Seung Soo Kim

Effects of pH and anions on the sorption of selenium ions onto magnetite.

This study analyzes the influence of carbonate and silicate, which are generally abundant in granitic groundwater, on the sorption of selenium ions onto magnetite in order to understand the behaviors of selenium in a radioactive waste repository. Selenite was sorbed onto magnetite very well below pH 10, but silicate and carbonate hindered the sorption of selenite onto magnetite. On the other hand, little selenate was sorbed onto magnetite in neutral and weak alkaline solutions of 0.02 M NaNO(3) or NaClO(4), matching the ionic strength in a granitic groundwater, even though silicate or carbonate was not contained in the solutions. The surface complexation constants between selenite and magnetite were obtained by using a geochemical program, FITEQL 4.0, from the experimental data, and the formation of an inner-sphere surface complex such as =FeOSeO(2)(-) was suggested for the sorption of selenite onto magnetite from the diffuse double layer model calculation.

Sorption of aqueous uranium(VI) ion onto a cation-exchangeable K-birnessite colloid

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 . 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 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 at pH 5.00 and ionic strength of 0.010 M , 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 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.

COMPARISON BETWEEN EXPERIMENTALLY MEASURED AND THERMODYNAMICALLY CALCULATED SOLUBILITIES OF UO₂ AND THO₂ IN KURT GROUND WATER

Solubility of a radionuclide is important for defining the release source term of a radioactive waste in the safety and performance assessments of a radioactive waste repository. When the pH and redox potential of the KURT groundwater were changed by an electrical method, the concentrations of uranium and thorium released from UO₂(cr) and ThO₂(cr) at alkali pH (8.1 ~ 11.4) and reducing potential (Eh -7 mole/L. Unexpectedly, the concentration of tetravalent thorium is slightly higher than that of uranium at pH = 8.1 and Eh= -0.2 V conditions, and this difference may be due to the formation of hydroxide-carbonate complex ions. When UO₂(s) and UO₂(am, hyd.), and ThO₂(s) and Th(OH)₄(am) were assumed as solubility limiting solid phases, the concentrations of uranium and thorium in the KURT groundwater calculated by the PHREEQC code were comparable to the experimental results. The dominating aqueous species of uranium and thorium were presumed as UO₂(CO₃)₃ 4- and Th(OH)₃CO₃ - at pH = 8.1 ~ 9.8, and UO₂(OH)₃- and Th(OH)₄(aq) at pH = 11.4.

Microbial copper reduction method to scavenge anthropogenic radioiodine

Unexpected reactor accidents and radioisotope production and consumption have led to a continuous increase in the global-scale contamination of radionuclides. In particular, anthropogenic radioiodine has become critical due to its highly volatile mobilization and recycling in global environments, resulting in widespread, negative impact on nature. We report a novel biostimulant method to effectively scavenge radioiodine that exhibits remarkable selectivity for the highly difficult-to-capture radioiodine of >500-fold over other anions, even under circumneutral pH. We discovered a useful mechanism by which microbially reducible copper (i.e., Cu2+ to Cu+) acts as a strong binder for iodide-iodide anions to form a crystalline halide salt of CuI that is highly insoluble in wastewater. The biocatalytic crystallization of radioiodine is a promising way to remove radioiodine in a great capacity with robust growth momentum, further ensuring its long-term stability through nuclear I− fixation via microcrystal formation.

Separation of selenite and selenate using magnetite

Selenium is one of the interesting elements in human body, because it`s important micro-nutrient for human health as the essential biological tissue in protein. Selenite () and selenate () are the dominant dissolved selenium species in natural water, and their toxicity and chemical properties are very different each other. Thus it is necessary to separate the two selenium species for understanding selenium behaviors in natural waters. Some reported methods, using an alumina-filled column and an ion chromatography, to separate the selenite and selenite may be difficult to directly apply to the natural water. Therefore magnetite selectively adsorbs selenite and selenate according to pH of solution, the separation of selenite and selenate using a magnetite-filled column was successfully obtained at weak alkali solutions. Moreover, the influence of dissolved anions in natural water at the selenite sorption onto magnetite was also investigated because they could hinder the sorption of selenite onto magnetite. In other to directly apply to the natural water, reactive sites of magnetite should be considered because dissolved silicate in natural water can hinder the adsorption of selenite onto magnetite.