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Page 1: Bentonite colloid studies - SKB · Bentonite colloid studies . BELBaR Helsinki 5. -7.3.2013 . . Finnish Research Programme on Nuclear Waste Management ... The release and stability

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Pirkko Hölttä Suvi Niemiaho

Outi Elo

University of Helsinki (UH) Department of Chemistry

Laboratory of Radiochemistry

Bentonite colloid studies

BELBaR Helsinki 5.-7.3.2013

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Finnish Research Programme on Nuclear Waste Management (KYT2014/BOA/KOLORA) Formation and stability of colloids Radionuclide sorption EU FP7 BELBaR WP3 Colloid/radionuclide and host rock interaction Grimsel Test Site Phase VI, Colloid formation and migration (CFM)

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Colloid projects

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To determine the release and stability of inorganic colloids in different groundwater conditions To study bentonite erosion To determine radionuclide sorption (Kd) on MX-80

bentonite powder and bentonite colloids as a function of ionic strength, pH and particle size To Study colloid/radionuclide and host rock

interaction in dynamic conditions To test and apply colloid characterization

methods

BELBaR Helsinki 5.-7.3.2013 3

Objectives

Page 4: Bentonite colloid studies - SKB · Bentonite colloid studies . BELBaR Helsinki 5. -7.3.2013 . . Finnish Research Programme on Nuclear Waste Management ... The release and stability

www.helsinki.fi/yliopisto BOA kick off 4.3.2011

Characterization methods Dynamic light scattering (DLS: Malvern Zetasizer

Nano ZS)

Asymmetrical flow field-flow fractionation (AsFlFFF) ICP- MS, ICP-OES Field emission scanning electron microscopy

(FESEM/EDX) DualBeam focused ion beam/scanning electron

microscope with EDS Atomic force microscopy (MultiMode V scanning

probe microscope) X-ray diffraction (XRD), small-angle X-ray scattering

(SAXS)

4

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The release and stability of bentonite colloids have been followed in diluted OLSO reference groundwater, sodium chloride and calcium chloride solutions (I = 0.001 – 0.1 M) Colloidal particle size distribution and zeta

potential has been determined applying the dynamic light scattering (DLS) method. Colloid concentration determination: −A standard series made from MX-80 bentonite applying

the DLS measurement count rate. −Al determination (ICP-MS)

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Formation and stability of bentonite colloids

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OLSO 0.001- 0.03 M

NaCl 0.001- 0.1 M

CaCl2 0.001- 0.1 M

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Zeta potential as a function of ionic strength in sodium chloride, calcium chloride and OLSO solutions after 2.5 years.

Stability of bentonite colloids

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Mean zeta potential of bentonite colloids in diluted OLSO reference groundwater.

Stability of bentonite colloids

-60

-40

-20

0

20

0 200 400 600 800 1000

Zeta

pot

entia

l [m

V]

Time [d]

0.1 M

0.04 M

0.02 M

0.01 M

0.005 M

0.001 M

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Bentonite colloid concentration

Estimated particle concentration of bentonite colloids in diluted OLSO reference groundwater.

0

5

10

15

20

25

0 200 400 600 800 1000

Part

icle

conc

entr

atio

n (g

L-1

)

Time (d)

0.001

0.005

0.01

0.02

0.03

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Radionuclide sorption

Determinations as a function of ionic strength, a batch method, 4 parallel samples. 85Sr and 152Eu sorption onto bentonite powder (MX-80) − NaCl and CaCl2 solutions (I = 0.001 – 0.1 M) 152Eu sorption on bentonite colloids, separated from MX-80. − NaCl and CaCl2 solutions and diluted OLSO (I = 0.5 M) − Solutions of 10 ionic strengths (I = 0.001 – 0.1 M) 85Sr sorption determination on bentonite colloids is under

way. Radionuclide sorption reversibility in static and dynamic

conditions. − method development under way

.

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20 mL NaCl/CaCl2-solution Sr-85 or 120 µl Eu-152 tracer 1 g Bentonite powder pH ~ 8 (Adjusted)

Shaking (1h/1-2 d/7 d) Sentrifugation (7500 rpm/30 min)

10 mL aliquot Radioactivity measurement (5 min) (Wizard 3'' gamma counter) Particle size and zeta potential determination

Filtration 1.2 µm (Isopore polycarbonate filter ) Radioactivity measurement (5 min) Particle size and zeta potential determination (Zetasizer)

Filtration 0.05 µm (Isopore polycarbonate filter ) Radioactivity measurement (5 min) Particle size and zeta potential determination (Zetasizer)

Drying and weighing of the filters

Desorption experiments

KYT1014 BOA seminar 31.1.2012 11

Sorption onto powdered bentonite

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90 mL OLSO/NaCl/CaCl2-solution Sr-85 or Eu-152 tracer Bentonite colloids solution

4.5 mL aliquot after 1h/1-2 d/7 d Ultracentrifugation (90000 rpm/60 min)

Solution: Radioactivity measurement (10 min) (Wizard 3'' gamma counter) Particle size determination (Zetasizer)

Solid phase: Drying and weighing

Desorption experiments

KYT1014 BOA seminar 31.1.2012 12

Sorption onto colloids

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Colloid concentration Bentonite powder in NaCl

Eu-152 sorption

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Eu-152 sorption on colloids

0

10

20

30

40

50

60

0 0.02 0.04 0.06 0.08

K d (m

3 /kg

)

Ionic strength (M)

1d

3d

7d

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Old fracture columns from Olkiluoto tonalite New crushed rock columns from Kuru Grey

granite and strongly altered tonalite and. − The hydraulic properties have been

determined using non-sorbing tracers (36Cl, 125I) without colloids

− Experiments 85Sr and 152Eu with and without colloids are under way

Natural fracture (0.9 m x 0.9 m) in Kuru Grey granite block – Experiments will start in the near future

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Colloid/radionuclide and host rock interaction

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0

0.0001

0.0002

0.0003

0.0004

0.0005

0 200 400 600 800 1000 1200 1400

dA/A

0 dt

(1/h

)

Time (h)

Sievi crushed rock column Sr-85 with and without colloids

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The formation and stability of bentonite colloids depends strongly on the ionic strength of the medium and the valence of the cations. In NaCl (0.001-0.1 M), CaCl2 and OLSO (0.001-

0.01 M) zeta potential was lower than -30 mV indicating stable colloids. Colloids were smaller and more stable in

monovalent (Na+) than in divalent (Ca2+) dominated solutions. The colloid concentration increased only in

0.001-0.01 M solutions.

Conclusions

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Thank you and welcome to laboratory of radiochemistry!


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