Mass Transfer & Porous Media (MTPM) - Andra

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P/<strong>MTPM</strong>/43The available data are consistent with a model considering very old, possibly connate pore water in thecentre of the anticline, which undergoes a transition towards fresh water in the limb. Preliminary modelcalculations yield results indicating that the observed tracer distributions are consistent with diffusion asthe dominating transport process. The nature of the anomaly in the faulted zone, identified for waterisotopes and helium but not for chloride, is currently not clear. It is yet to be shown whether it representsa natural but geologically young feature or whether it is related to processes since tunnel excavation.Further transport modelling in 1 and 2 dimensions is currently ongoing.Figure 1: Distribution of tracer contents across Opalinus Clay and adjacent formations. Shaded areaindicates faulted zone. a) Chloride profile. Open squares: squeezing test; open circles: seepage water;closed circles: aqueous leaching, considering a chloride-accessible porosity of 0.55 times water-lossporosity. b) δ 18 O profile. Closed circles: pore water; open squares: seepage water.References:Pearson F.J., Arcos D., Bath A., Boisson J.Y., Fernandez A.M., Gaebler H.E., Gaucher E.C., Gautschi A.Griffault L. Hernan P. Waber H.N. 2003. Mont Terri Project – Geochemistry of water in the OpalinusClay Formation at the Mont Terri Rock laboratory. Report of the FOWG, Geology Series, Nº 5, 319 pp.Rübel A. Sonntag Ch., Lippmann J., Pearson F.J., Gautschi A. 2002. Solute transport in formations of verylow permeability; profiles of stable isotope and dissolved noble gas contents of pore water in theOpalinus Clay, Mont Terri, Switzerland. Geochimica et Cosmochimica Acta. 66; 8, pp. 1311-1321.Page 508INTERNATIONAL MEETING, SEPTEMBER 17...>...18, 2007, LILLE, FRANCECLAYS IN NATURAL & ENGINEERED BARRIERSFOR RADIOACTIVE WASTE CONFINEMENT
P/<strong>MTPM</strong>/44REACTIVE DIFFUSION FRONT DRIVENBY AN ALKALINE PLUME IN COMPACTEDMG-HOMOIONIC BENTONITEJaime Cuevas , Raúl Fernández, Laura Sánchez, Raquel Vigil de la Villa,Manuel Rodríguez and Santiago Leguey.Universidad Autónoma de Madrid. Campus de Cantoblanco. Facultad de Ciencias. Departamentode Geología y Geoquímica. 28049 Madrid.ABSTRACTCement - bentonite interactions need to be studied since they will occur in deep geological repositories.They are specifically relevant in the clay host rock reference concept. The reactivity of a Mg-homoionicFEBEX bentonite was studied at 60 ºC in contact with a young cement water characterized by the leachingof alkaline hydroxides (K/Na 4/1 –OH, pH = 13.5 at 25 ºC) and with an evolved cement water controlledby the portlandite dissolution (Ca(OH) 2 , pH = 12.5 at 25 ºC). The experimental approach was to rundiffusion experiments carried out in a cylindrical compacted bentonite sample, 2.1 cm long with a diameterof 7.0 cm, which is exposed on one circular face to a solution of cementitious water. A second reservoirof fluid is located at the opposite face of the bentonite sample; this contained MgCl 2 solution which wasused during the homoionization process. The bentonite sample is maintained at a constant temperature of60 ºC throughout the experiments run for 6 and 12 months.The key processes investigated were to identify and confirm, considering previous studies (Sánchez et al.,200; Savage et al., 2007), the nature of the newformed mineral phases (i.e., zeolites, CASH and Mg-silicatephases) as a result high pH reactivity of bentonite. This was complemented by addressing the spatialextension affected by mineralogical and geochemical modifications in compacted bentonite, including theextension of cationic exchange.The diffusion of the hyperalkaline plume (OPC K/NaOH solution) through compacted bentonite (1.6 g/cm3dry density) produces a mineralogical alteration front characterized by a critically cemented rim ofapproximately 2-3 mm (Figure 1). The cemented material is characterized by a drastic reduction on itsexternal specific surface (from 80 to 20 m 2 /g) as well as the CEC (100 to 50 m 2 /g). The thickness of therim did not evolve with time, then, diffusion becomes very slow due to the reduction of porosity. The selfsealing of the high pH concrete-bentonite interface has been predicted in some models and this processshould be taken into account as a potential self-stopped reactivity scenario.The mineralogical composition of the rim is a mixture of poorly ordered, Mg-rich, clay materials, mainlybrucite, hydrotalcite and tri-octahedral Mg-smectite. Montmorillonite is partially dissolved and a part of itremained trapped within the newformed cements. The alteration rim has been accurately measured bymeans of EDX-chemical profiles in flat polished sections examined under SEM microscopy (Figure 2)Alkali-zeolites have not formed at all as far as no pore-space is available for these lower density silicates.Then, alkaline cations (mainly K + ) have diffused beyond the altered rim, affecting the whole 2.1 cm lengthof the compacted bentonite disc. The K + exchange in the montmorillonite is homogeneous in the bentoniteprobe but it did not saturate completely the exchangeable positions. This can be another indication of thestopped reactivity process. The same studies are being performed at 90 ºC in order to compare the extentof the diffusion and reaction processes.At pH 12.5 and 60 ºC there was not detected any significant mineralogical alteration. The main outcomeof these experiments evidence the very limited thickness of mineralogical alteration affecting a highlycompacted bentonite exposed to the effect of hyperalkaline solutions.INTERNATIONAL MEETING, SEPTEMBER 17...>...18, 2007, LILLE, FRANCECLAYS IN NATURAL & ENGINEERED BARRIERSFOR RADIOACTIVE WASTE CONFINEMENTPage 509
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Poster [MTPM]Mass Transfer & Porous
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P/MTPM/1The free energy cost of for
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P/MTPM/3DIFFUSION OF IONS IN UNSATU
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P/MTPM/4POROUS MEDIA CHARACTERIZATI
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P/MTPM/5Oxalate ionsQuartzQuartz +P
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P/MTPM/6borehole was capped with a
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P/MTPM/7Initial state with glass an
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P/MTPM/8The mesh of the elementary
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P/MTPM/9Moreover, using another sam
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P/MTPM/10Figure 1: Horizontal cross
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P/MTPM/11n t (mol)as received8 10 -
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P/MTPM/1210,9Degree of saturation (
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P/MTPM/13RESULTSFirst, we estimated
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P/MTPM/142.5Energy (M eV)1.6 1.7 1.
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P/MTPM/15C/Co10.90.80.70.60.50.40.3
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P/MTPM/16ModelIrmayvG-M1vG-M2vG-M3T
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P/MTPM/17Figure 1: Experimental HTO
Page 38 and 39: P/MTPM/18Diffusion experiments were
Page 40 and 41: P/MTPM/19Figure 1: Used mesh for co
Page 42 and 43: P/MTPM/201.81.61.41.2upstream compa
Page 44 and 45: P/MTPM/21490Pressure [bar]0 10 20 3
Page 46 and 47: 134P/MTPM/22through-diffusion exper
Page 48 and 49: P/MTPM/23HA (µg/g)3002001000(a):pH
Page 50 and 51: P/MTPM/24through each sample. The p
Page 52 and 53: P/MTPM/25FIRST RESULTSPreliminary c
Page 54 and 55: P/MTPM/26heterogeneous distribution
Page 56 and 57: P/MTPM/27Relative concentration (C-
Page 58 and 59: P/MTPM/280.75m0.25mTable 1: Cross s
Page 60 and 61: P/MTPM/29Figure 1: A. Scheme of the
Page 62 and 63: P/MTPM/30The presented theory is ex
Page 64 and 65: P/MTPM/31Furthermore, Van Loon et a
Page 66 and 67: P/MTPM/32RESULTSResults show that,
Page 68 and 69: P/MTPM/33Clay modellingPore size di
Page 70 and 71: P/MTPM/341.60E-11f H2-d total (kg.m
Page 72 and 73: P/MTPM/350.50η R ()0.400.300.200.1
Page 74 and 75: P/MTPM/36200Bq/g1801601401201008060
Page 76 and 77: P/MTPM/37Argilite (ionic strength 0
Page 78 and 79: P/MTPM/38-Samples cored at 12m were
Page 80 and 81: P/MTPM/39APPLICATIONSCORE 2D has be
Page 82 and 83: P/MTPM/40Figure 1: Sketch drawing o
Page 84 and 85: P/MTPM/41Figure 1: Thermal conducti
Page 86 and 87: P/MTPM/42Figure 2: Model of pore st
Page 90 and 91: P/MTPM/44Figure 1: Spatial extensio
Page 92 and 93: P/MTPM/45Relative concentration / (
Page 94 and 95: P/MTPM/46Figure 2: Swelling pressur
Page 96 and 97: P/MTPM/47then used in the transport
Page 98: P/MTPM/4820181614121086Gas pressure
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