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 PO4 3-+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.
Washing pre-treatment of municipal solid waste incineration(MSWI) fly ash blended with shale and sludge was utilized in the manufacture of light-weight aggregates and processed to form ceramic pellets.A formula uniform design was performed to arrange the mixture ratio of the materials.The optimal mixture ratio of the materials was determined by measuring the bulk density,granule strength,and 1 h water absorption of the pellets.It is shown that the optimal mixture ratios of materials,MSWI fly ash,shale,and sludge,are 23.16%,62.58%,and 14.25%(mass fraction),respectively.The performance testing indicators of light-weight aggregates are obtained under the optimum mixture ratio:bulk density of 613 kg/m3,granule strength of 821N,and 1 h water absorption of 11.6%,meeting 700 grade light-aggregate of GB/T 17431.2-1998 standard.The results suggest that utilization of MSWI fly ash in light-weight aggregates is an effective method and a potential means to create much more values.
To analyze the feasibility of utilization of thermal technology in fly ash treatment,thermal properties and microstructures of municipal solid waste incineration(MSWI) fly ash were studied by measuring the chemical element composition,specific surface area,pore sizes,functional groups,TEM image,mineralogy and DSC-TG curves of raw and sintered fly ash specimens.The results show that MSWI fly ash particles mostly have irregular shapes and non-typical pore structure,and the supersonic treatment improves the pore structure;MSWI fly ash consists of such crystals as SiO2,CaSO4 and silica-aluminates,and some soluble salts like KCl and NaCl.During the sintering process,mineralogy changes largely and novel solid solutions are produced gradually with the rise of temperature.Therefore,the utilization of a proper thermal technology not only destructs those persistent organic toxicants but also stabilizes hazardous heavy metals in MSWI fly ash.
