Mechanochemical degradation of tetrabromobisphenol A: Performance, products and pathway

Highlights: ► Fe + SiO2 shows better performance than CaO in mechanochemical destruction of TBBPA. ► Nonhazardous inorganic carbon and soluble bromide were the final products. ► Raman and FTIR imply the generation of inorganic carbon and removal of bromine atom. ► Tri-BBPA, bi-BBPA, mono-BBPA, BPA were the main intermediates during ball milling. ► The bromine was balanced and the degradation pathway was proposed. - Abstract: Tetrabromobisphenol A (TBBPA) is the most widely used brominated flame retardant (BFR), which has received more and more concerns due to its high lipophilicity, persistency and endocrine disrupting property in the environment. Considering the possible need for the safe disposal of TBBPA containing wastes in the future, the potential of mechanochemical (MC) destruction as a promising non-combustion technology was investigated in this study. TBBPA was co-ground with calcium oxide (CaO) or the mixture of iron powder and quartz sand (Fe + SiO2) in a planetary ball mill at room temperature. The method of Fe + SiO2 destructed over 98% of initial TBBPA after 3 h and acquired 95% debromination rate after 5 h, which showed a better performance than the CaO method. Raman spectra and Fourier transform infrared spectroscopy (FTIR) demonstrated the generation of inorganic carbon with the disappearance of benzene ring and C-Br bond, indicating the carbonization and debromination process during mechanochemical reaction. LC–MS–MS screening showed that the intermediates of the treatment with Fe + SiO2 were tri-, bi-, mono-brominated BPA, BPA and other fragments. Finally all the intermediates were also destroyed after 5 h grinding. The bromine balance was calculated and a possible reaction pathway was proposed.