Improving bromine fixation in co-pyrolysis of non-metallic fractions of waste printed circuit boards with Bayer red mud

Abstract A method to improve bromine fixation by co-pyrolysis of non-metallic fractions (NMFs) of waste printed circuit boards (WPCBs) with Bayer red mud (RM) has been developed. More than 78.59 wt% of bromine was fixed into the solid residues with an addition of 15 wt% RM after co-pyrolysis at 500 °C, comparing with 36.42 wt% without the RM addition. Metal oxides (Fe 2 O 3 , Al 2 O 3 , TiO 2 , and Na 2 O, etc.) in the RM contributed significantly to the bromine fixation. The bromine fixation percentages were 62.94, 65.05, 47.24, and 49.05 wt% with an individual addition of 15 wt% Fe 2 O 3 , Na 2 O, Al 2 O 3 , and TiO 2 , respectively. Metal oxides in the RM showed synergistic effects on the bromine fixation, and this can be attributed to the secondary reaction of Na 2 O and bromine decomposed from FeBr 3 . The mechanisms of bromine fixation by RM are formation of Br-M (M: Fe, Al, Ti, and Na) and O H bonds generated from the direct elimination and a two-step of dissociative adsorption and β-H elimination reactions between metal oxides and bromide.