ISO/TR 4688-1:2017

TECHNICAL ISO/TR
REPORT 4688-1
First edition
2017-04
Iron ores — Determination of
aluminium —
Part 1:
Flame atomic absorption
spectrometric method
Minerais de fer — Dosage de l’aluminium —
Partie 1: Méthode par spectrométrie d’absorption atomique dans
la flamme
Reference number
ISO/TR 4688-1:2017(E)
©
ISO 2017

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ISO/TR 4688-1:2017(E)

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ISO/TR 4688-1:2017(E)

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 samples . 3
7.1 Laboratory sample . 3
7.2 Preparation of predried test samples . 3
8 Procedure. 3
8.1 Number of determinations . 3
8.2 Test portion . 4
8.3 Blank test and check test . 4
8.4 Determination . 4
8.4.1 Decomposition of the test portion . 4
8.4.2 Treatment of the residue . 4
8.4.3 Preparation of the test solution . 4
8.4.4 Adjustment of the atomic absorption spectrometer. 5
8.4.5 Atomic absorption measurements . 5
9 Expression of results . 6
9.1 Calculation of mass fraction of aluminium . 6
9.2 General treatment of results . 6
9.2.1 Repeatability and permissible tolerance . 6
9.2.2 Determination of analytical result . 7
9.2.3 Between-laboratories precision . 7
9.2.4 Check for trueness . 7
9.2.5 Calculation of final result . 8
9.3 Oxide factor . 9
10 Test report . 9
Annex A (informative) Flowsheet of the procedure for the acceptance of analytical values
for test samples .10
Annex B (informative) Derivation of repeatability and permissible tolerance formulae .11
Annex C (informative) Precision data obtained by international analytical trials .12
Bibliography .13
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ISO/TR 4688-1:2017(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 on 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 the following
URL: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by ISO/TC 102, Iron ore and direct reduced iron, Subcommittee SC 2,
Chemical analysis.
This first edition Technical Report cancels and replaces the second edition (ISO 4688-1:2006), which
has been technically revised. It has been converted to a Technical Report as it is no longer suitable for
determination of aluminium as a referee method.
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TECHNICAL REPORT ISO/TR 4688-1:2017(E)
Iron ores — Determination of aluminium —
Part 1:
Flame atomic absorption spectrometric method
WARNING — This document may 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.
1 Scope
This document describes a flame atomic absorption spectrometric method for the determination of the
mass fraction of aluminium in iron ores.
This method is applicable to mass fractions of aluminium between 0,1 % and 5,0 % in natural iron ores,
iron ore concentrates and agglomerates, including sinter products.
2 Normative references
There are no normative references in this document.
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:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
4 Principle
The test portion is decomposed by treatment with hydrochloric acid and a small amount of nitric acid.
The mixture is evaporated to dehydrate silica, followed by dilution and filtration.
The residue is ignited and silica is removed by evaporation with hydrofluoric and sulfuric acids. The
residue is then fused with sodium carbonate and the cooled melt is dissolved in the filtrate.
The solution obtained is aspirated into the flame of an atomic absorption spectrometer using a
dinitrogen oxide/acetylene burner.
The absorbance values obtained for aluminium are compared with those obtained from the calibration
solutions.
5 Reagents
During analysis, use only reagents of recognized analytical grade and only distilled water or water of
equivalent purity.
5.1 Sodium carbonate (Na CO ), anhydrous.
2 3
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ISO/TR 4688-1:2017(E)

5.2 Hydrochloric acid, ρ 1,19 g/ml.
5.3 Nitric acid, ρ 1,4 g/ml.
5.4 Hydrochloric acid, ρ 1,19 g/ml, diluted 1 + 9.
5.5 Hydrofluoric acid, ρ 1, 13 g/ml, 40 % (mass fraction), or ρ 1,185 g/ml, 48 % (mass fraction).
5.6 Sulfuric acid, ρ 1,84 g/ml, diluted 1 + 1.
5.7 Background solution
Dissolve 10 g of high purity iron [minimum purity 99,9 % (mass fraction)] of mass fraction of aluminium
less than 0,002 %, in 50 ml of hydrochloric acid (5.2) and oxidize by adding nitric acid (5.3) drop by drop.
Evaporate until a syrupy consistency is obtained. Add 20 ml of hydrochloric acid (5.2) and dilute to
200 ml with water. Dissolve 17 g of sodium carbonate (5.1) in water and add it to the iron solution.
Transfer the solution to a 1 000 ml one-mark volumetric flask and dilute to volume with water.
5.8 Aluminium standard solution, 500 µg Al/ml.
Dissolve 0,5 000 g of high purity aluminium [minimum purity 99,9 % (mass fraction)] in 25 ml of
hydrochloric acid (5.2). Cool, transfer to a 1 000 ml one-mark volumetric flask, dilute to volume with
water and mix.
5.9 Aluminium calibration solutions
Transfer 2,0 ml; 5,0 ml; 10,0 ml; 20,0 ml; 40,0 ml; and 50,0 ml portions of aluminium standard solution
(5.8) to 200 ml volumetric flasks. Dilute to about 100 ml. Add 6 ml of hydrochloric acid (5.2) and 60 ml of
background solution (5.7) to each flask. Prepare a zero aluminium calibration solution by transferring
60 ml of the background solution to a 200 ml volumetric flask, and add 6 ml of hydrochloric acid (5.2).
Dilute all the solutions to 200 ml with water and mix. (For an atomic absorption spectrometer having
high sensitivity, smaller portions of the standard solution may be used.)
6 Apparatus
Ordinary laboratory apparatus, including one-mark pipettes and one-mark volumetric flasks complying
with the specifications of ISO 648 and ISO 1042, respectively, and the following.
6.1 Platinum crucible, of capacity 30 ml.
6.2 Muffle furnace, capable of maintaining a temperature of approximately 1 100 °C.
6.3 Atomic absorption spectrometer, equipped with a dinitrogen oxide/acetylene burner.
WARNING — Follow the manufacturer’s instructions for igniting and extinguishing the
dinitrogen oxide/acetylene flame to avoid possible explosion hazards. Wear tinted safety glasses
whenever the flame is burning.
The atomic absorption spectrometer used in this method should meet the following criteria.
a) Minimum sensitivity: the absorbance of the most concentrated aluminium calibration solution
(5.9) should be at least 0,3.
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ISO/TR 4688-1:2017(E)

b) Graph linearity: the slope of the calibration graph covering the top 20 % of the concentration range
(expressed as a change in absorbance) should not be less than 0,7 of the value of the slope for the
bottom 20 % of the concentration range determined in the same way.
c) Minimum stability: the standard deviation of the absorbance of the most concentrated calibration
solution and that of the zero calibration solution, each being calculated from a sufficient number of
repetitive measurements, should be less than 1,5 % and 0,5 %, respectively, of the mean value of
the absorbance of the most concentrated calibration solution.
The use of a strip-chart recorder and/or digital readout device is recommended to evaluate criteria a),
b) and c) and for all subsequent measurements.
NOTE Instrument parameters can vary with each instrument. The following parameters were successfully
used in several laboratories and they can be used as guidelines. Solutions were aspirated into a dinitrogen
oxide/acetylene flame of a premix burner.
Aluminium hollow cathode lamp, mA 25
Wavelength, nm 396,2
Dinitrogen oxide flow rate, l/min 13,8
Acetylene flow rate, l/min 6,6
In systems where the values shown above for gas flow rates do not apply, the ratio of the gas flow rates
may still be a useful guideline.
7 Sampling and samples
7.1 Laboratory sample
For analysis, use a laboratory sample of minus 100 µm particle 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 minus 160 µm.
NOTE A guideline on significant contents of combined water and oxidizable compounds is incorporated in
ISO 7764.
7.2 Preparation of predried test samples
Thoroughly mix the laboratory sample and,
...