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

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.