Bromine fixing ability of electric arc furnace dust during thermal degradation of tetrabromobisphenol: Experimental and thermodynamic analysis study

This work reports on the bromine fixing ability of a typical electric arc furnace dust (EAFD) upon its co-pyrolysis with tetrabormobisphenol (TBBA), the most widely used brominated flame retardant) both experimentally and theoretically following thermodynamic calculations. Experimentally, the following variables were considered in this investigation: EAFD: TBBA mass ratio (1:1, 1:2 and 1:3), pyrolysis heating rate and its final temperature and the effect of the NaCl and KCl presence in the dust. In the thermodynamic analysis the same parameters were studied excluding the heating rate. According to thermodynamic calculations, it was found that almost 100% of bromine, released as HBr during the thermal decomposition of TBBA, can be fixed by EAFD as metal bromides when 1:1 and 1:2 ratios where used. These metal bromides remain mainly in the solid form below 400 °C; above this temperature they commence evaporation leaving the reaction system. At 1:3 ratio almost 10% of the initial bromine contents is released in HBr gaseous form. Experimentally, it was found that about 70% of HBr is captured by EAFD when 1:1 and 1:2 ratios were used at temperatures below 350 °C, however, only 53% were captured when ratio 1:3 was used. At all conditions, the escaped gaseous HBr was as low as 6%. It was also found that high heating rates negatively affected the metal oxides ‘capacity to capture emitted HBr.