Bentonite pore distribution based on SAXS, chloride exclusion and NMR studies

Arto Muurinen (Corresponding Author), Torbjörn Carlsson, A. Root

Research output: Contribution to journalArticleScientificpeer-review

12 Citations (Scopus)

Abstract

Water-saturated bentonite is planned to be used in many countries as an important barrier component in high-level nuclear waste (HLW) repositories. Knowledge about the microstructure of the bentonite and the distribution of water between interlayer (IL) and non-interlayer (non-IL) pores is important for modelling of long-term processes. In this work the microstructure of water-saturated samples prepared from MX-80 bentonite was studied with nuclear magnetic resonance (NMR) and small-angle X-ray scattering spectroscopy (SAXS) coupled with chloride exclusion modelling. The sample dry densities ranged between 0.7 and 1.6 g/cm3. The NMR technique was used to get information about the relative amounts of different water types. Water in smaller volume domains has a shorter relaxation time than that in larger domains due to the average closer proximity of the water to the paramagnetic Fe at the layer surfaces. The results were obtained using 1H NMR T 1ρ relaxation time measurements with the short inter-pulse CPMG method. The interpretation of the NMR results was made by fitting a sum of discrete exponentials to the observed decay curves. The SAXS measurement on bentonite samples was used to get information about the size distribution of the IL distance of montmorillonite. The chloride porosity measurements and Donnan exclusion calculations were used together with the SAXS results to evaluate the bentonite microstructure. In the model, the montmorillonite layers were organized in stacks having IL water between the layers and non-IL water between the stacks. In the modelling, the number of layers in the stacks was used as fitting parameters which determined the IL and non-IL surface areas. The fitting parameters were adjusted so that the modelled chloride concentration was equal to the measured one. The NMR studies and SAXS studies coupled with the Cl porosity measurements provided very similar pictures of how the porewater is divided in two phases in bentonite.
Original languageEnglish
Pages (from-to)251-266
JournalClay Minerals
Volume48
Issue number2
DOIs
Publication statusPublished - 2013
MoE publication typeA1 Journal article-refereed

Fingerprint

Bentonite
X ray scattering
bentonite
nuclear magnetic resonance
Chlorides
spectroscopy
scattering
chloride
Nuclear magnetic resonance
Spectroscopy
Water
water
microstructure
montmorillonite
Relaxation time
Microstructure
Porosity
porosity
modeling
Radioactive Waste

Keywords

  • bentonite buffer
  • exclusion
  • high-level nuclear waste (hlw) repositories
  • microstructure
  • nmr
  • pore distribution
  • saxs

Cite this

Muurinen, Arto ; Carlsson, Torbjörn ; Root, A. / Bentonite pore distribution based on SAXS, chloride exclusion and NMR studies. In: Clay Minerals. 2013 ; Vol. 48, No. 2. pp. 251-266.
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Bentonite pore distribution based on SAXS, chloride exclusion and NMR studies. / Muurinen, Arto (Corresponding Author); Carlsson, Torbjörn; Root, A.

In: Clay Minerals, Vol. 48, No. 2, 2013, p. 251-266.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - Bentonite pore distribution based on SAXS, chloride exclusion and NMR studies

AU - Muurinen, Arto

AU - Carlsson, Torbjörn

AU - Root, A.

PY - 2013

Y1 - 2013

N2 - Water-saturated bentonite is planned to be used in many countries as an important barrier component in high-level nuclear waste (HLW) repositories. Knowledge about the microstructure of the bentonite and the distribution of water between interlayer (IL) and non-interlayer (non-IL) pores is important for modelling of long-term processes. In this work the microstructure of water-saturated samples prepared from MX-80 bentonite was studied with nuclear magnetic resonance (NMR) and small-angle X-ray scattering spectroscopy (SAXS) coupled with chloride exclusion modelling. The sample dry densities ranged between 0.7 and 1.6 g/cm3. The NMR technique was used to get information about the relative amounts of different water types. Water in smaller volume domains has a shorter relaxation time than that in larger domains due to the average closer proximity of the water to the paramagnetic Fe at the layer surfaces. The results were obtained using 1H NMR T 1ρ relaxation time measurements with the short inter-pulse CPMG method. The interpretation of the NMR results was made by fitting a sum of discrete exponentials to the observed decay curves. The SAXS measurement on bentonite samples was used to get information about the size distribution of the IL distance of montmorillonite. The chloride porosity measurements and Donnan exclusion calculations were used together with the SAXS results to evaluate the bentonite microstructure. In the model, the montmorillonite layers were organized in stacks having IL water between the layers and non-IL water between the stacks. In the modelling, the number of layers in the stacks was used as fitting parameters which determined the IL and non-IL surface areas. The fitting parameters were adjusted so that the modelled chloride concentration was equal to the measured one. The NMR studies and SAXS studies coupled with the Cl porosity measurements provided very similar pictures of how the porewater is divided in two phases in bentonite.

AB - Water-saturated bentonite is planned to be used in many countries as an important barrier component in high-level nuclear waste (HLW) repositories. Knowledge about the microstructure of the bentonite and the distribution of water between interlayer (IL) and non-interlayer (non-IL) pores is important for modelling of long-term processes. In this work the microstructure of water-saturated samples prepared from MX-80 bentonite was studied with nuclear magnetic resonance (NMR) and small-angle X-ray scattering spectroscopy (SAXS) coupled with chloride exclusion modelling. The sample dry densities ranged between 0.7 and 1.6 g/cm3. The NMR technique was used to get information about the relative amounts of different water types. Water in smaller volume domains has a shorter relaxation time than that in larger domains due to the average closer proximity of the water to the paramagnetic Fe at the layer surfaces. The results were obtained using 1H NMR T 1ρ relaxation time measurements with the short inter-pulse CPMG method. The interpretation of the NMR results was made by fitting a sum of discrete exponentials to the observed decay curves. The SAXS measurement on bentonite samples was used to get information about the size distribution of the IL distance of montmorillonite. The chloride porosity measurements and Donnan exclusion calculations were used together with the SAXS results to evaluate the bentonite microstructure. In the model, the montmorillonite layers were organized in stacks having IL water between the layers and non-IL water between the stacks. In the modelling, the number of layers in the stacks was used as fitting parameters which determined the IL and non-IL surface areas. The fitting parameters were adjusted so that the modelled chloride concentration was equal to the measured one. The NMR studies and SAXS studies coupled with the Cl porosity measurements provided very similar pictures of how the porewater is divided in two phases in bentonite.

KW - bentonite buffer

KW - exclusion

KW - high-level nuclear waste (hlw) repositories

KW - microstructure

KW - nmr

KW - pore distribution

KW - saxs

U2 - 10.1180/claymin.2013.048.2.07

DO - 10.1180/claymin.2013.048.2.07

M3 - Article

VL - 48

SP - 251

EP - 266

JO - Clay Minerals

JF - Clay Minerals

SN - 0009-8558

IS - 2

ER -