ISO 13291:1997
(Main)Zinc sulfide concentrates — Determination of zinc content — Solvent extraction and EDTA titrimetric method
Zinc sulfide concentrates — Determination of zinc content — 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
Koncentrati cinkovega sulfida - Določevanje cinka - Metoda s topilom in titrimetrijska metoda z EDTA
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INTERNATIONAL ISO
STANDARD 13291
First edition
1997-11-15
Zinc sulfide concentrates — Determination
of zinc content — 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
A
ISO 13291:1997(E)
---------------------- Page: 1 ----------------------
ISO 13291:1997(E)
Contents Page
11 Scope. 1
22.01Normative references . 1
33.02Principle . 1
41.03 Reagents . 2
51.04Apparatus. 3
61.05Sample. 3
71.06Procedure. 3
82 Expression of results .
5
92.01Precision . 6
10.02Test report. 8
Bagues de roulement.
02.03 0
AnnexesRondelles de butée. 0
A2((normative) Procedure for the preparation and
determination of the mass of a predried test portion . 9
B2((normative) Flowchart of the procedure for the
acceptance of analytical values for test samples. 11
C2((normative) Elements that interfere with this method . 12
D2((informative) Derivation of precision equations . 13
E2((informative) Bibliography . 18
© 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
---------------------- Page: 2 ----------------------
©
ISO ISO 13291:1997(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 13291 was prepared by Technical Committee
ISO/TC 183, Copper, lead and zinc ores and concentrates.
Annexes A to C form an integral part of this International Standard.
Annexes D and E are for information only.
iii
---------------------- Page: 3 ----------------------
©
INTERNATIONAL STANDARD ISO ISO 13291:1997(E)
Zinc sulfide concentrates — Determination of zinc content —
Solvent extraction and EDTA titrimetric method
1 Scope
This International Standard specifies a solvent extraction/titrimetric method for the determination of the zinc content
of zinc sulfide 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 I: 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
A test portion of zinc concentrate is dissolved in bromine and nitric acid. Any remaining insoluble residue is
dissolved in hydrofluoric and perchloric 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 must be
determined separately if present at concentration levels exceeding 0,05 %. Zinc is determined by titration with
EDTA solution at pH 5,5.
1) To be published. (Revision of ISO 1042:1983)
1
---------------------- Page: 4 ----------------------
©
ISO 13291:1997(E) ISO
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,
washed well with water followed by an acetone rinse and dried in an oven at 50°C.
4.2 Hydrochloric acid, (r 1,16 g/ml to 1,19 g/ml).
20
4.3 Bromine
4.4 Nitric acid, (r 1,42 g/ml)
20
4.5 Hydrochloric acid, (r 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.
4.6 Hydrofluoric acid, (r 1,13 g/ml to 1,15 g/ml)
20
4.7 Perchloric acid, (r 1,54 g/ml)
20
4.8 Ammonia, (r 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 (r 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.
2
---------------------- Page: 5 ----------------------
©
ISO ISO 13291:1997(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
5.1 Ordinary laboratory equipment and
5.2 Volumetric glassware, of class A complying with ISO 385-1, ISO 648 and ISO 1042 and used in
accordance with ISO 4787.
5.3 Platinum crucibles, of 25 ml capacity.
,
5.4 Balance capable of being read to 0,1 mg.
5.5 Oven, with temperature controlled at 105 °C ± 5 °C.
5.6 Muffle furnace, having a maximum required operating temperature higher than 800 °C.
5.7 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
Take 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.
3
---------------------- Page: 6 ----------------------
©
ISO 13291:1997(E) ISO
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 (5.7) and
bring gently to the boil to expel all bromine vapours. Cool, add 100 ml of water, heat to boiling, 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 material is present, filter through a medium speed 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 (5.3) (see Note)
and gently ash the paper in the muffle furnace (5.6) set at 800 °C. Add 2 ml of hydrofluoric acid (4.6) and then 5 ml
of perchloric acid (4.7). Heat until dense perchloric acid fumes appear. Allow to cool, dilute with about 25 ml of
water. Filter if a lead sulfate precipitate appears. Transfer the filtrate to the same one-mark volumetric flask used
above. Rinse the filter paper thoroughly and make up to the mark with water.
NOTE — If the sample contains lead, damage to the platinum crucible may occur. In this case, fusion with sodium peroxide in
a zirconium crucible is preferable.
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 (4.5) 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 (4.5) and 70 ml of ethanol (4.10) into each of the two separating funnels.
Shake well and discharge the contents from both funnels into the 400 ml low-form beaker.
7.5 Titration
Add successively 10 ml of sodium fluoride solution (4.12), 10 ml of thiourea solution (4.13), 20 ml of buffer solution
(4.14), 5 ml of potassium iodide solution (4.16) and 0,1 g of xylenol orange indicator (4.17).
Titrate with EDTA solution (4.15) until the colour changes from red to yellow. Titrate very slowly when approaching
the equivalence point. Note the volume, V , of titrant used.
t
7.6 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 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. Iron is added to the standard solution to assist in the determination of
turbidity in 7.4.
4
---------------------- Page: 7 ----------------------
©
ISO ISO 13291:1997(E)
The EDTA standard solution should be standardized as follows:
— Weigh into three separate 300 ml conical flasks, between 0,25 g and 1,625 g of zinc (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
— Add 15 ml of water, 15 ml of nitric acid (4.4) and 5 ml of iron stock solution (4.18). After dissolution of the zinc,
boil gently to expel nitrogen oxide gases.
— Cool and transfer to a 500 ml one-mark volumetric flask. Rinse the initial flask thoroughly and add the washings
to the volumetric flask. Make up to the mark. Continue the procedure as described in 7.4 and 7.5. Record the
volumes of EDTA standard solution used in the titrations as V , V and V .
1 2 3
Calculate the intermediate factor, fi , for each beaker using the following equation:
x
fi= m/ V for x = 1 to 3 --- (1a)
xx 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 solution, in millilitres.
x
If the range of values for fi , fi , fi exceeds 0,000 01 g/ml then repeat the standardization. Otherwise calculate the
1 2 3
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 = × . (2)
Zn
mH100−
where
f is the zinc equivalence factor, in grams per millilitre, determined in 7.6;
H is the hygroscopic moisture
...
SLOVENSKI STANDARD
SIST ISO 13291:2000
01-junij-2000
.RQFHQWUDWLFLQNRYHJDVXOILGD'RORþHYDQMHFLQND0HWRGDVWRSLORPLQ
WLWULPHWULMVNDPHWRGD]('7$
Zinc sulfide concentrates -- Determination of zinc content -- 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
Ta slovenski standard je istoveten z: ISO 13291:1997
ICS:
73.060.99 Druge rude Other metalliferous minerals
SIST ISO 13291:2000 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST ISO 13291:2000
---------------------- Page: 2 ----------------------
SIST ISO 13291:2000
INTERNATIONAL ISO
STANDARD 13291
First edition
1997-11-15
Zinc sulfide concentrates — Determination
of zinc content — 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
A
ISO 13291:1997(E)
---------------------- Page: 3 ----------------------
SIST ISO 13291:2000
ISO 13291:1997(E)
Contents Page
11 Scope. 1
22.01Normative references . 1
33.02Principle . 1
41.03 Reagents . 2
51.04Apparatus. 3
61.05Sample. 3
71.06Procedure. 3
82 Expression of results .
5
92.01Precision . 6
10.02Test report. 8
Bagues de roulement.
02.03 0
AnnexesRondelles de butée. 0
A2((normative) Procedure for the preparation and
determination of the mass of a predried test portion . 9
B2((normative) Flowchart of the procedure for the
acceptance of analytical values for test samples. 11
C2((normative) Elements that interfere with this method . 12
D2((informative) Derivation of precision equations . 13
E2((informative) Bibliography . 18
© 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
---------------------- Page: 4 ----------------------
SIST ISO 13291:2000
©
ISO ISO 13291:1997(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 13291 was prepared by Technical Committee
ISO/TC 183, Copper, lead and zinc ores and concentrates.
Annexes A to C form an integral part of this International Standard.
Annexes D and E are for information only.
iii
---------------------- Page: 5 ----------------------
SIST ISO 13291:2000
---------------------- Page: 6 ----------------------
SIST ISO 13291:2000
©
INTERNATIONAL STANDARD ISO ISO 13291:1997(E)
Zinc sulfide concentrates — Determination of zinc content —
Solvent extraction and EDTA titrimetric method
1 Scope
This International Standard specifies a solvent extraction/titrimetric method for the determination of the zinc content
of zinc sulfide 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 I: 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
A test portion of zinc concentrate is dissolved in bromine and nitric acid. Any remaining insoluble residue is
dissolved in hydrofluoric and perchloric 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 must be
determined separately if present at concentration levels exceeding 0,05 %. Zinc is determined by titration with
EDTA solution at pH 5,5.
1) To be published. (Revision of ISO 1042:1983)
1
---------------------- Page: 7 ----------------------
SIST ISO 13291:2000
©
ISO 13291:1997(E) ISO
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,
washed well with water followed by an acetone rinse and dried in an oven at 50°C.
4.2 Hydrochloric acid, (r 1,16 g/ml to 1,19 g/ml).
20
4.3 Bromine
4.4 Nitric acid, (r 1,42 g/ml)
20
4.5 Hydrochloric acid, (r 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.
4.6 Hydrofluoric acid, (r 1,13 g/ml to 1,15 g/ml)
20
4.7 Perchloric acid, (r 1,54 g/ml)
20
4.8 Ammonia, (r 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 (r 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.
2
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SIST ISO 13291:2000
©
ISO ISO 13291:1997(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
5.1 Ordinary laboratory equipment and
5.2 Volumetric glassware, of class A complying with ISO 385-1, ISO 648 and ISO 1042 and used in
accordance with ISO 4787.
5.3 Platinum crucibles, of 25 ml capacity.
,
5.4 Balance capable of being read to 0,1 mg.
5.5 Oven, with temperature controlled at 105 °C ± 5 °C.
5.6 Muffle furnace, having a maximum required operating temperature higher than 800 °C.
5.7 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
Take 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.
3
---------------------- Page: 9 ----------------------
SIST ISO 13291:2000
©
ISO 13291:1997(E) ISO
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 (5.7) and
bring gently to the boil to expel all bromine vapours. Cool, add 100 ml of water, heat to boiling, 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 material is present, filter through a medium speed 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 (5.3) (see Note)
and gently ash the paper in the muffle furnace (5.6) set at 800 °C. Add 2 ml of hydrofluoric acid (4.6) and then 5 ml
of perchloric acid (4.7). Heat until dense perchloric acid fumes appear. Allow to cool, dilute with about 25 ml of
water. Filter if a lead sulfate precipitate appears. Transfer the filtrate to the same one-mark volumetric flask used
above. Rinse the filter paper thoroughly and make up to the mark with water.
NOTE — If the sample contains lead, damage to the platinum crucible may occur. In this case, fusion with sodium peroxide in
a zirconium crucible is preferable.
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 (4.5) 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 (4.5) and 70 ml of ethanol (4.10) into each of the two separating funnels.
Shake well and discharge the contents from both funnels into the 400 ml low-form beaker.
7.5 Titration
Add successively 10 ml of sodium fluoride solution (4.12), 10 ml of thiourea solution (4.13), 20 ml of buffer solution
(4.14), 5 ml of potassium iodide solution (4.16) and 0,1 g of xylenol orange indicator (4.17).
Titrate with EDTA solution (4.15) until the colour changes from red to yellow. Titrate very slowly when approaching
the equivalence point. Note the volume, V , of titrant used.
t
7.6 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 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. Iron is added to the standard solution to assist in the determination of
turbidity in 7.4.
4
---------------------- Page: 10 ----------------------
SIST ISO 13291:2000
©
ISO ISO 13291:1997(E)
The EDTA standard solution should be standardized as follows:
— Weigh into three separate 300 ml conical flasks, between 0,25 g and 1,625 g of zinc (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
— Add 15 ml of water, 15 ml of nitric acid (4.4) and 5 ml of iron stock solution (4.18). After dissolution of the zinc,
boil gently to expel nitrogen oxide gases.
— Cool and transfer to a 500 ml one-mark volumetric flask. Rinse the initial flask thoroughly and add the washings
to the volumetric flask. Make up to the mark. Continue the procedure as described in 7.4 and 7.5. Record the
volumes of EDTA standard solution used in the titrations as V , V and V .
1 2 3
Calculate the intermediate factor, fi , for each beaker using the following equation:
x
fi= m/ V for x = 1 to 3 --- (1a)
xx x
where
fi is the factor obtained from the titration;
x
m is the mass of zinc weighed, in grams;
x
V is the
...
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