Effects of selected metal oxides on the dechlorination and destruction of PCDD and PCDF

OCDD and OCDF spiked silica/graphite based model fly ash containing various copper compounds and metal oxides were thermally treated under oxygen deficient conditions. All copper compounds tested showed a considerable dechlorination/hydrogenation reaction at 260 degrees C. After 30 min at 340 degrees C, less than 1% of the spiked OCDD and OCDF was recovered as T4CDD/F to OCDD/F. Other compounds tested demonstrated a lower rate of dechlorination compared to the copper compounds. However, all other metal oxides showed a small dechlorination effect at 260 degrees C, which was considerably increased at 340 degrees C. The model fly.ash containing the different copper compounds or metal oxides showed comparable PCDD and PCDF isomer patterns after thermal treatment. However, small differences were observed among the different tested compounds. The PCDD and PCDF isomer patterns on the model fly ashes were similar to patterns found during dechlorination experiments on fly ashes from waste incineration processes. Model fly ash containing Ca(OH)2 exhibited the highest destruction potential, but a low dechlorination potential. In contrast, model fly ash containing any of the remaining compounds tested, was found to predominantly dechlorinate the spiked OCDD and OCDF.