• Journal of the Mineralogical Society of Korea
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• v.15 no.4
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• pp.243-257
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• 2002

Ca-type and Na-type bentonites show the great difference of some physicochemical properties. Na exchanged bentonite is mainly used for the foundry and construction materials in domestic utilization. This study tries to identify in detail the differences of some physicochemical properties and thermal properties between Ca-type and Na-type bentonites. Also the adsorption behavior and interlayer expansion for the HDTMA (Hexadecyltrimethylammonium) exchanged and CP (Cetylprydinium) exchanged Ca-type and Na-type bentonites were compared. Na-type bentonite shows the strong alkaline property, high viscosity and swelling compared to Ca-type bentonite. However, two types are very similar for the cation exchange capacity and MB (Methylene Blue) adsorption. The decomposition of adsorbed and interlayer water of Na-type bentonite is caused in the lower temperature than Ca-type bentonite. And Ca-type bentonite shows the decomposition of structural water in the lower temperature than Na-type bentonite. The interlayer expansion of montmorillonite resulted to the intercalation of HDTMA and CP into bentonite is so strongly caused from 12～15 $\AA$ to $40\AA$ (basal spacing). HDTMA-bentonite is almost expanded to $37～38\AA$ when 200% CEC equivalent amount of HDTMA is added, and CP-bentonite is fullly expanded to 40 $\AA$ in the 140% CEC equivalent amount of CP It means that CP causes the stronger interlayer expansion of montmorillonite and easier adsorption than HDTMA. Adsorption behaviors of CP into bentonite is so stable and continuously sorbed in the proportion to the treatment of amount until 200% of the CEC equivalents. CP-bentonite shows the same adsorption behavior regardless of Ca-type or Na-type montmorillonite.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.6 no.2
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• pp.101-109
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• 2008

For the Kyungju bentonite which is considered as a candidate material for the buffer and backfill in the high-level waste repository, the thermal conductivities of compacted bentonite and a bentonite-sand mixture were measured. The thermal conductivities of the compacted bentonites with a dry density of 1.2 to $1.8\;Mg/m^3$ and the bentonite-sand mixture with a dry density of 1.6 and $1.8\;Mg/m^3$ were measured within the gravimetric water content range of 10wt% to 20wt% and the sand fraction range of 10 to 30wt%. The thermal conductivity of compacted bentonite and a bentonite-sand mixture increases with increasing dry density and sand weight fraction in the case of constant water weight fraction, and increases with increasing water weight fraction and sand weight fraction in the case of constant dry density. The empirical correlations to describe the thermal conductivity of compacted bentonite and a bentonite-sand mixture as a function of water fraction at each dry density were suggested. These correlations can predict the thermal conductivities of bentonite and a bentonite-sand mixture with a difference below 10%.

• Economic and Environmental Geology
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• v.55 no.3
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• pp.219-229
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• 2022

Bentonite is being considered as a candidate for buffer material in geological disposal systems for high-level radioactive wastes. In this study, the effect of cement-bentonite interactions on bentonite alteration was investigated by reviewing the literature on studies of cement-bentonite interactions. The major bentonite alteration by hyperalkaline fluids produced by the interaction of cementitious materials with groundwater includes cation exchange, montmorillonite dissolution, secondary mineral precipitation, and illitization. When the hyperalkaline leachate from the reaction of the cementitious material with the groundwater comes into contact with bentonite, montmorillonite, the main component of bentonite, is dissolved and a small amount of secondary minerals such as zeolite, calcium silicate hydrate, and calcite is produced. When montmorillonite is continuously dissolved, the physicochemical properties of bentonite may change, which may ultimately causes changes in bentonite performance as a buffer material such as adsorption capacity, swelling capacity, and hydraulic conductivity. In addition, the bentonite alteration is affected by various factors such as temperature, reaction period, pressure, composition of pore water, bentonite constituent minerals, chemical composition of montmorillonite, and types of interlayer cations. This study can be used as basic information for the long-term stability verification study of the buffer material in the geological disposal system for high-level radioactive wastes.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.5 no.1
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• pp.19-24
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• 2009

Bentonite-based grouting has been usually used for sealing a borehole installed for a closed-loop vertical ground heat exchanger in a geothermal heat pump system (GHP) because of its high swelling potential and low hydraulic conductivity. The bentonite-based grout, however, has relatively lower thermal conductivity than that of ground formation. Accordingly, it is common to add some additives such as silica sand into the bentonite-based grout for enhancing heat transfer. In this study, graphite is adapted to substitute silica sand as an addictive because graphite has very high thermal conductivity. The effect of graphite on the thermal conductivity of bentonite-based grouts has been quantitatively evaluated for seven bentonite grouts from different product sources. In addition, the viscosity of graphite-added bentonite grout was measured to evaluate the field pumpability of the grout.

• Journal of the Korean Chemical Society
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• v.21 no.5
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• pp.379-383
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• 1977

Since the organophilic bentonite disperses well in polymer matrix, a composite material of polymer and bentonite was studied for its mechanical properties. To increase the degree of dispersion and the bond in forces to the polymer matrix, bentonite, encapsulated by imidazoline, was used as a filler. Polyethylene powder of particle size of 100 mesh was used, and organophilic bentonite, so-called bentone, whose particle size was 250 mesh was also used in this experiment. V-type mixer was used for mixing and Banbury mixer was used for melt-blending. The sample specimen were made by heating the mixture in the plate press, and the specimen were formed as a sheet, exactly the same as the mold on the plate. Tensile strength, bending strength and compressive strength were studied specially. Tensile strength, elongation rate, bending strength and bending rate at constant pressure were decreased as the filler content increased. Compressive strength was increased as the filler content increased.

• Tunnel and Underground Space
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• v.30 no.3
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• pp.193-213
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• 2020

A mathematical model to simulate more realistically the penetration of compacted bentonite buffer installed in the deposition hole into the discontinuity in the excavation damaged zone formed at the inner wall of the deposition hole in the geological repository for spent fuel is developed. In this model, the penetration of compacted bentonite is assumed to be the flow of Bingham fluid through the parallel planar rock fracture. The penetration of compacted bentonite is analyzed using the developed model. The results show that the maximum penetration depth of compacted bentonite into the rock fracture is proportioned to the swelling pressure of saturated compacted bentonite and the aperture of rock fracture. However, it is in inverse proportion to the yield strength of compacted bentonite. The viscosity of compacted bentonite dominates the penetration rate of compacted bentonite, but has no influence to the maximum penetration depth.

• Polymer(Korea)
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• v.38 no.1
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• pp.62-68
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• 2014

To improve the compatibility of bentonite with rubber matrix, organo-modified bentonite was synthesized with a silane coupling agent, [3-(2-aminoethylamino)propyl]trimethoxysilane (AEAPTMS) in the suspension of bentonite. The structure and characteristics of organo-modified bentonite were investigated using FTIR-spectroscopy, thermogravimetric analysis (TGA) and X-ray diffraction (XRD). Ethylene-propylene-diene monomer (EPDM) rubber/organo-bentonite composites were compounded by a two-roll mill. The vulcanization and mechanical properties were studied. Results showed that the concentration of hydrochloric acid and $H_2O$ in the synthesis had significant influence on the modification of bentonite, which further contributed to the properties of the composites. Filled with 20 phr modified bentonite, the tensile strength and elongation at break of the rubber increased from 1.95 to 4.8 MPa and 300% to 500%, respectively.

• Journal of Soil and Groundwater Environment
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• v.26 no.5
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• pp.29-38
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• 2021

This study investigated the mineralogical properties of bentonite and illite and evaluated the Cs sorption at various concentrations (C_w≈1-10⁵ ㎍/L). Bentonite samples, collected from South Korea and USA, majorly consisted of Ca- and Na-montmorillonite, showed large cation exchange capacity (CEC, 91.4 and 47.3 meq/100 g) and specific surface area (SSA, 46.1 and 39.7 m²/g). In contrast, illite sample (USA) had relatively low values for 14.4 meq/100g of CEC and 29.3 m²/g of SSA, respectively. Bentonite and illite had different non-linear sorption for Cs along with C_w. At low C_w<10 ㎍/L, illite showed higher sorption capacity than bentonite despite low CEC because of the existence of specific sorption sites at the weathered mineral edge. However, as C_w increased, bentonite represented high sorption capacity because the cation exchange between Cs and interlayer cations was effective at high C_w conditions. These results implicated that the Cs concentration is important to evaluate the sorption performance of bentonite and illite. Finally, the Cuadros' kinetic model for illitization using various K concentrations (2×10^-5 and 1.7×10^-3 mol/L) and temperature (100-200℃) showed that up to 50% of the montmorillonite in bentonite could be converted to illite, suggesting that the illitization should be considered to evaluate the sorption performance of the bentonite in deep geological disposal repository.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.3
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• pp.231-239
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• 2005

This study was performed to investigate adsorption characteristics of MTBE and Cd depending upon types of clay minerals md their physicochemical properties. The adsorption characteristics were examined by batch adsorption test on various experimental parameters such as adsorption time, ratio of solution to soil, concentration of contaminants, content of organic matter, pH, and zeta potential. The adsorption efficiency of MTBE or Cd for three types of clays decreased in response to the increase of the ratio of solution to soil whereas their adsorbed amounts increased. MTBE was greatly adsorbed in the decreasing order of vermiculite, bentonite, and CTAB-bentonite while Cd was adsorbed in the decreasing order of bentonite, vermiculite, and CTA-bentonite. An equilibrium isotherm for MTBE was well fitted to Freundlich plotting whereas that for Cd was closely corresponded to Langmuir isotherm. The adsorbed amount of MTBE on bentonite and vermiculite showed the maximum at 1% and 5% of humic acid, thereafter diminished while the adsorbed amount of MTBE on CTAB-bentonite increased in proportion to humic acid. Conversely, the adsorbed amount of Cd on the addition of humic acid continued to increase regardless of types of adsorbents. For all types of adsorbents, adsorbed quantity and adsorption efficiency of Cd have been coincidently increased at pH 8 and they were further enhanced at pH 10 showing 90% adsorption efficiency. Upon pH rose, the zeta potential on each adsorbent began to decrease, while increasing Cd concentration led to decline of zeta potential, which in turn ascribed to lowering dispersion stability that could consequently enhance adsorption capability.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.561-577
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• 2021

The compacted bentonite buffer in a geological repository for high-level radioactive waste disposal is saturated due to groundwater inflow. Saturation of the bentonite buffer results in bentonite swelling and bentonite penetration into the rock discontinuities present around the disposal hole. The penetrated bentonite is exposed to groundwater flow and can be eroded out of the repository, resulting in bentonite mass loss which can affect the physical integrity of the engineered barrier system. Hence, the evaluation of buffer-rock interactions and coupled behavior due to groundwater inflow and bentonite penetration is necessary to ensure long-term disposal safety. In this study, the effects of the bentonite penetration and swelling on the physical properties of jointed rock mass were evaluated using the quasi-static resonant column test. Jointed rock specimens with bentonite penetration were manufactured using Gyeongju bentonite and hollow cylindrical granite rock discs obtained from the KAERI underground research tunnel. The effects of vertical stress and saturation were assessed using the P-wave and S-wave velocities for intact rock, jointed rock and jointed rock with bentonite penetration specimens. The joint normal and joint shear stiffnesses of each joint condition were inferred from the wave velocity results assuming an equivalent continuum. The joint normal and joint shear stiffnesses obtained from this study can be used as input factors for future numerical analysis on the performance evaluation of geological waste disposal considering rock discontinuities.