Study on the Destruction of PCDD/Fs and Synergistic Solidification of Heavy Metals in Fly Ash by Low-Temperature Pyrolysis with the Assistant of N-Doped Hierarchical Porous Carbon

There is an urgent need for energy-efficient disposal and resource utilization of the fly ashes from municipal solid waste incineration (MSWI). The low-energy pyrolysis-based detoxification of is a prerequisite for the harmless treatment and sustainable utilization of the fly ashes. In this study, the nitrogen-doped hierarchical porous carbon (NHPC) was prepared from the biomass-derived corn cobs and used to enhance the low-temperature destruction of PCDD/Fs in the MSWI fly ash. On thermal treatment in pure nitrogen (referring to pyrolysis in) at 350 °C for 30 min, the removal efficiencies of PCDD/Fs in fly ash based on mass (ηmass) and TEQ (ηTEQ) are 87.4% and 76.2%, respectively. After 5 wt.% NHPC is added in fly ash, the ηmass and ηTEQ values can be increased to 94.9% and 90.2%. The NHPC can enhance the decomposition and inhibit the regeneration of PCDD/Fs in fly ash, for the NHPC can regulate the structural properties and optimize the chemical environment of the fly ash. It can eliminate the need for the washing process. In addition, the leaching concentrations of heavy metals such as Cu, Zn, Pb and Cr in fly ash experience significant reductions of 83.3%, 73.7%, 35.6% and 22.9% when the fly ash is pyrolyzed at 350 °C with NHPC. This finding suggests that NHPC cannot only facilitate the decomposition of PCDD/Fs but also immobilizes the typical heavy metals in fly ash during low-energy pyrolysis. It is anticipated that the application of NHPC in the low-temperature pyrolysis of fly ash is of great energy-saving effect and can tackle the issues of PCDD/Fs and heavy metals for fly ash within a single step.