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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
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Objectives
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
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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!