• Resources Recycling
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• v.10 no.5
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• pp.29-35
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• 2001

This study was carried out to recover gold, silver and valuable metals from the printed circuit boards (PCBs) of waste computers. PCBs samples were crushed under 1 mm by a shredder and separated into 30% conducting and loft nonconducting materials by an electrostatic separator. The conducting materials contained valuable metals which were then used as feed materials for magnetic separation. 42% of magnetic materials from the conducting materials was removed by magnetic separation as nonvaluable materials and the others, 58% of non magnetic materials, was used as leaching samples containing 0.227 mg/g Au and 0.697 mg/g Ag. Using the materials of leaching from magnetic separation, more than 95% of copper, iron, zinc, nickel and aluminium was dissolved in 2.0M sulfuric acid solution, added with 0.2M hydrogen peroxide at $85^{\circ}C$. Au and Ag were not extracted in this solution. On the other hand, more than 95% of gold and 100% of silver were leached by the selective leaching with a mixed solvent (0.2M($NH_4$)$_2$$S_2$$O_3$,0.02M $CuSO_4$,0.4M $NH_4$OH). Finally, the residues were reacted with a NaCl solution to leach Pb whereas sulfuric acid was used to leach Sn. Recoveries reached 95% and 98% in solution, respectively.

• Korean Journal of Medicinal Crop Science
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• v.2 no.2
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• pp.162-167
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• 1994

This study was carried out to investigate the compositions of fatty acids, inorganic components and volatile organic acids from Korean valerian roots, Valeriana fauriei var. dasycarpa Hara and Valeriana officinalis var. latifolia Miq. The contents of total lipids ranged from 3.7 % to 4.5% and the major fatty acids were linoleic, linolenic and palmitic acid. Ash contents ranged from 4.3% to 6.3%. and the contents of Na, Fe, Zn and Cu showed some quantitative differences depending upon grown region or species. Fourty components were identified from acidic fraction of dichloromethane extract of V. fauriei var. dasycarpa Hara, of which the major components were 3-methyl butanoic, dimethoxy-2-propenoic. 3, 4-dimethoxy benzoic and 3-methyl pentanoic acid.

• Environmental Engineering Research
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• v.19 no.1
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• pp.15-22
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• 2014

In this study, the performances of various adsorbents-red mud, zeolite, limestone, and oyster shell-were investigated for the adsorption of multi-metal ions ($Cr^{3+}$, $Ni^{2+}$, $Cu^{2+}$, $Zn^{2+}$, $As^{3+}$, $Cd^{2+}$, and $Pb^{2+}$) from aqueous solutions. The result of scanning electron microscopy analyses indicated that the some metal ions were adsorbed onto the surface of the media. Moreover, Fourier transform infrared spectroscopy analysis showed that the Si(Al)-O bond (red mud and zeolite) and C-O bond (limestone and oyster shell) might be involved in heavy metal adsorption. The changes in the pH of the aqueous solutions upon applying adsorbents were investigated and the adsorption kinetics of the metal ions on different adsorbents were simulated by pseudo-first-order and pseudo-second-order models. The sorption process was relatively fast and equilibrium was reached after about 60 min of contact (except for $As^{3+}$). From the maximum capacity of the adsorption kinetic model, the removal of $Pb^{2+}$ and $Cu^{2+}$ were higher than for the other metal ions. Meanwhile, the reaction rate constants ($k_{1,2}$) indicated the slowest sorption in $As^{3+}$. The adsorption mechanisms of heavy metal ions were not only surface adsorption and ion exchange, but also surface precipitation. Based on the metal ions' adsorption efficiencies, red mud was found to be the most efficient of all the tested adsorbents. In addition, impurities in seawater did not lead to a significant decrease in the adsorption performance. It is concluded that red mud is a more economic high-performance alternative than the other tested adsorption materials for applying a removal of multi-metal in seawater.

• Economic and Environmental Geology
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• v.30 no.4
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• pp.279-289
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• 1997

Dark to pale green-colored, Cr-bearing sericites from hydrothermal alteration zone of the Narim gold deposit were investigated mineralogically and geochemically. The alteration zone is composed mineralogically of quartz, carbonate minerals and green sericite with minor amounts of chlorite, barite and sulfide minerals (pyrite, sphalerite, galena). The zone is enriched in As (967 to 1520 ppm), Cu (31 to 289 ppm), Ni (1027 to 1205 ppm), Pb (0.20 to 1.24 wt.%) and Zn (1.03 to 1.07 wt. %) compared with fresh rocks such as granitic gneiss, porphyritic biotite granite and basic dyke. The Cr, probably the chromophore element, is highly enriched in the alteration zone (1140 to 1500 ppm), host granitic gneiss (1200 ppm) and porphyritic biotite granite (1200 ppm). Occurrence and grain size of sericite are diverse, but most of the Cr-bearing sericites (150 to $200{\mu}m$ long and 20 to $30{\mu}m$ wide) occur along the boundaries between ore veins and host rocks (especially basic dyke and granitic gneiss). X-ray diffraction data of the sericite show its monoclinic form with unit-cell parameters of $a=5.202{\AA}$, $b=8.994{\AA}$, $c=20.103{\AA}$, ${\beta}=95.746^{\circ}$ and $V=935.83{\AA}^3$, which are similar with the normal 2M1-type muscovite. Representative chemical formula of the sericite is ($K_{1.54}Ca_{0.03}Na_{0.01}$)($Al_{3.42}Mg_{0.38}Cr_{0.14}Fe_{0.06}V_{0.02}$)($Si_{6.69}Al_{1.31}$)$O_{20}(OH)_4$. The Cr content increases with decrease of the octahedral Al content, and ranges from 0.36 to 2.58 wt.%. DTA and TG curves of the sericite show endothermic peaks at $342^{\circ}$ to $510^{\circ}$, $716^{\circ}$ to $853^{\circ}$ and $1021^{\circ}C$, which are due to the expulsion of hydroxyl group. The total weight loss by heating is measured to be about 8.8 wt. %, especially at $730^{\circ}C$. Infrared absorption experiments of the sericite show broad absorption band due to the O-H bond stretching vibration near the $3625cm^{-1}$, coupled with the 825 and $750cm^{-1}$ doublet. The vibration bands related with the H-O-Al and Si-O-Al bonds occur at $1030cm^{-1}$ and 500 to $700cm^{-1}$, respectively. Based on paragonite content of the sericite, the formation temperature of the Narim gold deposit is calculated to be $220{\pm}10^{\circ}C$.

• Corrosion Science and Technology
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• v.17 no.3
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• pp.101-108
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• 2018

AA7010 is an Al-Zn-Mg-Cu alloy containing Zr, developed as an alternate to traditional AA7075 alloy owing to their high strength combined with better fracture toughness. It is necessary to improve the corrosion resistance and surface properties of the alloy by incorporating plasma electrolytic oxidation (PEO) method. AA7010-T7452 aluminum alloy has been processed through the forging route with multi-stage working operations, and was coated with $10{\mu}m$ thick $Al_2O_3$ ceramic aluminina coating using the plasma electrolytic oxidation (PEO) method. The corrosion, stress corrosion cracking (SCC) and nano-mechanical behaviours were examined by means of potentiodynamic polarization, slow strain rate test (SSRT) and nano-indentation tests. The results indicated that the additional thermomechanical treatment during the forging process caused a fully recrystallized microstructure, which lead to the poor environmental cracking resistance of the alloy in 3.5% NaCl solution, despite the overaging treatment. Although the fabricated PEO coating improved general corrosion resistance, the brittle nature of the coating did not provide any improvement in SCC resistance of the alloy. However, the hardness and elastic modulus of the coating were significantly higher than the base alloy.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.179-180
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• 2012

Aluminum alloys are widely known as non-ferrous metal with light weight and high strength. Consequently, these materials take center stage in the aircraft and automobile industry. The Al7075 aluminum alloy is based on the Al-Zn-Mg-Cu and one of the strongest wrought aluminum alloys. Aluminum nitride has ten times higher thermal conductivity($319W/m{\cdot}K$) than Al2O3 and also has outstanding electric insulation($1{\times}1014{\Omega}{\cdot}cm$). Furthermore, it has high mechanical property (430 MPa) even though its co-efficient of thermal expansion is less than alumina For these reasons, it has great possibilities to be used for not only the field which needs high strength lightweight but also electronic material field because of its suitability to be applied to the insulator film of PCB or wafer of ceramic with high heat conduction. This paper investigates the mechanical properties and corrosion behavior of aluminum alloy Al7075 deposited with aluminum nitride thin films To improve the surface properties of Al7075 with respect to hardness, and resistance to corrosion, aluminum nitride thin films have been deposited by pulsed DC reactive magnetron sputtering. The pulsed DC power provides arc-free deposition of insulating films.

• Journal of the Mineralogical Society of Korea
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• v.13 no.3
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• pp.147-163
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• 2000

The mineralogy and chemical composition of reddish to brownish yellow residual soils, so called "Hwangto" have been examined according to representative host rocks. The result of the study indicates that Hwangto consists of 40-80% clay minerals and various minerals such as quartz, feldspar, hornblende, goethite, and gibbsite. Clay minerals include kaolinite, halloysite, illite, hydroxy interlayered vermiculite (HIV), mica/vermiculite interstratifield mineral and chlorite. The mineralogical constituents and contents of Hwangto were different depending on the types of host rocks. Moreover, the Jurassic granitic rocks contain relatively more kaolin minerals, whereas the Cretaceous granitic rocks contain more HIV and illite. In addition, reddish Hwangto contains relatively more kaolinite and HIV, and yellowish Hwangto contains more illite and halloysite. It is suggested that feldspars and micas of host rocks were chemically weathered into illite, halloysite, illite/vermiculite interstratified minerals, and HIV, and finally into kaolinite. Compared with their host rocks, the major chemical compositions of Hwangto tend to contain more $Al_2O_3,\;Fe_2O_3,\;H_2O$ in amount and less Ca, Mg, and Na. Hwangto contains relatively high amount of trace elements, P, S, Zr, Sr, Ba, Rb, and Ce including considerable amount of Li, V, Cr, Zn, Co, Ni, Cu, Y, Nb, La, Nd, Pb, Th in excess of 10 ppm. Relatively high amount of most trace elements were detected in the Hwangto. The major and minor chemical compositions of the Hwangto were different depending on the types of host rocks. However, their difference was in the similar range compared with the compositions of host rocks.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.956-959
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• 2001

In die and mould industry, major material such as cemented carbide is broadly used for increasing the life time and decreasing the cost. It is also required the development for the skills of wire-cut electrical discharge machining(WEDM), but the WEDMed surface was found to be worst due to the attached components of wire. Precision machining method like lapping is necessary for obtaining high quality surface. The lapping compound such as Al2O3 and SiC and cast iron lap can be used for lapping process. The components of Cu and Zn were found WEDMed surface of the specimen. As the result, the low quality of precision was obtained and the heat damage layer of the specimen was occurred. The value of surface hardness was deteriorated, and therefore finish process was required.

• Journal of Korean Society for Atmospheric Environment
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• v.2 no.2
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• pp.9-18
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• 1986

For identification and apportionment of sources emitting particulate matters in environment, the multi-elemental characterization of size-density fractionated particulate matters was carried out. Eight types of samples were tested; soil, flyash released from burning of bunker-Coil, diesel oil, coal, and soft coal, urban road-way dust, urban dust fall, and airborne particulate matter. The fractions of particulate matters obtained by heavy liquid separation methos with a series of dichloromethane-bromoform were then analyzed using atomic absorption spectrophotometry for Ni, Cr, Cu, An, Fe, Al, and Mg. Each sample showed a different concentration profile as a function of density, and a number of useful conclusions concerning characterization of elemental distribution were obtained. From the density distributions of elements in soil, the maximum value was found for all elements in the density range of 2.2 $\sim 2.9g.cm^{-3}$, including the density of $SiO_2$. However, the distribution of metallic compounds with the density lower than $2.2g.cm^{-3}$ was prevalent in urban roadway dust, urban dust fall, and airborne particulate matter. And the density distribution curves of these urban dusts also have the higher distribution at the density of 2.2 - 2.9g.cm^{-3}$, including the density of wind-blown silica. This tendency generally was prevalent in the natural source elements, such as Al, Fe, Mn, and Mg. The maximum values were found in the density ranges of 1.3 $\sim 2.2g.cm^{-3}$ from the density distribution of elements in oil fired flyash. These distributions of anthropogenic source elements, such as Zn, Ni, Cu, and Cr were higher predominately than those of natural source elements. And the higher distribution was found in the density range of $2.2 \sim 2.9g.cm^{-3}$ from the density distribution of elements in coal and soft-coal fired flyash. These distributions showed similar patterns to soil. But anthropogenic source elements somewhat predominated at the density ranges of $1.3 \sim 2.2g.cm{-3} and 2.9g.cm^{-3}$ to soil. Therefore the higher distribution of anthropogenic source elements in the density ranges of $1.3 \sim 2.2g.cm^{-3} and 2.9g.cm^{-3}$ was considered as anthropogenic origin.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.222-224
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• 2006

A non-vacuum process for $Cu(In,Ga)Se_2$ (CIGS) thin film solar cells from nanoparticle precursors was described in this work CIGS nanoparticle precursors was prepared by a low temperature colloidal route by reacting the starting materials $(CuI,\;InI_3,\;GaI_3\;and\;Na_2Se)$ in organic solvents, by which fine CIGS nanoparticles of about 20nm in diameter were obtained. The nanoparticle precursors were mixed with organic binder material for the rheology of the mixture to be adjusted for the doctor blade method. After depositing the mixture of CIGS with binder on Mo/glass substrate, the samples were preheated on the hot plate in air to evaporate remaining solvents ud to burn the organic binder material. Subsequently, the resultant (porous) CIGS/Mo/glass simple was selenized in a two-zone Rapid Thermal Process (RTP) furnace in order to get a solar ceil applicable dense CIGS absorber layer. Complete solar cell structure was obtained by depositing. The other layers including CdS buffer layer, ZnO window layer and Al electrodes by conventional methods. The resultant solar cell showed a conversion efficiency of 0.5%.