Iron ore pellets for blast furnace feedstocks — Determination of the free-swelling index

This document specifies a method to provide a relative measure for evaluating the increase in volume of iron ore pellets, when reduced in an unconstrained bed under conditions resembling those prevailing in the reduction zone of a blast furnace. It specifies the determination of the free-swelling index. This document is applicable to hot-bonded pellets.

Boulettes de minerais de fer pour l'alimentation de hauts fourneaux — Détermination de l'indice de gonflement libre

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Status
Published
Publication Date
09-Nov-2022
Current Stage
6060 - International Standard published
Due Date
03-Mar-2023
Completion Date
10-Nov-2022
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INTERNATIONAL ISO
STANDARD 4698
Third edition
2022-11
Iron ore pellets for blast furnace
feedstocks — Determination of the
free-swelling index
Boulettes de minerais de fer pour l'alimentation de hauts
fourneaux — Détermination de l'indice de gonflement libre
Reference number
ISO 4698:2022(E)
© ISO 2022
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ISO 4698:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
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Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
© ISO 2022 – All rights reserved
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ISO 4698:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 1

5 Sampling, sample preparation and preparation of test portions .................................................................... 1

5.1 Sampling and sample preparation ........................................................................................................................................ 1

5.2 Preparation of test portions ....................................................................................................................................................... 2

6 Apparatus .................................................................................................................................................................................................................... 2

7 Test conditions .......................................................................................................................................................................................................5

7.1 General ........................................................................................................................................................................................................... 5

7.2 Reducing gas ............................................................................................................................................................................................. 5

7.2.1 Composition ............................................................................................................................................................................ 5

7.2.2 Purity ............................................................................................................................................................................................ 5

7.2.3 Flow rate .................................................................................................................................................................................... 5

7.3 Heating and cooling gas .................................................................................................................................................................. 5

7.4 Temperature of the test portion ............................................................................................................................................. 5

8 Procedure ....................................................................................................................................................................................................................6

8.1 Number of determinations for the test ............................................................................................................................. 6

8.2 Reduction .................................................................................................................................................................................................... 6

8.3 Volume determination ..................................................................................................................................................................... 6

9 Expression of results ....................................................................................................................................................................................... 6

9.1 Calculation of the free-swelling index (V ) ................................................................................................................. 6

9.2 Repeatability and acceptance of test results ............................................................................................................... 7

10 Test report .................................................................................................................................................................................................................. 7

11 Verification ................................................................................................................................................................................................................ 7

Annex A (normative) Flowsheet of the procedure for the acceptance of test results .....................................8

Annex B (normative) Methods for determination of the volume of the test portion .......................................9

iii
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ISO 4698:2022(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 3, Physical testing.

This third edition cancels and replaces the second edition (ISO 4698:2007), which has been technically

revised.
The main changes are as follows:
— the dry medium displacement volumetric method has been included in Annex B.

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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ISO 4698:2022(E)
Introduction

This document 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 blast furnace processes.

This document 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 4698:2022(E)
Iron ore pellets for blast furnace feedstocks —
Determination of the free-swelling index

CAUTION — This document can involve hazardous materials, operations and equipment. This

document does not purport to address all of the safety issues associated with its use. It is the

responsibility of the user of this document to establish appropriate safety and health practices

and determine the applicability of regulatory limitations prior to its use.
1 Scope

This document specifies a method to provide a relative measure for evaluating the increase in volume

of iron ore pellets, when reduced in an unconstrained bed under conditions resembling those prevailing

in the reduction zone of a blast furnace. It specifies the determination of the free-swelling index.

This document is applicable to hot-bonded pellets.
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 3082, Iron ores — Sampling and sample preparation procedures
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 and the following 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

The volume of pellets in the test portion is measured at room temperature, using a volumetric

apparatus. The test portion is isothermally reduced under unconstrained conditions in a fixed bed at

900 °C, using a reducing gas consisting of CO and N , for 60 min. The volume of the reduced pellets is

measured at room temperature. The swelling index is calculated as the difference between the volume

of the pellets after and before reduction, expressed as a percentage.
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 −12,5 mm + 10,0 mm.

A test sample of at least 1 kg, on a dry basis, of whole-sized pellets shall be obtained.

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ISO 4698:2022(E)

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

At least four test portions, each one made up of 18 whole pellets, shall be obtained from the test sample

by random selection.
6 Apparatus
The usual laboratory apparatus and, in particular, the following shall be used.

6.1 Ordinary laboratory equipment, such as an oven, hand tools, a time-control device and safety

equipment.
Figure 1 shows an example of the test apparatus.
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ISO 4698:2022(E)
Key
Reduction tube Furnace
1 reduction-tube wall 8 electrically heated furnace
2 test portion holder 9 thermocouple for temperature regulation of furnace
3 gas inlet Gas-supply system
4 lid 10 gas cylinder
5 gas outlet 11 gas flow meter
6 thermocouple for measuring the reduction temperature12 mixing vessel
7 test portion
Figure 1 — Example of test apparatus (schematic diagram)

6.2 Reduction tube, made of non-scaling, heat-resistant metal to withstand temperatures higher

than 900 °C and resistant to deformation. The internal diameter shall be 75 mm ± 1 mm.

6.3 Test portion holder, a wire basket made of non-scaling, heat-resistant metal to withstand

temperatures higher than 900 °C. It shall comprise three levels, each made to receive six pellets, for a

total of 18 pellets. Alternatively, the test portion holder may be made by welding a tube to the centre of

three perforated plates, mutually parallel and equally spaced. The tube shall be top-opened and bottom-

closed to allow the thermocouple insertion up to the middle of the test portion. The set shall be made of

non-scaling, heat-resistant metal to withstand temperatures higher than 900 °C. The perforated plate

shall be 4 mm thick, with its diameter 1 mm less than the tube internal diameter, the holes in the plate

shall be 2 mm to 3 mm in diameter, at a pitch centre distance of 4 mm to 5 mm.
Figure 2 shows an example of a reduction tube with the test portion holder.
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ISO 4698:2022(E)
Dimensions in millimetres
Key
1 reduction-tube wall 6 opening for thermocouple insertion
2 test portion holder 7 test portion
3 opening for gas inlet Design of perforated plate when a wire basket is used
as the test portion holder.
4 lid Design of perforated plate when a test portion holder
with three levels is used.
5 opening for gas outlet

NOTE Dimensions not specified in the apparatus clause are shown for information only.

Figure 2 — Example of a reduction tube with test portion holder (schematic diagram)

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ISO 4698:2022(E)

6.4 Furnace, having a heating capacity and temperature control able to maintain the entire test

portion, as well as the gas entering the bed, at 900 °C ± 10 °C.

6.5 Gas-supply system, capable of supplying the gases and regulating gas flow rates.

6.6 Volumetric apparatus, capable of measuring the volume of the test portion to an accuracy of

0,2 ml.
Annex B shows examples of volumetric apparatus.
7 Test conditions
7.1 General

Volumes and flow rates of gases are measured at a reference temperature of 0 °C and at a reference

atmospheric pressure of 101,325 kPa.
7.2 Reducing gas
7.2.1 Composition
The reducing gas shall consist of:
CO 30,0 % ± 0,5 % (volume fraction)
N 70,0 % ± 0,5 % (volume fraction)
7.2.2 Purity
Impurities in the reducing gas shall not exceed:
H 0,2 % (volume fraction)
CO 0,2 % (volume fraction)
O 0,1 % (volume fraction)
H O 0,2 % (volume fraction)
7.2.3 Flow rate

The flow rate of the reducing gas, during the entire reducing period, shall be maintained at

15 l/min ± 1 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

fraction).

The flow rate of N shall be maintained at 10 l/min until the test portion reaches 900 °C, and at 15 l/min

during the temperature-equilibration period. During cooling, it shall be maintained at 5 l/min.

7.4 Temperature of the test portion

The temperature of the entire test portion shall be maintained at 900 °C ± 10 °C during the entire

reducing period and, as such, the reducing gas shall be preheated before entering the test portion.

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ISO 4698:2022(E)
8 Procedure
8.1 Number of determinations for the test
Carry out the test as many times as required by the procedure in Annex A.
8.2 Reduction

Determine the volume of the test portion (V ) to an accuracy of 0,2 ml, in accordance with one of the

methods specified in Annex B.

Place six pellets on each of the three levels of the test portion holder (6.3) and place it in the reduction

tube (6.2). Close the top of the reduction tube. Connect the thermocouple, ensuring that its tip is in the

centre of the test portion. Close the top of the reduction tube and insert it in the furnace.

Connect the gas-supply system (6.5).

Pass a flow of N through the test portion at a rate of at least 5 l/min and commence heating. When

the temperature of the test portion approaches 900 °C, increase the flow to 15 l/min ± 1 l/min. After

reaching 900 °C ± 10 °C, maintain the test portion under these conditions for 15 min.

DANGER — Carbon monoxide and the reducing gas, which contains carbon monoxide, are

toxic and therefore hazardous. Testing shall be carried out in a well-ventilated area or under a

ventilation hood. Precautions should be taken for the safety of the operator.

Introduce the reducing gas at a flow rate of 15 l/min ± 1 l/min to replace the N . After 60 min of

reduction, turn off the power.

Some pellets show a higher degree of swelling within a shorter reduction time than 60 min. Therefore,

a shorter reduction time may be used as an alternative when appropriate, e.g. 40 min.

Replace the reducing gas with N at a flow rate of 5 l/min. Remove the reduction tube from the furnace

(6.4) while maintaining the flow of N until the test portion reaches room temperature (below 50 °C).

8.3 Volume determination

Remove the test portion from the reduction tube and immediately determine and register the total

volume of the test portion (V ), applying the same method used for the determination of V .

1 0
9 Expression of results
9.1 Calculation of the free-swelling index (V )

The free-swelling index, V , expressed as a percentage, is calculated from Formula (1):

VV−
V = ×100 (1)
where
V is the volume, in millilitres, of the test portion before reduction;
V is the volume, in millilitres, of the test portion after reduction.
Record the result to one decimal place.
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ISO 4698:2022(E)
9.2 Repeatability and acceptance of test results

Follow the procedure in Annex A by using the repeatability value, r = 3,0 (%, absolute). The results shall

be reported to one decimal place.
10 Test report
The test report shall include the following information:
a) a reference to this document, i.e. ISO 4698:2022;
b) all details necessary for the identification of the sample;
c) the name and address of the test laboratory;
d) the date of the test;
e) the date of the test report;
f) the signature of the person responsible for the test;

g) details of any operation and any test conditions not specified in this document or regarded as

optional, as well as any incident which can have had an influence on the results;

h) the free-swelling index, V ;
i) the time of reduction, if it is not 60 min;
j) the type of volumetric method employed.
11 Verification

Regular checking of the apparatus is essential to ensure test result reliability. The frequency of checking

is a matter for each laboratory to determine.
The conditions of the following items shall be checked:
— reduction tube;
— temperature control and measurement devices;
— gas flow meters;
— purity of gases;
— recording system;
— time-control device;
— volumetric apparatus.

It is recommended that internal reference material be prepared and used periodically to check test

repeatability.
Appropriate records of verification activities shall be maintained.
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ISO 4698:2022(E)
Annex A
(normative)
Flowsheet of the procedure for the acceptance of test results
NOTE r: see 9.2.
Figure A.1 — Flowsheet of the procedure for the acceptance of test results
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ISO 4698:2022(E)
Annex B
(normative)
Methods for determination of the volume of the test portion
B.1 General

This annex specifies five methods for the determination of the volume of the test portion of hot-bonded

pellets.

As the use of mercury (Hg) should be avoided because of environmental concerns, methods using Hg to

determine the volume of the test portion are not recommended. The application of volumetric methods

without Hg, such as the ones described in B.3, B.5 and B.6, are preferable.
B.2 Mercury volumetric method
B.2.1 Principle

Determination of the volume of the test portion from the volume change of mercury when the test

portion is immersed in mercury.
B.2.2 Apparatus
An example of the mercury volumetric apparatus is shown in Figure B.1.
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ISO 4698:2022(E)
Key
1 measuring tube graduated in 1/10 ml
2 test portion holder
3 test portion
4 devices to retain test portion holder within the sample holder
5 o-rings
6 clamp for test portion holder and measuring tube
7 container with mercury
8 movable plunger
9 handle and gear box for moving plunger
10 stopper
Figure B.1 — Example of the mercury volumetric apparatus
B.2.3 Preparation of the sample

Oven-dry the test portion to constant mass at 105 °C ± 5 °C and cool it to room temperature.

B.2.4 Procedure
B.2.4.1 Set the volumetric apparatus as follows:
— Clamp the empty portion holder in the apparatus.

— Raise the level of the mercury with the plunger driven by the handle, so that the mercury surface is

level with the zero mark of the measuring tube.

— Fix the stopper so that the level of the mercury cannot be raised any more with the handle.

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ISO 4698:2022(E)

— Check that the stopper prevents further movement of the plunger when the mercury has reached

the zero mark of the tube.
— Lower the mercury into the container.

B.2.4.2 After the apparatus has been set, carry out the determination as follows:

— Take the test portion consisting of 18 pellets. Remove the test portion holder from the apparatus

and place the test portion in the holder. Clamp the test portion holder in the volumetric apparatus

and raise the mercury level until the fixed stopper prevents further movement of the plunger.

— Read the volume on the measuring tube. Repeat the determination and ensure that the same value

is obtained.

— Ensure that no mercury remains when the mercury is allowed to flow down through the test portion

for the last time.

— Remove the test portion holder and carefully pour the test portion into a bowl.

— Check the pellets one by one, to ensure that there is no mercury on them, and transfer them to

another bowl. Then pour any mercury left in the first bowl back into the container.

— When the determination has been carried out, carry out a careful check to ensure that there is no

free mercury on or near the apparatus. Collect any mercury that has been spilled and pour it into

the mercury waste-collection vessel in the laboratory.
B.3 Oleate-kerosene volumetric method
B.3.1 Principle

Determination of the volume of the test portion from the difference of the masses obtained both in air

and in water, after forming a thin hydrophobic film on the surface of the pellets with sodium oleate

aqueous solution and stabilizing the film with kerosene. Calculate the volume relative to the density of

water.
B.3.2 Test liquids
Prepare all reagents and water freshly as required.
B.3.2.1 Water, distilled or ion-exchange water.
B.3.2.2 Sodium oleate aqueous solution, c(C H COONa) = 0,1 mol/l
17 33
B.3.2.3 Kerosene, of reagent grade.
B.3.3 Apparatus

B.3.3.1 Container for test liquids (sodium oleate aqueous solution and kerosene), designed to allow

free movement within it of the cage containing the pellets. It shall be made of materials, such as glass,

which do not react with sodium oleate aqueous solution or kerosene.

B.3.3.2 Cage for immersion in test liquids, to hold the pellets during immersion in the reagents. It

shall be made of materials which do not react with sodium oleate aqueous solution or kerosene. It shall

be constructed so that the test portion can be stacked in the cage in two or three layers.

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ISO 4698:2022(E)

B.3.3.3 Cage for immersion in water, to hold the pellets during immersion in water. It shall be made

of material to which air bubbles will not adhere.
Figure B.2 shows an example of a cage for immersion in water.
Dimensions in millimetres
Figure B.2 — Example of a cage for immersion in water

B.3.3.4 Absorbent sponges, consisting of two pairs of sponges whose surfaces are covered with

gauze to absorb any reagent froth on the surface of the pellets.
Figure B.3 shows an example of absorbent sponges.
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ISO 4698:2022(E)
Key
1 sponge
2 gauze (fourfold)
3 pellets
Figure B.3 — Absorbent sponges

B.3.3.5 Weighing device, capable of weighing the test portion to an accuracy of 0,001 g.

B.3.3.6 Suspensory line, a suitable line, approximately 0,3 mm in diameter, for suspending the cage

in water.

B.3.3.7 Beaker, for containing the pellets to be weighed in water, with a suitable capacity which does

not contact the cage. The base-plane area shall be large enough to not significantly change the water

level when weighing the test portion.
B.3.3.8 Stand for the beaker, either wooden or metal.

Materials that generate static electricity, such as acrylic resin, should not be used.

B.3.3.9 Thermometer, graduated in units of 0,5 °C or less.
B.3.4 Procedure

B.3.4.1 Place the test portion in the cage (B.3.3.2) and immerse the cage with the test portion in the

sodium oleate solution (B.3.2.2) and leave for 30 min. Immediately before raising the cage, repeatedly

shake it to remove air bubbles adhering to the pellets.
Figure B.4 shows a general view of immersion in reagents.
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ISO 4698:2022(E)
Key
1 sodium oleate solution
2 pellets
3 cage
4 kerosene
Figure B.4 — General view of immersion in reagents

B.3.4.2 Remove the test portion from the solution and place the pellets, separated from each other,

in one pair of sponges (B.3.3.4). Then press the sponges slightly by hand for 10 s, to absorb the froth of

sodium oleate adhering to the test portion.

Next, rotate the test portion vertically to about 90°, line up another pair of sponges and press the

containers down again for 10 s to ensure that air bubbles are removed from the whole surface of the

test portion.
Use the fresh surface of the gauze.

B.3.4.3 Place the test portion, from which froth has been removed, in the cage (B.3.3.2). Then immerse

this cage containing the pellets in kerosene for about 10 s (see Figure B.4).

B.3.4.4 Remove the test portion from the kerosene and put it in a pair of sponges to absorb the

kerosene froth as described in B.3.4.2.

B.3.4.5 Place the test portion, from which froth has been removed, in the cage for immersion in water

(B.3.3.3). Then suspend the cage containing the test portion from the balance and shake the cage in the

water to remove air bubbles adhering to the surface of the test portion (see Figure B.5).

Record the mass of the test portion and the cage (m ) to three decimal places after immersing them in

water for 1 min.

NOTE Preliminary immersion of the cage in water will help prevent air bubbles from adhering to it.

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ISO 4698:2022(E)
Key
1 water 5 beaker
2 sinker 6 pellets
3 balance 7 cage
4 fishing line 8 stool
Figure B.5 — General view of mass determination in water

B.3.4.6 Remove the test portion from the cage and put it in the pair of sponges to absorb the water

adhering to the surfa
...

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