Microwave-Assisted Hydrothermal Treatment with Soluble Phosphate Added for Heavy Metals Solidification in MSWI Fly Ash

摘要

In this work, heavy metals in municipal solid waste incineration (MSWI) fly ash from circulating fluidized bed (CFB) and grate furnaces were solidified by microwave-assisted hydrothermal treatment. Three process additives of NaOH, Na2HPO4, and H2O were investigated to identify the optimal additive for most fly ash samples. The standard solid waste extraction procedure for measuring leaching toxicity, namely, the acetic acid buffer solution method (HJ/T 300-2007), was used to determine the heavy metal toxicity of all samples and experimental products. X-ray fluorescence, X-ray diffraction, and inductively coupled plasma atomic emission spectroscopy were used to determine the characteristics of fly ash, including chemical compositions, mineral structures, and leaching concentrations of heavy metals. The experimental results revealed that Na2HPO4 was an efficient additive in the microwave-assisted hydrothermal process for solidifying heavy metals in fly ash. Under certain conditions, heavy metals were cured completely with only 20 min of microwave heating. Several types of zeolites were formed during the disposal process, which contributed to the solidification of heavy metals. Moreover, PO43-ions also played an important role in curing heavy metals. Microwave-assisted hydrothermal treatment with the Na2HPO4 additive is demonstrated as an effective method for disposal of MSWI fly ash before transfer to landfills. Compared with previous studies, microwave assisted hydrothermal treatment offers a promising technology for management of MSWI fly ash with high efficiency and energy savings.