• Korean Chemical Engineering Research
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• v.49 no.1
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• pp.1-9
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• 2011

Platinum catalysts were prepared by impregnating platinum precursor on titania-, vanadia-, zirconia- and ceria-incorporated silicas followed by hydrogen peroxide treatment. The effects of the oxide incorporation and the hydrogen peroxide treatment in the preparation of the platinum catalysts on their platinum dispersion and catalytic activity in carbon monoxide oxidation were investigated. XRD, TEM, EXAFS, XPS and carbon monoxide chemisorption studies confirmed the high dispersion of platinum even on silica by the oxide incorporation and hydrogen peroxide treatment. However, the type of oxides incorporated on silica caused considerable variances in the adsorption and the catalytic activity in the oxidation of carbon monoxide on them. The incorporation of titania, zirconia and ceria on silica and further hydrogen peroxide treatment enhanced the platinum dispersion, resulting in the improved catalytic activities. Among the catalysts supported on the oxide-incorporated silicas, the platinum catalyst supported on zirconia-incorporated silica exhibited the highest activity because of the highest platinum dispersion due to the formation of Pt-O-Zr bonds.

• Resources Recycling
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• v.18 no.4
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• pp.14-23
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• 2009

In terms of resources recycling and resolving waste disposal problems, it is very important to recover precious metals like Au, Ag and Pd and valuable metals like Cu, Sn and Ni from the scraps of waste electrical and electronic equipment(WEEE) that consists of detective electrical and electronic parts discarded during manufacturing electrical and electronic equipments and waste electrical and electronic parts generated during disassembling them. In general, the scraps of WEEE are composed of various metals and alloys as well as refractory oxides and plastic components. Precious and valuable metals from the scraps of WEEE can be recovered by gas-phase-volatilization, hydrometallurgical, or pyrometallurgical processes. However, the gas-phase-volatilization and hydrometallurgical processes have been suggested but not yet commercialized. At the present time, most of the commercial plants for recovering precious and valuable metals from the scraps of WEEE adopt pyrometallurgical processes. Therefore, in this paper, the technical and environmental aspects on the important pyrometallurgical processes through literature survey are reviewed, and the scale-up result of a new pyrometallurgical process for recovering the precious and valuable metals contained in the scraps of WEEE using waste copper slag is presented.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.11
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• pp.1054-1062
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• 2010

Oxidative coupling reactions of humic substances (HS) can be catalyzed by a variety of natural extracellular enzymes and metal oxides. In this study, property changes of HS induced by a natural enzyme, horseradish peroxidase (HRP), and the effect of it to microfiltration (MF) were investigated. PAHA was transformed by oxidative coupling reaction with HRP and hydrogen peroxide ($H_2O_2$), verifying the catalytic effects of the HRP. Size exclusion chromatography (SEC) revealed that weight-average molecular weight (MWw) of PAHA was proportionally increased with the dosages of HRP and $H_2O_2$, indicating the transform action of HS into larger and complex molecules. An increase in the conformational stability of HS was achieved through the promotion of intermolecular covalent bondings between heterogeneous humic molecules. Spectroscopic analysis (fluorescence and infrared spectroscopy) proved that functional groups were transformed by the reaction. Additionally, HS and transformed products were undergone microfiltration (MF) to examine the treatment potential of them in a water treatment facility. Original HS could not be removed by MF but larger molecules of transformed products could be removed. Meanwhile, transformed products caused more fouling on the filtration than original HS. This results proved that natural organic matter (NOM) can be removed by MF after its increase in molecular size by oxidative coupling reaction.

• Journal of Korean Society of Environmental Engineers
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• v.37 no.4
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• pp.246-252
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• 2015

In steel factory, hot roller cleaning process produces a lot of iron oxide particles called as mill scale. Major components of these particles are wustite (FeO), magnetite ($Fe_3O_4$), and hematite ($Fe_2O_3$). In this study, we tried to produce pure magnetite from the mill scale because of the largest phosphate adsorption capacity of the magnetite. The mill scale was treated with acid (HCl+$H_2O_2$), base (NaOH), and acid-base ($H_2SO_4$+NaOH). Batch adsorption tests showed the acid and/or base treatment could increase the phosphate adsorption capacity of the iron oxides from 0.28 to over 3.11 mgP/g. Magnetite, which could be obtained by acid and base treatment of the mill scale, showed the best adsorption capacity. From the kinetic analysis, both Freundlich and Langmuir isotherm well described the phosphate adsorption behavior of the magnetite. In Langmuir model, maximum phosphate adsorption capacity was found to be 5.1 mgP/g at $20^{\circ}C$.

• Economic and Environmental Geology
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• v.29 no.1
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• pp.45-55
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• 1996

Although the Dongjin Au-Ag-Cu mine had been abandoned since about forty years ago, the results of this study on the dispersion patterns and contamination level of heavy metals in the hydrologic system flowing via the waste rump show that the environmental impacts from the mine wastes are still significant. The stream water in the vicinity of the waste rump is severely acidified (pH 3.8 to 4.4) and highly enriched in various dissolved heavy metals. The heavy metal contents of the stream water and stream sediments are systematically attenuated with increasing distance from the mine area. However, it is worth to note that continuous attenuation of heavy metal contents in both media were reenriched in downstream area more than 800 m apart from the mine because it can be acted as a secondary source of heavy metal pollution. The heavy metals, especially Cd, Cu and Zn of polluted downstream sediments mainly occur in Fe-Mn oxides and organic materials, which indicates that these elements are the main pollutants from the waste rump of the Dongjin mine. The heavy metal contents of crops, such as sesame, perilla, red Pepper and brown rice, collected from the polluted farm land in the downstream area are lower than those of land plants from stream sides, but significantly higher in Cd, Cr, Cu and Zn than those from the unpolluted farm land. Especially, almost all of the crops in polluted farm land have been severly contaminated by Cd (>0.4 ppm). On the other hand, the heavy metal contents of the crops collected from refreshed farm land by means of a soil addition method shows significantly lowered level comparing with those of polluted area, which indicates that a soil addition method was effective for the refreshment of polluted farm land by toxic metallic pollutants. Wormwoods from this area showed very high contents in a11 the heavy metals even in unpolluted area (Cd > 1 ppm, Cr > 1 ppm, Cu > 11 ppm, Pb> 4 ppm, Zn > 55 ppm), indicating that a special caution must be payed when one takes ingest them.

• Economic and Environmental Geology
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• v.41 no.6
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• pp.673-683
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• 2008

As-rich alluvial groundwaters occurring in the agricultural area of Mankyeong River watershed were geochemically studied. 15 out of 29 investigated wells (52%) showed As levels exceeding the WHO drinking water standard ($10{\mu}g/L$). Their chemistry is characterized by low Eh levels, low $NO_3$ and $SO_4$ concentrations, and high pH, alkalinity, Fe, $NH_4$, and $PO_4$ levels. This suggests that arsenic is enriched by the reductive dissolution of As-bearing Fe-/Mn-(hydro)oxides, the commonest process in Bangladesh and West Bengal of India, of which groundwaters are severely contaminated by As. It was also revealed that As concentrations in the area are strongly regulated by the presence of agrochemicals such as $NO_3$ and $SO_4$.

• Analytical Science and Technology
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• v.23 no.5
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• pp.498-504
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• 2010

It is very difficult to get stable ion peak intensity of ruthenium by thermal ionization mass spectrometry because of its high ionization potential and high volatility of its oxides which causes to lose much of ruthenium ions, so the intensity of the signal decrease quickly. Accordingly, a study was performed in oder to increase the ionization efficiency and to prevent sample losses due to volatilization and to check with isobaric effect by impurities in filament for the measurement of ruthenium isotopes. Both single filament and double filament were tested. The former was proved to be more efficient for the stable and strong intensity of signal and revealed less isobaric effect from the molybdenum (Mo) as a filament impurity. Also, when the temperature of filament increased too high, the isobaric effect from Mo greatly appeared. That is, Mo impurity from filament gave a serious effect for measuring the ruthenium isotopes. It was proved to be of importance that filament current should be slowly increased with time interval. Finally, ruthenium isotopes were accurately measured by correction with measuring $^{94}Mo/^{99}Ru$.

• Journal of Conservation Science
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• v.33 no.4
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• pp.297-312
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• 2017

In the ancient iron-making process, a slag former was often added so that iron and other minerals in the ore could be smoothly separated. However, there are insufficient data for judging whether a slag former was added. Thus, in this study, we conducted a smelting experiment to understand the material characteristics of a steel structure that differed depending on the addition of a slag former. It was found that the steel structure produced in the first experiment had a total Fe content of 39.45-52.94 wt%, which decreased to 34.89-38.92 wt% in the second and third experiments. CaO compounds such as calcite, gehlenite, and hercynite appeared, in addition to iron oxides, after the addition of a slag former. As a result of an assessment of whether a slag former was added by comparing the ratio between the components, it was found that the ratio of $CaO/SiO_2$ was 0.42. From a comparative analysis of $Al_2O_3/SiO_2$ and $CaO/SiO_2$, it was judged that the ratio of $Al_2O_3$ and $SiO_2$ can be utilized as an index to judge similar systems of smelting process (ore, furnace wall, and fuel).

• Journal of Sensor Science and Technology
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• v.1 no.2
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• pp.107-116
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• 1992

The optimum base material was selected by the thermal decomposition temperature of $CH_{3}CN$ on the surface of various metal oxides, and the FT-IR analyses of its products. On the surface of $SnO_{2}$, $CH_{3}CN$ was initiated to decompose at $130^{\circ}C$ and produced a lot of products at $200^{\circ}C$. The products from the reaction were found to be $H_{2}O$, $NH_{3}$ and CO, but $N_{2}O$ has started to produce at $320^{\circ}C$. The sensing characteristics of $SnO_{2}$ sensor to $CH_{3}CN$ are influenced by the absorbed species which are produced by the oxidation reaction of $CH_{3}CN$ on the surface of metal oxide. The gaseous species produced from the surface of sensing material in the oxidation reaction were found to be CO, $NH_{3}$, $H_{2}O$ and $NO_{x}$ etc.. It was assumed that the amount of $NO_{x}$ play a great role to the determining sensing properties. In the condition of 170 ppm $CH_{3}CN$, the sensitivity and optimum operating temperature of $SnO_{2}$ were 70% and $300^{\circ}C$, respectively. In this research, the response time of $CH_{3}CN$ to $SnO_{2}/Al_{2}O_{3}/Pd$ sensor added with 0.2 wt % Pd was found about 10 sec and sensitivity was also found relatively high.

• Journal of the Korean Vacuum Society
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• v.6 no.1
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• pp.9-19
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• 1997

The reaction mechanisms of dry cleaning with UV-excited chlorine radical for Zn, Fe and Ti trace contaminants on the Si wafer have been studied by SEM, AFM and XPS analyses in this work. The patterned Zn, Fe and Ti films were deposited on the Si wafer surface by thermal evaporation and changes in the surface morphology after dry cleaning with $Cl_2$and UV/$Cl_2$at $200^{\circ}C$ were studied by optical microscopy and SEM. In addition, changes in the surface roughness of Si wafer with the cleaning was observed by AFM. The chemical bonding states of the Zn, Fe and Ti deposited silicon surface were observed with in-line XPS analysis. Zn and Fe were easily cleaned in the form of volatile zinc-chloride and iron-chloride as verified by the surface morphology changes. Ti which forms involatile oxides was not easily removed at room temperature but was slightly removed by UV/$Cl_2$at elevated temperature of $200^{\circ}C$. It was also found that the surface roughness of the Si wafer increased after $Cl_2$and UV/$Cl_2$cleaning. Therefore, the metallic contaminants on the Si wafer can be easily removed at lower temperature without surface damage by a continuous process using wet cleaning followed by UV/$Cl_2$dry cleaning.