Young-Hwan Cho

Adsorption of UO22+ on natural composite materials

The prediction of the adsorption behavior of natural composite materials was studied by a single mineral approach. The adsorption of U(VI) on single minerals such as goethite, hematite, kaolinite and quartz was fully modeled using the diffuse-layer model in various experimental conditions. A quasi-thermodynamic database of surface complexation constants for single minerals was established in a consistent manner. In a preliminary work, the adsorption of a synthetic mixture of goethite and kaolinite was simulated using the model established for a single mineral system. The competitive adsorption of U(VI) between goethite and kaolinite can be well explained by the model. The adsorption behavior of natural composite materials taken from the Koongarra uranium deposit (Australia) was predicted in a similar manner. In comparison with the synthetic mixture, the prediction was less successful in the acidic pH range. However, the model predicted well the adsorption behavior in the neutral to alkaline pH range. Furthermore, the model reasonably explained the role of iron oxide minerals in the adsorption of U(VI) on natural composite materials.

Oxidation State Shift of Uranium during U(III) Synthesis with Cd(II) and Bi(III) in LiCl–KCl Melt

Synthesis of U 3+ with Cd 2+ or Bi 3+ was investigated in a LiCl―KCl eutectic melt at 500°C by using cyclic voltammetry (CV) and ultraviolet-visible (UV-vis) spectroscopy. CV results showed that the equilibrium potentials of the species are larger in sequence of U 0/3+ < Cd 0/2+ < U 3+/4+ < Bi 0+/3+ . UV-vis spectroscopy results exhibited that U 3+ was directly produced in the eutectic melt containing Cd 2+ . In BiCl 3 , U metal was oxidized to U 4+ by Bi 3+ , and then U 4+ was reduced to U 3+ by additional U. From these results, the reaction mechanisms taking place during the synthesis are proposed.

Sorption characteristics of137Cs onto clay minerals: Effect of mineral structure and ionic strength

The sorption behavior of137Cs onto kaolinite, bentonite, illite, and zeolite was studied at different ionic strengths of Na+, K+, Ca2+. A significant effect of ionic strengths on the sorption has been observed. Clay minerals with 2∶1 structure (bentonite, illite) showed much higher sorption than that of 1∶1 structure (kaolinite). Zeolite showed high selectivity for137Cs sorption. Sorption behavior of137Cs on clay minerals can be explained by their surface charge characteristics originated from mineral structure.

Scavenging of UO22+ using 4-sulfonic calix[6]arene in the presence of goethite

The scavenging of UO22+ using 4-sulfonic calix[6]arene in the presence of a strong adsorbent was studied as a function of pH. The adsorbent selected was goethite because of its strong affinity for UO22+ and its abundance in natural soils. In order to understand the underlying chemistry of the scavenging process, the adsorption of UO22+ and 4-sulfonic calix[6]arene onto goethite, respectively, and the extraction of adsorbed UO22+ from goethite surface were modeled using the triple-layer model. The model well explained the pH dependence of the adsorption and extraction processes. This work showed that maximum extraction was obtained around pH 10.5 in the presence of 12g/l goethite in the case of a 1:3TU(VI):Tcalixareneratio.

Constituent analysis of metal and metal oxide in reduced SIMFuel using bromine-ethyl acetate

We demonstrated that bromine in ethyl acetate can selectively separate metallic contents in lanthanide metal-oxide mixtures for analysis, which had been validated for uranium. This Br2-EtOAc dissolution method was applied to determine the constituents of metal and metal oxide in SIMFuel that was electrochemically reduced from oxide fuel in the molten salt. Compared with the analysis results obtained after dissolving the fuel in an acid solution, we concluded that the Br2-EtOAc method can be applied to uranium and rare earths but not to noble metals for the reduction yield determination.