assessment of bentonite characteristics...

Assessment of bentonite characteristics BOA KYT2014 midterm seminar 17 April 2013 M. Olin1, M. Kataja2, L. Korkiala-Tanttu3, P. Hölttä4, R. Serimaa4, M. Tiljander5, M. Laitinen6 ,E. Myllykylä1, A. Itälä1, J. Järvinen1

1VTT Technical Research Centre of Finland 2University of Jyväskylä 3Aalto University 4University of Helsinki 5Geological Survey of Finland 6Numerola Oy

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Introduction

Physicochemical reality Evolving external conditions in the repository (simulated in lab) Processes changing the bentonite Material properties – sodium bentonite

Bentonite buffer must fulfil some safety functions 1) closing of spent fuel, 2) beneficial chemical conditions, 3) mechanical protection Transport by diffusion only, prevent corrosion of copper, dampening of dislocations in earth

quakes, predictable conditions

Several research methods are available Theoretical Computational Experimental Natural analogues

Numerical modelling

Experimentalwork:

Lab and field

Theoretical and literature studies

Natural analogues

Theoreticalscience

Numerical methods

Science

Experimentaland

numerical results

Site and technical design

Experimental methods and analyses

Safety case

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T: -10…100 oC

P: 0.1…4 MPa +ice

ρd: 1…1 700 kg/m3 Montmorillonite + exchanged cations + other accessory minerals

I: 0.01 mM…1 M 1 mg/L…100 g/L Na-Ca-Cl + other ions, microbes, colloids

S: 0.3…1 Dry to fully saturated

Temperature Pressure Chemical composition

Water Solid: minerals + exchanged

cations Dissolved salts

Conditions + Thermodynamics

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Scales, bentonite properties and water

Scales, spatial Colloidal size Pore size Laboratory Small scale Pilot scale Repository scale

Time Nanoseconds in MD Lab = days to years Repository = years to

millenia

Bentonite properties Relative amount of

montmorillonite Cationic form of

montmorillonite Accessory minerals Grain size Initial water content “History” of the

samples Production Transport Processing

Water Humidity or saturation Composition

Electrolyte Groundwater

simulant Gases Colloids Microbes

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Structure and processes

Microstructure of bentonite

Processes of bentonite

Colloids: formation and RN transport

Microbes: analysis and effects

Cation exchange and diffusion

Dissolution and precipitation of montmorillonite

Dissolution and precipitation of other minerals

Deformations and stresses, friction

Pore size distribution vs.

density

Differences between Na and Ca (K, Mg too)

Number and distribution of water layers

Pores: free, interlamellar, diffuse layer

Mesoscale structure:

20 – 1000 nm

Wetting and homogenisation

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Safety functions: protect canister, and limit and delay release of RN Processes related to these shown below

RN

Alteration of montmorillonite

Ductility - chemical hardening

Canister survives in dislocations

Dissolution of montmorillonite

Formation and transport of colloids

Deformations and stresses, friction –

self healing

Microbial activity

Boxes of blue colour = BOA Boxes of green colour = other issues Boxes of yellow colour = safety functions

Montmorillonite losses by erosion Homogenisation


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Stucture related to processes

RN transport limited to diffusion, sorption

Corroding agents in and products out

Alteration of montmorillonite Ductility - chemical

hardening

Canister survives in dislocations

Dissolution of montmorillonite

Formation and transport of colloids

Deformations and stresses, friction –

self healing

Microbial activity

Boxes of blue colour = BOA Boxes of green colour = other issues Boxes of yellow colour = safety functions

Montmorillonite losses by erosion Homogenisation

Montmorillonite: solid part

Bound cations (Na, Ca, etc)

Water: free and bound

Minerals: solid and dissolved

Diffusion

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Experimental methods

Micro tomography

Nano tomography XRD

SAXS

Mechanical properties Basic

characterisation

ICP-MS analysis

NMR

Batch exp. Loose

bentonite

Coupled experiments





Cation exchangeand diffusion





density




Mesoscalestructure:

20 – 1000 nm


TEM SEM

Diffusion and

sorption ISE

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Modelling methods and tools

COMSOL Multiphysics

THC

THM Numerrin

Molecular: AccelRys

THC Geochemist’s Workbench

THC TOUGHREACT

THMC COMSOL

Molecular dynamics

Colloids DLVO

THMC(B) Numerrin





Cation exchangeand diffusion





density




Mesoscalestructure:

20 – 1000 nm


Mesoscale modelling

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Goals of BOA - Purpose

THMC(B)-model, sufficiently good over whole parameter space Concept based on experimental observations Needed parameter values and data must be available somehow Mathematical formulation consistent and completed Implementation possible to carry out by present computing methods, tools

and resources Characterisation and analysis methods, by which all needed

determinations can be done Accurate, repeatable and reliable

Process experiments, which support modelling and vice versa; supported characterisation and analysis methods Carefully selected set of experiments and tests

NOT a goal: to solve all bentonite issues, but instead to create operations model to study bentonite effectively

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Sub-tasks, methods and partners 2013 - Structure

2 THM and structure Microtomography - JyU XRD, SAXS - HYFL, VTT SEM-EPMA - GTK Block-shear - Aalto NMR - VTT THM - JyU, Aalto

3 THC, colloids and biology

4 THMCB

1 Coordination

THC, solubility -VTT Colloid formation - HYRL HR-ICP-MS -VTT Microbes - VTT

THM - JyU, Numerola THC ja THMC(B) - VTT, Numerola,

JyU

Overall - VTT Sub-projects - GTK - Aalto - JyU - HYFL - HYRL - UEF - Numerola

• VTT – VTT Technical Research Centre of Finland • GTK – Geological Survey of Finland • Aalto – Aalto university • HYFL – University of Helsinki, Physics • HYRL - University of Helsinki, Radio chemistry • JyU – University of Jyväskylä, Physics • UEF – University of Eastern Finland • Numerola - Numerola Oy

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Selected results - State

1. Dissolution of montmorillonite, VTT 2. Mineralogy of bentonite, GTK 3. Small-angle x-ray scattering patterns of Ca-montmorillonite in water as a

function of basal spacing, HYFL 4. Block shear experiments, Aalto 5. Phenomenological THM modeling and X-ray tomographic wetting/swelling

experiments, JyU & Numerola Oy) 6. Na/Ca selectivity coefficients of Na-montmorillonite at different

temperatures, VTT 7. The effect of colloids on radionuclide migration, HYRL 8. Modelling transport of water and ions and chemical reactions in

compacted bentonite – two flexible modelling platforms, VTT & Numerola 9. Measurement of chloride concentration in the pore water of compacted

bentonite with ion-selective electrode, VTT

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1. Dissolution of Na- and Ca-montmorillonite in groundwater simulants under anaerobic conditions

VTT, GTK and ERM (Etudes Recherches Matériaux, France) The dissolution rates obtained are in agreement with those presented in literature Dissolution is dependent on the experimental conditions

Water composition and temperature Elevated T and Higher pH have increasing effect on reactivity and thus on the solubility Poster in Montpellier, paper accepted to Clay Minerals

XRD results indicated that the nature of the smectite minerals did not change.

Instead, the experimental conditions more or less modified the structure of montmorilllonite (e.g. layer stacking).

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1. Dissolution VTT, GTK and ERM (Etudes Recherches Matériaux, France)

Figure. Evolution of Si concentrations in fresh (top) and saline waters (bottom) including linear fits for rate calculations. Calculated log rates below.

𝑅𝑅𝑅𝑅𝑆𝑆 = −1𝑣𝑆𝑆

𝑉𝑀𝑑𝐶𝑆𝑆𝑑𝑑

FRESH Na-MMT Ca-MMT 25°C, pH 8 -12.1 -12.0 60°C, pH 7.1 -11.0 -11.0 SALINE Na-MMT Ca-MMT 25°C, pH 11 -11.6 -11.6 60°C, pH 10.1 -10.6 -10.6

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2. Mineralogy of bentonite - GTK

Bentonite, a material consisting predominantly of smectite minerals. The focus of the research is to study

1. Acessory minerals of bentonite 2. Smectite mineralogy

Methods:

1. X-ray diffraction (XRD) 2. Scanning electron microscope (SEM) 3. Electron probe micro-analyzer (EPMA)

XRD: Qualitative

mineralcompositon

SEM: Concentrationof the mineral

phases

EPMA: Quantitative

analysisfrom mineral

phases

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2. SEM-feature –analyses

BSE*-image from sample MX-80 1.3 NaCl

Back-scattered electron

Fe-ox Kfp Pyr

Kfp

0,0

10,0

20,0

30,0

40,0

50,0

60,0

70,0

80,0

90,0

100,0

% total features % total area

% total features

% total area

Montmorillonite 66.8 96.3 K-fsp 22.2 3.3 Quartz 5.0 0.1 Sulfides 2.5 0.1 Plagioclase 3.0 0.2 Goethite 0.1 0.0004 Biotite 0.1 0.0009 Apatite 0.1 0.003 Monazite 0.1 0.001

Kfp = K-feldspar Pyr = pyrite Fe-ox = Fe-oxide

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% * Swy-2-O Swy-2-P SiO2 59.6 58.2 59.4 Al2O3 21.1 18.7 18.8 MgO 3.3 2.4 2.2 Na2O 2.5 0.3 0.6 FeO - 3.4 3.1 H2O+ 4.5 H2O- 8.9

Tot. H2O 13.4 16.7 15.5 Tot. 99.9

•Theoretical compositon (w-%) of montmorillonite. Olin et.al. 2011. Coupled behaviour of bentonite buffer. Results PUSKURI-project. VTT Research Notes 2587. 85 p.

The aim of the mineralogical research is to improve analysis techniques and knowledge about the behaviour of clay minerals.

2. Quantitative analysis (EPMA) from clay matrix

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3. Small-angle x-ray scattering patterns of Ca-montmorillonite in water as a function of basal spacing

According to SAXS results the well-ordered coherently scattering clay stacks include 6-8 platelets per stack. In the figure spacings corresponding to 1-4 water layer hydration states are denoted by 1W, 2W, 3W and 4W.

M Matusewicz et al. Clay Minerals 2013, in press

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• The microcracks (visible in black on the XMT image on the left) within the scattering beam (green circles) have the same orientation as the clay platelets within tactoids (seen in the SAXS patterns on the right).

3. Combined X-ray microtomography and x-ray scattering

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4. Block shear experiments

In total, 37 large shear box tests have been done, which have included seven different interfaces, namely: block / block, block / pellets, block / granulated bentonite, block / foundation bed, three different roughness stones / pellets. Based on the big shear box results, it was found that the interface

between granite stone and bentonite pellets yielded the highest value for friction angle. The interface between blocks exhibited the lowest friction angle. The interfaces between block / granulated bentonite and block / foundation material were resulted in similar shear strength parameters. The testing programme is continuing with the temperature and moisture

controlled tests. These results are under analysis. The test results will be published in submitted article and Master thesis.

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4. Interface friction angle (tan φ) for different materials and surface roughness index Ra

0102030405060708090100

00,10,20,30,40,50,60,70,80,9

1

Ra

(µm

)

tan φ

tan (φ) Ra (µm)

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5. Phenomenological THM modeling and X-ray tomographic wetting/swelling experiments (JyU, Numerola Oy)

A phenomenological THM model including swelling and finite plastic deformations has been developed and implemented numerically for -1D expansion in a channel (applicable in erosion studies) - Cylindrically symmetric 3D case - General 3D case The model will be first validated using X-ray tomographic data on wetting-

swelling process of small cylindrical samples. Additional experimental data on samples with high water content required before

application to bentonite buffer simulation.

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20 mm Force sensor

Venting channel Plastic tube (PEEK) Sintered blocks Bentonite sample Wetting channel

Monitoring wetting/swelling in 3D using X-ray tomographic technique

Preliminary results from model validation: Water content distribution and swelling displacement in a cylindrical sample (averaged over azimuthal angle)

Measured (JyU) Computed (Numerola)

X-ray tomographic scanner Sample holder with wetting system Compacted bentonite sample

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Formation and stability of colloids The release and stability of MX-80 bentonite

colloids have been followed as a function of ionic strength in diluted OLSO reference groundwater, NaCl and CaCl2 solutions (0.001–0.1 M). The particle size, concentration and zeta

potential were determined applying dynamic light scattering (DLS) and electrophoretic mobility.

7. The effect of colloids on radionuclide migration

Stability (above) and concentration (below) of bentonite colloids in OLSO (I=0.001−0.1 M). Bentonite colloids in diluted OLSO (I=0.001−0.03 M)

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Radionuclide sorption 85Sr and 152Eu sorption onto MX-80

bentonite powder and on separated bentonite colloids were determined in diluted OLSO, NaCl and CaCl2 solutions (I=0.001–0.1 M). In dilute solutions nearly all 85Sr and 152Eu

was sorbed onto colloids. The distribution coefficient (Kd) decreased when the ionic strength increased.

Conclusions The results confirmed the influence of ionic strength and valence of the cations on

the stability of bentonite colloids as well as on the sorption of radionuclides. Under prevailing saline groundwater conditions in Olkiluoto colloids are instable

but the influence of glacial melt waters has to be considered.

7. The effect of colloids on radionuclide migration

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6. Na/Ca selectivity coefficients of Na-montmorillonite at different

temperatures

Poster in Montpellier meeting (VTT) The initial experimental results show a slight

tendency to take more calcium inside the exchanger at higher temperatures. The exchange can be characterized using Gaines-Thomas

selectivity coefficients that are independent of the exchange composition. The produced theoretical curve agreed well with the experimental

adsorption data. Some of the new results are ready but are yet to be analysed Compacted experiments are starting.

Figure 1. Exchange isotherm of Na+ on Na-montmorillonite in perchlorate background for Na-Ca exchange.

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8. Modelling transport of water and ions and chemical reactions in compacted bentonite – two flexible modelling platforms

Poster in Montpellier and in TOUGH meeting, a paper submitted after TOUGH Numerola & VTT

Figure 2. As an example we applied a simple 1D-geometry of 0.1m length. The right boundary was closed for mass transport and the left side is only closed for bound water species. The initial state is given by assumption that all bound sites are occupied by stable sodium and in free water there is concentration of 100 mol/m3 stable sodium and chloride. At the left boundary there is the same total concentration, but the fraction of radioactive NaCl is 0.1%.

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9. Measurement of chloride concentration in the pore water of compacted bentonite with ion-selective electrode

Poster in Montpellier (VTT) The results indicate that it is possible to measure concentrations in the non-

interlamellar pores of compacted bentonite with ion-selective electrodes. The method can also support the microstructural studies of bentonite

Figure 3. The chloride concentration measured in the bentonite sample, the porosity which explains the measured concentration at the end of the measurement (blue line) and the concentration evaluated from the total chloride and total water in the sample (red line).

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Conclusions - Performance

Project is going on as planned Collaboration

Between BOA partners Domestic EU BELBaR

Many conference presentations Several accepted scientific articles Project group is now familiar with PA (Performance Assessment)

view

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VTT - 70 years of technology for business

and society

Assessment of bentonite characteristics�BOAIntroductionSlide Number 3Scales, bentonite properties and waterStructure and processesSlide Number 6Slide Number 7Experimental methodsModelling methods and toolsGoals of BOA - PurposeSub-tasks, methods and partners 2013 - StructureSelected results - State1. Dissolution of Na- and Ca-montmorillonite in groundwater simulants under anaerobic conditions�VTT, GTK and ERM (Etudes Recherches Matériaux, France) 1. Dissolution�VTT, GTK and ERM�(Etudes Recherches Matériaux, France)2. Mineralogy of bentonite - GTK2. SEM-feature –analysesSlide Number 173. Small-angle x-ray scattering patterns of Ca-montmorillonite in water as a function of basal spacing3. Combined X-ray microtomography and x-ray scattering 4. Block shear experiments4. Interface friction angle (tan f) for different materials and surface roughness index Ra5. Phenomenological THM modeling and X-ray tomographic wetting/swelling experiments (JyU, Numerola Oy)Slide Number 237. The effect of colloids on radionuclide migration7. The effect of colloids on radionuclide migration6. Na/Ca selectivity coefficients of Na-montmorillonite at different temperatures8. Modelling transport of water and ions and chemical reactions in compacted bentonite – two flexible modelling platforms9. Measurement of chloride concentration in the pore water of compacted bentonite with ion-selective electrodeConclusions - PerformanceSlide Number 30

assessment of bentonite characteristics...

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