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Effects of Radiation and Temperature on Iodide Sorption by Surfactant-Modified Bentonite
Choung, Sungwook,Kim, Minkyung,Yang, Jung-Seok,Kim, Min-Gyu,Um, Wooyong American Chemical Society 2014 Environmental science & technology Vol.48 No.16
<P>Bentonite, which is used as an engineered barrier in geological repositories, is ineffective for sorbing anionic radionuclides because of its negatively charged surface. This study modified raw bentonite using a cationic surfactant (i.e., hexadecyltrimethylammonium [HDTMA]-Br) to improve its sorption capability for radioactive iodide. The effects of temperature and radiation on the iodide sorption of surfactant-modified bentonite (SMB) were also evaluated under alkaline pH condition similar to that found in repository environments. Different amounts of surfactant, equivalent to the 50, 100, and 200% cation-exchange capacity of the bentonite, were used to produce the HDTMA-SMB for iodide sorption. The sorption reaction of the SMB with iodide reached equilibrium rapidly within 10 min regardless of temperature and radiation conditions. The rate of iodide sorption increased as the amount of the added surfactant was increased and nonlinear sorption behavior was exhibited. However, high temperature and γ-irradiation (<SUP>60</SUP>Co) resulted in significantly (∼2–10 times) lower iodide <I>K</I><SUB>d</SUB> values for the SMB. The results of FTIR, NMR, and XANES spectroscopy analysis suggested that the decrease in iodide sorption may be caused by weakened physical electrostatic force between the HDTMA and iodide, and by the surfactant becoming detached from the SMB during the heating and irradiation processes.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/esthag/2014/esthag.2014.48.issue-16/es501661z/production/images/medium/es-2014-01661z_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/es501661z'>ACS Electronic Supporting Info</A></P>
Migration Behavior of Cesium in the Subsurface Environment After Wildfires
Hyojin Bae,Sungwook Choung,Jina Jeong 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1
Forest fires produce various particulate organic matters (POMs) derived from the incomplete combution process of biomass. The POMs deposited in soil and sediments can affect the physicochemical properties of the subsurface environments. This study investigated the sorption and transport behavior of cesium (Cs) in soil-groundwater environment after wildfire. Soil samples were collected at two locations (GS1 & GS2) in Gangwon Province, Korea, at different depths (~5, ~20, and ~40 cm). The sampling site, where a large-scale forest fire occurred in 2017, was damaged almost 252 ha of forest. The soil characteristics were determined by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), total organic carbon (TOC) analysis and organic petrography, and batch and fixed-bed column experiments were performed to evaluate the Cs uptake and retardation. The XRD patterns of the soils indicated that the mineral compositions of soils were quartz, feldspars (e.g., orthoclase & albite) with minor muscovite/illite. Quartz and feldspars were abundant in all studied soils, and GS2 sample contained higher feldspars and phyllosilicate minerals than the GS1. The TOC contents were high (7–8wt%) in the topsoils, decreasing with depth. The SEM and organic petrographic analyses showed that various organic carbon particles such as textinite, ulminite, fusinite (charcoal) and char existed. Presence of charcoal and char is the evidence of wildfires, even though their amount was few. Batch sorption experiments revealed that the Kd value decreased non-linearly as the Cs concentrations increased, and the sorption isotherms were fitted well with the Freundlich model. The Kd values of each soil were much greater in topsoils compared to subsoils at all experimental Cs concentrations. In particular, the GS1 topsoil had higher sorption capacity for cesium than GS2 subsoils, although it had low phyllosilicate mineral contents with realtively rich organic matter. The breakthrough curve of column experiments with high concentration (C0 ? 1×105 μg·L?1) also exhibited remarkable Cs retardation phenomena in topsoils. Their retardation factors (Rf,Cs) were max. 4 times greater than those of subsoils, showing Rf,Cs ? 43 to 45 for topsoils. At low concentration (C0 ? 1×104 μg·L?1), the Rf,Cs of topsoils (? 284 to 374) was slightly greater than that of subsoils (? 270 to 271). These results imply that POMs caused by wildfires can play important role on the Cs sorption and transport in the subsurface environments.
Shin, Woosik,Choung, Sungwook,Han, Weon Shik,Hwang, Jeonghwan,Kang, Gyeongmin Elsevier 2018 Science of the Total Environment Vol.642 No.-
<P><B>Abstract</B></P> <P>Although soil contamination must be remediated by the polluters under current legal frameworks in numerous countries, the allocation of responsibilities for soil clean-up is still challenging in the case of multiple potentially responsible parties (PRPs). This study evaluated the individual contributions of two PRPs (Owners A & B) to heavy metal contamination in the soil environment near an abandoned smelter and compared the results with those from the conventional Gore Factor (GF) method. The soil in the study area was widely contaminated by various heavy metals. In particular, the arsenic concentration exceeded the local regulatory level of 25 mg kg<SUP>−1</SUP> at all investigated sites. Arsenic components were frequently observed in the form of iron oxides, and they decreased with increasing distance from the smelter chimney. This distribution supported the premise that the arsenic mainly originated from the chimney through oxidation processes of iron-containing ores under high temperature. The GF results attributed greater responsibility to Owner A than Owner B, while the estimated arsenic masses (based on the field investigation) indicated the contrary. These results could be caused by insufficient information for the GF evaluation, because the change in smelter ownership and long history of contamination obscure important data, such as the amount of total refined ores and the efficiency of air pollution prevention facilities in the smelter. Therefore, more field-based approaches must be considered more importantly for the evaluation of multiple PRPs' remediation responsibilities, especially in areas with long-term contamination.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Individual contribution of two smelter owners to soil contamination was evaluated. </LI> <LI> Arsenic pollution decreased with increasing distance from the smelter chimney. </LI> <LI> Conventional GF evaluation can often distort the individual contribution results. </LI> <LI> Pollutants released by the former owner were preserved well in the reclaimed sites. </LI> <LI> Field evidences must be prioritized to allocate remediation responsibilities. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Shin, Woosik,Choung, Sungwook,Han, Jeong-Hee,Han, Weon Shik,Jeon, Sodam,Ryu, Jong-Sik,Chang, Byung-Uck Pergamon Press 2017 Applied geochemistry Vol.85 No.2
<P><B>Abstract</B></P> <P>Bottled mineral-water is typically produced through filtering processes of groundwater in many countries. Although naturally occurring radioactive materials (NORMs) are present in ambient groundwater, the accumulation of NORMs to filters used by bottled mineral-water plants and their total radioactivity was never studied. The radioactivity of NORMs in water and filter samples were determined for a total of thirteen bottled mineral-water facilities in Korea. The NORM levels were quite low in raw water (i.e., groundwater before filtered), and uranium and radon contents were lowered after filtering. However, minor increases of uranium concentration were observed after the treatment processes in two mineral-water plants used only membrane filters. The measured surface radiations sharply increased at the filters installed at the front of water treatment processes regardless of filter types. Diverse radionuclides including lead and polonium were found inside these filters with comparatively high radioactivity. In particular, the estimated total radioactivity of one of the used filters exceeded 1 Bq g<SUP>−1</SUP> and 1000 kBq yr<SUP>−1</SUP> that are the guideline values regulated by the Nuclear Safety and Security Commission in Korea for by-products occurring after any treatment processes. The elevated radiation may result in potential risk during bottling, transport, and disposal processes, therefore, proper management and disposal of the filters should be considered in bottled mineral-water treatment facilities.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bottled mineral water is produced through physical filtering process of groundwater. </LI> <LI> Potential accumulation of natural occurring radioactive materials to filters was evaluated. </LI> <LI> Surface radiation dose rate increased sharply at the early stage filters (e.g., prefilter). </LI> <LI> Diverse radionuclides were found in the used filters with high radioactivity. </LI> <LI> Proper management and disposal need to be considered for the filters. </LI> </UL> </P>