ISO 16742:2014

INTERNATIONAL ISO
STANDARD 16742
First edition
2014-03-01
Corrected version
2015-09-15
Iron ores — Sampling of slurries
Minerais de fer — Échantillonnage des schlamms
Reference number
©
ISO 2014
© ISO 2014, Published in Switzerland
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ii © ISO 2014 – All rights reserved

Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 General considerations for sampling slurries . 2
4.1 Basic requirements . 2
4.2 Sampling errors . 3
4.3 Establishing a sampling scheme . 4
5 Fundamentals of sampling and sample preparation . 6
5.1 Minimization of bias . 6
5.2 Volume of increment for falling stream samplers to avoid bias . 7
5.2.1 Linear cross-stream cutter . 7
5.2.2 Vezin cutter . 8
5.3 Volume of increment for manual sampling to avoid bias . 8
5.4 Overall precision . 9
5.5 Quality variation .10
5.6 Sampling precision and number of primary increments .11
5.7 Precision of sample preparation and overall precision .11
6 Minimum mass of solids in gross and partial samples .12
6.1 General .12
6.2 Minimum mass of solids in gross samples .12
6.3 Minimum mass of solids in partial samples .13
7 Time-basis sampling .13
7.1 General .13
7.2 Sampling interval .13
7.3 Cutters .13
7.4 Taking of increments .14
7.5 Constitution of gross or partial samples .14
7.6 Division of increments and partial samples .14
7.7 Division of gross samples.14
7.8 Number of cuts for division .14
8 Stratified random sampling within fixed time intervals.14
9 Mechanical sampling from moving streams .15
9.1 General .15
9.2 Design of the sampling system .15
9.2.1 Safety of operators .15
9.2.2 Location of sample cutters .15
9.2.3 Provision for duplicate sampling .15
9.2.4 System for checking the precision and bias.15
9.2.5 Minimizing bias .16
9.3 Slurry sample cutters .16
9.3.1 General.16
9.3.2 Falling-stream cutters .17
9.3.3 Cutter velocities .17
9.4 Mass of solids in increments .17
9.5 Number of primary increments .17
9.6 Routine checking .18
10 Manual sampling from moving streams .18
10.1 General .18
10.2 Choosing the sampling location .18
10.3 Sampling implements .18
10.4 Volume of increments .18
10.5 Number of primary increments .19
10.6 Sampling procedures .19
11 Sampling of stationary slurries .19
12 Sample preparation procedures .20
12.1 General .20
12.2 Grinding mills .20
12.3 Sample division.20
12.4 Chemical analysis samples . .20
12.5 Physical test samples .20
13 Packing and marking of samples .20
Annex A (informative) Examples of correct slurry sampling devices .22
Annex B (informative) Examples of incorrect slurry sampling devices .25
Annex C (normative) Manual sampling implements .28
Bibliography .29
iv © ISO 2014 – All rights reserved

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 meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 102, Iron ore and direct reduced iron,
Subcommittee SC 1, Sampling.
This corrected version of ISO 16742:2014 incorporates the following correction:
— In Table 3, third row, the values in the second column (“Up to”) have been correctly aligned with the
corresponding values in the first column (“Over”).
INTERNATIONAL STANDARD ISO 16742:2014(E)
Iron ores — Sampling of slurries
WARNING — This International Standard may involve hazardous materials, operations, and
equipment, and does not purport to address all the safety issues 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 sets out the basic methods for sampling fine iron ore of nominal top
size <1 mm that is mixed with water to form a slurry. At very high ratios of fine solids to water when
the material assumes a soft plastic form (about 80 % solids depending on the particle size distribution
of the solids), the mixture is correctly termed a paste. Sampling of pastes is not covered in this
International Standard.
The procedures described in this International Standard apply to sampling of iron ore that is
transported in moving streams as a slurry. These streams can fall freely or be confined in pipes,
launders, chutes, spirals, or similar channels. Sampling of slurries in pressurized pipes is not covered
in this International Standard. The slurry stream can only be sampled satisfactorily at a transfer point
prior to the pressurized pipe at the end of the pipe when the slurry is no longer under pressure. In
addition, sampling of slurries in stationary situations, such as a settled or even a well-stirred slurry in
a tank, holding vessel, or dam, is not recommended and is not covered in this International Standard.
This International Standard describes procedures that are designed to provide samples representative
of the slurry solids and particle size distribution of the slurry under examination. After filtration of the
slurry sample, damp samples of the contained solids in the slurry are available for drying (if required)
and measurement of one or more characteristics in an unbiased manner and with a known degree of
precision. The characteristics are measured by chemical analysis, physical testing, or both.
The sampling methods described are applicable to slurries that require inspection to verify compliance
with product specifications, determination of the value of a characteristic as a basis for settlement
between trading partners, or estimation of a set of average characteristics and variances that describe
a system or procedure.
Provided flow rates are not too high, the reference method against which other sampling procedures
are compared is one where the entire stream is diverted into a vessel for a specified time or volume
interval, ensuring that all parts of the stream are diverted into the vessel for the same period of time.
This International Standard corresponds to the stopped-belt method described in ISO 3082. Reference
increments have to be taken as close as possible to increments taken using the sampling procedure
under evaluation.
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 3082, Iron ores — Sampling and sample preparation procedures
ISO 3084, Iron ores — Experimental methods for evaluation of quality variation
ISO 3085, Iron ores — Experimental methods for checking the precision of sampling, sample preparation
and measurement
ISO 3087, Iron ores — Determination of the moisture content of a lot
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.
4 General considerations for sampling slurries
4.1 Basic requirements
In this International Standard, a slurry is defined as iron ore of nominal top size <1 mm that is mixed
with water, which is frequently used as a convenient form to transport iron ore by means of pumps and
pipelines and under gravity in launders or chutes or through long distances in slurry pipelines. Tailings
from wet plants are also discharged as a slurry through pipelines to tailings dams. In many of these
operations, collection of increments at selected sample points is required for evaluation of the iron ore
in the slurry.
A gross or partial sample is constituted from a set of unbiased primary increments from a lot. The
sample containers and their contained combined increments are weighed immediately after collection
to avoid water loss by evaporation or spillage. Weighing is necessary to determine the percentage
of solids mass fraction in the gross sample. The gross or partial sample may then be filtered, dried,
and weighed. Alternatively, the gross or partial sample can be sealed in plastic bags after filtering for
transport and drying at a later stage.
Test samples are prepared from gross or partial samples after filtering and drying, after breaking up
any lumps that have formed during drying using a lump breaker, or forcing the sample through a sieve
of appropriate aperture. Test portions may then be taken from the test sample and analysed using an
appropriate analytical method or test procedure under prescribed conditions.
The objective of the measurement chain is to determine the characteristic of interest in an unbiased
manner with an acceptable and affordable degree of precision. The general sampling theory, which is
based on the additive property of variances, can be used to determine how the variances of sampling,
sample preparation, and chemical analysis or physical testing propagate and hence determine the total
variance for the measurement chain. This sampling theory can also be used to optimize mechanical
sampling systems and manual sampling methods.
If a sampling scheme is to provide representative samples, all parts of the slurry in the lot must have
an equal opportunity of being selected and appearing in the gross sample for testing. Any deviation
from this basic requirement can result in an unacceptable loss of trueness. A sampling scheme having
incorrect selection techniques, i.e. with non-uniform selection probabilities, cannot be relied upon to
provide representative samples.
Sampling of slurries should preferably be carried out by systematic sampling on a time basis (see
Clause 7). If the slurry flow rate and the solids concentration vary with time, the slurry volume and
the dry solids mass for each increment will vary accordingly. It needs to be shown that no systematic
error (bias) is introduced by periodic variation in quality or quantity where the proposed sampling
interval is approximately equal to a multiple of the period of variation in quantity or quality. Otherwise,
stratified random sampling should be used (see Clause 8).
Best practice for sampling slurries is to mechanically cut free-falling streams (see Clause 9), with a
complete cross section of the stream being taken during the traverse of the cutter. Access to free-falling
streams can sometimes be engineered at the end of pipes or by incorporating steps or weirs in launders
and chutes. If samples are not collected in this manner, non-uniform concentration of solids in the slurry
due to segregation and stratification of the solids can lead to bias in the sample that is collected. Slurry
flow in pipes can be homogenous with very fine particles dispersed uniformly in turbulent suspension
along the length and across the diameter of the pipe. However, more commonly, the slurry in a pipe
will have significant particle concentration gradients across the pipe and there may be concentration
fluctuations along the length of the pipe. These common conditions are called heterogeneous flow.
2 © ISO 2014 – All rights reserved

Examples of such flow are full pipe flow of a heterogeneous suspension or partial pipe flow of a fine
suspension above a slower moving or even stationary bed of coarser particles in the slurry.
For heterogeneous flow, bias is likely to occur where a tapping is made into the slurry pipe to locate
either a flush fitting sample take-off pipe or a sample tube projecting into the slurry stream for
extraction of samples. The bias is caused by non-uniform concentration profiles in the pipe and the
different trajectories followed by particles of different masses due to their inertia, resulting in larger or
denser particles being preferentially rejected from or included in the sample.
In slurry channels such as launders, heterogeneous flow is almost always present, and this non-
uniformity in particle concentration is usually preserved in the discharge over a weir or step. However,
sampling at a weir or step allows complete access to the full width and breadth of the stream, thereby
enabling all parts of the slurry stream to be collected with equal probability.
Sampling of slurries in stationary situations, such as a settled or even a well-stirred slurry in a tank,
holding vessel, or dam is not recommended and is not covered in this International Standard, because it
is virtually impossible to ensure that all parts of the slurry in the lot have an equal opportunity of being
selected and appearing in the gross sample for testing. Instead, sampling should be carried out from
moving streams as the tank, vessel, or dam is filled or emptied.
4.2 Sampling errors
The processes of sampling, sample preparation, and measurement are experimental procedures, and
each procedure has its own uncertainty appearing as variations in the final results. When the average
of these variations is close to zero, they are called random errors. More serious variations contributing
to the uncertainty of results are systematic errors, which have averages biased away from zero. There
are also human errors that introduce variations due to departures from prescribed procedures for
which statistical analysis procedures are not applicable.
Sampling from moving slurry streams usually involves methods that fall into three broad operational
categories as follows:
a) taking the whole stream part of the time with a cross-stream cutter as shown in Figure 1a) (based
on Reference [4]), usually when the slurry falls from a pipe or over a weir or step. Cuts 1 and 2
show correct sampling with the cutter diverting all parts of the stream for the same length of time.
Cuts 3, 4, and 5 show incorrect sampling where the cutter diverts different parts of the stream for
different lengths of time;
b) taking part of the stream all of the time as shown in Figure 1b) (based on Reference [4]) with an in-
stream point sampler or probe within a pipe or channel, which is always incorrect;
c) taking part of the stream part of the time as shown in Figure 1c) (based on Reference [4]), also with
an in-stream point sampler or probe within a pipe or channel, which is always incorrect.
12 34 5
a) Taking all of the stream part of the time
b) Taking part of the stream all of the time (always incorrect)
c) Taking part of the stream part of the time (always incorrect)
Key
1 correct
2 correct
3 incorrect
4 incorrect
5 incorrect
Figure 1 — Plan view of slurry volumes diverted by sample cutters
4.3 Establishing a sampling scheme
Most sampling operations are routine and are carried out to determine the average quality
characteristics of a lot as well as variations in quality characteristics between lots for monitoring
and controlling quality. In establishing a sampling scheme for routine sampling so that the required
precision for a lot can be obtained, it is necessary to carry out the following sequence of steps. This
sequence includes experimental procedures that are non-routine and carried out infrequently, e.g.
determining quality variation in step (d), particularly when a significant change has occurred to the
slurry source or to the sampling equipment. The procedure is as follows.
a) Define the purpose for which the samples are being taken. Sampling for commercial transactions is
usually the main purpose of sampling standards. However, the procedures described in this standard
are equally applicable to monitoring plant performance, process control and metallurgical accounting.
b) Define the lot by specifying the duration of slurry flow, e.g. one day of operation.
c) Identify the quality characteristics to be measured and specify the overall precision (combined
precision of sampling, sample preparation, and measurement) required for each quality
characteristic. If the required precision results in impractical numbers of increments and/or
partial samples, it can be necessary to adopt a poorer precision.
d) Determine the quality variation of the contained solids in the slurry and the precision of preparation
and measurement for the quality characteristics under consideration (see 5.5).
e) Determine the number of increments required to attain the desired precision (see 5.6).
f) Ascertain the apparent density of the solids in the slurry and the percentage solids mass fraction in
the slurry for determining the mass of the solids in each slurry increment (see 5.2).
4 © ISO 2014 – All rights reserved

g) Check that the procedures and equipment for taking slurry increments minimize bias (see 5.1).
h) Determine the sampling interval in minutes for time-basis systematic sampling (see Clause 7) or
stratified random sampling within fixed time intervals (see Clause 8).
i) Take slurry increments at the intervals determined in step (h) during the whole period of
handling the lot.
During sampling operations, partial samples can be combined to constitute a single gross sample for
analysis (see Figure 2). Alternatively, increments can be used to constitute partial samples for analysis,
which will also improve the overall precision of the measured quality characteristics of the lot. Other
reasons for separate preparation and analysis of partial samples are
— for convenience of materials handling,
— to provide progressive information on the quality of the lot, or
— to provide reference or reserve samples after division.
Each increment may also be analysed separately to determine the increment variance of quality
characteristics of the lot. In addition, assuming there is no correlation between adjacent increments,
it is recommended that the precision achieved in practice should be checked on an ongoing basis by
duplicate sampling where alternate increments are diverted to partial or gross samples A and B from
which two test samples are prepared and analysed. A substantial number of sample pairs is required
(preferably at least 20) to obtain a reliable estimate of precision (see ISO 3085).
In most situations, the solids in the slurry increment will not need to be crushed or pulverized to allow
further division, since most slurries contain only fine particles. However, if the particles are coarse
and particle size reduction is required to allow further division, it is necessary to re-determine the
minimum sample mass for the lot using the new nominal top size of the crushed solids (see 6.2).
The initial design of a sampling scheme for a new plant or a slurry with unfamiliar characteristics
should, wherever possible, be based on experience with similar handling plants and material types.
Alternatively, a substantial number of increments, e.g. 100, can be taken and used to determine the
quality variation of the contained solids, but the precision of sampling cannot be determined a priori.
Increment
Increment
First partial sample
Increment
Increment
Increment
Increment
Increment
Second partial sample
Increment
Lot Increment Gross sample
Increment
Increment
Increment
Last partial sample
Increment
Increment
Increment
Figure 2 — Example of a sampling plan where a single gross sample is constituted for analysis
5 Fundamentals of sampling and sample preparation
5.1 Minimization of bias
Minimization of bias in sampling and sample preparation is vitally important. Unlike precision, which
can be improved by collecting more slurry increments, preparing more test samples, or assaying more
test portions, bias cannot be reduced by replication. Consequently, sources of bias should be minimized
or eliminated at the outset by correct design of the sampling and sample preparation system. The
minimization or elimination of possible bias should be regarded as more important than improvement
of precision. Sources of bias that can be eliminated include sample spillage, sample contamination, and
incorrect extraction of increments, while a bias source that cannot be fully eliminated is that arising
from variable settling rates of particles with different size and apparent density during sample division
prior to filtration.
The guiding principle to be followed is that increments are extracted from the lot in such a manner that
all parts of the slurry have an equal opportunity of being selected and becoming part of the test sample
which is used for chemical or physical testing, irrespective of the size, mass, shape, or apparent density
of individual particles in the slurry. In practice, this means that a complete cross-section of the slurry
must be taken when sampling from a moving stream, otherwise bias is easily introduced.
6 © ISO 2014 – All rights reserved

The requirement of equal selection probabilities shall be borne in mind when designing a sampling
system and the practical rules that follow from this principle are as follows.
a) A complete cross-section of the slurry stream shall be taken when sampling from a moving stream.
b) There shall be no loss or spillage of the slurry sample.
c) The cutter aperture shall be at least three times the nominal top size of the particles in the slurry,
subject to a minimum of 10 mm.
d) The cutter slot length shall be substantially longer than the maximum depth of the falling slurry
stream relative to the direction of cut to intercept the full stream.
e) The cutter lips on straight path cutters shall be parallel, while the cutter lips of rotary cutters shall
be radial from the axis of rotation, and these conditions shall be maintained as the cutter lips wear.
f) The sample cutter shall travel through the slurry stream at uniform speed, not deviating by more
than ± 5 % at any point.
g) The angle of cutter chutes, sample chutes, and sample pipes shall be a minimum of 70° to the
horizontal.
The minimum cutter aperture and maximum cutter speed required to obtain an unbiased sample leads
to the smallest acceptable increment volume and associated mass of contained solids consistent with
these limiting specifications (see 5.2). However, in some circumstances, using this minimum mass
of solids can result in an unacceptably large number of increments to obtain the desired sampling
variance. In such cases, the volume of the slurry increment and hence the mass of contained solids shall
be increased above the smallest acceptable value.
Cutters shall be designed to accommodate the maximum size of the particles in the slurry and the
maximum slurry flow rate, from which the maximum volume and mass of solids in the increment can be
determined for equipment design purposes. The choice between mechanical and manual sampling shall
be based on the maximum possible increment volume and the consequential safety considerations.
Once a cutter has been installed, there should be regular checks on the average increment mass, which
should be compared with the mass predicted from the cutter aperture, cutter speed, and slurry flow
rate for falling-stream cutters (see 5.2). If the average mass of solids in the increment is too small
compared with the predicted mass of solids for the observed slurry flow rate, it is likely that the cutter
aperture is partially blocked and the sampling system should be investigated.
5.2 Volume of increment for falling stream samplers to avoid bias
5.2.1 Linear cross-stream cutter
At any sampling stage, the volume of each slurry increment taken by a linear cross-stream cutter can be
calculated as follows:
ql
G = (1)
l
v
c
where
G is the volume of increment, in cubic metres;
l
q is the slurry flow rate, in cubic metres per second;
l is the cutting aperture of the sampler, in metres;
v is the cutter speed, in metres per second.
c
However, there are strict limits on the minimum cutter aperture and the maximum cutter speed to ensure
the cutter takes an unbiased sample (see 9.3.2 and 9.3.3). These limits in turn impose a lower limit on the
volume of increment calculated using Formula (1) that needs to be collected to minimize bias.
From the volume of increment calculated using Formula (1), the mass of solids contained in the slurry
increment can then be calculated using Formula (2):
Gxρ
l s
m = (2)
l
where
m is the mass of solids contained in the increment, in kilograms;
l
ρ is the slurry density, in kilograms per cubic metre;
S
x is the percentage solids mass fraction in the slurry.
5.2.2 Vezin cutter
At any sampling stage, the volume of each slurry increment taken by a Vezin cutter can be calculated as
follows:
qθ
G = (3)
l
6R
where
G is the volume of increment, in cubic metres;
l
q is the slurry flow rate, in cubic metres per second;
θ is the cutter aperture opening, in degrees;
R is the rotating speed of the cutter, in revolutions per minute.
Once again, there are strict limits on the minimum cutter aperture and the maximum cutter speed to
ensure the cutter takes an unbiased sample (see 9.3.2 and 9.3.3). These limits, in turn, impose a lower
limit on the volume of increment calculated using Formula (3) that needs to be collected to minimize bias.
From the volume of increment calculated using Formula (3), the mass of solids contained in the slurry
increment can then be calculated using Formula (2).
5.3 Volume of increment for manual sampling to avoid bias
Under favourable conditions (for example, small and accessible slurry flows), manual cross-stream cuts
through free-falling streams can be used to extract increments without bias provided:
a) The full stream is cut in one action;
b) The sampling implement is moved through the stream by the operator as near as possible to
constant speed, which should not exceed the maximum speed limitation on mechanical cutters;
c) The minimum cutter aperture of the sampling implement satisfies the same width limit as for
mechanical cutters;
d) The combined weight of the sampling implement and the increment at the completion of the cut
takes into account occupational health and safety guidelines;
e) The dimensions of the sampling implement match the slurry flow rate and cutting speed to prevent
slurry reflux and overflow.
8 © ISO 2014 – All rights reserved

5.4 Overall precision
This International Standard is designed to attain the overall precision, β , at a probability level of
SPM
95 %, given in Table 1 for the total iron, silica, aluminia, phosphorus contents and the percent size
fraction of the lot. The precision shall be determined in accordance with ISO 3085.
Table 1 — Overall precision, β
SPM
Approximate overall precision, β
SPM
mass fraction, %
Mass of solids in the lot
Quality characteristics t
Over 70 000 45 000 30 000 15 000 Less than
100 000 to to to to 15 000
100 000 70 000 45 000 30 000
Iron content 0,38 0,40 0,42 0,45 0,49 0,55
Silica content 0,38 0,40 0,42 0,45 0,49 0,55
Aluminia content 0,13 0,14 0,15 0,16 0,18 0,20
Phosphorus content 0,003 7 0,003 8 0,004 0 0,004 2 0,004 5 0,004 8
Size – Pellet feed −45 μm fraction, mean 70 % 1,85 1,95 2,0 2,1 2,2 2,5
NOTE The values of β for iron, silica, aluminia, and phosphorus content, as well as sizing, are indicative and subject to
SPM
confirmation through international test work.
NOTE The overall precision for other physical characteristics and metallurgical properties is not specified
in this International Standard, because they are used to qualitatively compare the behaviour of iron ore slurries
during handling and reduction processes.
The overall precision, β , is a measure of the combined precision of sampling, sample preparation, and
SPM
measurement, and is twice the standard deviation of sampling, sample preparation, and measurement,
σ , expressed as an absolute percentage, i.e.
SPM
2 2 2
σ =+σσσ+ (4)
SPMS P M
βσ==22 σσσ++ (5)
SPMSPM SP M
σ
W
σ = (6)
S
n
where
σ is the sampling standard deviation;
S
σ is the sample preparation standard deviation;
P
σ is the measurement standard deviation;
M
σ is the quality variation of the slurry;
W
n is the number of primary increments.
Formulae (4), (5), and (6) are based on the theory of stratified sampling. The number of primary
increments to be taken for a lot is dependent on the sampling precision required and on the quality
variation of the slurry to be sampled. Thus, before the number of primary increments can be determined,
it is necessary to define:
a) the sampling precision, β , to be attained;
S
b) the quality variation, σ , of the slurry to be sampled.
W
When online sample preparation takes place within the sample plant away from the preparation
laboratory, the distinction between the terms sampling and sample preparation becomes unclear. The
precision of online sample preparation can be included in either the sampling precision or in the sample
preparation precision. The choice depends on how easy it is to separate the precision of secondary and
tertiary sampling from that of primary sampling. In any event, sample preparation also constitutes a
sampling operation, because a representative part of the sample is selected for subsequent processing.
The most rigorous approach is to break up the sampling standard deviation into its components for
each sampling stage, in which case Formula (4) becomes:
2 222 2
σσ= +++σσσ +σ (7)
SPMS1S2S3P M
where
σ is the sampling standard deviation for primary sampling;
S1
σ is the sampling standard deviation for secondary sampling;
S2
σ is the sampling standard deviation for tertiary sampling.
S3
Using this approach, the precision of each sampling stage can be separately determined and optimized,
resulting in a fully optimized sampling and sample preparation regime.
5.5 Quality variation
The quality variation, σ , is a measure of the heterogeneity of the lot and is the standard deviation of the
W
quality characteristics of increments within strata. The characteristics to be selected for determining
quality variation include the iron, silica, aluminia, and phosphorus contents and the percentage of a
given size fraction.
The value of σ shall be measured experimentally for each type or brand of iron ore slurry and for each
W
handling plant under normal operating conditions in accordance with ISO 3084 which assumes there is
no serial correlation between adjacent increments. The quality variation of the iron ore slurry can then
be classified into three categories according to its magnitude as specified in Table 2.
Table 2 — Classification of quality variation, σ
W
Classification of quality variation, σ
W
mass fraction, %
Quality characteristics
Large Medium Small
Iron content σ ≥ 2,0 2,0 > σ ≥ 1,5 σ < 1,5
W W W
Silica content σ ≥ 2,0 2,0 > σ ≥ 1,5 σ < 1,5
W W W
Aluminia content σ ≥ 0,6 0,6 > σ ≥ 0,4 σ < 0,4
W W W
Phosphorus content σ ≥ 0,015 0,015 > σ ≥ 0,011 σ < 0,011
W W W
Size of pellet feed −45 μm fraction mean σ ≥ 3 3 > σ ≥ 2,25 σ < 2,25
W W W
70 %
For iron ore slurries whose quality variation is unknown, measurements shall be conducted at the
earliest opportunity in accordance with ISO 3084 to determine the quality variation. Prior to the
determination of quality variation, the classification adopted shall be as follows:
a) when no prior information exists on the quality variation of the slurry or similar slurries, the slurry
shall be considered to have “large” quality variation;
b) when prior information exists on the quality variation of a similar slurry, the quality variation
classification of that slurry shall be adopted as the starting point.
10 © ISO 2014 – All rights reserved

When separate samples are taken for the determination of chemical composition, moisture content
and size distribution, the quality variation for the individual characteristics sh
...