In this study, we evaluated the performance of phosphate-functionalized silica in adsorbing uranium and provided insights into optimizing the initial conditions of the uranium solution (concentration and pH), which are often overlooked in uranium adsorption studies. While most studies take into account the effect of pH on both the surface charge of the adsorbents and the dissolved speciation of uranium in solution, they often overlook the formation of solid phases such as β-UO2(OH)2 (cr) and UO3· 2H2O(cr), leading to an overestimation of the adsorption capacity. To address this issue, we considered the speciation of U(VI) calculated using thermodynamic data. Our findings suggest that it is reasonable to evaluate the adsorption performance at pH 4 and concentration below 1.35 mM. The formation of β-UO2(OH)2 (cr) starts at 23 μM (pH 5) and 1 μM (pH 6) and increases sharply with increasing concentration. To avoid interference from the formation of solid phases, experiments should be conducted at lower concentrations, which in turn require very small msorbent/Vsolution ratios. However, controlling small amounts of sorbent can be challenging, and increasing the volume of the solution can generate significant amounts of radioactive waste. We also used UV-vis spectra analysis to investigate the formation of solid phases. We found that a 100 mg L-1 uranium solution resulted in the formation of colloidal particles in the solid phase after 2.5 hours at pH 6, while at pH 4, no significant changes in absorbance were observed over 120 hours, indicating a stable ion phase. Based on these conditions, we obtained an excellent adsorption capacity of 110 mg g-1.

The radiolytic decomposition of oxalic acid was investigated using gamma irradiation for decontamination of nuclear power systems. The study used high-purity analytical grade chemicals, with initial concentrations of oxalic acid prepared at 1, 2, 5, and 10 mM, and the initial pH was adjusted to 2-3 at each test condition. Gamma irradiation was performed using a high-level Co-60 source, and absorbed doses were 5, 10, 20, 30, and 50 kGy. The results showed that the efficiency of gamma irradiation decreased with longer gamma exposure time, and the G-value increased with the initial concentration of oxalic acid. Interestingly, the G-value decreased with accumulated radiation dose, but the removal increased. The dose constant ranged from 0.1695 to 0.0536 kGy-1 at different initial concentrations, and the G-value was inversely proportional to the dose constant. The study concluded that oxalic acid was successfully degraded by gamma irradiation, and 92% removal was obtained at the initial concentration of 10 mM. The mineralization of oxalic acid at higher concentrations was more difficult due to the great number of generated intermediates.

Phosphorus (P) removal by aluminum sulfate solution was investigated with varying pH and initial P concentrations. P removal was the highest at around pH 6. The pH range where P removal occurred was slightly wider at higher initial P concentrations. Compared to theoretical calculations, it was confirmed that AlPO4 precipitation was the main reason for P removal at low pH. At high pH, where there should be no AlPO4 precipitates, the P removal by adsorption of amorphous Al(OH)3 precipitates was experimentally observed. The P removal by adding amorphous Al(OH)3 precipitates prepared before the adsorption experiments, however, was lower than that by injecting aluminum sulfate solution because the prepared precipitates became larger, leading to less specific surface area available for adsorption. Ions other than sulfate had little influence on P removal.

고 에너지 (1.5 MeV) 이온 주입된 Boron의 농도와 silicon 기판의 초기 산소 농도의 변화에 따라 silicon기판에 형성된 결정 결함 및 금속 불순물의 Gettering 효율에 대하여 DLTS(Deep Level Transient Spectroscopy), SIMS(Secondary ion Mass Spectroscopy), BMD(Bulk Micro-Defect) analysis 및 TEM (Transmission Electron Microscopy)을 이용하여 연구하였다. 이온 주입 전후의 DLTS 결과를 확산로 및 RTA를 이용한 열처리 전후의 DLTS 결과와 비교할 때 이온 주입 전 시편에서 볼 수 있는 공공에 의한 깊은 준위는 열처리 온도의 증가에 따라 금속 불순물과 관련된 깊은 준위로 천이함을 알 수 있다. 또한 고온 열처리의 경우, 초기 산소 농도가 높을수록 깊은 준위의 농도가 감소함을 볼 때 초기 산소 농도가 높을 수록 gettering 효율 측면에서 유리한 것으로 사료된다