Choon Han

Reduction of COD and Color of Acid and Reactive Dyestuff Wastewater Using Ozone

Wastewaters obtained from bromamine acid dye and reactive dye manufacturing were treated by ozone bubbling in a cylindrical batch reactor for the purpose of reducing COD to below 150 mg/L, which is the environmental discharge standard of the Republic of Korea. Remarkable COD reduction and decolorization were observed at pH over 11. High inlet gas flowrate and high concentration of ozone gave better results. Little precipitation was observed under the conditions of remarkable COD reduction. At pH of 11, 15 LPM of inlet gas flowrate and 89.3 g/Nm3 of ozone flowrate, the COD of bromamine acid dyestuff wastewater was reduced to 95 mg/L after 90 minutes, and the COD of reactive dyestuff wastewater was reduced to 120 mg/L after 120 minutes. Decolorization was completed after 30 minutes of reaction.

Synthesis of single phase aragonite precipitated calcium carbonate in Ca(OH)2-Na2CO3-NaOH reaction system

The formation behavior of precipitated calcium carbonate polymorphs was investigated in three different supersaturation levels. Because the most easily adjustable and influential variable determining supersaturation is the ion concentration of the major reactants — Ca2+ and CO332− — the supersaturation can be adjusted by changing the ion concentration of these two ions. At high supersaturation, free energy is necessary for a decrease in nucleation, promoting the formation of a sphere-shaped vaterite, while aragonite and calcite were seen to co-exist at medium supersaturation. At low supersaturation, aragonite was mainly formed by mixing with some calcite. Hence, we considered that lower supersaturation was necessary to obtain a single phase aragonite. Furthermore, we found that the solubility of Ca(OH)2 was decreased with the addition of NaOH by a common ion effect. Thus, it is possible to perform an experiment at a lower Ca2+ concentration. The aragonite was synthesized by adding the Na2CO3 solution to the Ca(OH)2 slurry containing several concentrations of NaOH solution at 75°C and under the addition rate of Na2CO3 at 3 ml/min. The formation yield of calcite decreased when the NaOH concentration was increased. In conclusion, in the case of the reaction of the 2.5 M NaOH solution over 210 minutes, single-phase aragonite with an aspect ratio of 20 was obtained.

Characteristics of Uranium Adsorption/Desorption using Anion Exchange Resin

In this study, adsorption/desorption characteristics of uranium ion was investigated using an anion exchangeresin. After anionization of uranyl(UO2) ion, batch tests were conducted using A500/2788 as an anion exchange resin. Adsorption tests were conducted for various concentrations of acid, temperatures, concentrations of uranium ions and adroption times whereas desorption tests were conducted for various concentrations of H2SO4 and reaction times. According to test results, the highest adsorption of uranium ion was obtainde in 0.01 M H2SO4 solution while the adsorption decrease in the strong acidic solution. Also, the adsorption rate was found to adsorption capacity. Furthermore, the adsorption results were found to respond well to Langmuir isotherm equation and follow the pseudo second-order kinetic model. In case of desorption tests, the high desorption was obtained in concentrated H2SO4 solutions. Desorption of more than 70% was obtained at the beginning of 60 minutes while the desorption rate decreased gradually and reached to the equilibrium after 6 hours.