Ultrasonic-assisted Hydrothermal Synthesis Autoclaved Bricks from Municipal Solid Waste Incineration Fly Ash and Coal Fly Ash (MSWI-FA)

Abstract

Municipal solid waste incineration fly ash (MSWI) is considered as one of the hazardous wastes and requires to be well disposed to reduce the contaminant to the environment. Reference to the production of coal fly ash (FA) bricks, MSWI and FA were utilized to prepare autoclaved MSWI-FA block samples. Ultrasonic-assisted hydrothermal synthesis technology was used for production to explore the effect of ultrasonic pre-treatment. Compressive strength, dry density, and water absorption tests were conducted to determine the optimal ultrasonic parameters. Ultrasonic pre-treating mechanisms were investigated by SEM, FT-IR, particle size analysis, and BET. Furthermore, the micro-analyses of block samples were conducted. The heavy metal leaching concentration was studied to assess the environmental safety. The experimental results show that the ultrasonic pre-treating time, water bath temperature, and ultrasonic power of 3 h, 30 °C, and 840 W are the optimal, under which the compressive strength, dry density, and water absorption were 8.14 MPa, 1 417.48 kg/m³, and 0.38, respectively. It is shown that ultrasound destroys the surface structure of raw materials and smaller FA particles embed into MSWI. The particle size distribution of pre-treated raw materials mixture is wider and total pore volume is decreased by 6.3%. During hydrothermal processing, more Al-substituted tobermorite crystals are generated, which is the main source of higher strength and smaller pore volume of prepared block samples. The solidification/stabilization rates of Cu, Pb, and Zn increased by 30.77%, 4.76%, and 35.29%, respectively. This study shows a feasible way to utilize MSWI as raw material for construction.

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Wuhan University of Technology and Springer-Verlag GmbH Germany, Part of Springer Nature