ISO 925:2019

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

General Information

• Status: Published
• Publication Date: 15-Jul-2019
• ICS: 75.160.10 - Solid fuels
• Technical Committee: ISO/TC 27/SC 5 - Methods of analysis
• Drafting Committee: ISO/TC 27/SC 5/WG 2 - Carbon, hydrogen, nitrogen, oxygen and sulfur
• Current Stage: 9093 - International Standard confirmed
• Start Date: 19-Mar-2025
• Completion Date: 13-Dec-2025

Relations

• Revises: ISO 925:1997 - Solid mineral fuels - Determination of carbonate carbon content - Gravimetric method
• Effective Date: 26-May-2018

Overview

ISO 925:2019 - Solid mineral fuels - Determination of carbonate carbon content - Gravimetric method specifies a laboratory gravimetric procedure to measure carbonate carbon associated with solid mineral fuels (coal, coke, lignite). The method decomposes mineral carbonates with hydrochloric acid, captures the liberated carbon dioxide (CO2) in an absorption tube, and determines carbonate carbon gravimetrically by weighing the absorber. Note: results include any carbon from atmospheric CO2 absorbed by the fuel.

Key topics and technical requirements

• Principle: Acid decomposition of carbonates → CO2 liberated → CO2 absorbed on sodium hydroxide on an inert base → increase in absorber mass is measured.
• Reagents: ~3 mol/L hydrochloric acid; magnesium perchlorate (drying); hydrogen sulfide absorbents (copper(II) phosphate or copper(II) sulfate on pumice, or silver sulfate); sodium hydroxide on inert base; wetting agent; check-test reagents (anhydrous sodium or calcium carbonate).
• Apparatus: analytical balance (0.1 mg), reaction flask assembly (300 ml round-bottom, tap funnel, condenser, bulbed tube), absorption train (Mg(ClO4) drying tube; H2S absorbent + Mg(ClO4); CO2 absorber tube with NaOH + Mg(ClO4)), suction pump/flowmeter.
• Sample and preparation: analysis sample prepared to nominal top size 212 μm; equilibrate moisture to laboratory atmosphere; typical test portion 5.00 g (weighed to 0.01 g). For fuels >0.5% carbonate carbon, sample mass may be reduced pro rata to a minimum of 0.5 g.
• Operating conditions: air flow ~50 ml/min; condition apparatus 10 min; add 25 ml HCl, heat to boil after ~15 min, continue boiling ~30 min; cool and weigh CO2 absorption tube to constant mass.
• Calculations: carbonate carbon (%) Wc = 27.29 × (m2 / m1); CO2 (%) WCO2 = 100 × (m2 / m1), where m1 = mass of test portion (g) and m2 = increase in mass of the absorption tube (g). Report mean of duplicate determinations to 0.01%.
• Quality checks: perform airtightness/reagent check using ~60 mg of check reagent; acceptable result within ±10% of theoretical CO2.

Applications and users

ISO 925:2019 is suited for:

• Laboratories performing fuel analysis, carbon accounting and compositional testing of coal, coke and lignite.
• Quality control and QA/QC in mining, power generation, and coke production.
• Research groups studying mineral carbonate content or CO2 uptake in solid fuels.
• Regulatory and compliance testing where standardized carbonate carbon data are required.

Keywords: ISO 925:2019, carbonate carbon, solid mineral fuels, gravimetric method, CO2 content, absorption tube, hydrochloric acid, magnesium perchlorate.

Related standards

Normative references cited in ISO 925:2019 include:

• ISO 687, ISO 1170, ISO 5068-2, ISO 11722
• ISO 13909-4, ISO 13909-6, ISO 18283

These relate to sample preparation, moisture determination and calculation bases used together with ISO 925 analyses.

Standards Content (Sample)

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
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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
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.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.
...