ISO 5931:2000

INTERNATIONAL ISO
STANDARD 5931
First edition
2000-08-15
Carbonaceous materials used in the
production of aluminium — Calcined coke
and calcined carbon products —
Determination of total sulfur by the Eschka
method
Produits carbonés utilisés pour la production de l'aluminium — Coke calciné
et produits carbonés calcinés — Dosage du soufre total par la méthode
Eschka
Reference number
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not be
edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this file,
parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters
were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event
that a problem relating to it is found, please inform the Central Secretariat at the address given below.
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, elec-
tronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's mem-
ber body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.ch
Web www.iso.ch
Printed in Switzerland
©
ii ISO 2000 – All rights reserved

Contents Page
1 Scope . 1
2 Normative references . 1
3 Principle . 1
4 Reagents . 1
5 Apparatus . 2
6 Preparation of test sample . 2
7 Procedure . 3
8 Expression of results . 4
9 Precision . 5
10 Test report . 5
Annex
A Derivation of factors used in the calculation in clause 8 . 6
Bibliography. 7
©
ISO 2000 – All rights reserved iii

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical com-
mittees. Each member body interested in a subject for which a technical committee has been established has the
right to be represented on that committee. International organizations, governmental and non-governmental, in liai-
son with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 5931 was prepared by Technical Committee ISO/TC 47, Chemistry, Subcommittee SC 7,
Aluminium oxide, cryolite, aluminium fluoride, sodium fluoride, carbonaceous products for the aluminium industry.
Annex A of this International Standard is for information only.
©
iv ISO 2000 – All rights reserved

Introduction
Instrumental methods for a more rapid determination of total sulfur are now available. lf such a method is to be used,
it is important to demonstrate that the method is free from bias when compared to this reference method and will give
levels of repeatability and reproducibility which are the same as, or better than, those quoted for this reference
method (see clause 9).
©
ISO 2000 – All rights reserved v

INTERNATIONAL STANDARD ISO 5931:2000(E)
Carbonaceous materials used in the production of aluminium —
Calcined coke and calcined carbon products — Determination of
total sulfur by the Eschka method
1 Scope
This International Standard specifies a reference method for determining the total sulfur content of calcined coke and
calcined carbon products by the Eschka method, provided that they contain a minimum of 0,1 % by mass and prefer-
ably less than 4% by mass of sulfur.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publica-
tions do not apply. However, parties to agreements based on this International Standard are encouraged to investi-
gate the possibility of applying the most recent editions of the normative documents indicated below. For undated
references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain
registers of currently valid International Standards.
ISO 4787:1984, Laboratory glassware — Volumetric glassware — Methods for use and testing of capacity.
ISO 4788:1980, Laboratory glassware — Graduated measuring cylinders.
ISO 5069-2:1983, Brown coals and lignites — Principles of sampling — Part 2: Sample preparation for determination
of moisture content and for general analysis.
ISO 6375:1980, Carbonaceous materials for the production of aluminium — Coke for electrodes — Sampling.
3 Principle
A test portion is ignited in intimate contact with Eschka mixture in an oxidizing atmosphere to remove combustible
matter and to convert the sulfur to sulfate. The sulfate is then extracted using a hydrochloric acid solution and the sul-
fur content, in the form of sulfate, is determined gravimetrically by precipitation of the sulfate with barium chloride.
4Reagents
WARNING — Care should be exercised when handling the reagents, many of which are toxic and corrosive.
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only distilled
water or water of equivalent purity.
4.1 Eschka mixture.
Mix two parts by mass of light, calicined magnesium oxide with one part by mass of anhydrous sodium (or potas-
sium) carbonate. Pass the mixture entirely through a test sieve of 212m nominal size of openings.
4.2 Hydrochloric acid, concentrated, approximately 1,18 g/ml, approximately 36 % by mass.
©
ISO 2000 – All rights reserved 1

4.3 Potassium sulfate, solution.
� �
Weigh, to the nearest 0,1 mg, about 2 g of potassium sulfate, previously dried at a temperature of 105C1to10 C.
Dissolveinwateranddiluteto1l.
4.4 Barium chloride, approximately 85 g/l solution.
Dissolve 100 g of barium chloride dihydrate in water and dilute to 1 l. Filter before use through a close-textured, dou-
bly acid-washed filter-paper or filter-paper pad (see 5.8).
4.5 Methyl red, indicator solution.
Dissolve 1g of 2-(4-dimethylaminophenylazo) benzoic acid, sodium salt (methyl red) in1l of water.
4.6 Ammonia, concentrated solution, no less than 25 % by mass.
4.7 Silver nitrate, 17 g/l solution.
Dissolve 17 g of silver nitrate in water and dilute to 1 l. Store in a dark glass bottle.
5 Apparatus
5.1 Analytical balance, capable of weighing to the nearest 0,1 mg.
5.2 Graduated glassware, complying with the requirements for class A in ISO 4788 and in accordance with
ISO 4787.
�
5.3 Electrically heated muffle furnace, capable of being maintained at (800� 25) C.
The ventilation through the muffle furnace shall be such as to give about five air changes per minute.
5.4 Crucible, of platinum, silica or glazed porcelain, of approximately 25 ml capacity.
5.5 Flat plate, 6mm thick, of silica (or other suitable refractory material), which fits easily into the muffle furnace
(5.3).
5.6 Gooch crucible, with a maximum pore size of 7m, of glazed porcelain or sintered glass.
�
Before commencing the filtration, dry the Gooch crucible and pad for 1h in the air oven (5.7) at (130� 10) C and
weigh it to the nearest 0,1 mg.
�
5.7 Air oven, capable of being maintained at (1
...