ISO/TS 2597-4:2019

TECHNICAL ISO/TS
SPECIFICATION 2597-4
First edition
2019-09
Iron ores — Determination of total
iron content —
Part 4:
Potentiometric titration method
Minerais de fer — Dosage du fer total —
Partie 4: Méthode potentiométrique de titration
Reference number
ISO/TS 2597-4:2019(E)
©
ISO 2019

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ISO/TS 2597-4:2019(E)

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All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ISO/TS 2597-4:2019(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 2
6 Apparatus . 3
7 Sampling and samples . 4
7.1 Laboratory sample . 4
7.2 Preparation of test samples . 4
7.2.1 General. 4
7.2.2 Method specified in ISO 7764 . 4
7.2.3 Method specified in ISO 2596 . 5
8 Procedure. 5
8.1 Number of determinations . 5
8.2 Test portion . 5
8.3 Blank test and check test . 5
8.4 Determination of hygroscopic moisture content. 5
8.5 Determination . 5
8.5.1 Decomposition of the test portion . 5
8.5.2 Reduction . 6
8.5.3 Titration. 7
8.5.4 Blank test . 7
9 Expression of results . 8
9.1 Calculation of total iron content . 8
9.2 General treatment of results . 9
9.2.1 Repeatability and permissible tolerance . 9
9.2.2 Determination of analytical result . 9
9.2.3 Between-laboratories precision . 9
9.2.4 Check for trueness .10
9.2.5 Calculation of final result .11
9.2.6 Oxide factors .11
10 Test report .11
Annex A (normative) Flowsheet of the procedure for the acceptance of analytical values for
test sample .13
Annex B (informative) Volumetric titration cell and structure of instrument as follows .14
Annex C (informative) Types of detecting electrode .16
Annex D (informative) Derivation of precision statements .18
Annex E (informative) Computer program for end point of titration .19
Bibliography .22
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ISO/TS 2597-4:2019(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
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 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
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 102, Iron ore and direct reduced iron,
Subcommittee SC 2, Chemical analysis.
A list of all parts in the ISO 2597 series can be found on the ISO website.
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.
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TECHNICAL SPECIFICATION ISO/TS 2597-4:2019(E)
Iron ores — Determination of total iron content —
Part 4:
Potentiometric titration method
WARNING — This document can involve hazardous materials, operations and equipment. This
document does not purport to address all of the safety problems associated with its use. It is the
responsibility of the user of this document to establish appropriate health and safety practices
and determine the applicability of regulatory limitations prior to use.
1 Scope
This document specifies a potentiometric titration method for the determination of total iron content
of iron ores, using potassium dichromate as titrant after reduction of the iron(III) by tin(II) chloride
and titanium(III) chloride. The excess reductant is then oxidized by potassium dichromate solution.
This method is applicable to total iron contents between a mass fraction of 29,04 % and a mass fraction
of 72,02 % in natural iron ores and iron ore concentrates and agglomerates including sinter products.
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 648, Laboratory glassware — Single-volume pipettes
ISO 1042, Laboratory glassware — One-mark volumetric flasks
ISO 2596, Iron ores — Determination of hygroscopic moisture in analytical samples — Gravimetric, Karl
Fischer and mass-loss methods
ISO 3082, Iron ores — Sampling and sample preparation procedures
ISO 7764, Iron ores — Preparation of predried test samples for chemical analysis
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
For samples containing not more than a mass fraction of 0,1 % of vanadium, copper or manganese, the
test portion is treated with hydrochloric acid in the presence of tin chloride and the residue is filtered,
ignited and treated with hydrofluoric and sulfuric acids. The mixture is fused with potassium disulfate
and the cold melt is dissolved in water and hydrochloric acid and neutralized with ammonia solution.
The precipitate is filtered, washed with water, dissolved with hydrochloric acid and combined with
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ISO/TS 2597-4:2019(E)

the main iron solution, which is treated with potassium permanganate and evaporated. Finally, after
the combined solution is treated with correlative reagents, the total iron in solution is titrated by a
potentiometric titrator.
5 Reagents
During the analysis, use only reagents of recognized analytical grade, and only distilled water or water
of equivalent purity.
5.1 Hydrochloric acid, ρ 1,16 g/ml to 1,19 g/ml.
5.2 Hydrochloric acid, ρ 1,16 g/ml to 1,19 g/ml, diluted 1 + 1.
5.3 Hydrochloric acid, ρ 1,16 g/ml to 1,19 g/ml, diluted 2 + 100.
5.4 Hydrofluoric acid, a mass fraction of 40 % (ρ 1,13 g/ml) or a mass fraction of 48 % (ρ 1,19 g/ml).
5.5 Sulfuric acid, ρ 1,84 g/ml.
5.6 Sulfuric acid, ρ 1,84 g/ml, diluted 1 + 1.
Carefully pour 1 volume of reagent (5.5) into 1 volume of cold water.
5.7 Orthophosphoric acid, ρ 1,7 g/ml.
5.8 Sulfuric acid-orthophosphoric acid mixture.
Pour 150 ml of orthophosphoric acid (5.7) into about 400 ml of water while stirring, add 150 ml of
sulfuric acid (5.5), cool in a water bath, dilute with water to 1 l and mix well.
5.9 Ammonia solution, a mass fraction of 28 % (ρ 0, 90 g/ml) to a mass fraction of 30 % (ρ 0, 96 g/ml).
5.10 Hydrogen peroxide (H O ), a volume fraction of 30 % solution.
2 2
5.11 Hydrogen peroxide (H O ), a volume fraction of 30 % solution, diluted 1 + 9.
2 2
5.12 Tin(II) hydrochloric acid solution.
Dissolve 130 g of tin metal in about 500 ml of hydrochloric acid (5.1) and dilute with hydrochloric acid
to 1 l. This solution should be stored in a brown glass bottle. Use supernatant liquid as needed.
5.13 Tin(II) chloride solution, 100 g/l.
Dissolve 100 g of crystalline tin(II) chloride (SnCl ·2H O) in 200 ml of hydrochloric acid (5.1) by heating
2 2
the solution in a water bath. Cool the solution and dilute with water to 1 l. This solution should be
stored in a brown glass bottle with a small quantity of granular tin metal.
5.14 Potassium permanganate (KMnO ) solution, 25 g/l.
4
5.15 Potassium dichromate (K Cr O ) solution, 1 g/l.
2 2 7
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ISO/TS 2597-4:2019(E)

5.16 Titanium(III) chloride (TiCl ) solution, 20 g/l.
3
Dilute one volume of titanium(III) chloride solution (about a volume fraction of 20 % TiCl ) with nine
3
volumes of hydrochloric acid (5.2). Alternatively, dissolve 1,3 g of titanium sponge in about 40 ml of
hydrochloric acid (5.1) in a covered beaker, by heating in a water bath. Cool the solution and dilute with
water to 200 ml. Prepare fresh solutions as needed.
5.17 Potassium disulfate (K S O ), fine powder.
2 2 7
5.18 Iron, standard solution, 0,1 mol/l.
Transfer 5,58 g of pure iron (purity greater than a mass fraction of 99,9 %) to a 500 ml Erlenmeyer flask
and place a small filter funnel in the neck. Add 75 ml of hydrochloric acid (5.2) in small increments and
heat until dissolved. Cool and oxidize with 5 ml of hydrogen peroxide (5.10) added in small portions.
Heat to boiling and boil to decompose the excess hydrogen peroxide and to expel chlorine. Cool, transfer
to a 1 000 ml volumetric flask and mix well.
1,00 ml of this solution is equivalent to 1,00 ml of the standard potassium dichromate solution (5.19).
5.19 Potassium dichromate (99,9 % minimum purity), standard solution, 0,016 67 mol/l.
Pulverize about 6 g of potassium dichromate reagent in an agate mortar, dry at 140 °C to 150 °C for 2 h,
and cool to room temperature in a desiccator.
Transfer 4,903 g of this material to a 300 ml beaker, dissolve in about 100 ml of water, transfer
quantitatively to a 1 000 ml volumetric flask, make up to volume with water after cooling to 20 °C and
mix well. Record the temperature at which this dilution was made (20 °C) on the stock bottle. Measure
the temperature at each use to correct the volume of titrant used.
The volumetric flask should previously be calibrated by weighing the mass of water contained at 20 °C
and converting to volume.
Water used for preparation should previously be equilibrated at room temperature.
A calibrated thermometer, graduated in 0,1 °C divisions and having a marked dipping line, should
be used. Take a sufficient volume of standard solution for dipping the thermometer and transfer to a
suitable beaker. Measure the temperature of the solution, to the nearest 0,1 °C after dipping for more
than 60 s.
5.20 Indigo carmine [indigo-5,5′-disulfonic acid disodium salt (C H O N S Na )] solution,
16 8 8 2 2 2
0,1 g/100 ml.
Dissolve 0,1 g of indigo carmine in a cold mixture of 50 ml sulfuric acid (5.6) and 50 ml of water.
6 Apparatus
The pipette and volumetric flask specified shall conform to ISO 648 and ISO 1042, respectively.
Use ordinary laboratory apparatus and the following.
6.1 Weighing bottle, of approximate volume 10 ml and approximate mass 6 g.
6.2 Platinum crucible with a lid, capacity 25 ml to 30 ml and having a lid.
6.3 Weighing spatula, of a non-magnetic material or demagnetized stainless steel.
6.4 Muffle furnace, suitable for operation in the range 500 °C to 800 °C.
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ISO/TS 2597-4:2019(E)

6.5 Platinum electrodes, either as a pair or as a dual platinum electrode.
6.6 Magnetic stirrers and rotators or propeller rod stirrer, of chemically inert material and
variable speed.
6.7 Amperometric titrator, suitable for volumetric analysis, equipped with an ammeter (0,50 μA) or
an equivalent means for the electrometric indication of the end-point, equipped with a X-Y graph plotter.
6.8 Burettes, of suitable capacity (25 ml to 50 ml), conforming to class A specifications (or
equivalent), possessing preferably brown glass reservoir bottle and electro-volumeter.
The burette should be vented solely by an anhydrous atmosphere of suitable capacity. Fillers should not
be pressurized through the lower inlet of the burette.
6.9 Titration cells, preferably, brown glass vessels of 400 ml to 500 ml capacity. The entries for the
platinum electrodes should preferably be near the cell walls, while the burette tip should preferably be
centred to ensure rapid distribution of the added reagent.
NOTE A suitable titration cell is shown diagrammatically in Annex B and suitable platinum electrodes are
shown diagrammatically in Annex C.
7 Sampling and samples
7.1 Laboratory sample
For analysis, use a laboratory sample of 160 μm nominal top size, which has been taken and prepared
in accordance with ISO 3082. In the case of ores having significant contents of combined water or
oxidizable compounds, use a particle size of –160 μm.
NOTE A guideline on significant contents of combined water and oxidizable compounds is incorporated in
ISO 7764.
If the determination of total iron relates to a reducibility test, prepare the laboratory sample by
crushing and pulverizing, to less than 160 μm particle size, the whole of one of the reducibility test
portions which has been reserved for chemical analysis. In the case of ores having significant contents
of combined water or oxidizable compounds, use a particle size of less than 160 μm.
7.2 Preparation of test samples
7.2.1 General
Depending on ore type, proceed in accordance with either 7.2.2 or 7.2.3.
7.2.2 Method specified in ISO 7764
This method is not applicable to the following type of ores:
a) processed ores containing metallic iron;
b) natural or processed ores in which the sulfur content is higher than a mass fraction of 0,2 %;
c) natural or processed ores in which the content of combined water is higher than a mass fraction
of 2,5 %.
Thoroughly mix the laboratory sample and, taking multiple increments, extract a test sample in such a
way that it is representative of the whole contents of the container.
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ISO/TS 2597-4:2019(E)

7.2.3 Method specified in ISO 2596
This method is applicable to all type of ores. Thoroughly mix the laboratory sample and, taking multiple
increments, extract a test sample in such a way that it is representative of the whole contents of the
container. Bring the test sample into air-equilibrium with the laboratory atmosphere in accordance
with ISO 2596.
8 Procedure
8.1 Number of determinations
Carry out the analysis at least in duplicate in accordance with Annex A, independently, on one test
sample (see 7.2).
NOTE
...