Hydration sequence for swelling clays exchanged with mixed alkali/alkali-earth cations

HAL Id: hal-02445719

https://hal-cea.archives-ouvertes.fr/hal-02445719

Submitted on 20 Jan 2020

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Hydration sequence for swelling clays exchanged with mixed alkali/alkali-earth cations

F. Salles, Olivier Bildstein, J. Douillard, B. Prelot, J. Zajac, H. van Damme

To cite this version:

F. Salles, Olivier Bildstein, J. Douillard, B. Prelot, J. Zajac, et al.. Hydration sequence for swelling clays exchanged with mixed alkali/alkali-earth cations. Scientific Basis for Nuclear Waste Management XXXIX, Nov 2015, Montpellier, France. �hal-02445719�

1

Hydration sequence for

swelling clays exchanged with

mixed alkali/alkali-earth cations

F. Salles1_{, O. Bildstein}2_{, J.M. Douillard}1 B. Prélot1_{, J. Zajac}1_{, H. Van Damme}3 1 _{ICGM, Université Montpellier, France}

2 _{CEA Cadarache, France} 3 _{ESPCI, Paris, France}

2

Context of the study

• Disposal of radioactive wastes in deep geological repositories and multi-barriers concept

• Role of clays:

– limiting water fluxes in the repository – swelling and filling up technical gaps

– adsorbing RNs (in the interlayer space and onto surfaces)

Adsorption and

absorption of water

Clay

swelling

Cation

retention/mobility

3

Outline plan

• Objectives and experimental approach • Multi-scale structure of clays

• Thermoporometry results for Montmorillonites samples

saturated by alkaline cations: pore size distribution

• Consequences for the hydration sequence in clays as a

function of the interlayer cation nature

• Diffusion of the interlayer cation as a function of the

hydration state

4

Objectives and experimental approach

• Study the “clay-water” system by looking at the modifications of water properties

 “water in clays” is different from liquid water (or free water)!

• Thermoporometry = calorimetric technique sensitive to phase transitions of fluid confined in the porosity  2 nm < Pore radius < 50 nm (mesoporosity)

 Hypothesis: Pore size is the major parameter which influences the properties of the confined fluid

• Originality of these experiments: swelling material (homoionic Wyoming montmorillonite saturated by Li+_{, Na}+_{, K}+_{, Cs}+ _{and Ca}2+ _{cations & different RH}

investigated

 Common practice : DSC on saturated non-swelling samples = all pores are filled

 Saturation of studied porosity is necessary

• Quantify the evolution of the mesopore size as a function of RH

5 -500 -400 -300 -200 -100 0 100 200 300 400 500 -100 -80 -60 -40 -20 0 20 Temperature (°C) Heat ( mW)

Pore size distribution (PSD)

• Pore size distribution obtained with Brun equations (parameters result from fit with various materials) :

HR = 75%

 2 peaks = 2 well-defined families of pore size

R_p = A/DT + B

fusion

6

Multi-scale structure of clays

• Multi-scale

aspect

• Focus on

mesoporosity

20 µm 0.1 µm 15 nm

7

Results for RH ≤ 54%

 Na-mont (purified and exchanged MX80 Wyoming)  powder

 RH < 54%  no interpretable signal (pores not filled with water? not enough water?)

 Results for RH = 54%:

 Thermoporometry not conclusive alone but same results as BJH: pores filled at 54%  We verify that the effect of Rp is dominant

N2 adsorption isotherm 0 10 20 30 40 50 60 0 0,2 0,4 0,6 0,8 1 Relative Pressure P/P0 A d s o rb e d v o lu m e c m 3 /g ~ 2.5 nm BJH calculations from N₂ adsorption data

8

Results for RH > 54%

• Results for RH ranging from 75% to saturation  No free water at RH < 90% HR = 75% HR = 90% HR sat No free water FREE WATER Osmotic swelling

9

 Osmotic swelling in the mesopores occurs starting at RH ~ 54%

Interpretation(1): evidence for osmotic swelling in mesopores

• pore size in mesopores (for the 2 families)

Mesoscopic Swelling

10

Evolution of interlamellar space

0 2 4 6 8 10 12 14 16 18 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Relative humidity Int e rla y e r dis ta nce

Interpretation (2)

• Comparison with interlayer space (d001) measurements with XRD

(Ferrage, 2005)

Osmotic swelling in interlayer space

Crystalline swelling (2 layers of water)

Osmotic swelling occurs at RH > 80% in interlayer space compared to RH ~ 54% in mesopores

Osmotic swelling in mesopores

Na

11

Adsorption isotherms

XRD

Interpretation (3): hydration sequence

… towards a step-by-step model for the

hydration Thermoporometry + XRD _{Thermoporometry}

Na

Li

RH~0% 20<RH<80% RH<20% RH<10% RH>80%

12

Interpretation (4): hydration sequence

… towards a step-by-step model for the

hydration Water adsorption isotherms XRD Thermoporometry + XRD Thermoporometry RH~0% 20<RH<60% RH<20% RH<10% RH>90%

Cs

K

Ca

13

Coherence with the driving forces of hydration



For Li and Na-samples: Cation Hydration is the driving force

 For K, Rb and Cs-samples: Surface Hydration is the driving force



Changes of leading driving forces in agreement with the experimental behavior varying with the interlayer cation

Salles et al., J. Phys. Chem. C, 2007

-1000 -800 -600 -400 -200 0 200 400 0 50 100 150 200

Rayon du cation (en pm)

E n e rg ie s d 'h y d ra ta ti o n ( e n m J /m ²) Li Na K Rb Cs

Surface

Cation

Cation Radius (pm) Hy dra ti on ene rgie s (m J/m ²)

14

Towards the distinction between interlayer or mesopore water

• From experimental data: it is possible to estimate – m_{water in clay}  from water adsorption isotherm – m_{water in mesopore}  from thermoporometry data • It follows:

m

_{interlayer water}

= m

_{water in clay}

– m

_{water in mesopore}

• The theoretical quantity of water (=maximal amount) present in interlayer space can be determined from the following equation:

m

_{theoretical interlayer water}

=d

₀₀₁

* (S

_H2O

–S

_N2)

where S_H2O and S_N2 are the specific surface area as a function of RH* and d₀₀₁ is related to the interlayer space opening

15

Distinction of interlayer and mesopore water

The interlayer spaces are never completely filled

in montmorillonites, except for Cs-sample

Li-60% Li-80% Na-60% Na-80% K Cs Ca 0 200 400 600 800 1000 1200 1400

Water u

pt

ake (

mg/

g o

f cl

ay)

Samples

• Maximal water amount in interlayer space

- Water present in interlayer space

- Water present in mesopore space

16

Diffusion of Cations in swelling clays



For Li and Na-samples: Cation diffusion reaches values for bulk water  For K, Rb and Cs-samples: Slow diffusion



Diffusion behavior is varying with the interlayer cation  osmotic swelling

Li

Na

K

Cs

0

20

40

60

80

100

10

-14

10

-13

10

-12

10

-11

10

-10

10

-9

D

if

fu

si

o

n

C

o

e

ff

ic

ie

n

t

(m

²/

s)

Relative Humidity

17

Case of Montmorillonites with mixture Na/Ca



For Na/Ca-samples: Na+ _{diffusion reaches values lower than bulk water}  Influence of Ca2+ _{and repartition of cations ?}

0

20

40

60

80

100

10

-14

10

-13

10

-12

10

-11

10

-10

10

-9

D

if

fu

si

o

n

c

o

e

ff

ic

ie

n

ts

(

m

²/

s)

Relative Humidity

Na-Ca

Na

Ca

18

Conclusions

• Summary:

– Osmotic swelling in mesopores evidenced by original use of thermoporometry

– Free water is observed in mesopores only starting at RH > 90%

– Osmotic swelling occurs in mesopores before crystalline swelling is finished in the interlayer space (2nd layer of water)

– Sequence of hydration is depending on the interlayer cation nature

– Interlayer space water > mesopore water for all cations – Interlayer space is never completely filled by water at

RH<97% for all samples except Cs+_{-montmorillonite} – Impact of Na+ _{in the Na/Ca-sample}

19

20

Thermoporometry equations

• Theoretical equation

• Simplified equation (Brun et al. 1977)

T

B

A

R

_p

D







D







T T f sl p _o

v

dT

S

t

R

2



1

)

(

1

21

Material and method

• Na-mont (purified and exchanged MX80 Wyoming) 

powder

• Thermoporometry:

– fusion-solidification-fusion cycles (2°C/min for a range of

temperatures between -80°C and 0°C)

– RH conditions: 11%, 33%, 54%, 75%, 90% (for each RH

sample: equilibration for 1 month with saline solutions), saturated material (97% < RH < 99%)

– Study of hysteresis between adsorption-desorption – Hydration with liquid water or with water vapour for

saturated samples

22

Influence of hydration method

• Liquid water vs. vapour hydration process

RH sat

 2 fusion cycles are identical

 2 solidification cycles slightly different = no significant modification of pore structure

 No influence between the two modes of hydration

fusion

solidification

Hydration with liquid water

23

PSD: hysteresis between adsorption and

desorption

HR = 75% Adsorption

HR = 75% Desorption

 No notable differences for the first peak < 0.05 nm (experimental error)

 Difference for the second peak : hysteresis (observed also in water adsorption isotherms)