ISO 15634:2015

INTERNATIONAL ISO
STANDARD 15634
Second edition
2015-08-01
Iron ores — Determination of
chromium content — Flame atomic
absorption spectrometric method
Minerais de fer — Dosage du chrome — Méthode par spectrométrie
d’absorption atomique dans la flamme
Reference number
©
ISO 2015
© ISO 2015, Published in Switzerland
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ii © ISO 2015 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Principle . 1
4 Reagents . 1
5 Apparatus . 2
6 Sampling and samples . 3
6.1 Laboratory sample . 3
6.2 Preparation of predried test samples . 3
7 Procedure. 4
7.1 Number of determinations . 4
7.2 Test portion . 4
7.3 Blank test and check test . 4
7.4 Determination . 4
7.4.1 Decomposition of the test portion . 4
7.4.2 Removal of iron . 5
7.4.3 Treatment of the residue . 5
7.4.4 Preparation of the calibration solutions . 5
7.4.5 Preparation of the flame setting solution . 6
7.4.6 Adjustment of the atomic absorption spectrometer. 6
7.4.7 Atomic absorption measurements . 6
8 Expression of results . 6
8.1 Calculation of chromium content . 6
8.2 General treatment of results . 7
8.2.1 Repeatability and permissible tolerance . 7
8.2.2 Determination of analytical result . 7
8.2.3 Between-laboratories precision . 7
8.2.4 Check for trueness . 8
8.2.5 Calculation of final result . 9
8.3 Oxide factor for conversion to chromium oxide . 9
9 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 equations .11
Annex C (informative) Precision data obtained by international analytical trial .12
Bibliography .13
Foreword
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The committee responsible for this document is ISO/TC 102, Iron ore and direct reduced iron,
Subcommittee SC 2, Chemical analysis.
This second edition cancels and replaces the first edition (ISO 15634:2005), which has been
technically revised.
iv © ISO 2015 – All rights reserved

INTERNATIONAL STANDARD ISO 15634:2015(E)
Iron ores — Determination of chromium content — Flame
atomic absorption spectrometric method
WARNING — This International Standard may involve hazardous materials, operations, and
equipment. This International Standard does not purport to address all of the safety problems
associated with its use. It is the responsibility of the user of this International Standard to
establish appropriate health and safety practices and determine the applicability of regulatory
limitations prior to use.
1 Scope
This International Standard specifies a flame atomic absorption spectrometric method for the
determination of the chromium content of iron ores.
This method is applicable to chromium contents between 0,001 6 % and 0,1 % (mass fractions) in
natural iron ores, iron ore concentrates, and agglomerates including sinter products.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. 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 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
3 Principle
The test portion is decomposed by treatment with hydrochloric and nitric acids.
The major portion of iron in the filtrate is removed by extraction with 4-methylpentan-2-one.
The insoluble residue is ignited and the silicon dioxide is removed by evaporation with hydrofluoric
and sulfuric acids. The residue is fused with a mixture of sodium carbonate and sodium tetraborate,
and then dissolved with hydrochloric acid and combined with the main solution.
The solution is aspirated into the flame of an atomic absorption spectrometer using a nitrous oxide-
acetylene burner.
The absorbance values obtained are compared with those obtained from the calibration solutions.
4 Reagents
During the analysis, use only reagents of recognized analytical grade.
4.1 Water, complying with grade 2 as defined in ISO 3696.
4.2 Sodium carbonate, (Na CO ), anhydrous powder.
2 3
4.3 Sodium tetraborate, (Na B O ), anhydrous powder.
2 4 7
4.4 Lithium tetraborate, (Li B O ), anhydrous powder.
2 4 7
4.5 Hydrochloric acid, ρ 1,16 g/ml to 1,19 g/ml.
4.6 Hydrochloric acid, ρ 1,16 g/ml to 1,19 g/ml, diluted 2 + 1.
4.7 Hydrochloric acid, ρ 1,16 g/ml to 1,19 g/ml, diluted 1 + 1.
4.8 Hydrochloric acid, ρ 1,16 g/ml to 1,19 g/ml, diluted 2 + 100.
4.9 Nitric acid, ρ 1,4 g/ml.
4.10 Nitric acid, ρ 1,4 g/ml, diluted 1 + 1.
4.11 Hydrofluoric acid, ρ 1,13 g/ml, 40 % (mass fraction) or ρ 1,19 g/ml, 48 % (mass fraction).
4.12 Sulfuric acid, ρ 1,84 g/ml.
4.13 Sulfuric acid, ρ 1,84 g/ml, diluted 1 + 1.
4.14 Methylpentan-2-one, (methyl isobutyl ketone, MIBK).
4.15 Chromium standard solution A, 100 µg Cr/ml.
Dissolve 0,100 0 g of chromium metal [purity >99,9 % (mass fraction) (see Note of 4.16)] in 20 ml of
hydrochloric acid (4.7). After cooling, transfer to a 1 000 ml one-mark volumetric flask quantitatively,
dilute to volume with water (4.1), and mix.
4.16 Chromium standard solution B, 10 µg Cr/ml.
Transfer 100,0 ml of chromium standard solution A (4.15) to a 1 000 ml one-mark volumetric flask.
Dilute to volume with water and mix.
NOTE The purity of the metals stated on the certificates does not generally take into account the presence of
adsorbed gases like oxygen, carbon monoxide, etc.
5 Apparatus
Ordinary laboratory apparatus including one-mark pipettes and one-mark volumetric flasks complying
with the specifications of ISO 648 and ISO 1042, and the following.
5.1 Platinum crucible, of minimum capacity 25 ml.
5.2 Muffle furnace.
5.3 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 burner is in operation.
2 © ISO 2015 – All rights reserved

The atomic absorption spectrometer used in this method shall meet the following criteria:
a) Minimum sensitivity — The absorbance of the most concentrated calibration solution (see 7.4.4) is
at least 0,3;
b) Graph linearity — The slope of the calibration graph covering the top 20 % of the concentration
range (expressed as a change in absorbance) is not 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 are less than 1,5 % and 0,5 %, respectively of the mean value of the
absorbance of the most concentrated 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 and they can be used as guidelines:
— hollow-cathode lamp        10 mA;
— wavelength                 357,9 nm;
— dinitrogen oxide flow rate   ≈10 l/min;
— acetylene flow rate          5 l/min.
A dinitrogen oxide-acetylene flame was used.
In systems where the values shown above for gas flow rates do not apply, the ratio of the gas flow rates
can still be a useful guideline.
6 Sampling and samples
6.1 Laboratory sample
For analysis, use a laboratory sample of particle size of less than 100 µm which has been taken and
prepared in accordance with ISO 3082. In the case of ores containing significant contents of combined
water or oxidizable compounds, use a particle size of less than 160 µm.
NOTE A guideline on significant contents of combined water and oxidizable compounds is incorporated in
ISO 7764.
Ensure that the sample has not been pulverized in a nickel/chromium pot.
6.2 Preparation of predried test samples
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. Dry the test sample at (105 ± 2) °C as
specified in ISO 7764 (this is the predried test sample).
7 Procedure
7.1 Number of determinations
Carry out the analysis at least in duplicate in accordance with Annex A, independently on one
predried test sample.
NOTE The expression “independently” means that the second and any subsequent result is not affected
by the previous result(s). For this particular analytical method, this condition implies that the repetition of the
procedure be carried out either by the same operator at a different time or by a different operator including, in
either case, appropriate recalibration.
7.2 Test portion
Taking several increments, weigh to the nearest 0,000 2 g, app
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