ISO 13291:2006

INTERNATIONAL ISO
STANDARD 13291
Second edition
2006-06-15


Zinc sulfide concentrates —
Determination of zinc — Solvent
extraction and EDTA titrimetric method
Concentrés sulfurés de zinc — Dosage du zinc — Méthode par
extraction à l'aide d'un solvant et titrage à l'EDTA





Reference number
ISO 13291:2006(E)
©
ISO 2006

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ISO 13291:2006(E)
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ISO 13291:2006(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 1
3 Principle. 1
4 Reagents. 2
5 Apparatus . 3
6 Sample . 3
6.1 Test sample . 3
6.2 Test portion . 3
7 Procedure . 3
7.1 Number of determinations . 3
7.2 Blank test. 4
7.3 Dissolution of test portion . 4
7.4 Extraction . 4
7.5 Titration. 4
7.6 Determination of the titration factor of the EDTA standard solution . 5
8 Expression of results . 5
9 Precision. 6
9.1 Expression of precision . 6
9.2 Procedure for obtaining the final result . 6
9.3 Between-laboratories precision . 6
9.4 Check of trueness. 7
10 Test report . 8
Annex A (normative) Procedure for the preparation and determination of the mass of a predried
test portion . 9
Annex B (normative) Flowchart of the procedure for the acceptance of analytical values for test
samples. 11
Annex C (normative) Elements that interfere with this method . 12
Annex D (informative) Derivation of precision equations. 13
Bibliography . 18

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ISO 13291:2006(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 13291 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 13291:1997), which has been technically
revised.

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INTERNATIONAL STANDARD ISO 13291:2006(E)

Zinc sulfide concentrates — Determination of zinc — Solvent
extraction and EDTA titrimetric 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 solvent extraction/titrimetric method for the determination of the mass
fraction of zinc in zinc sulfide concentrates.
The method is applicable to zinc sulfide concentrates having a mass fraction of zinc in the range from 11 % to
62 %.
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, Laboratory glassware — Burettes
ISO 648, Laboratory glassware — One-mark pipettes
ISO 1042, Laboratory glassware — One-mark volumetric flasks
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4787, Laboratory glassware — Volumetric glassware — Methods for use and testing of capacity
ISO 9599, Copper, lead and zinc sulfide concentrates — Determination of hygroscopic moisture in the
analysis sample — Gravimetric method
ISO Guide 35, Reference materials — General and statistical principles for certification
3 Principle
A test portion of zinc concentrate is dissolved in bromine and nitric acid. Any remaining insoluble residue is
dissolved in sulfuric, nitric and hydrofluoric acids. A zinc thiocyanate complex is selectively extracted into
methyl isobutyl ketone, after screening of some elements with thiourea and citrate ions. Partially extracted
cadmium is screened with iodide ions before the final titration as explained in Annex C. Cobalt is extracted
and determined separately, if present at concentration levels exceeding 0,05 %. Zinc is determined by titration
with EDTA solution at pH 5,5.
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ISO 13291:2006(E)
4 Reagents
During the analysis, only reagents of recognized analytical grade and water that complies with grade 2 of
ISO 3696 shall be used.
4.1 Zinc metal, minimum purity 99,99 %, free from oxide prior to use.
The surface of the metal may be cleaned by immersing the metal in hydrochloric acid (4.2), diluted 1 + 9 for
1 min, then washing well with water, followed by an acetone rinse and drying in an oven at 50 °C.
4.2 Hydrochloric acid, (ρ 1,16 g/ml to 1,19 g/ml).

20
4.3 Bromine.
4.4 Nitric acid, (ρ 1,42 g/ml).
20
4.5 Hydrofluoric acid, (ρ 1,13 g/ml to 1,15 g/ml).
20
4.6 Hydrochloric acid, (ρ 1,16 g/ml to 1,19 g/ml) diluted (1 + 4).
20
Add 200 ml of hydrochloric acid (4.2) to 800 ml of water.
4.7 Sulfuric acid, diluted (1 + 1).
Add carefully and slowly, with stirring, 500 ml of sulfuric acid (ρ 1,84 g/ml) to 500 ml of water.
20
4.8 Ammonia, (ρ 0,89 g/ml).
20
4.9 4-methyl-2-pentanone (methyl isobutyl ketone).
4.10 Ethanol, pure or denatured.
4.11 Screening solution.
Dissolve 60 g of thiourea, 100 g of di-ammonium citrate and 200 g of ammonium thiocyanate in water and
dilute to 1 l. Filter if necessary.
4.12 Sodium fluoride solution (20 g/l).
Dissolve 20 g of sodium fluoride in water. Dilute to 1 l.
4.13 Thiourea solution (100 g/l).
Dissolve 100 g of thiourea in water and dilute to 1 l.
4.14 Buffer solution.
Dissolve 250 g of hexamethylenetetramine in water. Add 60 ml of acetic acid (ρ 1,05 g/ml) and dilute to 1 l.
20
4.15 EDTA standard volumetric solution (0,05 mol/l).
Dissolve 18,6 g of the di-sodium salt of ethylenediaminetetraacetic acid dihydrate (EDTA) in water. Dilute to
1 l.
4.16 Potassium iodide solution (1 000 g/l).
Dissolve 100 g of potassium iodide in water and dilute to 100 ml.
Prepare fresh on the day of use.
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ISO 13291:2006(E)
4.17 Xylenol orange indicator (1 % m/m).
Mix 1 g of the sodium salt of xylenol orange with 99 g of potassium nitrate crystals, by gently grinding in a
ceramic mortar with a pestle. Mixing is considered complete when the colour is uniform throughout.
4.18 Iron stock solution.
Dissolve 45 g of iron(III) nitrate nonahydrate [Fe(NO )⋅9H O] in water and dilute to 1 l.
3 3 2
5 Apparatus
Ordinary laboratory equipment and the following.
5.1 Volumetric glassware, of class A complying with ISO 385, ISO 648 and ISO 1042 and used in
accordance with ISO 4787.
5.2 Platinum crucibles, of 25 ml capacity.
5.3 Balance, capable of being read to 0,1 mg.
5.4 Oven, with its temperature controlled at 105 °C ± 5 °C.
5.5 Muffle furnace, having a maximum required operating temperature higher than 800 °C.
5.6 Laboratory hotplate.
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 dish or tray. Weigh, to the nearest 0,1 mg, 2,5 g of test sample. At the same time as the
test portion is weighed, 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.
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 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.
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ISO 13291:2006(E)
7.2 Blank test
Determine a reagent blank. It is advisable to perform duplicate blank determinations every time an analysis is
carried out on a laboratory sample. The blank samples are carried through the whole procedure, apart from
where no laboratory-sample test portion is required. However, 5 ml of iron stock solution (4.18) should be
added to assist in the determination of turbidity. The volume of EDTA titrant used is V .
b
7.3 Dissolution of test portion
Place the test portion in a 300 ml narrow-necked conical flask. Moisten the material with about 20 ml of water
and add 2 ml to 3 ml of bromine (4.3). Allow to react at ambient temperature for 15 min, swirling the flask and
contents from time to time. Add 15 ml of nitric acid (4.4) and leave for a further 15 min. Place the flask on a
hotplate (5.6) and bring gently to the boil, to expel all bromine vapours. Cool, add 100 ml of water, heat to
boiling and cool.
If no insoluble material is present, transfer the liquid to a 500 ml one-mark volumetric flask, rinsing the conical
flask thoroughly. Make up to the mark with water.
If insoluble residue is present, filter through a medium-speed cellulose filter paper into a 500 ml one-mark
volumetric flask. Rinse the filter thoroughly with water. Place the filter and insoluble residue in a platinum
crucible (5.2) and gently ash in the muffle furnace (5.5) set at 800 °C. Add 2 ml of dilute sulfuric acid (4.7),
2 ml of nitric acid (4.4) and 2 ml of hydrofluoric acid (4.5) and evaporate the solution nearly to dryness. Cool
and add water in small quantities, to dissolve the soluble salts. Filter through a medium-speed cellulose filter
paper and add the filtrate and washing solution to the 500 ml one-mark volumetric flask used above. Make up
to the mark with water.
If the sample contains lead, damage to the platinum crucible may occur. In this case, insoluble material should
be treated as follows.
Rinse the insoluble residue into a polytetrafluoroethylene beaker with a fine jet of water. Place the filter in a
porcelain crucible and gently ash the paper in the muffle furnace (5.5) at 600 °C to 700 °C. Allow the crucible
to cool to ambient temperature.
Rinse the material in the crucible by washing with a small quantity of water into the polytetrafluroethylene
beaker used above. Add 2 ml of dilute sulfuric acid (4.7), 2 ml of nitric acid (4.4) and 2 ml of hydrofluoric acid
(4.5) and evaporate the solution nearly to dryness. Cool and add water in small quantities, to dissolve the
soluble salts. Filter through a medium-speed cellulose filter paper and add the filtrate and washing solution to
the 500 ml one-mark volumetric flask used above. Make up to the mark with water.
Should it be confirmed that the filter paper contains no zinc, the procedure of ashing the filter may be omitted.
7.4 Extraction
Pipette 50,00 ml of the solution obtained in 7.3 into a 250 ml separating funnel. Add ammonia (4.8) dropwise
until a slight turbidity develops. Add 5 ml of dilute hydrochloric acid (4.6) and 50 ml of screening solution (4.11).
Mix well. Add 80 ml of 4-methyl-2-pentanone (4.9) and shake for 1 min. Allow the phases to separate and
slowly transfer the lower aqueous phase to another separating funnel. Perform a second extraction with 20 ml
of 4-methyl-2-pentanone (4.9). Separate the phases and discard the aqueous phase. Combine the two
separate organic phases in a 400 ml low-form beaker.
Place 1 ml of dilute hydrochloric acid (4.6) and 70 ml of ethanol (4.10) in each of the two separating funnels.
Shake well and discharge the contents from both funnels into the 400 ml low-form beaker.
7.5 Titrat
...