Chemical speciation and mobility of heavy metals in municipal solid waste incinerator fly ash

Chemical speciation is a significant factor that governs the toxicity and mobility of heavy metals in municipal solid waste incinerator fly ash. Sequential extraction procedure is applied to fractionate heavy metals(Pb, Zn, Cd, Cu, and Cr) into five defined groups: exchangeable, carbonate, Fe-Mn oxide, organic, and residual fractions. The mobility of heavy metals is also investigated with the aid of toxicity characteristic leaching procedure. In the fly ash sample, Pb is primarily presented in the carbonate(51%) and exchangeable(20%) fractions; Cd and Zn mainly exist as the exchangeable(83% and 49% respectively); Cu is mostly contained in the last three fractions(totally 87%); and Cr is mainly contained in the residual fraction(62%). Pb, Zn and Cd showed the high mobility in the investigation, thus might be of risk to the natural environment when municipal solid waste incinerator fly ash is landfilled or reutilized.

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

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.

Influence of SO_2 in incineration flue gas on the sequestration of CO_2 by municipal solid waste incinerator fly ash

The influence of CO2 content and presence of SO2 on the sequestration of CO2 by municipal solid waste incinerator （MSWI） fly ash was studied by investigating the carbonation reaction of MSWI fly ash with different combinations of simulated flue gas. The reaction between fly ash and 100% CO2 was relatively fast; the uptake of CO2 reached 87 g CO2/kg ash, and the sequestered CO2 could be entirely released at high temperatures. When CO2 content was reduced to 12%, the reaction rate decreased; the uptake fell to 41 g CO2/kg ash, and 70.7% of the sequestered CO2 could be released. With 12% CO2 in the presence of SO2, the reaction rate significantly decreased; the uptake was just 17 g CO2/kg ash, and only 52.9% of the sequestered CO2 could be released. SO2 in the simulated gas restricted the ability of fly ash to sequester CO2 because it blocked the pores of the ash.

Characteristics of the stabilized/solidified municipal solid wastes incineration fly ash and the leaching behavior of Cr and Pb

Fly ash is a hazardous byproduct of municipal solid wastes incineration （MSWI）. An alkali activated blast fumace slag-based cementifious material was used to stabilize/solidify the fly ash at experimental level. The characteristics of the stabilized/solidified fly ash, including metal leachability, mineralogical characteristics and the distributions of metals in matrices, were tested by toxic characteristic leaching procedure （TCLP）, X-ray diffrac- tion （XRD） and scanning electron microscopy-energy dispersive spectrometer （SEM-EDS） respectively. Contin- uous acid extraction was utilized to extract metal ions and characterize their leaching behavior. The stabilization/ solidification procedure for MSWI fly ash demonstrates a strong fixing capacity for the metals by the formation of C- S-H phase, hydrated calcium aluminosilicate and ettringite. The stabilized/solidified fly ash shows a dense and homogeneous microstructure. Cr is mainly solidified in hydrated calcium aluminosilicate, C-S-H and ettringite phase through physical encapsulation, precipitation, adsorption or substitution mechanisms, and Pb is mainly solidified in C-S-H phase and absorbed in the Si-O structure.

Low-carbon stabilization/solidification of municipal solid waste incineration fly ash

Municipal solid waste incineration(MSWI)fly ash(FA)is classified as hazardous waste,which requires additional treatment before disposal or further utilization.Stabilization/solidification(S/S)is regarded as a low-cost and high-efficient method for MSWI FA treatment.“Low-carbon S/S”has captured extensive interest in recent years,which could treat hazardous wastes and enable resource recycling in a sustainable way.This article introduced the state-of-art low-carbon S/S strategies for MSWI FA treatment.The immobilization mechanisms of pollutants in various matrices were also discussed.Prospects were raised to foster the actualization of sustainable management of MSWI FA.

Effect of Atmosphere on HCI Releasement during MSWI Fly Ash Thermal Treatment

Municipal solid waste incineration(MSWI)fly ash constitutes a hazardous waste.Melting disposal has been verified to be prospective for stabilizing heavy metals and dioxins.Release of contaminant HCl during MSWI fly ash thermal treatment leads to potential environmental risks.The behavior and transformation of chlorine are critical to the disposal strategy of MSWI fly ash.In this study,the pathway of HCl formation in MSWI fly ash thermal treatment under complex atmosphere was revealed.Results show that CaOHCl in fly ash was first decomposed to CaCl_(2),CaO and H_(2)O below 550°C,which provides H for HCl generation.Then,CaCl_(2),NaCl or KCl were reacted with H_(2)O to release HCI,during which process H_(2)O and O2 promote HCl formation,CO inhibit HCl production since H_(2)O is consumed in water-gas reaction.The initial temperature of HCl generation affected by the concentration of H_(2)O in the atmosphere.When temperature up to 1250°C,almost all NaCl or KCl were volatilized,HCl mainly from the reaction of chlorine-containing minerals with H_(2)O,such as Ca_(19.2)Mg_(2.8)(Si_(0.75)Al_(0.75))8 O36Cl_(2),Ca4(SiO4)(SO4)Cl_(2)and Ca10(SiO4)3Cl_(2)in N_(2),CO and air atmosphere separately.Moreover,in a reducing atmosphere,metals are more easily chlorinated by HCI,resulting in further consumption of HCI.The order of atmosphere for reducing HCl emissions should be CO>N_(2)>Air>>H_(2)O.

Effect of the MgO/SiO_(2) ratio on MgO–silica binders solidifying MSWI fly ash

To improve the effect of MgO–SiO_(2) binders solidifying municipal solid waste incineration fly ash(MSWI FA),MSWI FA solidified bodies with five MgO/SiO_(2) ratios(0.41~3.77)were investigated.The leaching behavior of solidified bodies was evaluated by leaching toxicity tests and pH-dependent experiments.In addition,hydration products in solidified bodies were analyzed by thermodynamic modeling and microstructure characterizations.The results showed that the variation in the MgO/SiO_(2) ratio had a significant effect on the leaching toxicity of the solidified bodies,because it affected the leachate pH and the composition of the hydration products of the solidified bodies.The acid and alkali resistance of the MSWI FA was enhanced through solidification with MgO–SiO_(2) binders.MgO can improve the alkalinity of the solidified bodies and facilitate the chemical precipitation of heavy metals.Moreover,silica fume,an industrial waste,can serve as a cost-effective measure.Overall,MgO–SiO_(2) binders demonstrated great potential as promising candidates for encapsulating MSWI FA.

Preparation of glass–ceramics from high-chlorine MSWI fly ash by one-step process

Municipal solid waste incinerated(MSWI) fly ash contains heavy metals and chloride,which is urgent to be disposed via an effective method.Herein,glass-ceramics,one of the recycling waste materials based on MSWI fly ash with high chloride content,have been developed from one-step process.MSWI fly ash and waste glass have been utilized as calcium and silicon sources,respectively.Glass-ceramics were successfully prepared by the one-step process.It is found that the increase in MSWI fly ash promotes the fracture of glass mesh(Si-O)and the generation of non-bridging oxygen,reducing the polymerization degree of glass network structure,which leads to the decrease in glass stability.The difference between glass transition temperature(T_(g)) and crystallization temperature(T_(c)) was narrowed,and crystallization activation energy of basic glass was reduced,which promoted crystallization.With lower crystallization activation energy(E=217.56 kJ·mol^(-1)) and high utilization rate of 50 wt% MSWI fly ash,the optimal glass-ceramics with spherical diopside,cuspidine and glass phase,excellent hardness of 7.97 GPa and bending resistance of 114.86 MPa are achieved.It is worth mentioning that most of the high content of chlorine in MSWI fly ash will evaporate during vitrification process;the residual chlorine as well as heavy metals can be present steadily in crystalline grains.Therefore,this study not only increases the attachment value of MSWI fly ash,but also eliminates the problems caused by high chlorine and heavy metals in MSWI fly ash.