsreceived(see www.iso.org/patents). Any trade name used in thisdocument constitutean endorsement.

isinformation given for the convenience of users and does not

For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISO’sadherence to the WTO principlesin the Technical Barriersto Trade (TBT) see the followingURL: Foreword - Supplementary information The committee responsiblefor this document is ISO/TC 183, Copper, lead, zinc and nickel ores and concentrates .

This third editioncancelsand replacesthe second edition(ISO 10378:2005),in which 6.2 has been technicallyrevised and the warning noticein A.3.1has been updated.

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ISO 10378:2016(E)

Introduction This InternationalStandard describesa method for the determination of the mass fractionof gold and silver in copper, lead, and zinc sulfide concentrates. This International Standard was prepared to enable laboratoriesto determine the mass fractionof gold and silverin suitablesamples using instrumentalmethods.

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INTERNATIONAL STANDARD

ISO 10378:2016(E)

Copper, lead and zinc sulfide concentrates — Determination of gold and silver— Fireassay gravimetric and flame atomic absorption spectrometric method WARNING — This InternationalStandard may involve hazardous materials,operations, and equipment. It is the responsibilityof the user of this InternationalStandard to establish appropriate health and safety practicesand determine the applicabilityof regulatory limitations priorto use.

1

Scope

This International Standard specifies a fire assay gravimetric and flame atomic absorption spectrometricmethod for the determinationof the mass fractionof gold and silverin copper,lead,and zinc sulfide concentrates as follows. — Copper concentrates The method isapplicableto the determinationof mass fractionsof gold from 0,5g/t to 300 g/t and of mass fractionsof silverfrom 25 g/t to 1 500 g/t in copper sulfide concentrates containing mass fractionsof copper from 15 % to 60 %.

— Lead concentrates The method isapplicableto the determinationof mass fractionsof gold from 0,1g/t to 25 g/t and of mass fractionsof silverfrom 200 g/t to 3 500 g/t in lead sulfide concentrates containing mass fractionsof leadfrom 10 % to 80 %.

— Zincconcentrates The method isapplicableto the determinationof mass fractionsof gold from 0,1g/t to 12 g/t and of mass fractions of silverfrom 10 g/t to 800 g/t in zinc sulfide concentrates containing mass fractionsof zincup to 60 %.

2

Normative references

The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application.For dated references, only the edition cited applies.For undated references,the latesteditionof the referenced document (includingany amendments) applies. ISO 385, Laboratoryglassware—

Burettes

ISO 648, Laboratoryglassware— Single-volumepipettes ISO 1042, Laboratoryglassware—

One-mark volumetricf lasks

ISO 3696, Water for analyticallaboratoryuse —

Specificationand testmethods

ISO 4787, Laboratoryglassware— Volumetricinstruments— Methods fortestingofcapacityand for use ISO 9599, Copper, lead and zinc sulfide concentrates— Determinationof hygroscopicmoisture in the analysis ample— Gravimetricmethod

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ISO 10378:2016(E)

3

Principle

3.1 General Fire assaying for the determination of gold and silvercomprises a seriesof steps to separate f irstlythe precious metals from most of the associatedmetals,followed by separationof the gold from silverand other metals preconcentratedinto a precious-metalalloy. The stagesthat comprise the determinationsare describedin 3.2 to 3.6 inclusive.

3.2

Fusion

The samples are fused in a crucibleafter mixing with a litharge-basedf lux which, under reducing conditions,collectsthe preciousmetals in a metalliclead button.

3.3

Cupellation

The base metals present in the lead button are substantiallyseparated from the precious metals by oxidizingfusion.Cupellationproduces a bead largelycomprising a silver-goldalloywith small quantities of other metals.

3.4

Parting

Gold isseparated from the primary bead by treatment with nitricacid.The gold prillisweighed. Gold prillshaving a mass lessthan 50 μg are dissolvedin aqua regia and the gold isdetermined by atomic absorption spectrometry (AAS).Silverisdetermined in the parting solutionby AAS. Retreatment

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All residues are retreated to maximize the recovery of gold and silver.The addition of collectorsfor either gold or silveris not required,as both metals are present in sufficientamounts to be readily visibleafter the cupellationstage.The second bead is dissolvedin acids followed by analysisof both metals by AAS.

3.6

Correction for blank contamination

Contamination by gold and silverimpuritiesin the reagents is corrected for by fusing the reagents without the testportion.

4

Reagents

During the analysis,use only reagents of recognized analyticalgrade and water that complies with grade 2 of ISO 3696. 4.1

Sodium carbonate ,anhydrous.

4. 2 Litharge (PbO),assay grade having a mass fractionof gold of lessthan 0,01 g/t and a mass fraction of silverof lessthan 0,2g/t.

4. 3 Silica,precipitated. 4.4 NOTE

Potassium nitrateor sodium nitrate Ifsodium nitrateisused,the masses specified for potassium nitratewillhave to be modi fied:

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ISO 10378:2016(E)

g of KNO

4.5

85 0 3

×

101 1

=

g of NaNO

3

Flour

4. 6 Borax ,fused anhydrous sodium tetraborate(borax glasspowder). 4. 7 Nitricacid,concentrated( ρ20 1,42g/ml),chlorideconcentration

C

If this condition exists,the difference between statisticallysignificant.

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(41) the reported result and the certified value is

17

ISO 10378:2016(E)

In Formulae (40) and (41),the symbols have the followingmeanings: μc isthe finalresult,in grams of gold or silverper tonne,of the certified reference material; Ac isthe certified value,in grams of gold or silverper tonne,of the certified reference material; C

9.4.2

isa quantity,in grams of gold or silverper tonne,depending on the type of the certified refer -ence materialused,as de fined in 9.4.2. Type of certified reference material (CRM) or reference material (RM)

The reference materials used for this purpose should be prepared and certified in accordance with ISO Guide 35. 9.4.2.1 Reference material certified/characterizedby an interlaboratorytestprogramme The quantity C (see 9.4.1),in grams of gold or silverper tonne,isgiven by Formula (24): Sr

2

C=2 SL

+

2

+

n

S2 A

{ c}

(42)

where 2

S {Ac}isthe variance of the certified value; n

isthe number of replicatedeterminations.

9.4.2.2 Reference material certified/characterizedby one laboratory The quantity C (see

NOTE isknown

2 SL

9.4.

1),in grams of gold or silverper tonne,isgiven by Formula (43):

2

Sr

2

C=2

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+

(43)

n

Itisrecommended that thistype of certified reference materialbe avoided,unlessthe particularCRM to have an unbiased certified value.

10 Test report The testreport shallincludethe followinginformation: a)

identificationof the sample;

b)

reference to thisInternationalStandard,i .eISO. 10378;

c)

mass fractionof gold of the sample, expressed in grams per tonne;

d)

mass fractionof silverof the sample, expressed in grams per tonne;

e)

date on which the testwas carriedout;

f)

any occurrences noticed during the determination that may have had an influence on the results.

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ISO 10378:2016(E)

Annex A (normative) Procedure for the preparation and determination of the mass of a predried testportion

A.1 General This Annex specifies a method for the preparation and determination of the mass of a predried test portion in the analysisof copper,lead,and zincsulfide concentrates.The method isapplicableto copper, lead, and zinc sulfide concentrates not susceptibleto oxidation and having hygroscopic moisture contentsranging from 0,05% to 2 %.

A.2 Principle The testportionto be used for analysisisdried in airin an oven maintained at 105 °C ± 5 °C.The dried test portion isthen weighed and used for the analysisNo. correctionfor hygroscopic moisture isrequired.

A.3 Reagents A.3.1 Desiccant, such as self-indicatingsilicagel or anhydrous magnesium

perchlorate.

WARNING — Care needs to be taken whenever disposingof exhaustedmagnesium perchlorate and allother laboratorychemicals.Environmentalregulationsoften apply.Users should seek specialist’sadvice to determine an appropriate,effective,health-conscious,safety-conscious, and environmentally sound means of disposal.

A.4 Apparatus Ordinary laboratoryequipment, and the following. A.4.1 Analyticalbalance,sensitiveto 0,1mg. A.4.2 Weighing airtightcovers.

vessels, of glass or silicaor corrosion-resistantmetal, with externallyf-itting

For small testportions(of mass lessthan 3 g),the mass of the vesselshallbe as small as possible,. e. lessthan 20 g. A.4.3 Laboratoryoven,capable of maintaining a temperature of 105 °C ± 5 °C.

A.5 Procedure A.5.1 Preparation of the weighing vessel Dry the weighing vesseland itscover ( A.4.2) by heating in the laboratory oven ( A.4.3) at 105 °C ± 5 °C for lh .Transfer the vesseland itscover to a desiccatorcontaininga suitablefresh desiccant(A.3.1) and allow coolingto ambient temperature.

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ISO 10378:2016(E)

A.5.2 Test portion Tare the dried weighing vesseland itscover (A.5.1) .Immediately add the mass of laboratory sample specified for analysis.An accurate totalmass of the testportion and weighing vesselisnot required at thispoint.

A.5.3 Determination of the dry mass of testportion Transfer the uncovered weighing vessel containing the test portion and the vessel cover to the laboratoryoven (A.4.3) and dry at 105 °C ± 5 °C for 2 h.After the 2 h period,remove the weighing vessel and dry testportion from the oven, replacethe vesselcover,and allow coolingto ambient temperature in the desiccator.When cool,remove the weighing vesselcontainingthe dry testportion and the vessel cover from the desiccatorand weigh to the nearest 0,1 mg (m6 ),after slightlyliftingthe cover and quicklyreplacingit.Transfer the testportion intothe appropriateanalyticalapparatus and immediately reweigh the empty weighing vesseland itscover.Record the mass (m7 ) to the nearest 0,1mg. For new concentrates of unknown characteristics,itisadvisableto repeat the drying for another 2 h at 105 °C ± 5 °C and to reweigh the weighing vesselcontainingthe testportion and the vesselcover to the nearest 0,1 mg ( between and 6

6 ) . The mass of the testportion can be considered to be constant ifthe difference ′

6

is lessthan or equal to 0,5 mg. Ifthiscondition is not achieved,the drying and

weighing steps should be repeated.

A.6 Calculationof the dry mass of the testportion The dry mass of the testportion ( 8=

6−

8 ),in

grams, isgiven by Formula (A.1): (A.1)

7

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isthe mass, in grams, of the dried testportion plus the weighing vesseland itscover;

7

isthe mass, in grams, of the empty weighing vesselplus itscover.

The mass of the dry testportion isthe mass to be used to calculatethe mass fractionof element in the laboratorysample on a dry basis.No correctionfor hygroscopic moisture isrequired.

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ISO 10378:2016(E)

Annex B (normative) Trialfusion

B.1 General The mass of oxidizingagent,potassium nitrateor sodium nitrate(4.4) in the charge depends on the reducing power of the testsample. A trialfusion iscarried out to ensure that the testfusion yieldsa lead button of mass between 45 g.

30 g and

B.2 Procedure Mix a test portion with the appropriate masses of flux components. Typical masses of flux components for copper,lead,and zincconcentratesare shown in Tables 1 to 3 ,respectively. Carry out the fusion as specified in 7.5. Weigh the lead button obtained from the fusion.Ifthe button weighs lessthan 30 g or more than 45 g,an adjustment of the oxidizing/reducing properties of the fusion mixture may be made using the following approximations: a)

the addition of 1 g of potassium nitratewilldecrease the button mass by 4 g;

b)

variationsin the mass of the test portion will affect the button size according to the following approximation: 1 g of sulfur in the testportion willyieldapproximately 19 g of lead;

c)

for roasted samples or other samples not giving at least30 g of lead button, f lour ( 4.5) may be added to increase the reducing propertiesof the charge; the flour shallbe thoroughly mixed with the other components in the charge (for information, 1 g of flour gives approximately 10 g to 12 g of lead) .

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ISO 10378:2016(E)

Annex C (normative) Blank determination

C.1 General A blank determination is carried out to determine the mass fraction of gold and silverof the assay reagents,principallylithargeIt.isrecommended that the blank determination be performed in duplicate.

C.2 Procedure Thoroughly mix the flux components with sufficientf lour (4.5).Typical masses of flux components for copper,lead,and zincconcentratesare shown in Tables 1 to 3,respectively,and potassium nitrate( 4.4 ) amount of flour (4.5) is usually 3 g to 4 g, as a reducing should be omitted from the components. The agent to produce a lead button of 30 g to 45 g. Continue the blank determination in accordance with 7.5 to 7.7. Combine the primary and secondary blank beads and determine the gold and silverconcentration of the blank solutionsin accordance with 7.9.

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ISO 10378:2016(E)

Annex D (normative) Inquartation

D.1 General To ensure complete partingof the bead,the ratioof silverto gold has to exceed 2,5to 1.Beads in which thisratiois not reached,i .ethose. in which the mass fractionof gold exceeds 30 % are inquarted. However, in caseswhere the silverisdetermined by AAS or ICP,the silvercannot be determined in the inquarted bead, and so separatedeterminationsfor gold and silverwillbe necessary.The gold should be determined by inquartationin accordance with thisannex, and the silverby the dissolutionmethod specified in 7.9without the partingoperation.

Ifthe silverisdetermined by the gravimetricmethod insteadof the procedure specified in 7.10,weigh the primary bead before the inquartationInquart. the bead in accordance with thisannex, carry out the partingby the procedure specified in 7.8,and determine the impuritiesin the partingsolutionand washing by the procedure specified in Annex G. NOTE 1 Ifthe approximate silverto gold ratioisknown to be lessthan 2,5to 1,the appropriatemass of silver to give a ratioof 4 to 1 can be added priorto the f irstfusion. NOTE 2 Ifthe mass of the gold islessthan 50 μg, the bead can be dissolvedwithout partingand the gold and silverconcentrationcan be determined as specified in 7.9.In such cases,inquartationisnot necessary.

Silvershould be determined by the method in 7.9 without parting,provided that the product of mass of the testportionby mass fractionof the silver,. emass. in the testportion,issmallerthan 7 500 μg. The testportionof 20 g,therefore,istoo much to determine the silver,where the mass fractionof the element exceeds325 g/t.

D.2 Procedure Weigh the bead priorto any attempt at parting(m0). Add a mass of silver(4 .10) sufficient o obtaina silverto gold ratioof 4 to 1. Wrap the bead and the silvertogetherin 0,5g of leadfoil(4 .9),cupelin accordancewith 7.6 to obtaina silverrichbead and determine the mass fractionof gold as specified in 7.8.

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ISO 10378:2016(E)

Annex E (normative) Determination of vaporizationlossof silverduring the cupellationprocess

E.1 General To prevent loss of silverduring the cupellation process, itisvery important that furnace conditions be as specified in 7.6.Itisrecommended that the lossof silverduring the cupellationprocessbe determined, to decideupon the furnace conditions.

Ifcomplete recovery is not obtained, the mass

fraction of silverof the test portion shallbe corrected.

E.2 Procedure Weigh the same mass of silver(4 .10) as the mass fractionof silverin the testportion.Wrap itin 40 g of lead foil(4.9) and cupel in accordance with 7.6 to obtaina silverbead.Retreat the cupel in accordance with 7.7 and combine the primary and secondary beads in the porcelain crucible. Add 10 ml of dilutenitricacid(4.8) to the beads ( 5.1 3) for 20 min, or untilthe reactionceases.

in the porcelain crucible and heat gently on a hotplate

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Determine silverconcentrationof the solutionsin accordance with 7.10.

E.3 Calculationof lossof silverduring the cupellationprocess Loss of silverduring the cupellationprocess(LAg ),expressed in percent, is given by Formula L

Ag

m−m1

=

×

m

(E.1): (E.1)

100

where m1

is the mass, in micrograms, of silverin the solutions;

m

isthe mass, in micrograms, of the silvermetal weighed.

E.4 Correction of mass fractionof silverof the testportion Ifsufficientrecovery of the testportion( w w w′

Ag

= 100

of silverduring the cupellation process is not obtained, the mass fraction of silver ) ,expressed in grams per tonne, should be corrected by Formula (E .2):

′

Ag

×

Ag

−L

100

(E.2)

Ag

where w

′ Ag

LAg

24

is the mass fraction of silver,in grams per tonne, of test portion calculated by Formula

(3);

is the loss of silver,in percent, calculated by Formula (E .1) .

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ISO 10378:2016(E)

Annex F (normative) Sulfuricacid —

Parting

F.1 General Ifthereisdanger of the gold sponge crumbling during the partingoperation,itisrecommended thatthe operationbe carriedout with sulfuricacid.

F.2 Reagent F.2.1

Sulfuricacid,concentrated(ρ20 1,84g/ml),chloridecontent