• Applied Chemistry for Engineering
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• v.33 no.1
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• pp.90-95
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• 2022

In the present work, biochar was prepared using Achyanthes japonica stem as a by-product of herbal medicine. In order to apply the prepared biochar to water treatment process, the adsorption characteristics of zinc and iron ions dissolved in water were investigated. When the experiments were performed for 2 h to remove 70 and 100 mg/L of zinc ions, the adsorption amounts of 32.3 and 31.0 mg/g were obtained, respectively. It was also found that the adsorption amount of Achyanthes japonica stem biochar for the removal process of zinc ion was three times higher than that of the activated carbon. In addition, when the experiments were performed for 2 h to treat 70 and 100 mg/L of iron ions, high adsorption amounts of 50.1 and 54.3 mg/g were achieved, respectively. In order to further enhance the removal efficiency of zinc and iron ions, a steam activation process was performed on the biochar of Achyanthes japonica stem. As a result, the removal efficiencies of 70 and 100 mg/L of zinc ions increased to 80 and 60%, respectively. Also, the removal efficiencies of 70 and 100 mg/L of iron ions were improved to 100 and 82%, respectively. In addition, when the biochar of Achyanthes japonica stem with a steam activation was compared with the untreated biochar of Achyanthes japonica stem, the specific surface area increased 37.3 times, and the total and macroporpous pore volumes were improved by 28.4 and 136 times, respectively. Therefore, the results can be used for economically and practically adsorbing zinc and iron ions contained in water.

• 한국해양학회지
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• v.28 no.3
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• pp.229-240
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• 1993

This study investigated the behaviour of sulfur species after the early diegenetic reduction of sulfate from pore solution in an anoxic intertidal flat deposit in the Banweol area of Kyeong-gi Bay, west coast of Korea. A total of seven sediment cores were collected during 1990∼1992 and were analyzed for their solid-phase sulfur species (acid-volatile sulfur, element sulfur, pyrite sulfur) as well as for chemical components in the pore solution, such as sulfate, ammonium, hydrogen sulfide, phosphate and Fe ion. The pore water sulfate oncentration was found to decrease rapidly downward from the sediment surface, while that of hydrogen sulfide, ammonium and phosphate showed and increase. The dissolved iron concentration in pore water, on the other hand, was found high in the surface layer of sediment, but fell sharply below this layer. these characteristic profiles of pore water sulfide and iron concentrations suggest that some reaction occurs between dissolved iron and sulfide ions, leading to the formation of various sulfide minerals in the sedimentary phase. The amount of inorganic sulfur species in the sediment increased downward, and showed a maximum of up to 7.9 mg/g. among the three species analyzed, acid-volatile sulfur (AVS) was dominant comprising more than 50% of the total. The amount of pyrite sulfur was greater than that of element sulfur. This implies that the formation of pyrite was restricted in this environment. the limited amount of element sulfur in this deposit may have discouraged the active formation of pyrite.

• Journal of the Korean institute of surface engineering
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• v.57 no.1
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• pp.22-30
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• 2024

This study reports a direct growth of carbon nanotubes (CNTs) on the surface of LiCoO₂ (LCO) powders to apply as highly efficient cathode materials in lithium-ion batteries (LIB). The CNT synthesis was performed using a thermal chemical vapor deposition apparatus with temperatures from 575 to 625 ℃. Ferritin molecules as growth catalyst of CNTs were mixed in deionized (DI) water with various concentrations from 0.05 to 1.0 mg/mL. Then, the LCO powders was dissolved in the ferritin solution at a ratio of 1g/mL. To obtain catalytic iron nanoparticles on the LCO surface, the LCO-ferritin suspension was dropped in silicon dioxide substrates and calcined under air at 550℃. Subsequently, the direct growth of CNTs on LCO powders was performed using a mixture of acetylene (10 sccm) and hydrogen (100 sccm) for 10 min. The growth behavior was characterized by scanning and transmission electron microscopy, Raman scattering spectroscopy, X-ray diffraction, and thermogravimetric analysis. The optimized condition yielding high structural quality and amount of CNTs was 600 ℃ and 0.5 mg/mL. The obtained materials will be developed as cathode materials in LIB.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.3
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• pp.226-232
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• 2013

Several pretreatment processes such as softening, coagulation and precipitation, activated carbon adsorption, ion-exchange and neutralization processes were studied to remove organics and inorganics for selection of the RO based reusing system of metal industry wastewater. The effects of the hydrophobic/hydrophilic fractions of the organics on DOC removal were tested and used to optimize the combination process. Among various pretreatment processes, softening could reduce 93.4% of hardness and could remove all hydrophobic organics from the effluent of metal industry wastewater. Softening followed by coagulation process could reduce DOC (Dissolved Organic Carbon) from 5.1 mg/L to 1.6 mg/L. In addition, as a result of physiochemical pretreatment to raw wastewater of metal industry, neutralization with NaOH showed an efficient removal of iron and TDS (Total Dissolved Solids) without increase in the hardness.

• Economic and Environmental Geology
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• v.42 no.5
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• pp.471-477
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• 2009

An experimental removal of dissolved uranium (U) exsiting as uranyl ion (${UO_2}^{2+}$) was carried out using Shewanella p., iron-reducing bacterium. By the microbial reductive reaction, initial U concentration ($50{\mu}M$) was constantly decreased, and most U were removed from solution after 2 weeks. Major mechanism that U was removed from the solution was adsorption, precipitation and mineralization on the microbe surface. Under the transmission electron microscopy, the U adsorbed on the microbe was observed as being crystallized and eventually enlarged to several ${\mu}m$ sizes of minerals by combining with individual microbes and organic exudates. It seems that such U growth and mineralization on the microbial surface could affect the U behavior in a radioactive waste disposal site. Thus, the biogechemical reaction of metal-reducing bacteria observed in this experiment could give an affirmative measure that the microbial activity may retard U movement in subsurface environment.

• Journal of the Korean Ceramic Society
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• v.56 no.4
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• pp.387-393
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• 2019

A N₂H₄-Cu(I)-HNO₃ solution was used to dissolve magnetite powders and a simulated oxide film on Inconel 600. The addition of Cu(I) ions to N₂H₄-HNO₃ increased the dissolution rate of magnetite, and the reaction rate was found to depend on the solution pH, temperature, and [N₂H₄]. The dissolution of magnetite in the N₂H₄-Cu(I)-HNO₃ solution followed the contracting core law. This suggests that the complexes of [Cu⁺(N₂H₄)] formed in the solution increased the dissolution rate. The dissolution reaction is explained by the complex formation, adsorption of the complexes onto the surface ferric ions of magnetite, and the effective electron transfer from the complexes to ferric ions. The oxide film formed on Inconel 600 is satisfactorily dissolved through the successive iteration of oxidation and reductive dissolution steps.

• Environmental Engineering Research
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• v.10 no.5
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• pp.205-212
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• 2005

The study was conducted to investigate the removal of heavy metals by using Hydroxyapatite(HAp) made from waste oyster shells and wastewater with high concentration of phosphorus. The maximum calcium concentration for the production of HAp in this study was released up to 361 mg/L at pH of 3 by elution experiments. When the pH was at adjusted 6, the maximum calcium released concentration was 41 mg/L. During the elution experiment, most of the calcium was released within 60 minutes. This reaction occurred at both pH levels of 3 and 6. The result of the XRD analysis for the HAp product used in this study shows the main constituent was HAp, as well as OCP. The pH was 8.6. As the temperature increased, the main constituent did not vary, however its structure was crystallized. When the pH was maintained at 3, the removal efficiency decreased as the heavy metal concentration increased. The order of removal efficiency was as follows: $Fe^{2+}$(92%), $Pb^{2+}$(92%) > $Cu^{2+}$(20%) > $Cd^{2+}$(0%). Most of these products were dissolved and did not produce sludge in the course of heavy metals removal. As the heavy metal concentration increased at pH of 6, the removal efficiency increased. The removal efficiencies in all heavy metals were over 80%. From the analysis of the sludge after reaction with heavy metals, the HAp was detected and the OCP peak was not observed. Moreover, lead ion was observed at the peaks of lead-Apatite and lead oxidant. In the case of cadmium, copper and iron ions, hydroxide forms of each ion were also detected.

• Korean Journal of Ecology and Environment
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• v.35 no.3 s.99
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• pp.213-219
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• 2002

The CellCaSi, a porous silicate material, was tested for the removal of phosphorus (P as phosphate) in water. The effect of the CellCaSi was investigated on the basis of both particle size (under 1,2, and 4 mm) and added amount (0, 1, 2.5, 5, and 10 g/1) of the CellCaSi. The removal efficiency of phosphorus was highest with a particle size of under 1 mm and also increased with an increasing amount of the CellCaSi. The pH change showed little effect on the phosphorus removal of the CellCaSi. The calcium ion was eluted from the CellCaSi into the water, while the aluminium and iron were not. The eluted calcium ion was combined with dissolved phosphorus and then precipitated. The highest removal efficiency of phosphorus was obtained by the combined addition of the CellCaSi, calcium chloride, and ferric chloride. That is, the phosphorus concentrations of 0.10 and 1.0 mg/1 decreased to 0.03 and 0.47 mg/l by the addition of the CellCaSi (1 g/l), calcium ion (30 mg/l), and ferric ion (1 mg/l) at day 8 after treatment. The water qualities at the end of the experiment were as follows: pH was 8.1 and conductivity was 318 ${\mu}$S/cm (a registered maximum conductivity of 500${\mu}$S/cm for raw and potable wafers).

• Journal of Soil and Groundwater Environment
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• v.25 no.2_spc
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• pp.16-27
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• 2020

Nitrate contamination has received much attention at local as well as regional scales. The domestic situation is not out of exception, and it has been reported to be very serious, particularly within agricultural areas as a result of excessive usage of nitrogen fertilizers. Meanwhile, nitrate can be naturally attenuated by denitrification in subsurface environments. The denitrification occurs through biotic (biological) and abiotic processes, and numerous previous studies preferentially focused the former. However, abiotic denitrification seems to be significant in specific environments. For this reason, this study reviewed the previous studies that focused on abiotic denitrification processes. Firstly, the current status of nitrate contamination in global and domestic scales is presented, and then the effect of geological media on denitrification is discussed while emphasizing the significance of abiotic processes. Finally, the implications of the literature review are presented, along with future research directions that warrant further investigations. The results of previous studies demonstrated that several geological agents could play a vital role in reducing nitrate. Iron-containing minerals such as pyrite, green rust, magnetite, and dissolved ferrous ion are known to be powerful electron donors triggering denitrification. In particular, it was proven that the rate of denitrification by green rust was comparative to that of biological denitrification. The results indicate that abiotic denitrification should be taken into account for more accurate evaluation of denitrification in subsurface environments.

• Resources Recycling
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• v.31 no.5
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• pp.26-33
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• 2022

Molybdenum is widely used in many materials; thus, its recovery from ores and secondary resources has attracted considerable attention. In this study, the leaching of molybdenite ore using hydrochloric acid containing sodium chlorate as an oxidizing agent was studied. The effects of several variables, such as the concentrations of HCl and NaClO₃, reaction temperature and time, and pulp density, on the leaching of the ore were investigated. Under strong acidic and oxidizing conditions, the sulfide in the ore was dissolved as a sulfate ion, which formed gypsum with Ca(II), leading to a decrease in the leaching percentage of Mo(VI) from the ore. The leaching percentage of molybdenum was greater than 90%, while those of iron, calcium, and silicon were 38, 29, and 67%, respectively, under the optimum conditions: 2.0 M HCl, 0.5 M NaClO₃, pulp density of 5 g/L, temperature of 90 ℃, and treatment time of 60 min.