An elevated temperature is expected at the deep geological repository (DGR) due to the decay heat from spent nuclear fuel and the positive geothermal gradient. The resulting elevated temperature would change the aqueous speciation and surface complexation of uranium, which is the major component in spent nuclear fuel. Since sorption reactions of uranium species on natural minerals determine the extent of uranium retardation, in this work the temperature-dependent adsorption of hexavalent uranium, U(VI), was studied by choosing alumina as the basic component mineral for complex aluminosilicates. Time-resolved laser fluorescence spectroscopy (TRLFS) was used to assess the dissolved and adsorbed U(VI) species on γ-Alumina in the pH range of 6.5–9.0 at temperatures of 25 to 70°C. Initial concentrations of U(VI), carbonate and calcium were 89 μM, 25 mM, and 3.0 mM, respectively. The parallel factor analysis (PARAFAC) was used for chemical speciation by spectrum deconvolution. In addition, a separate solution system with higher U(VI) concentrations (0.1 mM, 1.0 mM) and carbonate concentration of 25 mM was studied with attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy for adsorbed species at 25°C. The electrophoretic mobility measurements were also conducted at 25°C to assess the coordination mechanism of adsorbed species at 25°C. The uranyl hydrolysis species and uranyl tricarbonato species coexist in solution at 25°C. At the same temperature, both species were found to be adsorbed. ATR-FTIR could confirm the adsorption of uranyl tricarbonato species at 25°C, and the electrophoretic mobility measurements suggested that the reaction mechanism is an inner-sphere coordination. However, in comparison with aqueous speciation at 25°C, at elevated temperatures the available pH range of uranyl tricarbonato species was narrow and that for uranyl hydrolysis species was wider. It was evident that two hydrolysis species are adsorbed at elevated temperatures, but no tricarbonato species. The enhanced U(VI) adsorption was observed with temperatures. This could result from the transition of dominance from the concurrent adsorption of uranyl hydrolysis species and uranyl tricarbonato species to two hydrolysis species. It was seen that the trend of enthalpy of adsorption was endothermic. Combining the present results with temperature-dependent adsorption studies on silica and aluminosilicates, a reliable SCM for the subsurface system can be proposed to explain U(VI) migration.

수처리 및 의약바이오 분야에서 유효물질 분리에 활용되고 있는 알루미나 중공사 분리막은 얇은 두께로 인해 취 급 및 적용시 쉽게 파괴되는 단점이 있기 때문에 분리막의 강도를 100 MPa 이상으로 향상시키기 위한 연구가 필요하다. 본 연구에서는 나노입자의 함량을 0, 1, 3, 5 wt%로 증가시켰을 때 제조된 중공사 분리막의 특성을 평가하였다. 그 결과, 나노입 자의 함량이 증가함에 따라 중공사 분리막의 강도는 79 MPa에서 115 MPa로 증가하였으며, 밀도는 1.76 g/m3에서 1.88 g/m3 으로 증가하였고 기공률과 평균기공크기는 각각 51%에서 48%로, 416 nm에서 352 nm로 감소한 것을 확인하였다. 스폰지구 조가 발달하고 스폰지구조의 기공크기가 향상된 알루미나 중공사 분리막은 100 MPa 이상으로 기계적 강도가 향상되었으며, 약 100000 GPU의 높은 질소 투과도 및 약 3000 L/m2h의 높은 물 투과도를 나타내었다. 따라서, γ-알루미나 나노입자를 소 결조제로 첨가하는 것은 α-알루미나 중공사 분리막의 기계적 강도를 효과적으로 증진시키고 높은 투과성능을 유지할 수 있 는 매우 유효한 방법임을 확인하였다.