Pulps — Kraft liquor — Determination of total, active and effective alkali using potentiometric titration

This document specifies a potentiometric titration procedure for the determination of total, active and effective alkali in white and green liquors obtained and used in the kraft or sulphate pulping process. This document is not applicable for the analysis of liquors such as oxidized white liquors which contain significant amounts of polysulphides. The method given in this document is not intended for the determination of particular ionic species, such as sulphides or carbonates.

Pâtes — Liqueur Kraft — Détermination des alcalis totaux, actifs et effectif par titrage potentiométrique

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Status
Published
Publication Date
09-Mar-2023
Current Stage
6060 - International Standard published
Start Date
10-Mar-2023
Due Date
18-Dec-2023
Completion Date
10-Mar-2023
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INTERNATIONAL ISO
STANDARD 23774
First edition
2023-03
Pulps — Kraft liquor — Determination
of total, active and effective alkali
using potentiometric titration
Pâtes — Liqueur Kraft — Détermination des alcalis totaux, actifs et
effectif par titrage potentiométrique
Reference number
ISO 23774:2023(E)
© ISO 2023

---------------------- Page: 1 ----------------------
ISO 23774:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
  © ISO 2023 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 23774:2023(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents . 2
6 Apparatus . 2
7 Calibration and check of pH meter . 3
8 Procedure .3
9 Calculation . 3
10 Report . 4
Annex A (informative) Precision data . 5
Annex B (informative) Quantities and units for the characterization of white and green
liquors . 7
Bibliography .10
iii
© ISO 2023 – All rights reserved

---------------------- Page: 3 ----------------------
ISO 23774:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 6, Paper, board and pulps.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
  © ISO 2023 – All rights reserved

---------------------- Page: 4 ----------------------
INTERNATIONAL STANDARD ISO 23774:2023(E)
Pulps — Kraft liquor — Determination of total, active and
effective alkali using potentiometric titration
1 Scope
This document specifies a potentiometric titration procedure for the determination of total, active and
effective alkali in white and green liquors obtained and used in the kraft or sulphate pulping process.
This document is not applicable for the analysis of liquors such as oxidized white liquors which contain
significant amounts of polysulphides. The method given in this document is not intended for the
determination of particular ionic species, such as sulphides or carbonates.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
total alkali
total concentration of alkaline constituents determined by titration of a sample of the liquor with strong
acid to the third inflection point according to specific requirements
Note 1 to entry: The specific requirements are described in this document, ISO 23774:2023, Clauses 8 and 9
Note 2 to entry: See also Annex B.
3.2
active alkali
total concentration of alkaline constituents, except carbonates, as determined by titration of a sample
of the liquor with strong acid according to specific requirements
Note 1 to entry: The specific requirements are described in this document, ISO 23774:2023, Clauses 8 and 9
Note 2 to entry: In practice, active alkali is considered to be the sum of the concentrations of hydroxyl and
hydrosulphide ions, including hydroxyl ions formed by hydrolysis of sulphides. See also Annex B.
3.3
effective alkali
concentration of strongly alkaline constituents determined by titration of a sample of the liquor with
strong acid to the first inflection point according to specific requirements
Note 1 to entry: The specific requirements are described in this document, ISO 23774:2023, Clauses 8 and 9
Note 2 to entry: In practice, this is considered to be the concentration of hydroxyl ions, including those formed
from sulphides by hydrolysis. See also Annex B.
1
© ISO 2023 – All rights reserved

---------------------- Page: 5 ----------------------
ISO 23774:2023(E)
4 Principle
The determination of total, active and effective alkali in a liquor sample is based on an acidic dosage by
a strong acid of the alkaline species contained in the sample. The major alkaline species in green liquor
2−
− −
are hydroxyl ions (OH ), hydrosulphur ions (HS ), carbonate (CO ) and hydrogenocarbonate ions (
3

− −
HCO ), whereas in white liquor they are mainly hydroxyl ions (OH ) and hydrosulphur ions (HS ).
3
During the acidic dosage, these alkaline species lead to different inflexion points for specific pH ranges
as described in Clause 8.
A sample of the liquor is titrated with hydrochloric acid of known concentration. The pH value (or
a suitable function of the pH value) of the reaction mixture and the volume of hydrochloric acid are
recorded continuously and from the recorded data the consumption of acid at the inflection points is
determined.
NOTE The titration is preferably performed using an automatic titration equipment.
From the amounts of acid required to reach the three inflection points, the effective, active and total
alkali of the sample are calculated.
Precision data are available in Annex A.
5 Reagents
WARNING — The use of this document can involve hazardous materials, operations and
equipment. It does not purport to address all of the safety or environmental problems associated
with its use.
All chemicals shall be of analytical grade. The water used in the titration and in the preparation of
reagents shall be distilled or deionized.
5.1 Hydrochloric acid 1 M, the actual concentration of hydrochloric acid, HCl, shall be known to the
nearest 0,005 M.
5.2 Buffer solutions of known pH values near 4 and 9. Suitable buffer solutions are commercially
available. They can also be prepared in the laboratory as follows:
— Buffer solution, pH 4,01: In a 1 000 ml volumetric flask dissolve 10,12 g of potassium hydrogen
phthalate, KHC H O , in water and dilute to the mark. There is normally no need to dry the salt. The
8 4 4
solution is stable for 2 months.
— Buffer solution, pH 9,18: In a 1 000 ml volumetric flask dissolve 3,80 g of sodium tetraborate
decahydrate (borax), Na B O ⋅10H O, in water from which carbon dioxide has been expelled by
2 4 7 2
boiling. Dilute to the mark. The solution is stable for 6 weeks. The solution will absorb carbon
dioxide when in contact with ambient air. Therefore, keep the solution in a stoppered bottle and do
not leave the bottle open more than absolutely necessary.
6 Apparatus
The usual laboratory apparatus and, in particular, the following shall be used.
6.1 Automatic titration equipment, including glass and reference electrodes, that records the
titration curve (pH against titrant consumed) or any function of the titration curve, such as the first
2
  © ISO 2023 – All rights reserved

---------------------- Page: 6 ----------------------
ISO 23774:2023(E)
derivative, so that the inflection points of the titration curve can be determined. A combined pH glass
electrode may be used. Check the precision of the equipment as instructed in Clause 7.
For the analysis of green liquors, titratio
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 23774
ISO/TC 6
Pulps — Kraft liquor — Determination
Secretariat: SCC
of total, active and effective alkali
Voting begins on:
2022-12-08 using potentiometric titration
Voting terminates on:
2023-02-02
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 23774:2022(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2022

---------------------- Page: 1 ----------------------
ISO/FDIS 23774:2022(E)
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 23774
ISO/TC 6
Pulps — Kraft liquor — Determination
Secretariat: SCC
of total, active and effective alkali
Voting begins on:
using potentiometric titration
Voting terminates on:
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
RECIPIENTS OF THIS DRAFT ARE INVITED TO
ISO copyright office
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
CP 401 • Ch. de Blandonnet 8
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
CH-1214 Vernier, Geneva
DOCUMENTATION.
Phone: +41 22 749 01 11
IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: copyright@iso.org
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 23774:2022(E)
Website: www.iso.org
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
Published in Switzerland
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
ii
  © ISO 2022 – All rights reserved
NATIONAL REGULATIONS. © ISO 2022

---------------------- Page: 2 ----------------------
ISO/FDIS 23774:2022(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents . 2
6 Apparatus . 2
7 Calibration and check of pH meter . 3
8 Procedure .3
9 Calculation . 3
10 Report . 4
Annex A (informative) Precision data . 5
Annex B (informative) Quantities and units for the characterization of white and green
liquors . 7
Bibliography .10
iii
© ISO 2022 – All rights reserved

---------------------- Page: 3 ----------------------
ISO/FDIS 23774:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non­governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 6, Paper, board and pulps.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
  © ISO 2022 – All rights reserved

---------------------- Page: 4 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 23774:2022(E)
Pulps — Kraft liquor — Determination of total, active and
effective alkali using potentiometric titration
1 Scope
This document specifies a potentiometric titration procedure for the determination of total, active and
effective alkali in white and green liquors obtained and used in the kraft or sulphate pulping process.
This document is not applicable for the analysis of liquors such as oxidized white liquors which contain
significant amounts of polysulphides. The method given in this document is not intended for the
determination of particular ionic species, such as sulphides or carbonates.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
total alkali
total concentration of alkaline constituents determined by titration of a sample of the liquor with strong
acid to the third inflection point according to specific requirements
Note 1 to entry: The specific requirements are described in this document, ISO 23774:—, Clauses 8 and 9
Note 2 to entry: See also Annex B.
3.2
active alkali
total concentration of alkaline constituents, except carbonates, as determined by titration of a sample
of the liquor with strong acid according to specific requirements
Note 1 to entry: The specific requirements are described in this document, ISO 23774:—, Clauses 8 and 9
Note 2 to entry: In practice, active alkali is considered to be the sum of the concentrations of hydroxyl and
hydrosulphide ions, including hydroxyl ions formed by hydrolysis of sulphides. See also Annex B.
3.3
effective alkali
concentration of strongly alkaline constituents determined by titration of a sample of the liquor with
strong acid to the first inflection point according to specific requirements
Note 1 to entry: The specific requirements are described in this document, ISO 23774:—, Clauses 8 and 9
Note 2 to entry: In practice, this is considered to be the concentration of hydroxyl ions, including those formed
from sulphides by hydrolysis. See also Annex B.
1
© ISO 2022 – All rights reserved

---------------------- Page: 5 ----------------------
ISO/FDIS 23774:2022(E)
4 Principle
The determination of total, active and effective alkali in a liquor sample is based on an acidic dosage by
a strong acid of the alkaline species contained in the sample. The major alkaline species in green liquor
2−
− −
are hydroxyl ions (OH ), hydrosulphur ions (HS ), carbonate (CO ) and hydrogenocarbonate ions (
3

− −
HCO ), whereas in white liquor they are mainly hydroxyl ions (OH ) and hydrosulphur ions (HS ).
3
During the acidic dosage, these alkaline species lead to different inflexion points for specific pH ranges
as described in Clause 8.
A sample of the liquor is titrated with hydrochloric acid of known concentration. The pH value (or
a suitable function of the pH value) of the reaction mixture and the volume of hydrochloric acid are
recorded continuously and from the recorded data the consumption of acid at the inflection points is
determined.
NOTE The titration is preferably performed using an automatic titration equipment.
From the amounts of acid required to reach the three inflection points, the effective, active and total
alkali of the sample are calculated.
Precision data are available in Annex A.
5 Reagents
WARNING — The use of this document can involve hazardous materials, operations and
equipment. It does not purport to address all of the safety or environmental problems associated
with its use.
All chemicals shall be of analytical grade. The water used in the titration and in the preparation of
reagents shall be distilled or deionized.
5.1 Hydrochloric acid 1 M, the actual concentration of hydrochloric acid, HCl, shall be known to the
nearest 0,005 M.
5.2 Buffer solutions of known pH values near 4 and 9. Suitable buffer solutions are commercially
available. They can also be prepared in the laboratory as follows:
— Buffer solution, pH 4,01: In a 1 000 ml volumetric flask dissolve 10,12 g of potassium hydrogen
phthalate, KHC H O , in water and dilute to the mark. There is normally no need to dry the salt. The
8 4 4
solution is stable for 2 months.
— Buffer solution, pH 9,18: In a 1 000 ml volumetric flask dissolve 3,80 g of sodium tetraborate
decahydrate (borax), Na B O ⋅10H O, in water from which carbon dioxide has been expelled by
2 4 7 2
boiling. Dilute to the mark. The solution is stable for 6 weeks. The solution will absorb carbon
dioxide when in contact with ambient air. Therefore, keep the solution in a stoppered bottle and do
not leave the bottle open more than absolutely necessary.
6 Apparatus
The usual laboratory
...

ISO/FDIS 23774:2022(E)
ISO TC 6/WG 17
Date: 2022-10-1711-24

Pulps — Kraft liquor — Determination of total, active and effective alkali using potentiometric
titration

---------------------- Page: 1 ----------------------
ISO/FDIS 23774:2022(E)
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no
part of this publication may be reproduced or utilized otherwise in any form or by any means,
electronic or mechanical, including photocopying, or posting on the internet or an intranet, without
prior written permission. Permission can be requested from either ISO at the address below or
ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.orgwww.iso.org
Published in Switzerland
ii © ISO 2022 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/FDIS 23774:2022(E)
Contents
Foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
4 Principle . 5
5 Reagents . 5
5.1 General . 5
5.2 Hydrochloric acid 1 M . 5
5.3 Buffer solutions . 5
6 Apparatus . 6
7 Calibration and check of pH meter . 6
8 Procedure . 6
9 Calculation . 7
10 Report . 7
Annex A (informative) Precision data . 8
Annex B (informative) Quantities and units for the characterization of white and green
liquors . 10
Bibliography . 13
Foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
4 Principle . 5
5 Reagents . 5
5.1 General . 5
5.2 Hydrochloric acid 1 M . 5
5.3 Buffer solutions . 5
6 Apparatus . 6
7 Calibration and check of pH meter . 6
8 Procedure . 6
9 Calculation . 7
10 Report . 7
Annex A (informative) Precision data . 8
Annex B (informative) Quantities and units for the characterization of white and green
liquors . 10
© ISO 2022 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO/FDIS 23774:2022(E)
Bibliography . 13
iv © ISO 2022 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/FDIS 23774:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO
collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any
patent rights identified during the development of the document will be in the Introduction and/or on
the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the World
Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 6, Paper, board and pulps.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2022 – All rights reserved v

---------------------- Page: 5 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 23774:2022(E)

Proposed title: Pulps — Kraft liquor — Determination of total,
active and effective alkali using potentiometric titration
1 Scope
This document specifies a potentiometric titration procedure for the determination of total, active and
effective alkali in white and green liquors obtained and used in the kraft or sulphate pulping process.
This document is not applicable for the analysis of liquors such as oxidized white liquors which contain
significant amounts of polysulphides. The method given in this document is not intended for the
determination of particular ionic species, such as sulphides or carbonates.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
total alkali
total concentration of alkaline constituents determined by titration of a sample of the liquor with strong
acid to the third inflection point according to specific requirements
Note 1 to entry: The specific requirements are described in this document, ISO 23774:xxxx, clause :—, Clauses 8 and
9
Note 2 to entry: See also Annex B.
3.2
active alkali
total concentration of alkaline constituents, except carbonates, as determined by titration of a sample of
the liquor with strong acid according to specific requirements
Note 1 to entry: The specific requirements are described in this document, ISO 23774:xxxx, clause:—, Clauses 8 and
9
Note 2 to entry: In practice, active alkali is considered to be the sum of the concentrations of hydroxyl and
hydrosulphide ions, including hydroxyl ions formed by hydrolysis of sulphides. See also Annex B.
3.3
© ISO 2022 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO/FDIS 23774:2022(E)
effective alkali
concentration of strongly alkaline constituents determined by titration of a sample of the liquor with
strong acid to the first inflection point according to specific requirements
Note 1 to entry: The specific requirements are described in this document, ISO 23774:xxxx, clause:—, Clauses 8 and
9
Note 2 to entry: In practice, this is considered to be the concentration of hydroxyl ions, including those formed
from sulphides by hydrolysis. See also Annex B.
4 Principle
The determination of total, active and effective alkali in a liquor sample is based on an acidic dosage by a
strong acid of the alkaline species contained in the sample. The major alkaline species in green liquor are
2−
- − - − 2- Field Code Changed
hydroxyl ions (OH ), ), hydrosulphur ions (HS ), ), carbonate (CO3 )( CO ) and hydrogenocarbonate
3

- - − Field Code Changed
ions (HCO ),( HCO ), whereas in white liquor they are mainly hydroxyl ions (OH ) ) and hydrosulphur
3
3
- −
ions (HS ). ). During the acidic dosage, these alkaline species lead to different inflexion points for specific
pH ranges as described in Clause 8.
A sample of the liquor is titrated with hydrochloric acid of known concentration. The pH value (or a
suitable function of the pH value) of the reaction mixture and the volume of hydrochloric acid are
recorded continuously and from the recorded data the consumption of acid at the inflection points is
determined.
NOTE The titration is preferably performed using an automatic titration equipment.
From the amounts of acid required to reach the three inflection points, the effective, active and total alkali
of the sample are calculated.
Precision data are available in Annex A.
5 Reagents
All chemicals shall be of analytical grade. The water used in the titration and in the preparation of
reagents shall be distilled or deionized.
WARNING The use of this document can involve hazardous materials, operations and equipment. It
does not purport to address all of the safety or environmental problems associated with its use.
All chemicals shall be of analytical grade. The water used in the titration and in the preparation of
reagents shall be distilled or deionized.
5.1 5.1 Hydrochloric acid 1 M
The, the actual concentration of hydrochloric acid, HCl, shall be known to the nearest 0,005 M.
5.2 Buffer solutions
5.2 Buffer solutions of known pH values near 4 and 9. Suitable buffer solutions are commercially
available. They can also be prepared in the laboratory as follows:
— Buffer solution, pH 4,01:
In a 1 000 ml volumetric flask dissolve 10,12 g of potassium hydrogen phthalate, KHC H O , in
8 4 4
2 © ISO 2022 – All rights reserved

---------------------- Page: 7 ----------------------
ISO/FDIS 23774:2022(E)
water and dilute to the mark. There is normally no need to dry the salt. The solution is stable for
2 months.
— Buffer solution, pH 9,18:
In a 1 000 ml volumetric flask dissolve 3,80 g of sodium tetraborate decahydrate (borax),
Na B O⋅10H O, in water from which carbon dioxide has been expelled by boiling. Dilute to the
2 4 7 2
mark. The solution is stable for 6 weeks. The solution will absorb carbon dioxide when in contact
with ambient air. Therefore, keep the solution in a stoppered bottle and do not leave the bottle open
more than absolutely necessary.
6 Apparatus
The u
...

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