Mechanochemical dehalogenation of brominated flame retardants and preliminary application for recycling BFR-containing plastic waste

Hexabromocyclododecane (HBCD) is one of the most widely used brominated flame retardant (BFR), which has attracted increasing attention due to the persistence, bioaccumulation and adverse effect to wildlife and human. Considering the strong need for the disposal of HBCD containing waste, mechanochemical (MC) pretreatment technology was investigated to destroy BFRs as a dehalogenation method in this study. Silica and aluminium powders were used as additives, and mechanochemical method was applied to degrade BFRs for both HBCD powder and waste plastics. The results showed that HBCD was effectively degraded during mechanochemical treatment with the aid of Si-Al-based additives. The optimized condition was determined to be a SiO2/Al ratio = 7:2 with a reagent ratio of 15:1. The optimized mechanochemical method was applied to dispose of BFRs contained waste plastics. The results show that dehalogenation of plastics occurs during mechanochemical destruction and that smaller plastic particles accelerated dehalogenation. Finally, the reaction process and intermediates were studied to provide insight into the mechanochemical degradation mechanism of HBCD, and a possible reaction pathway was proposed.