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Eighteen years of steel–bentonite interaction in the FEBEX in situ test at the Grimsel Test Site in Switzerland
- Jebril Hadi, Paul Wersin, Vincent Serneels, Jean-Marc Greneche
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- Published online by Cambridge University Press:
- 01 January 2024, pp. 111-131
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Corrosion of steel canisters containing buried high-level radioactive waste is a relevant issue for the long-term integrity of repositories. The purpose of the present study was to evaluate this issue by examining two differently corroded blocks originating from a full-scale in situ test of the FEBEX bentonite site in Switzerland. The FEBEX experiment was designed initially as a feasibility test of an engineered clay barrier system and was recently dismantled after 18 years of activity. Samples were studied by ‘spatially resolved’ and ‘bulk’ experimental methods, including Scanning Electron Microscopy, Elemental Energy Dispersive Spectroscopy (SEM-EDX), μ-Raman spectroscopy, X-ray Fluorescence (XRF), X-ray Diffraction (XRD), and 57Fe Mössbauer spectrometry, with a focus on Fe-bearing phases. In one of the blocks, corrosion of the steel liner led to diffusion of Fe into the bentonite, resulting in the formation of large (width > 140 mm) red, orange, and blue colored halos. Goethite was identified as the main corrosion product in the red and orange zones while no excess Fe2+ (compared to the unaffected bentonite) was observed there. Excess Fe2+ was found to have diffused further into the clay (in the blue zones) but its speciation could not be unambiguously clarified. The results indicate the occurrence of newly formed octahedral Fe2+ either as Fe2+ sorbed on the clay or as structural Fe2+ inside the clay (following electron transfer from sorbed Fe2+). No other indications of clay transformation or newly formed clay phases were found. The overall pattern indicates that diffusion of Fe was initiated when oxidizing conditions were still prevailing inside the bentonite block, resulting in the accumulation of Fe3+ close to the interface (up to three times the original Fe content), and continued when reducing conditions were reached, allowing deeper diffusion of Fe2+ into the clay (inducing an increase of 10–12% of the Fe content).
Surfactant-Modified Clay Sorbents for the Removal of p-nitrophenol
- Ruta Ozola, Andrejs Krauklis, Juris Burlakovs, Maris Klavins, Zane Vincevica-Gaile, William Hogland
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- Published online by Cambridge University Press:
- 01 January 2024, pp. 132-142
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Organic pollutants are widespread and a known problem for the environment. p-nitrophenol (PNP) is one such pollutant found in effluents from various industries involved with pesticides, pharmaceuticals, petrochemicals, plastic, paper, and other materials. The objective of this research was to prepare and test organically modified clays using four different surfactants and to evaluate the removal efficiency of PNP from aqueous solutions. Organically modified clays have attracted great interest due to their wide applications in industry and environmental protection as sorbents for organic pollutants. Two natural smectite-dominated clay types from outcrops in Latvia and Lithuania as well as industrially manufactured montmorillonite (Mt) clay were modified using different nonionic (4-methylmorpholine N-oxide (NMO) and dimethyldodecylamine N-oxide (DDAO)) and cationic (benzyltrimethyl ammonium chloride (BTMAC) and dodecyltrimethyl ammonium chloride (DTAC)) surfactants. Modified clay materials were characterized by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and the Brunauer-Emmett-Teller method (BET) for surface area analysis. Sorption of PNP was investigated under various conditions, e.g. surfactant loading, initial PNP concentration, contact time, and pH. The novelty of the present study was to prepare innovative organo-sorbents based on manufactured as well as natural clay samples using cationic surfactants and nonconventional nonionic surfactants as modifiers. The sorption data combined with FTIR and XRD supplementary results suggests that nonionic organo-clay (Mt-DDAO_2) is the most effective sorbent and may serve as a low-toxicity immobilizer of pollutants such as phenols.
Removal Efficiency of Basic Blue 41 by Three Zeolites Prepared from Natural Jordanian Kaolin
- Mousa Gougazeh, Fethi Kooli, J.-Ch. Buhl
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- 01 January 2024, pp. 143-153
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The conventional method of zeolite synthesis involves an expensive hydrothermal step whereby a mixture of a metakaolinite, sodium hydroxide, and water is preactivated by thermal treatment between 400°C and 1000°C. The objective of the current study was to determine whether Jordanian kaolinite could be converted to zeolite materials without thermal pre-activation. The alkaline hydrothermal transformation of kaolinite into hydroxysodalite (HS) was achieved, then followed by a reaction with citric acid and solid sodium hydroxide to obtain Zeolite A, or by adding solid Na2SiO3 to prepare zeolite X. These materials were tested for their ability to serve as removal agents for Basic Blue 41 (BB-41) dye from artificially contaminated water, at concentrations ranging from 25 to 1000 mg/L. The maximum removal capacities were estimated using the Langmuir model, with a value of 39 mg/g for hydroxysodalite. Zeolite-X achieved the lowest value (19 mg/g). The feasibility of BB-41 removal was deduced from the Freundlich model for the zeolites studied. The reported low-cost method is proposed as an alternative way to reduce the cost of synthesizing zeolite, and the materials were shown to be potential candidates for the removal of BB-41 dye.
Effect of Hydration on Polytypism and Disorder in the Sulfate-Intercalated Layered Double Hydroxides of Li and Al
- Latha Pachayappan, P. Vishnu Kamath
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- 01 January 2024, pp. 154-162
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The double hydroxide of Li+ and Al3+ is an anionic clay comprising positively charged metal hydroxide layers and intercalated anions. While the structure of the iono-covalently bonded metal hydroxide layer is well known, relatively less knowledge is available regarding the manner in which the anions and water molecules are packed in the interlayer region. The sulfate ion is of special interest as it can potentially intercalate in a multiplicity of orientations and grow an extended hydration sphere. The sulfate-intercalated double hydroxide was synthesized by the imbibition of Li2SO4 into both the gibbsite and bayerite forms of Al(OH)3 to obtain layered double hydroxides with the nominal formula Li2Al4(OH)12SO4·nH2O (n = 4–8). The as-prepared compounds were poorly ordered and did not yield any structural information. Temperature-induced partial dehydration yielded ordered phases of different structures in the two systems. Simulation of the powder patterns of different model structures, followed by structure refinement in both direct and reciprocal spaces, showed that the gibbsite-derived phase yielded a two-layer polytype of hexagonal symmetry (space group P63/m). The local symmetry of the sulfate ion was close to D2d with one of the C2 axes of the SO42− being nearly parallel to the c axis of the crystal. The bayerite-derived phase yielded a one-layer polytype of monoclinic symmetry (space group C2/m). The sulfate ion was oriented with its C3 axes tilted away from the stacking direction. Cooling and rehydration (relative humidity ~70%) resulted in a reversible expansion of the basal spacing due to the ingress of water molecules from the ambient humidity into the interlayer region. Hydration in both cases resulted in turbostratic disorder. The disorder in the bayerite-derived phase was a result of random intergrowth of motifs with rhombohedral and monoclinic symmetries.
Prediction of swelling characteristics of compacted GMZ bentonite in salt solution incorporating ion-exchange reactions
- Guosheng Xiang, Yongfu Xu, Feng Yu, Yuan Fang, Yi Wang
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- Published online by Cambridge University Press:
- 01 January 2024, pp. 163-172
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Salt solutions have complex effects on the swelling characteristics of compacted bentonite; these effects are caused by the inhibitory action of salinity and the ion-exchange reaction between the solution and bentonite. In order to characterize the swelling properties of compacted bentonite in a salt solution, swelling deformation tests were carried out for Gao-Miao-Zi (GMZ) bentonite specimens in NaCl and CaCl2 solutions. Swelling characteristics decreased with increasing salt concentration. Swelling strains in NaCl solution were larger than those in CaCl2 solution, even though the ionic concentration of 1.0 mol/L (M) NaCl solution is larger than that of 0.5 M CaCl2. According to the exchangeable cations tests, cation exchange was different for specimens immersed in different salt solutions. The swelling fractal model was used to predict the swelling strains of compacted bentonite in a concentrated salt solution. In this model, the effective stress incorporating osmotic suction was applied to take the effect of salinity into consideration, and the swelling coefficient, K, was employed to describe the swelling properties affected by the variation in exchangeable cations. In the model, fractal dimension was measured by nitrogen adsorption, and the salt solution had little effect on fractal dimension. K was estimated by the diffuse double layer (DDL) model for osmotic swelling in distilled water. Comparison of fractal model estimations with experimental data demonstrated that the new model performed well in predicting swelling characteristics affected by a salt solution.
Grafted Sepiolites for the Removal of Pharmaceuticals in Water Treatment
- Tomás Undabeytia, Fernando Madrid, Juan Vázquez, José Ignacio Pérez-Martínez
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- Published online by Cambridge University Press:
- 01 January 2024, pp. 173-182
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The increased detection of pharmaceuticals in finished drinking water has become a growing cause of concern in recent years. The removal of atenolol, ranitidine, and carbamazepine by sepiolite, following functionalization of its surface by organosilane grafting, constituted the subject of this investigation. Silylated surfaces include octyl, γ-aminopropyl, 3-chloropropyl, and triphenyl moieties. The sorption of atenolol and ranitidine was higher on sepiolite functionalized with 3-chloropropyl, while carbamazepine showed a higher sorption on sepiolite with triphenyl groups. Filtration experiments of both ranitidine and carbamazepine on octyl- and triphenyl-sepiolite, respectively, showed a higher retention of ranitidine in comparison to carbamazepine, in spite of the fact that the number of sorption sites was lower due to its higher binding rate.