ISO 11535:2006

Iron ores — Determination of various elements — Inductively coupled plasma atomic emission spectrometric method

ISO 11535: 2006 specifies a method for the determination of aluminium, calcium, phosphorus, magnesium, manganese, silicon and titanium in iron ores by inductively coupled plasma atomic emission spectrometry.

Minerais de fer — Dosage de divers éléments — Méthode par spectrométrie d'émission atomique avec plasma induit par haute fréquence

General Information

• Status: Published
• Publication Date: 03-Dec-2006
• ICS: 73.060.10 - Iron ores
• Technical Committee: ISO/TC 102/SC 2 - Chemical analysis
• Drafting Committee: ISO/TC 102/SC 2 - Chemical analysis
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 24-Jun-2022

Relations

• Revises: ISO 11535:1998 - Iron ores — Determination of various elements — Inductively coupled plasma atomic emission spectrometric method
• Effective Date: 15-Apr-2008

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 11535
Second edition
2006-12-15

Iron ores — Determination of various
elements — Inductively coupled plasma
atomic emission spectrometric method
Minerais de fer — Dosage de divers éléments — Méthode par
spectrométrie d'émission atomique avec plasma induit par haute
fréquence




Reference number
ISO 11535:2006(E)
©
ISO 2006

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ISO 11535:2006(E)
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ISO 11535:2006(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 1
3 Principle. 2
4 Reagents. 2
5 Apparatus . 4
6 Sampling and samples. 4
6.1 Laboratory sample. 4
6.2 Preparation of predried test samples . 5
7 Procedure . 5
7.1 Number of determinations . 5
7.2 Test portion . 5
7.3 Blank test and check test. 5
7.4 Determination. 5
7.4.1 Decomposition of the test portion . 5
7.4.2 Adjustment of spectrometer. 6
7.4.3 Measurements. 7
8 Calculation of results . 7
8.1 Calibration graph . 7
8.2 Correction of spectral interference. 7
8.3 Standardization of calibration graph (drift correction). 9
8.4 General treatment of results. 10
8.4.1 Repeatability and permissible tolerances.10
8.4.2 Determination of analytical result. 10
8.4.3 Check for trueness . 11
8.4.4 Calculation of final result. 11
8.5 Oxide factors . 12
9 Test report . 12
Annex A (informative) Suggested calibration solutions . 13
Annex B (normative) Plasma-spectrometer performance tests. 15
Annex C (normative) Flowsheet of the procedure for the acceptance of analytical values for test
samples. 18
Annex D (informative) Derivation of repeatability and permissible tolerance equations . 19
Annex E (informative) Precision data obtained by international analytical trials. 20

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ISO 11535:2006(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 11535 was prepared by Technical Committee ISO/TC 102, Iron ore and direct reduced iron,
Subcommittee SC 2, Chemical analysis.
This second edition cancels and replaces the first edition (ISO 11535:1998), which has been technically
revised. It has been updated to alter the manner in which the precision data are presented.

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INTERNATIONAL STANDARD ISO 11535:2006(E)

Iron ores — Determination of various elements — Inductively
coupled plasma atomic emission 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 method for the determination of aluminium, calcium, phosphorus,
magnesium, manganese, silicon and titanium in iron ores by inductively coupled plasma atomic emission
spectrometry (ICP-AES).
This method is applicable to the mass-fraction ranges given in Table 1, in natural iron ores, iron ore concentrates
and agglomerates, including sinter products.
Table 1 — Mass-fraction ranges
Element Range of mass fractions
%
Al 0,07 to 3,30
Ca 0,012 to 6,80
Mg 0,008 to 1,90
Mn 0,012 to 1,70
P 0,011 to 1,60
Si 0,44 to 9,40
Ti 0,018 to 0,17
2 Normative references
The following referenced documents are indispensable for the application 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 — One-mark 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
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ISO 11535:2006(E)
3 Principle
The test portion is decomposed by fusion in a sodium carbonate/sodium tetraborate flux and the cooled melt
is dissolved in hydrochloric acid.
The solution is diluted to volume and measured on an ICP spectrometer. Final results are read from a
calibration graph prepared using standard solutions.
4 Reagents
During the analysis, use only reagents of recognized analytical grade and only water that complies with
grade 2 of ISO 3696.
4.1 Iron oxide (Fe O ), of minimum purity 99,99 % (mass fraction).
2 3
4.2 Sodium carbonate (Na CO ), anhydrous.
2 3
To produce final impurity levels in a solution below the detection limits determined or suggested in the
performance test, a high-quality grade is required.
4.3 Sodium tetraborate (Na B O ), anhydrous.
2 4 7
The same purity criteria as for the sodium carbonate are required.
4.4 Hydrochloric acid, ρ 1,16 g/ml to 1,19 g/ml.
The same purity criteria as for the sodium carbonate are required.
4.5 Hydrochloric acid, ρ 1,16 g/ml to 1,19 g/ml, diluted 1 + 1.
Add 500 ml of hydrochloric acid (4.4) to 500 ml of water and mix.
4.6 Nitric acid, ρ 1,4 g/ml.
The same purity criteria as for the sodium carbonate are required.
4.7 Stock solutions.
4.7.1 Phosphorus, 1 000 µg/ml.
Dry approximately 10 g of potassium dihydrogen orthophosphate (KH PO ) at 110 °C until a constant mass is
2 4
reached, and cool in a desiccator. Dissolve 4,393 6 g in about 200 ml of water in a 1 000 ml one-mark
volumetric flask. When the dissolution is complete, dilute to volume with water and mix.
4.7.2 Manganese, 1 000 µg/ml.
Dissolve 1,000 0 g of high-purity manganese metal in 20 ml of hydrochloric acid (4.5) in a covered tall-form
beaker while heating. When dissolution is complete, cool, transfer to a 1 000 ml one-mark volumetric flask,
dilute to volume with water and mix.
4.7.3 Magnesium, 1 000 µg/ml.
Dissolve 1,000 0 g of high-purity magnesium metal in 20 ml of hydrochloric acid (4.5) in a covered tall-form
beaker while heating. When dissolution is complete, cool, transfer to a 1 000 ml one-mark volumetric flask,
dilute to volume with water and mix.
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ISO 11535:2006(E)
4.7.4 Silicon, 1 000 µg/ml.
Accurately weigh 2,139 3 g of pure silicon oxide (finely ground, previously heated at 1 000 °C for 45 min) into
a platinum crucible (5.2). Mix with 5 g of sodium carbonate (4.2), and melt in a furnace at 1 000 °C for 15 min.
Dissolve the melt in 100 ml of warm water and transfer to a 1 000 ml one-mark volumetric flask; increase the
volume to approximately 500 ml with water, add 20 ml of hydrochloric acid (4.5), dilute to volume with water
and mix. Store in a polyethylene flask.
4.7.5 Aluminium, 1 000 µg/ml.
Dissolve 1,000 0 g of high-purity aluminium metal in 20 ml of hydrochloric acid (4.5) in a covered tall-form
beaker. Add about 4 drops of nitric acid (4.6). When dissolution is complete, add about 20 ml of water and heat
to liberate oxides of nitrogen. Cool and transfer to a 1 000 ml one-mark volumetric flask, dilute to volume with
water and mix.
4.7.6 Titanium, 1 000 µg/ml.
Dissolve 1,000 0 g of high-purity titanium metal in 100 ml of hydrochloric acid (4.5) in a covered tall-form
beaker while heating. When dissolution is complete, cool, transfer to a 1 000 ml one-mark volumetric flask,
dilute to volume with hydrochloric acid (4.5) and mix.
4.7.7 Calcium, 1 000 µg/ml.
Dry approximately 10 g of calcium carbonate (CaCO ) at 110 °C until a constant mass is reached, and cool in
3
a desiccator. Dissolve 2,497 2 g in 20 ml of hydrochloric acid (4.5) in a covered tall-form beaker while heating.
When dissolution is complete, cool, transfer to a 1 000 ml one-mark volumetric flask, dilute to volume with
water and mix.
4.8 Calibration and reference solutions
Calibration solutions are defined as the solutions required for plotting the calibration graphs of the elements
analysed. Their concentration ranges in solution, expressed in micrograms per millilitre, are determined with
reference to the performance parameter values and the linearity response of the instrument. A minimum of
10 solutions is necessary to cover the mass-fraction ranges given in Table 1. For test samples having
narrower concentration ranges, calibration solutions shall be prepared to cover the region of interest. If the
element concentration in solution exceeds 5 000 × detection limit (DL), a separate calibration graph shall be
prepared to cover the range.
In the case of non-linearity, either a less sensitive line is to be used or appropriate dilutions of sample and
calibration solutions are to be carried out.
NOTE For the suggested lines shown in Table 2, the calibration solutions prepared as recommended in Annex A will
be in agreement with the performance test figures.
To comply with the requirements of similarity between the test sample and the calibration solutions, iron, flux
and acids must be added (see Note 1 to Table A.1). For each calibration solution, the procedure
recommended in 7.4.1 is followed, replacing the test sample with the equivalent amount of iron oxide (4.1).
Prior to the final dilution to 200 ml, the stock solutions and hydrochloric acid (4.5) are added in sufficient
amounts to retain the final acid concentration (40 ml of HCl diluted 1+1) suggested in Annex A.
In addition, to comply with the requirements of similarity, calibration solutions and test samples are prepared
from reagents taken from the same containers to minimize purity differences between batches.
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ISO 11535:2006(E)
5 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.
5.1 Analytical balance, capable of weighing to the nearest 0,000 1 g.
5.2 Platinum or suitable platinum-alloy crucibles, having a minimum volume of 40 ml.
5.3 Bunsen burner, having an appropriate fuel/oxidant ratio to provide a minimum temperature of 500 °C.
5.4 Muffle furnace, to provide a minimum temperature of 1 020 °C.
5.5 Combined hotplate/magnetic stirrer.
5.6 Stirring bars, PTFE-coated, 10 mm long.
5.7 ICP spectrometer.
Any conventional ICP spectrometer may be used, provided that the instrument has been initially set up
according to the manufacturer's recommendations, and that it complies with the performance test (7.4.2.2)
carried out prior to the measurements.
Suggested analytical lines are shown in Table 2. These lines were found to be relatively free of significant
interferences from the matrix elements, but they shall be carefully evaluated for spectral interference,
background and ionization prior to their adoption. Failure to attain the recommended performance parameters
may indicate an interference.
For the analysis of samples having concentrations in the background equivalent concentration (BEC) region or
lower, as defined in Table 3, careful assessment of the need for background correction for the particular line
chosen is recommended prior to calibration and analysis
Table 2 — Suggested analytical lines
Element Wavelength
nm
Al 396,15 or 308,22
Ca 393,36 or 317,93
Mg 279,55 or 279,08
Mn 257,61
a
P 178,29
Si 251,61 or 288,16
Ti 334,94 or 336,12
a
Check and correct, if necessary, for interference by Mn.
6 Sampling and samples
6.1 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.
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ISO 11535:2006(E)
6.2 Preparation of predried test samples
Thoroughly mix the laboratory sample and, taking multiple increments, extract a test sample in such a manner
that it is representative of the whole contents of the container. Dry the test sample at 105 °C ± 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 C, 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 the particular analytical method, this condition implies that the repetition of the procedure is carried
out either by the same operator at a different time, or by a different operator, including appropriate recalibration in either
case.
7.2 Test portion
Taking several increments, weigh, to the nearest 0,000 2 g, approximately 0,5 g of the predried test sample
obtained in accordance with 6.2.
The test portion should be taken and weighed quickly to avoid re-adsorption of moisture.
7.3 Blank test and check test
In each run, one blank test and one analysis of a certified reference material of the same type of ore shall be
carried out in parallel with the analysis of the ore sample(s) under the same conditions. A predried test sample
of the certified reference material shall be prepared as specified in 6.2.
For the blank test, the equivalent amount of pure iron oxide (4.1) shall be used in place of the test sample.
The certified reference material should be of the same type as the sample to be analysed, and the properties
of the two materials should be sufficiently similar to ensure that in either case no significant changes in the
analytical procedure become necessary. Where a certified reference material is not available, a reference
material may be used (see 8.4.3).
Where the analysis is carried out on several samples at the same time, the blank value may be represented
by one test, provided that the procedure is the same and the reagents used are from the same reagent bottles.
Where the analysis is carried out on several samples of the same type of ore at the same time, the analytical
value of one certified reference material may be used.
7.4 Determination
7.4.1 Decomposition of the test portion
Add 0,80 g of sodium carbonate (4.2) to a platinum or suitable platinum-alloy crucible (5.2), transfer the test
portion (7.2) to the crucible and mix well using a platinum or stainless-steel rod. Add 0,40 g of sodium
tetraborate (4.3) and repeat the mixing using the metal rod. Pre-fuse the mixture to homogenize it.
The pre-fusion step may be carried out using a bunsen burner having a metallic holder to provide manual
agitation. The crucible temperature at this stage should reach the range 350 °C to 450 °C (slightly dull red
heat). The mixture melts within 2 min to 3 min without effervescence, and is completely fluid and ready for
high-temperature fusion within 5 min.
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ISO 11535:2006(E)
After the pre-fusion, place the crucible in a muffle furnace (5.4) set at 1 020 °C for 15 min. Remove the
crucible and gently swirl the melt as it solidifies. Allow to cool, then place a PTFE-coated stirring bar in the
crucible and place the crucible in a 250 ml low-form beaker. Add 40 ml of hydrochloric acid (4.5) directly to the
crucible, and 30 ml of water to the beaker. Cover and heat while stirring on a magnetic stirrer/hotplate (5.5)
until dissolution of the melt is complete.
The temperature of the recovery solution should be kept at approximately 70 °C.
NOTE 1 Continuous manual swirling is acceptable as an alternative to magnetic stirring.
Remove and rinse the crucible and stirrer, collecting the washings in the beaker. Cool the solution and
immediately transfer it to a 200 ml one-mark volumetric flask. Dilute to volume with water and mix. (This is the
test solution.)
NOTE 2 The immediate transfer of the recovered solution to the 200 ml volumetric flask, and the making up to volume,
prevent re-precipitation.
NOTE 3 The recommended dilution to 200 ml provides element concentrations in the solution compatible with the
performance test figures given in Table 3. Higher dilution rates may be required to cope with instrument linear response at
the high concentration ranges. In such situations, the calibration solutions are diluted in the same proportions.
NOTE 4 The use of an internal standard, such as yttrium or scandium, for improvement of the performance figures is
not acceptable, and is not necessary if the instrument complies with the performance test figures.
7.4.2 Adjustment of spectrometer
7.4.2.1 General
The ICP spectrometer shall be initially adjusted according to the manufacturer's recommendations and
laboratory practice for quantitative analysis.
7.4.2.2 Performance test
The performance test is devised with the purpose of evaluating the ICP performance parameters, to enable all
types of spectrometers to perform in equivalent conditions, allowing direct comparison of the data generated.
The test is based on the determination of the following three parameters:
⎯ detection limit (DL);
⎯ background equivalent concentration (BEC):
⎯ short-term precision (RSDN ).
min
The definitions of these terms and the procedure for their evaluation are given in Annex B.
The procedure shall be carried out as many times as necessary, with the optimization of the instrument
parameters after each round, until the figures obtained are lower than those given in Table 3. For elements
present in the sample solutions at concentrations higher than 5 000 × DL, the RSDN is the only performance
parameter to be assessed, and the target values are lower than those given in Table 3 for RSDN .
min
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ISO 11535:2006(E)
Table 3 — Recommended performance parameters
Element DL BEC RSDN
min
µg/ml µg/ml
%
Al 0,04 2,46 0,87
Ca 0,02 1,04 1,04
Mg 0,03 0,38 0,75
Mn 0,01 0,29 0,89
P 0,07 2,15 1,04
Si 0,07 2,67 0,95
Ti 0,01 0,24 0,78
7.4.3 Measurements
7.4.3.1 Calibration solutions
Aspirate the calibration solutions in order of increasing concentration, starting with the zero calibration solution.
Aspirate water between each solution and repeat the measurements at least twice. Take the average of the
two readings.
NOTE After initial calibration has been established, a two-point recalibration procedure can be used for routine
analysis. In this case, proceed according to 8.3.
7.4.3.2 Test solutions
Immediately after aspiration of the calibration solutions, start running the first test solution, followed by the
certified reference material (CRM). Continue aspirating test solutions and CRMs alternately. Aspirate water
between each measurement. This procedure should preferably be repeated at least twice.
8 Calculation of results
8.1 Calibration graph
Prepare a calibration graph by plotting the intensity values obtained from the calibration solution against its
equivalent element concentration.
Read the intensity values for the test solution and obtain their respective concentration values from calibration
graphs.
If spectral interferences are found to exist, corrections have to be carried out in accordance with 8.2.
Calibration graphs are preferably obtained using statistical procedures (e.g. least squares).
Computer-assisted spectrometers usually incorporate such a facility. Correlation coefficients and Root Mean
Square (RMS) values obtained should be within the laboratory acceptance criteria.
NOTE Calibration-graph drift-correction procedures may be used, provided that they are carried out in accordance
with 8.3 immediately before analysis of the test solutions.
8.2 Correction of spectral interference
A correction method for spectral interferences by using synthetic standard solution is recommended. The
procedure is described below.
Plot a calibration graph by using binary (iron plus flux and an analyte) synthetic solution series for the analyte
interfered element (named “i”). Suggested calibration solutions (Annex A) may be used as long as they are
prepared as independent sets of binaries.
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ISO 11535:2006(E)
Using the calibration graph for the analyte, determine the apparent content of possible interfering element
(named “j”) for the analyte (named “i”) by measuring the intensity of binary (iron plus flux and interfering
element named “j”) synthetic solution series.
The relationship between the actual content of interfering element (x ) and the apparent content of interfering
j
element (x ) is calculated by the least-squares method.
ij
xl=⋅x+b (1)
ij ij j
where
l is the coefficient of spectral interference of element (j) for analyte (i) under examination;
ij
b is a constant (negligibly small).
The l values are determined for all kinds of interfering elements for the analyte (i).
ij
Being corrected by the interference factor, the actual mass fraction (content) of the analyte is calculated as
follows:
⎯ each mass fraction of element, expressed as a percentage, is given by the following equation:
() −⋅V
ρρ 100
10
 =×  − ∑ (2)
xwl
ijij
6
m
10
⎯ or for V = 200 ml,
() −⋅200 (−)
ρρ ρ ρ
100
10 1 0
=× −∑ l l= −∑ (3)
xw w
ij ij j ij
6
mm50
10
where
x is the mass fraction of element (analyte), expressed as a percentage;
i
m is the mass, in grams, of the test portion;
ρ is the concentration, expressed in micrograms per millilitre, of the analyte in the test portion;
1
ρ is the concentration, expressed in micrograms per millilitre, of the analyte in the blank test;
0
w is the percentage by mass of the interfering element in the test portion;
j
l is the coefficient of spectral interference of element (j) for analyte (i) under examination, expressed
ij
as a percentage by mass, corresponding to 1 % of the interfering element;
V is the final volume of calibration and test solutions (200 ml as recommended in 4.8 and 7.4).
Over-correction of spectral interference is not acceptable. The allowable maximum value for correction is
about ten times the repeatability of analyte content under examination. If the correction value is greater than
this, the correction for ICP analysis should not be applied.
NOTE 1 If there is no interfering element, the term w containing the percentage of interfering element in Equation (2) is
j
equal to zero.
NOTE 2 For the suggested final calibration solution volume V = 200 ml and with no interfering element present,
Equation (2) reduces to:
ρρ −
10
 =
x
i
50 m
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ISO 11535:2006(E)
8.3 Standardization of calibration graph (drift correction)
Periodical checking and correction of the calibration graph, if used, shall be carried out as follows.
Take the two calibration solutions that correspond to the lowest and highest analyte content.
At the stage of plotting the calibration gr
...