Dejing Tao

Immobilization of simulated radionuclide 133Cs+ by fly ash-based geopolymer

The recent nuclear leak in Japan once again attracted peoples attention to nuclear safety problems. Because of their poor thermal stability, those low-cost materials such as cement and asphalt cannot be used for the solidification of the radioactive wastes. In this work, the solidification behavior of 133Cs(+) by fly ash-based geopolymer was investigated. Leaching tests (carried out in deionized water, sulfuric acid and magnesium sulfate solutions) revealed that the geopolymer solidification had lower cumulative fraction leaching concentration (CFLC) of 133Cs(+) than that of cemented form. The thermal stability (high-temperature and freeze-thaw resistance) and acid-resistance of the geopolymer were also both better than that of cement. The geopolymer solidification block can acquire a compressive strength up to 30 MPa after 2h calcination at 1000 °C. The morphology and mineral phases of the geopolymer and the geopolymer solidification block were characterized by SEM and XRD, and EDX analysis indicated that most of Cs associated with the amorphous geopolymer gel. These results gave encouragement for the idea that the fly ash-based geopolymer could be used as a low-cost and high-efficiency material for the immobilization of radioactive wastes.

Performance of Chloride Ions on Electrocatalytic Oxidation Process Using Ti-Nanotubes/PDDA-PbO2 Anode for Phenol Removal

AbstractThe performance of the electrocatalytic oxidation of phenol on poly(diallyldimethylammonium chloride) (PDDA)–modified PbO2 anodes in the presence of chloride ions was studied. The objective was to elucidate the influence of NaCl dosage, current density, initial phenol concentration, and initial pH on this catalysis process in the presence of Cl−. The results revealed that at low current densities, the presence of Cl− could greatly enhance the current efficiency by electrogenerating active chlorine, and the current density increased, but if competitive adsorption of ·OH radicals occurred, the removal efficiency did not improve significantly and the current efficiency decreased. This indicated that the pH value had a major impact on phenol, with optimal removal observed at approximately pH 6–7. In both acidic and alkaline solutions outside this optimal pH window, the removal efficiency deteriorated. The modified anode performs well for phenol degradation for a wide range of phenol concentrations und...