• Economic and Environmental Geology
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• v.56 no.5
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• pp.603-618
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• 2023

This study focused on evaluating the suitability of the WRK (waste repository Korea) bentonite as a buffer material in the SNF (spent nuclear fuel) repository. The U (uranium) adsorption/desorption characteristics and the adsorption mechanisms of the WRK bentonite were presented through various analyses, adsorption/desorption experiments, and kinetic adsorption modeling at various pH conditions. Mineralogical and structural analyses supported that the major mineral of the WRK bentonite is the Ca-montmorillonite having the great possibility for the U adsorption. From results of the U adsorption/desorption experiments (intial U concentration: 1 mg/L) for the WRK bentonite, despite the low ratio of the WRK bentonite/U (2 g/L), high U adsorption efficiency (>74%) and low U desorption rate (<14%) were acquired at pH 5, 6, 10, and 11 in solution, supporting that the WRK bentonite can be used as the buffer material preventing the U migration in the SNF repository. Relatively low U adsorption efficiency (<45%) for the WRK bentonite was acquired at pH 3 and 7 because the U exists as various species in solution depending on pH and thus its U adsorption mechanisms are different due to the U speciation. Based on experimental results and previous studies, the main U adsorption mechanisms of the WRK bentonite were understood in viewpoint of the chemical adsorption. At the acid conditions (＜pH 3), the U is apt to adsorb as forms of UO₂²⁺, mainly due to the ionic bond with Si-O or Al-O(OH) present on the WRK bentonite rather than the ion exchange with Ca²⁺ among layers of the WRK bentonite, showing the relatively low U adsorption efficiency. At the alkaline conditions (>pH 7), the U could be adsorbed in the form of anionic U-hydroxy complexes (UO₂(OH)₃^-, UO₂(OH)₄^2-, (UO₂)₃(OH)₇^-, etc.), mainly by bonding with oxygen (O^-) from Si-O or Al-O(OH) on the WRK bentonite or by co-precipitation in the form of hydroxide, showing the high U adsorption. At pH 7, the relatively low U adsorption efficiency (42%) was acquired in this study and it was due to the existence of the U-carbonates in solution, having relatively high solubility than other U species. The U adsorption efficiency of the WRK bentonite can be increased by maintaining a neutral or highly alkaline condition because of the formation of U-hydroxyl complexes rather than the uranyl ion (UO₂²⁺) in solution,and by restraining the formation of U-carbonate complexes in solution.

• Journal of the Korean Society of Food Science and Nutrition
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• v.38 no.6
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• pp.709-720
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• 2009

This study was conducted to identify daily caffeine intakes in beverages for elementary school children and to evaluate its effectiveness after nutrition education. The caffeine contents of 140 commercial beverages were analysed by high performance liquid chromatography-ultraviolet detector (HPLC-UV) and information about their consumption were obtained by surveying 267 children. Researchers gave nutrition education to the children, who were 6 to 11 years old and attended 9 classes of 3 elementary schools, by lecture, Powerpoint file and moving picture. Their preference and intake amount on beverages were investigated by questionnaire before and after nutrition education. The order on caffeine contents was coffee ($33.8{\pm}2.4{\sim}49.1{\pm}5.6\;mg/100\;mL$)> coffee milk ($10.6{\pm}3.3\;mg/100\;mL$)> cola ($6.0{\pm}2.4\;mg/100\;mL$)> green black oolong tea drink ($6.0{\pm}2.4\;mg/100\;mL$)> chocolate milk and chocolate drink ($1.6{\pm}0.7{\sim}1.7\;mg/100\;mL$)> black ice tea mix ($1.3{\pm}1.7\;mg/100\;mL$). The order on children's preference was carbonated drink and fruit and vegetable drink (27%)> sports drink (26%)> processed cocoa mix (7%)> milk (6%)> vitamin & functional drink (3%)> green tea drink (2%)> black tea drink and coffee (1%). The average daily caffeine intakes except tea drink was $5.9{\pm}11.2$ mg/person/day ($0.17{\pm}0.32$ mg/kg bw/day), ranged from $0.0{\sim}80.5$ mg/person/day for children. The sources of caffeine were coffee 57% (3.4 mg/person/day), coffee milk 20% (1.2 mg/person/day), carbonated drink 15% (0.9 mg/person/day), chocolate milk and chocolate drink 6% (0.4 mg/person/day), and vitamin & functional drink 2% (0.1 mg/person/day). After nutrition education, the preference of carbonated drink, coffee, vitamin drinks & functional drink was decreased significantly (p<0.05, p<0.05, p<0.01) and the intakes of carbonated drink, chocolate milk & chocolate drink, and vitamin & functional drink were also decreased significantly (p<0.01, p<0.05, p<0.01). This study has shown that nutrition education influences the preference and the intake behavior of caffeinated beverages.