Bentonite Samples Research Articles

Mathematical Modelling of the Removal of Basic Blue Dye from Effluent by a Mineral Membrane

Water contamination is a major challenge due to the discharging of wastes into the natural resources. In this study, a novel branched pore adsorption model was developed by utilizing external mass transfer coefficients, Kf , effective diffusivity, and lumped microspore diffusion rate parameters. This describes sorption kinetics from long-term adsorption that occurs between an adsorbent and an adsorbate. An investigation of the effects of dye concentration on Basic Blue 9 removal was conducted. Then by considering of initial and boundary conditions the government equations were solved. Using this model, the Basic Blue 9 (or methylene blue is an industrial inhibitor) was removed from a bentonite sample polluted by Basic Blue 9. The maximum adsorption capacity was achieved by using of Freundlich analysis. Based on the experimental data, theoretical concentration - time adjusted models were developed using a FORTRAN computer program to fit the experimental data more precisely and confirm the precision and accuracy of this research.

Prediction of Na- and Ca-montmorillonite contents and swelling properties of clay mixtures using Vis-NIR spectroscopy

The aim of this study was to evaluate whether Na- and Ca-montmorillonite and the swell-indicating properties (i.e., free swell index, water uptake capacity, and cation exchange capacity (CEC)) of clay mineral mixtures can be estimated using visible-near-infrared (Vis-NIR) spectral features. The data regarding four types of reference clay minerals (KGa-1b, kaolinite; IYd, illite; SWy-3, Na-montmorillonite; STx-1b, Ca-montmorillonite) and binary and ternary mixtures of the reference clay minerals (SWy-3/KGa-1b/IYd, and STx-1b/KGa-1b/IYd) with specific mass percentage ratios were used as a calibration dataset. The absorption spectral features could be correlated well with changes in the clay mineral content of the mixtures. The leave-one-out cross-validation results showed that the partial least square regression (PLSR) calibration models produced the best prediction in the following order: Na or Ca-montmorillonite, kaolinite, and illite amounts in the mixtures. The calibration models produced better predictions in the ascending order of CEC, free swell index, and water uptake capacity, regardless of the multivariate statistical methods and type of exchangeable cations in montmorillonite. Validation using an independent dataset indicated that the PLSR model predicted the Na- and Ca-montmorillonite content in clay mineral mixtures and bentonite samples. The results of this study provide the possibility of using Vis-NIR absorption spectral features as a screening tool for predicting the montmorillonite content with different interlayer cations in relatively pure clay soils (e.g., bentonite), if the calibration model is developed using the specific montmorillonite contained in the clay soil of interest.

Investigation of the suitability of activated and non-activated bentonites from the Imerys Mine (South Africa) for geosynthetic clay liners

Geosynthetic clay liners (GCLs) have become a suitable substitute for compacted clay liners used for prevention of leachate percolation from landfills and tailings dams into the groundwater system. The characteristics of most bentonites is improved through a process of activation by mixing with soda ash (Na2CO3). This paper presents the investigation results of the suitability of bentonites from the Imerys Mine in South Africa for use in GCLs. Both activated and non-activated bentonites were investigated through X-ray diffraction (XRD) analysis and swell index, fluid loss, plate water absorption and Atterberg limits tests. The XRD analysis results indicate that the activated and non-activated bentonite have a smectite content of 58% and 67%, respectively. The swell index of non-activated bentonite was significantly lower than that of activated bentonite. The activated bentonite samples tested at different times subsequent to activation revealed that a minimum of 4 weeks of activation time is required to fully activate it to the ideal soda ash to bentonite ratio of 1:16. The fluid loss tests displayed results slightly above the required minimum of 18 mL because of the low swell index of the bentonites tested. The activated and non-activated bentonites have absorption capacities of 133% and 121%, respectively. The plasticity index of the activated bentonite is 101%, 15% higher than the non-activated bentonite. The overall results concluded that the Imerys bentonite is a medium-quality bentonite with borderline index properties that requires at least 4 weeks of beneficiation to achieve complete activation to suitably be used as GCLs. Significance: The significance of this paper is the beneficiation process of bentonite in the geotextile industry. This study is relevant to geotechnical engineers, environmental geologists, engineering geologists and other related professionals working with geosynthetic clay liners whereby bentonite is the key ingredient. The study provides an optimum ratio of bentonite to sodium carbonate and the required time for beneficiation. We further recommend that quality control measures should be implemented to ensure complete activation of bentonite, including the blending process of different qualities of bentonite.

ASSESSMENT AND IDENTIFICATION OF POLYOL BASED ON PALM OIL AND NATURAL FILLING MATERIALS FOR RENEWABLE COATING PAINT APPLICATION

Chitosan/clay hybrid nanoparticles have been prepared as natural antibacterial and anticorrosion agents to enhance the protective function of polyurethane-based coating paints. Chitosan is a material with antibacterial properties because it contains acetamide group which is widely used for hygiene purposes in the medical field. Clay is a natural clay particle with a hollow structure that allows loading and release of active substances such as surfactant ions that can contribute to improving the properties of the material. The polyurethane in this study was obtained from palm oil oleic acid, which was processed into polyol, toluene diisocyanate was added to produce polyurethane. Coating paint is efficiently loaded with chitosan and clay active substances which are combined to form a hybrid composite. Based on the FTIR data of polyurethane showing the formation of a hydroxyl group on the palm oil epoxide compound, the reaction lasted for 2 hours at 60oC as evidenced by the absorption of the OH wave number which widened at 3305.99 cm-1. The value of the wavelength of the OH group in the bentonite sample before and after purification has decreased, proving that the intercalation of surfactants into the bentonite interlayer causes the hydrophilic nature of bentonite to change to hydrophobicity. The d-spacing layer of raw bentonite has a maximum reflection angle peak of 7.26o with a d-spacing value of 1.132 nm, and the d-spacing size increases to 1.631 nm at the peak of the maximum reflection angle of 4.49o after purification. The presence of absorption at 1064.71 cm-1 in shrimp shell chitosan indicates COC vibration.

Determination of elemental concentrations of radionuclides in Turkish bentonite and calculation of radiogenic heat generation

ABSTRACT Bentonite containing smectite group clay minerals is an industrial raw material with a wide range of uses. In this study, the concentration of uranium, thorium, and radioactive potassium in ninety bentonite samples collected from quarries in Turkey was determined using an energy-dispersive X-ray fluorescence spectrometer. The concentrations of uranium, thorium and potassium varied from 0.4 to 18.2 with an average of 4.3 mg/kg, 5.4 to 53.4 with an average of 22.7 mg/kg and 0.3 to 3.4 with an average of 1.4 mg/kg, respectively. The radiogenic heat generation caused by the ionising radiation emitted from these radioactive elements in bentonite samples was calculated in the range of 0.9 to 6.6 µW/m3 with an average of 2.8 µW/m3.

Bentonite swelling into a void under suction or water flow

In the context of the deep geological disposal of nuclear waste and to improve the understanding of the homogenisation process of bentonite barriers, in particular with regard to the filling of technological voids, tests were performed with compacted FEBEX bentonite samples hydrated under limited axial swelling conditions. The samples were saturated from the top surface using the vapour transfer technique (imposing suctions of 6 and 0.5 MPa), or with deionised water injected at a low flow rate either from the bottom surface or from the gap on top. The final water content of the samples saturated via vapour transfer was related to the suction imposed during the tests according to the water retention curve. Thus, the final water content of the samples tested under suction 6 MPa was lower and not enough to allow sufficient bentonite swelling to close the gap. In contrast, the samples saturated under suction 0.5 MPa reached higher water contents and were able to fill the gap before the equilibrium water content had been reached. In the tests performed with liquid water supplied through the gap, the samples were able to swell easily into the open void and the gap closed earlier than when hydration took place from the opposite end. In all the tests, the final water content of the bentonite was higher and the dry density lower towards the hydration surface. These gradients were more remarkable and persistent as the initial strain was larger. No completely homogeneous density or water content distribution was observed in any of the tests. These changes were also reflected in the pore size distribution. The pores of size larger than the upper limit of mercury intrusion porosimetry (~ 550 µm) were also quantified, which allowed a better representation of the pore size distribution of the more swollen samples. Although the void ratio corresponding to pores smaller than 200 nm (em) was initially higher, over time the volume of macropores (eM) increased more, giving place to an overall decrease in the em/eM ratio, which tended to be constant along the samples in the longest tests. In the first stages of hydration, the macropore void ratio and size considerably increased close to the gap in the tests with saturation from it.

COMPARATIVE ANALYSIS OF LOCAL AND FOREIGN BENTONITE AS DRILLING MUD IN NIGERIA PETROLEUM INDUSTRY

The Bentonite samples were crushed to finer particles and sun dried for 5 days, using a mortal to obtain the powder form. Further, the bentonite powder is activated by chemical reaction with soda ash (Na2CO3) resulted in improved montmorillonite content. The activation process increased the clay yield and swelling power, bentonite sample was then modified using oxalic acid and CTMABr. Bentonite powder is calcined at temperature of 600 oC for 1 hour. Finally, a combination of some analytical techniques such as X-ray Flourescence (XRF), Infrared spectroscopy in transmission mode (FTIR), Thermal analysis (TGA/DTG) were employed to characterize From the characterization results it is reported that the chemical constituents of natural bentonite Phase are Al, Si, Ca,Fe and Ti. Wyoming silica, alumina, sodium and calcium contents for bentonites are (45 wt%, 17wt%, 2.7 wt%, 1.77 wt%; 61.55wt%, 20.55wt%, 2.41 wt% ,1.32 wt%; 61.80 wt%, 20.44 wt%, 2.1 wt%, 1.4 wt%; 48.35 wt% , 12.15 wt %, 3.65 wt%, 6.68 wt%) respectively. However, in this work the silica (SiO2) values of the Local and Foreign bentonites (48.16wt % and 49. 87wt %) are similar to the values reported by Nweke et al, (2015) [45 wt%]; Tabak et al., (2007) [48.35 wt%] respectively. This work is useful as reference materials for further studies and for policy decision making. Keywords: Bentonites, Petroleum Industry, Drilling Muds, Thermal Analysis, Infrared Spectroscopy.

Bentonite barrier performance affected by precipitation of secondary minerals: Diffusivities of water and iodide ions in the presence of calcium carbonate

Precipitation of secondary minerals potentially affects the long-term barrier performance of bentonite, including hydraulic conductivity and diffusivity. In this regard, diffusion pathways of anions are expected to be preferentially clogged with secondary minerals, that may contribute to the containment of anionic radionuclides. However, experimental evidence is lacking because of the slow transport of reactants and complex alterations in the compacted bentonite. In this study, bentonite sample clogged with CaCO3 was prepared by an electrochemical technique. Then, through-diffusion experiments of HDO (deuterium water) and I− ions were conducted to elucidate the effect of CaCO3 on their effective diffusivities. Overall effective diffusivities were determined from through-diffusion experiments, and local effective diffusivities at the CaCO3 layer were determined from concentration gradients of tracers inside bentonite after reaching steady states of through-diffusion. A CaCO3 layer consisting of vaterite and calcite was precipitated in Na-bentonite; correspondingly, total porosity was maximally reduced from 0.57 to 0.35 at the CaCO3 layer. The overall effective diffusivity slightly decreased in the presence of CaCO3, while the local effective diffusivity at the CaCO3 layer considerably decreased for both HDO and I− ions. The impact of CaCO3 on the local effective diffusivity of I− ions was greater than that of HDO. The results suggest that long-term precipitation of secondary minerals originating from alterations of bentonite may decrease the diffusivity of radionuclides, particularly anions.

Evaluation of terrestrial radionuclide levels and concomitant radiological risks of bentonites used in many industries

ABSTRACT Bentonite is a soft, porous, easily shaped, and absorbent material rich in aluminum, sodium, and potassium. Bentonite is a mineral widely utilized as drilling mud, ore pelletizing, absorbent/adsorbent, bleaching agent, water impedance, coating, and raw material in various industries. In this study, radiometric measurements of 90 bentonite samples collected from 21 quarries in Turkey were performed using gamma-ray spectrometry. The radiological hazards caused by indoor exposure to adults due to the utilization of bentonites as raw materials in the construction industry and outdoor external exposures to quarry workers were evaluated by estimating the activity concentration index, annual effective doses, and lifetime cancer risk. The average activity concentrations of 226Ra, 232Th and 40K measured in bentonite samples were found as (50 ± 5) Bq/kg, (76 ± 4) Bq/kg and (373 ± 19) Bq/kg, respectively. The evaluation results reveal that the bentonites examined could be safely utilized as raw materials.

Investigating the Potential of Infrared Thermography to Inform on Physical and Mechanical Properties of Soils for Geotechnical Engineering

Knowledge of physical and mechanical properties of geomaterials is fundamental to characterise their response to external forcings (mechanical, climatic) at various scales. This is true, for instance, in slope stability assessments, civil engineering works, and agriculture. The direct evaluation of these properties in situ can be difficult, especially in inaccessible or vast areas, and so can be the sampling and subsequent testing in the laboratory—where ensuring the representativeness of the acquired data at the scale of analysis poses an additional challenge. Thus, empirical correlations with more readily determinable quantities remain a powerful and practical tool. Recently, several sensors, able to inform on various geomaterial properties, have been developed. However, applications have typically targeted rocks, while studies on uncemented geomaterials (soils, geotechnically speaking) are lacking. Here, we propose a simple method to evaluate the porosity and critical state friction angle of soils via infrared thermography, consisting of periodic acquisitions of images in infrared wavelengths. To demonstrate the method’s capability, we analysed the cooling behaviour of samples of bentonite, kaolin, and sand (for which an extensive characterisation exists in the literature), after compaction to different porosities and pre-heating in an oven. We interpreted the results by seeking the optimal time interval for which a cooling rate index (CRI) could be defined, which is best linked with the target property. We found that the CRI correlates very well with the critical state friction angle (R2 > 0.85) and that different materials show unique and strong (R2 = 0.86–0.99) relationships between their porosity and the CRI, which also varies in a material-specific fashion according to the explored time interval. Although a systematic investigation on a wide range of natural soils is warranted, we argue that our method can be highly informative and could be used to calibrate remote sensing-based full-scale implementations in situ for various purposes.

Efficiency of diesel-contaminated soil washing with different tween 80 surfactant concentrations, pH, and bentonite ratios

Soil contaminated with diesel fuel is a hazard to the environment and people; therefore, it needs to be remediated. Soil washing enhanced with Tween 80 (TW80), non-toxic and non-ionic surfactant, can effectively remove diesel from contaminated soils. In this study, the effects of 0.01%, 0.1%, 0.5%, 1%, and 1.5% (v/v) [TW80] concentrations; 0%, 5%, and 15% (w/w) bentonite; and variation in pH on washing efficiency were examined in a batch test. The prepared samples were physiochemically characterized on the basis of particle size, zeta potential, cation exchange capacity (CEC), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analysis. When the bentonite content in soil was 5% or 15%, 1.5% [TW80] solution exhibited the highest washing efficiency. The diesel removal efficiencies in soil with 0% bentonite were slightly higher than those in soils with 5% and 15% bentonite because of the increase in adsorption sites by bentonite; consequently, diesel could not be easily washed out. The extracted n-alkanes showed that the percentage of carbon number 20 was higher than that of the other even-numbered carbons in the retained washed samples analyzed by gas chromatography-mass spectrometry (GC-MS). In all the washing tests, the diesel removal efficiencies in soil with 15% bentonite and 0.1% [TW80] were lower than those in soil with 15% bentonite and water because of adsorption. The bentonite samples washed with TW80 have different morphologies, with a voluminous structure composed of the fusion of all layered structures, as supported by SEM results. Changes in the diesel content and residual TW80 content in the soil before and after washing were shown by the carbon content in the EDS results. The mechanism of the washing effect was investigated by CEC and zeta potential measurements. This study may aid in selecting appropriate conditions for improving washing efficiencies in future field applications.

Characterization of the remediation of chromium ion contamination with bentonite by terahertz time-domain spectroscopy

Heavy metal pollution of agricultural and urban soils limits economic progress in the rapidly developing society. Terahertz technology is applied to detect heavy metal pollutants under existence of multiple pathways of their dissemination. In this study, terahertz time-domain spectroscopy (THz-TDS) is employed as an advanced probing technique in combination with traditional detecting methods to measure the adsorption ability of trivalent chromium ions on bentonite. The concentration of chromium ions and the weight of bentonite are known to influence on the adsorption capacity of the latter. It is tested here by both qualitative and quantitative measurements of two mentioned parameters. The adsorption process of chromium ions by bentonite is monitored using THz-TDS. The adsorptions signal from samples at 0.5 THz gradually increases with the increase of bentonite weight or chromium ion concentration. It would appear to indicate that terahertz could be used for quantitative detection of metal ions. Secondly, the ratios of results obtained by inductively coupled plasma mass spectrometry (ICP-MS) and the THz-TDS ones are stabilized at 0.105 ± 0.014 as the bentonite weight or chromium ion concentration increase. Such finding confirms that terahertz technology can be used for the quantitative detection of metal ions. Using the relationship between the ICP-MS test results and the THz-TDS ones, the amplitude value of bentonite is obtained to be 13.925 at the concentration of chromium ions of 0.05 mol/L, the mass of bentonite sample involved in adsorption of 1.5 g, and the detection frequency in THz-TDS measurements of 0.5 THz. The adsorption coefficient of bentonite is calculated to be 1.44%. Increase of the chromium ion concentration to 0.2 mol/L, and the mass of bentonite involved in adsorption to 3 g leads to the increase of the amplitude corresponding to adsorbed chromium ions to about 19.463, and the adsorption coefficient to about 2.1%. Obtained results demonstrate that terahertz technology is promising to meet the ever-increasing requirements in mineral analyses for rapid detection of chemical contaminants and measurement of the adsorption efficiencies of materials.

Bentonite Powder XRD Quantitative Analysis Using Rietveld Refinement: Revisiting and Updating Bulk Semiquantitative Mineralogical Compositions

Bentonite is a claystone formed by a complex mineralogical mixture, composed of montmorillonite, illite, and accessory minerals like quartz, cristobalite, feldspars, carbonates, and minor amounts of iron oxy-hydroxides. Bentonite presents complexity at various scales: (1): a single mineral may present different chemical composition within the same quarry (e.g., feldspars solid solutions); (2): montmorillonite presents variability in the cation-exchange distribution while illite may be presented as mixed-layer with smectite sheets; and (3): hardness and crystal size are larger in accessory minerals than in clay minerals, preventing uniform grinding of bentonite. The FEBEX bentonite used is originally from Almería (Spain), and it is a predominantly calcium, magnesium, and sodium bentonite. This Spanish FEBEX bentonite has been hydrothermally altered at laboratory scale for 7–14 years. A thermal gradient was generated by heating a disk of pressed iron powder, simulating the metal waste canister, in contact with the compacted bentonite sample. Hydration was forced from the opposite direction. XRD recorded patterns were very similar. In order to minimize the bias of XRD semi-quantitative determination methods, Rietveld refinement was performed using BGMN software and different structural models. Confidence in the quantification of the main phases allows us to convincingly detect other subtle changes such as the presence of calcite in the hydration front, right at the interface between the saturated and unsaturated bentonite, or the presence of goethite, and not hematite, in the saturated bentonite, near the source of hydration. Smectite component was 72 ± 3% and the refinement was consistent with the presence of ~10% illite, comparable with previous characterizations.

Structural and Surface Modification of Oxalic-Acid-Activated Bentonites in Various Acid Concentrations for Bleaching Earth Synthesis—A Comparative Study

The aim of this study is to investigate the oxalic acid activation of bentonites containing different types of smectites, analyse their surface modification as a function of acid concentration and create good quality bleaching earths. In particular, two different bentonite samples (one containing aluminum and one containing ferruginous smectite), after being characterized through XRD, XRF and FT-IR analysis, are treated with oxalic acid at a concentration of 0.5, 0.7 and 1 M. Their structural modifications after treatment are observed through FT-IR spectra and surface area and porosity measurement (using the BET equation and the BJH method, respectively) combined with the determination of the main structural metals’ extraction from them (using an atomic adsorption spectrometer). The results showed that the ferruginous smectite is more susceptible to oxalic acid activation compared to the aluminum smectite, and all the final products have developed extra porosity in their structure while retaining the structure of smectite (even at 0.5 M acid concentration). The activated samples were used as bleaching earths in soybean oil, and the results proved that Lovibond yellow and red colours as well as the chlorophyll of oil (measured spectrophotometrically) were reduced to the values set by the specifications.

Removal of methylene blue from water by ultrasound-assisted adsorption using low-cost bentonites

This study focused on the comparison of ultrasound-assisted (UA) and conventional (shaking or stirring) adsorption techniques, taking into account the time-dependent adsorption capacities. Six different bentonite samples were used as adsorbents, and methylene blue (MB) was used as adsorbate. Effects of pH, contact time, MB initial concentration, and temperature on the UA-adsorption were also investigated. XRD analyzes showed that all the bentonite samples were mostly composed of montmorillonite clay minerals, while XRF analyzes showed that the samples contained high percentage of silicon and aluminum oxides (≥70 wt%). Maximum zeta potential values (37.1–42.1 mV) were measured at pH 12 and, to confirm this, maximum adsorption capacities were also determined at this point. Ultrasound irradiation significantly increased the adsorption capacities of all bentonite samples in the early stages. For example, the adsorption capacity of the B-1 bentonite sample was measured as 388 mg/g by UA-adsorption at the first 5th minute, while it was 286 mg/g by conventional (C) adsorption technique at the same time. All bentonite samples showed increasing adsorption capacity with increased temperature confirming endothermic reaction. Maximum adsorption capacities of B-1, B-2, B-3, B-4, B-5, and B-6 bentonite samples with the 96–100 % MB removal percentages at selected conditions (pH: 11–12, temperature: 25 °C, contact time: 60 min, and MB initial concentrations for B-1: 800, B-2: 700, B-3,4: 650, B-5: 600, and B-6: 500 mg/L) were measured as 398, 342, 320, 296, 288, and 243 mg/g, respectively. Pseudo-second-order kinetic model and Langmuir isotherm model with higher correlation coefficients were found to be more suitable to explain the adsorption of MB cations onto bentonites. In addition, maximum adsorption capacities of B-1, B-2, B-3, B-4, B-5, and B-6 samples at 25 °C calculated from Langmuir isotherm data determined as 500, 454.5, 400, 384.6, 370, and 357.1 mg/g, respectively.

New constraints on volcanism during Ordovician-Silurian transition: Insights from marine bentonites in northern Yili Block (NW China)

The Yili Block is located at the Chinese western Tianshan and is a constituent of the Kazakhstan microcontinent. It played an important role in the evolution of the SW Central Asian Orogenic Belt (CAOB). The Yili Block underwent the Paleozoic orogeny during the subduction and closure of the Junggar Ocean. Late Paleozoic arc-type magmatic rocks have been widely recorded in the Yili Block; however, it remains poorly constrained when and how the Junggar Ocean started to subduct beneath the Yili Block. In this study, we report new results of zircon LA-ICP-MS UPb dating and LuHf isotopic analysis on a series of bentonite beds in tightly folded upper Ordovician siliceous black shales of the Guozigou Section in the northern Yili Block. The occurrence of bentonite layers and associated sulfides within graptolite-bearing siliceous black shales indicates multiple marine volcanic eruptions. Magmatic zircons separated from seven representative bentonite samples yielded consistent UPb ages ranging from 449.5 ± 2.4 Ma to 444.8 ± 2.0 Ma (Katian). In situ zircon LuHf isotopic analyses show mostly positive εHf(t) values (−0.01 and 1.31 to 11.7) and Neoproterozoic single-stage Hf model ages (TDM1 = 0.6– 1.0 Ga). A linear correlation between the εHf(t) and TDM1 suggests that these zircons likely crystallized from a common magma originated from a depleted mantle source with variable involvement of Precambrian continental crust. Our new zircon ages and Hf isotopic data are comparable with those of the Middle-Late Ordovician continental arc-type magmatic rocks in the nearby Wenquan area, both indicating that the subduction of the Junggar Ocean beneath the northern Yili Block started in the Middle-Late Ordovician, and are therefore important for early Paleozoic paleogeographic and tectonic reconstruction of the Paleo-Asian Ocean domain. In addition, the Late Ordovician marine bentonites and black shales coincide with the worldwide intensive volcanic activities and related climate/environment changes during late Katian to Hirnantian. Thus, these new data also provide further arguments for possible causes of the global climate change and mass extinction during the Ordovician-Silurian transition.

Mineralogical and physico-chemical characterization of bentonite materials from the Oued Zemmour area (Oriental Rif, Nador-Morocco): Valorization in ceramic field

The Oued Zemmour deposit is associated to Neogene volcanism in the Kert basin, Nador area (Morocco), and thus one of the numerous bentonite occurrences in the Gourougou volcano's region. To assess their potential use, this article examines the Oued Zemmour bentonite deposit, helping with mineralogical, physicochemical, morphological, geotechnical analyses and ceramic performances. Mineralogical associations are essentially made of montmorillonite, K-feldspars and plagioclase, associated with lower quantities of calcite, dolomite and quartz. The main chemical composition in oxides is SiO2 and Al2O3. Geotechnical results show that the swelling index and Atterberg limits widely vary within the deposit, but all studied samples display high plastic and swelling qualities. The 10 representative bentonite samples of the area (Oz 1–Oz 10) were subjected to a ceramic technological assessment, and all samples have displayed good quality after dry pressing method and sintering at 1000°C without any defect or cracks (except for Oz 4, Oz 5, and Oz 8 samples). Therefore, two mixtures (Oz M and Oz M1) have been developed from the samples studied, using the same manufacturing protocol. The obtained ceramics were evaluated by studying their morphological structure and macroscopic aspect, as well as their bulk density, porosity, water absorption, shrinkage and tensile strength properties.

Distribution, Sedimentology and Origin of Mineralogical Assemblages from a Continental Na-bentonite Deposit in the Cretaceous Neuquén Basin (Argentina)

Collected samples of bentonite and associated facies from the Justina deposit of Cretaceous age (Anacleto Formation) have been studied. Facies analysis, mineralogical, and geochemical studies have been carried out using several techniques, including: XRD, FTIR, DTA-TGA, microscopy (OM, SEM-EDX), and chemical analysis. The deposit occurs in a shallow, saline lacustrine environment developed over a fluvial floodplain, with a thickness between 0.21 and 0.8 m intercalated between fine-grained siliciclastic facies. Three mineral assemblages were found. In assemblage 1, the bentonite has low content of detrital minerals and the smectite is sodic. In assemblage 2, the bentonite shows the occurrence of minor analcime and mica, slightly higher detrital mineral content and the smectite is sodic to sodic-calcic. The associated detrital facies (assemblage 3) is dominated by illite and a mixed layer of illite and calcic smectite (R0), subordinately kaolinite + chlorite, and locally low-ordered smectite. As inherited minerals are found: quartz, potassium feldspar, plagioclase, illite-mica, heavy minerals (monazite, zircon, apatite, titanomagnetite) and volcanic rock fragments (andesite, glass). Authigenic minerals are: sodium smectite, analcime, barite, celestine, gypsum, and hematite. A model for the formation of authigenic minerals is proposed, highlighting the formation of sodic smectite from the alteration of volcanic glass of trachyandesitic composition.

A method for measuring wetting and swelling of bentonite using X-ray imaging

A non-invasive method based on X-ray imaging for measuring deformation and water transport in wetting and swelling bentonite samples is introduced. Sequential X-ray images taken of the samples were used to calculate the attenuation coefficient and deformation. These results, together with careful calibration, allowed finding the dry density and water content distributions and their temporal evolution in the wetting and swelling samples. A specific correction technique, based on regularly taking reference X-ray images of aluminum plates of varying thickness, was developed and used to take into account X-ray beam instabilities and thus to improve the accuracy of density analysis. Large deformation, present in the experiments, was measured with an improved version of a block-matching algorithm. The X-ray imaging method was used here to measure the axial swelling of compacted MX-80 bentonite samples in a tube when in contact with saline solution (0.1 M NaCl). This setup mimics a scenario where bentonite, planned to be used as a buffer material in a nuclear waste repository placed deep in the bedrock, swells into a rock fracture filled by groundwater. The method yielded potentially valuable data on hydro-mechanical behavior of bentonite, which may be used in developing and validating material models to be used in safety assessment of nuclear waste repository concepts.

Hydraulic and physicochemical properties of dense thin bentonite layers permeated with variably mixed alkaline solutions of KOH and CaCl2 at various temperatures (25–75 °C) for 3 years

Hydraulic conductivity tests were performed using mixed alkaline solutions of KOH and CaCl2 (pH ∼12) on thin Na-bentonite layers under various temperature conditions (25–75 °C) for 3 years. For dense thin Na-bentonite (dry density of 1.12 Mg/m3) in a mixed alkaline solution of 0.03 M KOH and 0.03 M CaCl2, the hydraulic conductivities at 50 °C and 75 °C were approximately 10 times higher than that at 25 °C. The bentonite samples permeated with the mixed solution at 50 °C and 75 °C achieved almost complete cation exchange of Na ions by Ca and K ions. However, only slight cation exchange occurred in the bentonite specimens permeated at 25 °C, regardless of the type of permeant. The free swell index of the reacted bentonite permeated with a mixed solution of 0.03 M KOH and 0.03 M CaCl2 significantly decreased at 50 °C and 75 °C compared with that at 25 °C. X-ray diffraction analysis revealed that the decreases in the relative intensities of the peaks of accessory minerals, such as opal-cristobalite/tridymite, quartz, and feldspar, were enhanced at 50 °C and 75 °C.