EN 17289-3:2020
(Main)Characterization of bulk materials - Determination of a size-weighted fine fraction and crystalline silica content - Part 3: Sedimentation method
Characterization of bulk materials - Determination of a size-weighted fine fraction and crystalline silica content - Part 3: Sedimentation method
This document specifies the determination of the size-weighted fine fraction (SWFF) and the size-weighted fine fraction of crystalline silica (SWFFCS) in bulk materials by means of a sedimentation method using a liquid sedimentation technique.
The purpose of this document is to allow users to evaluate bulk materials with regard to their size-weighted fine fraction and crystalline silica content.
NOTE For preparation of the sample and determination of crystalline silica by X-ray Powder Diffractometry (XRD) or Fourier Transform Infrared Spectroscopy (FT-IR) see EN 17289-1.
Specific methods for the evaluation of SWFF for specific bulk materials are specified in several annexes.
This document is applicable for crystalline silica containing bulk materials which have been fully investigated and validated for the evaluation of the size-weighted fine fraction and crystalline silica.
Charakterisierung von Schüttgütern - Bestimmung einer größengewichteten Feinfraktion und des Anteils an kristallinem Quarz - Teil 3: Sedimentationsverfahren
Dieses Dokument legt die Bestimmung der größengewichteten Feinfraktion (SWFF) und der größen-gewichteten Feinfraktion von kristallinem Quarz (SWFFCS) in Schüttgütern mit einem Sedimentations-verfahren fest, bei dem eine Sedimentationstechnik mit Flüssigkeit eingesetzt wird.
Der Zweck dieses Dokuments besteht darin, Anwendern die Bewertung von Schüttgütern hinsichtlich deren größengewichteter Feinfraktion und des Gehalts an kristallinem Quarz zu ermöglichen.
ANMERKUNG Zur Probenvorbereitung und zur Bestimmung von kristallinem Quarz durch Röntgenpulverdiffrakto-metrie (en: X-ray powder diffractometry, XRD) oder Fourier-Transformations-Infrarot-Spektroskopie (FT-IR) siehe EN 17289-1.
Spezielle Verfahren für die Bewertung der SWFF bestimmter Schüttgüter werden in mehreren Anhängen festgelegt.
Dieses Dokument ist für kristallinen Quarz enthaltende Schüttgüter anwendbar, die zur Bewertung der größengewichteten Feinfraktion und des kristallinen Quarzes vollständig untersucht und validiert wurden.
Caractérisation des matériaux en vrac - Détermination de la fraction fine pondérée par taille et de la teneur en silice cristalline - Partie 3 : Méthode par sédimentation
Le présent document spécifie la détermination de la fraction fine pondérée par taille (SWFF) et de la fraction fine de silice cristalline pondérée par taille (SWFFCS) dans des matériaux en vrac au moyen d’une méthode par sédimentation en utilisant une technique de sédimentation dans un liquide.
L’objectif du présent document est de permettre aux utilisateurs d’évaluer des matériaux en vrac en ce qui concerne leur fraction fine pondérée par taille et leur teneur en silice cristalline.
NOTE Pour la préparation de l’échantillon et le dosage de la silice cristalline par l’analyse de poudre par diffraction de rayons X (XRD) et la spectroscopie infrarouge à transformée de Fourier (FT-IR), voir le FprEN 17289-1.
Des méthodes spécifiques pour l’évaluation de la SWFF de matériaux en vrac particuliers sont décrites dans plusieurs annexes.
Le présent document s’applique aux matériaux en vrac contenant de la silice cristalline, qui ont été entièrement étudiés et validés pour l’évaluation de la fraction fine pondérée par taille et de la silice cristalline.
Karakterizacija razsutih materialov - Določanje velikostno utežene fine frakcije in deleža kristaliničnega kremena - 3. del: Metoda sedimentacije
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-februar-2021
Karakterizacija razsutih materialov - Določanje velikostno utežene fine frakcije in
deleža kristaliničnega kremena - 3. del: Metoda sedimentacije
Characterization of bulk materials - Determination of a size-weighted fine fraction and
crystalline silica content - Part 3: Sedimentation method
Charakterisierung von Schüttgütern - Bestimmung einer größengewichteten Feinfraktion
und des Anteils an kristallinem Quarz - Teil 3: Sedimentationsverfahren
Caractérisation des matériaux en vrac - Détermination de la fraction fine pondérée par
taille et de la teneur en silice cristalline - Partie 3 : Méthode par sédimentation
Ta slovenski standard je istoveten z: EN 17289-3:2020
ICS:
13.040.30 Kakovost zraka na delovnem Workplace atmospheres
mestu
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN 17289-3
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2020
EUROPÄISCHE NORM
ICS 13.040.30
English Version
Characterization of bulk materials - Determination of a
size-weighted fine fraction and crystalline silica content -
Part 3: Sedimentation method
Caractérisation des matériaux en vrac - Détermination Charakterisierung von Schüttgütern - Bestimmung
de la fraction fine pondérée par taille et de la teneur en einer größengewichteten Feinfraktion und des Anteils
silice cristalline - Partie 3 : Méthode par sédimentation an kristallinem Quarz - Teil 3:
Sedimentationsverfahren
This European Standard was approved by CEN on 4 October 2020.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 17289-3:2020 E
worldwide for CEN national Members.
Contents Page
European foreword . 4
Introduction . 5
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Symbols and abbreviations . 7
5 Assumptions . 8
6 Determination of SWFF and SWFFCS by sedimentation . 10
6.1 Determination of sedimentation time . 10
6.2 Selection of sedimentation liquid . 10
6.3 Sample preparation, sedimentation and SWFF determination . 11
6.4 Use of a dispersant of deflocculant . 13
6.5 Determination of the SWFF and SWFFCS of mixtures of phases with different particle
densities . 13
6.6 SWFF of mixtures . 13
6.7 SWFFCS of mixtures of homogeneous particles . 13
6.8 SWFFCS of mixtures of heterogeneous particles . 14
Annex A (normative) Separation of the SWFF by sedimentation . 16
A.1 Derivation for calculating the sedimentation parameters . 16
A.2 Calculation of the SWFF after sedimentation . 20
Annex B (normative) Determination and isolation of the size-weighted fine fraction (SWFF)
of kaolins and kaolinitic clays by sedimentation . 22
B.1 General . 22
B.2 Use range . 22
B.3 Equipment and consumables . 22
B.4 Method . 23
B.5 Figures . 25
Annex C (normative) Other minerals which can be treated in a similar way to
kaolins/kaolinitic clays for SWFF and SWFFCS determination . 28
C.1 General . 28
C.2 Andalusite . 28
C.3 Mica . 29
C.4 Vermiculite . 30
C.5 Talc . 30
Annex D (normative) Determination of the size-weighted fine fraction (SWFF and SWFFCS)
of Diatomaceous Earth (DE) by sedimentation . 32
D.1 General . 32
D.2 Categories of diatomaceous earth . 32
D.3 Equipment and consumables . 32
D.4 Method . 32
D.5 Determination of SWFF by sedimentation . 33
D.6 Determination of SWFFCS . 33
D.7 Example . 33
Annex E (normative) Determination of the size-weighted fine fraction (SWFF) of feldspar
products by sedimentation . 35
E.1 General . 35
E.2 Use range . 35
E.3 Consumables . 35
E.4 Method . 35
Bibliography . 40
European foreword
This document (EN 17289-3:2020) has been prepared by Technical Committee CEN/TC 137
“Assessment of workplace exposure to chemical and biological agents”, the secretariat of which is held
by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by June 2021, and conflicting national standards shall be
withdrawn at the latest by June 2021.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Introduction
A method was developed in the industrial minerals industry for the purpose of determining the “size-
weighted relevant fine fraction” within the bulk material. This document sets out the methods which
can be used to measure and calculate the fine fraction of the bulk material and the fine fraction of the
crystalline silica, in several types of bulk materials. This information provides additional information to
users for their risk assessment and to compare bulk materials. It has been used in the industry and by
institutes previously under the acronym SWeRF. EN 17289 (all parts) is based on that industrial
method and specifies the analytical methods to determine the difference between materials with coarse
quartz and fine quartz, e.g. sands versus flour.
As further activities with the material (intentional or otherwise) can change the particle size
distribution, the size-weighted fine fraction can also change. Therefore, the method reports (in terms of
the mass fraction in the bulk material in percent) both, the total crystalline silica (CS) and the estimated
size-weighted fine fraction of CS.
Conventions as specified in EN 481 can be used as input for this document. However, the output of this
document is not related to the respirable fraction at the workplace and cannot be used to replace
workplace exposure measurements.
EN 17289 (all parts) specifies two procedures that can be used to estimate the size-weighted fine
fraction (SWFF) in bulk materials. It also specifies how the SWFF, once separated, can be further
analysed to measure the content of crystalline silica (SWFFCS). The method can be used for comparing
the fine fraction in different bulk samples. EN 17289 (all parts) uses the term fine fraction to indicate
that it does not analyse airborne particles, but it evaluates the proportion of particles in a bulk material
that, based on their particle size, have a potential to be respirable if they were to become airborne.
EN 17289 (all parts) also allows for the size-weighted fine fraction of crystalline silica (SWFFCS)
particles in bulk materials to be evaluated in terms of mass fraction in percent, if the fraction separated
is subsequently analysed by a suitable method.
In a comparison of similar bulk materials, in which the particle size distribution is the only variable, the
SWFF can provide useful information to guide material selection. For example, leaving all other factors
aside, a bulk material with a lower SWFF value can pose less of a risk in terms of potential occupational
exposure. For the actual exposure at the workplace, the handling etc. of the material, will play a major
role.
Concentrations of respirable dust, or respirable crystalline silica (RCS), in the workplace air, resulting
from processing and handling of bulk materials, will depend on a wide variety of factors and these
concentrations cannot be estimated using SWFF or SWFFCS values. SWFF and SWFFCS values are not
intended for workplace exposure assessments as they have no direct relationship with occupational
exposure.
The evaluation of bulk materials using SWFF is complementary to determining the dustiness according
to EN 15051-1 [1].
The difference between EN 17289 (all parts) and EN 15051-1 is that SWFF quantifies the fine fraction in
a bulk material while dustiness quantifies the respirable, thoracic and inhalable dust made airborne
from the bulk material after a specific activity (dustiness characterizes the material with relation to the
workplace atmosphere when working with the bulk material).
EN 17289 Characterization of bulk materials — Determination of a size-weighted fine fraction and
crystalline silica content consists of the following parts:
— Part 1: General information and choice of test methods;
— Part 2: Calculation method;
— Part 3: Sedimentation method.
NOTE This document is intended for use by laboratory experts who are familiar with FT-IR, XRD methods,
PSD measurements and other analytical procedures. It is not the intention of this document to provide instruction
in the fundamental analytical techniques.
1 Scope
This document specifies the determination of the size-weighted fine fraction (SWFF) and the size-
weighted fine fraction of crystalline silica (SWFFCS) in bulk materials by means of a sedimentation
method using a liquid sedimentation technique.
The purpose of this document is to allow users to evaluate bulk materials with regard to their size-
weighted fine fraction and crystalline silica content.
NOTE For preparation of the sample and determination of crystalline silica by X-ray Powder Diffractometry
(XRD) or Fourier Transform Infrared Spectroscopy (FT-IR) see EN 17289-1.
Specific methods for the evaluation of SWFF for specific bulk materials are specified in several annexes.
This document is applicable for crystalline silica containing bulk materials which have been fully
investigated and validated for the evaluation of the size-weighted fine fraction and crystalline silica.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
EN 481, Workplace atmospheres — Size fraction definitions for measurement of airborne particles
EN 1540, Workplace exposure — Terminology
EN 17289-1, Characterization of bulk materials — Determination of a size-weighted fine fraction and
crystalline silica content — Part 1: General information and choice of test methods
EN 17289-2:2020, Characterization of bulk materials — Determination of a size-weighted fine fraction
and crystalline silica content — Part 2: Calculation method
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 1540 and EN 17289-1 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
4 Symbols and abbreviations
CS crystalline silica
PSD particle size distribution
SWFF size-weighted fine fraction
SWFFCS size-weighted fine fraction of crystalline silica
5 Assumptions
The sedimentation method is based on the following assumptions:
a) all liquid that is extracted from the sedimentation vessel only comes from the space above the
extraction nozzle, and not from the space below the extraction nozzle. If this is not the case this will
result in a higher SWFF.
b) the particle size distribution of the bulk material is constant over the particle size range of interest,
i.e. from 1 µm to 12 µm (aerodynamic).
A constant particle size distribution is a PSD with a function that has a derivative which is constant,
see Formula (1). It is considered constant when classes of the same size contain the same fraction
of the total amount.
dd−
( )
min
fd × 100 (1)
( )
dd−
( )
max min
where
is the cumulative particle size distribution;
fd
( )
d is the particle size, in micrometres (µm);
is the minimum particle size, in micrometres (µm);
d
min
is the maximum particle size, in micrometres (µm).
d
max
NOTE d ≤ d ≤ d . See Figure 1 for an example.
min max
=
Key
X particle diameter (µm)
Y fraction (%)
1 constant cumulative particle size distribution
Figure 1 — Example of a constant cumulative PSD with d = 0,5 µm and d = 25 µm
min max
c) the particle size distribution of the sample does not have a narrow size distribution (relative span
d − d / dd× < 1,5) and at the same time, have a d in the range from 2 µm to
( )
90 10 90 10 ae,50
12 µm. Otherwise the error made could be more than 1 % (absolute value).For a relative span less
than 1,5 µm and d in the range from 2 µm to 6 µm, sedimentation overestimates the SWFF.
ae,50
For a relative span less than 1,5 µm and d in the range from 6 µm to 12 µm SWFFCS is
ae,50
underestimated. It is therefore recommended in these cases to use the calculation method instead
to determine SWFF. The mean reason for determining the SWFF using sedimentation is because,
although the PSD of the whole sample is known, the PSD of the crystallin silica is not. The CS can
either be in the coarse part of the PSD or in the fine part. However, in the case of a narrow
distribution it is likely to assume the CS practically has the same PSD as the whole sample. Since the
PSD is so narrow, sample and CS particles are automatically close to each other.
d) Stokes law is only valid for particles settling in a medium at low Reynolds number. The velocity of a
particle settling in a medium is limited by the drag force and this depends on the Reynolds number
for that particle. Although the density of liquids is much higher, so is their viscosity so that in the
end the difference between the Reynolds number of a particle in air and, for example, in water is
only a factor of 5. And although the constants for calculating the drag coefficient of particles depend
on the Reynolds number, the variation with Reynolds number within this range is very small and
can be neglected. Therefore, the dynamic form factor is assumed to be equal in both air and liquid.
e) in the material of interest all particles have the same and known particle density.
f) the sub sample is representative of the bulk material.
If these assumptions are not met, the calculation method shall be used as specified in EN 17289-2.
6 Determination of SWFF and SWFFCS by sedimentation
6.1 Determination of sedimentation time
The sedimentation time shall be calculated by Formula (2), which is based on Stokes’ law and the
convention given in EN 481. The derivation of it is given in Annex A.
ρ
p
ρ
18η 0
(2)
th=××
sup
ρρ− g
( )
pl
× I
R
where
t
is the time, in seconds (s), at which the size-weighted particle fraction of the collected
supernatant in an optimal way approaches the fraction collected according to the sampling
convention of respirable dust (see EN 481);
is the height of the column of supernatant liquid that is extracted at the calculated time, in
h
sup
metres (m);
η
is the viscosity of the fluid, in kilograms per metre per second (kg/m·s);
g
is the acceleration due to gravity, in metres per square seconds (m/s );
is the particle density of the particles, in kilograms per cubic metre (kg/m );
ρ
p
is the density of the liquid medium, in kilograms per cubic metre (kg/m );
ρ
l
3 3
is the unit density (1 000 kg/m [ = 1 g/cm ]);
ρ
−6
I is the respirable convention integral: 4,281 × 10 m.
R
For determining the SWFF of a sample, the particle density of that sample shall be used for ρ .
p
When SWFFCS is determined, the density of the crystalline silica polymorph of interest
(quartz or cristobalite) shall be used.
SWFFCS shall be used when the CS is the constituent of only interest. For the SWFFCS only the
sedimentation rate for the quartz (cristobalite etc.) particles are relevant. The fact that the
sedimentation time for other particles is not correct is not important since SWFFCS is needed. When the
SWFF of material with a different particle density is needed the procedure shall be repeated
with a sedimentation time as calculated by Formula (1) with the particle density of that material.
The height h to be separated is usually set at 0,1 m, but other heights can be used depending on the
sup
nature of the sample. In any case, the height h shall be less than half the total height h of the
sup tot
sedimentation liquid in the measuring cylinder (see B.4).
6.2 Selection of sedimentation liquid
A suitable sedimentation liquid shall be selected in order to meet the following requirements:
— the particles in the sample shall be completely de-agglomerated;
— the particles in the sample shall not dissolve, swell or disintegrate;
— the particles in the sample shall not react.
NOTE 1 Water is in most cases a suitable sedimentation liquid.
When necessary, a dispersant or deflocculant additive shall be used in appropriate quantities.
NOTE 2 De-agglomeration is the process where particles are separated from each other without breaking the
particles. Disintegration is the process in which particles are broken.
6.3 Sample preparation, sedimentation and SWFF determination
In order to ensure that the sedimentation is performed correctly, the Andreasen pipette method is used
[2], [3].
The following steps shall be executed to determine the SWFF or SWFFCS of a sample.
a) take a representative subsample of the bulk sample of approximately 1,0 g;
For coarse bulk material a pre-preparation is required to respect the limitations of the Andreasen
pipette method, e.g. sieving.
b) determine the mass m of the sample with a precision of 0,001 g;
tot
c) disperse the sample in 50 ml of sedimentation liquid in a 100 ml pre-weighted, dry and clean
beaker. The mass of the beaker shall also be determined with a precision of 0,001 g (see also
ISO 13317-2);
d) treat the sample in an ultrasonic bath or shaker until completely de-agglomerated;
NOTE 1 The de-agglomeration time will depend on the type of material.
e) if necessary, based on the characterization of the bulk material, add a suitable dispersant or
deflocculant to keep the particles from flocculating or coagulating. The use of this product will lead
to additional steps specified in 6.4;
For unknown bulk materials a full characterization is needed.
f) pour the dispersed sample in a graduated cylinder with 250 ml volume. Rinse out the sample jar
using the sedimentation liquid to ensure that no residue remains. Fill the cylinder up to 250 ml
with sedimentation liquid. Seal the open end of the cylinder and shake the contents thoroughly.
Then replenish the cylinder up till 250 ml and homogenize;
NOTE 2 The volume of solids is maximum 0,2 % of the volume of the total liquid to ensure unhindered
sedimentation of the separate particles.
For some minerals it can be required to use a plunger agitator. With the cylinder in place, agitate.
Then remove the plunger to replenish the cylinder up till 250 ml and homogenize.
g) place the cylinder in a location where it is at constant temperature and free from effects that could
cause currents in the liquid. The constant temperature can be achieved when using a water bath.
h
Leave to settle for the calculated time ( t ). Determine the height of the liquid column (m);
tot
h) from the cylinder, after calculated time ( t ), lower a pipette to h below the surface, draw the
sup
volume of the supernatant ( V ) above the tip of the pipette with a siphon or pipette and transfer
t
into the pre-weighed beaker.
Make sure that, whilst using the pipette, the tip of the pipette remains in the same place in the
cylinder; do not insert it deeper as the level descends;
NOTE 3 Placing a clip on the pipette and attaching it to the edge of the cylinder makes it easier to keep the
pipette in the right place.
i) place the beaker containing the supernatant on a hot plate to evaporate the liquid and heat gently
until dry. Then place the beaker in the oven at about 103 °C for at least 1 h or longer until
completely dry and transfer into a desiccator, leaving it to cool down to ambient temperature;
j) re-weigh the beaker to within an accuracy of 0,001 g and note the post-weight. Determine the mass
of the residue m by subtracting the mass of the pre-weighted beaker;
r
NOTE 4 The above procedure is repeated three times in order to check the reproducibility of the sedimentation
method for SWFF determination.
k) determine the SWFF of the sample by using Formula (3):
hm×
tot r
w × 100 (3)
SWFF
hm×
sup tot
where
is the size-weighted fine fraction, in percent (%);
w
SWFF
is the height of the total column of fluid that is used for sedimentation, in metres (m);
h
tot
is the height of the column of supernatant liquid that is extracted at the calculated time, in
h
sup
metres (m);
is the total mass that was dispersed, in grams (g);
m
tot
is the mass of the residue in the extracted supernatant, in grams (g) (see Figure A.2).
m
r
l) the SWFFCS of the sample shall be calculated by using Formula (4):
hm×
tot r
w × w (4)
SWFFCS CS
hm×
sup tot
where
is the size-weighted fine fraction of crystalline silica, in percent (%);
w
SWFFCS
is the height of the total column of fluid that is used for sedimentation, in metres (m);
h
tot
is the height of the column of supernatant liquid that is extracted at the calculated time, in
h
sup
metres (m);
=
=
is the total mass that was dispersed, in grams (g);
m
tot
is the mass of the residue in the extracted supernatant, in grams (g);
m
r
is the mass fraction of CS in the supernatant, in percent (%).
w
CS
NOTE 5 For a more detailed description of this method for the particular applications on kaolins and kaolinitic
clays, see Annex B. For SWFF and SWFFCS determination of some other minerals (andalusite, mica, vermiculite
and talc) which can be treated in a similar way to kaolins/kaolinitic clays see Annex C. For the particular
application on diatomaceous earth (DE) see Annex D, and for the particular application on feldspar products see
Annex E.
NOTE 6 Different settling times are usually used for determining the SWFF and SWFFCS, see 6.5 and 6.6.
6.4 Use of a dispersant of deflocculant
In order to get reliable results from the sedimentation test, the particles in the sample shall be
completely de-agglomerated. If necessary, a suitable dispersant or deflocculant shall be added to keep
the particles from flocculating or coagulating.
In this case, to adjust the mass of the samples when an additive has been added, a blank cylinder shall
be prepared by adding only the dispersant to the liquid. Also, three blank beakers shall be prepared.
These beakers shall be treated the same as specified in 6.3. Determine the mass of the residual additive
by taking the average of the residue mass in the three blank beakers. Deduct this average mass of
residual additive from the mass of the sample.
Any additive used shall be analysed by the same method (XRD/FTIR) for the crystalline silica
determination to ensure that there is no interference.
6.5 Determination of the SWFF and SWFFCS of mixtures of phases with different particle
densities
One of the parameters that determines the sedimentation time is the particle density of the particles.
If the material consists of multiple phases with different densities it is important to choose the correct
particle density since it will affect the sedimentation time. It is also important to know if the particles
are homogeneous or if they consist of multiple phases.
6.6 SWFF of mixtures
The SWFF of a material is determined using the particle density of that material. In order to determine
the SWFF, determine the particle density of the sample using a standard method and use that in the
calculation for the sedimentation time. It is assumed that all particles have an identical mass ratio of the
phases, i.e. the same particle density.
6.7 SWFFCS of mixtures of homogeneous particles
When the SWFFCS of a sample is needed and the crystalline silica particles are free, the density of the CS
shall be used for calculating the time of sedimentation. This will mean that too many or too little of the
other phase(s) will sediment out of the top layer, but this has no effect on the result of the SWFFCS.
For example, in a sample of feldspar containing quartz, the particle density of that sample shall be used
to calculate the SWFF.
If, however the SWFFCS is required, the density of the CS i.e. quartz shall be used. If both SWFF
and SWFFCS are needed, the sedimentation needs to be performed twice (once for each density).
6.8 SWFFCS of mixtures of heterogeneous particles
Heterogeneous particles consist of multiple phases, and the density of each particle is no longer known
since, in almost all cases, the ratio of the phases is different in each particle.
For the SWFFCS the selection of which density to use depends on whether the density of the other
phase(s) is higher or lower than that of the crystalline silica.
Phases of higher density, alongside the crystalline silica, will increase the overall density of a particle
causing it to settle more quickly. Similarly, phases of lower density, alongside the crystalline silica,
will decrease the overall density of a particle and cause it to settle more slowly.
The SWFFCS can be over– or underestimated if the wrong particle density is chosen to calculate
the sedimentation time. Figure 2 shows how SWFFCS is relatively increased or decreased when
particles have a density that is lower or higher than the density used to calculate time of sedimentation.
The effect also depends on the PSD of the material. Coarser materials with a narrow distribution have
a lower SWFFCS but in relative terms the deviation is larger than for finer material with a broader
distribution. The graph given in Figure 2 shows the relationship for a material with a constant PSD and
can be considered a good estimate for most materials.
Key
X density deviation (kg/m ) 1 relative deviation from the actual SWFFCS
Y effect on the SWFFCS (%)
Figure 2 — Effect on the SWFFCS as function of deviation in density for a constant PSD
The particle density for calculating the time of sedimentation shall be chosen as follows:
a) if the density of the other phase(s) is lower, effectively reducing the overall density of the particle,
then the density of crystalline silica shall be used to calculate the time of sedimentation.
This will result in a slightly higher result for the SWFFCS;
b) if the density of the other phase(s) is higher, effectively increasing the overall density of the particle,
then the average of the densities of crystalline silica and the other phases shall be used to calculate
the time of sedimentation. The reason for this average of densities is that particles containing CS
can have a fraction of CS ranging from 0 % to 100 %. By choosing the average density some
particles will have a too high density while others a too low density. But at the average density this
will cancel out and particles lost from the supernatant, because of their (too) high density, will be
compensated for by particles with a too low density, that will remain in the supernatant. Note that
when calculating this average density, the arithmetic average shall be used. There is no need to
weight the calculation for the proportions of each phase. It is to be expected that this will
overestimate the SWFFCS. One reason is that besides heterogeneous particles there will normally
also be a fraction of homogeneous CS particles. The other reason is that, although there is a balance
between ‘heavier’ particles lost against ‘lighter’ particles remaining, the lighter particles contain
more CS.
This approach will ensure that the SWFFCS result will always be equal to, or higher than, the actual
SWFFCS.
EXAMPLE 1 Feldspar (which has a lower density than quartz). In a sample of feldspar, particles consisting
of quartz and feldspar will have a density lower than that of quartz. The density of quartz is used for calculating
the time of sedimentation. These particles will settle more slowly than calculated and the SWFFCS result will be
higher than the actual SWFFCS (i.e. overestimated).
EXAMPLE 2 Iron ore (which has a higher density than quartz). Use 3 950 kg/m (the average of 5 250
for haematite and 2 650 for quartz) for calculating the time of sedimentation.
Annex A
(normative)
Separation of the SWFF by sedimentation
A.1 Derivation for calculating the sedimentation parameters
A.1.1 General
The probability that an inhaled particle reaches the alveoli of the lungs is given in EN 481
by the respirable convention including the inhalability factor. This separation of the respirable particles
is a function of the aerodynamic diameter with decreasing probability with increasing diameter.
In order to separate the SWFF a sample is dispersed in a liquid and left to settle. After a calculated time,
the top volume is extracted to a certain height. Since larger particles settle faster than smaller ones,
this will have resulted in a separation between coarse and fine particles. By choosing the right time
and height the separation by sedimentation approaches the respirable convention (see Figure A.1).
Key
X aerodynamic diameter (µm)
Y probability (%)
Rd
( )
respirable convention
d
( )
sedimentation S
Figure A.1 — Graph of the separation efficiencies of the respirable convention
and the sedimentation
Both the respirable convention as well as the separation by sedimentation are probability functions.
Rd specifies the probability for a particle to enter the alveoli (see EN 481) and S d specifies the
( ) ( )
probability that a particle remains in suspension. The SWFF is found by choosing the parameters for
sedimentation in such a way that the sum of all probabilities for all diameters is equal for both the
respirable convention as well as the sedimentation. This is done by equating the integrals of both
functions according to Formula (A.1).
dd=
d=∞
max
R ddd = S ddd (A.1)
( ) ( ) ( ) ( )
∫∫
d 0 d 0
where
is the respirable convention;
Rd
( )
is the sedimentation separation function;
S d
( )
d
is the geometric diameter, in micrometres (µm);
is the largest (geometric) diameter for a particle in the supernatant, in micrometres
d
max
(µm).
A.1.2 Integral of R(D)
According to EN 481, sampling of the respirable fraction of particles with aerodynamic diameter ( d )
ae
is the percentage E of the inhalable fraction E .
R I
Results in EN 481 are given as percentages but since the fraction is needed instead, it is divided by 100.
Function R(d) then becomes:
Rd E× E / 100 (A.2)
( ) ( )
ae I R
where
is the respirable convention;
Rd
( )
ae
is the aerodynamic diameter, in micrometres (µm);
d
ae
(−0,06d )
is 50(1+e ae );
E
I
is the cumulative log-normal distribution with geometric mean of 4,25 µm and a
E
R
geometric standard deviation of 1,5.
The integral of Rd cannot be solved analytically but can be determined numerically and this
( )
ae
integral (for aerodynamic particles with unit density (1 g/cm )) is:
d =∞
ae
−6
Rd d d 4,281 µm 4,281 ×10 m (A.3)
( ) ( ) ( ) ( )
∫ ae ae
d =0
ae
Using Stokes law, the integral for particles with density ρ becomes:
p
= =
=
==
d=∞
−6
4,281 × 10
(A.4)
R ddd =
( ) ( )
∫
ρ
d=0p
ρ
where
is the density of the particles, in kilograms per cubic metre (kg/m );
ρ
p
3 3
is the unit density (1 000 kg/m [ = 1 g/cm ]).
ρ
A.1.3 Integral of Sd
( )
According to Stokes law the sedimentation separation function for a fixed time is quadratic and can be
represented as
S d= 1−×C d (A.5)
( )
where
is the sedimentation separation function;
S d
( )
d is the geometric diameter, in micrometres (µm);
C is a constant (dependent on several factors but constant during sedimentation)
dd dd
max max
S ddd 1−×C d dd (A.6)
( ) ( ) ( )
)
(
∫∫
dd00
d
max
= d− Cd× (A.7)
d −× Cd (A.8)
max max
where
is the largest diameter for a particle in the supernatant, in micrometres (µm).
d
max
The probability to find a particle in the supernatant reduces with the inverse square of its diameter. At a
certain diameter the probability becomes zero. This is d .
max
= 0 (A.9)
S d = 1−×C d
( )
max max
C= (A.10)
d
max
Combining Formula (A.8) and (A.10):
∫ S ddd= d −× d (A.11)
( ) ( )
max max
d
max
=
==
=
==
dd− (A.12)
max max
= d (A.13)
max
Equating the integrals:
∫=R ddd ∫ S ddd (A.14)
( ) ( ) ( ) ( )
−6
4,281 × 10 2
= d (A.15)
max
ρ
p
ρ
−6
××4,281 10
(A.16)
d =
max
ρ
p
ρ
For the separation of the SWFF by sedimentation a sample is dispersed in a liquid and left to settle for a
certain time ( t ) after which the top volume is extracted to h . The largest particle in this volume has
sup
an aerodynamic diameter of d . This means:
max
hv ×t (A.17)
sup
d
( )
max
where
is the height of the column of supernatant fluid that is extracted at the calculated time,
h
sup
in metres (m);
v
is the settling velocity of a particle with diameter d ;
d max
( )
max
t
is the time, in seconds (s).
According to Stokes law:
ρρ− g
( )
pl
v d × (A.18)
d max
( )
max 18η
where
v is the settling velocity of a particle with diameter d , in metres per second (m/s);
d max
( )
max
is the largest diameter for a particle in the supernatant, in micrometres (µm);
d
max
η
is the dynamic viscosity of liquid, in kilograms per metre per second (kg/m∙s);
g
is the acceleration due to gravity, in metres per square second (m/s );
is the density of the particles, in kilograms per cubic metre (kg/m );
ρ
p
=
=
=
is the density of the liquid, in kilograms per cubic metre (kg/m );
ρ
l
Using Formula (A.16), (A.17) and (A.18):
−6
××4,281 10
ρ − ρ g
( )
pl
ht × × (A.19)
sup
18η
ρ
p
ρ
where
is the height of the column of supernatant fluid that is extracted at the calculated time, in m;
h
sup
η
is the dynamic viscosity of liquid, in kilograms per metre per second (kg/m∙s);
g 2
is the acceleration due to gravity, in metres per square second (m/s );
is the density of the particles, in kilograms per cubic metre (kg/m );
ρ
p
is the density of the liquid, in kilograms per cubic metre (kg/m );
ρ
l
3 3
is the unit density (1 000 kg/m [ = 1 g/cm ]);
ρ
t
is the time, in seconds (s).
With this formula h can be calculated to which the volume has to be extracted after a certain time of
sup
sedimentation. Or when a fixed height is chosen, the time of sedimentation can be calculated as:
ρ
p
ρ
18η
(A.20)
th=× ×
sup
ρ − ρ g
( )
pl
−6
××4,281 10
The sedimentation time is determined at the point where the integral of function Rd is equal to that
( )
of the sedimentation (see Formula (A.1). However, the function Rd is different from S d so that the
( ) ( )
collection efficiency for the sedimentation is only exactly the same as what can be expected according
to EN 481 in the case of a constant size distribution. In practice the differences are small and acceptable.
Only in the case of a narrow size distribution (with a d (aerodynamic) in the range from 6 µm to
12 µm) the difference can become too large. However, as long as the geometric standard deviation of
the size distribution is larger than 1,7, or the relative span ( ) is larger than 1,5,
d − d / dd×
( )
90 10 90 10
the difference between sedimentation and EN 481 is smaller than 1 %.
A.2 Calculation of the SWFF after sedimentation
The SWFF of a sample is calculated according to Formula (3).
For a representation of the sedimentation setup, see Figure A.2.
=
SIST E
...
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