• Title/Summary/Keyword: 칼슘벤토나이트

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A study on the Evaluation of Permeability and Structure for Calcium Bentonite-Sand Mixtures (칼슘 벤토나이트-모래 혼합차수재의 투수 및 구조 특성에 관한 연구)

  • Yun, Seong Yeol;An, Hyeon Kyu;Oh, Minah;Lee, Jai-Young
    • Journal of the Korean Geosynthetics Society
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    • v.18 no.2
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    • pp.1-10
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    • 2019
  • This study was intended to evaluate the water permeability and structure for calcium bentonite-sand mixtures to utilize calcium bentonite as a liner. This study conducted physico-chemical properties tests, compaction tests, permeability test and Scanning Electron Microscopy analysis (SEM) analysis. It was found the higher the ratio of calcium bentonite, the lower the dry density with coefficient of permeability, and the higher the optimum moisture content. In particular, SEM analysis was found the higher the ratio of calcium bentonite, the higher the area of the montmorillonite particles. In conclusion, the optimum coefficient of permeability that finds the landfill liner condition (must be less than $1{\times}10^{-7}cm/sec$) was obtained when the ratio of calcium bentonite was 40% or higher. These findings may improve the understanding of the calcium bentonite as a liner. Calcium bentonite shows a similar permeability to sodium bentonite 7% when mixed at 40% or more. Therefore, it is considered that calcium bentonite can be utilized as a liner.

An Experimental Study on the Erosion of a Compacted Calcium Bentonite Block (압축된 칼슘벤토나이트 블록의 침식에 대한 실험적 연구)

  • Baik Min-Hoon;Cho Won-Jin
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.3 no.4
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    • pp.341-348
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    • 2005
  • Bentonite has been considered as a candidate buffer material in the underground repository for the disposal of high-level radioactive waste because of its low permeability, high sorption capacity, self sealing characteristics, and durability in nature. In this study, the potential for separation of bentonite particles caused by the groundwater erosion was studied experimentally for a Korean Ca-bentonite under the relevant repository conditions. Results showed that bentonite particles can be generated at the bentonite/granite interface and mobilized by the water flow although the intrusion of bentonite into fracture by swelling pressure was observed to be small. Different processes of mobilization of theses colloids from the compacted bentonite block have been identified in this study. The concentration of particles eluted in water was increased as the flow rate increased. Thus the result reveals that the erosion of the bentonite surface due to the groundwater flow together with intrusion processes is the main mechanism that can mobilize bentonite colloids in the fracture of the granite.

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A Study on the Stability of the Ca-Bentonite Colloids Using a Dynamic Light Scattering Method (동적광산란 방법을 이용한 칼슘벤토나이트 콜로이드의 안정성에 대한 연구)

  • Baik Min-Hoon;Park Jong-Hoon;Cho Won-Jin
    • Journal of Soil and Groundwater Environment
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    • v.11 no.3
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    • pp.12-19
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    • 2006
  • In this study, the stability of Ca-bentonite colloids from Gyeongju area was studied by investigating the changes in the size of the bentonite colloids using a dynamic light scattering method depending on the geochemical conditions such as pH and ionic strength. Kinetic and equilibrium coagulation behavior of the bentonite colloids was investigated by changing the pH and ionic strength of the bentonite suspensions. The results showed that the stability of the bentonite colloids strongly depended upon contact time, pH, and ionic strength. It was also shown that the bentonite colloids were unstable at higher ionic strength greater than 0.01 M $NaClO_4$ at whole pH values considered. In addition, the stability ratio Wand the critical coagulation concentration (CCC) were also calculated using the data from the kinetic coagulation experiments. The stability ratio W was decreased as the ionic strength increased and varied with pH depending on the ionic strength. The CCC of the Ca-bentonite colloids was about 0.05 M $NaClO_4$ around pH 7.

Characteristic of Permeability with the Sand, Calcium Bentonite and Solidifier Mixtures according to Selective Reaction of TCE (트리클로로에틸렌(TCE) 선택적 반응에 따른 모래, 칼슘-벤토나이트 및 겔화제 혼합차수물의 투수 특성)

  • Yun, Seong Yeol;Choi, Jeong Woo;Oh, Minah;Lee, Jai-Young
    • Journal of the Korean Geosynthetics Society
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    • v.19 no.1
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    • pp.25-33
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    • 2020
  • To improvement the swelling characteristics of the existing cutoff wall against the moisture, the permeability of the sand, calcium bentonite and solidifier mixture according to the contact with trichloroethylene (TCE) was evaluated. Characteristics analysis and the permeability test of the research materials were performed. The permeability was decreased as the mixing ratio of the calcium bentonite was increased and it was increased as the mixing ratio of the solidifier was increased. In conclusion, when mixing 15% of calcium bentonite and more than 30% of solidifier, the permeability coefficient in the underground water movement was analyzed as more than α × 10-4 cm/sec showing that it does not block the underground water movement. In addition, as the permeability coefficient of mixtures after TCE reaction was analyzed as less than α ×10-7 cm/sec, it satisfied the condition of blocking layer (less than 1.0 × 10-6 cm/sec). Therefore, the calcium bentonite and solidifier can be utilized as barrier that showing the characteristic of percolation ability conversion in soil and underground water contaminated with TCE.

Mock-up Crack Reduction Performance Evaluation of Blast Furnace Slag Concrete Mixed with Expansive and Swelling Admixture (팽창재와 팽윤제가 혼입된 고로슬래그 콘크리트 Mock-up의 균열 저감 성능평가)

  • Sang-Hyuck Yoon;Won-Young Choi;Chan-Soo Jeon
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.11 no.4
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    • pp.552-559
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    • 2023
  • The purpose of this study is to evaluate the crack reduction performance of blast furnace slag concrete mixed with expansive and swelling admixtures. As a basic performance test, various ingredients such as blast furnace slag fine powder (BFS), calcium sulfoaluminate (CSA), bentonite, and hydroxypropyl methyl cellulose (HPMC) were used, and the results showed that bentonite showed superior performance compared to HPMC. Afterwards, a MOCK-UP test was conducted to evaluate cracking and drying shrinkage according to the mixing ratio. As a result, when bentonite and a small amount of calcium phosphate were added, drying shrinkage was reduced and cracking was reduced. In particular, a cement mixture consisting of 30 % BFS, 1 % bentonite, and 1 % calcium phosphate showed optimal crack-free performance. It is believed that BFS concrete will contribute to compensating for shrinkage through continuous expansion activity and can be used for field applications.

Dependency of Compatibility Termination Criteria on Prehydration and Bentonite Quality for Geosynthetic Clay Liners (사전투수 및 벤토나이트 품질에 따른 GCL의 투수종결기준에 미치는 영향평가)

  • Lee Jae-Myung;Shackelford Charles D.;Choi Jae-Soon;Jung Moon-Kyung
    • Journal of the Korean Geotechnical Society
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    • v.20 no.7
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    • pp.141-158
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    • 2004
  • The dependency of criteria used to terminate compatibility tests on the prehydration and quality of bentonite in geosynthetic clay liners (GCLs) is evaluated based on permeation with chemical solutions containing 5, 10, 20, 50, and 100 mM calcium chloride ($CaCl_2$). The hydraulic conductivity tests are not terminated before chemical equilibrium between the effluent and the influent chemistry has been established, resulting in test durations ranging from < 1 day to > 900 days, with longer test durations associated with lower $CaCl_2$ concentrations. The evaluation includes both physical termination criteria (i.e., volumetric flow ratio and steady hydraulic conductivity based on ASTM D 5084, ${\ge}2$ pore volumes of flow, constant thickness of specimen) and chemical termination criteria requiring equilibrium between influent and effluent chemistry (viz., electrical conductivity, pH, and $Ca^{2+}\;and\;Cl^-$ concentrations). For specimens permeated with 5, 10, and 20 mM $CaCl_2$ solutions, only the criterion based on chemical equilibrium in $Ca^{2+}$ concentration correlates well with equilibrium in hydraulic conductivity, regardless of prehydration or quality of bentonite. However, all of the termination criteria, except for the volumetric flow ratio and 2 pore volumes of flow for the prehydrated specimens, correlate well with equilibrium in hydraulic conductivity regardless of prehydration or quality of bentonite when permeated with 50 and 100 mM $CaCl_2$ solutions. The results illustrate the uniqueness of the termination criterion based on solute concentration equilibrium between the effluent and the influent with respect to both prehydration and quality of bentonite in the GCLs.

An Experimental Study on the Sorption Properties of Uranium(VI) onto Bentonite Colloids (벤토나이트 콜로이드에 대한 우라늄(VI) 수착특성에 대한 실험적 연구)

  • Baik Min-Hoon;Cho Won-Jin;Hahn Pil-Soo
    • Proceedings of the Korean Radioactive Waste Society Conference
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    • 2005.06a
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    • pp.239-247
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    • 2005
  • In this study, an experimental study on the sorption properties of uranium(VI) onto bentonite colloids generated from a domestic calcium bentonite (called as Gyeongju bentonite). Gyeongju bentonite has been considered as a potential candidate buffer material in the Korean disposal concept for high-level radioactive wastes. The size and concentration of the bentonite colloids used in the sorption experiment were measured by a filtration method. The result showed that the concentration of the synthesized bentonite colloid suspension was 5100ppm and the size of the most of bentonite colloids(over $98\%$) was in the range of 200-450nm in diameter. The amount of uranium lost by the sorption onto bottle walls, by precipitation, and by ultrafiltration or colloid formation was analyzed by carrying out some blank tests. The loss of uranium by the ultrafiltration was significant in the lower ionic strength(i.e., in the case of 0.001M $NaClO_4$) due to the cationic sorption effect onto the ultrafilter by a surface charge reversion. The distribution coefficient (or pseudo-colloid formation constant) for the sorption of uranium(VI) onto bentonite colloids was $10^4^{\sim}10^6$ mL/g depending upon pH and the distribution coefficient was highest in the neutral pH around 6.5.

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A Literature Review on Studies of Bentonite Alteration by Cement-bentonite Interactions (시멘트-벤토나이트 상호작용에 의한 벤토나이트 변질 연구사례 분석)

  • Goo, Ja-Young;Kim, Jin-Seok;Kwon, Jang-Soon;Jo, Ho Young
    • 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.