ISO 11794:2010
(Main)Copper, lead, zinc and nickel concentrates — Sampling of slurries
Copper, lead, zinc and nickel concentrates — Sampling of slurries
ISO 11794:2010 sets out the basic methods for sampling particulate material that is mixed with a liquid, usually water, to form a slurry. In industry and in the mining and mineral processing literature, slurry is also referred to as pulp, but this term is not used in ISO 11794:2010. At very high ratios of fine particulate solids to liquids where material assumes a soft plastic form, the mixture is correctly termed as a paste. Sampling of pastes is not covered in ISO 11794:2010. The procedures described in ISO 11794:2010 apply to sampling of particulate materials that are transported in moving streams as slurries, but not pressurized slurries. These streams may fall freely or be confined in pipes, launders, flumes, sluices, spirals or similar channels. Sampling of slurries in stationary situations, such as a settled or even a well-stirred slurry in a holding vessel or dam, is not recommended and is not covered in ISO 11794:2010. ISO 11794:2010 describes procedures that are designed to provide samples representative of the slurry solids and particle-size distribution of the slurry under examination. After draining the slurry sample of fluid and measuring the fluid volume, damp samples of the contained particulate material 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 describes a system or procedure.
Concentrés de cuivre, de plomb, de zinc et de nickel — Échantillonnage des schlamms
General Information
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 11794
First edition
2010-10-01
Copper, lead, zinc and nickel
concentrates — Sampling of slurries
Concentrés de cuivre, de plomb, de zinc et de nickel — Échantillonnage
des schlamms
Reference number
ISO 11794:2010(E)
©
ISO 2010
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ISO 11794:2010(E)
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ISO 11794:2010(E)
Contents Page
Foreword .v
1 Scope.1
2 Normative references.1
3 Terms and definitions .2
4 Principles of sampling slurries .2
4.1 General .2
4.2 Sampling errors .3
4.2.1 General .3
4.2.2 Preparation error, PE .4
4.2.3 Delimitation and extraction errors, DE and EE .4
4.2.4 Weighting error, WE .6
4.2.5 Periodic quality-fluctuation error, QE .6
3
4.3 Sampling and total variance.6
4.3.1 Sampling variance.6
4.3.2 Total variance .6
4.3.3 Sampling-stage method of estimating sampling and total variance .8
4.3.4 Simplified method of estimating sampling and total variance .9
4.3.5 Interleaved sample method of measuring total variance.10
5 Establishing a sampling scheme.11
6 Minimization of bias and unbiased increment mass .16
6.1 Minimization of bias .16
6.2 Volume of increment for falling-stream samplers to avoid bias .17
7 Number of increments .17
7.1 General .17
7.2 Simplified method .18
8 Minimum mass of solids contained in lot and sub-lot samples.18
8.1 Minimum mass of solids in lot samples.18
8.2 Minimum mass of solids in sub-lot samples.18
8.3 Minimum mass of solids in lot and sub-lot samples after size reduction.18
9 Time-basis sampling.19
9.1 General .19
9.2 Sampling interval.19
9.3 Cutters .19
9.4 Taking of increments .19
9.5 Constitution of lot or sub-lot samples .20
9.6 Division of increments and sub-lot samples.20
9.7 Division of lot samples .20
9.8 Number of cuts for division.20
10 Stratified random sampling within fixed time intervals.20
11 Mechanical sampling from moving streams.21
11.1 General .21
11.2 Design of the sampling system .21
11.2.1 Safety of operators.21
11.2.2 Location of sample cutters.21
11.2.3 Provision for duplicate sampling.21
11.2.4 System for checking the precision and bias .21
11.2.5 Avoiding bias .22
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ISO 11794:2010(E)
11.3 Slurry sample cutters .22
11.3.1 General.22
11.3.2 Falling-stream cutters .23
11.3.3 Cutter velocities.23
11.4 Mass of solids in increments.23
11.5 Number of primary increments .23
11.6 Routine checking.23
12 Manual sampling from moving streams.24
12.1 General.24
12.2 Choosing the sampling location .24
12.3 Sampling implements.25
12.4 Mass of solids in increments.25
12.5 Number of primary increments .25
12.6 Sampling procedures .25
13 Sampling of stationary slurries.26
14 Sample preparation .26
14.1 General.26
14.2 Sample division.26
14.3 Sample grinding.26
14.4 Chemical analysis samples .26
14.5 Physical test samples .27
15 Packing and marking of samples.27
Annex A (normative) Sampling-stage method for estimating sampling and total variance .28
Annex B (informative) Examples of correct slurry sampling devices .34
Annex C (informative) Examples of incorrect slurry sampling devices .37
Annex D (normative) Manual sampling implements.41
Bibliography .42
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ISO 11794:2010(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 11794 was prepared by Technical Committee ISO/TC 183, Copper, lead, zinc and nickel ores and
concentrates.
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INTERNATIONAL STANDARD ISO 11794:2010(E)
Copper, lead, zinc and nickel concentrates — Sampling
of slurries
WARNING — This International Standard may involve hazardous materials, operations and equipment.
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 particulate material that is mixed with a
liquid, usually water, to form a slurry. In industry and in the mining and mineral processing literature, slurry is
also referred to as pulp, but this term is not used in this International Standard. At very high ratios of fine
particulate solids to liquids where material assumes a soft plastic form, the mixture is correctly termed as a
paste. Sampling of pastes is not covered in this International Standard.
The procedures described in this International Standard apply to sampling of particulate materials that are
transported in moving streams as slurries, but not pressurized slurries. These streams may fall freely or be
confined in pipes, launders, flumes, sluices, spirals or similar channels. Sampling of slurries in stationary
situations, such as a settled or even a well-stirred slurry in a 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 draining the slurry sample of
fluid and measuring the fluid volume, damp samples of the contained particulate material 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 describes a system or procedure.
Provided that 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. This
method corresponds to the stopped-belt method described in ISO 12743.
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 12743, Copper, lead, zinc and nickel concentrates — Sampling procedures for determination of metal and
moisture content
ISO 12744, Copper, lead, zinc and nickel concentrates — Experimental methods for checking the precision of
sampling
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ISO 11794:2010(E)
ISO 13292, Copper, lead, zinc and nickel concentrates — Experimental methods for checking the bias of
sampling
ISO 20212, Copper, lead, zinc and nickel sulfides — Sampling procedures for ores and smelter residues
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 12743, ISO 12744, ISO 13292 and
ISO 20212 apply.
4 Principles of sampling slurries
4.1 General
In this International Standard, a slurry is defined as “any fluid mixture of a solid of nominal top size < 1 mm
that is mixed with water, which is frequently used as a convenient form to handle solids in bulk”. Slurry flows
are found in many mineral processing plants, with the water and entrained solids mixture being transported
through the plant circuits by means of pumps and pipelines and under gravity in sluices, flumes and launders.
In a number of operations, ore is transported to the mill in slurry form, and in others concentrates are
transported long distances in slurry pipelines. Tailings from wet plants are also discharged as slurries through
pipelines to the tailings dam. In many of these operations, collection of increments at selected sample points
is required for evaluation of the particulate material in the slurry.
A lot sample is constituted from a set of unbiased primary increments from a lot. The sample container is
weighed immediately after collection and combination of increments to avoid water loss by evaporation or
spillage. Weighing is necessary to determine the percentage of solids by mass in the slurry sample. The
sample may then be filtered, dried and weighed. Alternatively, the sample may be sealed in plastic bags after
filtering for transport and drying at a later stage. The liquid removed during filtration should be retained if it
needs to be analysed.
Test samples are prepared from samples after filtering and drying. Test portions may then be taken from the
test sample and analysed using an appropriate and properly calibrated 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 manual sampling methods and
mechanical sampling systems.
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 sample for testing. Hence, slurries are to be sampled in
such a manner that all possible primary increments in the set into which the slurry can be divided have the
same probability of being selected. Any deviation from this basic requirement can result in bias. 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 9). If
the slurry flow rate and the solids concentration vary with time, the slurry volume and the mass of dry solids
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 10).
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ISO 11794:2010(E)
Best practice for sampling slurries is to cut freely falling streams mechanically (see Clause 11), 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, alternatively, a full-stream sample by-line can
be added to a pipe that diverts the slurry into a holding tank, or weirs can be incorporated in launders, sluices
and flumes. 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 homogeneous with very fine particles, such as clays, 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 particle 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 particle 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 radial 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, 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 lot 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
4.2.1 General
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. Where 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.
The characteristics of the solids component of a slurry can be determined by extracting samples from the
slurry stream, preparing test samples and measuring the required quality characteristics. The total sampling
error TSE can be expressed as the sum of a number of independent components (Gy, 1992; Pitard, 1993).
Such a simple additive combination would not be possible if the components were correlated. The sampling
error, expressed as a sum of its components, is given by Equation (1):
TSE=+QE QE+QE+WED+ EE+ E+PE (1)
12 3
where
QE is the short-range quality-fluctuation error associated with short-range variations in quality of the
1
solids component of the slurry;
QE is the long-range quality-fluctuation error associated with long-range variations in quality of the
2
solids component of the slurry;
QE is the periodic quality-fluctuation error associated with periodic variations in quality of the solids
3
component of the slurry;
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ISO 11794:2010(E)
WE is the weighting error associated with variations in the slurry flow rate;
DE is the increment delimitation error introduced by incorrect increment delimitation;
EE is the increment extraction error introduced by incorrect increment extraction from the slurry;
PE is the preparation error (also known as accessory error) introduced by departures (usually
unintentional) from correct practices, e.g. during constitution of the lot sample, draining and filtering
away the water, and transportation and drying of the sample
The short-range quality-fluctuation error consists of two components, as shown by Equation (2):
QE=+FE GE (2)
1
where
FE is the fundamental error due to variation in quality between particles;
GE is the segregation and grouping error.
The fundamental error results from the composition heterogeneity of the lot, i.e. the heterogeneity that is
inherent to the composition of each particle making up the solids component of the lot. The greater the
differences in the compositions of particles, the greater the composition heterogeneity and the higher the
fundamental error variance. The fundamental error can never be completely eliminated. It is an inherent error
resulting from the variation in composition of the particles in the slurry being sampled.
The segregation and grouping error results from the distribution heterogeneity of the sampled material (Pitard,
1993). The distribution heterogeneity of a lot is the heterogeneity arising from the manner in which particles
are distributed in the slurry. It can be reduced by taking a greater number of smaller increments, but it can
never be completely eliminated.
A number of the components of the total sampling error, namely DE, EE and PE, can be minimized, or
reduced to an acceptable level, by correct design of the sampling procedure.
4.2.2 Preparation error, PE
In this context, the preparation error includes errors associated with non-selective sample-preparation
operations that should not change mass, such as sample transfer, draining and filtering, drying, crushing,
grinding or mixing. It does not include errors associated with sample division. Preparation errors, also known
as accessory errors, include sample contamination, loss of sample material, alteration of the chemical or
physical composition of the sample, operator mistakes, fraud or sabotage. These errors can be made
negligible by correct design of the sampling system and by staff training. For example, cross-stream slurry
cutters should have caps to prevent entry of splashes when the cutter is in the parked position, and care
needs to be taken during filtering to avoid loss of fines that are still suspended in the water to be discarded.
4.2.3 Delimitation and extraction errors, DE and EE
Delimitation and extraction errors arise from incorrect sample cutter design and operation. The increment
delimitation error, DE, results from an incorrect shape of the volume delimiting the slurry increment, and this
can be due to both design and operation faults. Because of the incorrect shape of the slurry increment volume,
sampling with non-uniform selection probabilities results. The average of DE is often non-zero, which makes it
a source of sampling bias. The delimitation error can be made negligible if all parts of the stream cross-section
are diverted by the sample cutter for the same length of time.
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ISO 11794:2010(E)
Sampling from moving slurry streams usually involves methods that fall into three broad operational
categories as follows (Pitard, 1993).
a) Taking the whole stream for part of the time with a cross-stream cutter as shown in Figure 1 a) (after
Pitard, 1993), usually where 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 to 5 show
incorrect sampling where the cutter diverts different parts of the stream for
...
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