• Analytical Science and Technology
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• v.23 no.6
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• pp.566-571
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• 2010

This paper describes the sorption behaviors of aqueous uranium ions on the K-birnessite. K-birnessite was synthesized by adding a concentrated HCl to an aqueous solution of $KMnO_4$. Physicochemical characteristics of the K-birnessite, such as structure, specific surface area and surface charge, were investigated. K-birnessite is a layered material and the $K^+$ ions exist in the interlayer of layered K-birnessite. BET specific surface area of the K-birnessite was 38.30 m2/g. The surface charge of K-birnessite was $-1.65\;C/m^2$ at pH 5.00 and ionic strength of 0.010 M $NaClO_4$, at which the sorption experiments of uranium ions were carried out. Uranium ions were incorporated into the interlayer of the K-birnessite by cation-exchange reaction with $K^+$ ions, and the distribution coefficient is quite similar to those of common ion-exchange materials. The results might be applicable in the retardation of migration of radioactive materials from the underground disposal site of high-level radioactive waste.

• Applied Chemistry for Engineering
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• v.4 no.1
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• pp.204-215
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• 1993

Epoxy-activated chitin was synthesized by the reaction of epichlorohydrin with chitin which was isolated from waste marine sources such as crab shell. Followed by the reaction of epoxy-activated chitin with hexamethylenediamine, the aminohexyl chitin was synthesized. The aminohexyl chitin was subsequently reacted with epichlorohydrin to prepare the epoxy-activated aminohexyl chitin. Finally, the tannin-immobilized chitin (Resin I) was synthsized by the reaction of tannin solution with epoxy-activated aminohexyl chitin. Using silane coupling agent, the tannin-immobilized chitosan(Resin II) was synthesized by the reaction of $\gamma$-glycidoxypropyltrimethoxy silane with chitosan which was prepared by the deacetylation of chitin. Upon the pH variation, adsorptivities of these immobilized tannins to the metal ions such as $Cu^{+2}$, $Ni^{+2}$, $Cr^{+6}$, $Co^{+2}$, $Ca^{+2}$, $Pb^{+2}$, $Ba^{+2}$, and $UO_2{^{+2}}$ ions were determined by batch method. The adsorptivity tendencies of these immobilized tannin to the most of metallic ions were increased with pH. Furthermore, the adsorptivities of Resin(I) and Resin(II) upon the variation of pH, contact time, amount of resin and concentration of metal ion were investigated. As a result, it was found that these immobilized tannin on both chitin and chitosan showed good adsorptivities for uranyl ion.

• Korean Chemical Engineering Research
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• v.43 no.1
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• pp.60-65
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• 2005

The electrosorption of U(VI) from waste water was carried out by using activated carbon fiber(ACF) felt electrode in a continuous electrosorption cell. In order to enhance the electrosorption capacity at lower potential, ACF felt was chemically modified in acidic, basic and neutral solution. Pore structure and functional groups of chemically modified ACF were examined, and the effect of treatment conditions was studied for the adsorption of U(VI). Specific surface area of all ACFs decreases by this treatment. The amount of acidic functional groups decreases with basic and neutral salt treatment, while the amount increases a lot with acidic treatment. The electrosorption capacity of U(VI) decreases on using the acid treated electrode due to the shielding effect of acidic functional groups. Base treated electrode enhances the capacity due to the reduction of acidic functional groups. The electrosorption amount of U(VI) on the base treated electrode at -0.3 V corresponds to that of ACF electrode at -0.9 V. Such a good adsorption capacity was not only due to the reduction of shielding effect but also the increase of $OH^-$ in the electric double layer on ACF surface by the application of negative potential.

• Journal of Radiation Protection and Research
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• v.36 no.4
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• pp.209-215
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• 2011

In order to investigate the soil-to-plant transfer factor (TF) of $^{99}Tc$ for Korean major upland crops (soybean, radish and Chinese cabbage), pot experiments were performed in a greenhouse. Soils were collected from four upland fields (two for soybean and two for radish and Chinese cabbage) around Gyeongju radioactive-waste disposal site. Three to four weeks before sowing, dried soils were mixed with a $^{99}Tc$ solution and the mixtures were put into pots and irrigated. TF values were expressed as the ratios of the $^{99}Tc$ concentrations in plants (Bq $kg^{-1}$-dry or fresh) to those in soils (Bq $kg^{-1}$-dry). There was no great difference in the TF value between soils. The TF values for soybean seeds were extremely lower than those for the straws, indicating a very low mobility of $^{99}Tc$ to seeds. As representative TF values of $^{99}Tc$, $1.8{\times}10^{-1}$, $1.2{\times}10^1$, $3.2{\times}10^2$ and $1.3{\times}10^2$ (for dry plants), arithmetic means for two soils, were proposed for soybean seeds, radish roots, radish leaves and Chinese cabbage leaves, respectively. In the case of the vegetables, proposals for fresh plants were also made. The proposed values are not sufficiently representative so successive updates are needed.

• Clean Technology
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• v.8 no.3
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• pp.119-128
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• 2002

In the present study the membrane filtration characteristics of a commercially available synthetic water-based cutting oil through two kinds of ultrafiltration membranes (HF1-45-CM50 and HF1-43-CM100) with molecular weight cut-offs of 50,000 and 100,000, respectively, have been investigated in detail. Among these membranes, the hydrophilic one (HF1-45-CM50) was found to show a satisfactory result for both the permeate flux and the permeability of oil components, whereas the permeate flux obtained with the hydrophobic membrane (HF1-43-CM100) appears to be significantly low, indicating that synthetic cutting oil was easily wetted on the hydrophobic membrane surface and induced more membrane fouling. The effect of material characteristics of the membrane on the filtration characteristics was found to be much more significant compared with the mean pore size of the membrane. Backflushing by nitrogen gas was applied to reduce the formation of a gel layer and membrane fouling. With the hydrophilic membrane, the backflushing was found to increase the permeate flux, whereas the backflushing resulted in a decrease in flux for the hydrophobic membrane. The flux recovery was observed to be highest when the membranes fouled with waste synthetic cutting oil were immersed into a cleaning solution for more than 72 hours and then backflushed by nitrogen gas.

• Clean Technology
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• v.14 no.2
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• pp.110-116
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• 2008

The radioactive wastes generated from the nuclear industry can be divided into the forms of solid, liquid, or gas. Radioactive methyl iodide, a gaseous radioactive waste, is absorbed by activated carbon with 5 wt% of Trietylenediamine (1,4-diazania-bicycle[2.2.2]octane, TEDA) impregnated on the surface. Methyl Iodide ($CH_3I$) is combined chemically with TEDA (the final product : I-TEDA). To recycle radioactive activated carbon, removal of I-TEDA from activated carbon is needed. A wet method for recycling impregnated active carbon was developed to remove radioactive I-TEDA using an acetonitrile solution, which produces lots of secondary wastes. We suggest the removal of I-TEDA by supercritical carbon dioxide with co-solvents. In this experiment, we used a quartz crystal microbalance (QCM) for measuring the removal rate of the I-TEDA. From the experimental results, methanol was found to be the optimum co-solvent, and the optimum conditions such as temperature, pressure, and co-solvent flow rate were obtained. Possibility of using supercritical fluid in the removal of I-TEDA from radioactive activated carbon was also discussed.

• Applied Biological Chemistry
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• v.42 no.1
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• pp.73-78
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• 1999

Acid mine drainage (AMD) results from sulfuric acid produced by the oxidation of pyrite, and contains large amounts of toxic elements. In the neutralization of AMD, iron and aluminum hydroxides are the major precipitates and those two can be separated with two-phase neutralization. In this study, removal of toxic elements by the two phases of neutralization was investigated using an AMD collected from the abandoned antimony mine in Gachang, Taegu. Contents of As, Cd, Cu, Mn, Pb and Zn in the AMD were higher than the criteria of river water quality or permissible waste water discharge. In the first phase, the AMD was neutralized to several % (25, 50, 75, 100, and 125) of $Fe(OH)_3$ equivalence point with solid $Ca(OH)_2$. In the second phase, the supernatant of the first phase neutralization was titrated to pH 7.5. After neutralization of the AMD to 100% of the $Fe(OH)_3$, equivalence point, most of Fe and Pb were removed but levels of As, Cd, Cu, Ni, Mn, and Zn were not reduced in the supernatant solution. In the second phase neutralization, levels of those toxic elements in the supernatants dropped below the wastewater discharge or river water quality criteria. This result suggests that the precipitate formed in the first phase of the neutralization process may be disposed without any special cares. Thus the two-phase neutralization scheme can reduce the cost of disposing precipitates containing toxic metals in comparison with the monophase neutralization scheme.

• Journal of the Korean Applied Science and Technology
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• v.33 no.4
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• pp.795-801
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• 2016

This study is on the denitrification process using the sodium alginate and $CaCl_2$ as a flocculant. Removal techniques of nitrate nitrogen from waste water are reverse osmosis, ion exchange, electro dialysis and biological method etc. We tried to remove nitrate nitrogen with flocculation and sedimentation method in the present study. Calcium alginate is expected to form a chelate bond with nitrate nitrogen in the solution. So the effects of flocculantt component, flocculation reaction time, molar ratio of the flocculant, flocculant injection rate are studied to determine the best removal rate of nitrate nitrogen. In addition, we tried to determine the nitrate nitrogen removal mechanism by analyzing the structure and component ratio of the configuration after the agglutination precipitate by FE-SEM and EDS. As a result, the nitrate nitrogen removal mechanism is turned out to form calcium-nitro-alginate, and the best mole ratio of flocculating agent is 1 : 1, the injection rate of the flocculant was up to 2%, the removal rate of the nitrate nitrogen to be 56.7% in the synthetic wastewater.

• Resources Recycling
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• v.24 no.2
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• pp.62-68
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• 2015

The high pure tin production was conducted from crude-tin containing waste solder by electro-refining process. The electro-refining process maintained at 0.2V produced tin with purity of 99.98%, whereas a little increase of voltage to 0.3 V resulted tin purity of 99.92%. The high pure tin of 3N in the present process was produced by fixing the voltage at 0.3V. Considering the high pure tin production, the current density was maintained within $100-120A/m^2$ with current efficiency of 94%. Addition of sulfuric acid of 20 ~ 25 g/L to the electrolyte solution was performed in order to keep Pb (lead) concentration below 100 mg/L in the final tin product. The anode slime generated during electro refining process was analyzed by X-ray diffraction (XRD) study to understand the phases of impurities in it. It detected the presence of Cu and Ag in the slime as in the form of $Cu_6Sn_5$, $Ag_3Sn$, whereas Pb occurred as $PbSO_4$ compound.

• KSBB Journal
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• v.11 no.6
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• pp.681-688
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• 1996

In the removal of phenolic precipitates formed by horseradish peroxidase (HRP) and $H_2O_2$ from waste water, the effects of the concentrations of phenolic compounds and $H_2O_2$ on the removal efficiency of various phenols were studied. More than 90% of various phenolic compounds were removed from the aqueous solutions (pH 5-7) by HRP and H2O2. The removal efficiency of phenolic compounds by HRP was reduced to a great extent when the initial concentration of $H_2O_2$ was over 10mM. Furthermore, no phenolic compounds were removed when 50mM of $H_2O_2$ was used. The HRP's turnover number, which indicates the number of phenolic molecules removed per one molecule of HRP, was the largest as 18047 for p-ethoxyphenol while it was the smallest as 1244 for m-chlorophenol when the initial concentrations of phenolic compounds and H2O2 were the same at 1mM. HRP which was separated from the aqueous solution containing phenol and $H_2O_2$ after 24hr of reaction revealed structural changes and diminished activity. The Soret absorbance near 404nm of this HRP sample was decreased to 48% of that of fresh HRP. The values of kcat and kcat/Km of this HRP sample for the oxidation of guaiacol were also reduced to 41% and 51% of those of fresh HRP, respectively. The removals of nonphenolic aromatic compounds such as benzene, ethylbenzene, and toluene (BET) by HRP and $H_2O_2$ were enhanced when phenols were coexisting in the aqueous solutions of BET.