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

Abstract

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.