Extraction of Silica and Iron Oxide from Municipal Solid Waste Incineration Ash and Biomass-fired Power Plant and It’s Application in the Production of Magnetic Mesoporous Silica for Tetracycline Adsorption

Abstract

Municipal solid waste incinerator and biomass power plant byproducts, namely bottom ash (BA) and fly ash (FA), are rich in silica and represent a potential source for the synthesis of silica-based materials. This study investigated the optimal conditions for alkaline fusion to extract silica from BA and FA, resulting in a supernatant solution that served as the source of silica for Magnetic mesoporous silica synthesis. To separate Fe2O3 from the ash, a low-temperature hydrothermal reaction was conducted using acid leaching, followed by efficient separation and extraction with methyl alcohol. Before experimentation, the mineralogical composition of the ashes was determined using X-ray fluorescence. Fourier transform-infrared (FTIR), X-ray diffraction (XRD) pattern, and scanning electron microscopy (SEM) were utilized to analyze the extracted silica and iron oxide from the ashes. Sequential extraction under these conditions yielded 71% extraction efficiency and 81% silica purification. However, the efficiency and purity of iron oxide separation are both relatively low. Subsequently, the silica and magnetic ash derived from the bottom ash were used to synthesize magnetic mesoporous silica (MMS) with a high adsorption capacity TC of 276.74 mg/g. FTIR, XRD, and SEM were also employed to characterize the MMS. Optimal conditions for overnight incubation at 60 °C and a pH of 6-8 were determined. The Langmuir isotherm and pseudo-second-order kinetic models were the optimal fitting models based on isotherm and kinetic equations. The adsorption process was identified as physisorption and spontaneous, as evidenced by the low entropy changes (ΔS°), negative enthalpy changes (ΔH°) of -15.94 kJ/mol, and negative Gibbs free-energy changes (ΔG°).