• 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.

• 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.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.7 no.4
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• pp.226-234
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• 2002

A sediment exposure experiment was conducted to investigate the influence of acid volatile sulfides (AVS) and simultaneously extracted metals (SEM) in sediments on the bioavailability and toxicity of Cd, Ni and Zn to a marine polychaetes Neanthes arenaceodentata. The test animals were exposed to contaminated sediments spiked by metal mixtures of Cd, Ni, Zn (0.5～15 $\mu$mol/g of total SEM) in low (～1 $\mu$mol/g), medium (～5 $\mu$mol/g) and high AVS series (～10 $\mu$mol/g) to determine bioaccumulation, mortality and individual growth rate in each treatment after 20 days. Cd and Zn bioaccumulation in test animals increased with increasing of overlying water (OW) concentration controlled by AVS. In contrast, Ni bioaccumulation increased with increase of SEM concentration. Mortalities and growth inhibitions of N. arenaceodentata observed in only treatments with ［SEM-AVS］>0, due to a high level of OW-Zn. With regard to the mortality, the 20-d LC5O value fur OW-Zn was 9.3(8.0$\pm$11.0) $\mu$M. The LOEC (Lowest Observed Effect Concentration) for Tissue-Zn was 7.8 $\mu$mol/g and the NOEC (No Observed Effect Concentration) was 6.2 $\mu$mol/g. Regarding the inhibition of individual growth rate, the LOEC fer Tissue-Zn was 5.9 $\mu$mol/g, and NOEC was 5.1 $\mu$mol/g. In this study, the toxicity of dissolved metals, especially for Zn, was overemphasized due to the reduced distribution coefficients (K$\_$d/s) of metals in the experimental sediments.

• Journal of Wetlands Research
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• v.11 no.3
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• pp.89-103
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• 2009

The Philippines is abundant with rich natural resources such as water. Because of rapid urbanization in the country, most of the water bodies are polluted as a result of domestic, agricultural and industrial activities. The Environmental Management Bureau (EMB) is the main government arm responsible for monitoring and inspection of affected water bodies. Only water bodies with at least four sampling events during dry and wet seasons were included in the assessment of water bodies that passed the DAO 90-34 water quality criteria. Water bodies were monitored for dissolved oxygen (DO), biochemical oxygen demand (BOD), total suspended solids (TSS), and total dissolved solids (TDS), heavy metals, fecal coliform contamination and nitrates. High pollutant concentrations from domestic, agricultural, industrial and nonpoint sources were observed from monitoring events due to inadequate sewage services and treatment facilities in the country. The objective of this paper was to present and evaluate the quality of the water bodies in the Philippines.

• Journal of Korea Foundry Society
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• v.17 no.6
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• pp.560-568
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• 1997

The dissolution behavior of secondary solidification phases in squeeze cast Al-3.9wt%Cu-1.5wt%Si-1.0wt%Mg has been studied using a combination of optical microscope, image analyzer, scanning electron microscope(SEM), energy dispersive spectrometer(EDS), X-ray diffractometer(XRD) and differential thermal analyzer (DTA). Special emphasis was placed on the investigation of the effects of the nonequilibrium heat treatment on the dissolution of the second solidification phases. Ascast microstructure consisted of primary solidification product of ${\alpha}-Al$ and secondary solidification products of $Al_2Cu$, $Mg_2Si$ and $Al_2CuMg$. Equilibrium and non-equilibrium solution treatments were carried out at the temperatures of $495^{\circ}C$, $502^{\circ}C$ and $515^{\circ}C$ for 3 to 5 hours. The amount of the dissolved secondary phases increased with increasing solution treatment temperature, for example, area fractions of $Al_2Cu$, $Mg_2Si$ and $Al_2CuMg$ were approximately 0%, 1.6% and 4.2% after solution treatment at $495^{\circ}C$ for 5hours, and were approximately 0%, 0.36% and 2% after solution treatment at $515^{\circ}C$ for 5hours. The best combination of tensile properties was obtained when the as-cast alloy was solution treated at $515^{\circ}C$ for 3hours followed by aging at $180^{\circ}C$ for 10 hours. Detailed DTA and TEM study showed that the strengthening behavior during aging was due to enhanced precipitation of the platelet type fine ${\theta}'$ phase.

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.1
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• pp.1-7
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• 2013

This study was on leaching test(KSLT, TCLP) of the aggregate for the products(RA-1) and for the site(RA-2) to evaluate the characteristics of contaminants and the possibility of contamination arising from the aggregate. On the basis pH, conductivity and heavy metal contents in the aggregate, RA-1 indicated higher than RA-2. As a result of the leaching test, the pollutants were eluted from the aggregate increased as the particle size of the aggregate was smaller. The pH in the aggregate had a strong alkali by a pH value of 9.0~12.3, the conductivity was higher in less than 10mm RA-1 due to the leaching of dissolved inorganic ions. The heavy metals satisfied the leaching standards of KSLT and less 10% was eluted from the aggregate. As a result of evaluating water pollution possibility of the aggregate, the pH displayed in items with a very high possibility of contamination, conductivity and turbidity did in item with a low possibility of contamination and on the other hand the heavy metals did in item with a very low possibility of contamination.

• Analytical Science and Technology
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• v.16 no.6
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• pp.466-474
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• 2003

This paper describes the concentrations of total dissolved iron (tFe) and $Fe^{2+}$ in rainwater and snow, the relationship of Fe species with other metals and ions in bulk rainwater, and the $Fe^{2+}$ generation mechanism in aqueous samples in rainwater of time series collection. Volume weight mean concentrations of tFe and $Fe^{2+}$ were 3.22 and $1.25{\mu}gL^{-1}$ in bulk rainwater, and 50.1 and $43.5{\mu}gL^{-1}$ in snow, respectively. $Fe^{2+}$ was significant fraction to the tFe, accounted for 3.25-93.4% of the tFe in rainwater and 87% in snow. We also investigated temporal variations of tFe, $Fe^{2+}$, other metals and ions in rainwater of time series collection during rain event. Although the concentration range of tFe was different from those of other species, a decreasing trend of tFe from the beginning of the rain event was similar with other species. However, though $Fe^{2+}$ did not show such a decreasing trend, $Fe^{2+}$/tFe was in good correlation with solar radiation. From the results of multiple linear regression analysis and thermodynamic calculations (Mineql+), $Fe^{2+}$ in our samples may be generated from photochemical reduction of $Fe^{3+}$ species (such as $Fe(OH)^{2+}$,$Fe(OH)^{2+}$ and Fe-oxalate) at daytime.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.1
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• pp.1-11
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• 1996

Mechanical alloying is an effective process to finely distribute inert dispersoids in an Al-TM(TM is a transition metal) system. It has been considered that high melting point aluminides are formed by precipitation from supersaturated Al(Ti) powder. This analysis is based on the fact that much higher content of TM than the solubioity can be dissolved in alpha aluminum during the high energy ball milling. Thus, decomposition behavior of Ti in the Al(Ti) was considered very important. But it is confirmed that the higher portion of Ti than Al(Ti) solid solution is existed as nano-sized Ti particles in the MA powders by high energy ball nilling from the XRD spectrum and TEM analysis in this study. Therefore, the role of undissolved TM particles affect the formation of aluminides should be suitably considered. In this study, we present experimental observation on the formation of $Al_3Ti$ fron mechanical alloyed Al-Ti alloys in the hyperperitectic region. This study showed that, in the mechanically alloyed Al-20wt%Ti specimen, intermediate phase of cubic $Al_3Ti$ and tetragonal $Al_{24}Ti_8$ formed at $300{\sim}400^{\circ}C$ and $400{\sim}500^{\circ}C$, respectively, before the MA state reaches to equilibrium at higher temperatures. The formation behavior of $Ll_2-Al_3Ti$ is interpreted by interdiffusion of Al and Ti in solid state based on the fact that large amount of nano-sized Ti particles exist in the milled powder. Present analysis indicated undissolved Ti particles of nanosize should have played an important role initiation the formation of $Al_3Ti$ phase during annealing.

• Korean Journal of Materials Research
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• v.20 no.8
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• pp.401-407
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• 2010

We studied the influence of different types of metal electrodes on the performance of solution-processed zinc tin oxide (ZTO) thin-film transistors. The ZTO thin-film was obtained by spin-coating the sol-gel solution made from zinc acetate and tin acetate dissolved in 2-methoxyethanol. Various metals, Al, Au, Ag and Cu, were used to make contacts with the solution-deposited ZTO layers by selective deposition through a metal shadow mask. Contact resistance between the metal electrode and the semiconductor was obtained by a transmission line method (TLM). The device based on an Al electrode exhibited superior performance as compared to those based on other metals. Kelvin probe force microscopy (KPFM) allowed us to measure the work function of the oxide semiconductor to understand the variation of the device performance as a function of the types metal electrode. The solution-processed ZTO contained nanopores that resulted from the burnout of the organic species during the annealing. This different surface structure associated with the solution-processed ZTO gave a rise to a different work function value as compared to the vacuum-deposited counterpart. More oxygen could be adsorbed on the nanoporous solution-processed ZTO with large accessible surface areas, which increased its work function. This observation explained why the solution-processed ZTO makes an ohmic contact with the Al electrode.

• Korean Journal of Metals and Materials
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• v.48 no.6
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• pp.506-513
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• 2010

The composite coatings of $(ZrO_2-8Y_2O_3)$/(Ni-22Cr-10Al-1Y) were prepared by the air plasma spraying method. They consisted of (Ni,Cr)-rich regions,$(ZrO_2-Y_2O_3)$-rich regions, and $Al_2O_3$-rich regions that were formed by oxidation of Al from (Ni-22Cr-10Al-1Y) during spraying. The coatings corroded at 800 and $900^{\circ}C$ in NaCl-$Na_2SO_4$ molten salts up to 50 hr. Ni, Cr and Al oxidized to NiO, $Cr_2O_3$ and ${\alpha}-Al_2O_3$, respectively. These oxides and $(ZrO_2-Y_2O_3)$ were dissolved off into the molten salts during hot corrosion, which resulted in the ever-lasting corrosion of the composite coatings. Chromium diffused out from the (Ni,Cr)-rich regions and oxidized to $Cr_2O_3$, which was most frequently found as surface scales. Aluminum retained in the (Ni,Cr)-rich regions were similarly diffused out.