• Journal of Korean Society of Water and Wastewater
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• v.31 no.4
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• pp.329-338
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• 2017

The problem of disposal of brine due to increased MD/RO desalination plant has recently become a big social issue. The chlor-alkali process through electrolysis of brine has been studied as a method to overcome this problem. In order to increase the electrolysis efficiency, a pretreatment process for removal of hard substances must be preceded. In this study, we investigated the mechanism of removal of hardness through chemical precipitation. As a result, Ca was greatly influenced by addition of $Na_2CO_3$, and Mg was strongly influenced by pH. Also, the addition of NaOH and $Na_2CO_3$ enabled simultaneous removal of Ca and Mg, and showed a removal efficiency of 99.9% or more. Finally, the residual concentrations of Ca and Mg in the brine after the reaction were 0.14 and 0.13 mg/L, respectively. Saturation index was calculated using Visual MINTEQ 3.1, and solid phase analysis of the precipitate was performed by FE-SEM and PXRD analysis. It was confirmed that precipitate formed by the formation of calcite and brucite.

• Journal of the Korea Organic Resources Recycling Association
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• v.22 no.2
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• pp.50-56
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• 2014

Conventional coagulation-gravity settling processes in heavy metal removal have a problem in coagulant cost and instability of the settling efficiency. The authors investigated the effects of pH and slow mixing conditions on heavy metal hydroxide precipitation and the particle size distribution of the precipitate for a precipitation-membrane separation process. The optimum pH values for the hydroxide precipitation ranged from 9 to 10. The addition of $FeCl_3$ did not enhance the heavy metal removal. 20 min of slow mixing at 70 rpm showed the maximum heavy metal removal to meet the water quality criteria for effluent discharge. More than 99.9% of the heavy metal precipitate particles were bigger than $2{\mu}m$.

• Journal of Environmental Science International
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• v.8 no.6
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• pp.711-716
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• 1999

This research explored the feasibility of preparing and utilizing a prefonned polymeric solution of Al(III) for coagulation in water treatment. Slow base(NaOH) injection into supersaturated aluminum chloride and aluminum sulfate solutions did produce high yields of Al polymers useful to water treatment applications. The method of characterization analysis was based on timed spectrophotometer with ferron as a color developing reagent. The hydrolytic Al species were divided into $monomeric(Al_a),\;polymeric(Al_b),\;and\;precipitate(Al_c)$ from the difference in reaction kinetics. The analysis of PACl's characteristics showed that the quantity of polymeric Al produced at value of$ r(OH_{added}/AI)=2.2$ was $83\%$ of the total aluminum in solution, as showing maximum contents and precipitated Al was dramatically increased when r was increased above 2.35. In addition, the characteristics of polyaluminum sulfate (PAS) showed that polymeric Al contained at r = 0.75 was $18\%$ of the total aluminum in solution. The synthesized PACI and PAS were stable during storing period, as indicating negligible aging effect. The effect of sulfate ion on PACI was dependent on the concentration of sulfate ion. That is, polymeric species decrease and precipitate species increase as sulfate ion concentration increased. It can be concluded that the sulfate cause the formation of $Al(OH)_{3(S)}$ at low pH. However, The effect of calcium ion was negligible for distribution of Al species.

• Resources Recycling
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• v.23 no.3
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• pp.37-43
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• 2014

A study has been made on the recovery of tin and copper from waste solder stripper by oxalate precipitation. With the increasing of the oxalic acid addition, tin was precipitated effectively and removed above 99.5% of tin when the oxalic acid, in an amount 1.0-1.5 times the stoichometric requirement, was added. But, in this case, only 2.0% of copper was precipitated and lead, iron were not precipitated. So, tin was selectively removed from the waste solution. With the increasing of the reaction temperature, the removal percentage of tin was increased and maximum value at arounf $60^{\circ}C$ and decreased with increase in the temperature any more. After filtering the precipitate and drying in oven, $SnO_2$ was obtained from the precipitate. After removal of tin in stripping solution, above 91% of copper was selectively removed by Cu-oxalate by addition of oxalic acid.

• Microbiology and Biotechnology Letters
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• v.42 no.2
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• pp.114-120
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• 2014

This study evaluated the effect of the zeta potential of silica-alumina on the behavior, in terms of purity, yield, fractional precipitation time, precipitate shape, size of fractional precipitation in the increased surface area, and the fractional precipitation process, for the purification of paclitaxel. As the zeta potential value of silica-alumina increased, the yield of paclitaxel concurrently increased while the precipitation time decreased. The use of alumina with the highest value of the zeta potential (+35.41 mV) as a surface area-increasing material dramatically reduced the precipitation time by 12 h compared with the results of the control. On the other hand, the purity of paclitaxel had almost no effect on changes in the zeta potential of silica-alumina. In addition, the precipitate size was inversely correlated with the absolute value of the zeta potential.

• Nuclear Engineering and Technology
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• v.52 no.1
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• pp.123-134
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• 2020

The interaction between UN and CdCl₂ in the LiCl-KCl molten eutectic was studied at 773 K. The reaction was controlled by sampling the melt, as well as by analysis of the resulting precipitate. The process was shown to proceed according to several parallel reactions. The summary reaction was determined to have two stages: a fast one and a slow one. The 19-53% UN → UCl₃ conversion was obtained for the molar ratio of CdCl₂/UN = 1.22-14.9. The rest of UN converts into the precipitate of complex composition (UNCl + U₂N₃ + U₄N₇ + UN₂). The increase in the CdCl₂/UN molar ratio from 1.22 to 14.9 resulted in the decrease in duration of the first "fast" stage of the process from 18 h to 1 h.

• Korean journal of food and cookery science
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• v.2 no.2
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• pp.55-61
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• 1986

This study was attempted to investigate the occurrence and the partial characteristics of pectinesterase (PE) in cucumbers. And the involvement of endogenous cucumber PE with the formation of insoluble pectic acid, in the presence of endogenous or added calcium ions, was also studied. The results of this study are as follows: 1) PE activity was detected in whole cucumber homogenate. 2) The optimum pH and temperature of this enzyme were found to be 8.5 and $50^{\circ}C$, respectively 3) When PE extract was added to 0.25% pectin solution, pectin gel was formed. The time required for the formation of pectin gel was reduced when the pectin solution was adjusted to the optimum conditions for PE activity(pH 8.5, $50^{\circ}C$) and $CaCl_2$ was added. 4) Cucumber juice which was heated to $100^{\circ}C$ for 10 minutes fatted to form any insoluble pectate precipitate. The formation of precipitate in cucumber juice was accelerated by preheating to $50^{\circ}C$, adjusting to pH 8.5 and addition of $CaCl_2$. 5) These results can be interpreted that endogenous PE in cucumber juice demethylates pectin, allowing interlinking of pectin molecules via divalent cation $(Ca^{++})$ and thus forming insoluble Ca-pectate. Therefore additional firming effects of cucumber can be expected to be obtained through activation of PE in conjunction with calcium ions.

• Korean Journal of Metals and Materials
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• v.48 no.1
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• pp.39-48
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• 2010

In order to investigate the effects of tempering temperature and heat-treatment path on the microstructural and mechanical properties of ASTM Gr.92 steels, four samples with different tempering temperatures and heat-treatment paths wer prepared. THeree experimental steels showed tempered martensitic microstructures, but the sample tempered at $810^{\circ}C$ was presumed to retain partially untempered martensitic microstructures due to a lower ${\alpha}$+${\gamma}$ phase regime. $M_{23}C_6$, V(C,N), and Nb(C,N) precipitates were observed in all samples. In addition $Cr_2N$ was observed to be precipitated finely and uniformly by isothermal heat-treatment. The lath width and precipitate size in the isothermal heat-treated samples were much smaller than those of the tempered-only specimens. Because of a fine and uniform precipitate, a reduction of lath width would enhance precipitation hardeing, and it was shown that mechanical propertiesincluding the hardness and tensile properties of the steels were improved by isothermal heat-treatment.

• Korean Journal of Materials Research
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• v.30 no.12
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• pp.678-686
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• 2020

Microstructural characteristics of directionally solidified René 80 superalloy are investigated with optical microscope and scanning electron microscope; solidification velocity is found to change from 25 to 200 μm/s under the condition of constant thermal gradient (G) and constant alloy composition (Co). Based on differential scanning calorimetry (DSC) measurement, γ phase (1,322 ℃), MC carbide (1,278 ℃), γ/γ' eutectic phase (1,202 ℃), and γ' precipitate (1,136 ℃) are formed sequentially during cooling process. The size of the MC carbide and γ/γ' eutectic phases gradually decrease with increasing solidification velocity, whereas the area fractions of MC carbide and γ/γ' eutectic phase are nearly constant as a function of solidification velocity. It is estimated that the area fractions of MC carbide and γ/γ' eutectic phase are determined not by the solidification velocity but by the alloy composition. Microstructural characteristics of René 80 superalloy after solid solution heat-treatment and primary aging heat-treatment are such that the size and the area fraction of γ' precipitate are nearly constant with solidification velocity and the area fraction of γ/γ' eutectic phase decreases from 1.7 % to 0.955 %, which is also constant regardless of the solidification velocity. However, the size of carbide solely decreases with increasing solidification velocity, which influences the tensile properties at room temperature.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.20 no.2
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• pp.193-207
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• 2022

Thermodynamically, TRUO_x, REO_x, and SrO_x can be chlorinated using ammonium chloride (NH₄Cl) as a chlorinating agent, whereas uranium oxides (U₃O₈ and UO₂) remain in the oxide form. In the preliminary experiments of this study, U₃O₈ and CeO₂ are reacted separately with NH₄Cl at 623 K in a sealed reactor. CeO₂ is highly reactive with NH₄Cl and becomes chlorinated into CeCl₃. The chlorination yield ranges from 96% to 100%. By contrast, U₃O₈ remains as UO₂ even after chlorination. We produced U/REO_x- and U/SrO_x-simulated fuels to understand the chlorination characteristics of the oxide compounds. Each simulated fuel is chlorinated with NH₄Cl, and the products are dissolved in LiCl-KCl salt to separate the oxide compounds from the chloride salt. The oxide compounds precipitate at the bottom. The precipitate and salt phases are sampled and analyzed via X-ray diffraction, scanning electron microscope-energy dispersive spectroscopy, and inductively coupled plasma-optical emission spectroscopy. The analysis results indicate that REO_x and SrO_x can be easily chlorinated from the simulated fuels; however, only a few of U oxide phases is chlorinated, particularly from the U/SrO_x-simulated fuels.