• Proceedings of the Korean Environmental Health Society Conference
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• 2004.12a
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• pp.51-62
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• 2004

Lime based stabilization/solidification (S/S) can be an effective remediation alternative for the immobilization of arsenic (As) in contaminated soils and sludges. However, the exact immobilization mechanism has not been well established, Based on previous research, As immobilization could be attributed to sorption and/or inclusion in pozzolanic reaction products and/or the formation of calcium-arsenic (Ca-As) precipitates. In this study, suspensions of lime-As were studied in an attempt to elucidate the controlling mechanism of As immobilization in lime treated soils. Aqueous lime-As suspensions (slurries) with varying Ca/As molar ratios (1:1, 1.5:1, 2:1, 2.5:1 and 4:1) were prepared and soluble As concentrations were determined. X-ray diffraction (XRD) analyses were used to establish the resulting mineralogy of crystalline precipitate formation. Depending on the redox state of the As source, different As precipitates were identified. When As (III) was used, the main precipitate formation was Ca-As-O. With As(V) as the source, Ca4(OH)2(AsO4)2${\cdot}$4H2O formed at Ca/As molar ratios greater than 1:1. A significant increase in As (III) immobilization was observed at Ca/As molar ratios greater than 1:1. Similarly, a substantial increase in As (V) immobilization was noted at Ca/As molar ratios greater than or equal to 2.5: 1. This observation was also confirmed by XRD. The effectiveness of both As (III) and As(V) immobilization in these slurries appeared to increase with increasing Ca/As molar ratios.

• Journal of the Korean GEO-environmental Society
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• v.13 no.2
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• pp.59-65
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• 2012

Solidification/Stabilization(S/S) is one of the remediation technologies that have been applied for treating inorganic hazardous wastes. This study investigated the reduction of arsenic concentration of arsenic-contaminated soil using by S/S. The binder plays a role in controlling the mobility and solubility of the contaminants in S/S process, so it is important to determine the optimum binder content. Therefore, this study evaluated the effectiveness of S/S using four different binders(cement, zero valent iron, and monosulfate and ettringite(cement-based synthesized materials) at the binder content ranged between 5%(wt.) and 20%(wt.). The leachability of arsenic in 1 N HCl was different depending on the types of binders: cement(71.41%) > monosulfate(47.45%) > ettringite(46.36%) > ZVI(33.08%) at the binder content of 20%. Additionally, three kinds of a mixture binder were prepared using cement and additives(monosulfate, ettringite, calcium sulfoaluminate(CSA)) and tested for arsenic reduction. The highest arsenic removal capacity was found at the mass ratio of cement to the additive, 4:1 in all experiments using a mixture binder, regardless of the additives types. A mixture binder(cement and additives) resulted in higher arsenic removal relative to the arsenic removal when cement was used alone.

• KSBB Journal
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• v.27 no.2
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• pp.75-85
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• 2012

Although, microbial arsenic mobilization by dissimilatory arsenate-reducing bacteria (DARB) and the practical use to the removal technology of arsenic from contaminated soil are expected, most previous research mainly has been focused on the geochemical circulation of arsenic. Therefore, in this review we summarized the previously reported DARB to grasp the characteristic for bioremediation of arsenic. Evidence of microbial growth on arsenate is presented based on isolate analyses, after which a summary of the physiology of the following arsenate-respiring bacteria is provided: Chrysiogenes arsenatis strain BAL-$1^T$, Sulfurospirillum barnesii, Desulfotomaculum strain Ben-RB, Desulfotomaculum auripigmentum strains OREX-4, GFAJ-1, Bacillus sp., Desulfitobacterium hafniense DCB-$2^T$, strain SES-3, Citrobacter sp. (TSA-1 and NC-1), Sulfurospirillum arsenophilum sp. nov., Shewanella sp., Chrysiogenes arsenatis BAL-$1^T$, Deferribacter desulfuricans. Among the DARB, Citrobacter sp. NC-1 is superior to other dissimilatory arsenate-reducing bacteria with respect to arsenate reduction, particularly at high concentrations as high as 60 mM. A gram-negative anaerobic bacterium, Citrobacter sp. NC-1, which was isolated from arsenic contaminated soil, can grow on glucose as an electron donor and arsenate as an electron acceptor. Strain NC-1 rapidly reduced arsenate at 5 mM to arsenite with concomitant cell growth, indicating that arsenate can act as the terminal electron acceptor for anaerobic respiration (dissimilatory arsenate reduction). To characterize the reductase systems in strain NC-1, arsenate and nitrate reduction activities were investigated with washed-cell suspensions and crude cell extracts from cells grown on arsenate or nitrate. These reductase activities were induced individually by the two electron acceptors. Tungstate, which is a typical inhibitory antagonist of molybdenum containing dissimilatory reductases, strongly inhibited the reduction of arsenate and nitrate in anaerobic growth cultures. These results suggest that strain NC-1 catalyzes the reduction of arsenate and nitrate by distinct terminal reductases containing a molybdenum cofactor. This may be advantageous during bioremediation processes where both contaminants are present. Moreover, a brief explanation of arsenic extraction from a model soil artificially contaminated with As (V) using a novel DARB (Citrobacter sp. NC-1) is given in this article. We conclude with a discussion of the importance of microbial arsenate reduction in the environment. The successful application and use of DARB should facilitate the effective bioremediation of arsenic contaminated sites.

• Economic and Environmental Geology
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• v.38 no.5 s.174
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• pp.525-534
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• 2005

Adsorption experiments for As(V) and As(III) onto the surfaces of aerobic Pseudomonas aeruginosa, which can be readily isolated from natural media, were conducted under nutrient-absent conditions. While a small amount of As(III) was adsorbed on the bacterial cell surfaces, As(V) was not effectively removed from the solution through adsorption. The result was likely due to the electrostatic repulsion between anionic compounds of aqueous As(V) and cell surfaces of f aeruginosa. However, the bacteria forming biofilm reduced a large amount of aqueous As(V) to As(III), which indicated that microorganisms in most oligotrophic, natural geologic settings can mediate the behavior of aqueous As. Biobarriers designed to remove the various heavy metals in contaminant plume may practically lead to the enhancement of toxicity and mobility of As.

• ETRI Journal
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• v.16 no.3
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• pp.1-10
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• 1994

Undoped GaAs has been successfully grown by chemical beam epitaxy (CBE) via surface decomposition process using arsine $(AsH_3)$ and trimethylgallium (TMG). Three distinct regions of temperature-dependent growth rates were identified in the range of temperatures from 570 to $690^{\circ}C$. The growth rates were found strongly dependent on the V/III ratio between 5 and 30. The growth rate at low V/III ratio seems to be determined by arsenic produced on the surface, whereas at high V/III ratio it shows dependence on the adsorption of TMG. Hall measurement and photoluminescence (PL) analysis show that the films are all p-type and that carbon impurities are primarily responsible for the background doping. Carbon concentrations have been found to be reduced by two orders of magnitude as compared to those of epilayers grown by CBE which employs TMG and arsenic obtained from precracked $AsH_3$ in a high temperature cell. It was also found that hydrogen atoms dissociated from unprecracked $AsH_3$ play an important role in removing hydrocarbon-containing species resulting in a significant reduction of car-bon impurities.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.416-419
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• 2002

There are being two prominent studying for Digital Radiography. Direct and Indirect method of Digital Radiography are announced for producing high quality digital image. The one is using amorphous selenium as photoconductor and the other is using phosphor layer as a light conversion. But each two systems have strength and weakness such as high voltage and blurring effect. In this study, we investigated the electrical characteristic of $multi-layer\left(CaWO_{4}+a-Se \right)$ as a photoconductor according to the changing arsenic composition ratio. This is a basic research for developing of Hybrid digital radiography which is a new type X-ray detector. The arsenic composition ratio of a-Se compound is classified into 7 different kinds which have 0.1%, 0.3%, 0.5%, 1%, 1.5%, 5%, 10% and were made test sample throught thermo-evaporation. The phosphor layer of $CaWO_4$ was overlapped on a-Se using EFIRON optical adhesives. We measured the dark and photo current about the test sample and compared the electrical characteristic of the net charge and signal-to-noise ratio. Among other things, test sample of compound material of 0.3% arsenic showed good characteristic of $2.45nA/cm^2$ dark current and $357.19pC/cm^2/mR$ net charge at $3V/{\mu}m$.

• Economic and Environmental Geology
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• v.55 no.2
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• pp.209-217
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• 2022

The purpose of this study was to confirm the dissolution of arsenic from the stabilized soil around abandoned coal mines by cultivation activities. Experimental soils were collected from the agricultural field around Okdong and Buguk coal mines, and the concentration of arsenic in the soil and the geochemical mobility were confirmed. The average arsenic concentration was 20 mg/kg. The soil with relatively high geochemical mobility of arsenic in the soil was used in the batch and column experiment. The limestone was mixed with soil for soil stabilization, and the mixing ratio was 3% of limestone, based on the soil weight. The phosphoric acid fertilizer (NH₄H₂PO₄) was added to the soil to simulate a cultivation condition according to the Rural Development Administration's rules. Comparative soil without mixing limestone was prepared and used as a control group. The arsenic extraction from soil was increased following the fertilizer mixing amount and it shows a positive relationship. The concentration of phosphate in the supernatant was relatively low under the condition of mixing limestone, which is determined to be result of binding precipitation of phosphate ions and calcium ions dissolved in limestone. Columns were set to mix phosphoric acid fertilizers and limestone corresponding to cultivation and stabilization conditions, and then the column test was conducted. The variations of arsenic extraction from the soil indicated that the stabilization was effectible until 10 P.V.; however, the stabilization effect of limestone decreased with time. Moreover, the geochemical mobility of arsenic has transformed by increasing the mobile fractions in soil compared to initial soil. Therefore, based on the arsenic extraction results, the cultivation activities using phosphoric fertilizer could induce a decrease in the stabilization effect.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.8
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• pp.619-626
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• 2009

The objective of this study was to evaluate the efficiency of Fe and Mn oxides coated granular activated carbons (FMOCGs) for the removal of arsenite and arsenate by oxidation and adsorption mechanisms using surface characterization and batch adsorption experiments. Within four manufactured adsorbents, Fe and Mn contents of FMOCG-1 was the highest (178.12 mg Fe/g and 11.25 mg Mn/g). In kinetic results, As(III) was removed by oxidation and adsorption with FMOCGs. Removal of arsenic by FMOCGs increased as pH value of the solution decreased. The adsorption isotherm results were well fitted with Langmuir isotherm. Adsorption amount of As(V) onto FMOCGs was higher than that of As(III) and the maximum adsorption capacities of FMOCGs for As(III) and As(V) were 1.38~8.44 mg/g and 2.91~9.63 mg/g, respectively.

• Journal of Environmental Health Sciences
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• v.47 no.6
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• pp.530-539
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• 2021

Background: In South Korea, areas around abandoned metal mines are designated as regions with high arsenic (As) contamination. However, studies assessing urinary As exposure, As metabolism, and relevant genetic polymorphisms in residents of these metal mine areas are lacking. Objectives: To identify factors associated with As exposure and evaluate the effects of MTHFR, As3MT, and GSTO1 genetic polymorphisms on As metabolism in residents of abandoned metal mine areas by measuring urinary As species. Methods: Urinary As species (arsenite [As³⁺], arsenate [As⁵⁺], monomethyl arsonic acid, and dimethylarsinic acid) were isolated using high-performance liquid chromatography in combination with inductively coupled plasma mass spectrometry (HPLC-ICP-MS). Four genetic polymorphisms (MTHFR A222V, MTHFR E429A, GSTO1 A140D, As3MT M287T) were analyzed in 144 residents of four areas around abandoned metal mines. Results: The study sample was comprised of 34.7% men and 65.3% women, with a mean age of 70.7±10.9 years. The urinary inorganic As concentration was higher among those consuming more than half locally produced rice (0.31 ㎍/L) than those consuming less than half such rice (0.18 ㎍/L). The urinary dimethylarsinic acid concentration was higher in the group that had consumed seafood in the past day (31.68 ㎍/L) than in those who had not (22.37 ㎍/L). Furthermore, individuals heterozygous in the MTHFR A222V and GSTO1 A140D polymorphism had higher urinary arsenic species concentrations than did individuals with a wild type or homozygous for the variant allele. Conclusions: Consumption of locally produced rice was associated with inorganic As exposure, whereas seafood consumption was associated with organic As exposure among residents of abandoned metal mine areas. There was no clear association between MTHFR A222V and GSTO1 A140D polymorphisms and As metabolism.

• Journal of Korean Society of Water and Wastewater
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• v.26 no.1
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• pp.149-157
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• 2012

Experiments for As(V) removal using synthesized $Ca{\cdot}Al$-monosulfate was performed from the water contaminated with arsenate. Monosulfate is known as LDHs (Layered Double Hydroxides) which is one of the anionic clay minerals. Monosulfate was synthesized mixing $C_3A$ (tricalcium aluminate), gypsum (calcium sulfate), and water with an intercalation method. The product form the synthesis was characterized by FE-SEM, WDXRF, PXRD, and FT-IR. Experiments with different doses of monosulfate were carried out for kinetic. As a result of experiment, the concentration of As(V) was reduced from 0.67 mM to 0.19 mM (0.67mM of monosulfate) and 0.178 mM (1.34 mM of monosulfate). The concentration of sulfate was increased with As(V) decrease. The result of PXRD showed that the d-spacing of inter layer ($d_{003}$ peak) was shifted from 8.927 ${\AA}$ to 8.095 ${\AA}$ because the sulfate in the inter layer of monosulfate was exchanged arsenate with water molecules bonded. From the FT-IR results, a new single band (800 cm-1) was observed after the reaction of monosulfate and As(V). The arsenic removal can be regarded as anion exchange mechanism that is one of the characteristics of LDHs from the results of PXRD and FT-IR analysis.