Effect of Atmospheres on Transformation of Heavy Metals during Thermal Treatment of MSWI Fly Ash: By Thermodynamic Equilibrium Calculation.

Facun Jiao,Chengli Wu,Tao Liu,Hanxu Li,Zhongbing Dong,Xulong Ma

doi:10.3390/molecules27010131

Facun Jiao, Chengli Wu + Show 4 more

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https://doi.org/10.3390/molecules27010131

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Abstract

The vaporization behaviors of eight heavy metals (Pb, Zn, Cu, Cd, Cr, Co, Mn, and Ni) in municipal solid wastes incineration (MSWI) fly ash during thermal treatment under air atmosphere (21% O2/79% N2), an inert atmosphere (100% N2), and a reducing atmosphere (50% CO/50% N2) were evaluated based on a thermodynamic equilibrium calculation by FactSage 8.1. The results show that the reducing atmosphere promotes the melting of MSWI fly ash, resulting in a more liquid phase than in air or an inert atmosphere. Except for Cd, the formation of liquids can dissolve heavy metals and reduce their vaporization ratio. In the air and inert atmospheres, Pb, Zn, Cu, Co, Mn, and Ni vaporize mainly in the form of metallic chlorides, while Cd volatilizes in the form of metallic Cd (g) and CdO (g). In the reducing atmosphere, Co, Mn, and Ni still vaporize as chlorides. Zn and Cd mainly vaporize in the form of Zn (g) and Cd (g), respectively. In terms of Pb, in addition to its chlorides, the volatiles of Pb contain some Pb (g) and PbS (g). Cr has a low vaporization ratio, accounting for 2.4% of the air atmosphere. Cr, on the other hand, readily reacts with Ca to form water-soluble CrCaO4, potentially increasing Cr leaching. Except for Cd, the results of this study suggest that the reducing atmosphere is used for the thermal treatment of MSWI fly ash because it promotes the melting of fly ash and thus prevents heavy metal vaporization.

Highlights

Fly ash from municipal solid wastes incineration (MSWI) is a hazardous waste because it contains a high concentration of heavy metals, dioxins, and other toxic compounds [1].Before landfilling, MSWI fly ash must be stabilized
The fraction of liquid phase in MSWI fly ash treated at various temperatures a
The change curves of the liq atmospheres is of first calculated because fly ash fusibility during thermal treatment plays

Summary

Introduction

Fly ash from municipal solid wastes incineration (MSWI) is a hazardous waste because it contains a high concentration of heavy metals, dioxins, and other toxic compounds [1].Before landfilling, MSWI fly ash must be stabilized. Fly ash from municipal solid wastes incineration (MSWI) is a hazardous waste because it contains a high concentration of heavy metals, dioxins, and other toxic compounds [1]. Thermal treatment is the most promising method for MSWI fly ash treatment because of the benefits of ash volume reduction, dioxin decomposition, stable slag properties, and low heavy metal leaching [2,3,4,5,6]. Fly ash melts and solidifies into glassy slag during the thermal treatment. Partial heavy metals in MSWI fly ash, on the other hand, vaporize during thermal treatment, potentially causing secondary pollution. As a result, clarifying the vaporization propensity of heavy metals in MSWI fly ash during thermal treatment is critical for developing technologies to prevent heavy metal vaporization

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