KURT 지하수 내 우라늄 화학종 분광 특성

정의창(Euo Chang Jung),김희경(Hee-Kyung Kim),조혜륜(Hye-Ryun Cho),차완식(Wansik Cha),백민훈(Min Hoon Baik) 대한지질학회 2021 대한지질학회 학술대회 Vol.2021 No.10

지하수에 포함된 우라늄(U) 화학종 규명(chemical speciation) 연구에서는 서로 다른 복합체(complex) 상태로 존재하는 화학종들을 구분하고, 그 농도를 결정하는 내용을 다룬다. 이 발표에서는 시간분해 레이저 형광 분광학(TRLFS, Time-Resolved Laser Fluorescence Spectroscopy) 기술을 이용하여 KURT 지하수에 존재하는 U 화학종 규명 연구를 수행한 결과에 대해 논의한다. 첫째, 수용액 속의 미량 U 정량 분석에 널리 이용되고 있는 TRLFS 기술을 소개하고, 이 기술을 응용하고 있는 표준 분석 장비의 작동 원리와 성능을 살펴본다. 둘째, KURT 지하수에 존재하는 U 정량 분석 결과에 대해 보고한다. 셋째, KURT 지하수에 존재하는 U(VI) (6가 우라늄) 화학종의 시간분해 형광 스펙트럼 특성에 대해 논의한다. 지하수에는 다양한 무기 이온 및 탄산염이 존재하며, 이 원소들과 결합함으로써 Ca₂UO₂(CO₃)(aq) 형태의 U(VI) 복합체 화학종으로 존재할 가능성에 대해서도 살펴본다. 저온(섭씨 5도 이하) 조건에서는 유기물에서 발생하는 형광이 U(VI) 화학종에서 발생하는 형광 측정을 방해하는 현상을 줄일 수 있으며, U 화학종의 형광 세기가 뚜렷하게 증가하므로 측정 감도가 개선된다는 것을 보였다.

용존 6가 우라늄 및 실리카 표면 흡착 6가 우라늄 화학종 분포 연구

정의창,김태형,조용흠,김희경,조혜륜,차완식,백민훈,윤종일,Jung, Euo Chang,Kim, Tae-Hyeong,Jo, Yongheum,Kim, Hee-Kyung,Cho, Hye-Ryun,Cha, Wansik,Baik, Min Hoon,Yun, Jong-Il 한국방사성폐기물학회 2020 방사성폐기물학회지 Vol.18 No.1

Dissolved hexavalent uranium can exist in the form of several different chemical species. Furthermore, species distributions depend on the pH value of the aqueous solution. Representatively, UO₂²⁺, UO₂OH⁺, (UO₂)₂(OH)₂²⁺, and (UO₂)₃(OH)₅⁺ species coexist in solutions at acidic and circumneutral pH values. When amorphous silica particles are suspended in an aqueous solution, the dissolved chemical species are easily adsorbed onto silica surfaces. In this study, it was examined whether the species distribution of the adsorbed U(VI) on a silica surface followed that of the dissolved U(VI) in an aqueous solution. Time-resolved luminescence spectra of three different dissolved species (UO₂²⁺, UO₂OH⁺, and (UO₂)₃(OH)₅⁺) and two different adsorbed species (≡SiO₂UO₂, ≡SiO₂(UO₂)OH^-, or ≡SiO₂(UO₂)₃(OH)^5-) were measured in the pH range 3.5-7.5. The spectral shapes of these chemical species were compared by changing the pH value; consequently, it was confirmed that the species distribution of the adsorbed U(VI) species was different from that of the dissolved U(VI) species.

이동식 레이저 유도 파열 검출 장치를 이용한 KURT 지하수 내 콜로이드 나노 입자 검출

정의창,조혜륜,박미리,백민훈,Jung, Euo-Chang,Cho, Hye-Ryun,Park, Mi-Ri,Baik, Min-Hoon 한국방사성폐기물학회 2011 방사성폐기물학회지 Vol.9 No.1

한국원자력연구원 내 지하 처분 연구시설(KURT)에서 채취한 지하수에 존재하는 나노 콜로이드 입자의 크기 및 농도를 현상에서 조사하기 위해 이동식 레이저 유도 파열 검출 장치를 개발하였다. 제작한 장치는 CCD 카메라를 이용하여 레이저 유도 플라즈마가 발생한 위치를 2-차원 영상으로 기록함으로써 광학적으로 입자의 크기를 결정할 수 있다. 크기가 정확히 알려진 폴리스틸렌 표준 입자를 이용하여 입자 크기 측정용 검정 곡선 (calibration curve)을 구했고, 이를 이용하여 지하 처분 연구시설에서 채취한 지하수 내 콜로이드 입자의 크기를 측정하였다. 지하수 내 존재하는 콜로이드 입자의 평균 크기는 $108{\pm}26$ nm 임을 보였고, 농도는 50 ppb 이하인 것으로 추정하였다. A mobile laser-induced breakdown detection (LIBD) system was developed for the field measurement of the size and concentration of aquatic colloidal nanoparticles sampled from Korea Atomic Energy Research Institute Underground Research Tunnel (KURT). The established LIBD apparatus is based on the optical detection of a laser-induced plasma by means of a two-dimensional optical imaging method for determining the size of nanoparticle. Calibration curve for determining the size of nanoparticle was obtained from the polystyrene reference particles of a well-defined size. The first direct application was made at KURT for investigating the particle sizes in groundwater. By comparing the size of particles in groundwater with the sizes of reference particles, the mean particle size of approximately $108{\pm}26$ nm with the concentration lower than 50 ppb was determined.

시간분해 레이저 유도 형광 분광학을 이용한 우라늄(VI) 가수분해 화학종 규명 연구

정의창,조혜륜,박경균,Jung, Euo-Chang,Cho, Hye-Ryun,Park, Kyoung-Kyun 한국방사성폐기물학회 2009 방사성폐기물학회지 Vol.7 No.3

Study on the chemical speciation of uranium(VI) species, ${UO_2}^{2+}$, $UO_2(OH)^+$, ${(UO_2)}_2{(OH)_2}^{2+}$, ${(UO_2)}_3{(OH)_5}^+$, has been peformed by using time-resolved laser-induced fluorescence spectroscopy. Speciation sensitivity which depends on the excitation wavelength was investigated. We obtained the speciation sensitivity in the order of $10^{-9}$ M concentration of U(VI) compounds at the excitation wavelength of 266 nm. The fluorescence spectrum and lifetime of ${UO_2}^{2+}$ were carefully measured at pH 1 and ion strength of 0.1 M. The spectrum showed the four characteristic peaks located around 488, 509, 533, 559nm and the fluorescence lifetime of $1.92{\pm}0.17{\mu}s$. The wavelength shifts of fluorescence peaks and the change of lifetimes for uranium hydrolysis compounds were compared with those of ${UO_2}^{2+}$. We report on the characteristic features, the shifts of peaks to the longer wavelength direction and the prolonged lifetimes, in the fluorescence of the U(VI) hydrolysis compounds.

방사분석과 분광학을 이용한 Am(III) 가수분해와 옥살레이트 착물 화학종 연구

김희경,조혜륜,정의창,차완식,Kim, Hee-Kyung,Cho, Hye-Ryun,Jung, Euo Chang,Cha, Wansik 한국방사성폐기물학회 2018 방사성폐기물학회지 Vol.16 No.4

When considering the long-term safety assessment of spent-nuclear fuel management, americium is one of the most radio-toxic actinides. Although spectroscopic methods are widely used for the study of actinide chemistry, application of those methods to americium chemistry has been limited. Herein, we purified $^{241}Am$ to obtain a highly pure stock solution required for spectroscopic studies. Quantitative and qualitative analyses of purified $^{241}Am$ were carried out using liquid scintillation counting, and gamma and alpha radiation spectrometry. Highly sensitive absorption spectrometry coupled with a liquid waveguide capillary cell and time-resolved laser fluorescence spectroscopy were employed for the study of Am(III) hydrolysis and oxalate (Ox) complexation. $Am^{3+}$ ions under acidic conditions exhibit maximum absorbance at 503 nm, with a molar absorption coefficient of $424{\pm}8cm^{-1}{\cdot}M^{-1}$. $Am(OH)_3(s)$ colloidal particles formed under near neutral pH conditions were identified by monitoring the absorbance at around 506-507 nm. The formation of ${Am(Ox)_3}^{3-}$ was detected by red-shifts of the absorption and luminescence spectra of 4 and 5 nm, respectively. In addition, considerable enhancements of the luminescence intensities were observed. The luminescence lifetime of ${Am(Ox)_3}^{3-}$ increased from 23 to 56 ns, which indicates that approximately six water molecules are replaced by carboxylate ligands in the inner-sphere of the Am(III). These results suggest that ${Am(Ox)_3}^{3-}$ is formed through the bidentate coordination of the oxalate ligands.

레이저유도파열검출 기술을 이용한 우라늄(VI) 가수분해물의 용해도 측정

조혜륜,박경균,정의창,지광용,Cho, Hye-Ryun,Park, Kyoung-Kyun,Jung, Euo-Chang,Jee, Kwang-Yong 한국방사성폐기물학회 2007 방사성폐기물학회지 Vol.5 No.3

레이저유도파열검출 기술을 이용하여 우라늄(VI) 가수분해물의 용해도를 측정하였다. 측정 용액의 우라늄 농도 범위는 $2{\times}10^{-4}{\sim}4{\times}10^{-6}\;M$, pH 범위는 $3.8{\times}7.0$, 그리고 이온 강도는 0.1 M $NaClO_4$이며, 온도는 $25.0{\pm}0.1^{\circ}C$로 유지하였다. 문헌에 제시된 가수분해 상수와 specific ion interaction theory(SIT)를 이용하여 이온 강도 I=0 일 때의 용해도 곱 (solubility product) 상수 ${\log}K^{\circ}_{sp}=-22.85{\pm}0.23$를 구하였다. 동일한 시료에 대해 흡수 및 형광 스펙트럼을 측정하여 가수분해 화학종의 존재를 확인하였다. $2{\times}10^{-4}\;M$ 우라늄 농도에서 용액 중에 존재하는 주요 가수분해 화학종은 $(UO_2)_2(OH)_2^{2+}$와 $(UO_2)_3(OH)_5^+$임을 보였다.

분광학을 이용한 흄산의 모델 리간드인 2,6-Dihydroxybenzoic acid와 우라늄(VI)의 착물형성 반응에 관한 연구

차완식,조혜륜,정의창,Cha, Wan-Sik,Cho, Hye-Ryun,Jung, Euo-Chang 한국방사성폐기물학회 2011 방사성폐기물학회지 Vol.9 No.4

UV-Vis 분광광도법과 시간분해 레이저 유도 형광분광법(TRLFS)을 이용하여 흄산의 모사 리간드로 사용한 2,6-Dihydroxybenzoate(DHB)와 U(VI)의 착물형성반응을 조사하였다. U(VI)-DHB 착물 고유의 전하이동 흡수 스펙트럼을 분석한 결과, 착물형성반응은 우라늄-리간드 비가 1:1 또는 1:2 착물을 형성하는 이중 평형반응이며, 산도에 따라 착물종의 분포가 변한다는 것을 밝혔다. 계산된 착물형성상수 (log $K_1$ and log $K_2$)는 $12.4{\pm}0.1$과 $11.4{\pm}0.1$이다. 이에 더하여, TRLFS 방법으로 조사한 결과, DHB는 U(VI) 화학종들의 형광 소광제(quencher)로서 역할을 한다는 것을 확인하였다. 특히, 확인된 U(VI) 화학종 모두(${UO_2}^{2+}$, $(UO_2)_2{(OH)_2}^{2+}$과 $(UO_2)_3(OH)_5{^+})$에서 정적 (static) 및 동적 (dynamic) 소광작용이 공존하는 것으로 관찰되었다. 시간분해 형광 스펙트럼으로부터 리간드 농도에 따른 U(VI) 화학종의 형광세기와 형광수명을 측정하였으며, Stern-Volmer 식을 이용하여 분석하였다. 결정된 정적소광계수(KS)는 ${UO_2}^{2+}$, $(UO_2)_2{(OH)_2}^{2+}$ 과 $(UO_2)_3(OH)_5+$에 대하여 각각 $4.2{\pm}0.1$, $4.3{\pm}0.1$ 과 $4.34{\pm}0.08$이다. Stern-Volmer 식을 이용한 분석 결과, 단일 또는 이중 배위자 구조(mono- and bi-dentate)의 U(VI)-DHB 착물이 모두 정적소광효과에 관여하는 바닥상태 착물임을 확인하였다. In this study the complex formation reactions between uranium(VI) and 2,6-dihydroxybenzoate (DHB) as a model ligand of humic acid were investigated by using UV-Vis spectrophotometry and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The analysis of the spectrophotometric data, i.e., absorbance changes at the characteristic charge-transfer bands of the U(VI)-DHB complex, indicates that both 1:1 and 1:2 (U(VI):DHB) complexes occur as a result of dual equilibria and their distribution varies in a pH-dependent manner. The stepwise stability constants determined (log $K_1$ and log $K_2$) are $12.4{\pm}0.1$ and $11.4{\pm}0.1$. Further, the TRLFS study shows that DHB plays a role as a fluorescence quencher of U(VI) species. The presence of both a dynamic and static quenching process was identified for all U(VI) species examined, i.e., ${UO_2}^{2+}$, $(UO_2)_2{(OH)_2}^{2+}$, and $(UO_2)_3{(OH)_5}^+$. The fluorescence intensity and lifetimes of each species were measured from the time-resolved spectra at various ligand concentrations, and then analyzed based on Stern-Volmer equations. The static quenching constants (log $K_s$) obtained are $4.2{\pm}0.1$, $4.3{\pm}0.1$, and $4.34{\pm}0.08$ for ${UO_2}^{2+}$, $(UO_2)_2{(OH)_2}^{2+}$, and $(UO_2)_3{(OH)_5}^+$, respectively. The results of Stern-Volmer analysis suggest that both mono- and bi-dentate U(VI)-DHB complexes serve as groundstate complexes inducing static quenching.

모세관 셀을 이용한 수용액 내 악티나이드 화학종의 고감도 검출

조혜륜,박경균,정의창,송규석,Cho, Hye-Ryun,Park, Kyuong-Kyun,Jung, Euo-Chang,Song, Kyu-Seok 한국방사성폐기물학회 2009 방사성폐기물학회지 Vol.7 No.2

Absorption spectra for a quantitative analysis of actinide elements such as U(VI) and Pu(V) were measured by using a liquid waveguide capillary cell (LWCC) which has an optical path length of 1.0 meter. In order to investigate radioactive elements, a LWCC is installed in a glove box and is coupled to a spectrophotometer with optical fibers. Limits of detection (LOD) for the system were determined as 0.74 and 0.35 M with molar absorption coefficients of 8.14${\pm}$0.07 (414 nm) and 17.00${\pm}$0.16 (569 nm) $M^{-1}cm^{-1}$ for U(VI) and Pu(V) ions, respectively. The measured LOD values are about 30 times more sensitive when compared to those achievable by using a conventional quartz cell with an optical path length of 1.0 cm. As an application with an enhanced sensitivity, a quantitative analysis for micromolar concentrations of Pu(V) has been performed to decrease the uncertainty in the formation constant of the Pu(VI)-OH complex.

카올리나이트에 대한 휴믹산 및 아메리슘 흡착거동 연구

이명호,이규환,박경균,정의창,송규석,신현상,Lee, Myung-Ho,Lee, Kyu-Whan,Park, Kyung-Kyun,Jung, Euo-Chang,Song, Kyu-Seok,Shin, Hyun-Sang 한국방사성폐기물학회 2010 방사성폐기물학회지 Vol.8 No.2

In this study, the adsorption reactions in the binary component system such as kaolinite-humic acid, kaolinite-americium and humic acid-americium were investigated. After performing the basic physico-chemical properties of the kaolinite, the adsorption reactions of the humic acid on the kaolinite were carried out with varying concentration of humic acid and ion strength, and pH. With increasing HA concentration and pH, the sorption of HA onto KA decreased, while the sorption of HA onto KA increased with increasing ionic stre ngth. Also, with varying pH, the adsorption reactions of the americium-kaolinite and americium-humic acid were studied. In the acid and neutral region, Am easily adsorbed on the HA, while the sorption of Am on the HA in the alkali region decreased because of electrostatic repulsion. The results from these studies make it possible to understand the characteristics of adsorption behaviour of the americium by the humic acid in the water environment.

Bioreduction of U(Ⅵ) by indigenous bacteria present in deep granitic groundwater

Dawoon Jeong(정다운),Min Hoon Baik(백민훈),Euo chang Jung(정의창),Myoung-Soo Ko(고명수),Wooyong Um(엄우용),Ji-Hun Ryu(류지훈) 대한환경공학회 2022 대한환경공학회 학술발표논문집 Vol.2022 No.11