• Proceedings of the Korean Radioactive Waste Society Conference
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• 2004.06a
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• pp.13-23
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• 2004

The characteristics of cesium and cobalt removal from soil around the TRIGA reactor using the electrokinetic method were analyzed and a device to restrain the pH increase in the soil column was suggested. When a NaCl solution was used as the electrolyte to raise the electric field strength, a precipitate was formed in the cathode in the soil column, resulting in a low removal efficiency. Thus, an acetate buffer solution (compound solution of $CH_3COONa$ and $CH_3COOH$) was injected into the soil column and acetic acid was periodically infected into the cathode reservoir to restrain any pH increase. Many $Cs^{2+}$ and $Co^{2+}$ ions were transferred by electromigration rather than electroosmosis during the initial remediation period, and no precipitate was formed in the soil column. 96% of the total amount of cesium in the soil column was removed after 5.9 days, while 94% of the total amount of cobalt was removed. Furthermore, the residual concentrations predicted by the developed model were similar to those obtained by experiment.

• Korean Journal of Environmental Agriculture
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• v.42 no.2
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• pp.83-92
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• 2023

Excess N and P from the livestock manure applied to farmlands, have entered the water systems and poses a serious threat to the natural environment. Consequently, there has been recent awareness towards the management of livestock manure and its related fields. In this study, piggery wastewater was collected from a piggery in Pohang city, Korea. At 800℃, thermal decomposition of a natural stone, magnesite (MgCO₃), yielded powered MgO with particle sizes ranging between 10 to 100 ㎛. Furthermore, NH₄⁺-N and PO₄^3--P were recovered as struvite precipitates from the piggery wastewater, by adjusting the pH with MgO and H₃PO₄. At pH 10, the recovery efficiencies of NH₄⁺-N and PO₄^3--P were found to be 86.1% and 94.1%, respectively. Using an X-ray Diffractometer (XRD), the struvite in the precipitate was confirmed to be consistent with standard pure struvite. Further, the purity of the struvite precipitate was analyzed using an energy dispersive X-ray (EDX) and thermal gravimetry-differential thermal analysis (TG-DTA), and found to be between 79.2% and 93.0%. Additionally, struvite-containing piggery wastewater and sawdust were mixed in a weight ratio of 2.5:1 and processed into a mature compost. The newly manufactured compost passed all quality standards required for first-class graded livestock composts. Moreover, this compost was sprayed directly onto the soil at the test site, and various parameters of the soil's effluent, such as total organic carbon (TOC), total nitrogen (T-N), total phosphorus (T-P), and dissolved oxygen (DO), were analyzed and measured. Based on these results, it is determined that the newly manufactured compost can more significantly reduce water pollution than commercial compost.

• Korean Journal of Materials Research
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• v.33 no.2
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• pp.77-86
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• 2023

High-temperature oxidation of a Ni-based superalloy was analyzed with samples taken from gas turbine blades, where the samples were heat-treated and thermally exposed. The effect of Cr/Ti/Al elements in the alloy on high temperature oxidation was investigated using an optical microscope, SEM/EDS, and TEM. A high-Cr/high-Ti oxide layer was formed on the blade surface under the heat-treated state considered to be the initial stage of high-temperature oxidation. In addition, a PFZ (γ' precipitate free zone) accompanied by Cr carbide of Cr₂₃C₆ and high Cr-Co phase as a kind of TCP precipitation was formed under the surface layer. Pits of several ㎛ depth containing high-Al content oxide was observed at the boundary between the oxide layer and PFZ. However, high temperature oxidation formed on the thermally exposed blade surface consisted of the following steps: ① Ti-oxide formation in the center of the oxide layer, ② Cr-oxide formation surrounding the inner oxide layer, and ③ Al-oxide formation in the pits directly under the Cr oxide layer. It is estimated that the Cr content of Ni-based superalloys improves the oxidation resistance of the alloy by forming dense oxide layer, but produced the σ or µ phase of TCP precipitation with the high-Cr component resulting in material brittleness.

• Journal of Soil and Groundwater Environment
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• v.7 no.2
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• pp.45-52
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• 2002

Water chemistry in the Munkyeong hot-spring expresses high values of EC(1,857 $mutextrm{s}$/cm), $HCO_3$(1,250 mg/l), $SO_4$(147.60 mg/l), Mg(43.05 mg/l), and Ca(279.43 mg/l). The precipitates of small quantity is formed in lower temperature, but much of in case apply heat by boiler. Although mineral that is settled from original ground water is most calcite, aragonite and calcite at the same time crystallized in boiler. The $CO_3$ is present predominantly as $HCO_3^{-}$ and $H_2$$CO_3$, $SO_4$, Mg and Ca are present as free ion. Ca is saturated with respect to carbonate such as aragonite and calcite but slightly undersaturated with respect to anhydrite and gypsum Al is saturated with diaspore and gibbsite. The precitptates are composed of carbonate such as calcite and aragonite and amorphous Fe-hydroxide.

• Journal of Technologic Dentistry
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• v.22 no.1
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• pp.69-78
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• 2000

The microstructure and corrosion behavior of commercially dental casting gold alloys were investigated to clarify the effect of burn-out temperature and cooling rate. In the case of water quenching after casting, only the αphase, which is typical dendritic microstructure of golda alloy, was detected. However, the precipitates along the grain boundary were detected only at the slow cooling rate and they increased inversely proportional to the burn-out temperature. This might be due to the time difference which solute atom could diffuse. EPMA and SEM results also demonstrated that the precipitate should be lamellar structure consisted of Ag rich phase(${\alpha}_1$) and Cu rich phase (${\alpha}_2$). In terms of corrosion, the galvanic coupling was formed due to the difference of composition between precipitates and matrix at the slow cooling rate. In the case of water quenching, the critical current density($i_p$) which indicate the degree of corrosion was lowest at $650^{\circ}C$ and below the burnout temperature, $i_p$ increased with it because of the effect of grain boundary segregation. But above the temperature, $i_p$ increased with it. This may be due to the strain field effect by residual thermal stress.

• Resources Recycling
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• v.9 no.3
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• pp.3-12
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• 2000

A Study on the cementation for the recovery of Cu, Ni and Co with Mn metallic powders in leaching solution from the manganese nodule that have removed Fe ions was studied. The results showed that the recovery efficiencies of metal ions with Mn powders increased when the temperature, pH and the concentration of chloride ions were increased in mixed solution. And the recovery efficiencies of Cu was 98% and not changed with the addition amounts of Mn powders but, in case of Co and Ni, the recovery efficiencies were increased with the addition amounts. The particle size of precipitate was about $5\mu\textrm{m}$. From the results of experiment we proposed the two-step cementation process for the recovery of Cu, Ni and Co with Mn powders.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.1
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• pp.55-59
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• 1999

The Rapid Expansion of Supercritical fluid Solutions (RESS) process was applied to particles coating. Microcapsules prepared by spray drying were used as the core particles, and two kinds of paraffin were used as the coating materials. Supercritical $CO_{2}$ solutions of paraffin were expanded through the short nozzle into the bed that was fluidized by air. Extraction temperature and pressure were varied at $50~120^{\circ}C$, $150~200\;kg/\textrm{cm}^2$, respectively. The thickness of theoritical coating layer ws measured, and precipitate coating layer on surface was analyzed by using SEM, FT-IR. The release behaviors of $Mg^{2+}$ ions were inspected by atomic absorbance spectrophtometer.

• Asian Journal of Atmospheric Environment
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• v.10 no.4
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• pp.190-196
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• 2016

The objective of this study is to obtain the optimal conditions to remove hydrogen fluoride (HF) generated from a variety of F-gas treatment processes. First, we selected $Ca(OH)_2$ and $CaCO_3$ as a reactant among the various alkali salts which have a high removal efficiency and a competitive price by forming a calcium fluoride precipitate. Additionally, various factors were investigated to improve the removal efficiency of HF. The conditions such as the settling time, agitating time and intensity, reaction temperature, and pH were considered as main factors. As a result, in the treatment process to remove HF through Ca-based alkali salts, the optimal conditions were a 120 min settling time, 30 min of agitation at 100 rpm, a pH of 4-8, and a reaction temperature of $40^{\circ}C$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.673-676
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• 1998

The Rapid Expansion of Supercritical fluid Solutions (RESS) process was applied to particles coating. Experiments were conducted in a fluidized bed with an internal nozzle in the center of the reaction tube. Pure glass beads (500~590$\mu$m, 74~149$\mu$m) and glass beads covered with brilliant blue were used as the core particles. Supercritical $CO_2$ solutions of paraffin were expanded through the nozzle into the bed that was fluidized by air. The precipitate coating materials on core surface was analyzed by using SEM, FT-IR. The releasing behavior of brilliant blue was inspected by atomic absorbance spectrophotometer. The release behavior of coated particles superior to noncoated particles.

• Journal of Pharmaceutical Investigation
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• v.40 no.3
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• pp.193-200
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• 2010

The objective of this study was to investigate the effects of sample preparation, HPLC conditions and peak measurement methods upon determining progesterone content of poly-d,l-lactide-co-glycolide microspheres. A series of the microspheres with different formulations was first prepared. To determine their actual drug contents, the microspheres were dissolved in tetrahydrofuran and diluted with various amounts of methanol to precipitate the polymer. After removal of polymeric precipitates, the filtrates were subject to HPLC analysis under versatile experimental conditions. Interestingly, the composition of a sample solution (e.g., the ratio of methanol to tetrahydrofuran) affected the magnitudes of both peak fronting and peak broadening of progesterone. Its peak became broader and more asymmetrical at lower methanol:tetrahydrofuran ratios. Furthermore, its peak height was influenced by the proportion of tetrahydrofuran in a sample solution. Such problems encountered with tetrahydrofuran were exacerbated when a larger volume of the sample solution was injected onto an analytical column. Under our experimental conditions a peak area measurement provided more accurate and reliable determination of progesterone content in various microspheres than a peak height determination. Optimizing the composition of a sample solution, HPLC chromatographic conditions and peak analysis methods was a prerequisite to an accurate determination of progesterone encapsulated within microspheres.