ISO 25319:2026

International
Standard
ISO 25319
First edition
Determination of metallic Fe in
2026-11
reduced iron (sponge Iron) and
briquette — Iron (III) chloride
titrimetric method
Dosage du Fe métallique dans le fer préréduit (fer spongieux) et
dans la briquette — Méthode titrimétrique au chlorure de fer
(III)
Reference number
© ISO 2026
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ii
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 Sampling and sample preparation . 3
7.1 Sample preparation .3
7.2 Laboratory sample .3
8 Procedure . 3
8.1 Number of determinations .3
8.2 Preparation of test portions .3
8.3 Determination .3
9 Expression of results . 4
9.1 Calculation of the metallic iron content .4
9.2 General treatment of result .4
9.2.1 Repeatability and Reproducibility .4
9.2.2 Determination of analytical result .5
10 Test report . 5
Annex A (Normative) Flowsheet of the procedure for the acceptance of test results . 6
Annex B (Normative) Calculation F correction factor of potassium dichromate . 7
Annex C (Informative) Results obtained, calculations performed and statistical assessment . 8
Bibliography . 14

iii
Foreword
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iv
International Standard ISO 25319:2026(en)
Determination of metallic Fe in reduced iron (sponge Iron)
and briquette — Iron (III) chloride titrimetric method
1 Scope
This method is applicable to a concentration range of 52,80 % mass fraction to 86,40 % mass fraction of the
metallic Fe.
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 385, Laboratory glassware — Burettes
ISO 10835, Direct reduced iron and hot briquetted iron — Sampling and sample preparation
ISO 11323, Iron ore and direct reduced iron — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 11323 apply.
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
0 +2
Iron present in the oxidation state Fe in the sample is oxidized to Fe by the action of FeCl . This reaction is
catalysed by ammonium chloride according to the following reaction:
2FeCl + Fe  3FeCl
3 2
2+
Fe is oxidized and titrated with potassium dichromate solution using the sodium diphenylamine sulfonate
indicator (or barium diphenylamine sulfonate) according to the following reaction:
2+ 2- + 3+ 3+
6Fe + Cr O + 14H  6Fe + 2Cr + 7H O
2 7 2
5 Reagents
During the analysis, use only reagents of recognized analytical reagent grade and only distilled water or
water of equivalent purity.
5.1 Iron (III) chloride solution 7 %
Add 117 g of iron (III) chloride hexahydrate to a 2 000 ml container holding 600 ml of water and agitate until
it is completely dissolved. Dilute with water to a volume of 1 000 ml.
NOTE For better dissolution of the iron (III) chloride, use hot water (60 °C to 80 °C). The ideal condition is a
complete dissolution of the salt resulting in a translucent solution.
5.2 Standard potassium dichromate solution, 0,016 67 mol/L
Add 4,903 1 g of dried potassium dichromate to a 2 000 ml container holding 600 ml of water and agitate
until it is completely dissolved. Dilute with water to a volume of 1 000 ml.
Prepare a standard potassium dichromate solution following the directions in Annex B
5.3 Mixed acid
Add 700 ml of water to a 2 000 ml beaker. Place the beaker in a cool place and add slowly with stirring
150 ml of phosphoric acid, 1,7 b/ml. Allow cooling. Add slowly with stirring 150 ml of sulfuric acid, 1,84 g/
ml and allow cooling (it is optional: placing the beaker in an ice-water bath). Dilute this mixture to 1 000 ml
with stirring.
5.4 Sodium diphenylamine sulfonate 2 g/l
Dissolve 0,2 g of powdered sodium diphenylamine sulfonate (C H NHC H SO Na) in a small volume of water
6 5 6 4 3
and dilute to 100 ml. Store this solution in a brown glass bottle.
5.5 Barium diphenylamine sulfonate 2 g/l
Dissolve 0,2 g of powdered barium diphenylamine sulfonate ((C H NHC H SO ) Ba)
...