Junjie Fan

A novel hydrothermal method to convert incineration ash into pollucite for the immobilization of a simulant radioactive cesium

The Fukushima nuclear accident in Japan on March 11, 2011 produced huge amounts of Cs-polluted incineration ashes; conventional solidification methods seem unsuitable for the treatment of large amounts of Cs-polluted ashes. A novel hydrothermal method was developed to directly convert Cs-polluted incineration ash (rice husk ash) into pollucite to immobilize Cs in its crystal structure in situ. Results revealed that pollucite could be synthesized readily over a wide range of added Cs (Cs/Si=0.2-0.6); the addition of more Cs (Cs/Si≥0.5) caused the formation of a small amount of cesium aluminosilicate (CsAlSiO4), which exhibits poor immobilization behavior for Cs. Pollucite could be formed even for a short curing time (1h) or at a low curing temperature (150°C). However, a high curing temperature or a long curing time favored the formation of a pure pollucite. With the added calcium hydroxide, a tough specimen with a flexural strength of approximately 22MPa could be obtained, which suggested that this technology may be applied directly to the solidification of Cs-polluted incineration ashes. Hydrogarnet and tobermorite formations enhanced the strength of the solidified specimens, and meanwhile the formed pollucite was present in a matrix steadily. Leaching test demonstrated that the amount of Cs that leached from the synthesized specimens was very low (0.49×10(-5)-2.31×10(-5)) and even lower than that from the reference hollandite-rich synroc (2.0×10(-2)), although a higher content of Cs was found in the synthesized pollucite specimens (6.0-31.7%) than in the reference (3.7%). Therefore, the hydrothermal conversion of Cs-polluted incineration ash into pollucite can be applied to immobilize Cs directly.

Hydrothermal solidification behavior of municipal solid waste incineration bottom ash without any additives

Municipal solid waste incineration (MSWI) bottom ash could be solidified with and without slaked lime (calcium hydroxide) addition by a hydrothermal method under steam pressure of 1.56 MPa at 200 °C for up to 72 h. Experimental results showed that CSH gel or tobermorite exerted a main influence on strength development, and without any additives CSH gel was easy to form, while slaked lime addition favored to form tobermorite. Tobermorite seemed to exert a larger effect on the strength development than CSH gel. Leaching results showed that the concentrations of heavy metals dissolved from the solidified specimens were effectively reduced after hydrothermal processing. The immobilization was mainly due to the tobermorite or CSH gel formation, and Pb2+ and Zn2+ seemed to be fixed more readily than Cr6+, which might be the reason that the structural Ca2+ within tobermorite or CSH gel was exchanged by Pb2+ and Zn2+ more easily than Cr6+. In addition, there existed a close relationship between leaching concentration and strength enhancement, and a higher strength seemed to exert a larger effect on immobilization of heavy metals.

Synthesis and microstructure analysis of autoclaved aerated concrete with carbide slag addition

Synthesis of autoclaved aerated concrete (AAC) has been carried out with carbide slag addition, and the carbide slag could be used as a main material to produce the AAC with the compressive strength about 2 MPa and the density below 0.6 g·cm−3. In this study, quartz sand acted as frame structure phase in the matrix, and quartz addition also influenced the Si/Ca of starting material. Tobermorite and CSH gel were formed readily at 62%, which seemed to enhance the compressive strength of samples. Curing time seemed to affect the morphology of phase produced, and specimen with the plate-like tobermorite formed at 10 h appeared to have a better compressive strength development than the fiber-like one at 18 h. The higher curing temperature seemed to favor the tobermorite and CSH gel formation, which also exerted a significant effect on the strength development of the samples. On the micro-scale, the formed CSH gel was filled in the interface of the matrix, and the tobermorite appeared to grow in internal-surface of the pores and interstices. The tobermorite or/and CSH formation seemed to densify the matrix, and therefore enhanced the strength of the samples.

Hydrothermal synthesis of rock to immobilise nuclide Cs

Abstract To deal with the soil polluted by radioactive nuclide Cs like that in Fukushima, Japan. As pollucite evolves via analcime into clay mineral finally in nature, the analcime and final pollucite should be synthesized from clay minerals. A hydrothermal technology has been applied to synthesize rock to immobilize radioactive Cs within soil for this purpose. The results showed that Gmelinite seemed to precipitate at lower Na/Al molar ratio of starting materials easily, while analcime formed at higher Na/Al. Pollucite was synthesized with meta-kaolin and different Cs compounds (CsOH or CsCl), and more pollucite was formed by CsOH addition, while Cs located inside structure of analcime (solid solution) with addition of CsCl. The pollucite morphology added by CsOH exhibited nano-scale spheroidal aggregate, while analcime gave morphology of triakioctahedron and hexagonal prism.

Hydrothermal synthesis of tobermorite from diatomite and its adsorption performance for methylene blue

Abstract Disposal of dyes wastewater effluents is one of the most important factors in many industries. Methylene blue is the most commonly used dyes in industries and is very difficult to degrade due to its complex structures. Diatomite is one of the excellent adsorbents owing to its unique properties. However, the small powder form of diatomite, which leads to a large amount sludge produced easily, has limited its wide application in environmental engineering. In our study, diatomite was solidified hydrothermally at low temperature (≤ 200°C) on the basis of sustaining the inherent properties of diatomite. The results showed that tobermorite was found to exert a positive effect on its strength and porosity, and also had higher methylene blue adsorption capability compared with diatomite. The thermodynamic parameters indicated that the adsorption of methylene blue with tobermorite formation was an endothermic and spontaneous process.