Iron ores — Determination of potassium — Flame atomic absorption spectrometric method

ISO 13312:2017 specifies a flame atomic absorption spectrometric method for the determination of the mass fraction of potassium in iron ores. This method is applicable to mass fractions of potassium between 0,002 5 % and 0,52 % in natural iron ores, iron ore concentrates and agglomerates, including sinter products.

Minerais de fer — Dosage du potassium — Méthode par spectrométrie d'absorption atomique dans la flamme

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Third edition
Iron ores — Determination of
potassium — Flame atomic absorption
spectrometric method
Minerais de fer — Dosage du potassium — Méthode par
spectrométrie d’absorption atomique dans la flamme
Reference number
ISO 13312:2017(E)
ISO 2017

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ISO 13312:2017(E)

© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
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ii © ISO 2017 – All rights reserved

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ISO 13312:2017(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 . 2
7 Sampling and samples . 4
7.1 Laboratory sample . 4
7.2 Preparation of predried test samples . 4
8 Procedure. 4
8.1 Number of determinations . 4
8.2 Test portion . 4
8.3 Blank test and check test . 4
8.4 Determination . 5
8.4.1 General. 5
8.4.2 Decomposition of the test portion . 5
8.4.3 Treatment of the solution. 5
8.4.4 Preparation of the set of calibration solutions . 5
8.4.5 Adjustment of atomic absorption spectrometer . 6
8.4.6 Atomic absorption measurements . 6
9 Expression of results . 6
9.1 Calculation of mass fraction of potassium . 6
9.2 General treatment of results . 7
9.2.1 Repeatability and permissible tolerance . 7
9.2.2 Determination of analytical result . 7
9.2.3 Between-laboratories precision . 7
9.2.4 Check for trueness . 8
9.2.5 Calculation of final result . 9
9.3 Oxide factor . 9
10 Test report . 9
Annex A (normative) 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
© ISO 2017 – All rights reserved iii

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ISO 13312:2017(E)

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
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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
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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 Technical Committee ISO/TC 102, Iron ore and direct reduced iron,
Subcommittee SC 2, Chemical analysis.
This third edition cancels and replaces the second edition (ISO 13312:2006), of which it constitutes a
minor revision with the following changes:
— in 7.2, a new sentence to make reference to ISO 2596 has been included;
— in 9.2.4, Formula (7) and the relevant descriptions have been modified to harmonize this subclause
across all International Standards for which ISO/TC 102/SC 2 is responsible;
— in 5.4, 5.5, 8.4.2 and 9.2.1, the footnotes have been moved to the appropriate place.
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Iron ores — Determination of potassium — 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
and determine the applicability of regulatory limitations prior to use.
1 Scope
This document specifies a flame atomic absorption spectrometric method for the determination of the
mass fraction of potassium in iron ores.
This method is applicable to mass fractions of potassium between 0,002 5 % and 0,52 % in natural iron
ores, 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 3696, Water for analytical laboratory use — Specification and test methods
ISO 7764, Iron ores — Preparation of predried test samples for chemical analysis
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 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 hydrofluoric acid, followed by
evaporation to dryness. The residue is wetted and the evaporation is repeated with a new portion of
hydrochloric acid. The residue is dissolved with hydrochloric acid followed by appropriate dilution. The
solution is aspirated into the air/acetylene flame of the atomic absorption apparatus.
© ISO 2017 – All rights reserved 1

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ISO 13312:2017(E)

The absorbance value obtained for potassium is measured in comparison with those obtained from
calibration solutions.
5 Reagents
During the analysis, use only reagents of recognized analytical grade and only water that complies with
Grade 2 of ISO 3696.
Reagents are to be selected or purified for the lowest possible blank value.
5.1 Hydrochloric acid, ρ 1,16 g/ml to 1,19 g/ml.
5.2 Hydrofluoric acid, ρ 1,13 g/ml, 40 % (mass fraction), or ρ 1,19 g/ml, 48 % (mass fraction).
5.3 Hydrochloric acid, ρ 1,16 g/ml to 1,19 g/ml, diluted 1 + 2.
5.4 Background solution.
Dissolve 43 g of high-purity iron oxide powder in 500 ml of hydrochloric acid (5.1). Allow to cool and
dilute with water to 1 000 ml.
Instead of iron oxide, the use of metallic iron with a suitable oxidant is permitted. The alkali content of
the oxidant shall be low.
5.5 Potassium, standard solution, 20 µg K/ml.
Pulverize about 3 g of high-purity potassium chloride in an agate mortar, dry in an oven at 105 °C to
110 °C for 2 h, and allow to cool to room temperature in a desiccator. Dissolve 1,907 g in water, dilute
with water to 1 000 ml in a volumetric flask and mix.
Transfer 10,0 ml of this solution to a 500 ml volumetric flask, dilute with water to volume and mix.
NOTE Glass equipment can be used.
Store this standard solution in a plastic bottle.
1 ml of this standard solution contains 20 µg of potassium.
6 Apparatus
Ordinary laboratory equipment, 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 Polytetrafluoroethylene (PTFE) beakers, of capacity 100 ml, provided with PTFE covers.
6.2 PTFE-coated magnetic stirring bars.
6.3 PTFE digestion bomb.
6.4 Plastic pipettes.
6.5 Plastic volumetric flasks and storage bottles.
6.6 Magnetic stirring hotplates.
NOTE Platinum vessels can be used instead of PTFE beakers.
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ISO 13312:2017(E)

Except where stated, glass equipment should be avoided, as it could contaminate the solutions.
To obtain reliable values, the equipment should be cleaned and checked as follows.
a) Rinse all volumetric ware, including the pipettes used for preparing the calibration solutions, with
dilute hydrochloric acid (5.3) before use. Check the calibration regularly or as needed.
b) Clean PTFE vessels and stirring bars by stirring with 50 ml of dilute hydrochloric acid (5.3) and by
heating for 15 min. Discard the rinsings and conduct a blank test in each vessel in turn, exactly as
specified in 8.3. If any absorbance value is above the limit specified in 8.3, the cleaning procedure
should be repeated or acid reagents of a higher purity should be used. At no stage should the
stirring bars be handled with the fingers.
c) Platinum vessels, exclusively used for potassium analysis according to this document, can be
cleaned by the same method as the PTFE vessels [see b)]. Otherwise, they should be pre-cleaned by
fusion with lithium tetraborate or lithium borate, until the absorbance readings fall to those for the
lithium salt alone.
d) Rinse storage bottles with dilute hydrochloric acid (5.3) before use.
6.7 Atomic absorption spectrometer.
WARNING — Follow the manufacturer’s instructions for igniting and extinguishing the
air/acetylene flame to avoid possible explosion hazards. Wear tinted safety glasses whenever
the burner is in operation.
The atomic absorption spectrometer shall meet the following criteria.
a) Minimum sensitivity: The absorbance of the most concentrated calibration solution (see 8.4.4) shall
be at least 0,25.
b) Graph linearity: The slope of the calibration graph covering the top 20 % of the concentration range
(expressed as a change in absorbance) shall 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, shall 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 will vary with each instrument. The following parameters were successfully
used in several laboratories

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