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Ref. No.: ISO/R 157 - 1960 (E)
IS0
OR G A N IZ AT I ON FOR STAND AR D I Z AT 1 ON
INTERN AT1 ON AL
IS0 RECOMMENDATION
R 157
DETERMINATION OF FORMS OF SULPHUR IN COAL
1st EDITION
June 1960
COPYRIGHT RESERVED
The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of 1SO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 157, Determination of'Forms of Sulphiir in Coal, was drawn
up by Technical Committee ISO/TC 27, Solid Mineral Fuels, the Secretariat of which is held by
the British Standards Institution (B.S.I.).
At the second meeting of the Technical Committee, held in London, in December 1951,
the question of the determination of forms of sulphur in coal was discussed for the first time,
and in July 1952, a draft proposal was circulated.
At the third meeting of ISO/TC 27, held in London, in November 1953, a second draft
proposal, modified in line with the comments received, was submitted to the Technical Committee,
together with a possible alternative method based on comments from Germany, but there was
not enough time to discuss them adequately. The members of the Committee were asked to
send in their comments in writing, and the subject was also taken up by Working Groupe No. 3,
Sulphur. At the latter's first meeting, in May 1954, it was agreed, after practical demonstra-
tions, that the reduction method could be regarded as a satisfactory alternative to the oxydation
method for the determination of pyritic sulphur.
A third draft proposal was worked out and discussed at the second metting of Working
Group No. 3, in October 1954, before being circulated to the members of ISO/TC 27 in January
J
1955. This draft, which contained alternative methods for sulfate sulphur (gravimetric and
titrimetric) and alternative methods for pyritic sulphur (oxidation and reduction), was examined,
together with a report on the experimental work on which was based, at the fourth meeting of
ISO/TC 27, held in Stockholm in June 1955. It was decided-with a reservation by France,
which would have preferred to see only one method standardized, to use the third draft proposal
as the basis for setting up a Draft IS0 Recommendation for the determination of forms of
sulphur.
This draft proposal was circulated in March 1956 to all the members of ISO/TC 27 for
ratification and, with minor changes, was adopted as a Draft IS0 Recommendation.
On 29 June 1957, the Draft IS0 Recommendation (NO 169) was distributed to all the
IS0 Member Bodies and was approved, subject to some modifications, by the following 24 (out
of a total of 38) Member Bodies:
Austria lndia * Portugal
Belgium * Ireland Romania
* Canada * Italy Spain
Czechoslovakia Japan Sweden
Denmark Mexico * Switzerland
* Germany Netherlands United Kingdom
* U.S.A.
* Greece * New Zealand
* Poland * Yugoslavia
Hungary
One Member Body opposed the approval of the Draft: France.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0
Council, which decided, in June 1960, to accept it as an IS0 RECOMMENDATION.
* These Member Bodies stated that they had no objection to the Draft being approved.
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ISO/R 157-1960 (E)
IS0 Recommendation R 157 June 1960
DETERMINATION OF FORMS OF SULPHUR IN COAL
1. PRINCIPLE
The principle to be applied for the determination of sulphur in coal depends on the form in which
the sulphur is combined in the coal.
Sulphur is usually combined in coal in three ways, as
inorganic sulphates,
iron pyrites (FeS,) and
organic sulphur compounds.
The amounts of sulphur so combined are known respectively as
sulphate sulphur,
pyritic sulphur,
organic sulphur.
1.1 Sulphate sulphur is determined by extracting coal with dilute hydrochloric acid and deter-
mining the sulphur in the extract,
either gravimetrically, see section 2, Gravimetric Method,
titrimetrically, see section 3, Titrimetric Method.
or
1.2 Pyritic sulphur is insoluble in dilute hydrochloric acid, but it is quantitatively dissolved by
dilute nitric acid under the experimental conditions described.
It is conveniently determined by an indirect method, that is by determining the amount of
iron combined in the pyritic state and calculating the amount of sulphur associated with
this iron, see section 4, Oxidation Method.
Alternatively, the coal is finely crushed to release the particles of pyrites, the sulphur in
which is reduced to hydrogen sulphide by reaction with nascent hydrogen and is absorbed
in cadmium acetate and determined iodometrically, see section 5, Reduction Method.
1.3 Organic sulphur is calculated by deducting the sum of percentages of “sulphate” and
“pyritic” sulphur from the total sulphur in the coal, see section 6.
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ISO/R 157-1960 (E)
2. SULPHATE SULPHUR - GRAVIMETRIC METHOD
2.1 Apparatus
All graduated apparatus should be of the best analytical quality obtainable, and the balance
used should be sensitive to 0.1 mg.
2.1.1 Electrically heated mufle furnace, capable of maintaining a substantially uniform tem-
perature zone at 800 f 25 OC, and a flat plate, 6 mm thick, of silica (or other suitable
insulating material), which fits easily in the muffle, or
2.1.2 Air oven, capable of being maintained at 130 & IO'C, for drying Gooch filters.
2.1.3 Coldfinger condenser (see Fig. 1 below).
Water inlet -=-.-I
16
FIG. 1. - Cold finger condenser
for the determination of sulphate and pyritic sulphur
2.2 Reagents
All reagents are to be of analytical reagent quality and distilled water is to be used throughout.
2.2.1 Hydrochloric acid, specific gravity d 1.18.
Hydrochloric acid. Dilute 420 ml of the hydrochloric acid (2.2.1) to 1 litre with water.
2.2.2
Hydrochloric acid. Dilute 42 ml of the hydrochloric acid (2.2.1) to 1 litre with water.
2.2.3
Barium chloride solution, 8.5 per cent (weight/volume). Dissolve 100 g of barium
2.2.4
chloride dihydrate in water and dilute to 1 litre. Filter before use through a close-
textured, double acid-washed filter paper or filter paper pad.
2.2.5 Ammonia solution, specific gravity d 0.88 or nearest obtainable.
Bromine water. Prepare a saturated solution of bromine in water.
2.2.6
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ISO/R 157-1960 (E)
I
2.2.7 Standard sulphate solution. Dissolve 0.600 O g of potassium sulphate in water and dilute
to 1 O00 ml. 10 ml of standard sulphate solution ~
0.008 O g of BaSO,.
2.2.8 Methyl orange indicator solution. Dissolve 0.5 g of dimethyl-amino-azobenzene-sul-
phonic acid (methyl orange) in 1 litre of water; filter the cold solution if a precipitate
separates.
2.3 Procedure
Before commencing the determination, mix the air-dried sample of coal, ground to pass a
sieve of 0.2 mm aperture, thoroughly for at least one minute, preferably by mechanical
means.
Weigh accurately about 5 g of the sample, transfer to a 250 ml conical flask, add 50 ml of
the hydrochloric acid (2.2.2) and fit a cold finger condenser (see Fig. 1) into the neck of the
flask. Boil for 30 minutes and filter through a medium-textured, double acid-washed paper.
Wash 6 times with the hydrochloric acid (2.2.3), using a total quantity of about 20 ml.
Discard the residual coal.
Add 1 ml of the bromine water (2.2.6) to the filtrate and boil for 5 minutes to ensure that all
the iron is in the ferric state. Precipitate the iron by adding the ammonia solution (2.2.5)
in a slow stream until a slight excess is present and add 5 ml in excess. Filter on a fast
toughened filter paper into a 250 ml beaker. Wash with hot water, preserving the precipitate
(precipitate A) for the determination of non-pyritic iron, if the Oxidation Method is to be
employed for the determination of pyritic sulphur (see clause 4.3, last paragraph).
To the filtrate add 2 or 3 drops of the methyl orange indicator solution (2.2.8) and then,
cautiously, add the hydrochloric acid (2.2.1) until the colour of the solution changes, then
add 1 ml of acid in excess. The volume of the solution should be between 150 and 250 ml.
10.0 ml of the standard sulphate solution (2.2.7), heat the covered beaker until the solu-
Add
tion boils and then reduce the heating slightly until ebullition ceases. Add 10 ml of the
cold barium chloride solution (2.2.4) from a pipette with a delivery time of approximately
20 seconds, so that the barium chloride falls into the centre of the hot solution, which is
being agitated. Keep the solution just below boiling point, without agitation, for 30 minutes
(see Note 1, page 6).
Filter, using one of the following techniques (see Note 2, page 6):
1. By gravity through an ashless, close-textured, double acid-washed filter paper of 10 to
12.5 cm diameter in a fluted, long-stemmed 60" funnel, or
2. By gravity through a filter paper pad prepared from ashless, double acid-washed paper, or
3. Under suction, using asbestos in a Gooch crucible, previously dried for 1 hour at
130 f 10 "C and weighed.
Wash the filter with hot water, using not more than 250 ml, until the last 20 ml of the washings
give not more than a faint opalescence with silver nitrate solution.
Place the wet filter paper (from technique 1 or 2) in a previously ignited and weighed silica,
porcelain or platinum capsule on the silica plate and insert into the muffle furnace for
15 minutes at 800 f 25 "C (see Note 3, page 6), then allow to cool and weigh. If a Gooch
crucible is used (technique 3), dry for 1 hour at 130 f 1O"C, then allow to cool and weigh.
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ISO/R 157-1960 (E)
NOTES
1. Period of standing. It has been shown that complete recovery of the barium sulphate can be made by
filtering after 30 minutes under the conditions recommended, namely, in the presence of hydrochloric
acid of concentration approximately 0.05 N and a large excess of barium ions. Under these conditions,
30 minutes standing time mentioned above.
the precipitate of barium sulphate should settle during the
2. Filtration of the precipitate. Rapid filtration is obtained by any of the techniques 1, 2 or 3, indicated in
clause 2.3.
Technique I. A filter circle should be carefully folded to fit the funnel.
Technique 2. To prepare the filter paper pad, shake double acid-washed filter paper clippings, in pieces
of approximately 1 cm2 area, with distilled water in a bottle until the paper is thoroughly disintegrated.
Place a 2.5 cm porcelain filter cone in a 7.5 cm funnel, close the stem of the funnel with a finger and add
distilled water until the cone is immersed and the funnel stem is full. Shake onto the cone sufficient pulp
to form a pad 5 nim thick and level it with a flat-ended glass rod. Allow the excess water to drain away
by removing the finger from the stem of the funnel 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 transferring the filter paper pad to the silica capsule, wipe the funnel successively with two halves
of a circle of ashless filter paper, which are then incinerated with the pad.
Technique 3. The Gooch crucible should be used with specially prepared filtration asbestos.
3. Ignition. Under these conditions ignition of the wet filter paper is achieved rapidly; with mechanical
loss is avoided by the use of a thick insulating plate.
2.3.1 Blank determination. Carry out a blank determination under the same conditions, but
omitting the coal. Add 10.0 ml of the standard sulphate solution (2.2.7) to the filtrate
before adding the methyl orange indicator solution (2.2.8). The weight of the barium
sulphate found in the blank determination is deducted from that obtained in the full
determination.
2.4 Calculation of results
If W = weight of sample, expressed in grammes,
a = weight of barium sulphate found in the full determination, expressed in
gr ammes,
=
weight of barium sulphate found in the blank determination, expressed in
b
grammes,
percentage of sulphate sulphur in the sample,
S, =
13.74 (a - b)
then s, =
W
2.5 Tolerances
The results of duplicate determinations carried out at different times in the same laboratory,
on the same sample, by the same operator using the same apparatus, should not differ by
more than 0.02 per cent of sulphate sulphur.
The means of the results of duplicate determinations carried out in different laboratories
on representative samples taken from the same bulk after the last stage of reduction should
not differ by more than 0.03 per cent of sulphate sulphur.
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ISO/R 157 - 1960 (E)
3. SULPHATE SULPHUR - TITRIMETRIC FINISH
3.1 Apparatus
All graduated apparatus should be of the best analytical quality obtainable, and the balance
used should be sensitive to 0.1 mg.
3.1.1 Cation exchanger. The glass column is 20 f 2 cm long, internal diameter 2.0 to 2.5 cm,
and contains 35 & 5 g of cation exchange resin. The column outlet is restricted with
either a sintered glass disk or an S-shaped capillary of 2 to 3 mm internal diameter.
The linear flow rate should be adjusted to approximately 4 cm/min.
3.2 Reagents
All reagents are to be of analytical reagent quality, and distilled water is to be used throughout.
3.2.1 Cation exchange resin* of analytical reagent quality, 0.5 to 1.5 mm.
3.2.2 Potassium iodide.
3.2.3 Hydrochloric acid, specific gravity d 1.18.
3.2.4 Hjdrochloric acid. Dilute 420 ml of the hydrochloric acid (3.2.3) to 1 litre with water.
3.2.5 Hydrochloric acid. Dilute 42 ml of the hydrochloric acid (3.2.3) to 1 litre with water.
3.2.6 Hydmgen peroxide, 30 per cent (weight/volume) (“100 volumes”).
3.2.7 Sodium hydroxide solution, 8 per cent (weight/volume). Dissolve 80 g of sodium hydroxide
in 1 litre of water.
3.2.8 Barium chromate solution, 3 per cent (weight/volume). To 30 g of barium chromate add
100 ml of water and 100 ml of perchloric acid (specific gravity d 1.54) and warm until
solution is complete. Dilute the solution to 1 litre and filter into a storage bottle
through a fine-textured double acid-washed filter paper or filter paper pad. Store
overnight before using.
The solution prepared from commercially available barium chromate should be tested
for suitability. This is done by using it to carry out duplicate determinations, by the
method described under “Procedure” (see clause 3.3), on accurately weighed portions
of between 0.13 and 0.14 g of potassium sulphate. If the mean of the results, expressed
as per cent of the amount of sulphur taken, is less than 99.5 or greater than 100.5, the
barium chromate in question should be rejected.
A satisfactory solution may be prepared by the following method: Dissolve 28.92 g
of barium chloride dihydrate in 500 ml of water. Dissolve 23.00 g of potassium chro-
mate in 500 ml of water. Heat both solutions almost to boiling point and add the
barium chloride solution slowly to the potassium chromate solution, stirring during
the addition. Boil for 5 minutes, filter by suction through a fine-textured double acid-
washed filter paper supported in a Buchner funnel and wash with hot water until the
last 20 ml of the washings give no more than a faint trace of opalescence with silver
nitrate solution.
Wash the precipitate by means of a jet of water into a 2 litre beaker, add 200 ml of
water and 100 ml of perchloric acid (specific gravity d 1.54) and warm until solution is
complete. Dilute the solution to 1 litre with water and filter into a storage bottle through
a fine-textured, double acid-washed filter paper or filter papzr pad.
* Suitable resins are known as Amberlite IR-120 (H) and Lewatit 22.
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ISO/R 157-1960 (E)
3.2.9 Sodium acetate solution, 13.6 per cent (weight/volume). Dissolve either 136 g of
anhydrous sodium acetate or 225 g of the trihydrate in water and dilute to 1 litre.
3.2.10 Sodium acetate solution, 0.9 per cent (weight/volume). Dissolve either 9 g of anhydrous
sodium acetate or 15 g of the trihydrate in water and dilute to 1 litre.
3.2.11 Ammonia solution. Dilute ammonia solution (specific gravity d 0.88 or nearest obtain-
able) with an equal volume of water. Store this solution over calcium oxide to remove
carbonate.
3.2.12
Standard suZphate solution. Dissolve 0.600 O g of potassium sulphate in water and
dilute to 1000 ml.
10 ml of standard sulphate solution = 1.033 ml of 0.1 N sodium thiosulphate solution
(3.2.13).
3.2.13 Sodium thiosulphate solution, approximately O. 1 N. Dissolve 25 g of sodium thiosulphate
pentahydrate in freshly boiled water, add 1 ml of chloroform and dilute to 1 O00 ml with
water. Standardize this solution before use with 0.1 N potassium iodate in the presence
of a trace of potassium iodide.
3.2.14
Mixed indicator solution.
J’
Solution A Dissolve O. 125 g of o-carboxybenzene-azo-dimethyl aniline (methyl red)
in 60 ml of ethanol or industrial methylated spirit and dilute to 100 ml
with water.
Solution B Dissolve 0.083 g of 3 : 7 bis-dimethylaminophenazothionium chloride
(methylene blue) in 100 ml of ethanol or industrial methylated spirit.
Store in a dark glass bottle.
Mix equal rolumes of solutions A and B. Discard the mixed solution after one week.
3.2.15 Phenol red indicator solution. Grind 1 g of phenolsulphonephthalem (phenol red) with
28.4 ml of a 0.4 per cent sodium hydroxide solution and dilute to 1 litre with water.
3.2.16 Starch indicator solution, 1 per cent (weight/volume). Suspend 1 g of soluble starch
in 5 ml of water, then add the suspension rapidly to 90 ml of boiling water. Boil for
1 minute and cool. Prepare fresh daily.
3.3 Procedure
J
Before commencing the determination, mix the air-dried sample of coal, ground to pass a
sieve of 0.2 mm aperture, thoroughly for at least one mi
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