Yeongkyoo Kim

Co-contamination of arsenic and fluoride in the groundwater of unconsolidated aquifers under reducing environments.

The co-contamination of arsenic (As) and fluoride (F(-)) in shallow aquifers is frequently observed worldwide, and the correlations between those contaminants are different according to the redox conditions. This study geochemically explores the reasons for the co-contamination and for the redox-dependent correlations by investigating the groundwater of an alluvial aquifer in Korea. Geochemical signatures of the groundwater in the study area show that the As concentrations are enriched by the reductive dissolution of Fe-(hydr)oxides, and the correlations between As and F(-) concentrations are poor comparatively to those observed in the oxidizing aquifers. However, F(-) concentrations are strongly dependent on pH. Desorption/adsorption experiments using raw soils and citrate-bicarbonate-dithionite treated soils indicated that Fe-(hydr)oxides are the important As and F(-) hosts causing the co-contamination phenomenon. The weaker correlation between F(-) and As in reducing aquifers is likely to be associated with sulfate reduction, which removes As from groundwater without changing the F(-) concentration.

Inorganic chemicals in an effluent-dominated stream as indicators for chemical reactions and streamflows

Abstract The chemical behavior of major inorganic ions in the streams of the Mankyung River area (South Korea) was investigated. Mixing with effluent from the Jeonju STP (a municipal sewage treatment plant in Jeonju City) was the most important process in regulating the water chemistry of the streams. The effluent was chemically distinct relative to the stream waters in inorganic composition. Behavior of various ions was evaluated by comparing their concentrations with the concentration of chloride, a conservative chemical species. It was revealed that concentrations of chloride and sulfate, the total concentration of major cations, and electrical conductivity in the stream were controlled only by mixing, indicating their conservative behavior similar to chloride. Alkalinity and concentration of nitrate, however, were regulated by various reactions such as mixing, photosynthesis, respiration, and decomposition of organic matter. Streamflows were estimated by observing chemical composition of the effluent and those of up/downstream waters. Estimated flows based on the conservative chemical parameters were nearly the same as those directly measured using an area–velocity method, indicating the validity of the chemistry-based method.

Mineral phases and mobility of trace metals in white aluminum precipitates found in acid mine drainage.

The white aluminum precipitates (S1,S2,S4-1,S4-2) collected at three different locations affected by acid mine and rock drainage were studied to characterize the mineral phases and mobility of trace metals. Chemical analysis, XRD, SEM, NMR, and sequential extraction method were mainly used. XRD data showed that most white aluminum precipitates are amorphous with small amount of gypsum, which was also confirmed by SEM. The (27)Al MAS NMR spectra provide more detailed information on the local environments of aluminum in those samples. The samples collected at two locations (S3, and S4-1 and S4-2) contain 4-coordinated aluminum, suggesting that the samples contain a significant amount of amorphous phase from Al13-tridecamer. Chemical data of calcium and sulfur with (27)Al MAS NMR spectra suggest that the relative amounts of amorphous phase from Al13-tridecamer, hydrobasaluminite, aluminum hydroxide, and gypsum are different for each sample. Different amount of amorphous phase from Al13-tridecamer in those samples are probably caused by the different geochemical conditions and hydrolysis by aging in water. Sequential extraction results show that water soluble fraction and sorbed and exchangeable fraction of trace metals in sample collected as suspended particles (S1) are higher than other samples, and can affect the ecological system in waters by releasing aluminum and trace metals. These results suggest that careful characterization of white aluminum precipitates is needed to estimate the environmental effects of those precipitates in acid mine drainage.

Arsenic concentration in porewater of an alkaline coal ash disposal site: Roles of siderite precipitation/dissolution and soil cover

The geochemical behavior of As in porewaters of an alkaline coal ash disposal site was investigated using multilevel samplers. The disposal site was in operation from 1983 until 1994 and was covered with 0.3-0.5m thick soils in 2001 when this study was initiated. Sequential extraction analyses and batch leaching experiments were also performed using the coal ash samples collected from the disposal site. The results suggest the important roles of siderite (FeCO(3)) precipitation/dissolution and soil cover, which have been ignored previously. Arsenic levels in the porewater were very low (average of 10microgL(-1)) when the site was covered with soil due to coprecipitation with siderite. The soil cover enabled the creation of anoxic conditions, which raised the Fe concentration by the reductive dissolution of Fe-(hydr)oxides. Because of the high alkalinity generated from the alkaline coal ash, even a small increase in the Fe concentration (0.66mgL(-1) on average) could cause siderite precipitation. When the soil cover was removed, however, an oxidizing condition was created and triggered the precipitation of dissolved Fe as (hydr)oxides. As a result, the dissolution of previously precipitated As-rich siderite caused higher As concentration in the porewater (average of 345microgL(-1)).

Effects of intermediate range structure on the 29Si NMR chemical shifts of framework silicates: Results for analcime

Abstract Seven natural analcime samples with atomic Si/Al ratios from 1.97 to 2.63 were investigated to explore the effects of intermediate range structure and Al for Si substitution up to the fourth nearest neighbor coordination shell on the 29Si NMR chemical shifts in the framework aluminosilicates. With increasing bulk Si/Al ratio, the 29Si chemical shifts of all Si(nAl) resonances become more negative (more shielded), consistent with previously reported trends for faujasite and LTA zeolite (Newsam 1985). For our analcimes, the total observed changes in chemical shift for the Si(3Al), Si(2Al), and Si(1Al) sites are ~0.5, 0.6, and 1.1 ppm, respectively, demonstrating that the effect of Si/Al ratio is more significant for the Si sites with a smaller number of next-nearest neighbor Al atoms. The mean value of the change in chemical shift per added Al on fourth nearest neighbor sites is ~2.8 ppm [2.3 ppm if Si(3Al) is excluded]. This value is similar to the results of recent QM/MM calculations and is somewhat larger than those previously reported for faujasite and LTA framework zeolite (~1.4 and 1.3 ppm). This difference correlates with the overall denser structure of analcime, including smaller cages and shorter Si-fourth neighbor distances. Combining these results with the known changes in 29Si chemical shifts for framework silicates due to changes in the first coordination shell, tetrahedral polymerization and second neighbor Al for Si substitution for tetrahedrally coordinated Si, we present an empirical relation between the changes in 29Si chemical shift and interatomic distance between Si and nearby atoms.

Crystallization and preliminary crystallographic studies of an antimicrobial protein from Pharbitis nil

An antimicrobial protein from seeds of Pharbitis nil (Pn-AMP) which shows an antifungal activity towards several agriculturally important plant pathogens has been crystallized in the presence of equimolar N-acetylglucosamine with sodium citrate as precipitant. The crystal belongs to the hexagonal space group P6(1)22 (or P6(5)22), with unit-cell parameters a = b = 29.33 (5), c = 133.44 (12) A. Native data were collected using a crystal at 100 K to a resolution of 1.78 A.

Mineralogical changes and distribution of heavy metals caused by the weathering of hydrothermally altered, pyrite-rich andesite

The weathering of pyrite-rich andesite in the southeastern part of Korea has led to acid rock drainage, creating severe environmental problems in the region. In this study, the mineral compositions and geochemical mobility of heavy metals in the bedrock, in addition to the weathering products, are investigated. Samples of bedrock and weathering products were collected from two sites in the Yangsan area. Site 2 shows considerably more weathering than site 1, due to the longer duration of weathering. The mineral compositions show that the bedrock at site 2 was more heavily altered by hydrothermal activity. The weathering products at site 2 contain jarosite and goethite with lower pH values than site 1, in which the samples are buffered by calcite. This indicates that the mineral compositions and pH values of the weathering products at the two sites are influenced by the primary mineral compositions of the bedrock and the duration of weathering. With the exception of Pb, the concentrations of heavy metals at site 1 are higher than those at site 2, probably due to higher concentrations in the bedrock. Moreover, the labile and acid-soluble fractions, which can be more readily released into the environment, are higher at site 1, mainly due to the shorter duration of weathering. Accordingly, the weathering process at site 1 carries more potential hazards to the environment than that at site 2. However, chemical weathering is locally impeded by calcite buffering at site 1. Although the concentrations of heavy metals at site 2 are lower than those at site 1, they are being continuously released due to the lower pH and longer and more and extensive weathering.

Biogeochemical Remediation of Cr(VI)-Contaminated Groundwater using MMPH-0 (Enterobacter aerogenes)

Indigenous bacteria isolated from contaminated sites play important roles to remediate contaminated groundwater. Chromium has the most stable oxidation states. Cr(VI) is toxic, carcinogenic, and mobile, but Cr(III) is less toxic and immobile. In this study, indigenous microorganism (MMPH-0) was enriched from Cr(VI) contaminated groundwater, and identified by 16S rRNA gene analysis. Using MMPH-0, the effect of stimulating with e-donors (glucose, lactate, acetate, and no e-donor control), respiration conditions, biomass, tolerance, and geochemical changes on Cr(VI) reduction were investigated in batch experiments for 4 weeks. The changes of Cr(VI) concentration and geochemical conditions were monitored using UV-vis-spectrophotometer and Eh-pH meter. And the morphological and chemical characteristics of MMPH-0 and precipitates in the effluents were characterized by TEM-EDS and SEM-EDS analyses. MMPH-0 (Enterobacter aerogenes) was able to tolerate up to 2000 mg/L Cr(VI) and reduce Cr(VI) under aerobic and anaerobic conditions. MMPH-0 performed faster and higher efficiency of Cr(VI) reduction with electron donors (over 70% after 1 week with e-donor, 10-20% after 4 weeks without e-donor). The changes of Eh-pH in effluents showing the tendency from oxidizing to reducing condition and a bit of acidic change in pH due to microbial oxidation of organic matters donating electrons and protons suggested the roles of MMPH-0 on Cr(VI) in the contaminated water catalyzing to transit geochemical stable zone for more stable or Cr(III) precipitates. TEM/SEM-EDS analyses of MMPH-0 and precipitates indicate direct and indirect Cr(VI) reduction: extracellular polymers capturing Cr component outside cells. These results suggested diverse indigenous bacteria and their biogeochemical reactions might enhance more effective and feasible remediation technology of redox sensitive heavy metals in metal-contaminated in groundwater.

Mineralogical and Chemical Characteristics of the Oyster Shells from Korea

SO2 가스 반응제로 사용되는 석회석의 대체 가능 물질로서 굴 패각의 광물학적 화학적 특성을 알아보았다. 생장환경에 따른 굴 패각의 특성을 파악하기 위하여 태안지역 및 통영지역의 굴 패각을 석회석과 비교하였고 추가로 보령 및 여수 지역의 굴 패각을 연구하였다. XRD 분석 결과 굴 패각은 아라고나이트로 구성되어 있는 폐각근 접합 부분 및 인대(ligament) 접합부분을 제외하고 방해석으로 구성되어 있으며 불순물로서 나타나는 해양 퇴적물이 패각 내 표면에 존재하거나 일부 패각 내 포유물 형태로 나타나기도 했다. 불순물 중 하나인 패각 표면의 따개비의 경우도 방해석으로 이루어져 있어 소성에 영향을 주지는 않을 것으로 판단된다. 현미경 관찰을 통하여 굴 패각의 미세구조를 파악할 수 있었다. 패각은 크게 각주층, 진주층, 초크층으로 구성되어 있는데 패각이 가장 큰 통영 굴 패각은 콘키올린(conchiolin)이라 불리는 단백질을 일부 함유하는 각주층과 진주층의 두께가 가장 작았으며 작은 크기의 태안 굴 패각의 경우 각주층과 진주층 두께가 가장 두꺼운 것으로 나타났다. 중간 크기의 패각 크기를 갖는 보령과 여수 굴 패각은 그 층들이 두 패각의 중간정도의 두께를 보여주었다. 이는 계속 바닷물 속에서 양식하는 통영과 조간대에서 공기와 바닷물 속에서 양식하는 태안의 생장 환경 차이로 판단된다. 굴 패각들은 석회석과 달리 상대적으로 높은 인과 황 함량을 보여주는데 이는 패각 내의 단백질에 의한 것이며 패각을 구성하고 있는 세 개의 층은 Mg 함량을 포함하여 일부 상이한 화학성분을 갖고 있기도 했다. 미량성분의 경우 패각의 경우 석회석 보다 Li의 함량이 상대적으로 많았으며 이는 바닷물 성분의 영향을 받았을 것으로 생각된다. 각 산지별 패각에서는 Zn의 함량 변화가 가장 커서 Zn의 함량은 생성환경에 가장 영향을 많이 받는 미량원소로 판단된다.

NMR investigation of octahedralcis-trans occupancy changes during I/S dehydroxylation

I/S clays (<1 μm size fraction) were analyzed by27Al NMR and infrared spectroscopy to investigate the double step dehydroxylation behavior which can be observed in many 2∶1 dioctahedral clays. The intensity changes of27Al NMR peaks for tetrahedral and octahedral sites during dehydroxylation were observed. The distorted oxygen polyhedra coordinating Al in the I/S dehydroxylates caused almost complete27Al signal loss from five-fold coordinated sites and some loss from the six-fold sites. After assessing the extent of dehydroxylation of 7 samples heated at 700°C for 1 hour by IR, theoretical six-fold Al NMR peak intensities were calculated based on two previously proposed dehydroxylation mechanisms and compared with the experimental ones. The calculations suggest that there is no movement of the octahedral cations during dehydroxylation in contrast with published XRD results. NMR results showed that the different dehydroxylation temperatures forcis- andtrans- vacant clays can be caused by the different OH−OH distances which required different energies for dehydroxylation.