Dual Positive Effects of Pre-Dechlorine and Low-Temperature Deep Reduction-Keeping on the PCDD/F Removal of Incineration Fly Ash

Abstract

Low-temperature thermal degradation of PCDD/Fs in incineration fly ash (IFA) has attracted widespread attention with the advantages of low energy consumption and high efficiency. However, in the process of industrialization, the inevitable O₂ leakage in the system has always been a technical bottleneck. Based on the characteristics of IFA and the mechanism of PCDD/F regeneration, this study first proposes a dual-strategy LTTD of predechlorination and reduction atmosphere-keeping. Predechlorination removes soluble chlorine and soluble metals while hydrolyzing CaClOH in IFA into Ca(OH)₂ to accelerate the detoxication of PCDD/Fs, and deep reduction atmosphere-keeping is created by introducing activated carbon to inhibit the possible PCDD/F regeneration. Compared with typical LTTD, synergistic application of dual-strategy LTTD can obtain 99.4 and 97.4% detoxification efficiencies of PCDD/Fs in the presence of 1 and 2% O₂, respectively. Based on the identification of congener distribution and density functional theory calculations, the dechlorination mechanism of acid chloride group-containing PCDD/F intermediates with the participation of CO and Ca(OH)₂ was proposed. Finally, the reproducibility of dual-strategy LTTD after optimization of working parameters was well verified and the proposed dual strategies are expected to provide a new direction for the industrialization of LTTD.