No abstract

The conversion of bottom ash from fluidized‐bed combustion of municipal solid waste (MSW) to zeolite, by means of alkaline hydrothermal treatment (HT), in 1M NaOH solution, is presented in this work. The transformation of the bottom ash was characterized by X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, surface area (BET‐N2), and scanning electron microscopy (SEM) analyses. As a result of the HT at 100°C, Na6[AlSiO4]6·4H2O, of the structural family of zeolites, together with Ca3AlFe(SiO4)(OH)8, of the structural family of hydrogarnets, began to appear; the surface area of the bottom ash increased 11 times. At 150°C, the amount of Na6[AlSiO4]6·4H2O increased and andradite, hydroxylian (Ca3Fe2(SiO4)3−x(OH)4−x), of the structural family of garnet, was formed. After 200°C of HT, Na6[AlSiO4]6·4H2O was massively formed together with aluminum tobermorite (Ca5Si5Al(OH)O17·5H2O); Ca3AlFe(SiO4)(OH)8 decreased. The surface area of the bottom ash increased 13 times. The conversion of bottom ash in zeolite is considered of great significance, opening new opportunities for stabilization and applications of this type of waste. Zeolite and also the other compounds—aluminum tobermorite, andradite, and Ca3AlFe(SiO4)(OH)8—can substitute a variety of ionic species, which allows the bottom ash to be useful for immobilizing toxic and radioactive wastes. An equivalent study was conducted in water instead of NaOH as a reference.

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The effect of the addition of nanosilica on the properties of cement pastes after 28 d of hydration was studied in a multi-scale approach through X-ray diffraction, thermal analysis, nitrogen adsorption analysis, infrared spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and compressive strength tests. The results showed an increase in strength resulting from the pozzolanic nature of the nanosilica, the reduction and refinement of the paste porosity and also the increase of the of calcium-silicate-hydrate gel polymerisation with the addition. Furthermore, NMR spectra suggested that the presence of nanosilica produces an inclusion of the Al 3 ion in the gel structure.