<p>The main issue of this thesis was to obtain information ondiffusion and sorption behaviour on organic colloids incompacted bentonite through experimental studies. It was tostudy if bentonite is an efficient barrier for organic colloidsor not. If colloids diffuse into bentonite in sufficientconcentrations, the speciation and sorption characteristics ofdiffusing radionuclides will change. Colloids might facilitatetransport, especially of radionuclides immobilised by strongsorption on bentonite.</p><p>Laboratory experiments were performed to determine thestability of humic substances (HS) and bentonite colloids insolutions of ionic strengths representative for deep graniticgroundwaters. The HS but not the bentonite colloids were foundto be stable in these conditions.</p><p>The competition between complexation with HS and sorption onbentonite of the cations Sr(II) and Eu(III) were studied inbatch experiments. Eu(III) was foundto complex with HS to bigextent. If HS is present in sufficient concentrations andstable in compacted bentonite, the Eu(III)-HS will be a speciesthat has to be accounted for. Sr(II) sorption decreases in thepresence of HS at ionic strength 0.01 M, but not at 0.1 M.Sr(II) sorbs weakly on bentonite and forms weak complexes withHS.</p><p>The diffusion of Sr(II) in bentonite compacted to 1.8 g/cm3dry density and equilibrated with 0.1 M NaClO4 solutions wasstudied with and without HS in the system. The HS concentrationwas varied between 0.1 and 0.2 g/l. The Sr(II) diffusion wasnot affected by the presence of HS, which is in agreement withthe competition data of complexation to HS and sorption onbentonite.</p><p>Diffusion of Co(II) and Eu(III) was studied in bentonite ofcompaction 0.6-1.8 g/cm3in the presence of HS. Eu(III)diffusion without HS in the system was studied as well. Co(II)diffusivity was found to increase significantly in the presenceof HS and the Kd-values decreased drastically. The decrease inthe Kd-values was found to be ionic strength dependent. This isexplained by HS complexation capacity decreases with increasingionic strength. The results indicate that the strongly surfacecomplexed Co(II) is mobilised by HS, but the Co-HS is not theonly diffusing Co(II) species in the experimental conditions ofthis study.</p><p>Considering that Eu(III) sorbs strongly on bentonite, thediffusivity of Eu(III) was found to be rather high at ionicstrength 0.01 M. The high diffusivity rates are explained bythat the cation-exchanged Eu(III) around 1 % of the totalsorption is in practise mobile. In the presence of HS, Eu(III)diffusivity increases and the sorption decrease drastically.The Eu(III)-HS seems to be the dominating Eu(III) species whenthe HS concentrations are sufficiently high, and the HSsorption and diffusivity govern the system.</p><p><b>Keywords:</b>Diffusion, sorption, complexation, stability,bentonite, humic substances, Sr(II), Co(II) and Eu(III).</p>

Th. doct.--Géol.--Lille 1, 2002. / Bibliogr. p. 273-293. Résumé en français et en anglais.

Thèse doctorat : Matériaux Polymères et Composites : Villeurbanne, INSA : 2003. / Titre provenant de l'écran-titre. Bibliogr. p. 245-258.

Thèse doctorat : Matériaux Polymères et Composites : Villeurbanne, INSA : 2006. / Titre provenant de l'écran-titre. Bibliogr. en fin de chapitre.

Th. doct.-ing.--Géol. de l'ingénieur--Nancy--I.N.P.L., 1984.

No description available.

Soil-bentonite (SB) slurry walls are one of the most popular techniques for minimizing the horizontal migration of contaminants. Backfill arching, or “hang-up” of the backfilled slurry, on the wall trench has the potential to significantly reduce the effectiveness of these barriers. This research was conducted to supplement the design and installation of an 11,000 m long slurry wall at PotashCorp’s mine in Rocanville, Saskatchewan. The slurry wall is being installed through low permeability glacial till containing permeable granular zones. This study was undertaken to improve the understanding of vertical stress distribution in these deep barriers. In particular, the objective of this study was to develop an understanding of the factors controlling arching and hydraulic conductivity (k) of SB walls. Slurry wall “hang-up” or arching is dependent on shear along the wall of the trench and on a coefficient of lateral earth pressure (K). Consolidated drained (CD) shear box tests were conducted to study the shear strength parameters of the backfill mixes. Six inch proctor mold was modified with load cells on the side walls to measure horizontal stresses along with consolidation. This was used to calculate coefficient of lateral earth pressure, K (which is the ratio of horizontal to vertical effective stress). The results of the laboratory testing program found that K was relatively independent of the percentage of fines present in the SB mix. It also showed that backfill angle of internal friction and k of the backfill decreased with increased fines content. The results of the laboratory testing program were used to model the vertical stress distribution in deep walls. An analytical model (discrete model) and a coupled seepage stress-strain finite element model (FEM) were used to predict vertical stress changes with time and depth for the different backfill materials. The primary conclusion of this research is that slurry wall backfill arching or “hang-up” significantly delays the magnitude and timing of vertical stress build-up in backfill. This loss of vertical stress results in backfill with lower density and higher hydraulic conductivity. The situation was found to be most critical for deep narrow slurry walls. Any advantage in using a coarser graded backfill was offset by higher backfill hydraulic conductivity. The net result is that the upper portions of slurry walls may not be able to achieve their hydraulic conductivity objectives as soon as expected, if at all. In addition, the backfill in the upper portion of the trench may be susceptible to chemical attack and osmotic consolidation. Construction of a 2 m high surcharge berm over the slurry wall was found to increase vertical effective stress and result in significantly lower (2 to 8 times) hydraulic conductivity values in the top 5 metres of the trench. The final hydraulic conductivity (k) at a depth of 5 m was approximately 75 % lower with a surcharge berm. Thus, construction of a surcharge berm over the slurry wall helps to satisfy the k requirement for SB walls and lowers the risk of osmotic consolidation.

The Advanced Fuel Cycle Initiative (AFCI) is a Department of Energy (DOE) program, that has been investigating technologies to improve fuel cycle sustainability and proliferation resistance. One of the program's goals is to reduce the amount of radioactive waste requiring repository disposal. Cesium and strontium are two primary heat sources during the first 300 years of spent nuclear fuel's decay, specifically isotopes Cs-137 and Sr-90. Removal of these isotopes from spent nuclear fuel will reduce the activity of the bulk spent fuel, reducing the heat given off by the waste. Once the cesium and strontium are separated from the bulk of the spent nuclear fuel, the isotopes must be immobilized. This study is focused on a method to immobilize a cesium- and strontium-bearing radioactive liquid waste stream. While there are various schemes to remove these isotopes from spent fuel, this study has focused on a nitric acid based liquid waste. The waste liquid was mixed with the bentonite, dried then sintered. To be effective sintering temperatures from 1100 to 1200 degrees C were required, and waste concentrations must be at least 25 wt%. The product is a leach resistant ceramic solid with the waste elements embedded within alumino-silicates and a silicon rich phase. The cesium is primarily incorporated into pollucite and the strontium into a monoclinic feldspar. The simulated waste was prepared from nitrate salts of stable ions. These ions were limited to cesium, strontium, barium and rubidium. Barium and rubidium will be co-extracted during separation due to similar chemical properties to cesium and strontium. The waste liquid was added to the bentonite clay incrementally with drying steps between each addition. The dry powder was pressed and then sintered at various temperatures. The maximum loading tested is 32 wt. percent waste, which refers to 13.9 wt. percent cesium, 12.2 wt. percent barium, 4.1 wt. percent strontium, and 2.0 wt. percent rubidium. Lower loadings of waste were also tested. The final solid product was a hard dense ceramic with a density that varied from 2.12 g/cm3 for a 19% waste loading with a 1200 degrees C sintering temperature to 3.03 g/cm3 with a 29% waste loading and sintered at 1100 degrees C. Differential Scanning Calorimetry and Thermal Gravimetric Analysis (DSC-TGA) of the loaded bentonite displayed mass loss steps which were consistent with water losses in pure bentonite. Water losses were complete after dehydroxylation at ~650 degrees C. No mass losses were evident beyond the dehydroxylation. The ceramic melts at temperatures greater than 1300 degrees C. Light flash analysis found heat capacities of the ceramic to be comparable to those of strontium and barium feldspars as well as pollucite. Thermal conductivity improved with higher sintering temperatures, attributed to lower porosity. Porosity was minimized in 1200 degrees C sinterings. Ceramics with waste loadings less than 25 wt% displayed slump, the lowest waste loading, 15 wt% bloated at a 1200 degrees C sintering. Waste loading above 25 wt% produced smooth uniform ceramics when sintered >1100 degrees C. Sintered bentonite may provide a simple alternative to vitrification and other engineered radioactive waste-forms.

Thèse de doctorat : Génie des Matériaux : Villeurbanne, INSA : 2000. / Titre provenant de l'écran-titre. Bibliogr. p. 165-174.

Thèse de doctorat : Physique, chimie et biologie de l'environnement : Strasbourg 1 : 2008. / Texte en anglais. Titre provenant de l'écran-titre. Bibliogr. p. 180-192.