oral session 12 : retention/sorption

Oral Session 12

Retention/sorptionChair: Pedro Hernan - Eric Giffaut

International Meeting, March 14-18, 2005, Tours, FranceClays in Natural & Engineered Barriers for Radioactive Waste Confinement

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IODIDE (I-) WEAK AFFINITY FOR CLAY MINERALS IN ANOXIC

AND ABIOTIC CONDITIONSTournassat Christophe1, Gaucher Eric1, Negrel Gabrielle2, Moussay Anne1

1. BRGM, French Geological Survey, 3, av. Claude Guillemin, BP 6009, 45060 Orléans Cedex 2,FRANCE

2. ANTEA, 3, av. Claude Guillemin, BP 6009, 45 060 Orléans Cedex 2, FRANCE

Iodide sorption isotherms are performed on samples from the Callovo-Oxfordian argilite (Andra URL,Bure, France) and on an Illite du Puy sample. The chemical experimental conditions are similar to thoseexpected in the natural formation (Eh, pH, and major ions concentrations). Experiments are conducted attwo different temperatures (25°C and 80°C) in an N2-atmosphere glove-box in order to avoid any contactwith O2, with added iodide concentrations ranging from 10-8 to 10-3 mol L-1, and with an experimenttime varying from 1 to 70 days. At low iodine concentration (from 10-8 to 10-6 mol L-1), the partition coefficient (Kd) of iodide onargilite is found to be negative (Figure 1). Leachate experiments show large variations on iodide concentrations extracted from the porewater. Despite of these fluctuations, one can estimate that iodineconcentration is approximately ten times higher in the porewater of the Callovo-Oxfordian formation(from 6 to 16 µmol L-1) than in the seawater (~ 0.5 µmol L-1). Furthermore, this extractable concentrationof iodine accounts for less than 10 % of the total iodine available in the sediment. Negative Kd are thenattributed to the extraction of iodine initially present in the argilite. This effect is even more pronouncedin the experiment conducted at 80°C after argilite one-month maturation at 120°C (Figure 2). At higheriodine concentration, sorption is not significant and Kd was determined to be zero in the limits of theerror bars. Furthermore, iodide sorption experiments on illite confirm that iodide is not sorbed by themost abundant clay mineral present in the formation, whatever the pH in the value range 5 to 9. Then,the iodine retention mechanism responsible for the past iodine accumulation in the Callovo-Oxfordianformation is not reactivated under the experimental conditions given above. These results are at variance with many other results published in the literature. Thorough examinationsof these previous studies allow us to point out the main influence of bacteria and O2 in the retentionmechanism of iodide in sedimentary rocks, iodide being efficiently incorporated in the sediment whenboth bacteria and O2 are available. A similar mechanism, involving probably algae and bacteria, is certainlyresponsible for a bio-accumulation of iodine in the Callovo-Oxfordian formation before diagenesis.Some previous studies, where bacteria were removed by chemical, thermal or radio sterilisation techniques,show weak but positive affinity for iodide on soils or sediments. At very low total iodine concentration(10-14 to 10-12 mol125I L-1), iodide conversion into iodate in the presence of O2, is likely to explain thesepositive sorption results. Recent studies, conducted in parallel with the present one in the framework of an Andra program on theradionuclides behaviour in far-field environments, show also weak iodide affinity for Callovo-Oxfordianargilite. These experiments were conducted in the same conditions than the present one but at traceiodine concentration and using radiotracers. We consider that these apparent contradictions with ourresults are due to the disturbing effect the natural high concentration of iodine in the Callovo-Oxfordianformation. A model of iodine distribution in the argilite is built to explain the whole data, including isotopic equilibria.As a conclusion, given the uncertainties due to the presence of natural iodine in the argilite, a Kd valueof 0 could be considered while simulating the diffusion of iodine from a nuclear waste disposal formation,due to the reductive and probably abiotic chemical conditions prevailing in argilite sedimentary rocks.Furthermore, we raise two problems. The first one deals with the interpretation of the results of iodide

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International Meeting, March 14-18, 2005, Tours, FranceClays in Natural & Engineered Barriers for Radioactive Waste ConfinementPage 188

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sorption isotherms that are conducted at very low concentrations in absence of control of the redox condi-tions. The second one deals with the interpretation of the result of iodide Kd or diffusion measurements attrace concentration of radiotracers when iodine is initially present at higher concentrations in the sedimentporewater.

Figure 1: Iodide Sorption isotherm on the argilite sample K100 at 25°C and after 24 hr of reaction.Partition coefficient (Kd) are plotted as a function of the iodide concentration at equilibrium. Solid content = 200 g L-1.

Figure 2: Iodide Sorption isotherm on the argilite sample K119 at 80°C and after 24 hr of reaction, following a maturation phase of one month at 120°C. Partition coefficient (Kd) are plotted as a functionof the iodide concentration at equilibrium. Solid content = 200 g L-1.

Acknowledgements:This research is a part of a study initiated, followed and supported by Andra (Agence nationale pour lagestion des déchets radioactifs), the French national radioactive waste management agency, in theframework of its program on the radionuclides behaviour in far-field environments.

∆rHApp in kJ.mol-1

smectite kaolinite

Cs+ no effect of temperature evidenced no effect of temperature evidenced

Ni2+ 32 ± 10 12 ± 05

Eu3+ 33 ± 10 77 ± 20


O/12/2

EXPERIMENTAL AND MODELING SORPTION OF Cs+, Ni2+, AND Ln3+ ONTO

CLAYS MINERALS UP TO 150°CEmmanuel Tertre1,2, Gilles Berger1, Sylvie Castet1, Michel Loubet1, Eric Giffaut2.

1. LMTG, UMR UPS-CNRS 5563, 14 av. E. Belin, 31400 Toulouse, France.2. Andra, 1-7 rue Jean Monnet, Parc de la Croix Blanche, 92298 Châtenay-Malabry Cedex, [email protected]

ABSTRACT:The effect of temperature on the sorption of cations onto a montmorillonite and a kaolinite was investigatedby running batch experiments at 25, 40, 80 (for the two minerals) and 150°C (only for montmorillonite).We measured the distribution coefficient (Kd) of Cs+, Ni2+ and 14 lanthanides (Ln3+) between solutionsand the montmorillonite (clay fraction of the MX80 bentonite) or the kaolinite (Georgia kaolinite KGb-1)at various pH and ionic strengths. Up to 80°C we used a conventional experimental protocol derived fromCoppin et al. (2002) [1]. At 150°C, the experiments were conducted in a PTFE reactor equipped with aninternal filter allowing the sampling of clear aliquots of solution.

The results show a weak but measurable influence of the temperature on the sorption. The Kd for Ni2+

and Ln3+ increase by a factor 2 to 5 whereas the temperature raises from 25 to 150°C. On the other hand,the effect of temperature on the sorption of Cs+ is only evidenced on the smectite at low ionic strengthand under alkaline conditions where the Kd decreases by a factor 3 between 25 and 150°C. For thesmectite at high ionic strength and kaolinite, no effect of the temperature is observed for the Cs+ sorption.The values of apparent enthalpies calculated are reported in the table 1.

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Table 1: Values of the apparent enthalpies for Cs+, Ni2+ and Eu3+ sorption on the clays minerals calculatedfrom Kd data obtained between 25 and 150°C,at 0.5M (NaClO4) and pH =7.0 ± 0.5.

A fractionation of the lanthanides spectrum is also observed, for the both minerals, at high pH and highionic strength whatever the temperature (presence of inner sphere complexes). For the kaolinite, this isillustrated on the figure 1.


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Figure 1: Kd of the REE, sorbed on the kaolinite, as a function of the atomic number, for different temperatures at pH=7.0 ± 0.4 and I=0.5M (NaClO4).

A classic complexation model (DLM), with site densities (and their pKa) obtained by acid/base titrationat 25°C and higher temperature (not presented here), explain our experimental results. As an example,figure 2 presents the comparison between our experimental data and the model for the sorption of Eu3+

on the smectite.

Figure 2: Comparison between experimental sorption data and DLM for the sorption of Eu3+ on thesmectite at 0.5M versus pH and T.

Reference:[1] Coppin F., Berger G., Bauer A., Castet S. and Loubet M., 2002. Sorption of lanthanides on smectite

and kaolinite. Chemical Geology 182, 57-68.


O/12/3

STRUCTURAL ASPECTS AND MECHANISMSOF ANION SORPTION ON HDPY+-MODIFIED

MX-80 MONTMORILLONITE: A MONTECARLO STUDY

A. Meleshyn, C. Bunnenberg

Center for Radiation Protection and Radioecology (ZSR), University of Hannover, HerrenhaeuserStr. 2, D-30419 Hannover, Germany

MX-80 bentonite has been proposed as filling material and as component of technical barriers in reposi-tories of radioactive waste, because among other favourable properties it also possesses a high sorptioncapacity for radionuclides in cationic form. The desirable sorption of anionic radionuclides is lacking innatural clay yet, but can be achieved by replacing the inorganic interlayer cations with certain organiccations [1]. Montmorillonite, representing the main sorption pool of bentonite clay, can be saturated withorganic cations above the CEC level, still containing at least 1/4 of initial amount of inorganic cations [2]as well as water [2-4] in the interlayer space. In experiments with HDPy+-modified MX-80 bentoniteBors et al. [1] showed that at HDPy+ loading of about 90% CEC bentonite was able to adsorb Cl-, I- andTcO4

- ions in the interlayer space. The deciding mechanisms of this sorption, its correlation with changingthe arrangement of HDPy+ ions in interlayer space [2, 3] as well as the detailed information about thisarrangement itself are not completely understood. However, this knowledge is very important for thetargeted optimization of sorption properties of organophilic bentonite and its applicability under repositoryconditions.In order to improve our understanding of the involved processes and the underlying structures, we havecarried out a series of NPT Monte Carlo simulations of MX-80 montmorillonite with increasing from 8%of CEC to 108% CEC interlayer content of HDPy+ ions. The interlayer contents of Cl-, Na+ ions and watermolecules change correspondingly to increase of interlayer content of HDPy+ ions. In these simulations,HDPy+ ion is modelled as a flexible structure, consisting of flexibly joined rigid units (pyridinium ring,CH2 or CH3 groups), so that it can change its conformation. Mineral layers, water molecules, organicand inorganic ions were allowed to move. OPLS-AA force field [5] was used to represent interactionsin the system. Layer spacings, interlayer structure and potential energies were sampled for averaging inthe thermodynamic equilibrium state.Simulation results are in perfect agreement with experimental assumptions that HDPy+ ions adoptmonolayer, bilayer and pseudotrilayer arrangements depending on their concentration in the interlayerspace [2, 6]. Calculated layer spacings, increasing in respond to increasing content and changingarrangements of HDPy+ ions, are in very good agreement with experimental values [1, 2] as well. Theresults assume that the sorption of Cl- ions is only possible when pseudotrilayer arrangement of HDPy+

ions is adopted in the interlayer space. Furthemore, analysis of interlayer structure suggests two possiblemechanisms of Cl- adsorption by or-ganophilic montmorillonite and clarifies the function of water inits interlayer space.

References:[1] Bors, J.; Dultz, St.; Riebe, B. (1999): Retention of radionuclides by organophilic bentonite. Eng.

Geol. 54, 195-206.

[2] Greenland, D.J.; Quirk, J.P. (1962): Adsorption of 1-n-alkyl pyridinium bromides by montmorillonite.Clay Miner. 9, 484-499.

[3] Lee, S.Y.; Kim, S.J. (2003): Dehydration behaviour of HDTMA-exchanged smectite. Clay Miner.38, 225-232.

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[4] Dultz, St.; Riebe, B. Bunnenberg, C. (2004): Temperature effects on iodine adsorption on organo-clayminerals. II. Structural effects. Appl. Clay Sci. (in press).

[5] Kaminski, G.; Duffy, E. M.; Matsui, T.; Jorgensen, W. L. (1994): Free energies of hydra-tion ofhydrocarbons from the OPLS all-atom model. J. Phys. Chem. 98, 13077-13082.

[6] Lagaly, G. (1982): Layer charge heterogeneity in vermiculites. Clays Clay Miner. 30, 215-222.


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SURFACE COMPLEXATION MODELINGUSING MULTI-COMPONENTS APPROACH:

EXAMPLES OF PREDICTIONS AND SIMPLIFICATIONS

N. Marmier1, C. Hurel1, E. Giffaut2

1. LRSAE, University of Nice Sophia Antipolis, Faculté des Sciences, 28 avenue Valrose, 06108Nice cedex 2, France.

2.Andra, 1-7 rue Jean Monnet, Parc de la Croix Blanche, 92298 Châtenay-Malabry Cedex, France.

The French underground research laboratory for the assessment of a deep radwastes disposal feasibilitywill be located in a calloxo-oxfordian argilite layer. Major components in the argilite material are claysand calcite, but numerous accessory phases, such as iron oxides and pyrite, could also be present. Theretention properties of the argilite surface are of course an important parameter which can limitedmigration of radioelement in the far field and are investigated by Kd measurements. Concurrently tothis work, surface complexation model using the multi-components (bottom up) approach is used as anhelp for interpretation. In a first step, the ability for prediction of the component additivity concept (ADTS model) was testedby confrontations with experiments. To simulate an argilite surface, different mixtures of previouslycharacterized bentonite, calcite, iron oxydes, and pyrite are suspended in an synthetic groundwater containing a radioelement in various aqueous conditions (with varying pH, radioelements concentrations,and relative mineral amounts). Radionuclides chosen for the sorption experiments are Cs, Eu, and Se,which represent a large range of chemical behaviour. Results show that mass action law (MAL) data foractive phases (bentonite and iron oxides), including surface complexation constants and sites densitiesdetermined in independent experiments, can be used in calculations without any change. Surfaces ofcalcite and pyrite do not required an explicit parameterization in the model for the tested experimentalconditions (low M/V ratios), but dissolved ions (such as calcium, carbonates,...), competing in surfaceand/or solution reactions, are taken into account with their own quantified reactivity. Dissolved silicatesand their interference with aqueous and surface species are also considered. In a second step, the solid phases responsible of the global retention in given aqueous conditions areidentified, and simplifications in the description of the mixture are proposed.

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QUANTITATIVE DETERMINATION OF 99Tc(IV) EIGENCOLLOÏDS

BY A NOVEL COLUMN PRECIPITATIONCHROMATOGRAPHY TECHNIQUE

E. Breynaert, A. Maes

Laboratory for Colloid Chemistry, Katholieke Universiteit Leuven, Kasteelpark Arenberg, 23, B-3001Leuven, BELGIUM, ([email protected])

Technetium-99, a redox-sensitive fission product is one of the key elements in long-term nuclear wastestorage and management, because of its long half-life (2.5x105 years) and its potential high mobility.Under oxidizing conditions, technetium is present as pertechnetate, a highly soluble, anionic speciesthat doesn’t exhibit any significant sorption on minerals and sediments (Lieser and Bauscher 1987).Under reducing conditions, pertechnetate is reduced to Tc(IV) which hydrolyses and eventually formsa TcO2 precipitate. Sekine et al. (Sekine et al. 2002) have visualized, by transmission electronmicroscopy, the formation of stable Tc(IV) colloids upon reduction of pertechnetate by radiolysis. Maeset al. (2003; 2004) have demonstrated that the reduction of pertechnetate in the presence of dissolvedorganic matter leads to an association of colloidal Tc(IV) species with the organic matter, probablythrough a hydrophobic sorption mechanism.

To investigate the formation of Tc(IV) colloids upon reduction of pertechnetate, the hydrolysis behaviourof Tc4+ was evaluated theoretically in the framework of a partial charge model (PCM), developed byHenry et al. (1992) to predict the reactivity of cations in aqueous solutions towards condensation andcomplexation via the their hydrolysis behaviour. This PCM is based on the electronegativity equalizationtheorem, initially formulated by Sanderson (1951) and afterwards theoretically supported by the workof Parr et al. (1978). The PCM framework was successfully applied to technetium to explain the pHdependent hydrolysis behaviour of Tc4+ that was experimentally determined throughout the previousdecades. Based on the calculated hydrolysis behaviour the reactivity of the hydrolysed species towardscondensation was evaluated as function of the pH. This resulted in the definition of a pH region whereTc(IV) eigencolloïd formation was possible.

After the prediction of their existence, the formation of 99Tc-eigencolloïds can only be successfullymodelled if there is a methodology φ quantitatively measure these species. Until now, no easily accessibleanalysis methodology existed which can be used to quantitatively determine 99Tc-eigencolloïds in aqueous solutions. Therefore a new Column Precipitation Chromatography (CPC) technique, capable ofquantitatively measuring 99Tc-eigencolloïds in aqueous solutions was developed. The CPC technique isbased on the destabilisation and precipitation of eigencolloïds by poly-cations in a confined porousmatrix. After precipitation onto the column the colloids can be quantitatively eluted, upon oxidation topertechnetate by a peroxide eluent. The formation of 99Tc-eigencolloïds upon reduction of pertechnetateby hydrazine was followed quantitatively in filtered (0.2 µm) reactive reducing mixtures until 4 hoursafter the start of the reduction. This showed a gradually decreasing pertechnetate concentration and agrowing eigencolloïd population.

The authors acknowledge financial support from KULeuven University

References:Henry, M., J. P. Jolivet and J. Livage (1992). “Aqueous Chemistry of Metal-Cations - Hydrolysis,Condensation and Complexation.” Structure and Bonding 77: 153-206.

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Lieser, K. H. and C. Bauscher (1987). “Technetium in the Hydrosphere and in the Geosphere .I.Chemistry of Technetium and Iron in Natural-Waters and Influence of the Redox Potential on theSorption of Technetium.” Radiochimica Acta 42(4): 205-213.

Maes, A., C. Bruggeman, K. Geraedts and J. Vancluysen (2003). “Quantification of the interaction ofTc with dissolved boom clay humic substances.” Environmental Science & Technology 37(4): 747-753.

Maes, A., K. Geraedts, C. Bruggeman, J. Vancluysen, A. Roßberg and H. Hennig (2004). “Evidence forthe Formation of Technetium Colloids in Humic Substances by X-Ray Absorption Spectroscopy.”Environmental Science & Technology 38(7): 2044-2051.

Parr, R. G., R. A. Donnelly, M. Levy and W. E. Palke (1978). “Electronegativity - Density FunctionalViewpoint.” Journal of Chemical Physics 68(8): 3801-3807.

Sanderson, R. T. (1951). “An Interpretation of Bond Lengths and a Classification of Bonds.” Science114(2973): 670-672.

Sekine, T., H. Narushima, Y. Kino, H. Kudo, M. Z. Lin and Y. Katsumura (2002). “Radiolytic formationof Tc(IV) oxide colloids.” Radiochimica Acta 90(9-11): 611-616.


O/12/6

EXPERIMENTAL INVESTIGATIONS OF COLLOIDS AND EU(III)/NI(II)

ADSORPTION PROPERTIES OF THE CALLOVO-OXFORDIAN

CLAYSTONE FROM BURE (FRANCE)GdR FORPRO: Raymond Michels1, Pierre Faure1,Marcel Elie1, Gilles Montavon2 ,

Mourad Azouazi2, Valérie Moulin3, Pascal Reiller4, Florence Casanova4, Florence Mercier3,Nicole Barré3, Pauline Michel1,Yann Hautevelle1, Danièle Bartier1, Luis Martinez1, Bernd Grambow2

1. UMR CNRS 7566 G2R , Faculté des sciences, BP 236, 54501 Vandœuvre-lès-Nancy Cedex, France2. UMR 6457 SUBATECH, Ecole des Mines de Nantes, BP 20722, 44307, Nantes cedex 3, France3. UMR CEA-CNRS-UEVE 8587, 91191 Gif sur Yvette Cedex, France4- CEA, DEN/DPC, 91191

Gif sur Yvette Cedex, France

INTRODUCTIONThis work aimed to study the retention potential and colloidal transport properties of Eu(III) and Ni(II) ofthe Callovo-Oxfordian claystone from the underground laboratory site of Bure (France). The investigationwas based on the study of the raw claystone as well as experimentally oxidized samples to test the effectsof air alteration on the generation properties of colloids and retention potential of Eu(III) and Ni(II).

EXPERIMENTAL AND ANALYTICAL 1) The mineral content was analyzed by Xray diffraction as well as XPS photoelectron spectroscopy.

The organic matter was characterized by optical and electron microscopy, elemental analysis, Rock-Evalpyrolysis, molecular geochemistry.

2) Artificial oxidation was performed by submitting an aliquot of Callovo-Oxfordian claystone to air in aventilated oven at 130°C for 2h to 1024h.

3) Colloids were extracted from suspension of powdered raw and oxidized (512h) samples (fraction<300µm)by sedimentation.

4) Size distribution of colloids was determined by photon correlation spectroscopy. 5) Retention capacity of the samples (raw shale, oxidized shale as well as isolated kerogen) with respect

to Eu(III) and Ni(II) was studied by batch experiments under air conditions. Isotherms were measuredusing a typical water composition of the Callovo-Oxfordian claystone.

RESULTSKerogen. Kerogen occurs as particles up to several hundreds of microns, mainly vitrinite and inertinite,some amorphous material with rare algal remains. Electron microscopy reveals the presence of kerogenrich patches associated with pyrite, as well as very fine particles of a few microns in size disseminatedthroughout the mineral network, and very much in association to calcite. Elemental analysis of isolatedkerogen indicates that H/Cat=0.96 and O/Cat=0.23. Pyrolysis-gc-ms combined with TMAH methylationreveals a molecular signature predominated by aromatic moieties, with lesser contributions of aliphatic aswell as phenolic compounds and long chain carboxylic acids. Results indicate that kerogen is a mixturebetween oxidized higher plants material and lesser marine algae remains. Very fine kerogen particlesdisseminated throughout the mineral network are most likely to participate to the formation of colloids. Dichloromethane extractible organic matter. The dichloromethane soluble hydrocarbons are of lowamount (77 to 87µg/g of rock for the samples studied). The extracts are composed up to 62% of polarcompounds (asphaltenes and resins), the remaining composition being equally shared by aromatic andaliphatic hydrocarbons. Hydrocarbons are very typical of the Callovo-Oxfordian from Bure and are

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homologous series of n-alkanes, iso and cyclo alkanes (among which biomarkers like steranes, diasteranes,hopanes) as well as alkyl-naphtalenes, alkyl-phenanthrenes, alkyl-dibenzothiophenes, alkylpyrenes,aromatic steroids and hopanoids. The resin fraction, in addition to macromolecular material containslong chain carboxylic acids.Results of oxidation experiments. Xray diffraction and XPS photoelectron spectroscopy reveal that thechemistry of the minerals is not significantly affected by oxidation, nor is the specific surface of thesamples. On the contrary, the organic material shows clear alteration. The oxidation of the kerogen leadsto an increase of the extractible hydrocarbons amounts from 6 to 15µg/g of rock after 1024h of oxidation.The kerogen as well as the extractible polar compounds are enriched in oxygenated compounds (especiallycarboxylic acid functions as revealed by pyrolysis-gcms and FTIR). The alteration affected also themolecular markers, and lead to the definition of molecular ratios characterizing the degree of alterationwhich were crosscalibrated with available natural oxidation data.Colloids from the raw and oxidized samples. Colloids were extracted from the raw sample as well asfrom the 512h oxidized sample. The size of the colloids as determined by photon correlation spectroscopyreveals the presence of a heterogenous population at 250nm when filtration at 0.45µm was applied.Filtration at 0.2µm allowed to separate the heterogeneous population into a mixture of particles of 5, 40and 80nm.Eu(III) and Ni(II) retention properties of the raw and oxidized claystone. The Kd values obtained forthe 0.2µm and 20nm filtered solutions were always the same for each system studied. This indicates thatcolloids are not a major migration phase for Eu(III) and Ni(II). This may be explained by 1) the relativelow abundance of colloidal particles in the solution 2) the fact that the difference in affinity of Eu(III)and Ni(II) for the colloidal and solid phases is not strong enough to allow the colloids to compete withthe rock as far as retention is concerned. The effect of the colloidal phase on the retention was thereforeneglected. Oxidation increases significantly the retention capacity of the claystone. The removal of thedichloromethane soluble fraction did not lead to a significant decrease in Kd values for Eu(III) and Ni(II).A slight increase was rather observed for Ni(II), indicating that new adsorption sites may have been madeaccessible. The chloroform extractible fraction may therefore not be an important fraction for the adsorptionprocess. It was shown earlier that minerals are not significantly affected by air oxidation, while kerogenis. The increase of adsorption after oxidation may be attributed to the formation of new oxygenatedorganic functions in the kerogen. Quantitative analysis of the data using a multi-site Langmuir model(one site is the clay+calcite while the second is the kerogen in 1.1 weight percent contribution) indicatesthat kerogen contributes for 35% for Ni(II) and 12% for Eu(III) in the total sorption on the raw rock.For the oxidized rock, the increase of retention is of a factor 2 for Eu(III) to 3 for Ni(II).

CONCLUSIONColloids are indeed present in the Callovo-Oxfordian claystone from Bure, however in low amount.They do not significantly contribute to the retention potential of the rock for Eu(III) and Ni(II).Oxidation has a significant effect on the retention properties of the rock by increasing Kd values by afactor of about 3. Newly formed organic functions on the kerogen are most likely responsible for theincrease in retention of Eu(III) and Ni(II).

oral session 12 : retention/sorption

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