Keun-Young Lee

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.

Comparative study of simultaneous removal of As, Cu, and Pb using different combinations of electrokinetics with bioleaching by Acidithiobacillus ferrooxidans

Different designs of electrokinetics were applied to simultaneously remove arsenic, copper, and lead from contaminated soils. Single electrokinetics (control) resulted in superior removal efficiencies for Cu (73.5%) and Pb (88.5%), though the removal of As (3.11%) was relatively little. Sequential bioelectrokinetics of bioleaching with Acidithiobacillus ferrooxidans and electrokinetics enhanced the removal of As (25%), while Pb exhibited a significant decrease in removal efficiency (10.6%), due to the formation of insoluble compounds. In order to improve the overall performance, integrated bioelectrokinetics was designed by inoculating A. ferrooxidans into the electrolyte after 5 or 15 days of electrokinetics. Lead (75.8%) and copper (72%) were effectively removed through electrokinetics, after which arsenic (35%) was more efficiently removed by bioleaching-enhanced electrokinetics. A pilot-scale experiment indicated that integrated bioelectrokinetics is an effective means of remediation of soils contaminated with multiple heavy metals and arsenic.

Evaluation of the Behavior of Uranium Peroxocarbonate Complexes in Na–U(VI)–CO3–OH–H2O2 Solutions by Raman Spectroscopy

In this work, the formation of uranium species and their stabilities in Na-U(VI)-CO(3)-OH-H(2)O(2) solutions at different pHs are studied by Raman spectroscopy. In this solution, the UO(2)(O(2))(CO(3))(2)(4-) species was formed together with three other uranium species of UO(2)(O(2))(2)(2-), UO(2)(CO(3))(3)(4-), and a speculated uranium species of the uranyl carbonate hydroxide complex, UO(2)(CO(3))(x)(OH)(y)(2-2x-y), which showed remarkable Raman peaks at approximately 769, 848, 811, and 727 cm(-1), respectively. The UO(2)(O(2))(CO(3))(2)(4-) species disappeared at pH conditions where bicarbonate dominated, and its Raman peak could be clearly observed in only a narrow pH range from approximately 9 to 12. When the pH of the solution increased further, the UO(2)(O(2))(CO(3))(2)(4-) species changed to UO(2)(CO(3))(3)(4-) and the UO(2)(CO(3))(x)(OH)(y)(2-2x-y) species. Moreover, the UO(2)(O(2))(CO(3))(2)(4-) species continuously decomposed into uranyl tricarbonate in the carbonate solution at an elevated temperature because of the instability of the peroxide ion, O(2)(2-), in alkaline conditions.

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.

Treatment of radioactive waste seawater by coagulation–flocculation method using ferric hydroxide and poly acrylamide

This work studied a coagulation–flocculation system using ferric hydroxide and poly acrylamide flocculant to find the effective condition to remove the radionuclides of Co, Mn, Sb, Ru, and Sr remaining in solution after Cs removal by adsorption for the treatment of radioactive waste seawater generated in a disastrous nuclear power plant accident like Fukushima Daiichi. The coagulation–flocculation mechanism was studied, and the performance characteristics of the coagulation–flocculation system was evaluated in views of decontamination yield of the elements, residual turbidity of treated solution, settling speed of flocs, and generated total floc volume, etc. The total removal yield of target radio nuclides of Co, Mn, Sb, and Ru was more than 99% in seawater at pH 8.

Evaluation of recovery characteristic of acidic and alkaline solutions from NaNO3 using conventional electrodialysis and electrodialysis with bipolar membranes

We compared the electrodialysis performance for HNO3 and NaOH recovery from NaNO3 solution by conventional electrodialysis (ED) and electrodialysis with bipolar membranes (EDBM) at constant current and constant voltage. The individual resistances of the components of the electrodialysis systems were also evaluated. The electrodialysis extent for HNO3 and NaOH recovery from NaNO3 solution was almost proportional to the total amount of electricity supplied to the system, regardless of the operation mode and the electrodialysis systems. For the same volume of feed solution, the energy consumption and current efficiency differed depending on the operation mode and the electrodialysis system. In both the ED and EDBM systems, the conductivity of the feed solution strongly affected the overall cell resistance after approximately 50% of the ions in the feed solution had migrated.

Application of Waste Resources for the Stabilization of Heavy Metals (Pb, Cu) in Firing Range Soils

In this study, a heavy metal stabilization treatment using waste resource stabilizing agents was utilized on army firing range soil contaminated with Pb and Cu. Both calcined oyster shells (COS; 5% w/w) and waste cow bone (WCB; 3% w/w) were applied for a wet-curing duration of 28 days. Following the stabilization treatment, the process efficiency was evaluated by various extraction methods for Pb and Cu. Neutral and weak acid extraction methods, such as water soluble extraction and SPLP, did not show positive results for heavy metal stabilization with very low leachability. On the other hand, TCLP and 0.1 N HCl extraction showed that the stabilizing agents significantly reduced the amount of the heavy metals leached from the soil, which strongly supports that the treatment efficiency is positively evaluated in acidic leaching conditions. Specifically, in the 0.1 N HCl extraction, the reduction efficiencies of Pb and Cu leaching were 99.9% and 83.9%, respectively. From the sequential extraction results, a difference between Pb and Cu stabilization was observed, which supports that Pb stabilization is more effective due to the formation of insoluble Pb complexes. This study demonstrates that the application of waste resources for the stabilization of heavy metals is feasible.

A Concept for an Emergency Countermeasure Against Radioactive Wastewater Generated in Severe Nuclear Accidents Like the Fukushima Daiichi Disaster

Abstract This work studied a concept of prompt countermeasure to minimize the accumulation of radioactive wastewater generated in severe nuclear accidents like the Fukushima Daiichi accident. A sequential precipitation process for the removal of Cs, Sr, I, and residual nuclides of Co, Mn, Sb, and Ru was suggested as a way to embody this concept. The process was confirmed to be possible as an effective and rapid emergency treatment for radioactive wastewater using many experiments with non-radioactive and active nuclides. Cobalt ferrocyanide—impregnated chabazite zeolite, Ba-impregnated 4A zeolite, and Ag-impregnated 13X zeolite were chosen as adsorbents for Cs, Sr, and I in this work had very high selectivities and fast adsorption rates with decontamination factors (DFs) on the order of 102 to 103. The adsorbent powders were rapidly settled in solution within 5 to 10 min by adding a coagulant of ferric ions. The residual nuclides could be removed by coprecipitation using ferric ion and flocculation using anionic polyacrylamide with DFs of more than 100 within 10 min.

Evaluation of the stability of precipitated uranyl peroxide and its storage characteristics in solution

This work studied the stability of uranyl peroxide, which can be obtained as the final product of several processes to treat uranium mixture waste and uranium ore, in solution using various temperature, pH, and ionic strength conditions. The change in concentration of dissolved uranium and hydrogen peroxide from uranyl peroxide, the form of the dissolved uranium species, and the change in morphology of dissolved uranyl peroxide were investigated for 100 or more days. Uranyl peroxide was stable in distilled water at elevated temperatures, but dissolved in other solutions at temperatures higher than 40 °C; a greater amount of uranyl peroxide dissolved in more acidic conditions at elevated temperatures. Uranyl ions that dissolved from uranyl peroxide were able to be recovered as uranyl peroxide in the solution where the dissolution occurs by adding hydrogen peroxide. After the precipitation of uranyl peroxide, the uranyl concentration in the supernatant is low enough for the supernatant to be recycled or released into the environment. The morphologies of the partially dissolved uranyl peroxide and the re-precipitated uranyl peroxide from dissolved uranyl ions were different from that of the initial uranyl peroxide.