ISO 11258:2007

INTERNATIONAL ISO
STANDARD 11258
Second edition
2007-10-15

Iron ores for shaft direct-reduction
feedstocks — Determination of the
reducibility index, final degree of
reduction and degree of metallization
Minerais de fer pour charges utilisées dans les procédés par réduction
directe — Détermination de l'indice de réductibilité, du degré final de
réduction et du degré de métallisation




Reference number
ISO 11258:2007(E)
©
ISO 2007

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ISO 11258:2007(E)
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ISO 11258:2007(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Principle. 2
5 Sampling, sample preparation and preparation of test portions. 2
6 Apparatus . 2
7 Test conditions . 3
8 Procedure . 4
9 Expression of results . 5
10 Test report . 7
11 Verification . 8
Annex A (normative) Flowsheet of the procedure for the acceptance of test results . 11
Annex B (informative) Derivation of equation for reducibility. 12
Annex C (informative) Derivation of equation for degree of metallization from R . 14
90

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ISO 11258:2007(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 11258 was prepared by Technical Committee ISO/TC 102, Iron ore and direct reduced iron,
Subcommittee SC 3, Physical testing.
This second edition cancels and replaces the first edition (ISO 11258:1999), which has been revised to
homogenise with other physical test standards prepared.
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ISO 11258:2007(E)
Introduction
This International Standard concerns one of a number of physical test methods that have been developed to
measure various physical parameters and to evaluate the behaviour of iron ores, including reducibility,
disintegration, crushing strength, apparent density, etc. This method was developed to provide a uniform
procedure, validated by collaborative testing, to facilitate comparisons of tests made in different laboratories.
The results of this test should be considered in conjunction with other tests used to evaluate the quality of iron
ores as feedstocks for direct reduction processes.
This International Standard may be used to provide test results as part of a production quality control system,
as a basis of a contract, or as part of a research project.

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INTERNATIONAL STANDARD ISO 11258:2007(E)

Iron ores for shaft direct-reduction feedstocks — Determination
of the reducibility index, final degree of reduction and degree of
metallization
CAUTION — This International Standard may involve hazardous materials, operations and equipment.
This standard does not purport to address all of the safety issues associated with its use. It is the
responsibility of the user of this International Standard to establish appropriate safety and health
practices and determine the applicability of regulatory limitations prior to its use.
1 Scope
This International Standard specifies a method to provide a relative measure for evaluating the extent and
ease to which oxygen can be removed from iron ores, when reduced under conditions resembling those
prevailing in shaft direct-reduction processes. It specifies the determination of the reducibilty, final degree of
reduction and degree of metallization.
This International Standard is applicable to lump ores and hot-bonded pellets.
2 Normative references
The following referenced documents are indispensable for the application of this International Standard. For
dated references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 2597-1:2006, Iron ores — Determination of total iron content — Part 1: Titrimetric method after tin(II)
chloride reduction
1)
ISO 3082:2000 , Iron ores — Sampling and sample preparation procedures
ISO 5416:2006, Direct reduced iron — Determination of metallic iron — Bromine-methanol titrimetric method
ISO 9035:1989, Iron ores — Determination of acid-soluble iron(II) content — Titrimetric method
ISO 9507:1990, Iron ores — Determination of total iron content — Titanium(III) chloride reduction methods
ISO 11323:2002, 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.

1) Under revision to incorporate ISO 10836, Iron ores — Method of sampling and sample preparation for physical testing
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ISO 11258:2007(E)
4 Principle
The test portion is isothermally reduced in a fixed bed, at 800 °C, using a reducing gas consisting of H , CO,
2
CO and N and is weighed continuously or at specified time intervals until 90 min of reduction is reached.
2 2
The rate of reduction is calculated at the oxygen/iron ratio of 0,9 and the final degree of reduction is calculated
from the oxygen mass loss after 90 min (R ). The degree of metallization is calculated either by an equation
90
based on R or by chemical analysis of the reduced product.

90
5 Sampling, sample preparation and preparation of test portions
5.1 Sampling and sample preparation
Sampling of a lot and preparation of a test sample shall be in accordance with ISO 3082.
The size range for pellets shall be 50 % − 16,0 mm + 12,5 mm and 50 % − 12,5 mm + 10,0 mm.
The size range for lump ores shall be 50 % − 20,0 mm + 16,0 mm and 50 % − 16,0 mm + 10,0 mm.
A test sample of at least 2,5 kg, on a dry basis, of the sized material shall be obtained.
Oven-dry the test sample to constant mass at 105 °C ± 5 °C and cool it to room temperature before
preparation of the test portions.
NOTE Constant mass is achieved when the difference in mass between two subsequent measurements becomes
less than 0,05 % of the initial mass of the test sample.
5.2 Preparation of test portions
Collect each test portion by taking ore particles at random.
NOTE Manual methods of division recommended in ISO 3082, such as riffling, can be applied to obtain the test
portions.
At least 5 test portions, each of approximately 500 g (± the mass of 1 particle) shall be prepared from the test
sample: 4 test portions for testing and 1 for chemical analysis.
Weigh the test portions to the nearest 1 g and register the mass of each test portion on its recipient label.
6 Apparatus
6.1 General
The test apparatus shall comprise:
a) ordinary laboratory equipment, such as an oven, hand tools, a time-control device and safety equipment;
b) a reduction-tube assembly;
c) a furnace, equipped with a balance for permitting the mass loss of the test portion to be read at any time
during the test;
d) a system to supply the gases and regulate the flow rates;
e) a weighing device.
Figure 1 shows an example of the test apparatus.
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ISO 11258:2007(E)
6.2 Reduction tube, made of non-scaling, heat-resistant metal to withstand temperatures higher than
800 °C and resistant to deformation. The internal diameter shall be 75 mm ± 1 mm. A removable perforated
plate, made of non-scaling, heat-resistant metal to withstand temperatures higher than 800 °C, shall be
mounted in the reduction tube to support the test portion and to ensure uniform gas flow through it. The
perforated plate shall be 4 mm thick, with its diameter 1 mm less than the internal diameter of the tube. The
holes in the plate shall be 2 mm to 3 mm in diameter at a pitch center distance of 4 mm to 5 mm.
Figure 2 shows an example of a reduction tube.
6.3 Furnace, having a heating capacity and temperature control able to maintain the entire test portion, as
well as the gas entering the bed, at 800 °C ± 5 °C.
6.4 Porcelain balls, having a size range between 10,0 mm and 12,5 mm, and of sufficient quantity to form
a double-layer bed on the perforated plate.
6.5 Balance, capable of weighing the reduction-tube assembly, including the test portion, to an accuracy of
1 g. The balance shall have an appropriate device to suspend the reduction-tube assembly.
6.6 Gas-supply system, capable of supplying the gases and regulating gas flow rates. It shall be ensured
that a frictionless connection between the gas-supply system and the reduction tube does not affect the
weight loss determination during reduction.
6.7 Weighing device, capable of weighing the test sample and test portions to an accuracy of 1 g.
7 Test conditions
7.1 General
Volumes and flow rates of gases are as measured at a reference temperature of 0 °C and at a reference
atmospheric pressure of 101,325 kPa (1,013 25 bar).
7.2 Reducing gas
7.2.1 Composition
The reducing gas shall consist of:
CO 30 % ± 1 % (volume fraction)
CO 15 % ± 1 % (volume fraction)
2
H 45 % ± 1 % (volume fraction)
2
N 10 % ± 1 % (volume fraction)
2
7.2.2 Purity
Impurities in the reducing gas shall not exceed:
O 0,1 % (volume fraction)
2
H O 0,2 % (volume fraction)
2
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ISO 11258:2007(E)
7.2.3 Flow rate
The flow rate of the reducing gas, during the entire reducing period, shall be maintained at
50 L/min ± 0,5 L/min.
7.3 Heating and cooling gas
Nitrogen (N ) shall be used as the heating and cooling gas. Impurities shall not exceed 0,1 % (volume
2
fraction).
The flow rate of N shall be maintained at 25 L/min until the test portion reaches 800 °C and at 50 L/min
2
during the temperature-equilibration period. During cooling, it shall be maintained at 25 L/min.
7.4 Temperature of the test portion
The temperature of
...