The primary oxide components of the bottom ash and the vitrified bottom ash slag from municipal solid waste incineration (MSWI) are CaO, Al2O3, SiO2, Fe2O3, Na2O and MgO. As a main subsystem, CaO-Na2O-SiO2 is found to be important for the phase transformation during thermal processing of the bottom ash. In the present work, thermodynamic modeling was carried out on this ternary oxide system based on literature data and authors own the experimental results. The modified associate species model was chosen to perform the assessment and calculations, which allows a more accurate representation of the thermodynamic properties over a wide concentration range of the complex oxide system, especially for high silica composition region. The Na2O-SiO2 phase diagram calculated with the newly generated database is in a good agreement with the experimental results. The pseudobinary systems CaO·SiO2-Na2O·SiO2 and Na2O·2SiO2-Na2O·2CaO·3SiO2 were evaluated. The phase diagram in the more than 50 wt％ silica region of the ternary system is predicted reasonably well in comparison with experimental data. The phase relations in low SiO2-containing area and phase Na2O·3CaO·6SiO2 need to be further refined. A group of model parameters was obtained which will be used to evaluate quaternary and more complex oxide systems in the future.
Zhan ZHANG Yanping XIAO Jack VONCKEN Yongxiang YANG Rob BOOM Nan WANG Zongshu ZOU
Department of Materials Science and Engineering, Delft University of Technology, 2628 CD, Delft, The Department of Materials Science and Engineering, Delft University of Technology, 2628 CD, Delft, The Department of Geotechnology, Delft University of Technology, 2628 CN, Delft, The Netherlands Department of Materials Science and Engineering, Delft University of Technology, 2628 CD, Delft, The Department of Ferrous Metallurgy, Northeastern University, 110819, Shenyang, China