Bentonite Samples Research Articles

Microbial diversity in bentonite, a potential buffer material for deep geological disposal of radioactive waste

Many countries are considering long-term disposal of nuclear waste in deep geological repositories (DGRs), encapsulated in metal containers, surrounded by a barrier, and emplaced in the host rock. Bentonite is found to be a safe barrier material because of its physical and chemical properties. The bentonite montmorillonite interlayer contains adsorbed organic matter and microorganisms, and therefore biogeochemical activity must be considered. This study focused on investigating the microbial diversity in Chinese bentonite by 16S rRNA analysis via Illumina sequencing to determine how these microorganisms can potentially influence DGR performance. The bentonite sample contained high microbial diversity, dominated by Archaea and abundant other bacteria. The community of Archaea included Nitrososphaera, Thermogymnomonas, and Methanobrevibacter, which are thought to play significant roles in nitrogen cycling, H2 and O2 consumption, CH4 production, and organic matter degradation. These processes can generate excessive pressure and may compromise the safety of DGRs, and therefore the use of bentonite as a barrier material should be carefully considered.

Sorption Ability of Bentonite Rocks from Yogyakarta to Eliminate the Radiocesium Elements in Solution

This activity was to examine the ability of bentonite minerals from Yogyakarta to absorb the radiocesium contained in the solution. The purposes of the experiment were to determine sorption ability of bentonite mineral from Yogyakarta to absorb radiocesium in solution or groundwater and to enrich the Indonesia bentonite capability database to absorb radiocesium. The bentonite material was planned to be used as a buffer material of the engineered barrier system on the radwaste disposal facility in the future. The contact time, the presence of Na and K ions in the solution, as well as the variable of dissolved CsCl concentration were considered as experiment parameters. The value of Kd was also used as the indicator of radiocesium sorption into the bentonite samples. The experiment results shown that the maximum of Kd value was about 6800 mL/g for sample-1, and the presence of dissolved Na and K ions in the solution could reduce the values of Kd which were 800 and 300 mL/g for sample-1, respectively. Determination of isotherm sorption of radiocesium by bentonite from Yogyakarta was approximated by using linear equation or Freundlich law.

Congo red dye removal from aqueous solution by acid-activated bentonite from sarolangun: kinetic, equilibrium, and thermodynamic studies

The abundant natural bentonite from Sarolangun deposit of Jambi Province, Indonesia, has been successfully activated by a wet acid activation method and applied as a low-cost, and environmental-friendly adsorbent for Congo red dye removal from aqueous solution. The activated bentonite samples were characterized by powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), N2 adsorption-desorption, and X-ray fluorescence (XRF). The batch adsorption technique has been conducted to study the adsorption behavior of Congo red on activated bentonite. The effects of operational parameters toward the Congo red adsorption on activated bentonite, including adsorbent dosage, initial pH, contact time, initial concentration, and temperature were investigated. Moreover, the properties of adsorption kinetics, adsorption isotherm, and adsorption thermodynamic were also investigated. The results of material characterization showed that acid-activated bentonite has better properties than natural bentonite. For instance, the surface area of acid-activated bentonite elevated almost five-fold compared with natural bentonite. The batch adsorption study showed that the Congo red adsorption on acid-activated bentonite was significantly affected by adsorbent dosage, initial pH, contact time, dye concentration, and temperature. The adsorption kinetics investigation revealed that adsorption was best evaluated by a pseudo-second-order model rather than pseudo-first-order model. The adsorption equilibrium study described that the adsorption process followed the Langmuir isotherm model. The result of thermodynamic investigation revealed that the adsorption process occurred spontaneously and favorably in high-temperature conditions.

Thermal history of Lower Palaeozoic rocks from the East European Platform margin of Poland based on K-Ar age dating and illite-smectite palaeothermometry

Large-scale shale gas prospecting in the Polish part of the East European Platform did not discover large reserves of this resources. The article presents new research indicating that one of the reasons for the lack of shale gas relates to the thermal history of the Lower Palaeozoic rocks. Illite-smectite palaeothermometry was used to reconstruct the history of the platform and determine the maximum temperatures to which these rocks were subjected. The age of illitisation was also constrained using the K-Ar method. This method allowed precise dating of the maximum age of thermal transformations due to the deposition of numerous pyroclastic horizons (K-bentonite) throughout the entire geological profile from the Cambrian to the Silurian. Isotopic dating was made on over 53 samples of Lower Palaeozoic bentonites and low-grade metamorphic clays. These results were supplemented by analysis of the degree of thermal (smectite to illite) transformation in the profiles of 37 deep boreholes. 11 zones could be distinguished with different tectonic histories within the Polish part of the East European Platform edge. Maximum heating occurred in this region at about 320–340 Ma, corresponding to the Early Carboniferous or the turn of the Early and Late Carboniferous, phase A of the Variscan orogeny, known as the Sudetian phase. In the southern part of study area, the maximum of thermodiagenesis is slightly younger – 270–290 Ma, which responds to the Early Permian, the Asturian phase, the last phase of the Variscan orogeny. This means that the generation of hydrocarbons occurred before significant Mesozoic exhumation of the Polish part of the East European Platform, which led to the escape of a considerable amount of the gas generated. The study also presents the results of an interlaboratory comparison of illite age dating using the K-Ar and Ar-Ar methods. The comparison was conducted to find out what realistic error should be considered when interpreting geological K-Ar dating results.

Characterization of Sardinian Bentonite

The employment of clays in industry and on laboratory scale is still of interest, despite their long history. The chemical-physical characteristics of such materials are strongly related to their geographical origin and the availability of proper characterization techniques is of great importance in order to gain as more information about their behavior when utilized as filling materials. In the present contribution, a physical characterization by meaning of Thermogravimetry and N2 physisorption analyses of samples of bentonite collected from the deposit of S´Aliderru in the north of Sardinia (Italy) is reported.

Experimental investigation of the effect of airgaps in preventing desiccation of bentonite in geosynthetic clay liners exposed to high temperatures

This paper investigates whether the introduction of an airgap above a composite liner made of a geomembrane (GMB) and a Geosynthetic Clay Liner (GCL) can decrease thermal loads on the GCL, reduce the risk of bentonite desiccation and/or help maintain its low hydraulic conductivity. A composite liner, subject to 20 kPa overburden load, over a well graded sand was subjected to a thermal gradient. In addition, to the reference base case in which no airgap was present, two designs included air gaps through the placement of a 10 mm and 20 mm-thick geocomposites (GC) on top of the GCL-GMB, respectively.Temperatures on top of the GCLs were found to be significantly reduced by the presence of air gaps, relative to the reference base case. All three designs resulted in GCL desiccation cracks at the end of the tests, due to the relatively high temperature gradients and low water retention of the subsoil, even in the presence of air gaps. However, X-Ray imaging revealed that crack patterns in bentonite samples from designs with air gaps were finer and narrower. Subsequent rehydration (and permeation tests) with distilled water indicated that significant self-healing of bentonite was in evidence in all three cases. However, while in the absence of an air gap the saturated hydraulic conductivity was found to be 2.8 times its pre-heating value, no significant increase was recorded for other two cases. X-Ray imaging of rehydrated samples confirmed that more effective healing had occurred in samples with an air gap.

The development of nanotechnology bentonite as adsorbent of metal Cadmium (Cd)

Cadmium (Cd) is a heavy metal that is toxic to the environment. Cadmium in the environment can be derived from natural processes such as weathering of living creatures and plants or animals from mining and industrial waste. To overcome the heavy metal pollution in the environment can be used adsorption method. The adsorbent used in the study is bentonite. The purpose of this study was to determine the absorption efficiency bentonite to the metal cadmium. Bentonite samples from the area of Jambi Province. Bentonite is divided managed bentonite inactive, active bentonite and bentonite are processed in the industry. The parameters studied in this research are a variation of the mass of bentonite, contact time and adsorption capacity. Measurements were made using Spectrometry Atomic Absorption (AAS). The results showed that the activated bentonite not have the absorptive capacity of the metal cadmium that is better than the activated bentonite. Efficiency absorption cadmium metal bentonite with a mass of 0.5 g and a contact time of 120 minutes was 90.5%, while bentoit activated with HCl efesiensinya only 32.70%.

Influence of the purification of bentonite clay from new deposits in the state of Paraíba-Brazil for use in water-based drilling fluids

Abstract Bentonite clay is used all around the world as an additive in drilling fluids. However, impurities present in this material can compromise the compatibility of the clay-fluid system. The present study aimed to analyze the effects of the purification of bentonite samples from new deposits in the state of Paraíba, Brazil, in order to make them usable in water-based drilling fluids. The samples were first purified by centrifugation, and their characteristics were determined using the following techniques: laser granulometry, X-ray diffraction, chemical analysis, cation exchange capacity, thermogravimetric analysis, and differential thermal analysis. After these determinations, the polycationic clay samples were made sodic through the addition of sodium carbonate (Na2CO3) in the proportion of 125 meq/100 g of dry clay. The rheological and filtration properties (apparent viscosity, plastic viscosity, and filtrate volume) were then tested. The results showed that the purification process was efficient for removing accessory minerals such as quartz, iron, and carbonates. With regard to rheological and filtration properties, the results following centrifugation showed that the material can be suitable for use in water-based drilling fluids.

Очищення водних систем від надлишку фосфатів за допомогою бентоніту, активованого надвисокочастотним випромінюванням

Вивчено сорбційні властивості бентоніту, опроміненого мікрохвилями, на прикладі вилучення ним фосфат-іонів із концентрованих розчинів. Використано фізико-хімічні методи аналізу та графічно-аналітичну обробку результатів експериментів. Досліджено нативні (необроблені) зразки сорбенту та зразки, опромінені мікрохвилями у два способи: а) попереднє промивання бентоніту чистою водою під дією мікрохвиль ("стимуляція"); б) опромінення мікрохвилями суспензії бентоніту безпосередньо в робочих розчинах фосфатів ("пряме опромінення"). Показано, що останній спосіб активації збільшує сорбційну здатність бентоніту за фосфат-іоном порівняно з нативним та "стимульованим" сорбентом. Криві адсорбції фосфат-іонів бентонітом під час "прямого опромінення" розчину мікрохвилями добре описано моделлю Ленгмюра. Гранична рівноважна адсорбція фосфатів (ємність моношару) становить 6,13 мг/г для способу "прямого опромінення", порівняно з 2,54 мг/г ("стимульований" зразок) та 1,15 мг/г (нативний зразок). Припущено, що внаслідок опромінення суспензії мікрохвилями можливо подолати активаційний бар'єр та зароджуються мікрокристали нерозчинних фосфатів на поверхні кристалів сорбенту. Внаслідок цього різко збільшується сорбційна ємність бентоніту за фосфат-іоном. Відзначено значний вплив кислотності та температури розчину на параметри адсорбції фосфат-іонів бентонітом.

Rate and acceleration effects on residual strength of kaolin and kaolin–bentonite mixtures in ring shearing

Rate effects on residual strength play an important role in predicting and evaluating the behaviour of reactivated landslides and in the application of test results and procedures. Although the rate dependency of residual strength has been investigated extensively, there is a lack of consistency in the experimental results. In particular, the effect of the shear rate on the residual strength of high-plasticity, low-permeability soils is not well understood. Additionally, field observations suggest that the sliding velocity of a soil block in the residual state is not constant and that its acceleration may affect the residual strength of the soil. However, the effect of acceleration changes on the residual strength of soil has not yet been investigated. The main objectives of this study are to elucidate the rate dependency of the residual strength of high-plasticity soils and investigate the effect of acceleration. In addition, the effect of the test procedure on the rate effect is also examined. A number of kaolin and kaolin–bentonite samples were tested using the Bishop-type ring shear device. The single-stage procedure which the shear rate was not changed during shearing, was conducted on individual specimens with shear rates from 0.02 to 20 mm/min to investigate the rate effect. The accelerations of 0.028 and 0.014 mm/min2 were applied in multi-stage procedure with shear rates increasing gradually from 0.002 to 20 mm/min to examine the acceleration effect. The test results show that the bentonite content significantly affects the rate effect on the residual strength of kaolin–bentonite mixtures. For instance, in the single-stage procedure, the presence of just 10% bentonite changes the rate effect from positive to negative. This may be due to the generation of unknown excess pore water pressure under fast shearing. Furthermore, the test results also show that the type of rate effect observed depends on the test procedure. For mixture samples of 90% kaolin and 10% bentonite, the rate effect is negative in the single-stage procedure but positive in the multi-stage procedure. The analysis of the experimental results suggests that the effect of acceleration can be neglected in determining the residual strength.

Thixotropic evaluation of bentonitic clay dispersions modified with nonionic surfactants for organic drilling fluids

Abstract The use of nonionic surfactants to modify the surface of bentonite is still quite restricted, although many advantages of that method can be found in the literature, like superior stability and low toxicity. On the other hand, problems involving the fluidity and viscosity of dispersions used in organic drilling fluids have become more and more challenging to colloid science. Therefore, the present study had the purpose of assessing the thixotropic behavior of dispersions of Brazilian bentonite organophilizated with nonionic surfactants for use in organic drilling fluids. Bentonite samples were organophilizated by a combination of two nonionic surfactants, being the process evaluated by X-ray diffraction and thermogravimetric analysis, in which the amount of nonionic surfactants incorporated was quantified. Fluid evaluation followed current standards. The flow curves of the organophilic clays revealed pseudoplastic behavior and the presence of hysteresis, which suggested thixotropy, with a relation between the thixotropy and the apparent viscosity of the final dispersions. Most of the process parameters evaluated showed significant effects on the value of d001 and the overall performance. Factors like clay type and organophilization method also directly affect the thixotropic behavior of dispersions. One of the samples can be considered promising for use in organic drilling fluids.

Preparation and Characterization of Magnetite-Bentonite Nano Composites from Native Bentonite Mines of Kerman-Iran

Bentonite is a kind of crystalline clay mineral with the major constituent of montmorillonite. Bentonite mines should be investigated in different areas with different climatic and environmental conditions. Kerman, is a province in the southeast of Iran famous for its rich resources of bentonite mines. In the present study, the physical and chemical characteristics of the supplied bentonites from three different mines of Kerman (Kheirabad, Tang-e Quchan and Horjand) were investigated. Kheirabad sodium bentonite sample was selected as a potent adsorbent of organic and inorganic pollutants due to high swelling index. Besides, magnetite nano composites were synthesized by stabilizing Fe₃O₄ nanoparticles on desired bentonite. The properties of nanocomposites were studied using FTIR, XRD, VSM, BET and TEM analyses.

Investigation of Cs(I) and Sr(II) removal using nanoporous bentonite

ABSTRACTBentonites are types of clays made up the dominant constituent of montmorillonite. Four types of nano-porous and nano-structured commercial bentonite clays were studied in detail for their physicochemical and mineralogical properties vs. Cs and Sr adsorption. The instrumental analyses to study samples were X-ray diffraction (XRD), X-ray fluorescence (XRF), Brunauer–Emmett–Teller (BET) surface area measurements, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and thermogravimetry (TG). The XRF and peaks of XRD patterns at 2θ = 8, 19.9, 35, 55, and 62 clearly indicated that the main component of the bentonite samples was montmorillonite. The BET analysis showed that B1 has the highest specific surface area among the other samples which its single and multiple point BET surface area were equal to 84.85 and 85.94 m2 g−1, respectively. These values represents the amount of montmorillonite and adsorption capacity of samples. The physicochemical, structural and morphological characteristics of different samples were investigated through instrumental analysis. The results of separation processes of Cs(I) and Sr(II) showed 59.75 and 45.5% adsorption capacities for B3 and B2 which were the highest values among the others. The results lead to the conclusion that samples B3 had a good adsorption capacity to remove Cs(I) and Sr(II).

Laboratory characterization and discrete element modeling of shrinkage and cracking in clay layer

The performance of a variety of geostructures, such as compacted clay liners, earth dams, and pavement embankments, is compromised by soil cracking. Experiments are set up to monitor the drying process of a clay layer under controlled temperature and humidity conditions. The gravimetric water content and images are captured automatically. Volumetric shrinkage of the bentonite sample as well as the crack patterns are determined from images. The monitored volumetric strain development is used to implement the discrete element method (DEM) to simulate the drying shrinkage and desiccation cracking. Model parameters are calibrated through unconfined compression tests on clay specimens at different water contents. This simplified calibration procedure allows characterization of the soil behaviors in the mesoscale and bypass the complex physicochemical processes involved. The initiation and propagation of cracks from the DEM model agree well with the phenomena observed in the laboratory experiments. The influence of boundary constraint and sample thickness on the crack patterns is analyzed, which includes the use of hydrophobic coating to diminish the boundary constraint. Major features of desiccation cracking can be replicated with the computational procedures. Boundary constraint, including surface roughness and strength of boundary layer, is found to significantly influence the final crack patterns.

Geochemical conditions for the formation of Mg silicates phases in bentonite and implications for radioactive waste disposal

The present study evaluates the formation of magnesium silicates phases as a result of the alkaline alteration of FEBEX bentonite in long-term experiments. The results are relevant in the context of radioactive waste disposal since the bentonite barrier will partly change its original mineralogy and condition its long-term geochemical behavior. Bentonite samples from an in situ experiment of interaction with a CEM-II-type concrete performed for 13 years in a rock gallery and a laboratory experiment of interaction with a CEM-I-type concrete performed for 10 years provide some experimental evidences on the mineralogical alteration. Results required multiple analytical techniques to resolve the nature of the Mg silicates. X-ray diffraction, thermogravimetric analyses, scanning electron microscopy, infrared spectroscopy and 27Al and 29Si nuclear magnetic resonance have been used. The mineralogical alteration is complex since several Mg silicates may coexist in the same region not only with themselves but also with carbonates and calcium (aluminium) silicate hydrates. Brucite intercalation in the interlayer of smectite, previously reported as a chlorite-like phase in a former study, is observed. In addition, a serpentine-type mineral phase was better observed in the in situ samples, at least by XRD, and a 2:1 trioctahedral phyllosilicates was better observed in the laboratory samples. Formation of Mg silicates in the bentonite barrier may buffer the Ca alkaline front originated in concrete and may decrease the porosity at the concrete-bentonite interface.

Gas transport in compacted bentonite after 18 years under barrier conditions

The FEBEX in situ test was a full-scale experiment performed at the Grimsel Test Site (Switzerland) under natural conditions to reproduce the Engineered Barrier System of an underground repository for nuclear waste. After 18 years of operation under natural hydration from the granitic host rock and heating from a heater simulating the waste canister, the experiment was dismantled. The gas permeability of bentonite samples taken during dismantling at different positions around the heater was determined in a custom-built equipment.The gas permeability of the samples decreased with their water content and dry density. The samples closest to the heater had lower water content and higher dry density, whereas the samples closest to the granite had the highest water content and lowest dry density. Thus, the gas permeability of the samples was related to their position in the barrier, tending to be lower towards the granite, where the degree of saturation was higher, and hence, the void ratio accessible for gas flow, lower. The void ratio accessible for gas flow expresses the ratio between gas accessible volume and particle volume and is computed as e(1−Sr). Because of the high water saturation of most of the barrier after the long operation period, the accessible void ratio was below 0.15 in all the samples tested. The gas permeability of these samples was related to their accessible void ratio in the same way as expected for the FEBEX reference bentonite, decreasing with it according to a power law. In this respect no changes on the gas transport properties of the bentonite took place during operation.The increase of confining pressure during testing resulted for most samples in an irreversible increase in dry density and consequently a decrease of the gas permeability. Beyond a confining stress of 4 MPa no gas flow took place through any of the wetter samples. In contrast, flow took place through the drier samples even for confining pressures as high as 9 MPa.

Cosmetic and pharmaceutical qualifications of Egyptian bentonite and its suitability as drug carrier for Praziquantel drug

The aim of this paper is to characterize and evaluate newly discovered bentonite deposits in Egypt for pharmaceutical and cosmetic applications as well as its suitability as carrier for Praziquantel drug. The study was performed for the raw bentonite sample, purified bentonite sample and alkali activated purified bentonite sample. The raw bentonite sample composed mainly of montmorillonite contaminated by little amounts of quartz and calcite, while the purified sample composed of montmorillonite without detected mineral impurities and matches the mineralogical properties of Wyoming bentonite as an international standard. Geochemically, the studied raw and purified samples appear to high purity with a chemical composition close to those of Wyoming bentonite and match the pharmacopeia specifications. The chemical properties in addition to the textural properties of the surface area, porosity, particle size distribution qualify the bentonite products to use as a function in powder, emulsion and creams. Investigation of pharmacopeia properties of pH, sedimentation volume and swelling capacity revealed the suitability of the raw and purified samples for pharmaceutical and cosmetic applications. Moreover, the microbiological tests indicated that the samples free from harmful microbial pathogens. At the optimum conditions of time (240 min), bentonite dose (250 mg) and reaction temperature (60 °C), the obtained encapsulation percentages of Praziquantel drug are 62%, 78.4% and 93.2% for raw bentonite, purified and alkali activated bentonite, respectively. The releasing percentage of the drug using an intestinal buffer at pH 7.4 is more efficient and the maximum obtained values were obtained after 420 min. The obtained releasing values are 71%, 79.2% and 87.4% for raw bentonite, purified bentonite and alkali activated bentonite, respectively

Smectite in bentonite: Near infrared systematics and estimation of layer charge

Abstract The facile and accurate measurement of the layer charge of dioctahedral smectite has been demonstrated recently by means of the O-D method, an infrared-based technique capable of recording the exact position of a dangling O-D (O H) bond stretch of interlayer water. The present work attempts to transfer this know-how to the near-infrared (NIR) spectra of natural bentonites in anticipation of even higher throughput capabilities. For this reason, the NIR systematics of ~ 70 bentonites in both natural and Na-exchanged form have been analyzed against the mid-infrared-derived layer charges of the same samples. The as determined layer charges were not biased by the nature of the interlayer cations (Ca2 +, Mg2 +, Na+). A linear correlation between the (ν + δ) combination modes of H2O and Al2OH at ~ 5250 and 4525 cm− 1, respectively, was established, confirmed on a broader collection of bentonite samples, and discussed in terms of interlayer and layer chemistry. The (ν + δ) H2O wavenumber was found to correlate linearly with layer charge, but the slope was dependent on interlayer cation due to the cation-dependence of the bending δ Η2Ο fundamental mode. Additionally, PLS chemometric modeling of the NIR spectra was employed successfully to provide layer charge predictive algorithms, desensitized from the effect of interlayer cation (Ca2 +, Mg2 +, Na+).

Synthesis of Cr/Al<sub>2</sub>O<sub>3</sub>- Bentonite Nanocomposite as the Hydrocracking Catalyst of Castor Oil

Synthesis and characterization of Cr/Al2O3-bentonite nanocomposite as a hydrocracking catalyst of castor oil have been conducted. The catalyst was prepared according to the following method. At the first step, bentonite was activated using H2SO4 to obtain H-bentonite, after that the activated clay was pillarized by Al2O3, Next, a salt solution of Cr (NO3)3·9H2O was impregnated in the pillared bentonite sample, followed by calcination and reduction to obtain the final catalyst, i.e. Cr/Al2O3-bentonite. The catalysts including unpillared bentonite were characterized using infrared spectrometer (FT-IR), X-Ray diffractometer (XRD), X-ray Fluorescence spectrometer (XRF), Transmission Electron Microscope (TEM) and gas sorption analyzer. GC-MS analysis was conducted to characterize the hydrocracking product. The research results showed that pillarization of bentonite caused an increasing of the basal spacing of bentonite in an amount of 1.01 nm. Although Chrom was unevenly dispersed on the bentonite and it probably blocked the bentonite framework resulted in the decrease of catalyst specific surface area, Cr/Al2O3-bentonite catalyst gave the best conversion of 64.03%. The GC-MS analysis data showed that the hydrocracking products contained various kinds of organic compounds such as acetone, acetic acid, methyl benzene, octane, heptanal, 2-octene, 1-undecanoic acid, 9-octadecenal and 10-undecenoic acid.

Hydraulic and mechanical properties of compacted bentonite after 18 years in barrier conditions

Abstract The FEBEX “in situ” test was performed at an underground laboratory in Grimsel (Switzerland) with the aim of studying the behaviour of components in the near-field of a nuclear waste repository. A gallery of 2.3 m in diameter was excavated through the granite and two heaters, simulating the thermal effect of the wastes, were placed inside, surrounded by a barrier of highly-compacted bentonite blocks. In 2015, after 18 years of operation, the experiment was dismantled. Some of the bentonite samples taken were tested in the laboratory to characterize, among others, their physical state and determine their permeability and swelling capacity. There were significant changes in water content and dry density across the bentonite barrier: their distribution was radial around the axis of the gallery, with the water content decreasing from the granite towards the axis of the gallery and the dry density following the inverse pattern. The swelling capacity of the samples was related to their position in the barrier. In the internal, drier part of the barrier an increase of the swelling capacity with respect to the reference bentonite was detected, whereas the samples from the external part swelled less than expected. This was attributed to the different salinity of the samples. The hydraulic conductivity was mainly related to the dry density of the samples and decreased with respect to the reference bentonite. This decrease was not related to the position of the samples and could be related to the microstructural reorganization of the bentonite during the 18-year operation –which brought about an average decrease in the pore size– and to the low hydraulic gradients applied to determine the permeability of the samples retrieved.