• Resources Recycling
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• v.18 no.5
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• pp.19-25
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• 2009

Molybdenite concentrate ($MoS_2$) is the major mineral for the molybdenum industry, of which the industrial processing is first converted to technical grade molybdenum trioxide ($MoO_3$) by its oxidative roasting and purification, used as a raw material for manufacturing several molybdenum compounds. In the present work, detailed experimental results for the oxidative roasting of low grade Mongolian molybdenite concentrate are presented. The experiments were carried out in the temperature range of 793 to 823 K under an oxygen partial pressure range of 0.08 atm to 0.21 atm by using a thermogravimetric analysis technique. The molybdenite concentrate was an average particle size of $67\;{\mu}m$. In the oxidative roasting of low grade Mongolian molybdenite concentrate, more than 95% of molybdenite was converted to molybdenum trioxide in 60 min. at 828 K. The lander equation was found to be useful in describing the rates of the oxidative roasting and the reaction order with respect to oxygen concentration in a gaseous mixture with nitrogen was 0.11 order.

• Journal of the Korea Organic Resources Recycling Association
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• v.10 no.2
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• pp.117-124
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• 2002

This study was carried out to investigate variation of heavy metal contents for feed materials during composting and to evaluate the effect of pre-treatment methods on heavy metal analysis. Dry ashing, $HNO_3-HClO_4$, aqua-regia, HCl reflux, $HNO_3-HClO_4-HF$, autoclaving methods of $HNO_3$, HCl, and $HNO_3(2+1)$ were used as pre-treatment for heavy metal analysis. In analyzing standard material SRM 2781, recovery efficiencies of pre-treatment methods were 50-60% for Cr and Zn, >100% for Ni, and 80-90% for Cd and Cu. Recovery efficiency of dry ashing for SRM 2781 was the lowest. In composting raw material, Cd concentration by autoclaving methods was 3 to 4 times higher than the other methods and recovery efficiency of dry ashing was also the lowest. During composting, Cd content was the highest in autoclaving. Cr and Cu concentrations were the lowest in dry ashing and aqua-regia, respectively. Variation coefficients of Pb and Zn between pre-treatment methods were generally low.

• Resources Recycling
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• v.20 no.4
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• pp.36-45
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• 2011

The recovery of platinum group metals (PGMs) from the leach solution of spent auto-catalyst and the wash solution of the leach residue was investigated in the laboratory scale experiments by the cementation process using metal powders as the reductant. In this study, the effect of Al, Mg and Zn powders on the cementation process was particularly examined. Aluminum powder was selected as the most suitable reductant for the cementation of PGMs. At the cementation time of 10 minute under the aluminium stoichimetric amount of 19.3 and the reaction temperature of $50{\sim}60^{\circ}C$, the recovery of platinum group metals from the leach solution of the spent auto-catalyst was found to be 99.3%, 99.4%, 90.2% for Pt, Pd and Rh, respectively. Under the same conditions with the aluminium stoichimetric amount of 45, the recovery of platinum group metals from the wash solution of the leach residue of spent catalyst was observed to be 97%, 97% and 90% for Pt, Pd and Rh, respectively. In addition, it was possible to upgrade the platinum group metals in the precipitates obtained from the cementation process by about 10% through the removal of metal impurities by the nitric acid leaching at ambient temperature.

• Fashion & Textile Research Journal
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• v.8 no.4
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• pp.458-464
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• 2006

The adsorption ability of heavy metal ions from the aqueous solution by chitosan, which it is well known natural biopolymer, has been investigated. The fundamental study in this research is focusing on the physicochemical adsorption utilizing the chitosan as a organic chelating adsorbent, adsorb especially heavy metal ions from the waste liquid solution. The adsorption ability of the chitosan between metal ions, having different characteristics with Mw of 188,600, 297,200, and 504,200 g/mol and degree of deacetylation (DD) of 86.92% and 100% were investigated targeting on the $Ni^{2+}$, $Co^{2+}$, $Zn^{2+}$, and $Pb^{2+}$ ions, respectively. The uptake of heavy metal ions with chitosan was performed by atomic absorption flame emission spectrophotometer (AAS) as conducted residual metal ions. It was found that chitosan has an strong adsorption capacity for some metals under certain conditions. Chitosan, which have 100% degree of deacetylation showed high adsorption recovery ratio and have an affinity for all kinds of heavy metals. In contrast, the molecular weight of chitosan was not completely affected on metal ion adsorption.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.337-341
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• 1997

The purpare of this research is to develope a FEM program for analyzing solidification processes of axisymmetic casting, considering phase changes and the contact between the metal and mold. Temperture recovery method is employed for considering the phase changes releasing the latent heat. A gap element is employed for modeling the interface between the model and metal in finding deformed shapes. In order to verify the developed program, an axisymmetric aluminum casting processes is simulated. Temperature distribution, phase front position, and shrinkaga and porosity creation are compared with measurement, FIDAP results, and ANSYS results, and good agreements are examined.

• Toxicological Research
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• v.24 no.2
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• pp.119-127
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• 2008

The objectives of this study were to examine the lung injury and inflammation caused by manual metal arc stainless steel(MMA-SS) welding fume inhalation and to evaluate the recovery process. Sprague-Dawley rats were exposed to MMA-SS welding fumes for 2 h per day in a whole-body exposure chamber, with a total suspended particulate(TSP) concentration of $51.4{\pm}2.8mg/m^3$(low dose) or $84.6{\pm}2.9mg/m^3$(high dose) for 30 days. The animals were sacrificed after 30 days of exposure as well as after a 30-day recovery period. To assess the inflammatory or injury responses, cellular and biochemical parameters as well as cytokines were assayed in the bronchoalveolar lavage fluid(BALF). MMA-SS welding fume exposure led to a significant elevation in the number of alveolar macrophages(AM) and polymorphonuclear cells(PMN). Additionary, the values of $\beta$-n-acetyl glucosaminidase($\beta$-NAG) and lactate dehydrogenase(LDH) in the BALF were increased in the exposed group when compared to controls. After 30 days of recovery from exposure, a significant reduction in inflammatory parameters of BALF was observed between the exposed and recovered groups. Slight, but significant elevations were noted in the number of AM and PMN in the recovered groups, and AM that had been ingested fume particles still remain in the lungs. In conclusion, these results indicated that welding fumes induced inflammatory responses and cytotoxicity in the lungs of exposed rats. Fume particles were not fully cleared from lungs even after a 30-day recovery period.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.289.2-289.2
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• 2016

In-Ga-Zn-O(IGZO) receive great attention as a channel material for thin film transistors(TFTs) as next-generation display panel backplanes due to its superior electrical and physical properties such as a high mobility, low off-current, high sub-threshold slope, flexibility, and optical transparency. For the purpose of fabricating high performance IGZO TFTs, a thermal recovery process above a temperature of $300^{\circ}C$ is required for recovery or rearrangement of the ionic bonding structure. However diffused metal atoms from source/drain(S/D) electrodes increase the channel conductivity through the oxidation of diffused atoms and reduction of $In_2O_3$ during the thermal recovery process. Threshold voltage ($V_{TH}$) shift, one of the electrical instability, restricts actual applications of IGZO TFTs. Therefore, additional investigation of the electrical stability of IGZO TFTs is required. In this paper, we demonstrate the effect of Ti diffusion and modulation of interface traps by carrying out an annealing process on IGZO. In order to investigate the effect of diffused Ti atoms from the S/D electrode, we use secondary ion mass spectroscopy (SIMS), X-ray photoelectron spectroscopy, HSC chemistry simulation, and electrical measurements. By thermal annealing process, we demonstrate VTH shift as a function of the channel length and the gate stress. Furthermore, we enhance the electrical stability of the IGZO TFTs through a second thermal annealing process performed at temperature $50^{\circ}C$ lower than the first annealing step to diffuse Ti atoms in the lateral direction with minimal effects on the channel conductivity.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2006.05a
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• pp.78-85
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• 2006

In textile industries, waste effluent containing zinc is generated during the manufacture of rayon yarn from the wood pulp or cotton linters. Due to the strict environmental regulations and the presence of toxic metallic and other constituents, the discharge of industrial effluents in the sewage or disposal of solid sludge as landfill is restricted. Before recycling of zinc as zinc sulphate solution to the spinning-bath of the rayon manufacturing plant the zinc sulphate solution must be free from calcium, which is deleterious to the process as gypsum precipitates with the increase in concentration and forms scale in the bath. In the present work an attempt has been made to develop a process following solvent extraction technique using thiophosphinic extractants, Cyanex 272 and 302 modified with isodecanol and diluted in kerosene to recover zinc from rayon effluent. Various process parameters viz. extraction of zinc from different concentration of solution, distribution ratio, selective extraction, O/A ratio on extraction and stripping from the loaded organic, complex formation in the organic phase etc. have been studied to see the feasibility of the process. The extractant Cyanex 302 has been found selective for the recovery of 99.99% of zinc from the effluent above equilibrium pH 3.4 maintaining the O/A ratio of 1/30 leaving all the calcium in the raffinate. It selectively extracted zinc in the form of complex $[R_{2}Zn.3RH]_{org}$ and retained all the calcium in the aqueous raffinate. The zinc from the loaded Cyanex 302 can be stripped with 10% sulphuric acid at even O/A ratio of 10 without affecting the stripping efficiency. The stripped solution thus obtained could be recycled in the spinning bath of the rayon plant. The raffinate obtained after the recovery of zinc could be disposed safely without affacting environment.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.8
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• pp.632-638
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• 2012

The prepartion of various metal oxide nanostructures via hydrothermal method, hydrolysis, thermal evaporation and electrospinning and their applications to chemoresistive sensors have been investigated. Hierarchical and hollow nanostructures prepared by hydrothermal method and hydrolysis showed the high response and fast responding kinetics on account of their high gas accessibility. Thermal evaporation and electrospinning provide the facile routes to prepare catalyst-loaded oxide nanowires and nanofibers, respectively. The loading of noble metal and metal oxide catalyst were effective to achieve rapid response/recovery and selective gas detection.

• Journal of Sensor Science and Technology
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• v.25 no.2
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• pp.103-109
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• 2016

Recent light-enhanced metal oxide gas sensors are reviewed in this article. The basic mechanisms of a light-enhanced metal oxide gas sensor are discussed. Many literatures reveal that the standalone sensitivity and the response/recovery time enhancements enabled by the exposing light are not as high as the performance enhancement provided by external heating. Therefore, both optimal amount of external heating and exposed light intensity are necessary to increase the performance of these light-enhanced gas sensors. The development of highly light sensitive materials and structures is important to lower the overall power consumptions of the sensors.