Debromination and Decomposition Mechanisms of Phenolic Resin Molecules in Ball Milling with Nano-Zerovalent Iron

Nonmetallic particles from waste-printed circuit boards are toxic pollutants due to their brominated flame-retardant content. Developing green technology for the disposal of nonmetallic particles is a significant task. To our knowledge, this paper might be the first to report the ball milling of nonmetallic particles with nano-zerovalent iron. The results indicated that the content of bromine on the surface of nonmetallic particles ball-milled with nano-zerovalent iron was reduced by 50%. Phenolic resin macromolecules were decomposed to methylbenzene, phenol, etc., and graphitic carbon and amorphous carbon appeared. The reason for the decomposition of phenolic resin molecules was presented. Nano-zerovalent iron, as an electron donor, transferred electrons to pentabromodiphenyl ether molecules during ball milling. The C-Br bond was stretched, and the bond length increased, which promoted the debromination process. We also found that in the pentabromodiphenyl ether molecule, the C-Br bond in the para position on the benzene ring with more Br atoms and the C-O bonds were broken first. Additionally, the reaction pathway from resin macromolecules to methylbenzene and phenol etc. was presented and discussed. This paper provides a detailed mechanism by which ball milling achieves the decomposition of brominated flame-retardant molecules.