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Jang, Jiseon,Lee, Dae Sung Elsevier 2018 Journal of nuclear materials Vol.504 No.-
<P><B>Abstract</B></P> <P>A three-dimensional barium-sulfate-impregnated reduced graphene oxide (BaSO<SUB>4</SUB>-rGO) aerogel was successfully synthesized by a facile one-step hydrothermal method and was used as an adsorbent to remove strontium from aqueous solutions. The characterized elemental composition, crystal structure, and morphology of the prepared aerogel confirmed that barium sulfate particles were firmly anchored on the surface of the rGO sheets and exhibited a porous 3D structure with a high surface area of 129.37 m<SUP>2</SUP>/g. The mass ratio of BaSO<SUB>4</SUB> in the BaSO<SUB>4</SUB>-rGO aerogel substantially affected strontium adsorption, and the optimal BaSO<SUB>4</SUB>/rGO ratio was found to be 1:1. The synthesized BaSO<SUB>4</SUB>-rGO aerogel not only reached adsorption equilibrium within 1 h, but also showed much higher adsorption capacity than an rGO aerogel. The experimental data were well fitted to a pseudo-second-order kinetic model and the adsorption behavior followed the Langmuir isotherm. The adsorption capacity of strontium on BaSO<SUB>4</SUB>-rGO aerogels remained relatively high even under ionic competition in simulated seawater. These results showed that the BaSO<SUB>4</SUB>-rGO aerogel is an efficient and promising adsorbent for the treatment of strontium in aqueous solutions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> 3D barium-sulfate-impregnated reduced graphene oxide aerogels were synthesized. </LI> <LI> The mass ratio of BaSO<SUB>4</SUB> in the aerogels substantially affected strontium adsorption. </LI> <LI> The Langmuir isotherm gave the best fit to the experimental adsorption data. </LI> <LI> The strontium adsorption capacity was relatively high even with competing ions in simulated seawater. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Jang, Jiseon,Lee, Dae Sung Elsevier 2018 The Science of the total environment Vol.615 No.-
<P><B>Abstract</B></P> <P>Magnetite nanoparticles supported on organically modified montmorillonite (MNP-OMMTs) were successfully synthesized by a facile coprecipitation method. The surface of natural clay was modified using a cationic surfactant, hexadecyltrimethylammonium. The synthesized MNP-OMMTs were used as an adsorbent to remove iodide from aqueous solutions. The maximum adsorption capacity of the adsorbent was 322.42mg/g, which is much higher than other previously reported adsorbents for removing iodide in aqueous solution. The experimental data were well fitted to a pseudo-second-order kinetic model, and the adsorption behavior followed the Langmuir isotherm. A thermodynamic study indicated that iodide adsorption was spontaneous and endothermic. The individual and combined effects of key process parameters (pH, temperature, and initial iodide concentration) were studied using a response surface methodology. The maximum iodide removal efficiency of 93.81% was obtained under the optimal conditions of pH3.9, a temperature of 41.3°C, and an initial iodide concentration of 113.8mg/L.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel MNP-OMMT was synthesized by a facile coprecipitation method. </LI> <LI> XRD, FT-IR, TGA, and MPMS analyses confirmed successful synthesis of MNP-OMMT. </LI> <LI> The MNP-OMMT was an excellent adsorbent for iodide adsorption. </LI> <LI> RSM was employed to determine the optimal conditions for enhanced iodide removal. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Rice straw-based biochar beads for the removal of radioactive strontium from aqueous solution
Jang, Jiseon,Miran, Waheed,Divine, Sewu D.,Nawaz, Mohsin,Shahzad, Asif,Woo, Seung Han,Lee, Dae Sung Elsevier 2018 Science of the Total Environment Vol.615 No.-
<P><B>Abstract</B></P> <P>Biochars from agricultural residues have recently attracted significant attention as adsorbents for purifying contaminated water and wastewater. In this study, the removal of strontium from aqueous solutions was investigated using rice straw-based biochar (RSBC) beads in both batch and continuous fixed-bed column systems. The RSBC beads had negatively charged surfaces and exhibited a large surface area (71.53m<SUP>2</SUP>/g) with high micro-porosity. The synthesized beads showed a maximum adsorption capacity of 175.95mg/g at an initial strontium concentration of 10g/L at 35°C and pH7. Furthermore, they showed a good selectivity toward strontium ions in the presence of competing ions such as Al<SUP>3+</SUP>, Mg<SUP>2+</SUP>, and K<SUP>+</SUP>. The effects of different operating conditions like flow rate and initial strontium concentration were investigated in the fixed–bed column reactor. The Thomas, Adams–Bohart, and Yoon–Nelson models were applied to the experimental data to predict the breakthrough curves using non-linear regression. Both the Thomas and the Yoon–Nelson models were appropriate for describing entire breakthrough curves under different operating conditions. Overall, RSBC beads demonstrate great potential as efficient adsorbents for the treatment of wastewater polluted with strontium in a continuous operation mode.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Rice straw-based biochar (RSBC) powder and beads were synthesized and characterized. </LI> <LI> Negatively charged RSBC beads showed a large surface area with high micro-porosity. </LI> <LI> The strontium adsorption capacity was high even in the presence of competing ions. </LI> <LI> A fixed-bed column reactor packed with RSBC beads was used for strontium removal. </LI> <LI> Both the Thomas and Yoon–Nelson models gave the best fit to the experimental data. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Radiological Safety Assessment for a Near-Surface Disposal Facility Using RESRAD-ONSITE Code
Jang, Jiseon,Kim, Tae-Man,Cho, Chun-Hyung,Lee, Dae Sung Korean Radioactive Waste Society 2021 방사성폐기물학회지 Vol.19 No.1
Radiological impact analyses were carried out for a near-surface radioactive waste repository at Gyeongju in South Korea. The RESRAD-ONSITE code was applied for the estimation of maximum exposure doses by considering various exposure pathways based on a land area of 2,500 ㎡ with a 0.15 m thick contamination zone. Typical influencing input parameters such as shield depth, shield materials' density, and shield erosion rate were examined for a sensitivity analysis. Then both residential farmer and industrial worker scenarios were used for the estimation of maximum exposure doses depending on exposure duration. The radiation dose evaluation results showed that 60Co, 137Cs, and 63Ni were major contributors to the total exposure dose compared with other radionuclides. Furthermore, the total exposure dose from ingestion (plant, meat, and milk) of the contaminated plants was more significant than those assessed for inhalation, with maximum values of 5.5×10-4 mSv·yr-1 for the plant ingestion. Thus the results of this study can be applied for determining near-surface radioactive waste repository conditions and providing quantitative analysis methods using RESRAD-ONSITE code for the safety assessment of disposing radioactive materials including decommissioning wastes to protect human health and the environment.