ISO 12739:1997
(Main)Zinc sulfide concentrates — Determination of zinc content — Ion-exchange/EDTA titrimetric method
Zinc sulfide concentrates — Determination of zinc content — Ion-exchange/EDTA titrimetric method
Concentrés sulfurés de zinc — Dosage du zinc — Méthode par échange d'ions et titrage à l'EDTA
Koncentrati cinkovega sulfida - Določevanje cinka - Metoda ionske izmenjave/titrimetrijska metoda z EDTA
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INTERNATIONAL ISO
STANDARD 12739
First edition
1997-11-15
Zinc sulfide concentrates — Determination
of zinc content — Ion-exchange/EDTA
titrimetric method
Concentrés sulfurés de zinc — Dosage du zinc — Méthode par échange
d'ions et titrage à l'EDTA
A
Reference number
ISO 12739:1997(E)
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ISO 12739:1997(E)
Contents Page
1 Scope . 1
2 Normative references . 1
3 Principle . 1
4 Reagents . 2
Apparatus .
5 3
6 Sample . 3
7 Procedure . 4
8 Expression of results . 6
9 Precision . 6
Test report .
10 8
Annexes
A Ion exchange resins and columns . 9
B Procedure for the preparation and determination of the mass of
a predried test portion . 11
C Determination of cadmium by atomic absorption spectrometry . 13
D Flowchart of the procedure for the acceptance of analytical
values for test samples . 15
E Effect of potentially interfering elements . 16
F Derivation of precision equations . 17
G Bibliography . 21
© ISO 1997
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 the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet central@iso.ch
X.400 c=ch; a=400net; p=iso; o=isocs; s=central
Printed in Switzerland
ii
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©
ISO ISO 12739:1997(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.
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.
International Standard ISO 12739 was prepared by Technical Committee
ISO/TC 183, Copper lead and zinc ores and concentrates.
Annexes A to D form an integral part of this International Standard.
Annexes E to G are for information only.
iii
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©
INTERNATIONAL STANDARD ISO ISO 12739:1997(E)
Zinc sulfide concentrates — Determination of zinc content —
Ion-exchange/EDTA titrimetric method
1 Scope
This International Standard specifies an ion-exchange titrimetric method for the determination of the zinc content of
zinc concentrates. The method is applicable to zinc sulfide concentrates with zinc content in the range from
11 % (m/m) to 62 % (m/m).
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this
International Standard. At the time of publication, the editions indicated were valid. All standards are subject to
revision, and parties to agreements based on this International Standard are encouraged to investigate the
possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain
registers of currently valid International Standards.
ISO 385-1:1984, Laboratory glassware — Burettes — Part 1: General requirements.
ISO 648:1977, Laboratory glassware — One-mark pipettes.
1)
ISO 1042:— , 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.
ISO Guide 35:1989, Certification of reference materials — General and statistical principles.
3 Principle
The test portion of zinc concentrate is dissolved in hydrochloric, nitric and sulfuric acids. The acidity is adjusted to
about 2 mol/l with respect to hydrochloric acid. Zinc is adsorbed on a strongly basic anion exchange resin. Some
interfering ions are removed by elution with 2 mol/l hydrochloric acid solution. Zinc is eluted with an ammonia-
ammonium chloride solution. Zinc is determined in the eluate by titration with EDTA at a pH of approximately 5,6
using xylenol orange indicator.
___________
1) To be published. (Revision of ISO 1042:1983)
1
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ISO
ISO 12739:1997(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, 99,99 % minimum purity, free from oxide prior to use.
The surface of the metal may be cleaned by immersing the metal in hydrochloric acid (4.3), diluted 1 + 9 for 1 min,
washed well with water followed by an acetone rinse and dried in an oven at 50 °C.
4.2 Xylenol orange indicator (0,1 % m/m)
Mix 0,1 g of the sodium salt of xylenol orange with 100 g of potassium nitrate crystals by gently grinding in a
ceramic mortar with a pestle. Mixing is considered complete when colour is uniform throughout.
4.3 Hydrochloric acid (r 1,16 g/ml to 1,19 g/ml)
20
4.4 Hydrochloric acid, diluted (1 + 1)
Add 500 ml of hydrochloric acid (4.3) to 500 ml of water.
4.5 Hydrochloric acid, diluted (1 + 5)
Add 100 ml of hydrochloric acid (4.3) to 500 ml of water.
4.6 Nitric acid (r 1,42 g/ml)
20
4.7 Nitric acid, diluted (1 + 1)
Add 500 ml of nitric acid (4.6) to 500 ml of water.
4.8 Sulfuric acid, diluted (1 + 1)
Add carefully and slowly, with stirring 500 ml of sulfuric acid (r 1,84 g/ml) to 500 ml of water.
20
4.9 Sulfuric acid, diluted (1 + 100)
Add 20 ml of dilute sulfuric acid (4.8) to 1 000 ml of water.
4.10 Hydrofluoric acid (r 1,13 g/ml to 1,15 g/ml)
20
4.11 Ammonia solution, diluted (7 + 100)
Add 70 ml of aqueous ammonia solution (r 0,89 g/ml) to 1 000 ml of water.
20
4.12 Ammonia-ammonium chloride solution
Dissolve 20 g of ammonium chloride in 1 l of dilute ammonia solution (4.11).
4.13 Hydrochloric acid-ascorbic acid solution
Dissolve 0,25 g of ascorbic acid in 100 ml of dilute hydrochloric acid (4.5). Prepare fresh on day of use.
2
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ISO 12739:1997(E)
4.14 Ammonium fluoride solution (50 g/l)
Dissolve 50 g of ammonium fluoride in water and dilute to 1 l.
4.15 Sodium thiosulfate solution (100 g/l)
Dissolve 100 g of sodium thiosulfate pentahydrate in water and dilute to 1 l.
4.16 Buffer solution (pH = 5,5)
Dissolve 250 g of ammonium acetate and 25 ml of concentrated acetic acid (r 1,05 g/ml) in water and dilute to 1 l.
20
4.17 Para-nitrophenol indicator solution (2 g/l)
Dissolve 0,2 g of para-nitrophenol in water and dilute to 100 ml.
4.18 EDTA standard volumetric solution (0,1 mol/l)
Dissolve 37,2 g of the di-sodium salt of ethylenediaminetetraacetic acid dihydrate (EDTA) in water and dilute to 1 l.
5 Apparatus
5.1 Class A volumetric glassware complying with ISO 385-1, ISO 648 and ISO 1042 and used in accordance
with ISO 4787.
5.2 Balance, capable of being read to 0,1 mg.
5.3 Laboratory hotplate
5.4 Muffle furnace, capable of operating at 800 °C.
5.5 Platinum crucibles, of 25 ml capacity.
5.6 Ion exchange columns, with general dimensions shown in annex A.
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 B).
6.2 Test portion
Taking multiple increments, extract a test portion of 0,5 g, weighed to the nearest 0,1 mg, from the test sample in
such a manner that it is representative of the contents of the dish or tray. 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 B may be used to prepare predried test portions directly from the
laboratory sample.
3
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ISO
ISO 12739:1997(E)
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.
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. The volume of EDTA titrant used is V .
b
7.3 Dissolution of test portion
Place the test portion in a 300 ml conical beaker. Add 25 ml of hydrochloric acid (4.3). Cover with a watch glass and
heat beaker and contents gently for 5 min.
Add 20 ml of dilute nitric acid (4.7) and 15 ml of dilute sulfuric acid (4.8). Heat and evaporate the solution to about
5 ml. Cool and add with caution about 50 ml of water and boil the solution.
Cool the solution to room temperature and filter it into a 300 ml beaker through a medium-speed cellulose filter
paper. Wash the beaker and filter paper thoroughly with dilute sulfuric acid (4.9), collecting the washings in the
same beaker.
If an acid-insoluble material is present, place the filter and insoluble residue in a platinum crucible (5.5) (see note
below) and gently reduce the paper to ashes in the muffle furnace (5.4) at 800 °C. Allow the crucible and residue to
cool to ambient temperature. Add 2 ml of dilute sulfuric acid (4.8), 2 ml of nitric acid (4.6) and 2 ml of hydrofluoric
acid (4.10) 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
initial solution obtained above as described in paragraphs 1 to 3.
Heat to evaporate the combined filtrates to a volume of 60 ml to 80 ml. Cool and add 16 ml of hydrochloric acid
(4.3). Dilute to 100 ml with water.
NOTE — If the sample contains lead, damage to the platinum crucible may occur. An alternative fusion with a zirconium
crucible and sodium peroxide may be preferable.
7.4 Preparation of the ion-exchange column
Examples of ion-exchange columns which are suitable for use are shown in annex A. Pack water-soaked cotton or
glass wool pads into the bottom of the column to a thickness of about 5 mm. This will retain resin in the column
during use.
Soak the resin overnight in distilled water to make a slurry. With the stopcock open carefully transfer the slurry into
the column to form a settled bed. This resin bed is formed by about 16 ml of the swollen resin. Close the stopcock
and put about a 5 mm thickness of water-soaked glass wool or cotton wool on top of the resin.
NOTE — It is essential to ensure that the resin is covered by liquid at all times because air trapped in a resin causes
“channelling”, i.e. uneven flow rate and poor efficiency in the ion exchanger. If air enters the resin bed, it is recommended that
the column be emptied and then repacked.
Pass about 100 ml of hydrochloric acid (4.5) through the column ensuring that the resin is covered at all times.
Adjust the flow rate to about 5 ml/min using the stopcock control. The resin can be rapidly regenerated at any time
by passing 100 ml of water and then 100 ml of dilute hydrochloric acid (4.5) through the column ensuring that the
resin is always covered with liquid.
4
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ISO
ISO 12739:1997(E)
7.5 Adsorption of zinc on ion-exchange column
Quantitatively transfer the test solution obtained in 7.3 to the ion-exchange column at a flow rate of about 5 ml/min.
Rinse the beaker with small increments of dilute hydrochloric acid (4.5) and transfer the washings to the column.
A total washing volume of 100 ml should be sufficient. Continue to drain the column until the liquid is 5 mm above
the top wool plug.
Pass 100 ml of hydrochloric-ascorbic acid solution (4.13) through the column in small quantities. Then pass 100 ml
of dilute hydrochloric acid (4.5) through the column. Collect the eluate in a 500 ml beaker and discard.
7.6 Elution of zinc from ion-exchange column
Elute the adsorbed zinc from the column by passing 180 ml of ammonia-ammonium chloride solution (4.12) through
the resin at a flow rate of less than 5 ml/min. Collect the eluate in a 500 ml beaker.
NOTE — The column should now be regenerated in preparation for the next test solution using the procedure described
in 7.4.
7.7 Titration
Add 2 to 3 drops of para-nitrophenol indicator solution (4.17) to the column eluate obtained in 7.6. Add dilute
hydrochloric acid (4.4) until the colour of the solution changes from yellow to colourless.
NOTE 1 A pH meter may be used to adjust the pH to a value 5,5 to 5,7 instead of using the para-nitrophenol indicator. Care
should be taken to ensure that the electrodes are washed off with water before continuing the procedure.
Add successively to the solution, 20 ml of buffer solution (4.16), 3 ml of ammonium fluoride solution (4.14) and 5 ml
of sodium thiosulfate solution (4.15). Add 0,5 g of xylenol orange indicator (4.2) and swirl to dissolve. Titrate with
EDTA standard solution (4.18) until the colour changes from red to yellow. Record the volume, V , of EDTA standard
t
solution required.
NOTE 2 If the test sample contains cadmium it will be eluted with the zinc and will be titrated during the procedure in 7.7. The
cadmium concentration must be determined separately and a correction made for its presence. The method for the
determination of cadmium is given in annex C. The effect of other elements commonly found in zinc concentrates is discussed
in annex E.
7.8 Determination of the titration factor of the EDTA standard solution
NOTE — In order to obtain a relative accuracy of between 0,1 % and 0,2 %, it is necessary to standardize the EDTA standard
solution with zinc at the same time and under the same conditions as the analysis. It is thus advisable for the calibration to
follow the complete set of operating conditions set down for the analysis. Likewise to improve the repeatability of the calibration
it is useful to prepare several zinc reference solutions.
The EDTA standard solution should be standardized as follows:
— Weigh into three separate 500 ml beakers between 0,055 g and 0,31 g of high purity zinc metal (4.1), to the
nearest 0,000 1 g, depending on the zinc content of the test sample. Record these masses as m , m and m .
1 2 3
— To each beaker add 15 ml of dilute hydrochloric acid (4.4). Heat gently to dissolve the metal, cool and add
150 ml of ammonia-ammonium chloride solution (4.12).
— Add 2 to 3 drops of para-nitrophenol indicator solution (4.17). Add dilute hydrochloric acid (4.4) until the colour
changes from yellow to colourless. Alternatively a pH meter may be used as indicated in note 1 in 7.7
— Add successively 20 ml of buffer solution (4.16), 3 ml of ammonium fluoride solution (4.14) and 5 ml of sodium
thiosulfate solution (4.15). Add 0,5 g of xylenol orange indicator (4.2) and swirl to dissolve. Titrate each beaker
with EDTA standard solution (4.18) until the colour changes from red to yellow and record the volume as V , V
1 2
and V .
3
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ISO
ISO 12739:1997(E)
— Calculate the intermediate factor, fi , for each beaker using the following formula:
x
fi = m /V for x = 1 to 3 . . . (1a)
x x x
where
fi is the factor obtained from the titration;
x
m is the mass of zinc weighed, in grams;
x
V is the volume of EDTA standard solution, in millilitres.
x
If the range of values for fi , fi and fi exceeds 0,000 01 g/ml then repeat the standardization.
1 2 3
Otherwise calculate the mean factor as follows:
fi++fi fi
12 3
f
= . . . (1b)
3
8 Expression of results
The zinc content of the test portion, W , expressed as a percentage by mass, is given by the following equation:
zn
VV−×f× 100
()
100
tb
W= − 0,581c× . . . (2)
zn
m 100−H
where
V is the volume of EDTA standard solution (4.18), in millilitres, used to titrate the test solution;
t
V is the volume of EDTA standard solution (4.18), in millilitres, used to titrate the blank solution;
b
f is the zinc equivalence factor, in grams per millilitre, determined in 7.7;
m is the mass, in grams, of the test portion;
c is the cadmium concentration, expressed as a percentage by mass;
H is the hygroscopic moisture content, as a percentage of the test portion (in the case of predried test portion
being used H = 0).
Calculate the zinc content of the test portion to the second decimal place.
9 Precision
9.1 Expression of precision
The precision of this analytical method is expressed b
...
SLOVENSKI STANDARD
SIST ISO 12739:2000
01-junij-2000
.RQFHQWUDWLFLQNRYHJDVXOILGD'RORþHYDQMHFLQND0HWRGDLRQVNH
L]PHQMDYHWLWULPHWULMVNDPHWRGD]('7$
Zinc sulfide concentrates -- Determination of zinc content -- Ion-exchange/EDTA
titrimetric method
Concentrés sulfurés de zinc -- Dosage du zinc -- Méthode par échange d'ions et titrage à
l'EDTA
Ta slovenski standard je istoveten z: ISO 12739:1997
ICS:
73.060.99 Druge rude Other metalliferous minerals
SIST ISO 12739:2000 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST ISO 12739:2000
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SIST ISO 12739:2000
INTERNATIONAL ISO
STANDARD 12739
First edition
1997-11-15
Zinc sulfide concentrates — Determination
of zinc content — Ion-exchange/EDTA
titrimetric method
Concentrés sulfurés de zinc — Dosage du zinc — Méthode par échange
d'ions et titrage à l'EDTA
A
Reference number
ISO 12739:1997(E)
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SIST ISO 12739:2000
ISO 12739:1997(E)
Contents Page
1 Scope . 1
2 Normative references . 1
3 Principle . 1
4 Reagents . 2
Apparatus .
5 3
6 Sample . 3
7 Procedure . 4
8 Expression of results . 6
9 Precision . 6
Test report .
10 8
Annexes
A Ion exchange resins and columns . 9
B Procedure for the preparation and determination of the mass of
a predried test portion . 11
C Determination of cadmium by atomic absorption spectrometry . 13
D Flowchart of the procedure for the acceptance of analytical
values for test samples . 15
E Effect of potentially interfering elements . 16
F Derivation of precision equations . 17
G Bibliography . 21
© ISO 1997
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 the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet central@iso.ch
X.400 c=ch; a=400net; p=iso; o=isocs; s=central
Printed in Switzerland
ii
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SIST ISO 12739:2000
©
ISO ISO 12739:1997(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.
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.
International Standard ISO 12739 was prepared by Technical Committee
ISO/TC 183, Copper lead and zinc ores and concentrates.
Annexes A to D form an integral part of this International Standard.
Annexes E to G are for information only.
iii
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SIST ISO 12739:2000
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SIST ISO 12739:2000
©
INTERNATIONAL STANDARD ISO ISO 12739:1997(E)
Zinc sulfide concentrates — Determination of zinc content —
Ion-exchange/EDTA titrimetric method
1 Scope
This International Standard specifies an ion-exchange titrimetric method for the determination of the zinc content of
zinc concentrates. The method is applicable to zinc sulfide concentrates with zinc content in the range from
11 % (m/m) to 62 % (m/m).
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this
International Standard. At the time of publication, the editions indicated were valid. All standards are subject to
revision, and parties to agreements based on this International Standard are encouraged to investigate the
possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain
registers of currently valid International Standards.
ISO 385-1:1984, Laboratory glassware — Burettes — Part 1: General requirements.
ISO 648:1977, Laboratory glassware — One-mark pipettes.
1)
ISO 1042:— , 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.
ISO Guide 35:1989, Certification of reference materials — General and statistical principles.
3 Principle
The test portion of zinc concentrate is dissolved in hydrochloric, nitric and sulfuric acids. The acidity is adjusted to
about 2 mol/l with respect to hydrochloric acid. Zinc is adsorbed on a strongly basic anion exchange resin. Some
interfering ions are removed by elution with 2 mol/l hydrochloric acid solution. Zinc is eluted with an ammonia-
ammonium chloride solution. Zinc is determined in the eluate by titration with EDTA at a pH of approximately 5,6
using xylenol orange indicator.
___________
1) To be published. (Revision of ISO 1042:1983)
1
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ISO 12739:1997(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, 99,99 % minimum purity, free from oxide prior to use.
The surface of the metal may be cleaned by immersing the metal in hydrochloric acid (4.3), diluted 1 + 9 for 1 min,
washed well with water followed by an acetone rinse and dried in an oven at 50 °C.
4.2 Xylenol orange indicator (0,1 % m/m)
Mix 0,1 g of the sodium salt of xylenol orange with 100 g of potassium nitrate crystals by gently grinding in a
ceramic mortar with a pestle. Mixing is considered complete when colour is uniform throughout.
4.3 Hydrochloric acid (r 1,16 g/ml to 1,19 g/ml)
20
4.4 Hydrochloric acid, diluted (1 + 1)
Add 500 ml of hydrochloric acid (4.3) to 500 ml of water.
4.5 Hydrochloric acid, diluted (1 + 5)
Add 100 ml of hydrochloric acid (4.3) to 500 ml of water.
4.6 Nitric acid (r 1,42 g/ml)
20
4.7 Nitric acid, diluted (1 + 1)
Add 500 ml of nitric acid (4.6) to 500 ml of water.
4.8 Sulfuric acid, diluted (1 + 1)
Add carefully and slowly, with stirring 500 ml of sulfuric acid (r 1,84 g/ml) to 500 ml of water.
20
4.9 Sulfuric acid, diluted (1 + 100)
Add 20 ml of dilute sulfuric acid (4.8) to 1 000 ml of water.
4.10 Hydrofluoric acid (r 1,13 g/ml to 1,15 g/ml)
20
4.11 Ammonia solution, diluted (7 + 100)
Add 70 ml of aqueous ammonia solution (r 0,89 g/ml) to 1 000 ml of water.
20
4.12 Ammonia-ammonium chloride solution
Dissolve 20 g of ammonium chloride in 1 l of dilute ammonia solution (4.11).
4.13 Hydrochloric acid-ascorbic acid solution
Dissolve 0,25 g of ascorbic acid in 100 ml of dilute hydrochloric acid (4.5). Prepare fresh on day of use.
2
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ISO 12739:1997(E)
4.14 Ammonium fluoride solution (50 g/l)
Dissolve 50 g of ammonium fluoride in water and dilute to 1 l.
4.15 Sodium thiosulfate solution (100 g/l)
Dissolve 100 g of sodium thiosulfate pentahydrate in water and dilute to 1 l.
4.16 Buffer solution (pH = 5,5)
Dissolve 250 g of ammonium acetate and 25 ml of concentrated acetic acid (r 1,05 g/ml) in water and dilute to 1 l.
20
4.17 Para-nitrophenol indicator solution (2 g/l)
Dissolve 0,2 g of para-nitrophenol in water and dilute to 100 ml.
4.18 EDTA standard volumetric solution (0,1 mol/l)
Dissolve 37,2 g of the di-sodium salt of ethylenediaminetetraacetic acid dihydrate (EDTA) in water and dilute to 1 l.
5 Apparatus
5.1 Class A volumetric glassware complying with ISO 385-1, ISO 648 and ISO 1042 and used in accordance
with ISO 4787.
5.2 Balance, capable of being read to 0,1 mg.
5.3 Laboratory hotplate
5.4 Muffle furnace, capable of operating at 800 °C.
5.5 Platinum crucibles, of 25 ml capacity.
5.6 Ion exchange columns, with general dimensions shown in annex A.
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 B).
6.2 Test portion
Taking multiple increments, extract a test portion of 0,5 g, weighed to the nearest 0,1 mg, from the test sample in
such a manner that it is representative of the contents of the dish or tray. 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 B may be used to prepare predried test portions directly from the
laboratory sample.
3
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SIST ISO 12739:2000
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ISO 12739:1997(E)
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.
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. The volume of EDTA titrant used is V .
b
7.3 Dissolution of test portion
Place the test portion in a 300 ml conical beaker. Add 25 ml of hydrochloric acid (4.3). Cover with a watch glass and
heat beaker and contents gently for 5 min.
Add 20 ml of dilute nitric acid (4.7) and 15 ml of dilute sulfuric acid (4.8). Heat and evaporate the solution to about
5 ml. Cool and add with caution about 50 ml of water and boil the solution.
Cool the solution to room temperature and filter it into a 300 ml beaker through a medium-speed cellulose filter
paper. Wash the beaker and filter paper thoroughly with dilute sulfuric acid (4.9), collecting the washings in the
same beaker.
If an acid-insoluble material is present, place the filter and insoluble residue in a platinum crucible (5.5) (see note
below) and gently reduce the paper to ashes in the muffle furnace (5.4) at 800 °C. Allow the crucible and residue to
cool to ambient temperature. Add 2 ml of dilute sulfuric acid (4.8), 2 ml of nitric acid (4.6) and 2 ml of hydrofluoric
acid (4.10) 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
initial solution obtained above as described in paragraphs 1 to 3.
Heat to evaporate the combined filtrates to a volume of 60 ml to 80 ml. Cool and add 16 ml of hydrochloric acid
(4.3). Dilute to 100 ml with water.
NOTE — If the sample contains lead, damage to the platinum crucible may occur. An alternative fusion with a zirconium
crucible and sodium peroxide may be preferable.
7.4 Preparation of the ion-exchange column
Examples of ion-exchange columns which are suitable for use are shown in annex A. Pack water-soaked cotton or
glass wool pads into the bottom of the column to a thickness of about 5 mm. This will retain resin in the column
during use.
Soak the resin overnight in distilled water to make a slurry. With the stopcock open carefully transfer the slurry into
the column to form a settled bed. This resin bed is formed by about 16 ml of the swollen resin. Close the stopcock
and put about a 5 mm thickness of water-soaked glass wool or cotton wool on top of the resin.
NOTE — It is essential to ensure that the resin is covered by liquid at all times because air trapped in a resin causes
“channelling”, i.e. uneven flow rate and poor efficiency in the ion exchanger. If air enters the resin bed, it is recommended that
the column be emptied and then repacked.
Pass about 100 ml of hydrochloric acid (4.5) through the column ensuring that the resin is covered at all times.
Adjust the flow rate to about 5 ml/min using the stopcock control. The resin can be rapidly regenerated at any time
by passing 100 ml of water and then 100 ml of dilute hydrochloric acid (4.5) through the column ensuring that the
resin is always covered with liquid.
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©
ISO
ISO 12739:1997(E)
7.5 Adsorption of zinc on ion-exchange column
Quantitatively transfer the test solution obtained in 7.3 to the ion-exchange column at a flow rate of about 5 ml/min.
Rinse the beaker with small increments of dilute hydrochloric acid (4.5) and transfer the washings to the column.
A total washing volume of 100 ml should be sufficient. Continue to drain the column until the liquid is 5 mm above
the top wool plug.
Pass 100 ml of hydrochloric-ascorbic acid solution (4.13) through the column in small quantities. Then pass 100 ml
of dilute hydrochloric acid (4.5) through the column. Collect the eluate in a 500 ml beaker and discard.
7.6 Elution of zinc from ion-exchange column
Elute the adsorbed zinc from the column by passing 180 ml of ammonia-ammonium chloride solution (4.12) through
the resin at a flow rate of less than 5 ml/min. Collect the eluate in a 500 ml beaker.
NOTE — The column should now be regenerated in preparation for the next test solution using the procedure described
in 7.4.
7.7 Titration
Add 2 to 3 drops of para-nitrophenol indicator solution (4.17) to the column eluate obtained in 7.6. Add dilute
hydrochloric acid (4.4) until the colour of the solution changes from yellow to colourless.
NOTE 1 A pH meter may be used to adjust the pH to a value 5,5 to 5,7 instead of using the para-nitrophenol indicator. Care
should be taken to ensure that the electrodes are washed off with water before continuing the procedure.
Add successively to the solution, 20 ml of buffer solution (4.16), 3 ml of ammonium fluoride solution (4.14) and 5 ml
of sodium thiosulfate solution (4.15). Add 0,5 g of xylenol orange indicator (4.2) and swirl to dissolve. Titrate with
EDTA standard solution (4.18) until the colour changes from red to yellow. Record the volume, V , of EDTA standard
t
solution required.
NOTE 2 If the test sample contains cadmium it will be eluted with the zinc and will be titrated during the procedure in 7.7. The
cadmium concentration must be determined separately and a correction made for its presence. The method for the
determination of cadmium is given in annex C. The effect of other elements commonly found in zinc concentrates is discussed
in annex E.
7.8 Determination of the titration factor of the EDTA standard solution
NOTE — In order to obtain a relative accuracy of between 0,1 % and 0,2 %, it is necessary to standardize the EDTA standard
solution with zinc at the same time and under the same conditions as the analysis. It is thus advisable for the calibration to
follow the complete set of operating conditions set down for the analysis. Likewise to improve the repeatability of the calibration
it is useful to prepare several zinc reference solutions.
The EDTA standard solution should be standardized as follows:
— Weigh into three separate 500 ml beakers between 0,055 g and 0,31 g of high purity zinc metal (4.1), to the
nearest 0,000 1 g, depending on the zinc content of the test sample. Record these masses as m , m and m .
1 2 3
— To each beaker add 15 ml of dilute hydrochloric acid (4.4). Heat gently to dissolve the metal, cool and add
150 ml of ammonia-ammonium chloride solution (4.12).
— Add 2 to 3 drops of para-nitrophenol indicator solution (4.17). Add dilute hydrochloric acid (4.4) until the colour
changes from yellow to colourless. Alternatively a pH meter may be used as indicated in note 1 in 7.7
— Add successively 20 ml of buffer solution (4.16), 3 ml of ammonium fluoride solution (4.14) and 5 ml of sodium
thiosulfate solution (4.15). Add 0,5 g of xylenol orange indicator (4.2) and swirl to dissolve. Titrate each beaker
with EDTA standard solution (4.18) until the colour changes from red to yellow and record the volume as V , V
1 2
and V .
3
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ISO
ISO 12739:1997(E)
— Calculate the intermediate factor, fi , for each beaker using the following formula:
x
fi = m /V for x = 1 to 3 . . . (1a)
x x x
where
fi is the factor obtained from the titration;
x
m is the mass of zinc weighed, in grams;
x
V is the volume of EDTA standard solution, in millilitres.
x
If the range of values for fi , fi and fi exceeds 0,000 01 g/ml then repeat the standardization.
1 2 3
Otherwise calculate the mean factor as follows:
fi++fi fi
12 3
f
= . . . (1b)
3
8 Expression of results
The zinc content of the test portion, W , expressed as a percentage by mass, is given by the following equation:
zn
VV−×f× 100
()
100
tb
W= − 0,581c× . . . (2)
zn
m 100−H
where
V is the volume of EDTA standard solution (4.18), in millilitres, used to titrate the test solution;
t
V is the volume of EDTA standard solution (4.18), in millilitres, used to titrate the blank solution;
b
f is t
...
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