Jei-Kwon Moon

Preparation of Organic-Inorganic Composite Adsorbent Beads for Removal of Radionuclides and Heavy Metal Ions

Composite ion exchanger beads were prepared to remove the strontium and silver ions in acidic solution. Potassium titanate and nickelferrocyanate powder, which are acid resistant inorganic ion exchangers were synthesized and then mixed with polyacrylonitrile (PAN) binder to form a PAN-potassium titanate and a PAN-nickelferrocyanate composite ion exchanger beads. Spherical composite beads could be obtained by adjusting the viscosities of the composite dope in the range of 700–1000 cP. The composite beads porosities such as macropore volume and pore size were increased in proportion to the contents of PVP (polyvinylpyrrolidone) which was used as the porosity modifying chemical. The synthesized composite ion exchangers were evaluated on their adsorption characteristics for the Ag1 and Sr21 ion solutions of pH 2.

Effects of the different conditions of uranyl and hydrogen peroxide solutions on the behavior of the uranium peroxide precipitation.

The dynamic precipitation characteristics of UO(4) in different solution conditions (pH, ionic strength, uranium and H(2)O(2) concentrations) were characterized by measuring changes in the absorbance of the precipitation solution and by monitoring the change of particle size in a circulating particle size analyzer. The precipitation solution conditions affected the precipitation characteristics such as the induction time, precipitation rate, overall precipitation time, and particle size in a complex manner. With increases in both pH and ionic strength, the induction time was prolonged, and the individual particle size decreased, but the individual particles tended to grow by aggregation to form larger precipitates. The uranium concentration and the ionic strength of the solution affected the induction time and precipitation rate to the greatest extent.

Equilibrium, kinetic and thermodynamic study of cesium adsorption onto nanocrystalline mordenite from high-salt solution.

In this study, the equilibrium, kinetics and thermodynamics of cesium adsorption by nanocrystalline mordenite were investigated under cesium contamination with high-salt solution, simulating the case of an operation and decommissioning of nuclear facilities or an accident during the processes. The adsorption rate constants were determined using a pseudo second-order kinetic model. The kinetic results strongly demonstrated that the cesium adsorption rate of nano mordenite is extremely fast, even in a high-salt solution, and much faster than that of micro mordenite. In the equilibrium study, the Langmuir isotherm model fit the cesium adsorption data of nano mordenite better than the Freundlich model, which suggests that cesium adsorption onto nano mordenite is a monolayer homogeneous adsorption process. The obtained thermodynamic parameters indicated that the adsorption involved a very stable chemical reaction. In particular, the combination of rapid particle dispersion and rapid cesium adsorption of the nano mordenite in the solution resulted in a rapid and effective process for cesium removal without stirring, which may offer great advantages for low energy consumption and simple operation.

Biosorption of uranium(VI) from aqueous solution by biomass of brown algae Laminaria japonica

The uranium(VI) adsorption efficiency of non-living biomass of brown algae was evaluated in various adsorption experimental conditions. Several different sizes of biomass were prepared using pretreatment and surface-modification steps. The kinetics of uranium uptake were mainly dependent on the particle size of the prepared Laminaria japonica biosorbent. The optimal particle size, contact time, and injection amount for the stable operation of the wastewater treatment process were determined. Spectroscopic analyses showed that uranium was adsorbed in the porous inside structure of the biosorbent. The ionic diffusivity in the biomass was the dominant rate-limiting factor; therefore, the adsorption rate was significantly increased with decrease of particle size. From the results of comparative experiments using the biosorbents and other chemical adsorbents/precipitants, such as activated carbons, zeolites, and limes, it was demonstrated that the brown algae biosorbent could replace the conventional chemicals for uranium removal. As a post-treatment for the final solid waste reduction, the ignition treatment could significantly reduce the weight of waste biosorbents. In conclusion, the brown algae biosorbent is shown to be a favorable adsorbent for uranium(VI) removal from radioactive wastewater.

Evaluation of the stability of uranyl peroxo-carbonato complex ions in carbonate media at different temperatures

This work studied the stability of peroxide in uranyl peroxo carbonato complex ions in a carbonate solution with hydrogen peroxide using absorption and Raman spectroscopies, and evaluated the temperature dependence of the decomposition characteristics of uranyl peroxo carbonato complex ions in the solution. The uranyl peroxo carbonato complex ions self-decomposed more rapidly into uranyl tris-carbonato complex ions in higher temperature carbonate solutions. The concentration of peroxide in the solution without free hydrogen peroxide represents the concentration of uranyl peroxo carbonato complex ions in a mixture of uranyl peroxo carbonato complex and uranyl tris-carbonato complex ions. The self-decomposition of the uranyl peroxo carbonato complex ions was a first order reaction, and its activation energy was evaluated to be 7.144×10(3) J mol(-1). The precipitation of sodium uranium oxide hydroxide occurred when the amount of uranyl tris-carbonato complex ions generated from the decomposition of the uranyl peroxo carbonato complex ions exceeded the solubility of uranyl tris-carbonato ions in the solution at the solution temperature.

EVALUATION OF FERROCYANIDE ANION EXCHANGE RESINS REGARDING THE UPTAKE OF Cs + IONS AND THEIR REGENERATION

Ferrocyanide-anion exchange resin was prepared and the prepared ion exchange resins were tested on the ability to uptake ion. The prepared ion exchange resins were resin-KCoFC, resin-KNiFC, and resin-KCuFC. The three tested ion exchange resins showed ion exchange selectivity on the ion of the surrogate soil decontamination solution, and resin-KCoFC showed the best ion uptake capability among the tested ion exchange resins. The ion exchange behaviors were explained well by the modified Dubinin-Polanyi equation. A regeneration feasibility study of the spent ion exchange resins was also performed by the successive application of hydrogen peroxide and hydrazine. The desorption of the ion from the ion exchange resin satisfied the electroneutrality condition in the oxidation step; the desorption of the ion in the reduction step could also be reduced by adding the ion.

Removal of cesium ions from clays by cationic surfactant intercalation

We propose a new approach to remediate cesium-contaminated clays based on intercalation of the cationic surfactant dodecyltrimethylammonium bromide (DTAB) into clay interlayers. Intercalation of DTAB was found to occur very rapidly and involved exchanging interlayer cations. The reaction yielded efficient cesium desorption (∼97%), including of a large amount of otherwise non-desorbable cesium ions by cation exchange with ammonium ions. In addition, the intercalation of DTAB afforded an expansion of the interlayers, and an enhanced desorption of Cs by cation exchange with ammonium ions even at low concentrations of DTAB. Finally, the residual intercalated surfactants were easily removed by a decomposition reaction with hydrogen peroxide in the presence of Cu2+/Fe2+ catalysts.

Design of a heavy-duty manipulator for dismantling of a nuclear power plant

Some of the nuclear power plants in Korea have reached their end of life-cycle, and the importance of developing dismantling techniques has been emphasized. We designed a manipulator for decommissioning a reactor pressure vessel. We analyzed the work environment for disassembly and the workspace of the manipulator, and verified the validity of kinematic variables through a kinematic simulation. We verified through a dynamics simulation that each joint of the designed manipulator can be operated within the maximally allowed torque despite a load of 250 kg. Finally, we verified through the stress analysis that the manipulator is designed to secure at least two times higher safety factor.

Crevice corrosion properties and chemical thermodynamic evaluation of the corrosion system

Abstract Crevice corrosion properties of 304 Stainless Steel (304SS) and Alloy 600 in aqueous oxalic acid solution were evaluated and the results were analyzed by chemical thermodynamic calculation. The corrosion rate of 304SS in the low pH region was highly accelerated, however that of Alloy 600 was not. Crevice corrosion resistance of those alloys critically relies on the formation of protective layer (NiC2O4) which was formed on the surface of Alloy 600 only. FeC2O4 did not contribute to corrosion resistance which was formed on the surface of 304SS at the low pH region.

A Reductive Dissolution Study of Magnetite

Magnetite dissolution tests using a hydrazine base solution were performed at a temperature range of 90 to 150 °C. The dissolution rate of magnetite increased with [N2H4], time, and temperature. The optimum solution pH in the experimental range was 3. The addition of copper ion to the hydrazine base solution greatly increased the magnetite dissolution rate. This was explained by the complex formation between N2H4 and Cu ions, and the reducing power of the hydrazine-Cu complex to the ferric ions of magnetite. The reductive decontamination solution can be applied below 100 °C by the addition of copper ions. The chemical decontamination of a Type 304 stainless steel specimen using a hydrazine base reductive decontamination solution was also performed. The contact dose rate was greatly decreased by the repetitive application of NP and the hydrazine base solution.Copyright