Mechanistic insights into the chlorination volatilization of oxidized heavy metals via novel staggered chlorination roasting

Abstract

Improper handling of heavy metal-containing solid waste poses significant environmental risks. However, developing an effective heavy metal elimination method is still a challenge. Our study introduces a novel method of staggered chlorination roasting. The volatilization and removal effects of two chlorinating agents, NH₄Cl and CaCl₂, on typical key heavy metals, Zn and Cu, were investigated. Compared with the use of a single chlorinating agent, this method, which uses NH₄Cl for low-temperature decomposition and CaCl₂ for high-temperature reactions, significantly extends the chlorination reaction time, overtly enhancing the chlorination volatilization effect. This study elucidated the influence of the chlorinating agent content, temperature, and time on the elimination of heavy metal oxides. The results demonstrated that when the two chlorinating agents were added at a ratio of 2:3, roasting at 1100 °C for 60 min resulted in the highest volatilization rates of Zn (99.9%) and Cu (98.7%). Thermodynamic equilibrium and equilibrium phase composition calculations were conducted to explore the effects of the chlorinating agents and mineral components (SiO₂, Al₂O₃, Fe₂O₃, and CaO) on chlorination roasting. In the staggered chlorination mode, the chlorine-containing gases generated effectively mitigate the influence of mineral components, thereby suppressing interactions between oxidized heavy metals and mineral constituents. This suppression enhances the chlorination and volatilization of heavy metals. This study proposes a novel staggered chlorination roasting method based on composite chlorinating agents, offering a new approach for the collaborative and efficient removal of multiple heavy metals from solid waste.

Graphical abstract