• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.5
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• pp.199-205
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• 2018

A geopolymer was produced from coal ash generated from an integrated gasification combined cycle (IGCC) plant and its water resistance was evaluated. For this purpose, the geopolymer specimens were immersed in water for 30 days to measure changes in microstructure and alkalinity of the immersion liquid. Particularly, the experiment was carried out with foaming status of the geopolymers and parameters of room temperature aging condition, and immersion time. The foamed geopolymer containing 0.1 wt% Si-sludge had pores with a diameter of 1 to 3 mm and exhibited excellent foamability. Also, the calcium-silicate-hydrate crystal phase appeared in the foamed geopolymer. In the geopolymer immersion experiment, the pH of the immersion liquid increased with time, because the un-reacted alkali activator remained was dissolved in the immersion liquid. From the pH change of the immersion liquid, it was found that geopolymer reaction in the foamed specimen was completed faster than the non-foamed specimen. Through this study, it was possible to successfully produce foamed and non-foamed geopolymers recycled from IGCC coal ash. Also the necessary data for the safe application of IGCC coal ash-based geopolymers to areas where water resistance is needed were established; for example, the process conditions for room temperature aging time, effect of foaming status, immersion time and so on.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.9
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• pp.735-742
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• 2009

The bone of spinal animals has a hydroxylapatite ($Ca_{10}(PO_4)_6(OH)_2$, HAp) structure which is well known as an excellent inorganic ion exchanger for various heavy metal ions in solutions. In this study, the reusability of cow-bone, pig-bone and fish-bone as a potential material for the removal of heavy metals in solutions was evaluated from the removal of Cu(II) ion in batch tests. The surface properties of three bones, calcined at different temperatures, were measured with SEM, XRD, FT-IR analyses. From the SEM analysis, a clear development of heterogeneity as well as pores having small diameter was observed as the calcination temperature increased. The results of X-ray diffraction analysis showed well developed crystallinity on the surface of calcined bones obtained at higher temperatures, suggesting a transform of amorphous type to crystalline type. Fourier transform infrared (FT-IR) analysis showed disappearance of water molecule on the surface of HAp and organic functional groups of the HAp with increasing the calcination temperatures. Cu(II) removal in the control test was below 15%. By the way, additional 40% increase of Cu(II) removal was observed in the presence of calcined bones. For three bones, Cu(II) removal was decreased as the calcined temperature increased. Cu(II) removal was increased as the solution pH increased due to a favorable condition for the cation exchange as well as precipitation.

• Economic and Environmental Geology
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• v.37 no.1
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• pp.143-151
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• 2004

This study focused on examining the possibility of recycling mine solid waste as environmental materials, especially for porous media. Basic properties including mineralogical compositions, chemical compositions, and particle size distribution of the tailings from the Sangdong W mine were checked. The mineralogical and chemical compositions of the tailings samples were not much different in depth. According to Korean Standard Leaching Test for Wastes(KSLT), concentrations of heavy metals leached from the tailings were below the standard values. As a result of particle size analysis, the median diameter (d$_{50}$) of the tailings was in the range of 10 to 30 ${\mu}{\textrm}{m}$. The stable tailings slurry made up of 3 ${\mu}{\textrm}{m}$ in d$_{50}$ was prepared using Attrition Mill. The milling condition was 40 vol% in slurry concentration, 700 rpm in stirring speed, and 1 hour in milling time. PEI was added as dispersing agent. Concentrated slurry was extended to 3 times by foaming method. In the case of 3 times foamed slurry, the total and open porosity of ceramic supports sintered at 1,075$^{\circ}C$ for 90 minutes was about 80% and 72%, respectively. Pore size was in the range of 30∼350${\mu}{\textrm}{m}$. Therefore, the tailings could be recycled starting material for environmental materials such as macroporous ceramic support.

• Journal of the Korea Concrete Institute
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• v.26 no.2
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• pp.201-210
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• 2014

The present study proposes a phased model to assess the lifecycle $CO_2$ amount of concrete structures. The considered system boundary is from cradle to recycling, which includes constituent material, transportation, batching and mixing in ready-mixed concrete plant, use and demolition of structure, and crushing and recycling of demolished concrete. The $CO_2$ uptake of concrete by carbonation during lifetime (40 years) of a structure and the recycling life (20 years) after demolition is estimated using a simple approach generalized to predict the carbonation depth from the surfaces of concrete element and recycled aggregates. Based on the proposed phased model, a performance evaluation table is realized to straightforwardly examine the lifecycle $CO_2$ amount of concrete structures. The proposed model demonstrates that the contribution of ordinary portland cement (OPC) to lifecycle $CO_2$ emission of the concrete structure occupies approximately 85%. Furthermore, the $CO_2$ uptake is estimated to be approximately 15~18% of the lifecycle $CO_2$ emissions of concrete structures, which corresponds to be 19~22% of the emissions from OPC production. Overall, the proposed $CO_2$ performance table is expected to be practically useful as a guideline to determine the $CO_2$ emission or uptake at each phase of concrete structures.

• Resources Recycling
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• v.24 no.1
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• pp.58-65
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• 2015

Although Korea is a top market sharing and world leading producer and developer of flat panel display devices, relevant recycling technology is not up to her prestigious status. Besides, most of the waste glass arising from flat panel displays is currently land-filled. The present paper mainly reviews on development of recycling systems for waste TFT-LCD glass from end-of-life LCD TVs and monitors and TFT-LCD process waste of crushed glass particles with target end uses of raw material for high strength concrete pile and glass fibers, respectively. Waste LCD glass was recycled to fabricate ingredients for high strength concrete piles with enhanced physical properties and spherical foam products. The waste LCD glass recycling technology is already developed to fabricate long and short fibers at commercial level. In view of these, future R & D on waste LCD glass materials is to be directed toward implementation of commercial materials recycling system therefrom.

• The Journal of Engineering Geology
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• v.27 no.3
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• pp.245-253
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• 2017

Vietnam CFBC fly ash has high CaO content and can be used as a solidification agent for soft ground improvement. However, most fly ash is treated as landfill or waste. In order to utilize fly ash as a solidification agent for soil improvement, the characteristics of fly ash must be accurately determined. In this study, laboratory tests were conducted on fly ash from four CFBC power plants to evaluate the utility of Vietnam fly ash as a solidification agent. As a result of analyzing the physical properties, it was analyzed that all four samples were suitable as material for solidification agent and have suitable particle size for the improvement of soft ground. As a result of analysis of chemical characteristics, it was analyzed that the fly ash of one place could be used as a solidification agent because of the high content of free-CaO. The remaining three fly ash was not suitable for use as a solidification agent due to low Free-CaO content. However, it has a chemical composition similar to that of general fly ash in Korea, so it can be recycled in various ways.

• Journal of the Korean Society for Marine Environment & Energy
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• v.11 no.1
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• pp.42-45
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• 2008

It has been reported that FRP (fiber reinforced plastic) can be recycled by separating into layers instead of crushing into powder. F-fiber obtained from roving layer separated from FRP, has bigger tensile strength than the bundle of glass fibers of which FRP was made (more than 90%). SEM image of F-fiber shows the presence of some resin. Under the proposition of usage of F-fiber in the concrete material, tensile strength is examined after soaking in a basic solution (NaOH+KOH). The reaction mechanism of strength loss may be considered as an attack of hydroxide ion ($OH^-$) on a chemical bond of Si-O-Si of glass fiber. The simulation graph of the strength loss data implies certain reaction mechanism. While in the early stage kinetically controlled reaction results in a fast drop of tensile strength, after 30 days dispersion rate of hydroxide ion plays a major role in strength loss. This result is similar to the one for the AR glass. An extrapolation of the graph would make an assumption about the lift time of F-fiber possible.

• Resources Recycling
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• v.27 no.5
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• pp.61-68
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• 2018

The aluminum dross is oxide generated on the surface of the molten metal during the aluminum melting process and it is divided into white dross and black dross according to presence of the Salt flux. White dross has high metal content and is recycled via the melting process. Black dross is largely berried, because the it has a low metal content and difficulty in separating the components. Black dross contains a salt components such as NaCl and KCl, and inorganic materials such as $Al_2O_3$ and MgO, and it is necessary to study the technology to recover and recycle such valuable resources. In this study, a process for recycling aluminum black dross was proposed. The inorganic and soluble substances present in the black dross were separated through crushing-dissolution-solid/liquid separation-decompression evaporating. By controlling the ratio of water and black dross, the recovery condition of the separated product was optimized and we confirmed the highest Salt flux recovery efficiency 91 wt.% at black dross:water ratio 1:9. Finally, Through the synthesis of zeolite using recovered ceramic material, the materialization possibility of black dross was confirmed.

• Korean Chemical Engineering Research
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• v.54 no.6
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• pp.806-811
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• 2016

Organosolv pretreatment is the process to frationation of lignocellulosic feedstocks to enhancement of enzymatic hydrolysis. This process has advantages that organic solvents are always easy to recover by distillation and recycled for pretreatment. The chemical recovery in organosolv pretreatment can isolate lignin as a solid material and carbohydrates as fermentable sugars. For the economic considerations, using of low-molecular-weight alcohols such as ethanol and methanol have been favored. When acid catalysts are added in organic solvent, the rate of delignification could be increased. Mineral acids (hydrochloric acid, sulfuric acid, and phosphoric acid) are good catalysts to accelerate delignification and xylan degradation. In this study, the biomass was pretreated using 40~50 wt% ethanol at $170{\sim}180^{\circ}C$ during 20~60 min. As a results, the enzymatic digestibility of 2-stage pretreatment of rigida using 50 wt% ethanol at $180^{\circ}C$ was 40.6% but that of 1-stage pretreatment was 55.4% on same conditions, therefore it is shown that the pretreatment using mixture of the organosolv and catalyst was effective than using them separately.

• Journal of Bio-Environment Control
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• v.25 no.1
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• pp.49-56
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• 2016

This study was conducted to develop the disinfection system using electric shock for recycled nutrient solution in recycling soilless culture. Stainless steel (SUS 316) was found as the most appropriate electrode material for electrical disinfection system from the view of high electrical conductivity, low electric resistance, and low price. There were no changes in nutritional elements when the electric shock passed through the nutrient solution by stainless steel electrode. The amount of electric current increased with width than thickness of the electrode. The farther the distance between the electrodes was increased the time to reach out the aimed amount of current. The electric shock was applied to Ralstonia solanacearum and Fusarium oxysporum as representative bacteria and also fungi. Any of those pathogens were killed with the percentage of higher than 97% in the condition of 15VDC or 24VDC.