ISO 157:1996
(Main)Coal — Determination of forms of sulfur
Coal — Determination of forms of sulfur
Specifies methods of determining the sulfate and pyrite sulfur contents of coals, including brown coals and methods of calculating the amount of organic sulfur present. Replaces the first edition.
Charbon — Détermination de la teneur en différentes formes de soufre
Premog - Ugotavljanje načina vezave žvepla
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-februar-1998
3UHPRJ8JRWDYOMDQMHQDþLQDYH]DYHåYHSOD
Coal -- Determination of forms of sulfur
Charbon -- Détermination de la teneur en différentes formes de soufre
Ta slovenski standard je istoveten z: ISO 157:1996
ICS:
73.040 Premogi Coals
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
IS0
INTERNATIONAL
STANDARD
Second edition
1996-06-o 1
Coal - Determination of forms of sulfur
Char-bon - DGtermination de la teneur en diffgrentes formes de soufre
Reference number
IS0 157:1996(E)
IS0 157:1996(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work of
preparing International Standards is normally carried out through IS0
technical committees. Each member body interested in a subject for which
a technical committee has been established has the right to be rep-
resented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
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.
International Standard IS0 157 was prepared by Technical Committee
ISO/TC 27, Solid mineral fuels, Subcommittee SC 5, Methods of analysis.
This second edition cancels and replaces the first edition (IS0 157:1975),
of which it constitutes a technical revision.
Annex A of this International Standard is for information only.
0 IS0 1996
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Orga nization Standardi zation
for
Case postale 56 l CH-121 1G eneve 20 l Switzerland
Printed in Switzerland
@ IS0 IS0 157:1996(E)
Introduction
For many purposes, a knowledge of the total sulfur content of a coal is
sufficient, but for certain work it is also necessary to know how the sulfur
is distributed between the coal substance and the mineral matter. In
particular, such information may be required in connection with coal classi-
fication and cleaning.
Sulfur is usually present in coal in three forms, viz:
sulfate sulfur, i.e. the sulfur present in the form of inorganic sulfates;
a)
b) pyritic sulfur, i.e. the sulfur present in the form of pyrites and marca-
site;
c) organic sulfur, i.e. the sulfur present in the form of organic sulfur
compounds.
This page intentionally left blank
IS0 157:1996(E)
INTERNATIONAL STANDARD @ IS0
Coal - Determination of forms of sulfur
Section 1: General
IS0 5069-Z: 1983, Brown coals and /ignites - Prin-
1.1 Scope
ciples of sampling - Part 2: Sample preparation for
determination of moisture content and for general
This International Standard specifies methods of
analysis.
determining the sulfate and pyritic sulfur contents of
coals, including brown coals and Iignites, and of
calculating the amount of organic sulfur present.
1.3 Principle
1.2 Normative references
The procedure described in this International Standard
The following standards contain provisions which,
utilizes the differential solubilities of sulfates and
through reference in this text, constitute provisions of
pyrites in dilute hydrochloric and nitric acids under
this International Standard. At the time of publication,
reflux conditions, such that each can be taken in
the editions indicated were valid. All standards are
solution successively and determined directly.
subject to revision, and parties to agreements based
on this International Standard are encouraged to
A general schematic representation of the procedure
investigate the possibility of applying the most recent
is given in figure 1.
editions of the standards indicated below. Members
of IEC and IS0 maintain registers of currently valid
International Standards.
1.4 Preparation of the test sample
IS0 331:1983, Coal - Determination of moisture in
the analysis sample - Direct gravimetric method.
The test sample is the general analysis test sample
prepared in accordance with IS0 1988 or IS0 5069-2,
IS0 334: 1993, Solid mineral fuels - Determination of
as appropriate.
total sulfur - Eschka method.
Grind about 25 g of the sample to pass a sieve of
IS0 351 :I 995, Solid mineral fuels - Determination of
aperture 75 urn and ensure that its moisture content
total sulfur - High temperature combustion method.
is in equilibrium with the laboratory atmosphere,
exposing it if necessary in a thin layer for the mini-
IS0 1015: 1992, Brown coals and /ignites - Determi- mum time required to achieve equilibrium.
nation of moisture content - Direct volumetric
method.
Before commencing the determination, thoroughly
mix the test sample for at least 1 min, preferably by
IS0 1170:1977, Coal and coke - Calculation of analy- mechanical means.
ses to different bases.
If the results are to be calculated other than on an air-
IS0 1988: 1975, Hard coal - Sampling. dried basis (see 6.1) then, after weighing the test
portion (see 2.4), determine the moisture content
using a further portion of the test sample by the
IS0 5068: 1983, Brown coals and /ignites - Determi-
method described in IS0 331, IS0 1015 or IS0 5068,
nation of moisture content - Indirect gravimetric
as appropriate.
method.
IS0 157:1996(E)
Coal sample (2 g to 8 g)
1 Reflux in dilute hydrochloric acid
Filtrate Insoluble residue
(Iron in + 2 and + 3 oxidation states)
ic ac id
Add hydrogen peroxide
(Iron in + 3 oxidation state) Filtrate (contains insoluble residue
pyritic iron) (discard)
1 Add ammonia solution
2 Filter
1 Add hydrogen peroxide
2 Boil
4-l
3 COOL
Filtrate Precipitate
(discard)
Alternative finishes
1 Adjust pH
2 Add potassium sulfate solution
3 Boil
Determination of Determination Determination
4 Add bar ium chlor ide solution
pyritic iron by of pyritic iron of pyritic iron
5 Filter
atomic absorption by titrimetry by calorimetry
spectroscopy
I I
Precipitate
Filtrate
(discard)
Gravimetric Calculate pyritic
sulfur from
determination
pyritic iron
of sulfate sulfur
NOTE - Organic sulfur = Total sulfur - (sulfate sulfur + pyritic sulfur)
Figure 1 - General schematic representation of the procedure
IS0 157:1996(E)
@ IS0
Section 2: Separation of sulfate and pyritic sulfur
Dilute 420 ml of the hydrochloric acid (2.2.1) to 1 litre
2.1 Principle
with water.
The test portion is extracted with dilute hydrochloric
acid to bring both the sulfate sulfur and the non-pyritic
2.2.3 Nitric acid, dilute, approximately 9 % (mlm).
iron into solution. The pyritic iron and sulfur remain in
the residue which is separated by filtration.
Dilute 130 ml of concentrated nitric acid [approximate-
ly 70 % (mlm)] to 1 litre with water.
2.2 Reagents
2.3 Apparatus
WARNING - Care must be exercised when handling
the reagents, many of which are toxic and corrosive.
2.3.1 Analytical balance, capable of weighing to the
nearest 0,l mg.
During the analysis, unless otherwise stated, use only
reagents of recognized analytical reagent grade and
only distilled water or water of equivalent quality.
2.3.2 Graduated glassware, conforming to the
requirements for class A in the International Stan-
dards prepared by lSO/TC 48, Laboratory glassware
2.2.1 Hydrochloric acid, concentrated, approximately
and related apparatus.
36 % (m/m).
2.3.3 Cold-finger condenser, to fit loosely into the
2.2.2 Hydrochloric acid, dilute, approximately
neck of a 250 ml conical flask (see figure 2).
15 % (m/m).
Approximate dimensions in millimetres
Water inlet -
----
- Water outlet
@ 38
Figure 2 - Cold-finger condenser for the determination of sulfate and pyritic sulfur
IS0 157:1996(E) @ IS0
2.4.2 Extraction
2.4 Procedure
Transfer the test portion to a 250 ml conical flask, add
50 ml of the dilute hydrochloric acid (2.2.2) and fit the
2.4.1 Test portion
cold-finger condenser (2.3.3) into the neck of the
flask. Boil for 30 min, ensuring that a slow stream of
Take a test portion of the mass given in table 1 for the
water is passing through the cold finger. Remove the
expected total sulfur content, weighing to the nearest
condenser and thoroughly rinse back into the flask.
0,l mg.
Filter the mixture through a medium-textured, doubly
acid-washed filter paper into a tall-form beaker. Wash
the residue three times with the dilute hydrochloric
Table 1 - Test portion
acid (2.2.2) and a further three times with hot distilled
water, using a total volume of approximately 30 ml.
Total sulfur content Mass of test portion Retain the filtrate for the determination of sulfate
sulfur (see Section 3). Immediately transfer the
% (m/m)
g
washed, undissolved residue and filter paper to a
< 0,7
250 ml conical flask, add 50 ml of the dilute nitric acid
0,7 to 2,0
(2.2.3) and retain for the determination of pyritic sulfur
> 2,0
(see Section 4).
IS0 157:1996(E)
@ IS0
Section 3: Determination of sulfate sulfur
3.3.3 Electrically-heated muffle furnace, capable of
3.1 Principle
being maintained at 800 “C + 25 OC, with an adequate
ventilation rate.
The sulfate sulfur extracted by dilute hydrochloric acid
from the test portion is determined gravimetrically by
3.3.4 Crucible, of platinum, silica or glazed por-
precipitation with barium chloride.
celain, of capacity approximately 25 ml.
3.3.5 Flat plate, 6 mm thick, of silica or other suit-
3.2 Reagents
able refractory material, which fits easily into the
muffle furnace (3.3.3).
WARNING - Care must be exercised when handling
the reagents, many of which are toxic and corrosive.
3.3.6 Gooch crucible, of glazed porcelain or sin-
tered glass.
During the analysis, unless otherwise stated, use only
reagents of recognized analytical reagent grade and
only distilled water or water of equivalent purity.
3.3.7 Air oven, capable of being maintained at a
temperature of 130 “C + 10 “C.
3.2.1 Hydrogen peroxide, solution, approximately
3.3.8 Filter cone, made of porcelain, of diameter
30 % (m/m).
25 mm.
3.2.2 Methyl red, indicator solution.
3.4 Procedure
Dissolve 1 g of 2-(4-dimethylaminophenylazo)benzoic
acid, sodium salt (methyl red) in 1 litre of water.
To the filtrate from the hydrochloric acid extraction
(see 2.4.2), add 5 ml of the hydrogen peroxide sol-
3.2.3 Ammonia, concentrated, solution not less than ution (3.2.1) and boil for 5 min to convert all the sol-
25 % (m/m). uble iron to the + 3 oxidation state. While still hot,
add 2 or 3 drops of the methyl red indicator solution
(3.2.2) followed by the ammonia solution (3.2.3), drop
3.2.4 Hydrochloric acid, concentrated, approxi-
by drop, until the solution is just alkaline (yellow
mately 36 % (m/m).
colour) and then add a further 5 drops in excess. Filter
the resultant precipitate on a toughened fast filter
3.2.5 Potassium sulfate, approximately 2 g/l sol-
paper into a 250 ml beaker. Wash thoroughly with hot
ution.
water, discarding the precipitate. Cautiously add the
concentrated hydrochloric acid (3.2.4) to the filtrate,
Dissolve approximately 2 g of potassium sulfate in
drop by drop, until the colour of the solution changes
water and dilute to 1 litre.
to pink and then add a further 1 ml in excess. The
volume of the solution shall be between 150 ml and
3.2.6 Barium chloride, approximately 85 g/l sol-
250 ml.
ution.
Add 25,0 ml of the potassium sulfate solution (3.2.5)
Dissolve 100 g of barium chloride dihydrate in water
from a one-mark pipette. Cover the beaker with a
and dilute to 1 litre. Filter before use through a close-
watch glass, heat the covered beaker until the solu-
textured, doubly acid-washed filter-paper or filter-pad.
tion boils and then reduce the heating slightly until
ebullition ceases. Add 10 ml of the cold barium chlo-
Silver nitrate, approximately 17 g/l solution.
3.2.7
ride solution (3.2.6) from a pipette with a delivery time
of approximately 20 s, held so that the barium chloride
Dissolve 17 g of silver nitrate in water and dilute to
falls into the centre of the hot solution, whilst this is
1 litre. Store in a dark glass bottle.
being agitated. Keep the solution just below boiling
point, without agitation, for 30 min.
Filter the solution using one of the following tech-
3.3 Apparatus
niques.
3.3.1 Analytical balance, capable of weighing to the
a) By gravity through an ashless, close-textured,
nearest 0,l mg.
doubly acid-washed filter paper of diameter
100 mm to 125 mm. Carefully fold the filter paper
3.3.2 Graduated glassware, conforming to the and fit it into a fluted, long-stemmed 60° funnel,
requirements for class A in the International Stan- so that the stem remains full of liquid during the
filtration.
dards prepared by ISOITC 48.
IS0 157:1996(E) @ IS0
By gravity through a filter-paper pad prepared sulfate solution (3.2.5) to the filtrate before adding the
b)
from ashless, doubly acid-washed filter paper. To methyl red indicator solution (3.2.2).
prepare the filter-paper pad, shake doubly acid-
washed filter-paper clippings, in pieces of area ap-
with water in a bottle until the
proximately 1 cm*,
3.6 Expression of results
paper is thoroughly disintegrated. Place a filter
cone (3.6.8) in a filter funnel of diameter 75 mm,
The sulfate sulfur content, WS,~, of the sample, ex-
close the stem of the funnel with a finger and add
pressed as a percentage by mass, is given by the
water until the cone is immersed and the funnel
equation
stem is full. Shake sufficient paper pulp onto the
cone to form a pad 5 mm thick and level it with a
m2
flat-ended glass rod. Allow the ex
...
IS0
INTERNATIONAL
STANDARD
Second edition
1996-06-o 1
Coal - Determination of forms of sulfur
Char-bon - DGtermination de la teneur en diffgrentes formes de soufre
Reference number
IS0 157:1996(E)
IS0 157:1996(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work of
preparing International Standards is normally carried out through IS0
technical committees. Each member body interested in a subject for which
a technical committee has been established has the right to be rep-
resented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
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.
International Standard IS0 157 was prepared by Technical Committee
ISO/TC 27, Solid mineral fuels, Subcommittee SC 5, Methods of analysis.
This second edition cancels and replaces the first edition (IS0 157:1975),
of which it constitutes a technical revision.
Annex A of this International Standard is for information only.
0 IS0 1996
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Orga nization Standardi zation
for
Case postale 56 l CH-121 1G eneve 20 l Switzerland
Printed in Switzerland
@ IS0 IS0 157:1996(E)
Introduction
For many purposes, a knowledge of the total sulfur content of a coal is
sufficient, but for certain work it is also necessary to know how the sulfur
is distributed between the coal substance and the mineral matter. In
particular, such information may be required in connection with coal classi-
fication and cleaning.
Sulfur is usually present in coal in three forms, viz:
sulfate sulfur, i.e. the sulfur present in the form of inorganic sulfates;
a)
b) pyritic sulfur, i.e. the sulfur present in the form of pyrites and marca-
site;
c) organic sulfur, i.e. the sulfur present in the form of organic sulfur
compounds.
This page intentionally left blank
IS0 157:1996(E)
INTERNATIONAL STANDARD @ IS0
Coal - Determination of forms of sulfur
Section 1: General
IS0 5069-Z: 1983, Brown coals and /ignites - Prin-
1.1 Scope
ciples of sampling - Part 2: Sample preparation for
determination of moisture content and for general
This International Standard specifies methods of
analysis.
determining the sulfate and pyritic sulfur contents of
coals, including brown coals and Iignites, and of
calculating the amount of organic sulfur present.
1.3 Principle
1.2 Normative references
The procedure described in this International Standard
The following standards contain provisions which,
utilizes the differential solubilities of sulfates and
through reference in this text, constitute provisions of
pyrites in dilute hydrochloric and nitric acids under
this International Standard. At the time of publication,
reflux conditions, such that each can be taken in
the editions indicated were valid. All standards are
solution successively and determined directly.
subject to revision, and parties to agreements based
on this International Standard are encouraged to
A general schematic representation of the procedure
investigate the possibility of applying the most recent
is given in figure 1.
editions of the standards indicated below. Members
of IEC and IS0 maintain registers of currently valid
International Standards.
1.4 Preparation of the test sample
IS0 331:1983, Coal - Determination of moisture in
the analysis sample - Direct gravimetric method.
The test sample is the general analysis test sample
prepared in accordance with IS0 1988 or IS0 5069-2,
IS0 334: 1993, Solid mineral fuels - Determination of
as appropriate.
total sulfur - Eschka method.
Grind about 25 g of the sample to pass a sieve of
IS0 351 :I 995, Solid mineral fuels - Determination of
aperture 75 urn and ensure that its moisture content
total sulfur - High temperature combustion method.
is in equilibrium with the laboratory atmosphere,
exposing it if necessary in a thin layer for the mini-
IS0 1015: 1992, Brown coals and /ignites - Determi- mum time required to achieve equilibrium.
nation of moisture content - Direct volumetric
method.
Before commencing the determination, thoroughly
mix the test sample for at least 1 min, preferably by
IS0 1170:1977, Coal and coke - Calculation of analy- mechanical means.
ses to different bases.
If the results are to be calculated other than on an air-
IS0 1988: 1975, Hard coal - Sampling. dried basis (see 6.1) then, after weighing the test
portion (see 2.4), determine the moisture content
using a further portion of the test sample by the
IS0 5068: 1983, Brown coals and /ignites - Determi-
method described in IS0 331, IS0 1015 or IS0 5068,
nation of moisture content - Indirect gravimetric
as appropriate.
method.
IS0 157:1996(E)
Coal sample (2 g to 8 g)
1 Reflux in dilute hydrochloric acid
Filtrate Insoluble residue
(Iron in + 2 and + 3 oxidation states)
ic ac id
Add hydrogen peroxide
(Iron in + 3 oxidation state) Filtrate (contains insoluble residue
pyritic iron) (discard)
1 Add ammonia solution
2 Filter
1 Add hydrogen peroxide
2 Boil
4-l
3 COOL
Filtrate Precipitate
(discard)
Alternative finishes
1 Adjust pH
2 Add potassium sulfate solution
3 Boil
Determination of Determination Determination
4 Add bar ium chlor ide solution
pyritic iron by of pyritic iron of pyritic iron
5 Filter
atomic absorption by titrimetry by calorimetry
spectroscopy
I I
Precipitate
Filtrate
(discard)
Gravimetric Calculate pyritic
sulfur from
determination
pyritic iron
of sulfate sulfur
NOTE - Organic sulfur = Total sulfur - (sulfate sulfur + pyritic sulfur)
Figure 1 - General schematic representation of the procedure
IS0 157:1996(E)
@ IS0
Section 2: Separation of sulfate and pyritic sulfur
Dilute 420 ml of the hydrochloric acid (2.2.1) to 1 litre
2.1 Principle
with water.
The test portion is extracted with dilute hydrochloric
acid to bring both the sulfate sulfur and the non-pyritic
2.2.3 Nitric acid, dilute, approximately 9 % (mlm).
iron into solution. The pyritic iron and sulfur remain in
the residue which is separated by filtration.
Dilute 130 ml of concentrated nitric acid [approximate-
ly 70 % (mlm)] to 1 litre with water.
2.2 Reagents
2.3 Apparatus
WARNING - Care must be exercised when handling
the reagents, many of which are toxic and corrosive.
2.3.1 Analytical balance, capable of weighing to the
nearest 0,l mg.
During the analysis, unless otherwise stated, use only
reagents of recognized analytical reagent grade and
only distilled water or water of equivalent quality.
2.3.2 Graduated glassware, conforming to the
requirements for class A in the International Stan-
dards prepared by lSO/TC 48, Laboratory glassware
2.2.1 Hydrochloric acid, concentrated, approximately
and related apparatus.
36 % (m/m).
2.3.3 Cold-finger condenser, to fit loosely into the
2.2.2 Hydrochloric acid, dilute, approximately
neck of a 250 ml conical flask (see figure 2).
15 % (m/m).
Approximate dimensions in millimetres
Water inlet -
----
- Water outlet
@ 38
Figure 2 - Cold-finger condenser for the determination of sulfate and pyritic sulfur
IS0 157:1996(E) @ IS0
2.4.2 Extraction
2.4 Procedure
Transfer the test portion to a 250 ml conical flask, add
50 ml of the dilute hydrochloric acid (2.2.2) and fit the
2.4.1 Test portion
cold-finger condenser (2.3.3) into the neck of the
flask. Boil for 30 min, ensuring that a slow stream of
Take a test portion of the mass given in table 1 for the
water is passing through the cold finger. Remove the
expected total sulfur content, weighing to the nearest
condenser and thoroughly rinse back into the flask.
0,l mg.
Filter the mixture through a medium-textured, doubly
acid-washed filter paper into a tall-form beaker. Wash
the residue three times with the dilute hydrochloric
Table 1 - Test portion
acid (2.2.2) and a further three times with hot distilled
water, using a total volume of approximately 30 ml.
Total sulfur content Mass of test portion Retain the filtrate for the determination of sulfate
sulfur (see Section 3). Immediately transfer the
% (m/m)
g
washed, undissolved residue and filter paper to a
< 0,7
250 ml conical flask, add 50 ml of the dilute nitric acid
0,7 to 2,0
(2.2.3) and retain for the determination of pyritic sulfur
> 2,0
(see Section 4).
IS0 157:1996(E)
@ IS0
Section 3: Determination of sulfate sulfur
3.3.3 Electrically-heated muffle furnace, capable of
3.1 Principle
being maintained at 800 “C + 25 OC, with an adequate
ventilation rate.
The sulfate sulfur extracted by dilute hydrochloric acid
from the test portion is determined gravimetrically by
3.3.4 Crucible, of platinum, silica or glazed por-
precipitation with barium chloride.
celain, of capacity approximately 25 ml.
3.3.5 Flat plate, 6 mm thick, of silica or other suit-
3.2 Reagents
able refractory material, which fits easily into the
muffle furnace (3.3.3).
WARNING - Care must be exercised when handling
the reagents, many of which are toxic and corrosive.
3.3.6 Gooch crucible, of glazed porcelain or sin-
tered glass.
During the analysis, unless otherwise stated, use only
reagents of recognized analytical reagent grade and
only distilled water or water of equivalent purity.
3.3.7 Air oven, capable of being maintained at a
temperature of 130 “C + 10 “C.
3.2.1 Hydrogen peroxide, solution, approximately
3.3.8 Filter cone, made of porcelain, of diameter
30 % (m/m).
25 mm.
3.2.2 Methyl red, indicator solution.
3.4 Procedure
Dissolve 1 g of 2-(4-dimethylaminophenylazo)benzoic
acid, sodium salt (methyl red) in 1 litre of water.
To the filtrate from the hydrochloric acid extraction
(see 2.4.2), add 5 ml of the hydrogen peroxide sol-
3.2.3 Ammonia, concentrated, solution not less than ution (3.2.1) and boil for 5 min to convert all the sol-
25 % (m/m). uble iron to the + 3 oxidation state. While still hot,
add 2 or 3 drops of the methyl red indicator solution
(3.2.2) followed by the ammonia solution (3.2.3), drop
3.2.4 Hydrochloric acid, concentrated, approxi-
by drop, until the solution is just alkaline (yellow
mately 36 % (m/m).
colour) and then add a further 5 drops in excess. Filter
the resultant precipitate on a toughened fast filter
3.2.5 Potassium sulfate, approximately 2 g/l sol-
paper into a 250 ml beaker. Wash thoroughly with hot
ution.
water, discarding the precipitate. Cautiously add the
concentrated hydrochloric acid (3.2.4) to the filtrate,
Dissolve approximately 2 g of potassium sulfate in
drop by drop, until the colour of the solution changes
water and dilute to 1 litre.
to pink and then add a further 1 ml in excess. The
volume of the solution shall be between 150 ml and
3.2.6 Barium chloride, approximately 85 g/l sol-
250 ml.
ution.
Add 25,0 ml of the potassium sulfate solution (3.2.5)
Dissolve 100 g of barium chloride dihydrate in water
from a one-mark pipette. Cover the beaker with a
and dilute to 1 litre. Filter before use through a close-
watch glass, heat the covered beaker until the solu-
textured, doubly acid-washed filter-paper or filter-pad.
tion boils and then reduce the heating slightly until
ebullition ceases. Add 10 ml of the cold barium chlo-
Silver nitrate, approximately 17 g/l solution.
3.2.7
ride solution (3.2.6) from a pipette with a delivery time
of approximately 20 s, held so that the barium chloride
Dissolve 17 g of silver nitrate in water and dilute to
falls into the centre of the hot solution, whilst this is
1 litre. Store in a dark glass bottle.
being agitated. Keep the solution just below boiling
point, without agitation, for 30 min.
Filter the solution using one of the following tech-
3.3 Apparatus
niques.
3.3.1 Analytical balance, capable of weighing to the
a) By gravity through an ashless, close-textured,
nearest 0,l mg.
doubly acid-washed filter paper of diameter
100 mm to 125 mm. Carefully fold the filter paper
3.3.2 Graduated glassware, conforming to the and fit it into a fluted, long-stemmed 60° funnel,
requirements for class A in the International Stan- so that the stem remains full of liquid during the
filtration.
dards prepared by ISOITC 48.
IS0 157:1996(E) @ IS0
By gravity through a filter-paper pad prepared sulfate solution (3.2.5) to the filtrate before adding the
b)
from ashless, doubly acid-washed filter paper. To methyl red indicator solution (3.2.2).
prepare the filter-paper pad, shake doubly acid-
washed filter-paper clippings, in pieces of area ap-
with water in a bottle until the
proximately 1 cm*,
3.6 Expression of results
paper is thoroughly disintegrated. Place a filter
cone (3.6.8) in a filter funnel of diameter 75 mm,
The sulfate sulfur content, WS,~, of the sample, ex-
close the stem of the funnel with a finger and add
pressed as a percentage by mass, is given by the
water until the cone is immersed and the funnel
equation
stem is full. Shake sufficient paper pulp onto the
cone to form a pad 5 mm thick and level it with a
m2
flat-ended glass rod. Allow the excess water to
-m3 x13,74
Ws,s =
drain away by removing the finger from the stem
ml
and lightly tamp the pad round the edges with the
glass rod as drainage ceases. A final wash with
water renders the filter ready for use. After trans-
mass, in grams, of the test portion
is the
ml
ferring the filter-paper pad to the crucible, wipe
for hydrochloric acid extraction;
taken
the funnel successively with two halves of an
ashless filter paper which are then incinerated
is the mass, in grams, of barium sulfate
m2
with the pad.
found i n the determination;
c) By suction through a pad of mineral fibre used for
is the mass, in grams, of barium sulfate
filtration in a Gooch crucible. Before commencing
found in the blank test.
the f
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NORME ISO
INTERNATIONALE 157
Deuxième édition
1996-06-01
Charbon — Détermination de la teneur
en différentes formes de soufre
Coal — Determination of forms of sulfur
A
Numéro de référence
Avant-propos
L'ISO (Organisation internationale de normalisation) est une
fédération mondiale d'organismes nationaux de normalisation
(comité membres de l'ISO). L'élaboration des Normes
internationales est en général confiée aux comités techniques de
l'ISO. Chaque comité membre intéressé par une étude a le droit de
faire partie du comité technique créé à cet effet. Les organisations
internationales, gouvernementales et non gouvernementales, en
liaison avec l'ISO participent également aux travaux. L'ISO
collabore étroitement avec la Commission électrotechnique
internationale (CEI) en ce qui concerne la normalisation
électrotechnique.
Les projets de Normes internationales adoptés par les comités
techniques sont soumis aux comités membres pour vote. Leur
publication comme Normes internationales requiert l'approbation de
75 % au moins des comités membres votants.
La Norme internationale ISO 157 a été élaborée par le comité
technique ISO/TC 27, Combustibles minéraux solides, sous-comité
SC 5, Méthodes d'analyse.
Cette deuxième édition annule et remplace la première édition
(ISO 157:1975), dont elle constitue une révision technique.
L’annexe A de la présente Norme internationale est donnée
uniquement à titre d’information.
© ISO 1996
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ii
©
ISO ISO 157:1996(F)
Introduction
Dans de nombreux cas, il est suffisant de connaître la teneur en
soufre total du charbon, mais certains travaux nécessitent parfois
de connaître la façon dont le soufre est réparti entre la substance
charbonneuse et les matières minérales. La nécessité de posséder
ces informations peut notamment être en rapport avec la
classification et le nettoyage du charbon.
Le soufre se trouve habituellement dans le charbon sous trois
formes, à savoir:
Sulfate de soufre dit soufre «sulfate»:
a) soufre sulfate, c'est-à-dire le soufre présent sous forme de
sulfates inorganiques;
b) soufre pyritique, c'est-à-dire le soufre présent sous forme de
pyrites et de marcassite;
c) soufre organique, c'est-à-dire le soufre présent sous forme de
composés sulfurés organiques.
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NORME INTERNATIONALE ISO ISO 157:1996(F)
Charbon — Détermination de la teneur en différentes
formes de soufre
Section 1: Généralités
1.1 Domaine d'application
La présente Norme internationale spécifie des méthodes permettant de déterminer la teneur en soufre
«sulfate» et en soufre pyritique présents dans les charbons, y compris les charbons bruns et les lignites,
et permettant de calculer la quantité de soufre organique présent.
1.2 Références normatives
Les normes suivantes contiennent des dispositions qui, par suite de la référence qui en est faite,
constituent des dispositions valables pour la présente Norme internationale. Au moment de la
publication, les éditions indiquées étaient en vigueur. Toute norme est sujette à révision et les parties
prenantes des accords fondés sur la présente Norme internationale sont invitées à rechercher la
possibilité d'appliquer les éditions les plus récentes des normes indiquées ci-après. Les membres de la
CEI et de l'ISO possèdent le registre des Normes internationales en vigueur à un moment donné.
Charbon — Détermination de l'humidité de l'échantillon pour analyse — Méthode
ISO 331:1983,
gravimétrique directe.
Combustibles minéraux solides — Dosage du soufre total — Méthode Eschka.
ISO 334:1992,
ISO 351:1984, Combustibles minéraux solides — Dosage du soufre total — Méthode par
combustion à haute température
.
ISO 1015:1992, Charbons bruns et lignites — Détermination de l'humidité — Méthode volumétrique
directe.
ISO 1170:1977, Charbon et coke — Calculs pour les analyses par rapport à différentes bases.
ISO 1988:1975, Charbons et lignites durs — Échantillonnage.
ISO 5068:1983, Charbons bruns et lignites — Détermination de l'humidité — Méthode gravimétrique
indirecte.
ISO 5069-2:1983,Charbons bruns et lignites — Principes d’échantillonnage — Partie 2: Préparation
des échantillons pour la détermination de l'humidité et pour l'analyse générale.
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ISO
1.3 Principe
Le mode opératoire décrit dans la présente Norme internationale exploite les différences de solubilité
des sulfates et des pyrites dans les acides chlorhydrique et nitrique dilués sous reflux, de sorte que l'un
et l'autre puissent être prélevés successivement en solution et dosés directement.
Une représentation schématique générale du mode opératoire est indiquée à la figure 1.
1.4 Préparation de l'échantillon pour essai
L'échantillon pour essai est l'échantillon destiné aux analyses générales, préparé conformément à
l'ISO 1988 ou à l'ISO 5069-2 selon les cas.
Moudre environ 25 g d'échantillon de manière à leur faire traverser un tamis de 75 μm d'ouverture de
maille et en veillant à ce que le taux d’humidité de l'échantillon soit équilibré dans l'atmosphère d'essai,
et en l'exposant si nécessaire à l'état de couche mince, pendant la durée minimale nécessaire pour
parvenir à l'équilibre.
Avant de commencer le dosage, bien homogénéiser l'échantillon pour essai pendant au moins 1 min, de
préférence par un moyen mécanique.
S'il est prévu de calculer les résultats autrement que sur un charbon sec à l'air (voir 6.1), déterminer,
après avoir pesé la prise d'essai (voir 2.4), le taux d’humidité en utilisant une portion supplémentaire de
l'échantillon pour essai, en appliquant la méthode décrite dans l’ISO 331, l’ISO 1015 ou l’ISO 5068 selon
les cas.
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ISO
NOTE — Soufre organique = soufre total – (soufre sulfate + soufre pyritique)
Figure 1 — Représentation schématique générale du mode opératoire
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ISO
Section 2: Séparation du soufre sulfate et du soufre pyritique
2.1 Principe
La prise d'essai est extraite avec de l'acide chlorhydrique dilué, afin de faire passer à la fois le soufre
sulfate et le fer non pyritique en solution. Le fer et le soufre pyritiques restent présents dans le résidu
qui résulte de la séparation par filtration.
2.2 Réactifs
AVERTISSEMENT — Apporter le plus grand soin à la manipulation des réactifs, un grand nombre
d'entre eux étant toxiques et corrosifs.
Au cours de l’analyse, sauf indication différente, utiliser uniquement des réactifs de qualité analytique
reconnue, et de l'eau distillée ou de l’eau de pureté équivalente.
2.2.1 Acide chlorhydrique, concentré, à environ 36 % (m/m).
2.2.2 Acide chlorhydrique, dilué, à environ 15 % (m/m).
Diluer 420 ml d'acide chlorhydrique (2.2.1) à 1 litre avec de l'eau.
2.2.3 Acide nitrique, dilué, à environ 9 % (m/m).
Diluer 130 ml d'acide nitrique concentré [environ 70 % (m/m)] à 1 litre avec de l'eau.
2.3 Appareillage
2.3.1 Balance analytique, permettant la pesée à 0,1 g près.
2.3.2 Verrerie graduée, conforme aux prescriptions de classe A selon les Normes internationales
Verrerie de laboratoire et appareils connexes
élaborées par l'ISO/TC 48, .
2.3.3 Réfrigérant doigt de gant, adaptable au col d'une fiole conique de 250 ml (voir figure 2).
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ISO
Dimensions approximatives en millimètres
Figure 2 — Réfrigérant doigt de gant destiné au dosage du soufre sulfate et du soufre pyritique
2.4 Mode opératoire
2.4.1 Prise d'essai
Prélever une prise d'essai de la masse indiquée dans le tableau 1 en fonction de la teneur en soufre
total escomptée, en pesant à 0,1 mg près.
Tableau 1 — Prise d'essai
Teneur en soufre total Masse de la prise d'essai
% (m/m) g
< 0,7 8
0,7 à 2,0 5
< 2,0 2
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ISO
2.4.2 Extraction
Transvaser la prise d'essai dans une fiole conique de 250 ml, ajouter 50 ml d'acide chlorhydrique dilué
(2.2.2) et adapter le réfrigérant (2.3.3) au col de la fiole. Faire bouillir pendant 30 min, en veillant à ce
que l'eau traverse le condenseur selon un débit lent. Ôter le réfrigérant et rincer soigneusement vers
l'intérieur de la fiole. Filtrer le mélange sur un papier à grain moyen lavé à deux reprises avec de l'acide
chlorhydrique dans un bécher de grande contenance. Laver trois fois le résidu avec de l'acide
chlorhydrique dilué (2.2.2) et trois fois supplémentaires avec de l'eau distillée chaude, en utilisant un
volume total d'environ 30 ml. Conserver le filtrat destiné au dosage du soufre sulfate (voir section 3).
Transvaser immédiatement le résidu lavé non dissous et le papier filtre dans une fiole conique de
250 ml, ajouter 50 ml d'acide nitrique dilué (2.2.3) et conserver l'ensemble pour le dosage du soufre
pyritique (voir section 4).
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ISO
Section 3: Dosage du soufre «sulfate»
3.1 Principe
La teneur en soufre «sulfate» extrait de la prise d'essai à l'aide d'acide chlorhydrique dilué est
déterminée par un dosage gravimétrique par précipitation avec du chlorure de baryum.
3.2 Réactifs
AVERTISSEMENT — Apporter le plus grand soin à la manipulation des réactifs, dont plusieurs
sont toxiques et corrosifs.
Au cours de l’analyse, sauf indication différente, utiliser uniquement des réactifs de qualité analytique
reconnue, et de l'eau distillée ou de l’eau de pureté équivalente.
m/m
3.2.1 Peroxyde d'hydrogène, solution à environ 30 % ( ).
3.2.2 Rouge de méthyle, solution d'indicateur.
Dissoudre 1 g d'acide 2-(4-diméthylaminophénylazo)benzoïque, sel de sodium (rouge de méthyle) dans
1 litre d'eau.
3.2.3 Ammoniac, solution concentrée, de concentration au moins égale à 25 % (m/m).
, concentré, à environ 36 % (m/m).
3.2.4 Acide chlorhydrique
3.2.5 Sulfate de potassium, solution à environ 2 g/l.
Dissoudre environ 2 g de sulfate de potassium dans de l'eau et diluer à 1 litre.
3.2.6 Chlorure de baryum, solution à environ 85 g/l.
Dissoudre 100 g de chlorure de baryum dihydrate dans de l'eau et diluer à 1 litre. Filtrer, avant
utilisation, à travers un papier filtre ou un tampon de papier filtre à grain fin, lavé à deux reprises avec de
l'acide.
3.2.7 Nitrate d'argent, solution à environ 17 g/l.
Dissoudre 17 g de nitrate d'argent dans de l'eau et diluer à 1 litre. Conserver dans une bouteille en verre
teinté.
3.3 Appareillage
3.3.1 Balance analytique, permettant la pesée à 0,1 mg près.
, conforme aux prescriptions de classe A selon les Normes internationales
3.3.2 Verrerie graduée
élaborées par l'ISO/TC 48.
3.3.3 Four à moufle électrique, pouvant être maintenu à 800 °C ± 25 °C, équipé d'une vitesse
d'aération adéquate.
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ISO
3.3.4 Creuset, en platine, silice ou porcelaine émaillée, d'environ 25 ml de contenance.
3.3.5 Plaque, de 6 mm d'épaisseur, en silice ou en un autre matériau réfractaire convenable, pouvant
être facilement introduite dans le four à moufle (3.3.3).
3.3.6 Creuset de Gooch, en porcelaine émaillée ou en verre fritté.
3.3.7 Étuve à circulation d'air, pouvant être maintenue à une température de 130 °C ± 10 °C.
3.3.8 Cône de filtration, en porcelaine, de 25 mm de diamètre.
3.4 Mode opératoire
Ajouter, au filtrat recueilli par extraction à l'acide chlorhydrique (voir 2.4.2), 5 ml de solution de peroxyde
d'hydrogène (3.2.1) et faire bouillir pendant 5 min afin que tout le fer soluble soit converti à l'état
d'oxydation +3. La solution étant toujours chaude, ajouter 2 ou 3 gouttes de solution d'indicateur au
rouge de méthyle (3.2.2), puis la solution d'ammoniac (3.2.3), au goutte à goutte, jusqu'à ce que la
solution soit juste alcaline (couleur jaune), et rajouter 5 gouttes en excès. Filtrer le précipité résultant à
travers un papier à filtration rapide renforcé, vers un bécher de 250 ml. Laver soigneusement avec de
l'eau chaude, en rejetant le précipité. Ajouter précautionneusement l'acide chlorhydrique concentré
(3.2.4) dans le filtrat, au goutte à goutte, jusqu'à ce que la couleur de la solution vire au rose, puis
rajouter 1 ml en excès. Le volume de la solution doit être compris entre 150 ml et 250 ml.
Ajouter 25,0 ml de solution de sulfate de potassium (3.2.5) à l'aide d'une pipette à trait de repère unique.
Couvrir le bécher à l'aide d'un verre de montre, échauffer le bécher couvert jusqu'à l'ébullition de la
solution, puis réduire légèrement l'échauffement jusqu'à ce que l'ébullition cesse. Ajouter 10 ml de
solution de chlorure de baryum froide (3.2.6) à l'aide d'une pipette ayant un temps d'écoulement
d'environ 20 s, en faisant en sorte que le chlorure de baryum tombe au milieu de la solution chaude, tout
en pratiquant une agitation. Maintenir la solution juste au-dessous de son point d'ébullition pendant
30 min, sans agiter.
Filtrer la solution selon l'une des techniques suivantes:
a) Par gravité sur un filtre exempt de cendres, à grain fin, lavé à deux reprises avec de l'acide, ayant
un diamètre compris entre 100 mm et 125 mm. Laver soigneusement le papier filtre et l'introduire
dans un entonnoir à 60° cannelé et à longue tige, de manière que le col reste rempli de liquide durant
la filtration.
b) Par gravité à travers un tampon de papier filtre confectionné à l'aide de papier filtre exempt de
cendres lavé à deux reprises avec de l'acide. Pour préparer le tampon de papier filtre, agiter des
morceaux de papier filtre pliés, lavés à deux reprises avec de l'acide et mesurant environ 1 cm², dans
une bouteille remplie d'eau, jusqu'à la désintégration complète du papier. Disposer le cône filtrant
(3.3.8) dans un entonnoir de filtration de 75 mm de diamètre, obturer le col de l'entonnoir avec un
doigt et ajouter de l'eau jusqu'à ce que le cône soit immergé et que le col de l'entonnoir soit rempli.
Agiter une quantité suffisante de pâte à papier dans le cône pour former un tampon de 5 mm
d'épaisseur et égaliser celui-ci à l'aide d'une tige à extrémité plate. Laisser s'égoutter l'excédent d'eau
en retirant le doigt du col et en pressant légèrement le tampon au niveau des bords avec la tige en
verre, jusqu'à ce que l'égouttement soit terminé. Rendre le tampon prêt à l'emploi en pratiquant un
dernier lavage à l'eau. Après avoir transféré le tampo
...
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