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POSIVA Report 1998-1

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Name:

Bentonite Swelling Pressure in Strong NaCI Solutions Correlation of Model Calculations to Experimentally Determined Data

Writer:

Ola Karnland

Language:

English

Page count:

35

ISBN:

951-652-039-1; 1239-3096

Summary:

Working report: POSIVA-raportti POSIVA 98-01, 35 sivua
ISBN 951-652-039-1


BENTONITE SWELLING PRESSURE IN STRONG NaCl SOLUTIONS β€”
Correlation of model calculations to experimentally determined data


ABSTRACT

A number of quite different quantitative models concerning swelling pressure in
bentonite clay have been proposed. This report discusses a number of models which
possibly can be used also for saline conditions. A discrepancy between calculated and
measured values was noticed for all models at brine conditions. In general the models
predicted a too low swelling pressure compared to what was experimentally found. An
osmotic component in the clay/water system is proposed in order to improve the
previous conservative use of the thermodynamic model. Calculations of this osmotic
component is proposed to be made by use of the clay cation exchange capacity and
Donnan equilibrium. Calculations made by this approach showed considerably better
correlation to literature laboratory data, compared to calculations made by the previous
conservative use of the thermodynamic model. A few verifying laboratory tests were
made and are briefly described in the report.

The improved model predicts a substantial bentonite swelling pressure also in a
saturated sodium chloride solution if the density of the system is sufficiently high. This
means in practice that the buffer in a KBS-3 repository will give rise to an acceptable
swelling pressure, but that the positive effects of mixing bentonite into a backfill
material will be lost if the system is exposed to brines.


Keywords: bentonite, brine, Donnan, model, montmorillonite, osmosis, repository, salt,
swelling pressure


POSIVA-raportti POSIVA 98-01, 35 sivua
ISBN 951-652-039-1


BENTONITE SWELLING PRESSURE IN STRONG NaCl SOLUTIONS β€”
Correlation of model calculations to experimentally determined data


ABSTRACT

A number of quite different quantitative models concerning swelling pressure in
bentonite clay have been proposed. This report discusses a number of models which
possibly can be used also for saline conditions. A discrepancy between calculated and
measured values was noticed for all models at brine conditions. In general the models
predicted a too low swelling pressure compared to what was experimentally found. An
osmotic component in the clay/water system is proposed in order to improve the
previous conservative use of the thermodynamic model. Calculations of this osmotic
component is proposed to be made by use of the clay cation exchange capacity and
Donnan equilibrium. Calculations made by this approach showed considerably better
correlation to literature laboratory data, compared to calculations made by the previous
conservative use of the thermodynamic model. A few verifying laboratory tests were
made and are briefly described in the report.

The improved model predicts a substantial bentonite swelling pressure also in a
saturated sodium chloride solution if the density of the system is sufficiently high. This
means in practice that the buffer in a KBS-3 repository will give rise to an acceptable
swelling pressure, but that the positive effects of mixing bentonite into a backfill
material will be lost if the system is exposed to brines.


Keywords: bentonite, brine, Donnan, model, montmorillonite, osmosis, repository, salt,
swelling pressure


Keywords:

bentonite; brine; Donnan; model; montmorillonite; osmosis; repository; salt; swelling pressure

File(s):

Bentonite Swelling Pressure in Strong NaCI Solutions Correlation of Model Calculations to Experimentally Determined Data (pdf) (2.2 MB)


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