Effect of homogenization on the microstructure and exclusion of chloride in compacted bentonite

Arto Muurinen (Corresponding Author), Ola Karnland, Jarmo Lehikoinen

Research output: Contribution to journalArticleScientificpeer-review

21 Citations (Scopus)

Abstract

In the present work, the effect of homogenization on the microstructure and exclusion of chloride in compacted bentonite was studied. The experiments were performed with MX-80 bentonite, from which easily dissolving components, e.g. chlorides and gypsum, had been removed to ensure that the excess ions in the pore water came from the external solution alone. In the first case, the bentonite was homogenized by dispersing the clay powder in deionized water with ultrasound.
The extra water was subsequently squeezed out in order to obtain the desired clay density. In the second case, the samples were compacted to the desired density at the outset and then saturated with deionized water.
Thereafter, both sample types were equilibrated with 0.1 M NaCl solution through filter plates. In the third case, the compacted samples were equilibrated directly with 0.1 M NaCl solution. The concentrations in the pore water at the end of equilibration were determined by dispersing the bentonite samples in deionized water.
The concentrations in the pore water of the samples saturated first with deionized water were clearly lower than those saturated directly with 0.1 M NaCl solution. This probably reflects the effect of homogenization and a smaller size of the external pores on the chloride concentrations.
The model results calculated with the Donnan model by assuming a homogenous bentonite structure were lower than the measured values. Excellent agreement between experimental and model results could be obtained by assuming a dual-porosity structure.
Original languageEnglish
Pages (from-to)485-490
JournalPhysics and Chemistry of the Earth
Volume32
Issue number1 - 7
DOIs
Publication statusPublished - 2007
MoE publication typeA1 Journal article-refereed

Fingerprint

Bentonite
bentonite
homogenizing
exclusion
Deionized water
Chlorides
microstructure
chlorides
chloride
Microstructure
porewater
Water
water
porosity
dispersing
Calcium Sulfate
clay
dual porosity
clays
Powders

Keywords

  • bentonite
  • nuclear waste
  • nuclear waste management
  • porosity
  • exclusion
  • microstructure
  • Donnan model
  • radionuclide migration
  • radionuclides

Cite this

Muurinen, Arto ; Karnland, Ola ; Lehikoinen, Jarmo. / Effect of homogenization on the microstructure and exclusion of chloride in compacted bentonite. In: Physics and Chemistry of the Earth. 2007 ; Vol. 32, No. 1 - 7. pp. 485-490.
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Effect of homogenization on the microstructure and exclusion of chloride in compacted bentonite. / Muurinen, Arto (Corresponding Author); Karnland, Ola; Lehikoinen, Jarmo.

In: Physics and Chemistry of the Earth, Vol. 32, No. 1 - 7, 2007, p. 485-490.

Research output: Contribution to journalArticleScientificpeer-review

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N2 - In the present work, the effect of homogenization on the microstructure and exclusion of chloride in compacted bentonite was studied. The experiments were performed with MX-80 bentonite, from which easily dissolving components, e.g. chlorides and gypsum, had been removed to ensure that the excess ions in the pore water came from the external solution alone. In the first case, the bentonite was homogenized by dispersing the clay powder in deionized water with ultrasound. The extra water was subsequently squeezed out in order to obtain the desired clay density. In the second case, the samples were compacted to the desired density at the outset and then saturated with deionized water. Thereafter, both sample types were equilibrated with 0.1 M NaCl solution through filter plates. In the third case, the compacted samples were equilibrated directly with 0.1 M NaCl solution. The concentrations in the pore water at the end of equilibration were determined by dispersing the bentonite samples in deionized water. The concentrations in the pore water of the samples saturated first with deionized water were clearly lower than those saturated directly with 0.1 M NaCl solution. This probably reflects the effect of homogenization and a smaller size of the external pores on the chloride concentrations. The model results calculated with the Donnan model by assuming a homogenous bentonite structure were lower than the measured values. Excellent agreement between experimental and model results could be obtained by assuming a dual-porosity structure.

AB - In the present work, the effect of homogenization on the microstructure and exclusion of chloride in compacted bentonite was studied. The experiments were performed with MX-80 bentonite, from which easily dissolving components, e.g. chlorides and gypsum, had been removed to ensure that the excess ions in the pore water came from the external solution alone. In the first case, the bentonite was homogenized by dispersing the clay powder in deionized water with ultrasound. The extra water was subsequently squeezed out in order to obtain the desired clay density. In the second case, the samples were compacted to the desired density at the outset and then saturated with deionized water. Thereafter, both sample types were equilibrated with 0.1 M NaCl solution through filter plates. In the third case, the compacted samples were equilibrated directly with 0.1 M NaCl solution. The concentrations in the pore water at the end of equilibration were determined by dispersing the bentonite samples in deionized water. The concentrations in the pore water of the samples saturated first with deionized water were clearly lower than those saturated directly with 0.1 M NaCl solution. This probably reflects the effect of homogenization and a smaller size of the external pores on the chloride concentrations. The model results calculated with the Donnan model by assuming a homogenous bentonite structure were lower than the measured values. Excellent agreement between experimental and model results could be obtained by assuming a dual-porosity structure.

KW - bentonite

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KW - nuclear waste management

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KW - exclusion

KW - microstructure

KW - Donnan model

KW - radionuclide migration

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