ISO 609:2025

Coal and coke - Determination of carbon and hydrogen - High temperature combustion method

This document specifies a method of determining the total carbon and the total hydrogen in coal and coke by a high temperature combustion method.

Charbon et coke — Dosage du carbone et de l'hydrogène — Méthode par combustion à haute température

General Information

• Status: Published
• Publication Date: 15-May-2025
• ICS: 73.040 - Coals
• ICS: 75.160.10 - Solid fuels
• Technical Committee: ISO/TC 27/SC 5 - Methods of analysis
• Drafting Committee: ISO/TC 27/SC 5 - Methods of analysis
• Current Stage: 6060 - International Standard published
• Start Date: 16-May-2025
• Due Date: 20-May-2026
• Completion Date: 16-May-2025

Relations

• Revises: ISO 609:1996/Cor 1:1996 - Solid mineral fuels - Determination of carbon and hydrogen - High temperature combustion method - Technical Corrigendum 1
• Effective Date: 27-May-2023
• Revises: ISO 609:1996 - Solid mineral fuels - Determination of carbon and hydrogen - High temperature combustion method
• Effective Date: 27-May-2023

Overview

ISO 609:2025 - "Coal and coke - Determination of carbon and hydrogen - High temperature combustion method" specifies a laboratory procedure for determining total carbon and total hydrogen in coal and coke by high‑temperature combustion and gravimetric absorption. The third edition (2025) updates the 1996 version and defines equipment, reagents, sample preparation, combustion conditions and calculations so results include carbonates and hydrogen in moisture and silicates (with provision for corrections).

Keywords: ISO 609:2025, coal and coke, high temperature combustion method, determination of carbon and hydrogen, total carbon, total hydrogen.

Key topics and technical requirements

• Principle: Burn a known mass of sample in oxygen at ~1 350 °C; convert hydrogen to H2O and carbon to CO2; absorb and determine products gravimetrically.
• Apparatus: furnace with a 125 mm hot zone reaching 1 350 °C, auxiliary zone to keep the silver gauze roll at ~600–800 °C, refractory combustion tube (≈28 mm OD, 650 mm length), combustion boats, and Midvale absorption tubes.
• Absorption train: arranged in the flow direction with magnesium perchlorate (for water), sodium hydroxide on inert base (for CO2), then magnesium perchlorate again; glass wool used to prevent carry‑over.
• Reagents: anhydrous magnesium perchlorate, coarse sodium hydroxide on inert base (self‑indicating preferred), alumina lining, sodium tetraborate titrant, hydrogen peroxide, mixed indicators and oxygen (hydrogen‑free). Safety warnings are specified for toxic/corrosive reagents and disposal of perchlorate.
• Procedure highlights: sample preparation, conditioning of the absorption train, combustion steps, blank tests, simultaneous moisture determination and corrections (for moisture and carbonate carbon), and gravimetric/titrimetric calculations.
• Quality: Clauses on precision (repeatability and reproducibility) and detailed test reporting requirements are included.

Applications and users

ISO 609:2025 is intended for:

• Analytical laboratories performing routine and reference testing of coal and coke.
• Quality control teams in mining, coke production and power generation to determine fuel composition.
• Engineers and researchers assessing fuel properties for combustion performance, emissions estimation and material balance.
• Regulatory bodies and certification agencies requiring standardized composition data for trade and environmental compliance.

Practical benefits: reliable total carbon/hydrogen values for calorific calculations, emissions inventories, process optimization and contract quality verification.

Related standards

• ISO 625 - alternative method for carbon/hydrogen determination.
• Normative references cited: ISO 687, ISO 925, ISO 5068‑2, ISO 11722, ISO 13909‑4 / ISO 13909‑6, ISO 18283.

Using ISO 609:2025 ensures reproducible, internationally comparable measurements of carbon and hydrogen in coal and coke by a well‑specified high‑temperature combustion method.

Standards Content (Sample)

International
Standard
ISO 609
Third edition
Coal and coke — Determination
2025-05
of carbon and hydrogen — High
temperature combustion method
Charbon et coke — Dosage du carbone et de l'hydrogène —
Méthode par combustion à haute température
Reference number
© ISO 2025
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: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and materials . 2
6 Apparatus . 2
7 Preparation of the apparatus . 7
7.1 Preparation of the combustion tube .7
7.2 Location of the silver gauze roll .7
7.3 Conditioning the absorption train .8
8 Preparation of test sample . 9
9 Procedure . 9
9.1 Initial operations .9
9.2 Combustion of the test portion .9
9.3 Completion .9
10 Blank test .10
11 Expression of results . 10
11.1 Total carbon .10
11.2 Organic carbon .11
11.3 Total hydrogen .11
11.4 Total hydrogen mass fraction, less that present as moisture .11
11.5 Additional information.11
12 Precision .12
12.1 Repeatability limit . 12
12.2 Reproducibility limit . 12
13 Test report .12
Annex A (informative) Derivation of factors used in calculations .13
Bibliography .15

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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The procedures used to develop this document and those intended for its further maintenance are described
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of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
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This document was prepared by Technical Committee ISO/TC 27, Coal and coke, Subcommittee SC 5, Methods
of analysis.
This third edition cancels and replaces the second edition (ISO 609:1996), which has been technically
revised. It also incorporates the Technical Corrigendum ISO 609:1996/Cor. 1:1996.
The main changes are as follows:
— the normative references have been updated;
— Clause 3 has been added and subsequent clauses have been renumbered;
— Figures 1, 2, 3 and 4 have been modified to add keys;
— Clause 9 has been revised;
— Annex A has been revised.
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
Introduction
ISO 625 gives an alternative method to the one specified in this document.

v
International Standard ISO 609:2025(en)
Coal and coke — Determination of carbon and hydrogen —
High temperature combustion method
1 Scope
This document specifies a method of determining the total carbon and the total hydrogen in coal and coke
by a high temperature combustion method.
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, Coke — Determination of moisture in the general analysis test sample
ISO 925, Solid mineral fuels — Determination of carbonate carbon content — Gravimetric method
ISO 5068-2, Brown coals and lignites — Determination of moisture — 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, Coal and coke — Mechanical sampling — Part 4: Preparation of test samples of coal
ISO 13909-6, Coal and coke — Mechanical sampling — Part 6: Preparation of test samples of coke
ISO 18283, Coal and coke — Manual sampling
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Principle
A known mass of coal or coke is burnt in a stream of oxygen, at a temperature of 1 350 °C, in a tube impervious
to gases. All the hydrogen is converted to water and all the carbon to carbon dioxide. These products are
absorbed by suitable reagents and determined gravimetrically. The chlorine and oxides of sulfur which are
formed are retained by a silver gauze roll at the outlet end of the tube.
The results include the carbon in the carbonates and the hydrogen combined in the moisture and in the water
of constitution of silicates. A determination of moisture is carried out at the same time, and an appropriate
correction is applied to the hydrogen value obtained by combustion. A determination of carbon dioxide may
also be made and the total carbon value corrected for the presence of mineral carbonates.

5 Reagents and materials
WARNING — Care shall 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.
5.1 Magnesium perchlorate, anhydrous, less than 1,2 mm in size and preferably within the size range
1,2 mm to 0,7 mm.
WARNING — Determine any local regulations when disposing of exhausted magnesium perchlorate
prior to use. Regeneration of magnesium perchlorate shall not be attempted, owing to the risk of
explosion.
5.2 Sodium hydroxide on an inert base, preferably of a coarse grading, for example 3,0 mm to 1,5 mm,
but not finer than the grading 1,2 mm to 0,7 mm, and preferably of the self-indicating type.
5.3 Aluminium oxide (alumina), finely divided, approximately 0,1 mm in size.
5.4 Sodium tetraborate, standard volumetric solution, c(Na B O ) = 0,025 mol/l.
2 4 7
Dissolve 9,534 2 g of sodium tetraborate decahydrate in water and dilute to 1 litre. Mix thoroughly.
5.5 Hydrogen peroxide, mass fraction approximately 30 %.
5.6 Pure silver gauze, of mesh approximately 1 mm, made of wire approximately 0,3 mm in diameter.
5.7 Oxygen, hydrogen-free, preferably prepared from liquid air and not by electrolysis. Electrolytically
prepared oxygen shall be passed over red-hot copper oxide before use to remove any trace of hydrogen.
5.8 Mixed indicator solution
5.8.1 Solution A
Dissolve 0,125 g of 2-(4-dimethylaminophenylazo) benzoic acid, sodium salt (methyl red) in 100 ml of water.
5.8.2 Solution B
Dissolve 0,083 g of 3,7-bis(dimethylamino)phenothiazine-5-ylium chloride (methylene blue) in 100 ml of
water. Store in a dark bottle.
5.8.3 Mixed solution
Mix equal volumes of solution A and solution B. Store in a dark bottle. The shelf life of the mixed solution is
one week.
5.9 Air, compressed.
5.10 Glass wool.
6 Apparatus
6.1 Analytical balance, capable of determining the mass to the nearest 0,1 mg.
6.2 Graduate glassware, class A.

6.3 Two purification trains, one for absorbing water vapour and carbon dioxide from the oxygen used
for the combustion and the other for similarly treating the air used for sweeping out the absorption train
before and after a determination. Assemble each train using a series of U-tubes or Midvale tubes containing
the following reagents in the order stated, in the direction of flow:
a) magnesium perchlorate (5.1) for absorbing water;
b) sodium hydroxide on an inert base (5.2) for absorbing carbon dioxide;
c) magnesium perchlorate (5.1) for absorbing the water evolved in the reaction between carbon dioxide
and sodium hydroxide.
The purification trains shall be large enough to render frequent recharging unnecessary, even with
continuous use.
NOTE Midvale tubes that have been freshly packed with absorbent and used in the purification train are thereby
conditioned for subsequent use in the absorption train.
6.4 Combustion assembly
6.4.1 Furnace, an electrically heated furnace or furnaces, designed to carry a combustion tube (6.4.2) and
heat it to 1 350 °C over a distance of 125 mm in the hot zone, and yield a temperature-distribution profile
similar to that shown in Figure 1. The heating unit normally requires an auxiliary furnace to ensure that the
silver gauze roll (6.9) is maintained at the correct temperature (approximately 600 °C to 800 °C). Suitable
furnace types are, for example:
a) molybdenum or tungsten wire wound;
b) platinum or platinum-rhodium wire wound;
c) heated by silicon carbide rods.
NOTE 1 Furnace type c) has the lowest initial cost and has proved satisfactory in use.
NOTE 2 Furnaces of the type normally used for the determination of carbon or sulfur in steel are not suitable
because of the absence of the auxiliary section required to maintain the silver gauze roll at the correct temperature.

Key
X distance from inlet end, mm
Y temperature, °C
1 combustion tube
2 silver gauze roll
3 heat-resistant mineral fibre
Figure 1 — Typical temperature-distribution curve for furnace
6.4.2 Combustion tube, of approximately 28 mm external diameter, 3 mm wall thickness and 650 mm
length, made of refractory aluminous porcelain which is impervious to gases up to a temperature of
1 400 °C. The end of the combustion tube shall be lagged with a suitable heat-resistant mineral fibre to
prevent condensation in the tube.
6.4.3 Combustion boat, of iron-free, unglazed porcelain, approximately 60 mm long, 12,5 mm wide and
10 mm deep for hard coal and coke samples and approximately 75 mm long, 15 mm wide and 10 mm deep
for brown coal and lignite, capable of withstanding a temperature of 1 350 °C.
Combustion boats shall not blister, discolour or change in mass on heating in oxygen at 1 350 °C for 3 h. A
suitable boat lasts for about 10 to 20 determinations and shall then be discarded because of the accumulation
of fused ash. For coals with a high ash mass fraction, it might be convenient to line the boat with alumina
before adding the sample, in order to prevent fusion of the ash to the boat.
6.5 Absorption train, for absorbing the water and carbon dioxide evolved by the combustion of the
sample. Midvale tubes (Figure 2), which provide a large area of reaction, are used in order to reduce the

back-pressure in the apparatus, and so obviate the danger of leakage through the rubber sleeve carrying the
pusher. Assemble the train using the following reagents in the order stated, in the direction of flow:
a) magnesium perchlorate (5.1) for absorbing the water evolved during the combustion;
b) sodium hydroxide on an inert base (5.2) for absorbing the carbon dioxide;
c) magnesium perchlorate (5.1) for absorbing the water evolved in the reaction between carbon dioxide
and sodium hydroxide.
Dimensions in millimetres
Key
1 indicator spot
2 hollow stopper
Figure 2 — Midvale tube
Place glass wool (5.10), previously dried at 105 °C for 1 h, above and below the absorbents to prevent the
carry-over of dust or the adsorbent particles by the flow of oxygen, and to prevent the cracking of the Midvale
tube by the heat of reaction. A typical absorption train with details of the pack
...