ISO 11724:2019

INTERNATIONAL ISO
STANDARD 11724
Third edition
2019-06
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 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 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. 7
9.1 General . 7
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
Foreword
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This document was prepared by Technical Committee ISO/TC 27, Solid mineral fuels, Subcommittee
SC 5, Methods of analysis.
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minor revision. This document incorporates changes related to dated references and other minor items
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iv © ISO 2019 – All rights reserved

INTERNATIONAL STANDARD ISO 11724:2019(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 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:
— ISO Online browsing platform: available at http: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
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.
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/kg 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 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.
6.2 Polypropylene bottles or polystyrene vials, ta
...