Svensk Kärnbränslehantering AB beslutade 2009 att bygga ett slutförvar av använt kärnbränsle i anslutning till kärnkraftverket i Forsmark. Tekniken för slutförvaret går ut på att omge kapslarna med bentonitlera som skydd mot vatten och bergsrörelser. Studier har dock påpekat att bentonitleran riskerar att kemiskt erodera om jonstyrkan (baskatjonerna) i grundvattnet som omsluter förvaringen blir för låg. Baskatjoner består av natrium, kalium, kalcium och magnesium. Dessa joner är viktiga för bland annat att neutralisera syror i mark och vatten. Förekomsten av dessa har sedan 90-talet minskat men kan påverkas av både ökad nederbördsmängd och ökad temperatur i vissa regioner. Baskatjoner kan lakas ur marken när pH minskar eller komma via deposition från nederbörden. Studien syftar till att utreda vilka faktorer som påverkar dels förekomsten av baskatjoner, dels dess trender i tre olika vattentyper i Forsmark: grunt grundvatten, sjövatten och vattendrag. Dataunderlaget för baskatjonerna kom från Svensk Kärnbränslehantering AB och nederbördsmängd och temperatur från Sveriges Meteorologiska och Hydrologiska Institut. De statistiska testerna som utfördes var främst Wilcoxon rank-sum test, Spearmans rangkorrelation, Mann-Kendalls trend- test och Sen’s slope-metoden. Analyserna har utförts med statistikprogramvaran R och de geografiska med QGIS. Resultatet visade att flera provtagningspunkter låg på en låg altitud och inom samma delavrinningsområde. Det fanns små skillnader i baskatjonskoncentrationen i de tre vattentyperna oberoende av berggrund, jordart eller terräng. Dock återfanns högst koncentration i de flesta fall i grunt grundvatten vilket kunde bero på höga halter natrium från havsvattnet samt kalksten i jordlagren. Korrelationerna var få varav sulfat var den som tydligast visade på ett förhållande med baskatjonerna i alla tre vattentyperna. Inte heller kunde en samvariation med temperatur och nederbörd statistiskt säkerställas. Trenderna visade på minskande koncentration av baskatjoner i grunt grundvatten och i sjövatten. Om dessa trender fortsätter utifrån studiens resultat kan det på sikt finnas en risk för erodering av bentonitleran runt kapslarna till följd av landhöjning och utbyte av det nuvarande bräckta grundvattnet. / The Swedish Nuclear Fuel and Waste Management Company decided in 2009 to build a final repository for spent nuclear fuel in connection with the nuclear power plant in Forsmark. The technology for the final repository involves surrounding the capsules with bentonite clay as protection against water and rock movements. However, studies have pointed out that the bentonite clay is at risk of chemically eroding if the ionic strength of the groundwater surrounding the repository becomes too low. Base cations consist of sodium, potassium, calcium, and magnesium. These ions are important for neutralizing acids in soil and water. The occurrence of these has decreased since the 90s but can be affected by both increased rainfall and increased temperature in certain regions. Base cations can further be leached from the soil when the pH decreases or come via deposition from precipitation. This study aims to investigate which factors affect the presence of base cations and their trends in three different types of water in Forsmark: shallow groundwater, lake water and stream water. The data set for the base cations came from the Swedish Nuclear Fuel and Waste Management Company and rainfall and temperature from the Swedish Meteorological and Hydrological Institute. The statistical tests performed were mainly the Wilcoxon rank-sum test, Spearman's rank correlation, Mann-Kendall's trend test and Sen's slope method. The analyzes have been performed with the statistical software R and the geographic ones with QGIS. The result showed that several sampling points were at a low altitude and within the same sub-catchment. There were small differences in base cation concentration in the three water types regardless of bedrock, soil type or terrain. However, the highest concentration was found in most cases in shallow groundwater, which could be due to high levels of sodium from seawater and limestone in the soil layers. The correlations were few, of which sulfate was the one that most clearly showed a relationship with the base cations in all three water types. Nor could a co-variation with temperature and precipitation be statistically ensured. The trends showed a decreasing concentration of base cations in shallow groundwater and in lake water. If the trends continue based on the results, in the long term there may be a risk of erosion of the bentonite clay that surrounds the capsules because of land uplift and replacement of the current brackish ground water.

Canada is in the process of implementing a Deep Geologic Repository (DGR) to dispose of used nuclear waste. Adsorption behaviour of both Se(-II) and Tc(IV) onto granite, shale, limestone, illite, and MX-80 bentonite has been elucidated. Se(-II) adsorption onto granite and MX-80 bentonite displays a decrease in Rd with an increase in solution pH. Se(-II) adsorption onto granite decreases with an increase in solution ionic strength. Se(-II) adsorption onto MX-80 bentonite does not return evidence which supports an apparent effect due to the ionic strength. Tc(IV) adsorption onto shale, limestone, illite, and MX-80 bentonite remains constant as the solution pH increases. Ionic strength does not affect the magnitude of Tc(IV) adsorption across the adsorbents, however an increase in ionic strength accelerates Tc(IV) adsorption. Se(-II) surface complexation models are best simulated with the following surface complexes: ≡Feldspar_sSe-, ≡Biotite_sOH2HSe, ≡Albite_sSe-, ≡Montmorillonite_sSe-, and ≡Montmorillonite_sOH2HSe. Tc(IV) adsorption is best simulated with: ≡Biotite_sOTcO(OH), ≡Quartz_sOTcO(OH), (≡Feldspar_sOH)2TcO(OH)-, ≡Montmorillonite_sOTcO(OH), (≡Albite_sOH)2TcO(OH)-, ≡Illite_sOTcO(OH), and ≡Chlorite_sOTcO(OH). Se(-II) adsorption onto granite and MX-80 bentonite in CR-10 solution returns Rd values of (1.80 ± 0.10) m3∙kg-1 and (0.47 ± 0.38) m3∙kg-1, respectively. Tc(IV) adsorption onto granite and MX-80 bentonite in CR-10 solution returned Rd values of (1.47 ± 0.25) m3∙kg-1 and (2.19 ± 0.33) m3∙kg-1, respectively. Tc(IV) adsorption onto shale, limestone, illite, and MX-80 bentonite in SR-270-PW solution returned Rd values of (0.16 ± 0.10) m3∙kg-1, (0.44 ± 0.21) m3∙kg-1, (1.86 ± 0.44) m3∙kg-1, and (0.23 ± 0.10) m3∙kg-1, respectively. This thesis will further deepen the understanding of Se(-II) and Tc(IV) adsorption. / Thesis / Doctor of Philosophy (PhD) / Determining the adsorption of Se(-II) and Tc(IV) onto granite, shale, limestone, illite, and MX-80 bentonite is beneficial to choosing a location within Canada to locate a used nuclear fuel repository. This thesis aims to quantify the adsorption behaviour of Se(-II) and Tc(IV) in Ca-Na-Cl and Na-Ca-Cl solutions with respect to a varying solution ionic strength and pH. Quantification of the adsorption was accomplished with adsorption experiments used in conjunction with geochemical simulations. New simulated surfaces specific to granite, shale, and MX-80 bentonite have been developed to complete these simulations. A final achievement was quantifying the adsorption of Se(-II) and Tc(IV) in groundwater representative solutions specific to locations considered for the used nuclear fuel repository.

In this work 23Na MAS NMR was validated as a successful quantitative method for studies of exchanging sodium in bentonites useful, in particular, for studies of ion-exchange kinetics. Na-enriched bentonites equilibrated in a re-circulated process water at iron-oxide pelletizing plants may acquire properties of Ca-bentonites after already 20 minutes of the equilibration time, since >50 % of sodium ions will be exchanged by calcium ions during first minutes of bentonite placed in contact with the process water. It was shown that all sodium activated bentonites used in this study exchange >50% of sodium in Na+/Ca2+ and ca 20 % of sodium in binary Na+/Mg2+ systems with the same bentonite/solution ratio and same concentrations of these ions in aqueous solutions as in the process water at a pelletizing plant. In total, approximately 50 % of the exchangeable sodium in original bentonites was exchanged after equilibrating of bentonites in the process water already after 20 minutes. Experimental Na+/Ca2+ exchange curves for ‘model’ Ca2+(aq) solutions and for process water are very similar as Ca2+ is the dominant constituent in the process water. Since bivalent ions (Ca2+ and Mg2+) that present in the process water readily replace Na+ ions, Na-bentonite transforms into Ca- or Mg- bentonite, which have worse rheological, swelling and, therefore, binding properties. This ion-exchange process can influence the binder performance in the pelletizing process. Taking into account that fluorapatite is one of the components present in a blend of minerals processed, possible interactions between orthophosphate (the principal anionic component of apatites) and bentonites in aqueous suspensions are considered. It was found that sorption of orthophosphate on Ca-montmorillonite follows a different pattern from sorption of orthophosphate on aluminum oxides and kaolinite. While there is a small amount of sorption below pH 7, which may involve inner-sphere complexation and precipitation of AlPO4 to Al-OH edge sites on the montmorillonite crystals, most sorption of orthophosphate occurs at higher pH. Both macroscopic sorption measurements and solid-state 31P MAS NMR suggest that above pH 7 there is precipitation of proton depleted calcium phosphate phases. Based on both 31P chemical shifts and 31P chemical shift anisotropies it was concluded that the principal precipitated phased are most likely ‘brushite-like’ phases. Very short spin-lattice T2(31P) relaxation times (≤100 μs) for the orthophosphate/bentonite systems can possibly be explained by the presence of paramagnetic Fe in bentonites. Since there are insufficient concentrations of soluble Fe species in the supernatant solution that may give rise to the observed effects, it is likely that orthophosphate is precipitated as thin layers on the surfaces of montmorillonite crystals, where phosphorus may interact with Fe atoms present in the crystal lattice. PO4-tetrahedra in sorbed species can be also distorted giving rise to a larger 31P CSA than for pure ‘apatite-like phases’. 29Si MAS and 1H-29Si CP/MAS NMR experiments on bentonite samples also performed in this work provide information about impurities of quartz in bentonites, a level of substitution of aluminum by iron atoms in the structure of montmorillonite and about the degree of hydration of montmorillonite. 29Si NMR experiments on bentonite incubated with waterglass in aqueous suspensions at concentrations of sodium silicates as in the process water demonstrated that one can follow the process of polymerization of waterglass in solutions and also detect sodium silicates polymerized on surfaces of bentonites already after 1 hour of incubation. Polymerized waterglass sorbed on bentonite surfaces may also alter rheological, swelling and, therefore, binding properties of sodium-activated bentonites used in pelletization of iron-oxide ores.

A laboratory test program was conducted to investigate the effects of temperature, solution strength, and applied stress over increasing conditioning durations on cation exchange processes in sodium bentonite (Na-B) geosynthetic clay liners (GCLs). The test program was intended to determine if the variables of temperature, solution strength, and applied stress had beneficial or detrimental effects on the engineering behavior of Na-B GCLs in municipal solid waste (MSW) landfills and laboratory testing applications. Needlepunched-reinforced, double non-woven Na-B GCL specimens were conditioned in fluids of increasing ionic strength (DI water, 2 mM CaCl2, 50 mM CaCl2, and 200 mM CaCl2 representing control, pore water, mild MSW leachate, and harsh MSW leachate, respectively), temperatures of 5 degrees C, 20 degrees C, 40 degrees C, and 60 degrees C, and overburden stresses (30 kPa and 500 kPa representing stresses experienced by cover and bottom liner systems, respectively) which are all representative of geoenvironmental conditions observed in MSW landfill barrier systems. Cation exchange in the bentonite component of all conditioned Na-B GCL specimens was quantified by measuring the bound cation (BC) complexes and cation exchange capacities (CEC) of the specimens using inductively coupled plasma-optical emission spectroscopy (ICP-OES) analysis and by conducting index tests to determine the dimensional characteristics, swell index, and gravimetric moisture content of the specimens. For zero stress conditions, periodic measurements of electrical conductivity, total dissolved solids, sodium and calcium cation concentration, and temperature of the conditioning fluids were recorded to supplement bound cation complex data. For applied stress conditions, electrical conductivity, total dissolved solids, and temperature of the conditioning fluid were recorded. For zero stress conditions, 152 mm x 152 mm Na-B GCL specimens were conditioned in all conditioning fluids and temperatures over increasing time durations ranging from 4 hours to 32 days. For applied stress conditions, 60-mm-diameter Na-B GCL specimens were conditioned in 50 mM CaCl2 conditioning fluid at all temperatures for 4 to 16 days under the applied overburden stresses of 30 kPa and 500 kPa. Temperature, solution strength, and applied stress were all observed to affect cation exchange in the bentonite component of Na-B GCLs. Cation exchange processes were observed to increase with increasing temperature, increasing solution strength, and decreasing applied overburden stress. The majority of cation exchange processes were observed to occur within 8 to 10 days for specimens conditioned under zero stress. Cation exchange processes were observed to have a higher sensitivity to changes in solution strength (up to 625% increase in the change of Na+ BC from DI water to 200 mM CaCl2) compared to changes in temperature (up to 52% increase in the change of Na+ BC from 5 degrees C to 60 degrees C) in zero stress conditions. Changes in the bound cations of the Na-B GCL specimens over time were not reflected in the periodic electrical conductivity measurements taken of the high strength conditioning fluids. The results of this study can be used for quality assurance evaluations of in-service GCLs using thresholds developed for index properties. From the numerical thresholds determined in this study, hydrated Na-B GCL specimens sampled from the field conditioned under zero stress that exhibit swell indices greater than or equal to approximately 70% of the swell index reported by the manufacturer and gravimetric moisture contents of greater than or equal to approximately 200% will likely exhibit adequate hydraulic barrier performance. Hydrated Na-B GCL specimens sampled from the field conditioned under zero stress that exhibit swell indices of less than or equal to approximately 20% of the swell index reported by the manufacturer and gravimetric moisture contents of less than or equal to approximately 100% will likely exhibit inadequate hydraulic barrier performance. The Na-B GCL component of cover liner systems may be susceptible to high rates of cation exchange due to experiencing low overburden stress and elevated temperatures compared to typical earth temperatures. The Na-B GCL component of bottom liner systems may exhibit low rates of cation exchange due to experiencing high overburden stress and cooler temperatures.

Pu (III) is one of the key elements in the safety assessments of Canadian deep geological repository program (DGR). Sorption is a potential mechanism for retarding radionuclide transport from a DGR to the environment. In the current scenario, Pu (III) is considered to be a dominant radioactive element in the deep geological groundwater. Eu, considered to be a chemical analogue of Pu (III), its sorption behavior is now the target of our research. This thesis investigates the sorption properties of Eu on MX-80 under saline reducing conditions, and highly saline reducing conditions. The thermodynamic sorption modelling of Eu is also need to be applied. A surface sorption model is also developed by applying computer program for Eu (III) on MX-80 to investigate the sorption mechanisms of Eu (III) sorption. / Thesis / Master of Applied Science (MASc)

<p>Bentonite clays and Fe-reducing bacteria have been independently identified as important geochemical agents possessing the ability to influence metal(loid) mobility in aqueous environments. In the context of metal(loid) immobilization, however, the interactions occurring between Fe-reducing bacteria and bentonite clays remain largely undescribed. This thesis examines the immobilization of Cu²⁺, Cd²⁺, and As⁵⁺ from aqueous solution by natural bentonite clays, and compares sorption to sterile bentonite clays with sorption in the presence of Fe-reducing bacteria. The research questions under investigation in this thesis are: 1) What are the influences of potentially metal-tolerant Fe-reducing bacteria on metal(loid) uptake by bentonite clay sorbents of varying smectite content and on the stability of bentonite clay-sorbed metal(loid)s?; and 2) Are there differences in the influence of Fe-reducing bacteria on Cd²⁺ and Cu²⁺ sorption to bentonite clays when As⁵⁺, a reducible, metabolically-available metalloid, is present in solution?</p> <p>While the influence of bacterial augmentation on Cu²⁺ sorption was negligible in these experiments, Cd²⁺ sorption was enhanced in the presence of Fe-reducing bacteria, and most profoundly, As displayed time-dependent desorption during the experimental timeframe in the presence of Fe-reducing bacteria. These results highlight the existence of potential limitations to the use of bentonite clay sorbents for metal(loid)-contaminated wastewater reclamation, identifying the microbially-vulnerable nature of metal(loid) sorption reactions. Abundant facets concerning clay-bacterial-metal(loid) interactions exist which require further characterization and experimentation to generate deeper understanding of the potential utility of, as well as limitations to, the use of clay mineral-based sorbents for the sequestration of toxic metal(loid)s from aqueous solution.</p> / Master of Science (MSc)

Soil-bentonite cutoff walls are commonly used to contain contaminants in the subsurface. A key property in determining the effectiveness of a cutoff wall is its hydraulic conductivity. There are important difficulties and uncertainties regarding the accuracy of commonly used methods of measuring the hydraulic conductivity of cutoff walls. When predicting contaminant transport through cutoff walls, common practice is to use the average hydraulic conductivity of the wall. There are some cases, however, such as circumferential cutoff walls with inward hydraulic gradients, where it is also important to consider the variability in hydraulic conductivity from point to point in the wall in contaminant transport studies. A pilot-scale facility was envisioned where subsurface barrier issues such as those mentioned above could be studied. In 1998, the Subsurface Barrier Test Facility (SBTF) was constructed. In this facility, pilot-scale subsurface barriers can be installed using real construction equipment and tested in a controlled environment. The effectiveness of various methods of measuring the hydraulic conductivity of cutoff walls was studied by building and testing three pilot-scale soil-bentonite cutoff walls at the SBTF. The following currently used test methods were evaluated: API tests on grab samples, lab tests on undisturbed samples, piezometer tests (slug tests), and piezocone soundings. The use of slug tests in cutoff walls was improved in this research in the areas of avoiding hydraulic fracture and accounting for the close proximity of the trench walls. The SBTF allows for measurement of the global, average hydraulic conductivity of an installed pilot-scale cutoff wall, which is a useful value to compare to the results of the above-mentioned tests. The two main factors differentiating the results of the different test methods used for the pilot-scale walls were remolding and sample size. Remolding of the API samples significantly reduced the hydraulic conductivity of these samples compared to the hydraulic conductivity measured in lab tests on undisturbed samples, which were of similar size. For the other tests, the degree and extent of remolding were less significant compared to in the API tests. For these tests, the scale of the measurement is believed to be the main factor differentiating the results. Hydraulic conductivity was found to increase as the sample volume increased, with the global measurement of the average hydraulic conductivity producing the highest value. The influence of variability in hydraulic conductivity on contaminant transport through cutoff walls was studied from a theoretical standpoint using the one-dimensional advection-diffusion equation. Charts were developed that can be used to estimate the flux through a cutoff wall based on knowledge of the average hydraulic conductivity of the wall and an estimate of the variability in hydraulic conductivity. Data sets of hydraulic conductivity from lab tests on soil-bentonite samples from four cutoff wall case histories were used to estimate typical values of variability. The contaminant transport analyses showed that the effect of variability may be significant when the hydraulic gradient opposes the concentration gradient, which is the case for a circumferential cutoff wall with an inward hydraulic gradient. The goal of a circumferential cutoff wall with an inward hydraulic gradient is to reduce the outward diffusive flux of contaminant by inducing an inward advective flux. The effect of variability in hydraulic conductivity is to reduce the effectiveness of this scheme. / Ph. D.

A soil-bentonite cutoff wall is a type of subsurface vertical barrier constructed by back-filling a trench with a mixture of soil, bentonite, and water. Although soil-bentonite cutoff walls are common, their mechanical behavior is not well understood. Current design procedures do not consider the final stress state of the consolidated soil-bentonite backfill or deformations in adjacent ground. The final stress state in the completed wall is important because it influences the hydraulic conductivity of the cutoff (Barrier 1995), the cutoff's susceptibility to hydraulic fracture, and the magnitude of deformations adjacent to the cutoff wall. Deformations adjacent to the cutoff wall can be significant and can cause damage to adjacent structures. The objectives of this research are to 1) add to the current body of knowledge of the properties of soil-bentonite mixtures, 2) evaluate constitutive models and select a model to represent soil-bentonite, 3) model a soil-bentonite cutoff wall using finite elements, and 4) investigate the influence of several factors on the deformations in adjacent ground. These objectives were met by first summarizing information from the literature on soil-bentonite properties and then performing a laboratory testing program on different soil-bentonite mixtures. Five constitutive models were evaluated to determine how well they match the data from the laboratory testing program. A model referred to as the RS model was chosen to best represent soil-bentonite, and provided a good match of the soil-bentonite behavior. The RS model, which is a special case of a more complicated existing model, is a non-associative Modified Cam Clay type model that has parameters to change the yield surface and plastic potential surface into ellipses of varying shapes. The RS model was implemented into the finite element program SAGE. A finite element model was developed using SAGE to simulate all stages of construction of a soil-bentonite cutoff wall including excavation of a trench under bentonite-water slurry, replacement of the bentonite-water slurry with soil-bentonite backfill, and consolidation of the soil-bentonite backfill. The model was calibrated with a well-documented case history, and predicted deformations in adjacent ground were close to measured deformations. Evaluation of the model indicates that there is good confidence in the prediction of deformations in adjacent ground, but there is lower confidence in the predicted stresses in the consolidated soil-bentonite and settlement of the backfill in the trench. A parametric study was then performed using the finite element model assuming sand sites of varying density and OCR. Deformations in adjacent ground were calculated for various soil conditions, soil-bentonite properties, and trench configurations. A correlation was found between maximum calculated settlement in adjacent ground and factor of safety against trench / Ph. D.

Este trabalho, propõe nova tecnologia para tratamento de efluentes gerados pelas indústrias de laticínios. Atualmente este tipo de efluente, quando tratado, utiliza o processo biológico para reduzir a carga orgânica, contudo, este método, algumas vezes, não garante a remoção completa dos compostos orgânicos. Assim, é sugerido a utilização de argila bentonitica sódica para a adsorção da lactose como tratamento terciário do efluente da indústria de laticínios. A comprovação deste evento assim como sua quantificação foi realizada através de duas técnicas distintas: análise térmica e difração de raios-X. Os resultados obtidos foram positivos, pois comprovou-se não só a adsorção como também a absorção do material orgânico, no caso, a lactose na argila avaliada. Verificou-se a capacidade da argila bentonitica de Wyoming ab-adsorver até 50% da lactose. Assim, este trabalho oferece alternativa para o tratamento terciário do efluente das indústrias de laticínios. / This work considers new technology for effluent treatment generated by the dairy industries. Currently this type of effluent, when treated, uses the biological process to reduce the organic load, however, this method, some times, does not guarantee the complete removal of organic composites. Thus, the sodium bentonite use is suggested for the adsorption of the lactose as tertiary treatment of the effluent one of the dairy industry. The evidence of this event as well as its quantification was carried through two distinct techniques: thermal analysis and x-ray diffraction. The gotten results had been positive, therefore the adsorption not only proved the absorption of the organic material, in the case, the lactose in the evaluated clay. It was verified capacity of the Wyoming bentonite of to ab-adsorption up to 50% of the lactose. Therefore, this work offers alternative for the tertiary effluent treatment of the dairies industries.

Este trabalho, propõe nova tecnologia para tratamento de efluentes gerados pelas indústrias de laticínios. Atualmente este tipo de efluente, quando tratado, utiliza o processo biológico para reduzir a carga orgânica, contudo, este método, algumas vezes, não garante a remoção completa dos compostos orgânicos. Assim, é sugerido a utilização de argila bentonitica sódica para a adsorção da lactose como tratamento terciário do efluente da indústria de laticínios. A comprovação deste evento assim como sua quantificação foi realizada através de duas técnicas distintas: análise térmica e difração de raios-X. Os resultados obtidos foram positivos, pois comprovou-se não só a adsorção como também a absorção do material orgânico, no caso, a lactose na argila avaliada. Verificou-se a capacidade da argila bentonitica de Wyoming ab-adsorver até 50% da lactose. Assim, este trabalho oferece alternativa para o tratamento terciário do efluente das indústrias de laticínios. / This work considers new technology for effluent treatment generated by the dairy industries. Currently this type of effluent, when treated, uses the biological process to reduce the organic load, however, this method, some times, does not guarantee the complete removal of organic composites. Thus, the sodium bentonite use is suggested for the adsorption of the lactose as tertiary treatment of the effluent one of the dairy industry. The evidence of this event as well as its quantification was carried through two distinct techniques: thermal analysis and x-ray diffraction. The gotten results had been positive, therefore the adsorption not only proved the absorption of the organic material, in the case, the lactose in the evaluated clay. It was verified capacity of the Wyoming bentonite of to ab-adsorption up to 50% of the lactose. Therefore, this work offers alternative for the tertiary effluent treatment of the dairies industries.