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

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 (FeO, AlO, TiO, and NaO, 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% FeO, NaO, AlO, and TiO, respectively. Metal oxides in the RM showed synergistic effects on the bromine fixation, and this can be attributed to the secondary reaction of NaO and bromine decomposed from FeBr. The mechanisms of bromine fixation by RM are formation of Br-M (M: Fe, Al, Ti, and Na) and OH bonds generated from the direct elimination and a two-step of dissociative adsorption and β-H elimination reactions between metal oxides and bromide.