Mechanism of high concentration phosphorus wastewater treated by municipal solid waste incineration fly ash

Abstract

The mechanism of removing phosphate by MSWI (municipal solid waste incineration) fly ash was investigated by SEM (scanning electron microscopy) with EDS (energy dispersion spectrum), XRD (X-ray diffraction), FT-IR (Fourier transform infrared spectroscopy), BET (specific surface area), and BJH (pore size distribution). The results indicate that the removal rate of phosphate (100 mg/L) in 50 mL phosphorus wastewater reaches at 99.9% as the dosage of MSWI fly ash being 0.9000 g under room temperature. The specific surface area of MSWI fly ash is less than 6.1 m2/g and the total pore volume is below 0.021 cm3/g, suggesting that the absorption capacity of calcite is too weak to play an important role in phosphate removal. SEM images show that drastic changes had taken place on its specific surface shape after reaction, and EDS tests indicate that some phosphate precipitates are formed and attached onto MSWI fly ash particles. Chemical precipitation is the main manner of phosphate removal and the main reaction is: 3Ca2++2 PO43−+xH2O→Ca3(PO4)2↓·xH2O. Besides, XRD tests show that the composition of MSWI fly ash is complex, but CaSO4 is likely to be the main source of Ca2+. The soluble heavy metals in MSWI fly ash are stabilized by phosphate.