Sewage sludge ash contaminated with radiocesium: Solidification with alkaline-reacted metakaolinite (geopolymer) and Portland cement.

This study contributes toward developing measures for the disposal of radiocesium-contaminated sewage sludge ash (SSA). Here, we prepared two types of solidified bodies containing 30 wt% radiocesium-bearing SSA. The material used for the two solidified bodies were alkaline-reacted metakaolinite (geopolymer) and ordinary Portland cement (OPC). Cement has been used for solidification of low-level radioactive wastes, and geopolymer is a candidate of cement alternative materials. The characteristics of these solidified bodies were investigated by various aspects including mechanical strength, transformation of SSA components during solidification, and radiocesium confinement ability by leaching test. The compressive strength of geopolymer- and OPC-solidified bodies at 30 wt% SSA content was more than 40 MPa. After static leaching test at 60 °C, 137Cs was hardly leached out from the geopolymer-solidified bodies containing SSA at 30 wt% to ultrapure water (<0.1%), whereas more than 30% 137Cs was leached from the OPC-solidified bodies containing SSA at 30 wt% even though only ~9% of 137Cs in the SSA is soluble. These results strongly indicate that geopolymer is far superior to OPC for solidifying radiocesium-bearing SSA.

Proposed Cesium-free Mineralization Method for Soil Decontamination: Demonstration of Cesium Removal from Weathered Biotite.

The removal possibility of sorbed Cs from weathered biotite (WB), which is considered a major Cs adsorbent in the soil of Fukushima, has been investigated by the addition of an NaCl-CaCl2 mixed salt powder with a 1:1 ratio of Na and Ca and subsequent heat treatment under a reduced pressure of 14 Pa. X-ray fluorescence analysis was used to determine the Cs removal rate at elevated temperatures. The structural changes and new phases formed were determined using powder X-ray diffraction as well as electron diffraction and X-ray microanalysis in a transmission electron microscope. We found that Cs was completely removed from the specimen heated at 700 °C, where WB completely decomposed and augite was formed. On the basis of this finding, we propose the Cs-free mineralization method as a new soil-decontamination process in which Cs minerals are transformed by heating with certain additives into minerals that cannot incorporate Cs.

Mechanism of Cs Removal from Fukushima Weathered Biotite by Heat Treatment with a NaCl-CaCl2 Mixed Salt.

An in situ extended X-ray absorption fine structure (in situ EXAFS) spectroscopic analysis at high temperature was conducted to investigate the mechanism of Cs removal from weathered biotite (WB) from Fukushima, induced by heating with a mixed salt of NaCl and CaCl2. This indicated that most Cs remained in WB during heating at 200-700 °C. In addition, the in situ EXAFS spectra gradually changed on heating with the mixed salt and a completely different spectrum was observed for the sample after cooling from 700 °C to room temperature (RT). Ex situ EXAFS measurements and X-ray fluorescence analyses were also conducted on samples after heat treatment and removal of the mixed salt to clarify the temperature dependence of the Cs removal ratio. On the basis of the results of radial structure function analysis obtained from in situ EXAFS, we concluded that almost all of the Cs was removed from WB by heating at 700 °C with the mixed salt, and that Cs formed Cs-Cl bonds after cooling to RT from 700 °C. In contrast, although more than half of the Cs present was removed from WB by heat treatment at 500 °C, most Cs was surrounded by silica tetrahedrons, maintained by Cs-O bonds. On the basis of these results, different Cs removal processes are suggested for the high-temperature (600-700 °C) and low-temperature (400-500 °C) regions.

Use of a DNA film on a self-assembled monolayer for investigating the physical process of DNA damage induced by core electron ionization.

PURPOSE: A novel two-layer sample composed of a deoxyribonucleic acid (DNA) film and self-assembled monolayer (SAM) was prepared on an inorganic surface to mimic the processes in which DNA is damaged by soft X-ray irradiation. MATERIALS AND METHODS: A mercaptopropyltrimethoxysilane (MPTS) SAM was formed on a sapphire surface, then oligonucleotide (OGN) molecules were adsorbed on the MPTS-SAM. The thicknesses and chemical states of the layers were determined by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray fine structure (NEXAFS) around the phosphorus (P) and sulfur (S) K-edges. To induce the damage to the OGN molecules, the sample was irradiated with synchrotron soft X-rays. The chemical state of the OGN molecules before and after irradiation was examined by NEXAFS around the nitrogen (N) K-edge region. RESULTS: The thickness of the MPTS-OGN layer was approximately 7.7 nm. The S atom of the OGN molecules was located at the bottom of the OGN layer. The peak shape of the N K-edge NEXAFS spectra of the MPTS-OGN layers clearly changed following irradiation. CONCLUSIONS: The MPTS-OGN layer formed on the sapphire surface. The chemical states and the structure of the interface were elucidated using synchrotron soft X-rays. The OGN molecules adsorbed on the MPTS films decomposed upon exposure to soft X-ray irradiation.

Highly durable carbon-supported Pt catalysts prepared by hydrosilane-assisted nanoparticle deposition and surface functionalization.

Hydrosilane enabled the formation of Pt nanoparticles and the silane functionalization of a carbon support material in one pot. The metal/Si-modified carbon composites are highly durable during catalytic methane oxidation.

Selective adsorption of atomic hydrogen on a h-BN thin film.

The adsorption of atomic hydrogen on hexagonal boron nitride (h-BN) is studied using two element-specific spectroscopies, i.e., near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and x-ray photoelectron spectroscopy (XPS). B K-edge NEXAFS spectra show a clear change in the energy region of the π* band before and after reaction with atomic deuterium. On the other hand, N K-edge NEXAFS spectra show only a little change. B 1s XPS spectra show a distinct component at the low binding energy side of a main component, while N 1s XPS spectra show peak broadening at the high binding energy side. These experimental results are analyzed by the discrete variational Xα method with a core-hole effect and are explained by a model in which hydrogen atoms are preferentially adsorbed on the B sites of h-BN. Based on the experimental and theoretical results, we propose a site-selective property of BN material on adsorption of atomic hydrogen.

Chemical-state-selective mapping at nanometer scale using synchrotron radiation and photoelectron emission microscopy.

For surface analyses of semiconductor devices and various functional materials, it has become indispensable to analyze valence states at nanometer scale due to the rapid developments of nanotechnology. Since a method for microscopic mapping dependent on the chemical bond states has not been established so far, we have developed a photoelectron emission microscopy (PEEM) system combined with synchrotron soft X-ray excitation. The samples investigated were Si/SiO(x) micro-patterns prepared by O(2)(+) ion implantation in Si(001) wafer using a mask. PEEM images excited by various photon energies around the Si K-edge were observed. The lateral spatial resolution of the system was about 41 nm. The brightness of each spot in PEEM images changed depending on the photon energy, due to the X-ray absorption intensity of the respective chemical state. Since the surface of this sample was topographically flat, it has been demonstrated that the present method can be applied to observations of the microscopic pattern, depending not on the morphology, but only on the valence states of silicon. We have also in-situ measured the changes of the PEEM images upon annealing, and elucidated the mechanism of the lateral diffusion of oxygen and valence states of silicon at the nanometer scale.