Iron ores — Sampling of slurries

ISO 16742:2014 sets out the basic methods for sampling fine iron ore of nominal top size The procedures described in ISO 16742:2014 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.

Minerais de fer — Échantillonnage des schlamms

General Information

Status
Published
Publication Date
02-Mar-2014
Technical Committee
Drafting Committee
Current Stage
9093 - International Standard confirmed
Completion Date
08-Jul-2019
Ref Project

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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 16742:2014(E)
©
ISO 2014

---------------------- Page: 1 ----------------------
ISO 16742:2014(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2014, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
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Tel. +41 22 749 01 11
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copyright@iso.org
www.iso.org
ii © ISO 2014 – All rights reserved

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ISO 16742:2014(E)

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
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ISO 16742:2014(E)

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

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ISO 16742:2014(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 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”).
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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
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ISO 16742:2014(E)

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

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ISO 16742:2014(E)

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
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ISO 16742:2014(E)

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).
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ISO 16742:2014(E)

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 over
...

DRAFT INTERNATIONAL STANDARD ISO/DIS 16742
ISO/TC 102/SC 1 Secretariat: JISC
Voting begins on Voting terminates on

2013-04-05 2013-07-05
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION  •  МЕЖДУНАРОДНАЯ ОРГАНИЗАЦИЯ ПО СТАНДАРТИЗАЦИИ  •  ORGANISATION INTERNATIONALE DE NORMALISATION


Iron ores — Sampling of slurries
Minerais de fer — Échantillonnage des schlamms

ICS 73.060.10









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REFERRED TO AS AN INTERNATIONAL STANDARD UNTIL PUBLISHED AS SUCH.
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THEY ARE AWARE AND TO PROVIDE SUPPORTING DOCUMENTATION.
©  International Organization for Standardization, 2013

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ISO/DIS 16742

COPYRIGHT PROTECTED DOCUMENT


©  ISO 2013
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any
means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission.
Permission can be requested from either ISO at the address below or ISO’s member body in the country of the requester.
ISO copyright office
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Fax + 41 22 749 09 47
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Published in Switzerland

ii © ISO 2013 – All rights reserved

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Iron Ores - Sampling of Slurries – DIS 16742 ISO/TC 102/SC 1 N 1079
Contents Page
Foreword .v
1 Scope.1
2 Normative references.1
3 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.17
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ISO/TC 102/SC 1 N 1079 Iron Ores - Sampling of Slurries – DIS 16742
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 . 18
10.6 Sampling procedures . 19
11 Sampling of stationary slurries. 19
12 Sample preparation procedures. 19
12.1 General. 19
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 . 21
Annex B (informative) Examples of incorrect slurry sampling devices . 23
Annex C (normative) Manual sampling implements . 26

iv © ISO 2003 — All rights reserved

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Iron Ores - Sampling of Slurries – DIS 16742 ISO/TC 102/SC 1 N 1079
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.
This Working Draft was prepared by Technical Committee ISO/TC 102/SC 1, Iron ores and direct reduced iron
- Sampling.

© ISO 2003 — All rights reserved v

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Iron Ores - Sampling of Slurries – DIS 16742 ISO/TC 102/SC 1 N 1079

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 may fall freely or be confined in pipes, launders, chutes, spirals or
similar channels. Sampling of slurries in pressurised pipes is not covered in this International Standard. The
slurry stream can only be sampled satisfactorily at a transfer point prior to the pressurised 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 method
corresponds to the stopped-belt method described in ISO 3082. Reference increments shall be taken as
close as possible to increments taken using the sampling procedure under evaluation.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the cited edition applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
IS0 565, Test sieves – Metal wire cloth, perforated metal plate and electroformed sheet – Nominal top sizes of
openings.
IS0 3082, Iron ores – Sampling and sample preparation procedures.
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ISO/TC 102/SC 1 N 1079 Iron Ores - Sampling of Slurries – DIS 16742
IS0 3084, Iron ores – Experimental methods for evaluation of quality variation.
IS0 3085, Iron ores – Experimental methods for checking the precision of sampling, sample preparation and
measurement.
IS0 3086, Iron ores – Experimental methods for checking the bias of sampling.
IS0 3087, Iron ores – Determination of the moisture content of a lot.
IS0 4701, Iron ores – Determination of size distribution by sieving.
IS0 11323, Iron ore and direct reduced iron – Vocabulary.
3 Definitions
For the purpose of this International Standard, the 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 by mass in the
gross sample. The gross or partial sample may then be filtered, dried and weighed. Alternatively, the gross
or partial sample may 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 optimise 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
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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 freely falling streams (see Clause 9), with a complete
cross section of the stream being taken during the traverse of the cutter. Access to freely 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 may 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. 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, heterogenous 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, 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 1(a) (after Pitard,
1993), 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 1(b) (after Pitard, 1993) 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 1(c) (after Pitard, 1993), also with an in-
stream point sampler or probe within a pipe or channel, which is always incorrect.

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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
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precision results in impractical numbers of increments and/or partial samples, it may 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 by mass in the slurry
for determining the mass of the solids in each slurry increment (see 5.2).
g) Check that the procedures and equipment for taking slurry increments minimise 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 may be combined to constitute a single gross sample for analysis
(see Figure 2). Alternatively, increments may 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:
a) For convenience of materials handling;
b) To provide progressive information on the quality of the lot; or
c) 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 pulverised 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.
Sampling of slurries in stationary situations, such as a settled or e
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