ISO 20336:2025

International
Standard
ISO 20336
Second edition
Coal and coke — Determination
2025-02
of total sulfur by Coulomb
titration method
Charbon et coke — Détermination de la teneur totale en soufre
par la méthode de titrage de Coulomb
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagent and materials . 1
6 Apparatus . 2
7 Preparation of test sample . 4
8 Procedure . 5
8.1 Preparation of test .5
8.2 Calibration .5
8.3 Calibration procedure .5
8.4 Procedure .6
8.5 Calibration check .6
9 Expression of result . 6
10 Precision . 7
10.1 Repeatability limit .7
10.2 Reproducibility limit .7
11 Test report . 7

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 27, Coal and coke, Subcommittee SC 5, Methods
of analysis.
This second edition cancels and replaces the first edition (ISO 20336:2017), which has been technically
revised.
The main changes are as follows:
— replaced “solid mineral fuels” with “coal and coke” and “content” with “mass fraction”;
— added Figure 2 of a purified air stream supply system;
— added a note to 8.1.4.
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
The objective of this document is to provide an alternative method for determining the total sulfur mass
fraction in coal and coke with high-temperature combustion by Coulomb titration using automated
instruments.
v
International Standard ISO 20336:2025(en)
Coal and coke — Determination of total sulfur by Coulomb
titration method
1 Scope
This document specifies an alternative method of determining the total sulfur mass fraction of coal and
coke by high-temperature combustion by Coulomb titration.
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 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
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
In the presence of the catalyst, a sample of known mass is combusted at 1 150 °C in a stream of purified air.
The sulfur oxides are formed and dissolved in the electrolytic solution. The sulfur dioxides are titrated by the
iodine and bromine librated from the electrolysis of the potassium iodide and potassium bromide solution.
The quantity of the electricity consumed by electrolysis is integrated and used to calculate the mass fraction
of sulfur dioxides. The instrument is calibrated with certified reference materials. The percentage of total
sulfur in the sample is calculated according to the sulfur dioxides mass fraction and the prior calibration.
5 Reagent and materials
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only
distilled water or water of equivalent purity.
5.1 Potassium iodide.
5.2 Potassium bromide.
5.3 Glacial acetic acid.
5.4 Self-indicating silica gel, industrial grade.
5.5 Sodium hydroxide, chemical grade.
5.6 Electrolytic solution, composed of 5 g of potassium iodide (5.1) and 5 g of potassium bromide (5.2)
dissolved in (250 to 300) ml of water, then add 10 ml of glacial acetic acid.
5.7 Glass wool.
5.8 Aluminosilicate wool.
5.9 Catalyst, tungsten trioxide.
5.10 Certified reference materials (CRMs), coal or coke.
6 Apparatus
6.1 Instrument, for de
...