Kansallisen ydinjätehuollon tutkimusohjelma (KYT 2010)Kansallisen ydinjätehuollon tutkimusohjelma (KYT 2010)

Kolmenarvoisten aktinidien kiinnittyminen savi- ja

(hydr)oksidimineraalien pinnoille

Sorption of trivalent actinides onto clay- and (hydr)oxide minerals

Nina Huittinen

Radiokemian laboratorio, Helsingin Yliopisto

26.09.2008

1 - General background

Deep geological formations are considered for the long-term disposal of radioactive waste

Knowledge of geochemical processes essential for a thorough nuclear waste disposal safety assessment – e.g. solid-water

interface reactions and redox- and complexation reactions in solution

For a thorough safety assessment over long

time-scales, understanding of atomic- and

molecular scale interactions of radionuclides

with the solid-water environment is imperative

2 – Project motivations

Trivalent actinides Am and Cm are together with Pu responsible for the long-term radiotoxcicity

of spent fuel.

Trivalent oxidation state soluble – radionuclide dissolution and migration

Minerals Gibbsite α-Al(OH)3 – used e.g. as a model mineral for aluminosilicates and

iron oxides/hydroxides found in vast quantities in natural systems Kaolinite Al2Si2O5(OH)4 – one of the main mineral components of clay-rich

host formations Silica SiO2 – presence of silica ubiquitous in most natural materials and

groundwaters, colloids

Pu(III) Am(III) Cm(III)

3 – Aim of project

Characterization of present reactive OH-groups on the mineral surface

Determination of surface sites involved in An(III)/Ln(III) sorption

Characterization of sorption mechanisms and surface complexes

Possible interactions of radionuclides with present mineral phases

4 - Methods

Mineral synthesis – clean minerals FTIR - identification of OH groups and knowledge of specific bonding to

the surface Solid state NMR- identification of OH groups and knowledge of specific

bonding and coordination to the surface TRLFS – knowledge of An(III) hydration sphere and surface complexes SEM XRD N2-BET

Micro electrophoresis ICP-MS

Mineral characterization

5 – Objectives for 2008

Mineral synthesis

Mineral characterization

Basic sorption studies and mass balance studies (master’s thesis)

IR experiments

NMR experiments

International collaboration with INE, Karlsruhe, Germany - Inclusion of 5-

sulphosalicylic acid (model compound for humic acids) to study ternary

surface complex formation

6 – Results 2008

Kaolinite synthesis and characterization - Université de Poitiers, France Gibbsite synthesis and characterization, Department of Chemistry,

University of Helsinki Silica purchase EVONIK industries

6 – Results 2008

Sorption studies and mass balance studies with all chosen minerals

3 4 5 6 7 8 9 10 11 120

20

40

60

80

100

100 ppb in 0.1M NaClO4

10 ppb in 0.1M NaClO4

1 ppb in 0.1M NaClO4

1 ppm in 0.1M NaClO4

10 ppm in 0.1M NaClO4

% S

orp

tion

pH

Silikan zetapotentiaali 0,01 M NaClO4

-50

-40

-30

-20

-10

0

10

0 1 2 3 4 5 6 7 8 9

pH

zeta

-po

ten

tiaa

li

3 4 5 6 7 8 9

1

2

3

4

5

log

Kd

pH

Toinen typpikaapissa tehty koe. 0,01 M NaClO4. Eu 1 ppm. silika 2g/l.

1E-12 1E-11 1E-10 1E-9 1E-8 1E-7 1E-6 1E-5 1E-41E-7

1E-6

1E-5

1E-4

1E-3

0,01

0,1

pH 3,45 pH 4,20 - 4,30 pH 4,5 - 4,65 pH 4,7 - 4,9 pH 5,3 - 5,6 pH 6,15 - 6,45 pH 7,00 - 7,30

[Eu

](m

ol/g

)

[Eu](mol/l)

Europiumin isotermit silikaan 0,01 M NaClO4. Silika 2 g/l.

4 5 6 7 8 9 10 11 12 13-15

-10

-5

0

5

10

15

20

25

30

35

40

45

0,1M 0,01M Milli Q

Z p

ote

ntia

l [m

V]

pH

intersection pH ~ 11

1E-7 1E-6 1E-5 1E-4 1E-3 0,011E-4

1E-3

0,01

0,1

1

pH 4,93 - 5,19pH 5,99 - 6,45pH 6,63 - 7,34

[Eu

](m

ol/g

)

[Eu](mol/l)

Europiumin isotermit gibbsiittiin 0,01 M NaClO4. Gibbsiitti 2 g/l.

Modeling → mass balance of Eu3+, H+, Al3+/Si2+, anions in solid and liquid phase respectively

ξ-potential measurements → net charge of mineral surfaceBatch experiments Ln(III) sorption as a function of pH → Kd values and titration curves

Isotherm experiments – concentration of adsorbed Ln(III) as a function of Ln(III) concentration in solution→ types of OH groups

6 – Results 2008

IR-studies, FTIR- NesteOil Oy Finland, ATR-FTIR - Department of

Chemistry, University of Helsinki

3700 3600 3500 3400 3300 3200 3100

0,05

0,10

0,15

0,20

0,25

0,30

Abs

orba

nce

Wavenumber [cm-1]

Gibbsite pH 4 Gibbsite pH 8

3620 OH1

3524 OH2

3455 OH3, OH6

3430 OH3?

3396 OH5, OH6

3379 OH3, OH5, OH6

intralayer OHinterlayer OH

Gibbsite – 6 structural OH groups

1- Intralayer OH groups oriented parallel to the (001) face (OH1, OH2 and OH4)

2- Interlayer OH groups oriented nearly perpendicular to the (001) face (OH3, OH5 and OH6)

3700 3600 3500 3400 3300

0,00

0,05

0,10

0,15

0,20

0,25

ab

sorb

an

ce

wavenumbers [cm-1]

Gibbsite + 50 ppm Eu(III) Gibbsite Gibbsite + 20 ppm Eu(III)

7 – Outlook

October 2008 – Spring 2009: Collaboration with the Instute for nuclear

waste management (INE), Forschungszentrum Karlsruhe, Germany

TRLFS investigations using synthetic kaolinite and Cm(III)

Addition of model ligand to mineral/metal ion system

Possibly investigations using well characterized humic acid and natural

montmorillonite

5-sulfosalicylic acidS

O

O

OH

O

OH

OH

7 - Outlook

2009-2011

NMR-studies, National Institute of Chemical Physics and Biophysics, Tallinn,

Estonia

IR studies using alumina and silica, possibly kaolinite

Surface complexation modeling

4-5 publications

Ph.D dissertation