ISO 925:2019
(Main)Solid mineral fuels — Determination of carbonate carbon content — Gravimetric method
Solid mineral fuels — Determination of carbonate carbon content — Gravimetric method
This document specifies a gravimetric method of determining the carbon in the mineral carbonates associated with solid mineral fuels. NOTE The result obtained will include any carbon from atmospheric carbon dioxide absorbed by the fuel.
Combustibles minéraux solides — Dosage du carbone sous forme de carbonate — Méthode gravimétrique
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INTERNATIONAL ISO
STANDARD 925
Fourth edition
2019-07
Solid mineral fuels — Determination
of carbonate carbon content —
Gravimetric method
Combustibles minéraux solides — Dosage du carbone sous forme de
carbonate — Méthode gravimétrique
Reference number
©
ISO 2019
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 1
6 Apparatus . 2
7 Preparation of the test sample . 3
8 Procedure. 4
8.1 Check test . 4
8.2 Determination . 5
8.2.1 Preparation . 5
8.2.2 Conditioning . 5
8.2.3 Reaction and completion . 5
9 Expression of results . 5
10 Precision . 6
10.1 Repeatability limit . 6
10.2 Reproducibility critical difference . 6
11 Test report . 7
Annex A (informative) Derivation of factors used in calculations in this document .8
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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 27, Solid mineral fuels, Subcommittee
SC 5, Methods of analysis.
This fourth edition cancels and replaces the third edition (ISO 925:1997), of which it constitutes a minor
revision. The changes compared to the previous edition are as follows:
— the normative references have been updated and the dates removed;
— the references in Clause 7 have been updated.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2019 – All rights reserved
INTERNATIONAL STANDARD ISO 925:2019(E)
Solid mineral fuels — Determination of carbonate carbon
content — Gravimetric method
1 Scope
This document specifies a gravimetric method of determining the carbon in the mineral carbonates
associated with solid mineral fuels.
NOTE The result obtained will include any carbon from atmospheric carbon dioxide absorbed by the fuel.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 687, Solid mineral fuels — Coke — Determination of moisture in the general analysis test sample
ISO 1170, Coal and coke — Calculation of analyses to different bases
ISO 5068-2, Brown coals and lignites — Determination of moisture content — Part 2: Indirect gravimetric
method for moisture in the analysis sample
ISO 11722, Solid mineral fuels — Hard coal — Determination of moisture in the general analysis test
sample by drying in nitrogen
ISO 13909-4, Hard coal and coke — Mechanical sampling — Part 4: Coal — Preparation of test samples
ISO 13909-6, Hard coal and coke — Mechanical sampling — Part 6: Coke — Preparation of test samples
ISO 18283, Hard coal and coke — Manual sampling
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
4 Principle
A known mass of sample is treated with hydrochloric acid, which reacts with the carbonates present
to liberate carbon dioxide. The carbon dioxide resulting from the decomposition of the carbonates is
absorbed and weighed.
5 Reagents
WARNING — Care should be exercised when handling reagents, many of which are toxic and
corrosive.
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only
distilled water, or water of equivalent purity.
NOTE Distilled water can be freed from carbon dioxide by boiling gently for 15 min.
5.1 Hydrochloric acid, approximately 3 mol/l.
5.2 Hydrogen sulfide absorbent, any of the following:
a) copper(II) phosphate, granular, particle size 1,2 mm to 0,7 mm;
NOTE 1 Copper(II) phosphate granules can be prepared as follows.
Mix copper(II) phosphate powdered reagent to a stiff paste with 1 % starch solution. Press through a sheet
of metal, perforated with apertures of approximately 1 mm diameter. Dry the extruded material at 110 °C.
Sieve to recover the desired size fraction.
b) copper(II) sulfate, deposited on a supporting base of ground pumice;
NOTE 2 A suitable absorbent, based on copper(II) sulfate, can be prepared as follows.
Prepare pumice by crushing and sieving to obtain the 2,8 mm to 0,7 mm fraction. Transfer approximately
60 g of the prepared pumice to an evaporating basin, covering with a saturated solution of copper(II) sulfate,
evaporate to dryness with constant stirring, and heat at 150 °C to 160 °C for 3 h to 4 h. Cool in a desiccator
and store in a glass-stoppered bottle.
c) silver sulfate, granular.
5.3 Magnesium perchlorate, anhydrous, particle size 1,2 mm to 0,7 mm.
WARNING — Due regard shall be taken of local regulations when disposing of exhausted
magnesium perchlorate. It is essential that regeneration of magnesium perchlorate is not
attempted, owing to the risk of explosion.
5.4 Sodium hydroxide, on an inert base, preferably of coarse grading, for example 1,7 mm to 1,2 mm,
and preferably of the self-indicating type.
5.5 Wetting agent, suitable for use in acid solution.
NOTE A liquid wetting agent at a concentration of 100 ml/l or ethanol (a volume fraction of 95 %) are
suitable.
5.6 Check test reagent, either of the following:
a) anhydrous sodium carbonate;
b) anhydrous calcium carbonate.
6 Apparatus
6.1 Analytical balance, capable of weighing to the nearest 0,1 mg.
6.2 Graduated glassware, conforming to the requirements for Grade A in the International Standards
prepared by ISO/TC 48, Laboratory glassware and related apparatus.
6.3 Purification tube, consisting of an absorption tube containing sodium hydroxide on an inert base
(5.4). Absorption tubes may be U-tubes or Midvale tubes (which reduce back-pressure and, hence, risk of
2 © ISO 2019 – All rights reserved
leakage). The tops of the reagent columns should be covered with a layer of glass wool to guard against
entrainment of any fine particles in the circulating air.
6.4 Reaction flask assembly, comprising a 300 ml round-bottomed flask fitted with a tap funnel, a
double-surface condenser and a bulbed tube.
6.5 Absorption train, consisting of three absorption tubes a), b) and c) packed, respectively, as follows.
a) Magnesium perchlorate (5.3) to dry the gas.
b) Hydrogen sulfide absorbent (5.2) followed by a protective layer of magnesium perchlorate (5.3).
The connection from this tube to tube c) shall be fitted at its outlet end with a stopcock or other
means of closure.
c) Sodium hydroxide on an inert base (5.4), to absorb carbon dioxide generated in the reaction flask,
followed by a protective layer of magnesium perchlorate (5.3) to absorb water produced in the
reaction between carbon dioxide and sodium hydroxide. This tube shall be fitted with stopcocks or
other means of closure at the inlet and outlet ends.
6.6 Air circulation equipment, a suction pump, capable of drawing air at a rate of 50 ml/min through
the apparatus, connected through a flowmeter to a tee-piece fitted with a stopcock (the air vent).
6.7 Heating source, for the reaction flask. Either an electric heating mantle to accommodate a 300 ml
flask or a small gas burner. An example of a suitable assembly of the apparatus is illustrated in Figure 1.
7 Preparation of the test sample
The test sample shall be the analysis sample, prepared to a nominal top size of 212 μm. Sample
preparation procedures shall be in accordance with ISO 13909-4, ISO 13909-6 or ISO 18283, as
appropriate. The moisture content of the sample shall be equilibrated with the laboratory atmosphere
by exposure in a thin layer on a tray. Exposure time shall be kept to a minimum.
Before commencing the determination, thoroughly mix the equilibrated test sample for at least one
minute, preferably by mechanical means.
If the results are to be calculated other than on an “air-dried” basis (see Clause 9), then, after weighing
the test portion (see 8.2), determine the moisture content using a further portion of the test sample by
the method described in ISO 687, ISO 5068-2 or ISO 11722, a
...
INTERNATIONAL ISO
STANDARD 925
Fourth edition
2019-07
Solid mineral fuels — Determination
of carbonate carbon content —
Gravimetric method
Combustibles minéraux solides — Dosage du carbone sous forme de
carbonate — Méthode gravimétrique
Reference number
©
ISO 2019
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 1
6 Apparatus . 2
7 Preparation of the test sample . 3
8 Procedure. 4
8.1 Check test . 4
8.2 Determination . 5
8.2.1 Preparation . 5
8.2.2 Conditioning . 5
8.2.3 Reaction and completion . 5
9 Expression of results . 5
10 Precision . 6
10.1 Repeatability limit . 6
10.2 Reproducibility critical difference . 6
11 Test report . 7
Annex A (informative) Derivation of factors used in calculations in this document .8
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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 27, Solid mineral fuels, Subcommittee
SC 5, Methods of analysis.
This fourth edition cancels and replaces the third edition (ISO 925:1997), of which it constitutes a minor
revision. The changes compared to the previous edition are as follows:
— the normative references have been updated and the dates removed;
— the references in Clause 7 have been updated.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2019 – All rights reserved
INTERNATIONAL STANDARD ISO 925:2019(E)
Solid mineral fuels — Determination of carbonate carbon
content — Gravimetric method
1 Scope
This document specifies a gravimetric method of determining the carbon in the mineral carbonates
associated with solid mineral fuels.
NOTE The result obtained will include any carbon from atmospheric carbon dioxide absorbed by the fuel.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 687, Solid mineral fuels — Coke — Determination of moisture in the general analysis test sample
ISO 1170, Coal and coke — Calculation of analyses to different bases
ISO 5068-2, Brown coals and lignites — Determination of moisture content — Part 2: Indirect gravimetric
method for moisture in the analysis sample
ISO 11722, Solid mineral fuels — Hard coal — Determination of moisture in the general analysis test
sample by drying in nitrogen
ISO 13909-4, Hard coal and coke — Mechanical sampling — Part 4: Coal — Preparation of test samples
ISO 13909-6, Hard coal and coke — Mechanical sampling — Part 6: Coke — Preparation of test samples
ISO 18283, Hard coal and coke — Manual sampling
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
4 Principle
A known mass of sample is treated with hydrochloric acid, which reacts with the carbonates present
to liberate carbon dioxide. The carbon dioxide resulting from the decomposition of the carbonates is
absorbed and weighed.
5 Reagents
WARNING — Care should be exercised when handling reagents, many of which are toxic and
corrosive.
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only
distilled water, or water of equivalent purity.
NOTE Distilled water can be freed from carbon dioxide by boiling gently for 15 min.
5.1 Hydrochloric acid, approximately 3 mol/l.
5.2 Hydrogen sulfide absorbent, any of the following:
a) copper(II) phosphate, granular, particle size 1,2 mm to 0,7 mm;
NOTE 1 Copper(II) phosphate granules can be prepared as follows.
Mix copper(II) phosphate powdered reagent to a stiff paste with 1 % starch solution. Press through a sheet
of metal, perforated with apertures of approximately 1 mm diameter. Dry the extruded material at 110 °C.
Sieve to recover the desired size fraction.
b) copper(II) sulfate, deposited on a supporting base of ground pumice;
NOTE 2 A suitable absorbent, based on copper(II) sulfate, can be prepared as follows.
Prepare pumice by crushing and sieving to obtain the 2,8 mm to 0,7 mm fraction. Transfer approximately
60 g of the prepared pumice to an evaporating basin, covering with a saturated solution of copper(II) sulfate,
evaporate to dryness with constant stirring, and heat at 150 °C to 160 °C for 3 h to 4 h. Cool in a desiccator
and store in a glass-stoppered bottle.
c) silver sulfate, granular.
5.3 Magnesium perchlorate, anhydrous, particle size 1,2 mm to 0,7 mm.
WARNING — Due regard shall be taken of local regulations when disposing of exhausted
magnesium perchlorate. It is essential that regeneration of magnesium perchlorate is not
attempted, owing to the risk of explosion.
5.4 Sodium hydroxide, on an inert base, preferably of coarse grading, for example 1,7 mm to 1,2 mm,
and preferably of the self-indicating type.
5.5 Wetting agent, suitable for use in acid solution.
NOTE A liquid wetting agent at a concentration of 100 ml/l or ethanol (a volume fraction of 95 %) are
suitable.
5.6 Check test reagent, either of the following:
a) anhydrous sodium carbonate;
b) anhydrous calcium carbonate.
6 Apparatus
6.1 Analytical balance, capable of weighing to the nearest 0,1 mg.
6.2 Graduated glassware, conforming to the requirements for Grade A in the International Standards
prepared by ISO/TC 48, Laboratory glassware and related apparatus.
6.3 Purification tube, consisting of an absorption tube containing sodium hydroxide on an inert base
(5.4). Absorption tubes may be U-tubes or Midvale tubes (which reduce back-pressure and, hence, risk of
2 © ISO 2019 – All rights reserved
leakage). The tops of the reagent columns should be covered with a layer of glass wool to guard against
entrainment of any fine particles in the circulating air.
6.4 Reaction flask assembly, comprising a 300 ml round-bottomed flask fitted with a tap funnel, a
double-surface condenser and a bulbed tube.
6.5 Absorption train, consisting of three absorption tubes a), b) and c) packed, respectively, as follows.
a) Magnesium perchlorate (5.3) to dry the gas.
b) Hydrogen sulfide absorbent (5.2) followed by a protective layer of magnesium perchlorate (5.3).
The connection from this tube to tube c) shall be fitted at its outlet end with a stopcock or other
means of closure.
c) Sodium hydroxide on an inert base (5.4), to absorb carbon dioxide generated in the reaction flask,
followed by a protective layer of magnesium perchlorate (5.3) to absorb water produced in the
reaction between carbon dioxide and sodium hydroxide. This tube shall be fitted with stopcocks or
other means of closure at the inlet and outlet ends.
6.6 Air circulation equipment, a suction pump, capable of drawing air at a rate of 50 ml/min through
the apparatus, connected through a flowmeter to a tee-piece fitted with a stopcock (the air vent).
6.7 Heating source, for the reaction flask. Either an electric heating mantle to accommodate a 300 ml
flask or a small gas burner. An example of a suitable assembly of the apparatus is illustrated in Figure 1.
7 Preparation of the test sample
The test sample shall be the analysis sample, prepared to a nominal top size of 212 μm. Sample
preparation procedures shall be in accordance with ISO 13909-4, ISO 13909-6 or ISO 18283, as
appropriate. The moisture content of the sample shall be equilibrated with the laboratory atmosphere
by exposure in a thin layer on a tray. Exposure time shall be kept to a minimum.
Before commencing the determination, thoroughly mix the equilibrated test sample for at least one
minute, preferably by mechanical means.
If the results are to be calculated other than on an “air-dried” basis (see Clause 9), then, after weighing
the test portion (see 8.2), determine the moisture content using a further portion of the test sample by
the method described in ISO 687, ISO 5068-2 or ISO 11722, a
...
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