ISO 15237:2025
(Main)Coal — Determination of total mercury
Coal — Determination of total mercury
This document specifies a procedure for the determination of the total mercury mass fraction of coal.
Charbon — Dosage du mercure total
General Information
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Standards Content (Sample)
International
Standard
ISO 15237
Third edition
Coal — Determination of total
2025-05
mercury
Charbon — Dosage du mercure total
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 definition . 1
4 Principle . 1
5 Reagents . 2
6 Apparatus . 2
7 Preparation of sample . 3
8 Oxygen bomb combustion procedure . 3
8.1 General .3
8.2 Combustion of coal .3
9 Preparation of test solution . 3
10 Atomic absorption analysis . 4
10.1 Calibration .4
10.2 Analytical procedure .4
11 Direct combustion analysis . 5
12 Expression of results . 5
13 Precision . 5
13.1 Repeatability limit .5
13.2 Reproducibility critical difference .5
14 Test report . 5
Bibliography . 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 third edition cancels and replaces the second edition (ISO 15237:2016), which has been technically
revised.
The main changes are as follows:
— Clause 2 has been updated;
— a new Clause 11 specifying direct combustion analysis has been added and subsequent clauses have been
renumbered;
— Formula (1) has been modified;
— the reporting requirement for results has been modified.
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
Mercury occurs naturally in coal. It is an element that can be released during the combustion process.
The determination of the total mercury mass fraction of coal cannot be accomplished satisfactorily by
traditional ashing and digestion procedures because of the volatility of the element.
Quantitative recovery can be achieved by strict adherence to the procedure set out in this document.
Instrumental methods for a more rapid determination of total mercury mass fraction are available. If such a
method is used, it is important to demonstrate that the method is free from bias, when compared with this
reference method, and gives levels of repeatability and reproducibility which are the same, or better than,
those quoted for the reference method (see Clause 10).
v
International Standard ISO 15237:2025(en)
Coal — Determination of total mercury
1 Scope
This document specifies a procedure for the determination of the total mercury mass fraction of coal.
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 1928, Coal and coke — Determination of gross calorific value
ISO 3696, Water for analytical laboratory use — Specification and test methods
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 — Preparation of test samples of coal
ISO 18283, Coal and coke — Manual sampling
ASTM 6722, Standard Test Method for Total Mercury in Coal and Coal Combustion Residues by Direct Combustion
Analysis
3 Terms and definition
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
The sample is burned in an oxygen bomb, the mercury species formed during combustion being absorbed
in water. The mercury species present in the water are reduced by stannous chloride and quantified by
flameless cold vapour atomic absorption spectroscopy.
It is reported that lithium borohydride (LiBH ) and sodium borohydride (NaBH ) are satisfactory for the
4 4
reduction instead of stannous chloride. Laboratories using these reductants must demonstrate that the
performance is equivalent to that using stannous chloride.
Alternately, direct combustion with quantification by atomic absorption spectroscopy.
5 Reagents
WARNING — Care shall be exercised when handling the reagents, many of which are toxic and
corrosive.
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade.
5.1 Water, conforming to Grade 1 of ISO 3696.
5.2 Oxygen, free from combustible matter and having a purity of at least 99,5 %.
5.3 Nitric acid solution, 10 % volume fraction, prepared by diluting 100 ml of concentrated nitric acid
(relative density 1,42) to 1 litre with water. The 10 % volume fraction solution shall have a mercury mass
concentration less than 0,1 µg/l.
5.4 Mercury standard stock solution, 1 000 µg/ml, prepared by dissolving 1,0 g of high purity mercury
in 5 ml of 25 % volume fraction nitric acid solution and diluting to 1 000 ml.
The mercury standard stock solution may also be prepared from commercially available certified mercury
solution.
Other high purity (> 99,9 %) mercury salts or oxides may be used with appropriate adjustment of the mass taken.
5.5 Mercury standard solution, 0,1 µg/ml, prepared by diluting 5,0 ml of mercury standard stock solution
(5.4) to 500 ml with water and then diluting 10,0 ml of the intermediate solution to 1 litre with water.
This mercury standard solution shall be prepared daily.
5.6 Potassium permanganate solution, 50 g/l, prepared by dissolving 5 g of potassium permanganate
(KMnO ) in water and diluting to 100 ml.
The mercury mass fraction of the potassium permanganate shall be below 0,05 µg/g.
5.7 Hydroxylammonium chloride solution, 15 g/l, prepared by dissolving 1,5 g of hydroxylammonium
chloride (HONH Cl) in water and diluting to 100 ml.
The mercury mass fraction of the hydroxylammonium chloride shall be below 0,005 µg/g.
5.8 Reducing agent, stannous chloride solution, 100 g/l, prepared by dissolving 10 g of stannous
chloride dihydrate (SnCl ⋅2H O) in 45 ml of concentrated hydrochloric acid solution (relative density 1,19)
2 2
and cautiously diluting to 100 ml with water.
The mercury mass fraction of the stannous chloride dihydrate shall be below 0,01 µg/g.
NOTE See also Note 1 to 10.2 regarding the use of flow injection techniques.
6 Apparatus
6.1 Balance, capable of determining mass by weighing to the nearest 0,1 mg.
6.2 Oxygen combustion bomb, constructed in accordance with ISO 1928. The ignition wire shall be
platinum or chromium-nickel alloy. The combustion bomb shall be constructed of materials that are not
affected by the combustion process or products. In particular, the combustion bomb shall be constructed of
material that is free from mercury. This can be verified by washing the interior
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