ISO 11724:2016

INTERNATIONAL ISO
STANDARD 11724
Second edition
2016-12-01
Solid mineral fuels — Determination of
total fluorine in coal, coke and fly ash
Combustibles minéraux solides — Détermination de la teneur totale
en fluor dans le charbon, le coke et les cendres
Reference number
ISO 11724:2016(E)
©
ISO 2016

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ISO 11724:2016(E)

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ISO 11724:2016(E)

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 Sample . 5
7.1 Coal and coke . 5
7.2 Fly ash . 5
8 Procedure. 5
8.1 Number of determinations . 5
8.2 Preparation of test sample . 5
8.3 Blank tests . 5
8.4 Pyrohydrolysis procedure . 5
8.4.1 Apparatus conditioning . 5
8.4.2 Pyrohydrolysis . 5
8.4.3 Pyrohydrolysate processing . 6
8.5 Solution measurement . 6
8.5.1 General. 6
8.5.2 Direct-comparison ISE method . 6
8.5.3 Analyte-addition ISE method . 7
8.5.4 IC method . 7
9 Calculations. 8
9.1 General . 8
9.2 Direct-comparison ISE method . 8
9.3 Analyte-addition ISE method . 9
9.4 IC method . 9
10 Expression of result . 9
11 Precision .10
11.1 Repeatability limit .10
11.2 Reproducibility critical difference .10
12 Test report .10
Bibliography .11
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ISO 11724:2016(E)

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
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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 documents 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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
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Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/TC 27, Solid mineral fuels, Subcommittee SC 5,
Methods of analysis.
This second edition cancels and replaces the first edition (ISO 11724:2004), of which it constitutes a
minor revision. This document incorporates changes related to dated references and other minor items
following its systematic review.
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INTERNATIONAL STANDARD ISO 11724:2016(E)
Solid mineral fuels — Determination of total fluorine in
coal, coke and fly ash
1 Scope
This document specifies a method for the determination of total fluorine in coal, coke and fly ash.
From measurement of the total fluorine alone, it is not possible to estimate the amount of fluorine
released to the environment by utilization of the coal and subsequent disposal of the ash residue.
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 589, Hard coal — Determination of total moisture
ISO 687, Solid mineral fuels — 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 5069-2, Brown coals and lignites — Principles of sampling — Part 2: Sample preparation for
determination of moisture content and for general analysis
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
3 Terms and definitions
No terms and definitions are defined in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
4 Principle
Mixing of the sample of coal, coke or fly ash with silica, and pyrohydrolysis in a tube furnace at
approximately 1 200 °C in an atmosphere of oxygen and water vapour. Absorption of the volatilized
fluorine compounds in a suitable solution and processing for determination by ion-selective electrode
(ISE) or ion chromatographic (IC) techniques.
5 Reagents
CAUTION — Care shall be exercised when handling reagents, some of which are toxic and
corrosive.
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ISO 11724:2016(E)

During the analysis, use only reagents of recognized analytical grade and only distilled water, or water
of equivalent purity.
5.1 Silica of top size 75 µm, ignited at 1 000 °C for 1 h.
CAUTION — Fine silica is dangerous to health if inhaled.
5.2 Solutions for ISE measurement
5.2.1 Standard fluorine solution (1 g contains 200 µg of F).
a) For direct-comparison method
Dissolve 0,221 0 g ± 0,000 2 g of dry (110 °C for 1 h) sodium fluoride in approximately 400 ml of
water contained in a tared plastic bottle, dilute to 500 g ± 0,5 g net with water, and mix.
b) For analyte-addition method
Dissolve 0,221 0 g ± 0,000 2 g of dry (110 °C for 1 h) sodium fluoride in a tared plastic bottle
containing 150 ml of water and 100 g of buffer (5.2.3). Dilute to 500 g ± 0,5 g net with water and mix.
5.2.2 Absorption solution (0,025 mol/l NaOH).
Dissolve 2,0 g of sodium hydroxide in about 500 ml of water. Transfer to a tared 2,5 l plastic bottle,
dilute to 2 000 g net with water, and mix.
5.2.3 Buffer (pH 6,5).
Dissolve 10,0 g of potassium nitrate, 5 g of 1,2-cyclohexylenedinitrilotetraacetic acid (CDTA) and 115 g
of ammonium acetate in 350 ml of water. Adjust the pH to 6,5 with glacial acetic acid. Dilute to 500 g net
with water and mix.
5.2.4 Solution for conditioning fluoride ISE.
Weigh 20 g of water, 20 g of absorption solution (5.2.2) and 10 g of buffer (5.2.3) into a polystyrene vial
(6.2). Add approximately 200 mg of standard fluorine solution [of 5.2.1 a) or 5.2.1 b)] and mix.
5.3 Solutions for IC measurement
5.3.1 Standard fluorine solution (1 g contains 200 µg of F).
Dissolve 0,221 0 ± 0,000 2 g of dry (110 °C for 1 h) sodium fluoride in approximately 400 ml of water
contained in a tared plastic bottle, dilute to 500 g ± 0,5 g net with water, and mix.
5.3.2 Absorption solution for IC measurement.
Dissolve 0,300 g of sodium hydrogen carbonate and 1,120 g of sodium carbonate in approximately
500 ml of water and dilute to 2 l.
5.4 Oxygen, compressed.
6 Apparatus
6.1 Vials, made of glass or polystyrene, of capacity 10 ml to 30 ml with tightly fitting snap-on plastic caps.
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ISO 11724:2016(E)

6.2 Polypropylene bottles or polystyrene vials, tared, of capacity 125 ml, wide necked with linerless
leak-proof screw caps.
6.3 Balances: a balance capable of weighing to the nearest 0,000 1 g; a balance capable of weighing
approximately 200 g to the nearest 0,001 g; a balance capable of weighing 600 g to the nearest 0,01 g;
and a balance capable of weighing 3 000 g to the nearest 0,1 g.
6.4 Polyethylene dispensing bottles, for the standard fluorine solution (5.2.1), absorption solution
(5.2.2) and buffer (5.2.3).
6.5 Micropipette, of variable volume, ranging to at least 1 ml.
This is a satisfactory alternative to the 250 ml polyethylene dispensing bottle (6.4) for delivery of small
weighed volumes of standard fluorine solution (5.2.1).
6.6 Apparatus for tube-furnace pyrohydrolysis (see Figure 1).
6.6.1 Steam generator, consisting of the following:
a) round-bottom flask, 2 l capacity;
b) heating mantle, 2 l capacity;
c) Y-piece, glass, 10 mm diameter;
d) oxygen distribution tube, porosity 0;
e) stopcocks, one three-way and one two-way.
6.6.2 Silica-tube furnace and accessories.
The apparatus is similar to that used in ISO 351.
a) Silica tube, made of pure silica (25 mm outer diameter, 20 mm inner diameter), of length (typically
700 mm) appropriate to the particular furnace used (generally of an approximate length of
400 mm). Preferably, the gas outlet end should be narrowed to a tubule of approximately 7 mm
diameter.
NOTE Combustion tubes of alternative refractory compositions do not have adequate thermal stress
characteristics for operation with this method.
b) Silicone stoppers, 20 mm diameter, positioned at inlet end (and outlet, if applicable) of the silica
tube described in a).
c) Combustion boats, made of high-alumina unglazed porcelain (approximately
97 mm × 16 mm × 12 mm), preignited at 1 000 °C for 1 h.
d) Silica pusher and T-tube, comprising a silica push rod (5 mm diameter and 500 mm long) fused at
one end to provid
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