ISO 15237:2025

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

• Status: Published
• Publication Date: 08-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: 09-May-2025
• Due Date: 20-May-2026
• Completion Date: 09-May-2025

Relations

• Revises: ISO 15237:2016 - Solid mineral fuels - Determination of total mercury content of coal
• Effective Date: 27-May-2023

Overview

ISO 15237:2025 - Coal - Determination of total mercury specifies a reference laboratory method for measuring the total mercury mass fraction in coal. The third edition updates procedures for sample handling, introduces a direct combustion option, modifies formulae and reporting requirements, and remains the benchmark for validating faster instrumental methods. The standard emphasizes quantitative recovery of mercury - a volatile element - by strict procedural control.

Key Topics

• Scope and principle
  • Defines a procedure to determine total mercury in coal using oxygen bomb combustion with absorption of combustion products in water, followed by cold-vapour atomic absorption spectroscopy (CV-AAS).
  • Allows alternative reductants (stannous chloride, LiBH4, NaBH4) or direct combustion analysis if equivalence to the reference method is demonstrated.
• Reagents and materials
  • Specifies reagent grades and preparations: mercury stock and working standards, 10% nitric acid, potassium permanganate stabilizer, hydroxylammonium chloride, and stannous chloride reducing solution.
• Apparatus and cleanliness
  • Requires an oxygen combustion bomb constructed from mercury-free materials, silica crucible, precision balance, and an atomic absorption spectrometer with a flameless cold-vapour system.
  • Includes checks for bomb contamination and instructions for cleaning and blank determination.
• Sample preparation and procedure
  • Sample prep per ISO 13909‑4 / ISO 18283, moisture equilibration, and ~1 g test portions (or smaller if bomb design dictates).
  • Combustion steps: water in bomb, oxygen charge, firing, controlled venting, and quantitative recovery of washings into acidified volumetric flasks.
• Calibration and analysis
  • Matrix-matched calibration standards (e.g., 3, 5, 10 µg/L) stabilized with permanganate; measurement by CV‑AAS and reporting of results on specified bases.
• Quality and precision
  • Includes blank procedures, repeatability/reproducibility requirements, and test report content.

Applications

• Environmental monitoring of mercury content in coal feedstocks.
• Fuel quality control for power plants and utilities concerned with mercury emissions.
• Regulatory compliance testing where accurate total mercury mass fraction is required.
• Reference method for validating faster or automated mercury analyzers (e.g., direct combustion instruments).

Who uses this standard

• Analytical and environmental laboratories performing coal analysis.
• Coal producers and quality assurance teams.
• Power generation and combustion facilities monitoring fuel contaminants.
• Regulatory bodies and test method developers validating alternative mercury measurement methods.

Related Standards

• ISO 1928 (gross calorific value)
• ISO 3696 (laboratory water)
• ISO 13909-4 / ISO 18283 (sampling/preparation)
• ISO 5068-2 / ISO 11722 (moisture determination)
• ASTM 6722 (direct combustion total mercury in coal)

Keywords: ISO 15237:2025, total mercury, coal, mercury determination, oxygen bomb combustion, cold‑vapour AAS, direct combustion, mercury mass fraction.

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
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 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
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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, 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
...