Study of Preparation of Polyaluminum Ferric Sulfate Flocculant from Municipal Solid Waste Incineration Fly Ash

In this investigation, polyaluminum sulfate (PAFS), an inorganic flocculant, was synthesized using municipal solid waste incineration (MSWI) fly ash. The morphology and structure of PAFS were characterized using x-ray diffraction and Fourier-transform infrared spectroscopy (FTIR). A single-factor flocculation experiment explored the impact of polymerization duration, temperature, stirring speed, and pH on the preparation of PAFS. Optimal removal of kaolin turbidity was achieved with a polymerization time of 60 min, a stirring speed of 100 rpm, a temperature of 40°C, and a pH of 10, resulting in a maximum turbidity removal rate of 32.75%. To enhance the turbidity reduction capability of PAFS, upgraded experiments were conducted using FeSO4·7 H2O as an additive. These experiments demonstrated that the modified flocculant significantly improved turbidity removal, achieving 74.95% under consistent conditions with a pH of 3.5 and an FeSO4·7 H2O addition of 1 g, corresponding to a 1∶5 ratio to fly ash. The characterization of the flocculant revealed that PAFS is a composite material containing hydroxyl groups, iron ions, and chloride ions, forming a network structure of interconnected molecular chains with a dense configuration. The adsorption bridging by high-molecular-weight iron sulfate polymers with branch-like structures plays a critical role in turbidity elimination. This study presents a novel method for the utilization of MSWI fly ash in environmental management.