Bentonite Mixtures Research Articles

Discrete geometry model of heat in granular bentonite barriers

The mineral-engineered barrier in the planned repository for radioactive waste in Switzerland is being designed as a granular bentonite mixture. The infiltrating pore water from the (clayey) host rock will start to resaturate the granular barrier after its emplacement. The discrete structure of the mineral barrier requires a more detailed analysis, because the porosity alone applied in the continuum approach cannot adequately describe the heat transfer. Towards this analysis, three granular size fractions have been arranged into square or hexagonal packings and considered in the heat transfer model presented in this paper. The six different granular arrangements are set either in a planar or in a cylindrical spatial system. A major feature of the approach is providing the modelled systems with an interstitial fluid of smoothly adjustable thermophysical parameters, approximating variable water contents. The effective thermal conductivity of various systems is an important output of the model. The calculation of the temperature equilibrium period directly depends on this parameter and represents a step towards a solution for the reliable determination of the resaturation timescale. The validity of the modelled effective thermal conductivities was confirmed by laboratory experiments on real granular bentonite.

Hydraulic and mechanical characteristics of compacted sand–bentonite: tyre chips mix for its landfill application

Compacted sand–bentonite mixtures are generally placed at waste dumping places as a means of avoiding contaminant movement to reduce or remove the potential for groundwater pollution. Owing to their almost impermeable nature and high pollutant adsorption tendency, bentonite generally treated as a liner material to avoid subsurface contamination. Cracks are formed in the landfill liner due to the desiccation, large interlayer shrinkage and differential settlement of bentonite. Fibres are commonly added to sand–bentonite mixture to act as a reinforcing material to eliminate the development of tensile cracks. Waste tyre chips are derived from the tyre retreated technique, and it can be included as short fibre in sand–bentonite mixture for the use as landfill barrier material. Hydraulic conductivity and shear strength are the two important parameters of the liner material, which are considered for hydraulic, and stability analysis in landfill application. In this context, consolidation and consolidated undrained tests were performed to study the hydraulic and mechanical behaviour of sand–bentonite mixture mixed in a proportion of 80:20 and mixed with 0, 5, 10 and 15% of waste tyre chips. From the consolidation test, swelling pressure and swelling potential reduced maximal at 15% of tyre chip content. Hydraulic conductivity and negative pore water pressure altered significantly with the application of tyre chips. Effective internal angle of friction enhanced from 24.9° to 30.5° and critical state parameter improved from 0.738 to 1.429 with the presence of 15% of tyre chips. Test result suggested that maximum of 10% of tyre chips can be used as a landfill liner and 15% tyre chips would be benefited for landfill cover.

Effect of pore water chemistry on the behaviour of a kaolin–bentonite mixture during drying and wetting cycles

The behaviour of a kaolin–bentonite mixture with different pore water chemistry, i.e. distilled water, NaCl and CaCl2 solutions, was investigated through a number of cyclic drying and wetting tests. Experimental tests were carried out on compacted samples of the expansive soil (i.e. mixture of 80% kaolin and 20% bentonite) in a modified oedometer with different pore water chemistry under a surcharge pressure of 10 kPa. The vertical and radial deformations of the samples were determined during different stages of drying and wetting. In addition, the soil–water characteristic curve was established by the filter paper technique for samples with different pore water chemistry. The results indicate that the shrinking–swelling deformation was nearly the same when the equilibrium condition was attained. Furthermore, the paths of drying and wetting converged to an S-shaped curve at equilibrium condition. This curve consists of one linear and two curvilinear portions, and the majority of the deformation occurred in the linear section. The hysteresis phenomenon was also studied through the void ratio and suction, and the results indicated that the hysteresis is gradually diminished with increasing the number of drying and wetting cycles.

Evaluation of a sand bentonite mixture as a shaft/borehole sealing material

Abstract The mechanical and hydrological characteristics of compacted sand bentonite mixtures with bentonite contents ranging from 5 to 40% were investigated in the laboratory in order to assess their use as a waste isolation material and to select an optimum sand bentonite mixture. Laboratory tests included compaction, compaction permeability, unconfined compression and direct shear tests which led to a recommendation to select a mixture with a bentonite content of 30% for the isolation of underground geological waste disposal repositories. This study complements the previous studies of the authors of this manuscript by determining the mechanical and hydrological properties of sand bentonite mixtures that possess bentonite contents > 30% to determine the geotechnical properties (i.e., unconfined compressive strength, Young's modulus, cohesion and angle of internal friction) and the mechanical behavior of these relatively high levels of bentonite mixtures for the first time in the literature.

Dielectric characterization of bentonite clay at various moisture contents and with mixtures of biomass in the microwave spectrum

ABSTRACTThis study assesses the potential for using bentonite as a microwave absorber for microwave-assisted biomass pyrolysis based on the dielectric properties. As bentonite is a hygroscopic material, the effect of bound water content on dielectric properties was addressed in this study. Dielectric properties of bentonite at different moisture contents were measured using a coaxial line dielectric probe and vector network analyser in the microwave frequency range from 0.2 to 4.5 GHz at room temperature. Further, dielectric properties of mixtures of bentonite with biomass were measured from 1.5 to 20 GHz as mixtures of bentonite with biomass could have microwave processing applications such as the thermochemical conversion of biomass to biofuel. Both dielectric constant and dielectric loss factor increased linearly with increasing moisture content. Measurements on biomass and bentonite mixtures show a quadratic increase in dielectric constant and loss factor with increasing bentonite content and with moisture contents ranging from 9.5% (pure bentonite) to 11.4% (pure biomass) wet basis. At 915 MHz, dielectric constant ranged from 2.0 to 6.2 and dielectric loss ranged from 0.2 to 2.7, respectively. At 2450 MHz, dielectric constant ranged from 1.8 to 5.1 and dielectric loss ranged from 0.7 to 2.6, respectively.

Effect of slag and bentonite on shear strength parameters of sandy soil

A series of direct shear tests were implemented on three different types of specimens (i.e., clean Perth sand, sand containing 10, 20 and 30% bentonite, sand containing 1, 3 and 5% slag, and sand containing 10, 20 and 30% bentonite with increasing percentages of added slag (1%, 3% and 5%). This paper focuses on the shear stress characteristics of clean sand and sand mixtures. The samples were tested under different three normal stresses (100, 150 and 200 kPa) and three curing periods of no curing time, 7 and 14 days. It was observed that the shear stresses of clean sand and mixtures were increased with increasing normal stresses. In addition, the use of slag has improved the shear strength of the sand-slag mixtures; the shear stresses rose from 128.642 kPa in the clean sand at normal stress of 200 kPa to 146.89 kPa, 154 kPa and 161.14 kPa when sand was mixed with 1%, 3% and 5% slag respectively and tested at the same normal stress. Internal friction angle increased from 32.74 in the clean sand to 34.87, 37.12 and 39.4 when sand was mixed with 1%, 3% and 5% slag respectively and tested at 100, 150, and 200 kPa normal stresses. The cohesion of sand-bentonite mixtures increased from 3.34 kPa in 10% bentonite to 22.9 kPa, 70.6 kPa when sand was mixed with 20% and 30% bentonite respectively. All the mixtures of clean sand, different bentonite and slag contents showed different behaviour; some mixtures exhibited shear stress more than clean sand whereas others showed less than clean sand. The internal friction angle increased, and cohesion decreased with increasing curing time.

Evaluation on expansive performance of the expansive soil using electrical responses

Light structures, such as highways and railroads, built on expansive soils are prone to damages from the swelling of their underlain soil layers. Considerable amount of research has been conducted to characterize the swelling properties of expansive soils. Current swell characterization models, however, are limited by lack of standardized tests. Electrical methods are non-destructive, and are faster and less expensive than the traditional geotechnical methods. Therefore, geo-electrical methods are attractive for defining soil characteristics, including the swelling behavior. In this study, comprehensive laboratory experiments were undertaken to measure the free swelling and electrical resistivity of the mixtures of commercial kaolinite and bentonite. The electrical conductivity of kaolinite-bentonite mixtures was measured by a self-developed four-electrode soil resistivity box. Increasing the free swelling rate of the kaolinite-bentonite mixtures (0.72 to 1 of porosity of soils samples) led to a reduction in the electrical resistivity and an increase in conductivity. A unique relationship between free swelling rate and normalized surface conductivity was constructed for expensive soils by eliminating influences of porosity and m exponent. Therefore, electrical response measurement can be used to characterize the free swelling rate of expensive soils.

Characteristic study for the uranium and cesium sorption on bentonite by using XPS and XANES

X-ray photoelectron spectroscopy (XPS) and synchrotron X-ray techniques of absorption near edge structure (XANES) were used to probe the coordination numbers and chemical states of absorption atoms to characterize the retention processes of uranium and cesium transportation in bentonite. The results of XPS showed that minor Van der Waals force interaction near the surface of bentonite were found while cesium adsorbed onto bentonite. The result of XANES showed that the uranium valence state greater than 6, and the cesium valence state also find greater than 1. The uranium valence state of mixture of bentonite and UO2(NO3)2·6H2O solvent is greater than 6. It maybe due to the strong electron negativity of NO3 −. From the results of added CsNO3 to bentonite also find the cesium valence state greater than 1. Checking the atom valence state may be able to identify nuclide migration mechanism, which is fundamental information to estimate nuclide migration to biosphere in natural environments.

Preparation of Mo/HZSM-5/Bentonite Catalyst for Methane Aromatization in a Fluidized Bed Reactor

Abstract Methane aromatization is a promising technology for the transformation of natural gas to added-value products. The main objective of this work was to obtain a catalyst with suitable performance and good mechanical stability for methane aromatization reaction in fluidized bed reactors. The selected catalyst was Mo/H-ZSM-5/bentonite mixture. Mo/ZSM-5 was chosen as the active material, since it provides good selectivity to aromatics but the particle size of the zeolite was too small for operation in a fluidized bed and a binder was needed. We prepared two series of catalysts with two different zeolites. We tested several heating velocities (1, 7 and 10 °C min‒1) in the different stages of catalyst synthesis. Methane conversion and selectivity to aromatic products improved when using gentle thermal treatments, increasing 2% and 10%, respectively, for the best catalyst tested.

Assessment and statistical evaluation of suction characteristics obtained via filter paper technique on zeolite–bentonite mixtures

Filter paper technique (FPT) is known to measure both matric and total suctions in a wide measurement range. However, it has many individual errors due to the uncertainty of calibration curve and sensitivity of the measurements to the temperature and relative humidity variations. Besides, the ASTM procedure for FPT does not specify any sample preparation and repetition for experiments. In this regard, this study covers the reliability of suction measurements using the FPT and its application on zeolite–bentonite mixtures (ZBMs), which were proposed for use of liner material in the literature. A calibration curve for Whatman No. 42 filter paper was constructed and compared to the other calibration curves given in the literature. Due to large scatter of calibration curves, total suction measurement is found to be inconvenient for suction values under 1000 kPa. An improvement in sample preparation and necessary minimum numbers of tests are also suggested. When preparing the test specimen, the compacted sample is recommended not to be cut but to be compacted separately as upper and lower parts where the contact filter paper to be placed in between in order to obtain good contact area to measure the matric suction accurately. The necessary minimum numbers of tests for ± 10% accuracy band in a confidence level of 95% for ASTM procedure on ZBMs are suggested. Repetitions were found to vary depending on the suction type and bentonite content. Repetitions of six and eight times are recommended for 10% ZBMs for matric and total suction measurements, respectively. Similarly, for 20% ZBMs the repetitions of six and ten times are found for matric and total suction measurements, respectively. In addition, the influence of index properties and compaction states on suction was also investigated. Matric suction values decrease from dry of optimum water content to the wet of optimum water content and approach to zero for higher water contents. The suction values are found to increase with decreasing water contents where the dry density and the void ratio were constant. On the other hand, for a given water content, matric suction values are found to be increasing with increasing dry densities, while the void ratio was decreasing being more evident at relatively higher saturation degrees.

Enhancing the Lifting Capacity of Drilling Fluids in Vertical Oil Wells

Of the many functions that are performed by the drilling fluid, the most important is to transport cuttings from the bit up the annulus to the surface. Various drilling fluid have been widely used in the oil industry to improve lifting capacity. In this study, three mud type have been used which they are, oil base mud, X-anthan polymer and a mixture of CMC and bentonite ,by using Carrying Capacity Index calculation (CCI) , the Xanthan gave good values of CCI than other studied drilling fluid. By using Sifferman chart and field data from well in south of Iraq and API equation to find cutting concentration in the annulus, The results showed that the used of thick mud increase the lifting capacity and decrease volumetric drill cuttings in the annulus but the using thin mud lead to decrease lifting capacity and increase volumetric drill cuttings in the annulus .The results show that the mud viscosity and flow rate have important role in hole cleaning. Also, the effect of annulus velocity and flow pattern on cutting transport ratio is studied by using field data. The effect of cutting size and OD of drill pipe is also studied. Cutting size is one of the parameters that influence the hole cleaning; large size cutting makes the hole cleaning more difficult. The reducing of annular size of hole by increasing the OD of drill pipe lead to increasing the annular velocity.

Effect of zeolite utilization on volume change and strength properties of expansive soil as landfill barrier

A sand–Na–bentonite mixture is widely used as engineering barrier material, which usually possesses hydraulic conductivity below the regulatory limit (10−7 cm/s). However, in some areas natural Na–bentonite is not readily available; instead, an abundantly prevailing local expansive soil can be an alternative. This study assesses the suitability of a local expansive soil mixed with zeolite, easily obtained from natural reserves in Turkey, proposed to be used as a landfill liner in a semi-arid climate. The choice of zeolite is due to its already well-understood high adsorption capacity for heavy metals as well as its pozzolanicity. The volume change, strength, and hydraulic conductivity characteristics were studied with respect to durability through ageing. When an expansive soil to zeolite ratio of 0.5 was used, the results indicated improved properties with curing. Swell potential was observed to decrease by 85% within a 90 day curing period, while a 30%–34% reduction was noted in shrinkage and compressibility characteristics. The hydraulic conductivity was observed to remain below the regulatory limit under all confining pressure ranges studied, provided the curing time was at least 90 days. Moreover, the mixture attained improved strength characteristics with time, and proved to be sustainable over the period studied. Therefore, it was concluded that expansive soil mixed with zeolite could be a good alternative to sand–Na-bentonite, mainly in developing areas of growing population and environmental degradation.

Membrane behavior of compacted sand–bentonite mixture

Semi-permeable membrane behavior contributes to the containment function of engineered barriers used for waste containment by restricting the migration of dissolved chemical species (solutes) such as aqueous-phase contaminants. The existence of membrane behavior has been demonstrated extensively for virtually all categories of bentonite-based containment barriers except compacted sand–bentonite mixtures. Accordingly, membrane tests were conducted on two specimens of a compacted sand–bentonite mixture comprising 15% bentonite (dry weight) with sufficiently low hydraulic conductivity (i.e., ≤1.0 × 10−9 m/s) to be suitable for use as a waste containment barrier. Despite the imposition of relatively complex chemical conditions, including the use of tap water versus de-ionized water as a circulating liquid and incomplete flushing (leaching) of soluble salts from the specimens prior to membrane testing, the results were in good agreement with those previously reported for other bentonite-based engineered barriers when exposed to similar or the same types of salts and salt concentrations. Also, both compacted soil–bentonite specimens exhibited similar magnitudes of membrane behavior, with measured membrane efficiencies ranging from 0.395 ± 0.053 to 0.063 ± 0.012 when exposed to source KCl solutions with concentrations ranging from 5 to 80 mmol/L, respectively. Thus, compacted sand–bentonite mixtures suitable for use as engineered containment barriers can exhibit semi-permeable membrane behavior, thereby potentially enhancing the containment function of the barriers.

Mechanical Properties of an Artificially Cemented Clayey Material

Abstract As part of an ongoing investigation on the behavior of the brittle cemented sensitive clays of eastern Canada, static penetrometer and vane shear tests had to be performed in the laboratory. Because it was impossible to sample undisturbed blocks of clay of the necessary size, an artificial model material was developed to simulate the response of sensitive clays, namely, brittle response at low stresses and loss of strength upon remolding. The model material consists of a mixture of kaolinite, bentonite, portland cement, and water. Two mixes were produced: a softer 6.25 % cement content and a stiffer 14 % cement content. It is shown that the materials are characterized by stress-strain behaviors similar to those of soft to medium sensitive clays. It is also shown that the artificially bonded materials simulate quite well other mechanical properties of sensitive clays of eastern Canada, such as high water contents and void ratios; brittle failure at low confining pressures; high G u/Su ratios, where Gu=shear modulus and Su=undrained shear strength; and severe collapse of the structure for vertical effective stresses in excess of the materials’ preconsolidation pressures. Specimens cured 21 days were used successfully for laboratory indentation, vane shear, and unconfined and triaxial compression tests, as well as oedometer tests. In addition, the variation of the undrained shear strength of the 14 % cement content specimens was followed for a maximum curing period of one year, by means of vane shear tests and unconfined compression tests.

Monitoring long-term evolution of engineered barrier systems using magnets: Magnetic response

Remote and non-destructive monitoring of the stability and performance of Engineered Barrier Systems for Geological Disposal Facility of is gaining considerable importance in establishing the safety cases for Higher Activity Wastes disposal. This study offers an innovative use of mineral magnetism for monitoring groundwater saturation of the barrier. Four mixtures of permanent magnets (Nd-Fe-B, coated and uncoated; SmCo and AlNiCo) and bentonite were reacted for 4, 8 and 12 months with mildly-saline, high-pH leachates, representing the fluids saturating a time-evolved engineered barrier. Coupled hysteresis and thermomagnetic analyses demonstrate how Nd-Fe-B feature a time-dependent transition from square-like ferromagnetic to superparamagnetic loop via pot-bellied and wasp-waist loops, whereas SmCo and AlNiCo do not show so extensive corrosion-related variations of the intrinsic and extrinsic magnetic properties. This study allowed to identify magnetic materials suitable for shorter- (Nd-Fe-B) and longer-term (SmCo and AlNiCo) monitoring purposes.

The Strength of Moulding Sand Consisting of a Mixture of Bentonite, Tapioca Flour, and Sago Flour as a New Binder Formula to Improve the Quality of Al-Si Cast Alloy

The major factors determining the quality of sand casting products are the base sand and the composition of the sand mould and the binding material. In the foundry industry, the most commonly used binder for creating sand moulds is bentonite. However, the price of bentonite is likely to keep rising. This study aimed at discovering a new binder formula associated with the effect of binder composition i.e. bentonite, tapioca flour, and sago flour on the basis of its mechanical and physical properties. The new formula was expected to be a better binder in the production of sand moulds, resulting in high-quality casting products with minimal defects. Moreover, it is probable to be much more economical than bentonite. This research focused on testing the moulding sand composition with a number of different binders, i.e. bentonite, tapioca flour, and sago flour, each in a different proportion. The mixture of the moulding sand with each of the three binders will be tested in terms of its mechanical properties including compressive, shear, and tensile strength. Based on the test results, sago flour has the highest dry compressive strength of 28.6 N/cm2, whereas bentonite has the highest wet compressive strength, i.e. 11.83 N/cm2 and the highest wet shear strength i.e. 3.16 N/cm2. The binder with the highest dry shear strength is tapioca flour with 18.16 N/cm2. Regarding the tensile strength value, bentonite has the highest wet tensile strength of 0.85 N/cm2, while sago flour has the highest dry tensile strength of 1.73 N/cm2.

Static liquefaction of very loose sand–slag–bentonite mixtures

Static liquefaction is a highly destructive mechanism in the failure of soil deposits caused by a sudden loss of effective stress accompanied by vast deformations and a rapid build-up of pore water pressure that can cause soils to behave like liquids. This study examined liquefaction phenomena in saturated clean Perth sand, sand containing 3% bentonite, sand containing slag (2%, 4%, and 6%), and sand containing both 3% bentonite and slag (2%, 4%, and 6%). Undrained static triaxial compression tests were implemented on very loose mixtures at three initial confining pressures (100, 150, and 200kPa). Static liquefaction (zero deviatoric stress and zero effective confining pressure) was observed at the lowest relative density and the lowest confining pressure. The liquefaction potential of the clean sand and the sand mixtures decreased with increases in confining pressure and relative density. The slag reduced the liquefaction susceptibility by reducing the inter-particle voids and producing a stable fabric. The optimum slag content was found to be 4%. Mixing clean sand with 3% bentonite produced a vulnerable fabric which exhibited high compressibility and a high level of excess pore water pressure. All sand–slag–bentonite mixtures showed non-flow behaviour and low excess pore water pressure. The mixture of sand with 4% slag and 3% bentonite exhibited the highest effective stress and the lowest excess pore pressure. It was revealed that the normalisation between the maximum and the minimum deviatoric stresses, namely, the brittleness index, can be used to quantify the liquefaction potential of clean sand and sand-slag-bentonite mixtures.

Preliminary electrochemical corrosion monitoring of iron in mixture cement paste–bentonite

ABSTRACTIn the context of the French 500-m deep radioactive waste repository, electrochemical impedance spectroscopy and a methodology based on complex impedance analysis were carried out to follow the hydration of grout containing cement–bentonite mixture and iron corrosion together. The grout was initially a paste, and solidified with time. After a 100-day-curing, the temperature of the system (grout + steel) was increased from room temperature to 80°C to simulate the effect of a nuclear waste overpack. At room temperature, the ionic conductance exhibited a continuous decrease followed by an increase at 80°C. After an initial drop, the corrosion rate increased to a quasi-steady state value at around 1.5 µm/year at 21°C. At 80°C, the corrosion rate increased to about 30 µm/year before gradually dropping to much lower values. Eventually, then the passivation of iron seemed to occur since the corrosion rate has decreased continuously down to 0.1 µm/year.This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.

Hydraulic Performance of Organo Clay Enhanced Sand Bentonite as Secondary Liner

The leakage of petroleum from the storage tanks poses a serious threat to soil and groundwater. Hence an additional layer of impermeable material is usually provided as secondary containment systems in underground and above ground storage systems meant to store petroleum products. However the use of conventional mineral liner material is found to be ineffective for their use in secondary containment system to contain organic fluids. The conventional liner materials such as compacted sand–bentonite (SB) mixtures needs to be amended with materials of high organic sorption capacity. Therefore studies were carried out to assess the hydraulic performance of sand bentonite mixture amended with different percentages of organo clay (SOB) and to evaluate their possible use in secondary containment of petroleum product. The hydraulic conductivity of different SOB mixtures compacted at optimum conditions was evaluated with water and diesel as permeants. The coefficient of permeability was measured for various mixtures under different loads varying from 0 to 300 kPa. The permeability coefficient was evaluated both for loading and unloading cases. A decrease in the coefficient of permeability with diesel by an order of two, was observed on increasing the organo clay content from 0 to 10% in SB mix, where as a reverse trend was noted with water as permeant. The hydraulic performance of SOB mixture was found to be largely influenced by the proportion of organo clay, the nature of pore fluid and the applied pressure suggesting a need for careful proportion of mixture to be used as secondary liner.

The Strength of Moulding Sand Consisting of a Mixture of Bentonite, Tapioca Flour, and Sago Flour as a New Binder Formula to Improve the Quality of Al-Si Cast Alloy

The major factors determining the quality of sand casting products are the base sand and the composition of the sand mould and the binding material. In the foundry industry, the most commonly used binder for creating sand moulds is bentonite. However, the price of bentonite is likely to keep rising. This study aimed at discovering a new binder formula associated with the effect of binder composition i.e. bentonite, tapioca flour, and sago flour on the basis of its mechanical and physical properties. The new formula was expected to be a better binder in the production of sand moulds, resulting in high-quality casting products with minimal defects. Moreover, it is probable to be much more economical than bentonite. This research focused on testing the moulding sand composition with a number of different binders, i.e. bentonite, tapioca flour, and sago flour, each in a different proportion. The mixture of the moulding sand with each of the three binders will be tested in terms of its mechanical properties including compressive, shear, and tensile strength. Based on the test results, sago flour has the highest dry compressive strength of 28.6 N/cm2, whereas bentonite has the highest wet compressive strength, i.e. 11.83 N/cm2 and the highest wet shear strength i.e. 3.16 N/cm2. The binder with the highest dry shear strength is tapioca flour with 18.16 N/cm2. Regarding the tensile strength value, bentonite has the highest wet tensile strength of 0.85 N/cm2, while sago flour has the highest dry tensile strength of 1.73 N/cm2.